power systems consulting tres amigas interconnection ... · power systems consulting tres amigas...

POWER SYSTEMS CONSULTING

TRES AMIGAS INTERCONNECTION

SYSTEM IMPACT STUDY: PHASE 1

Issued: December 21, 2011

Revised: January 3, 2012

Report Number: 2011-E6276-1.R00

Prepared For:

Public Service New Mexico (PNM)

Alvarado Square

Albuquerque, NM 87158

Power Systems Consulting

ABB Inc.

940 Main Campus Drive

Raleigh, NC 27606

Legal Notice

This document, prepared by ABB Inc., is an account of work sponsored by Public Service Company

of New Mexico (PNM). Neither PNM nor ABB Inc., nor any person or persons acting on behalf of

these parties: (i) makes any warranty or representation, expressed or implied, with respect to the use

of any information contained in this document, or that the use of any information, apparatus, method,

or process disclosed in this document may not infringe privately owned rights, or (ii) assumes any

liabilities with respect to the use of or for damages resulting from the use of any information,

apparatus, method, or process disclosed in this document.

- i -

Power Systems Consulting Technical Report

ABB Inc. 2011-E6276-1.R00

Title

Tres Amigas Interconnection System Impact Study: Phase 1

Dept.

Consulting

Date

12/16/2011

Pages

Author(s): Reviewed by: Approved by:

K. Timko ABB

G. Nail PNM

T. Duane PNM

D. Dickmander ABB W. Wong ABB

J. Mechenbier PNM

PNM authored were Executive Summary and Section 11

ABB authored were Sections 1-10 and 12-13

Both Companies reviewed the report

Executive Summary:

In response to a wire-to-wire interconnection request from Tres Amigas LLC (“Tres

Amigas”), a System Impact Study (“Study”) was performed based on the non-tariff System

Impact Study Agreement dated March 3, 2011. The purpose of this Study was to evaluate the

interconnection of the proposed first 750 MW stage of Tres Amigas voltage source converter

(“VSC”) HVDC station (“Project”) paralleling PNM’s existing 200 MW HVDC converter

station (“Blackwater Station”) that interconnects the Southwest Power Pool (“SPP”), and

Western Electricity Coordinating Council (“WECC”) grids together. ABB, Inc. was retained

by PNM to perform analysis with support from PNM.

Background:

The Tres Amigas Superstation is envisioned to interconnect the Electric Reliability Council of

Texas (“ERCOT”), SPP, and WECC grids employing three VSC HVDC stations. The

ultimate build out of the Tres Amigas Superstation is envisioned to have a capacity of 5,000

MW. Stage 1 of the Project, as defined for the Study, is the interconnection of a 750 MW

VSC HVDC link between the WECC and SPP grids approximately in parallel with PNM’s

Blackwater Station located near Clovis, New Mexico. The interconnection will be between

the PNM Blackwater Station and the SPP 345 kV transmission system at the Tolk generating

station (1065 MW coal plant) east of Muleshoe, Texas. Construction is scheduled to begin in

June 2012 with an expected commercial operating date in March 2015.

Figure 1 shows a high level illustration of the Project interconnection configuration.

ii

Figure 1. Project Interconnection Configuration

StudyScope:

The Study evaluated interconnecting and transferring power in and out of the Project on an

“as available” basis only using non-firm transmission capacity due to the lack of firm

available transmission capacity. Existing transmission service commitments combined with

pending transmission service requests from Blackwater in an east to west direction outstrip the

transmission capacity of the BA-Blackwater 345 kV line (“BB line”). Previous technical

analysis has identified that substantial additional voltage support facilities must be built to

accommodate transfers at the level expected with the Project even if the existing and pending

commitments are reduced to zero. Firm power transfers in the west to east direction over the

B-A – Blackwater 345 kV line are constrained by a limitation on long-term firm available

transmission capacity from Four Corners to Albuquerque arising from congestion on WECC

Path 48 (“Path 48”). New transmission to increase Path 48 capability must be constructed for

firm deliveries to Blackwater and, therefore, the Study evaluated only off-peak load

conditions to assess impacts of the Project.

Future studies will be required to identify the necessary transmission line and station additions

for utilization of the Project that exceeds the “as available” service limitations assumed in the

Study once users of Tres Amigas make firm point-to-point transmission delivery service

requests and nothing in this Study is intended to imply any right to receive transmission

service from PNM until such upgrades are defined and in-service.

The objectives for the Study are listed below:

1. Assess the short circuit capacity at the Blackwater Station to determine if there is

sufficient system strength to support operation of Tres Amigas and Blackwater

Station.

2. Analyze the reactive power and AC voltage control strategies between the Tres

Amigas and Blackwater HVDC converters.

3. Assess steady state and dynamic performance on the PNM transmission system with

the addition of Stage 1.

Consideration was given to both peak and off-peak system conditions with the Blackwater

Station in operation at rated capacity and with the Blackwater Station operating in Static Var

Compensator (“SVC”) mode.

iii

Short Circuit Capability Assessment

The results of the short circuit capability assessment determined that there is not sufficient

short circuit capability at the Blackwater Station to support the simultaneous operation of the

Project and the existing 200 MW Blackwater Station. The short circuit requirements for the

Project converters are not fully known due to the simplified positive sequence models used for

the Study. To provide enough short circuit capability to support the operation of both the

Project and Blackwater Station, the Study assumed this capacity would be provided by

synchronous condensers Tres Amigas would locate at the Project station. To maintain

acceptable dynamic system performance, the size of the synchronous condenser was

established at 250 MVA.

Steady-State Performance

The powerflow analysis shows that substantial additional voltage support will be required to

accommodate the combined total power transfer of the Project and the Blackwater Station.

The westbound power transfer from the Project and Blackwater result in a total power transfer

requirement of 950 MW on the BB line. The total current associated with this transfer

requirement remained below the conductor thermal rating (1076 MVA) but exceeds the BB

line wavetrap rating (717 MVA) and the voltage stability limit of 371 MVA identifyied in the

analysis1.

When modeling the full transfer requirement in the eastbound direction, the thermal rating of

the BB line was exceeded due to additional current requirements associated with increased

power losses and reactive flows on the BB line. The maximum transfer that could be

accomodated without exceeding the thermal limit was 925 MW. As with the westbound

direction, the maximum transfer was found to be limited to 480 MW without substantial

additional voltage support along the BB line and to no more than 717 MVA without

replacement of the BB line wavetraps. If power output from wind farms connected to the BB

line is scheduled eastbound, it is possible that from time to time the full combined capability

of the Project and Blackwater Station could be utilized. This is not specifically explored in

the analysis.

The additional voltage support requirements identified along the BB line to support the total

power transfer from west-to-east included the addition of 450 Mvar of mechanically switched

shunt capacitor (MSSC) banks at the Guadalupe 345 kV station in order to maintain stable

operation for worst case off-peak system conditions. Based on requirements for the various

system configurations examined, a maximum step size of 150 Mvar for the MSSCs is

recommended. In addition to the MSCCs, the addition of a ±250 Mvar SVC at Guadalupe is

required to meet dynamic stability performance requirements. This SVC will also compensate

for the switching of MSSC banks which would otherwise result in unacceptably large voltage

changes.

The outage of the BB line for the westbound transfers can cause 115 kV station voltages in the

Albuquerque area to rise above acceptable limits. These voltage levels can exceed equipment

limitations and could lead to insulation failure. Currently, PNM does not have automatic

1 This voltage stability limit was established by powerflow studies. Due to its length, the BB has

relatively low surge impedance loading (426 MVA). Without compensation, it cannot be loaded much

more than the surge impedance loading because angle stability cannot be maintained.

iv

voltage-controlled shunt devices in the system that could be used to limit the 115 kV voltages

near the Albuquerque area for this type of disturbance. PNM Power System Operations

protocols indicate that voltages in excess of 1.08 pu cannot be mitigated quickly enough by

operator intervention. For this reason, an automatic voltage-controlled shunt reactor at the BA

115 kV station may be required.

Dynamic Stability Performance

Dynamic stability violations were identified for off-peak system conditions. The violations

occur for a single line to ground fault with delayed clearing (breaker failure scenario) at the B-

A 345 kV station resulting in the double line outage of both BA-Rio Puerco 345 kV circuits.

This contingency is the driver for the size requirements of the 250 Mvar SVC at Guadalupe.

Even with the SVC, remedial actions are required for this contingency. The following

scenarios were considered:

1. Runback of the Tres Amigas power schedule combined with tripping the MSSC banks at

Guadalupe.

2. Tripping Tres Amigas and the Guadalupe MSSC banks

3. Tripping Tres Amigas, the Blackwater Station, and the Guadalupe MSSC banks

The results of the study indicate that either scenario 1 or 2 is sufficient to stabilize the system.

Short Circuit Analysis

Short circuit studies were conducted to determine if the existing circuit breakers, particularly

at Blackwater and BA, can handle the increased fault currents associated with the Tres

Amigas project. Based on these results, the existing circuit breakers are adequate.

v

Blackwater Facilities

The interconnection of the project will require the addition of a 345 kV three breaker ring bus

at Blackwater. The existing station consists of a single breaker for isolating the Blackwater

Station from the BB line.

Conclusion

The results presented in this report show that the Project will require several system

improvements for the “as available” transmission service scenario assumed in the Study. The

full transfer level is summarized in the table below:

The minimum system improvements to support full transfer on an “as available” basis

include:

250 MVA synchronous condenser to be located at the Project station.

3 - 150 Mvar MSSC banks to be located at the Guadalupe 345 kV station.

±250 Mvar SVC to be located at the Guadalupe 345 kV station.

Expand the Blackwater Station from a single breaker to a three breaker 345 kV ring bus

station.

Reconductor the BA-Guadalupe 345 kV line.

Replace the communication wave trap on the BB line.

The Study also identified the maximum transfer in or out of the Project absent the system

improvements identified above other than expansion of the Blackwater switchyard. These

maximum transfers are summarized in the table below:

Without System Improvements

Transfer Direction Tres Amigas (MW) Blackwater (MW) Total (MW)

East to West 377 / 480 200 577 / 680 East to West 450 / 676 off-line 450 / 676 West to East 355 / 371 200 555 / 571 West to East 450 / 550 off-line 450 / 550

The first number reflects reduced transfer levels to address apparent operational limitations of

the Project likely resulting from the lack of adequate short-circuit capacity at the Blackwater

345 kV switchyard. The limitations are implied by the behavior of the dynamic model

provided for the Project. The second number reflects voltage stability limitations of the BB

line.

Discussions with Tres-Amigas have indicated that estimates for the scenario without system

improvements are of primary interest. As a result cost estimates included in the Study are

limited to expansion of the Blackwater 345 kV station into a three breaker ring bus. The cost

estimate and schedule are summarized below:

With System Improvements


East to West 750 200 950 West to East 750 200 950

vi

Interconnection item Cost

Estimated

Time for construction

Expand the Blackwater Station from a single to three breakers $7 M 18 months

The results of this analysis are preliminary and may be modified based on more detailed

technical study (Phase 2) to analyze the control interactions between devices, temporary over-

voltages, coordination of control and protection, evaluation of single pole switching, low

order harmonic resonance, AC filter performance and dynamic over voltages.

The results of the Study are based on available data and assumptions made at the time of

conducting the Study. The results provided in this report may not apply if any of the data,

models and/or other assumptions used to perform the Study change.

Rev No. Revision Description Date Authored by Reviewed by Approved by

0 Initial Draft Report 12/08/2011 K. Timko

G. Nail T. Duane

D. Dickmander W. Wong

J. Mechenbier

DISTRIBUTION:

George Nail, PNM

Jeff Mechenbier, PNM

Tom Duane, PNM

vii

TABLE OF CONTENTS

1 INTRODUCTION............................................................................................................................... 1

2 PLANNED TRES AMIGAS FACILITIES – STAGE 1 .................................................................. 3

3 STUDY PROCESS.............................................................................................................................. 5

3.1 SETUP OF PSLF BASE CASES ......................................................................................................... 5 3.2 INVESTIGATION OF SHORT CIRCUIT CAPABILITY AT THE BLACKWATER STATION ......................... 6 3.3 REACTIVE POWER AND AC VOLTAGE CONTROL STRATEGIES ....................................................... 7

3.3.1 Voltage Stability Analysis .................................................................................................... 8 3.3.2 Dynamic Analysis for Small-Signal Disturbances ............................................................... 8

3.4 LARGE-SIGNAL DYNAMIC EFFECTS ON PNM SYSTEM .................................................................. 9

4 STUDY CRITERIA ...........................................................................................................................10

5 STUDY CONDITIONS AND ASSUMPTIONS ..............................................................................11

5.1 BASE CASES .................................................................................................................................11 5.2 MODELS ........................................................................................................................................21

5.2.1 Blackwater HVDC Model ...................................................................................................21 5.2.2 Tres Amigas VSC Model ....................................................................................................22 5.2.3 Tres Amigas Synchronous Condenser Model .....................................................................22 5.2.4 Guadalupe Dynamic Reactive Compensation Model ..........................................................23 5.2.5 SPS Equivalent Machine Models ........................................................................................23

6 STEADY-STATE ANALYSIS ..........................................................................................................25

7 SHORT CIRCUIT CAPABILITY ASSESSMENT ........................................................................33

8 VOLTAGE STABILITY ANALYSIS ..............................................................................................35

9 CLOSED-LOOP DYNAMIC ANALYSIS .......................................................................................37

10 DYNAMIC STABILITY ANALYSIS ..............................................................................................38

10.1 CONTINGENCIES CASE LIST ..........................................................................................................38 10.2 STABILITY RESULTS .....................................................................................................................38 10.3 REMEDIAL ACTIONS .....................................................................................................................43

10.3.1 Tres Amigas DC Power Runback .......................................................................................44 10.3.2 Tripping Tres Amigas and Guadalupe Fixed Reactive Compensation ................................47 10.3.3 Tripping Tres Amigas, Blackwater, and Guadalupe Fixed Reactive Compensation ...........47

11 PNM TRANSFER ANALYSIS WITHOUT DYNAMIC VOLTAGE SUPPORT .......................49

11.1.1 Transfer Case development .................................................................................................49 11.2 VOLTAGE STABILITY ....................................................................................................................49 11.3 STABILITY ANALYSIS ...................................................................................................................50

12 CONCLUSIONS AND RECOMMENDATIONS ...........................................................................52

13 REFERENCES ...................................................................................................................................56

1

1 Introduction

The Tres Amigas SuperStation Project (“Tres Amigas” or “Project”) is envisioned to

interconnect the Electric Reliability Council of Texas (“ERCOT”), Southwest Power Pool

(“SPP”), and Western Electricity Coordinating Council (“WECC”) grids employing three

voltage source converter (“VSC”) HVDC stations. The ultimate capacity of the project is

envisioned to have a capacity of 5,000 MW. Stage 1 of the project is the interconnection of a

750 MW VSC HVDC link between the WECC and SPP grids, in parallel with the PNM

Blackwater HVDC converter station (“Blackwater Station”) located near Clovis, New Mexico.

The proposed connection to the SPP system will be at the Tolk generating station via an

approximately 56 mile, 2-conductor bundle, 1272 kcmil single circuit 345 kV transmission line.

The connection at the Blackwater Station consists of a single circuit 22 mile transmission line of

similar design. Construction of the Tres Amigas is scheduled to begin June 2012. The expected

commercial operating date for Phase 1 is March, 2015.

Figure 1 shows a high level illustration of the Tres Amigas Phase I interconnection configuration.

Figure 1 - Tres Amigas Phase 1 Interconnection Configuration

Tres Amigas, LLC has requested a wires-to-wires interconnection with PNM. PNM entered into

a Non-Tariff Study Agreement with Tres Amigas, LLC to assess both the short circuit capability

at the Blackwater Station and the steady state and dynamic effects associated with the proposed

interconnection of the Tres Amigas project to the PNM transmission system. ABB, Inc. was

retained by PNM to perform a System Impact Study (“Study”).

The Study will evaluate delivery of power in and out of Tres Amigas beyond Blackwater Station

on an “as available” basis only using non-firm transmission capacity. For Blackwater power

transfers from east to west, existing and pending requests today outstrip the transmission

capacity of the Blackwater-BA 345 kV line (“BB line”). Based on previous technical analysis,

even if the existing commitments are reduced to zero, without additional voltage support, the

Tres Amigas’s ability to deliver power would be constrained. For Blackwater power transfers

from west to east, on the other hand, a limitation on long-term firm transmission capacity from

Four Corners to Albuquerque arising from congestion on WECC Path 48 (“Path 48”) will require

2

new transmission to be constructed for firm deliveries to Blackwater and therefore the Study will

evaluate only off-peak load conditions to assess possible impacts of the proposed interconnection

of the Tres Amigas on the PNM transmission system for Path 48.

PNM and Tres Amigas, LCC acknowledge and agree that future studies will be required once

users of Tres Amigas make firm point-to-point transmission delivery service and that nothing in

this Study will constitute an offer of transmission service or confers upon Tres Amigas any right

to receive transmission service from PNM.

Study Objectives

Based on the above information and additional information supplied by PNM in response to the

Tres Amigas’ interconnection request, the objectives of this Study for PNM were as follows:

1. Base case development

2. Assess the short circuit capability at the Blackwater Station to determine if there is

sufficient short-circuit capability to support the Tres Amigas interconnection at the

Blackwater Station.

3. Analyze the reactive power and AC voltage control strategies between the Tres Amigas

and Blackwater HVDC converters.

4. Assess steady state and dynamic effects on the PNM transmission system with the

addition of Stage 1.

5. Report

Following this Study a more detailed technical study will be performed employing a 3-phase

model to analyze all the control features at Blackwater Station, NM Wind Energy Center

wind farm, and the Argonne Mesa wind farm along with its static var compensator (referred

to as “STATCOM”). This analysis will be performed at a later date and will evaluate the

impact of the Tres Amigas Stage 1 converter with regard to control interactions between

devices, temporary over-voltages, coordination of control and protection, evaluation of single

pole switching, low order harmonic resonance and AC filter performance, and dynamic over

voltages

3

2 Planned Tres Amigas Facilities – Stage 1

Stage 1 of the Tres Amigas project involves the construction of a 750 MW VSC HVDC link

between the PNM system at Clovis, NM and the SPP system at the Tolk generating station in

Amarillo, Texas. The proposed link is in parallel with the existing Blackwater HVDC station at

Clovis. The HVDC facility consists of:

A 750 MW, 399 kV two-terminal VSC HVDC system to be supplied by Alstom Grid UK

LTD. The reactive power capability curves for the VSC converters are illustrated below in

Figure 2. Data for the transformers supplying both converter stations is shown below in Table

1.

Approximately 56 miles of 2-conductor bundle, 1272 kcmil single circuit 345 kV transmission

line for the connection to the SPP system at the Tolk generating station.

Approximately 22 miles of 2-conductor bundle, 1272 kcmil single circuit 345 kV transmission

line for the connection to the PNM Blackwater Station.

Table 1 - Converter Transformer Data

Description Station A Station B

Nominal MVA rating 825 MVA 825 MVA

Vector Group YNd11yn

Nominal Line Winding Voltage 345.0 kVrms 345.0 kVrms

Rated Valve Winding Voltage 399.0 kVrms

Valve winding voltage range: Nominal

Maximum

Minimum

399.0 kVrms

462.0 kVrms

320.0 kVrms

Transformer impedance between the line winding and valve winding

(on 825 MVA, 399kV base) 0.157 pu

Impedance tolerance 5.0%

4

Figure 2 - Reactive Power Capacity of the Converter

-600

-400

-200

0

200

400

600

800

-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800

Real Power (P), MW

Reac

tive

Pow

er (Q

), M

var

Nominal AC System Voltage

Minimum AC System Voltage

Maximum AC System Voltage

5

3 Study Process

The impact on the performance of the PNM transmission system of transmitting 750 MW via the

Tres Amigas interconnection was determined by conducting steady-state and dynamic stability

analyses using the process described below. The objective of this analysis was to identify

whether the transfers lead to steady state criteria violations or system instability with respect to

rotor angle and voltage stability. To this end, the following tasks have been completed:

1. Base case development

2. Short circuit capability assessment.

3. Assessment of the reactive power and AC voltage control strategies between the Tres

Amigas and Blackwater HVDC converters.

4. Steady state and dynamic assessment

The applicable WECC criteria were used to evaluate the results of this study.

3.1 Setup of PSLF Base Cases

All Phase 1 tasks use GE PSLF as the analysis tool, and therefore require PSLF power flow

models as a precondition. Starting with the pre-project base conditions modeled in the 2015

(HS) peak load and 2013-14 (HW1A) off-peak load power flow conditions provided by PNM,

system performance was analyzed for a number of normal and contingency conditions. The pre-

and post-project analysis of the Tres Amigas interconnection included the following base

conditions:

Pre-Project Analysis: 1) E-W (east to west) Operation: Blackwater at 200MW

2) W-E (west to east)Operation: Blackwater at 200 MW

3) SVC Operation: Blackwater in SVC mode (0 MW transfer)

Post-Project Analysis: 1) E-W Operation: Blackwater and Tres Amigas at 200 + 750 = 950 MW

2) E-W Operation: Without dynamic reactive voltage support

a. Blackwater 200 MW E-W

b. Blackwater off-line

3) W-E Operation: Blackwater and Tres Amigas at 200 + 750 = 950 MW

4) W-E Operation: Without dynamic reactive voltage support

a. Blackwater 200 MW

b. Blackwater off-line

5) SVC Operation:

a. Blackwater in SVC mode; Tres Amigas at 750 MW, E-W

b. Blackwater in SVC mode; Tres Amigas at 750 MW, W-E

E-W power flow cases were based on PNM 2015 peak system conditions while W-E cases were

based on the PNM 2013-14 off-peak system conditions, due in large part to the transmission

capacity limitations arising from congestion on Path 48. Existing firm transmission

6

commitments on the PNM’s transmission system were reduced to analyze the power delivery

capability (power in or out) of Tres Amigas up to 750 MW. All powerflow cases were

developed with input from PNM regarding load and generation dispatch. Furthermore, in order

to accommodate the high transfer levels on the BB line anticipated with the Tres Amigas project

and to maintain acceptable system performance2 at the 750 MW transfer level, additional fixed

and/or dynamic reactive compensation was modeled at the Guadalupe 345 kV station, along with

a synchronous condenser at Tres Amigas 345 kV station. Post project cases without the reactive

compensation at the Guadalupe 345 kV station and the synchronous condenser at Tres Amigas

were analyzed to determine the Tres Amigas maximum transfer capability without system

improvements.

It should also be noted that since the Tres Amigas HVDC will interconnect with the SPP system

at the Tolk generating station, an equivalent model of the Southwestern Public Service Company

(SPS) transmission system in the Texas panhandle was integrated into power flow models

provided by PNM. The equivalent provided by SPS was intended to improve the accuracy of the

PNM-side study by including the impedance between the SPS Blackwater and Tres Amigas

stations. No effort was made in this study to assess the impact of the Tres Amigas addition on

the SPS network. SPS will be investigating these aspects separately.

3.2 Investigation of Short Circuit Capability at the Blackwater Station

When a VSC HVDC transmission is operated in grid-parallel mode, i.e., the converters are

connected via ac transmission to a high-inertia ac network, an inner-loop current control strategy

is typically used. This strategy requires that the ac system at the point of interconnection has

sufficient strength (sufficient short circuit capacity) to ensure stable operation of the VSC. In

other words, for grid-parallel operation of the Tres Amigas VSC HVDC converters, the Tres

Amigas project will require a minimum short circuit strength at the Blackwater 345 kV station.

The Blackwater HVDC, on the other hand, also has certain short circuit requirements. Line-

commutated, thyristor-based HVDC technology requires the presence of a synchronizing voltage

of sufficient strength (short-circuit capacity) for commutation. As a rule of thumb, conventional

HVDC converters typically will require a short-circuit strength of at least 2 to 3 times the MW

rating of the HVDC line in order to operate reliably. This comparison is captured in a quantity

called the Short Circuit Ratio, SCR, as follows:

HVDC

SC

MW

MVASCR

For example, a 1000 MW HVDC system connected to an ac bus with a short circuit capacity of

2500 MVA would have an SCR of 2500/1000 = 2.5. The minimum SCR for conventional

HVDC converters is generally considered to be 2 to 3.

Line-commutated converters also consume significant amounts of reactive power in the

conversion process. For this reason, shunt capacitor and ac filter banks are required on the ac

2 The powerflow and stability performance criteria provided by PNM are given in Section 4 below.

7

bus at the converter, effectively increasing the fundamental frequency driving point impedance

of the ac network. This effect is captured in a refinement of the above equation, yielding the

Effective Short Circuit Ratio (ESCR) as follows:

HVDC

bankscapSC

MW

MVARMVAESCR

For example, adding 625 MVAR of filter and shunt capacitor banks to the system described

above yields an ESCR of (2500-625)/1000 = 1.9, which is very low. Present design guidance for

conventional HVDC is to avoid situations where the ESCR is less than 2.0.

The results of the short circuit capability assessment were therefore intended to evaluate the need

for additional short-circuit capacity at the Blackwater station in order to support the parallel

operation of the Tres Amigas 750 MW and Blackwater 200 MW HVDC interconnections. The

short circuit functionality of PSLF was used in combination with the power flow base cases

provided by PNM to evaluate the three-phase short circuit levels at the Blackwater 345 kV bus

for critical system conditions. Where short circuit machine data, Xd’’, was unavailable via the

power flow base case or the PSLF dynamics database, typical values of Xd’’ based on machine

ratings were used. The results of this task provide an indication as to which system conditions

may not meet the short-circuit requirements for both Blackwater and Tres Amigas, and will

therefore require supplementary synchronous generation and/or synchronous condensers.

3.3 Reactive Power and AC Voltage Control Strategies

The Blackwater HVDC incorporates sophisticated control functions that balance reactive power

and control of the Blackwater 345 kV ac voltage by careful coordination of ac filter and reactor

bank switching, tap changer operation, and converter firing angle calculation. Parallel operation

of the Blackwater and Tres Amigas converters was therefore analyzed to ensure an appropriate

overall strategy for reactive power and ac voltage control, and to identify the potential for control

interactions between the converters.

In conjunction with the recent Blackwater HVDC Upgrade project, ABB has developed a highly

detailed model of the Blackwater HVDC system and its controls for use in PSLF. The user

defined models include representations of the following control features:

Filter bank switching and tap changer operation: Emulated in powerflow solution model.

Closed-loop ac voltage controls, firing angle calculations: Simulated in dynamics model.

The fast-acting closed loop controls that affect firing angle calculation are fully represented in

the dynamics model. The powerflow model emulates the effect of the slower-acting filter bank

and tap changer control loops to establish a steady-state voltage reference for Blackwater.

The Blackwater PSLF model described above is assumed to be a reasonable starting point for

assessment of the impact of the Tres Amigas addition, i.e.

8

1) Shunt compensation requirements to support the additional power flow on the BB line

2) Steady-state voltage stability of the combined Blackwater / Tres Amigas system

3) Closed-loop dynamic voltage stability of the combined Blackwater / Tres Amigas system

To address the first two effects above, Q-V analysis was used to analyze the BB line injections.

This line has relatively high series impedance and shunt admittance and these characteristics play

a significant role in the overall performance of the system. For item 3 above, dynamic

simulation of the combined Blackwater/Tres Amigas system was used for the evaluation.

3.3.1 Voltage Stability Analysis

Items 1 and 2 listed above can be evaluated by using Q-V analysis for voltage stability. Q-V

analysis is used to determine the amount of reactive power required to hold a given voltage at a

given bus, with consideration given to contingencies. Each point on the Q-V curve is a separate

powerflow solution. The presence of reactive power reserves is indicated by a curve that goes

below zero, and the amount of the reserves for a given bus voltage is the distance from the zero

Q axis to the Q-V curve at that bus voltage. The Q-V curve is also useful in identifying systems

near voltage collapse, as its shape becomes flat (low dQ/dV) at the voltage stability limit. Stable

system performance is indicated when the Q-V curve has positive slope (positive dQ/dV).

Unstable system performance is identified when the Q-V curve has negative slope (negative

dQ/dV). The point where the Q-V curve flattens out and reaches a minimum value is an area of

voltage instability. For example, as the curve flattens, it only takes a small change in reactive

power to result in a large change in voltage. At the minimum point, an increase in reactive

power could either increase or decrease the voltage.

In addition to identifying the stability limit, the bottom of the Q-V curve defines the minimum

reactive power requirement for stable operation. When the minimum point on the Q-V curve is

above the zero Q axis, the powerflow case will not solve without additional reactive

compensation. In this event, the minimum point indicates how much compensation is needed at

the designated bus in order to maintain the voltage at that minimum point. Without additional

compensation, the voltage will collapse which is indicated by powerflow cases that do not solve.

For the present study, Q-V analysis was performed at the anticipated point of the minimum

system voltage during high transfers via the Blackwater and Tres Amigas interconnections, in

other words, at the Guadalupe 345 kV station. The Q-V analysis was performed in PSLF using

powerflow analysis methods and the power flow cases established in Task 1 above.

3.3.2 Dynamic Analysis for Small-Signal Disturbances

To address the closed-loop dynamic voltage stability of the combined Blackwater/Tres Amigas

system, dynamic simulations of the following scenarios were performed:

1) Blackwater and Tres Amigas at 200+750 = 950 MW, E-W:

- Switch MSSC at Blackwater

- Switch shunt reactor at Guadalupe

2) Blackwater and Tres Amigas at 200+750 = 950 MW, W-E:


9


3) Blackwater in SVC mode; Tres Amigas at 750 MW, E-W:



4) Blackwater in SVC mode; Tres Amigas at 750 MW, W-E:



The dynamic analysis for the small-signal disturbance conditions described above was performed

in PSLF using the Blackwater HVDC user-defined dynamics model, the Tres Amigas HVDC

dynamics model provided by Tres Amigas, and the base power flow conditions established

above in Task 1. The generic vwscc model in PSLF was used to represent the assumed SVC at

Guadalupe 345 kV station.

3.4 Large-Signal Dynamic Effects on PNM System

The purpose of the large-signal dynamic analysis was to assess the impact of the proposed Tres

Amigas interconnection on the PNM transmission system for selected large-signal contingency

scenarios and conditions. Using positive sequence analysis methods, the overall performance of

the system was evaluated in terms of the following:

Disturbances to PNM system voltage profile

Rotor-angle stability of PNM system

Voltage stability of PNM system

The steady-state conditions established previously in Task 1 were used as the initial conditions

for dynamic simulations of the N-1 and N-2 contingencies specified by PNM. PSAS scripts

were used for both case automation and result presentation, including the identification of

voltage and branch loading violations due to the Project. Plots for the dynamic cases are

provided as appendices to this study report.

It should be noted that this assessment is to be considered only an approximate investigation of

possible impact of the proposed Tres Amigas interconnection. It is recognized that future studies

will be required if Tres Amigas or others seek to obtain firm point-to-point delivery service.

10

4 Study Criteria

Powerflow and stability performance criteria provided by PNM are given below in Table 2 and

in the paragraphs to follow.

Table 2 - Power Flow Performance Criteria

Area Conditions Load Limits Voltage (pu) Voltage

Drop Application

EPEC (Area 11)

Normal < Normal Rating

0.95 - 1.05 69kV and above

0.95 - 1.10 Artesia 345 kV

0.95 - 1.08 Arroyo 345 kV PST source side

0.90 - 1.05 Alamo, Sierra Blanca and Van Horn 69kV

Contingency < Emergency Rating

0.925 - 1.05 7% 60 kV to 115 kV

0.95 - 1.07 7% Artesia 345kV

0.95 - 1.08 7% Arroyo 345kV PST source side

0.90 - 1.05 Alamo, Sierra Blanca and Van Horn 69kV

0.95 - 1.05 7% Hidalgo, Luna, or other 345 kV buses

PNM

(Area 10)

Normal ALIS < Normal Rating 0.95-1.05 46 kV and above*

Contingency N-1 < Emergency Rating

0.925-1.08*** 6%** 46 kV to 115 kV

0.90 – 1.08*** 6%** 230 kV and above

Contingency N-2 < Emergency Rating 0.90-1.08*** 10% 46 kV and above*

Tri- State (zones

120-123)

Normal ALIS < Normal Rating 0.95-1.05 All buses

Contingency N-1 < Emergency Rating

0.90-1.1 6%** 69 kV and above except Northeastern NM and Southern NM

0.90-1.1 7%** 69 kV and above in Northeastern NM and

Southern NM

Contingency N-2 < Emergency Rating 0.90-1.1 10% All buses

*Taiban Mesa and Guadalupe 345 kV voltage 0.95 and 1.1 p.u. under normal and contingency conditions. **Tri-State Voltage Criteria, April 2008 – Correspondence to TSS. *** Provided operator action can be utilized to adjust voltages back down to 1.05

All equipment loadings must be below their normal ratings under normal conditions.

All line loadings must be below their emergency ratings for both single and double

contingencies. All transformers and equipment with emergency rating should be below their

emergency rating.

Following fault clearing for single contingencies, voltage on load buses may not dip more than

25% of the pre-fault voltage or dip more than 20% of the pre-fault voltage for more than 20

cycles. For double contingencies, voltage on load buses may not dip more than 30% of the pre-

fault voltage or dip more than 20% of the pre-fault voltage for more than 40 cycles.

Voltage stability criteria requires: “The most reactive deficient bus must have adequate reactive

power margin for the worst single contingency to satisfy either of the following conditions for

n-i outages, whichever is worse: (i) a 5% increase beyond maximum forecasted loads or (ii) a 5%

increase beyond maximum allowable interface flows. The worst single contingency is one that

causes the largest decrease in the reactive power margin.” For double contingencies (i.e., breaker

failures) the reactive margin requirement is reduced to an increase of 2.5%% beyond maximum

load or flows.

11

5 Study Conditions and Assumptions

5.1 Base Cases

Table 3 below summarizes the eight base power flow cases developed as part of this

investigation. As noted in the table, all E-W power flow cases are based on the PNM 2015

Heavy Summer peak case, while W-E cases are based on the PNM 2013-14 HW1A off-peak

case.

Table 3 - Powerflow Base Conditions

Case Direction

Blackwater

Schedule

(MW)

Tres

Amigas

Schedule

(MW)

Description

2015 Peak East-to-West

200 0 Pre-project

0 0 Pre-project; Blackwater in SVC mode

200 750 Post-project

0 750 Post-project; Blackwater in SVC mode

2013-14 Off-peak West-to-East

200 0 Pre-project

0 0 Pre-project; Blackwater in SVC mode

200 750 Post-project

0 750 Post-project; Blackwater in SVC mode

Figures 3 through 10 below illustrate the base power flow conditions developed for this study.

Figure 11 illustrates the equivalent model of the SPS transmission system in the Texas panhandle

integrated into the power flow models provided by PNM.

12

Figure 3 - Peak East-to-West; Blackwater at 200 MW (Pre-project)

13

Figure 4 - Peak East-to-West; Blackwater in SVC mode (Pre-project)

14

Figure 5 - Peak East-to-West; Blackwater at 200 MW, Tres Amigas at 750 MW

15

Figure 6 - Peak East-to-West; Blackwater in SVC mode, Tres Amigas at 750 MW

16

Figure 7 - Off-peak West-to-East; Blackwater at 200 MW (Pre-project)

17

Figure 8 - Off-peak West-to-East; Blackwater in SVC mode (Pre-project)

18

Figure 9 - Off-peak West-to-East; Blackwater at 200 MW, Tres Amigas at 750 MW

19

Figure 10 - Off-peak West-to-East; Blackwater in SVC mode, Tres Amigas at 750 MW

20

Figure 11 - SPS System Equivalent

21

As noted previously, all full transfer cases with the Tres Amigas HVDC system modeled at

750 MW include additional reactive compensation at the Guadalupe 345 kV station. Table 4

below summarizes the combinations of switched and dynamic reactive compensation modeled at

Guadalupe for each of the system configurations listed in Table 3. The level of static reactive

compensation required for each base case was based on the results of the steady-state analysis

presented in Section 6 below. Dynamic reactive compensation was sized based on the results of

the dynamic stability assessment presented in Section 10. Specifically, the N-2 breaker failure

contingency at the B-A 345 kV station was the dimensioning case for the ±250 MVAr SVC

listed in Table 4

Table 4 Guadalupe 345 kV Reactive Compensation

Case Direction

Blackwater

Schedule

(MW)

Tres

Amigas

Schedule

(MW)

Guadalupe Reactive Compensation

Static

(MVAr)

Dynamic

(MVAr)

2015 Heavy

Summer East-to-West

200 0 0 0

0 0 0 0

200 750 350 ±250

0 750 150 ±250

2013-14 HW1A

Off-peak West-to-East

200 0 0 0

0 0 0 0

200 750 450 ±250

0 750 200 ±250

5.2 Models

5.2.1 Blackwater HVDC Model

The PSLF powerflow and stability models for the 200 MW back-to-back Blackwater HVDC

system is fully documented in reports [1] and [2]. The model includes the following control

functions:

Measurements

DC Bus Voltage Processing and Constant Power Control

Current Control

o AC Voltage Dependent Current Order Limiter

o Current Control Amplifier

o SVC Regulator

Voltage Control

o Overvoltage Limiter

o AC Voltage Regulator

o Voltage Regulator

Firing Control

22

The following functions are not included in the PSLF dynamics model:

2nd harmonic damping

Single phase auto reclosure detection

5.2.2 Tres Amigas VSC Model

The PSLF stability model for the 750 MW, 399 kV Tres Amigas VSC HVDC system to be

supplied by Alstom Grid UK LTD is documented in [3].

5.2.3 Tres Amigas Synchronous Condenser Model

In anticipation of the additional short circuit capacity that will be required at the Blackwater/Tres

Amigas 345 kV station for operation of the Tres Amigas HVDC system at 750 MW, a 250 MVA

synchronous condenser was modeled at the Tres Amigas 345 kV station via a 13.8/345 kV, 7%

GSU transformer. The machine model is set to regulate the 345 kV voltage in both the

powerflow and dynamic simulations. The following synchronous condenser parameters were

modeled in the PSLF dynamic simulations:

Table 5 - Blackwater/Tres Amigas Synchronous Condenser Model

Parameter Value Parameter Value

Machine Model: genrou Exciter: esac8b

MVA 250.0 Tr 0.00

Tpdo 12.350 Kpr 200.00

Tppdo 0.058 Kir 5.00

Tpqo 0.188 Kdr 10.00

Tppqo 0.188 Tdr 0.10

H 4.000 Vrmax 35.00

D 0.000 Vrmin 0.00

Ld 2.476 Ka 10.00

Lq 1.180 Ta 0.00

Lpd 0.385 Te 1.20

Lpq 1.180 Vfemax 0.00

Lppd 0.257 Vemin 0.00

L1 0.146 Ke 1.00

S1 0.180 Kc 0.55

S12 0.708 Kd 1.10

Ra 0.0024 e1 6.50

rcomp 0.000 se1 0.30

xcomp 0.000 e2 9.00

accel 0.500 se2 3.00

Vtmult 0.00

Spdmlt 0.00

The parameters chosen for the machine and excitation system models used in the study are based

on typical synchronous condenser parameters from [4]. The size of the unit is to be determined

during the course of the study.

23

5.2.4 Guadalupe Dynamic Reactive Compensation Model

An additional ±250 MVar of dynamic reactive compensation was modeled at the Guadalupe

345 kV station in order to accommodate the higher transfer levels on the BB line anticipated with

the Tres Amigas project. The dynamic compensation was modeled in this study as a static var

compensator (“SVC”) using the PSLF vwscc model. As noted previously, the size of this SVC is

based on the results of the dynamic stability assessment and will be discussed in more detail in

Section 10. The parameters selected for the model are listed below in Table 6.

Table 6 - Guadalupe SVC Model

Parameter Value

SVC Model: vwscc

Ts1 0.00

Vemax 99.00

Ts2 0.00

Ts3 0.30

a 1.00

b 1.00

Ts4 0.00

Ts5 0.00

Ksvs 300.00

Ksd 0.00

Bmax 2.50

Bpmax 2.50

Bpmin -2.50

Bmin -2.50

Ts6 0.000

Dv 99.00

Xc 0.00

Tc 0.00

Td1 0.00

5.2.5 SPS Equivalent Machine Models

Machine data for all machines represented in the SPS equivalent are listed below in Table 7.

Each machine was represented as a voltage source behind the machine subtransient reactance

using the static classical user model, epcgencls. The machine reactances listed below are in per

unit on the assumed machine base. The GSU reactances were supplied in per unit on a 100

MVA base.

Table 7 - SPS Equivalent Machine Models

Machine kV ID

Machine

Base

(MVA)

Xd’’

(pu)

GSU

Base

(MVA)

XGSU

(pu)

XSRC

(pu)

511541 SWEETWT6 230 2 200.00 0.160 100.0 0.062 0.1420

523097 HITCHLAN 345 1 490.00 0.250 100.0 0.034 0.0850

523978 HARR BUS 230 1 1030.00 0.280 100.0 0.029 0.0562

524044 NICHOLS 230 1 400.00 0.230 100.0 0.047 0.1045

525481 PLANT X 230 1 441.00 0.230 100.0 0.045 0.0972

525543 TOLK_6 230 1 1600.00 0.310 100.0 0.025 0.0440

525830 TUCO 230 230 1 168.00 0.180 100.0 0.074 0.1811

526337 JONES 6 230 1 700.00 0.290 100.0 0.025 0.0664

24

Machine kV ID

Machine

Base

(MVA)

Xd’’

(pu)

GSU

Base

(MVA)

XGSU

(pu)

XSRC

(pu)

527849 LEA CO 2 230 1 500.00 0.250 100.0 0.055 0.1050

527865 CUNNHAM 230 1 450.00 0.250 100.0 0.079 0.1346

511456 O.K.U.-7 345 1 100.00 0.120 100.0 0.082 0.2020

Based on the PGEN values supplied for the machines modeled on the SWEETWT6 and

YOAKUM 230 kV stations, and on the NOBLE 345 kV station, an SVC model was used to

represent these machines in the dynamic simulations. Data for the vwscc SVC model used is

listed below in Table 8.

Table 8 - SPS SVC Models

Parameter Value

SVC Model: vwscc

Ts1 0.00

Vemax 99.00

Ts2 0.00

Ts3 0.20

a 1.00

b 1.00

Ts4 0.00

Ts5 0.00

Ksvs 300.00

Ksd 0.00

Bmax 9.00

Bpmax 9.00

Bpmin -9.00

Bmin -9.00

Ts6 0.000

Dv 99.00

Xc 0.00

Tc 0.00

Td1 0.00

25

6 Steady-State Analysis

Table 9 summarizes transmission facilities overloaded as a result of the Tres Amigas addition.

Note that transmission facilities that are overloaded in the original pre-project base cases are not

included in the table below. Table 10 through Table 13 summarize steady-state voltage

violations in the post-project base cases, both with and without contingencies. Post-contingency

voltage violations were determined with TCUL transformers locked and only generators and

continuously-controlled shunt banks, i.e., SVCs, regulating.

For operation of the Tres Amigas HVDC transmission facility at 750 MW, loadings on the

Taiban Mesa-Blackwater 345 kV circuit exceed the 753 MVA normal/emergency ratings for all

base conditions with the exception of the 2015 peak case with Blackwater operating in SVC

mode. However, it should be noted that the 753 MVA rating is a wave trap limitation. Once this

limitation is removed, the circuit rating will be 1076 MVA. Pre-contingency voltage violations,

comparing post-project voltages with Tres Amigas operating at 750 MW to pre-project

conditions, include the Ojo and Taos 345 kV stations in the peak cases, and the HLWR_1 and

Duran 115.00 kV stations, and the Torrance 115.00 kV and 34.5 kV buses in the off-peak cases.

The remaining pre-contingency voltage violations noted in the tables below were also found to

be violations in the original pre-project base cases.

With the exception of the Alamo 69 kV station, which is flagged as a voltage violation in both

the pre- and post-project systems for both peak and off-peak conditions, there are no additional

post-contingency voltage violations for peak conditions with east-to-west transfers on both

Blackwater and Tres Amigas. For off-peak conditions, however, with Blackwater and Tres

Amigas operating at a combined west-to-east loading of 950 MW, voltage stability issues are

evident for N-2 contingencies involving outages of the two BA-Rio Puerco 345 kV circuits. The

powerflow case for this contingency would not solve under these conditions, due to a voltage

collapse. For an outage of a single San Juan-Rio Puerco 345 kV circuit, the powerflow case

converges but violations of the 6% N-1 voltage drop criteria are evident at numerous area 10 and

zone 121 buses. With Blackwater operating in SVC mode for a total west-to-east transfer of

750 MW, the outage of both BA-Rio Puerco 345 kV circuits solves but voltage violations exceed

the N-2 10% voltage drop criteria at a number of area 10 and zone 121 buses. A preliminary

investigation appears to indicate that additional reactive compensation at the B-A 115 kV bus

may be an effective means of remedying voltage issues brought on as a result of this outage.

Outages on the BB line under heavy west-to-east conditions cause a voltage rise that would

benefit from additional reactive compensation in this area. Further investigation will be needed

to determine what mitigations are will be needed to operate with criteria.

In the off-peak west-to-east transfer case, if the Aragonne Mesa and NM Wind Energy Center

wind farms are off-line, the BA–Guadalupe 345 kV line becomes overloaded due to transmission

losses and the reactive power requirements of the line. In this operating scenario, the project was

reduced to 725 MW west-to-east transfers, which allowed the line to be operated at its rated

limit. To operate the project at the full output, the BA-Guadalupe 345 kV line would have to be

reconductored because of the high intermittency of the wind farms.

26

Table 9 - Overloaded Transmission Facilities

From To ID Loading Rating

(MW)

Loading

(%) MW MVAr MVA

2015 Peak East-to-West Transfers; Blackwater at 200 MW; Tres Amigas at 750 MW

BLACKWTR 345 kV TAIBANMS 345 kV 1 949.2 102.2 954.7 753.01 120.9

2015 Peak East-to-West Transfers; Blackwater in SVC Mode; Tres Amigas at 750 MW

None

2013-2014 Off-Peak West-to-East Transfers; Blackwater at 200 MW; Tres Amigas at 750 MW

BLACKWTR 345 kV TAIBANMS 345 kV 1 -969.1 333.2 1024.8 753.0 131.6

2013-2014 Off-Peak West-to-East Transfers; Blackwater in SVC Mode; Tres Amigas at 750 MW

BLACKWTR 345 kV TAIBANMS 345 kV 1 -769.2 155.6 784.8 753.0 100.4

1. The 753 MVA rating for the Blackwater-Taiban Mesa 345 kV circuit is a wave trap limitation. When removed,

the circuit rating will be 1076 MVA.

27

Table 10 - Steady-State Voltage Violations 2015 Peak East-to-West Transfers; Blackwater at 200 MW; Tres

Amigas at 750 MW

Bus Area/Zone Voltage

(pu)

Voltage

Drop

(%)

Notes

Post-Project, Pre-Contingency Voltage Violations1

ALAMO 69.00 kV 11 1.1050 -0.0544 Violation in Pre-project Case

OJO 345.00 kV 10 1.0594 1.5182 Voltage exceeds 1.05 pu voltage criteria

ARGONNE4 138.00 kV 10 1.0599 -1.7048 Violation in Pre-project Case


TAOS 345.00 kV 121 1.0617 1.5837 Voltage exceeds 1.05 pu voltage criteria

CINIZA 13.80 kV 122 0.9256 0.0508 Violation in Pre-project Case

Post-Contingency N-1 Voltage Violations: FOURCORN-WESTMESA 345.00 1 Outage

ALAMO 69.00 kV 11 1.1039 -0.1178 Violation in Pre-contingency Case

Post-Contingency N-1 Voltage Violations: SAN_JUAN-RIOPUERC 345.00 1 Outage


Post-Contingency N-1 Voltage Violations: B-A-NORTON 345.00 1 Outage


Post-Contingency N-1 Voltage Violations: RIOPUERC-WESTMESA 345.00 1 Outage


Post-Contingency N-1 Voltage Violations: RIOPUERC-BA 345.00 2 Outage


Post-Contingency N-1 Voltage Violations: WESTMESA-ARR___PS 345.00 1 Outage


Post-Contingency N-1 Voltage Violations: B-A 345.00/115.00 1 Outage



RIOPUERC-BA 345.00 2 Outage





Post-Contingency N-2 Voltage Violations: WESTMESA-SANDIA 345.00 1 Outage

WESTMESA 345.00/115.00 1 Outage


1. Pre-contingency voltage violations compare post-project voltages for base conditions with Tres Amigas operating

at 750 MW to the corresponding pre-project voltages.

28

Table 11 -Steady-State Voltage Violations 2015 Peak East-to-West Transfers; Blackwater in SVC Mode; Tres

Amigas at 750 MW


(pu)

Voltage

Drop

(%)

Notes


ALAMO 69.00 kV 11 1.1053 0.0022 Violation in Pre-project Case

OJO 345.00 kV 10 1.0562 1.8159 Voltage exceeds 1.05 pu voltage criteria



TAOS 345.00 kV 121 1.0587 1.9399 Voltage exceeds 1.05 pu voltage criteria

CINIZA 13.80 kV 122 0.9265 0.1408 Violation in Pre-project Case


























29

Table 12 - Steady-State Voltage Violations 2013-14 Off-Peak West-to-East Transfers; Blackwater at 200 MW;

Tres Amigas at 750 MW


(pu)

Voltage

Drop

(%)

Notes



HLWR_1 115.00 kV 10 1.0522 1.4050 Voltage exceeds 1.05 pu voltage criteria



TORRANCE 34.50 kV 120 1.0531 1.4269 Voltage exceeds 1.05 pu voltage criteria

DURAN 115.00 kV 120 1.0519 1.4181 Voltage exceeds 1.05 pu voltage criteria


CINIZA 13.80 kV 122 0.9253 -0.0249 Violation in Pre-project Case





12ST_TAP 46.00 kV 10 0.9305 -7.3863 6% voltage drop criteria exceeded

ARRIBA 115.00 kV 10 0.9552 -7.5988 6% voltage drop criteria exceeded

ARRIBA_T 115.00 kV 10 0.9555 -7.5955 6% voltage drop criteria exceeded

BACA 46.00 kV 10 0.9293 -7.3959 6% voltage drop criteria exceeded

VALENCIA 46.00 kV 10 0.9318 -7.3754 6% voltage drop criteria exceeded


GALLINAT 115.00 kV 10 0.9554 -7.5969 6% voltage drop criteria exceeded

ALCA_TAP 69.00 kV 121 0.9427 -6.2311 6% voltage drop criteria exceeded

BLACKLAK 69.00 kV 121 0.9611 -6.8538 6% voltage drop criteria exceeded

BLACKLAK 115.00 kV 121 0.9686 -6.5699 6% voltage drop criteria exceeded

HERNANDZ 69.00 kV 121 0.9418 -6.3145 6% voltage drop criteria exceeded

HERNANDZ 115.00 kV 121 0.9704 -6.8297 6% voltage drop criteria exceeded

OJO 115.00 kV 121 0.9784 -6.4946 6% voltage drop criteria exceeded

ROWE_TAP 115.00 kV 121 0.9676 -6.6361 6% voltage drop criteria exceeded

SPRINGER 69.00 kV 121 0.9785 -6.5361 6% voltage drop criteria exceeded

SPRINGER 115.00 kV 121 0.9602 -6.2948 6% voltage drop criteria exceeded

STORRIE 69.00 kV 121 0.9582 -7.7337 6% voltage drop criteria exceeded


TAOS 69.00 kV 121 0.9664 -6.6451 6% voltage drop criteria exceeded



YORKCANY 69.00 kV 121 0.9596 -7.0324 6% voltage drop criteria exceeded

YORKCANY 115.00 kV 121 0.9435 -6.9097 6% voltage drop criteria exceeded

OJOCALIT 115.00 kV 121 0.9711 -6.7055 6% voltage drop criteria exceeded

OJOCALI 115.00 kV 121 0.9709 -6.7088 6% voltage drop criteria exceeded

CIMARRON 115.00 kV 121 0.9585 -6.3807 6% voltage drop criteria exceeded

RAINVL_T 115.00 kV 121 0.9528 -7.3661 6% voltage drop criteria exceeded

RAINVL1 115.00 kV 121 0.9537 -7.3661 6% voltage drop criteria exceeded

CRUZALTAT 115.00 kV 121 0.9712 -6.4346 6% voltage drop criteria exceeded

CRUZALTA 115.00 kV 121 0.9712 -6.4346 6% voltage drop criteria exceeded



30


(pu)

Voltage

Drop

(%)

Notes


ALAMO 69.00 kV 11 1.0726 0.1292 Violation in Pre-contingency Case









Case not solved.









31

Table 13 - Steady-State Voltage Violations 2013-14 Off-Peak West-to-East Transfers; Blackwater in SVC

Mode; Tres Amigas at 750 MW


(pu)

Voltage

Drop

(%)

Notes



HLWR_1 115.00 kV 10 1.0515 1.2682 Voltage exceeds 1.05 pu voltage criteria




DURAN 115.00 kV 120 1.0513 1.2848 Voltage exceeds 1.05 pu voltage criteria


CINIZA 13.80 kV 122 0.9286 -0.0173 Violation in Pre-project Case


















12ST_TAP 46.00 kV 10 0.8933 -10.8673 Voltage less than the 0.9 pu voltage criteria

ARRIBA 115.00 kV 10 0.9241 -11.1266 10% voltage drop criteria exceeded

ARRIBA_T 115.00 kV 10 0.9244 -11.1216 10% voltage drop criteria exceeded

BACA 46.00 kV 10 0.8921 -10.8822 Voltage less than the 0.9 pu voltage criteria

CANYON 46.00 kV 10 0.9170 -10.3171 10% voltage drop criteria exceeded

CAPITOL 46.00 kV 10 0.9085 -10.4326 10% voltage drop criteria exceeded

COLINAS 115.00 kV 10 0.9336 -10.2126 10% voltage drop criteria exceeded

ELDORAD# 115.00 kV 10 0.9349 -10.1004 10% voltage drop criteria exceeded

ELDRADOT 115.00 kV 10 0.9350 -10.0983 10% voltage drop criteria exceeded

FT_MARCY 46.00 kV 10 0.9109 -10.4031 10% voltage drop criteria exceeded

HICKOX 46.00 kV 10 0.9084 -10.4332 10% voltage drop criteria exceeded

PECOS 46.00 kV 10 0.9291 -10.1348 10% voltage drop criteria exceeded

VALENCIA 46.00 kV 10 0.8947 -10.8503 Voltage less than the 0.9 pu voltage criteria


32


(pu)

Voltage

Drop

(%)

Notes

ZIA_2 46.00 kV 10 0.9341 -10.0519 10% voltage drop criteria exceeded

GALLINAT 115.00 kV 10 0.9243 -11.1238 10% voltage drop criteria exceeded

ROWE 24.90 kV 121 0.9194 -10.5755 10% voltage drop criteria exceeded

ROWE_TAP 115.00 kV 121 0.9291 -10.6850 10% voltage drop criteria exceeded



RAINVL_T 115.00 kV 121 0.9319 -10.0103 10% voltage drop criteria exceeded

RAINVL1 115.00 kV 121 0.9328 -10.0102 10% voltage drop criteria exceeded







Post-Contingency N-1 Voltage Violations: B-A – Guadalupe 345.00 1 Outage (25 worst 115 kV voltages)

RIOPUERC 115 kV 10

1.091

Need to get

this

Voltage violation

NORTON_1 115 kV 10 1.09 Voltage violation

VALENCIA 115 kV 10 1.09 Voltage violation

ARRIBA_T 115 kV 10 1.089 Voltage violation

GALLINAT 115 kV 10 1.089 Voltage violation

NORTON_2 115 kV 10 1.089 Voltage violation

ARRIBA 115 kV 10 1.088 Voltage violation

STORRIE 115 kV 10 1.088 Voltage violation

AN_TAP 115 kV 10 1.087 Voltage violation

B-A 115 kV 10 1.087 Voltage violation

SHELLTAP 115 kV 10 1.087 Voltage violation

CDELRIO 115 kV 10 1.086 Voltage violation

CUCHILLA 115 kV 10 1.086 Voltage violation

ZAFARANT 115 kV 10 1.086 Voltage violation

BUCKMAN 115 kV 10 1.086 Voltage violation

BECKNER 115 kV 10 1.085 Voltage violation

MEJIA 115 kV 10 1.085 Voltage violation

MEJIA_T 115 kV 10 1.085 Voltage violation

MGLLUJAN 115 kV 10 1.085 Voltage violation

RODEO_T 115 kV 10 1.085 Voltage violation

STATEPEN 115 kV 10 1.085 Voltage violation

ZIA_1 115 kV 10 1.085 Voltage violation

ZIA_2 115 kV 10 1.085 Voltage violation



33

7 Short Circuit Capability Assessment

As stated previously, the results of the short circuit capability assessment were intended to

evaluate the need for additional short-circuit capacity at the Blackwater station in order to

support the parallel operation of the Tres Amigas and Blackwater HVDC interconnections. The

short circuit functionality of PSLF was used in combination with the power flow base cases

provided by PNM to evaluate the three-phase short circuit levels at the Blackwater 345 kV

station for critical system conditions. Where the subtransient machine reactance, Xd’’, was

unavailable in the power flow base case or the PSLF dynamics database, typical values of Xd’’ based on machine ratings were used. All short circuit cases were run with the Tres Amigas and

Blackwater HVDC stations, including all filter and capacitor banks, disconnected. Post-project

cases included a 250 MVA synchronous condenser at the Blackwater/Tres Amigas 345 kV

station. The results of this analysis are listed below in Table 11.

In general, it can be stated that short circuit levels are greater for the off-peak versus peak cases

due primarily to the fact that the off-peak cases include local wind farm generation at Lonesome

Mesa, Aragonne Mesa, and the NM Wind Energy Center, all of which contribute on the order of

280 MVA to the short circuit level at Blackwater. Pre-project SCR’s range from 2.5 for the peak

case and 4.2 for the off-peak case for the N-2 outage of the two BA-Rio Puerco 345 kV circuits,

to 3.4 and 4.8 with all transmission facilities in service in the peak and off-peak cases,

respectively.

Short circuit levels are on the order of 450 MVA greater for the post project system

configuration with the addition of the synchronous condenser at the Tres Amigas 345 kV station.

However, the post-project SCR’s for Blackwater and Tres Amigas operating at a combined

loading of 950 MW are much lower, ranging from 1.0 and 1.4 for outages of the two BA-Rio

Puerco 345 kV circuits in the peak and off-peak cases, respectively, to 1.2 and 1.5 with all

transmission facilities in service. Since the short circuit requirements for the Tres Amigas VSC

converters were unknown at the time of the study, it is unclear as to exactly what conditions may

prove to be too weak to provide for stable operation of both systems at 950 MW. It was

therefore not possible to estimate synchronous condenser size based on the short circuit levels

indicated in the system models provided. Condenser sizing will be based on dynamic

performance requirements and the results provided by the dynamic stability analysis.

Table 14 - Blackwater 345 kV Short Circuit Levels

Case Contingency

Impedance Fault

MVA Magnitude

(pu)

Angle

(deg)

PRE-PROJECT CASES

Peak 200 MW

All Transmission Facilities in Service 0.1468 81.1 681.20

Four Corners-West Mesa 345 kV Outage 0.1508 80.0 663.13

Rio Puerco-San Juan 345 kV Outage 0.1572 79.1 636.13

BA-Norton 345 kV Outage 0.1487 81.2 672.49

Rio Puerco-West Mesa 345 kV Outage 0.1558 80.9 641.85

BA-Rio Puerco 345 kV #1 Outage 0.1506 80.9 664.01

West Mesa-Arroyo PS 345 kV Outage 0.1482 80.7 674.76

B-A Transformer Outage 0.1492 81.3 670.24

B-A Transformer and Rio Puerco-BA Outages 0.1547 81.2 646.41

34

Case Contingency

Impedance Fault

MVA Magnitude

(pu)

Angle

(deg)

BA-Rio Puerco 345 kV #1 & 2 Outages 0.1969 78.1 507.87

West Mesa Transformer and West Mesa-Sandia Outages 0.1468 81.2 681.20

Off-Peak 200 MW












POST-PROJECT CASES

Peak 950 MW












Off-Peak 950 MW












35

8 Voltage Stability analysis

The reactive shunt compensation requirements to support the additional power flow on the BB

line and the steady-state voltage stability of the combined Blackwater/Tres Amigas systems have

been evaluated using Q-V analysis, the results of which are presented below in Figures 12 and 13

and summarized in Table 15. For the purposes of this study, additional dynamic reactive

compensation was only considered at the Guadalupe 345 kV station.

Table 15 - Q-V Analysis at the Guadalupe 345 kV Station

Case

HVDC Schedule

Contingency

Reactive Power Requirements

Blackwater

(MW)

Tres

Amigas

(MW)

@ 1.05 pu

Voltage

(MVar)

@ 1.00 pu

Voltage

(MVar)

Minimum

(MVar)

Voltage at

Minimum

(pu)

2015 Peak; East-to-

West Transfers 200 750

All Transmission

Facilities in Service 381 261 85 0.908

0 750 All Transmission

Facilities in Service 197 66 < -148 < 0.900

2013-2014 Off-

Peak; Peak; West-to-East Transfers


Facilities in Service 488 Unstable 461 1.034


Facilities in Service 168 43 -37 0.962

As indicated in Table 15, up to 488 MVar of additional reactive compensation is required at the

Guadalupe 345 kV station in order to maintain stable operation at 1.05 pu voltage. Worst case

conditions occur for the 2013-2014 off-peak case with the BB line loaded via west-to-east

transfers of 950 MW on Blackwater and Tres Amigas. Based on the minimum voltage column

in Table 12, voltage collapse is indicated for Guadalupe 345 kV voltages of 1.034 pu or less with

all transmission facilities in service. With Blackwater in SVC mode, reactive reserves in excess

of 148 MVar are available for peak conditions while up to 37 MVar are available for off-peak

conditions with west-to-east transfers. As noted previously in Section 5.1, Table 4, the base case

powerflow conditions established for this study include as fixed MSSC banks on the Guadalupe

345 kV station the 1.05 pu voltage reactive power requirements determined above. The

additional reactive compensation required to dynamically support the Tres Amigas addition is

documented in the dynamic stability analysis presented in Section 10.

36

Figure 12 - 2015 Peak East-to-West QV Analysis

Figure 13 - 2013-2014 Off-Peak West-to-East QV Analysis

37

9 Closed-Loop Dynamic Analysis

To address the closed-loop dynamic voltage stability of the combined Blackwater/Tres Amigas

system, dynamic simulations of capacitor/reactor switching scenarios at Blackwater and

Guadalupe were performed for the following system conditions:

1) Blackwater and Tres Amigas at 950 MW, E-W, peak

2) Blackwater and Tres Amigas at 950 MW, W-E, off-peak

3) Blackwater in SVC mode; Tres Amigas at 750 MW, E-W, peak

4) Blackwater in SVC mode; Tres Amigas at 750 MW, W-E, off-peak

The results of this analysis are summarized below in Table 16. The study results are documented

in Appendix A. Please note that a checked column in the tables indicates that the case was stable

or that the transient voltage dip criteria of the PNM Standards have been satisfied for that

particular contingency and system configuration.

As indicated by the plots in Appendix A, all cases are stable and meet the PNM stability

performance criteria with no evidence of control instabilities in either the Blackwater or Tres

Amigas controls.

Table 16 - 2015 Small-Signal Stability Results

Case No. Stable

Voltage Dip Criteria

< 25%1

< 30%2

> 20% for less than 20 cycles1


2015 Peak; East-to-West Transfers; Blackwater at 200 MW; Tres Amigas at 750 MW

Disconnect 25.6 MVar capacitor at Blackwater 60 kV

Reconnect 65 MVar reactor at Guadalupe 345 kV

2015 Peak; East-to-West Transfers; Blackwater in SVC Mode; Tres Amigas at 750 MW



2013-14 Off-Peak; West-to-East Transfers; Blackwater at 200 MW; Tres Amigas at 750 MW



2013-14 Off-Peak; West-to-East Transfers; Blackwater in SVC Mode; Tres Amigas at 750 MW



1. PNM N-1 Voltage Dip Criteria


38

10 Dynamic Stability Analysis

Stability conditions were studied for the eight scenarios listed in Section 5.1 and the

contingencies listed in Section 9.1 below. The results of the stability study are given in the

following sections.

10.1 Contingencies Case List

Contingencies considered as part of this stability analysis are summarized below in Table 17.

Table 17 - Case List for Stability Analysis

Case No. Case Description Pre-project Post-project

No Disturbance All Transmission Facilities in Service

3p-FW

3-Phase fault on Four Corners-West Mesa 345 kV line at

West Mesa 345 kV. Trip Four Corners-West Mesa 345 kV

line in 4 cycles.

3p-WW

3-Phase fault on Rio Puerco-San Juan 345 kV line at Rio

Puerco 345 kV. Trip Rio Puerco-San Juan 345 kV line in 4

cycles.

3p-NB 3-Phase fault on B-A-Norton 345 kV line at B-A 345 kV.

Trip B-A-Norton 345 kV line in 4 cycles.

3p-RW

3-Phase fault on Rio Puerco-West Mesa 345 kV line at Rio

Puerco 345 kV. Trip Rio Puerco-West Mesa 345 kV line in

4 cycles.

3p-BR 3-Phase fault on BA-Rio Puerco 345 kV line at BA 345.

Trip BA-Rio Puerco line in 4 cycles.

3p-EP 3-Phase fault on West Mesa-Arroyo PS 345 kV line at West

Mesa 345. Trip West Mesa-Arroyo PS line in 4 cycles.

3pBAxfm 3-Phase fault at BA 115 kV. Trip BA 345/115 transformer

in 4 cycles.

1p-RP-BAxfm 1-Phase fault at BA 345 kV. Trip BA 345/115 transformer

and Rio Puerco-BA 345 kV line in 12 cycles.

1p-BR2 1-Phase fault on BA-Rio Puerco 345 kV line at BA 345.

Trip both BA-Rio Puerco lines in 12 cycles.

1p-WSxfm

1-Phase fault at West Mesa 345 kV. Trip West Mesa

345/115 transformer and West Mesa-Sandia 345 kV line in

12 cycles.

These contingencies were examined for both pre-project and post-project conditions, as

appropriate, using the eight powerflow scenarios listed in Table 3. The study results are fully

documented in Appendices B and C for 2015 peak powerflow conditions and 2013-14 off-peak

powerflow conditions, respectively.

10.2 Stability Results

The results of the stability analysis are presented in the appendices of this report. The plots

included in each appendix are as follows:

The 6 largest bus voltage magnitude deviations

The 6 largest bus voltage angle deviations

The 6 largest bus frequency deviations

The 6 largest bus generator speed deviations

39

Blackwater HVDC quantities

Tres Amigas HVDC quantities

Guadalupe and Tres Amigas Reactive Compensation

Appendix B contains the results for the pre- and post-project system configuration for 2015 peak

powerflow conditions. Appendix C presents the results for the pre- and post-project system

configuration for 2013-14 off-peak powerflow conditions. The results for the B-A 345 kV, N-2

breaker failure contingency with remedial actions are presented in Appendix D.

Table 18 through Table 21 below summarize the results. Please note that a checked column in

the tables indicates that the case was stable or that the transient voltage dip criteria of the PNM

Standards have been satisfied for that particular contingency and system configuration.

40

Table 18 - 2015 Peak Stability Results; East-to-West Transfers

Case No. Stable


Notes < 25%1

< 30%2



Blackwater at 200 MW (pre-project)

No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

1p-RP-BAxfm

1p-BR2 Marginally unstable

1p-WSxfm

Blackwater in SVC Mode (pre-project)

No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

1p-RP-BAxfm

1p-BR2

1p-WSxfm

Blackwater at 200 MW; Tres Amigas at 750 MW

No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

1p-RP-BAxfm

1p-BR2 Stable with voltage violations

1p-WSxfm

Blackwater in SVC Mode; Tres Amigas at 750 MW

No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

41

1p-RP-BAxfm

1p-BR2 Stable with voltage violations

1p-WSxfm



Stability violations occur for the N-2 single phase breaker failure fault at the B-A 345 kV bus

with outages of both BA-Rio Puerco 345 kV circuits (“1p-BR2”). As noted in the short circuit

analysis, this scenario is the weakest post contingency configuration considered in this study.

Post fault recovery for this contingency is only marginally stable in the pre-project case with

Blackwater at 200 MW. Blackwater HVDC quantities exhibit a low magnitude oscillation with

very low damping well after the initial fault recovery. With Tres Amigas in operation at

750 MW, system recovery is stable for Blackwater operating in either SVC mode or at 200 MW.

The voltage violations for these cases are listed below in Table 19.

Table 19 - 2015 Peak System Conditions; Case 1p BR2

Bus

Initial

Voltage

(pu)

Voltage Dip

(%)

Time

(sec)

Duration

(cycles)


TAIBANMS 345 kV 1.0343 91.068 1.4062 1.3

3AMIGAS 345 kV 1.0484 78.927 2.3854 1.2

BLACKWTR 345 kV 1.0484 78.478 2.3854 1.2

GUADLUPE 345 kV 1.0483 66.424 1.4062 1.3

ARGONNE4 138 kV 1.0582 66.424 1.4062 1.3

ARGONNE3 138 kV 1.0622 66.424 1.4062 1.3

B-A 345 kV 1.0244 38.774 1.4062 1.3

NORTON 345 kV 1.0267 34.529 2.4271 3.7


BLACKWTR 345 kV 1.0489 46.583 2.2604 1.2

3AMIGAS 345 kV 1.0497 46.398 2.2604 1.2

TAIBANMS 345 kV 1.0188 45.378 2.2604 1.2

GUADLUPE 345 kV 1.0496 31.813 2.2604 1.2

ARGONNE4 138 kV 1.0595 31.813 2.2604 1.2

ARGONNE3 138 kV 1.0635 31.813 2.2604 1.2

42

Table 20 - 2013-2014 Off-Peak Stability Results; West-to-East Transfers

Case No. Stable


Notes < 25%1

< 30%2



Blackwater at 200 MW (pre-project)

No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

1p-RP-BAxfm

1p-BR2

1p-WSxfm

Blackwater in SVC Mode (pre-project)

No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

1p-RP-BAxfm

1p-BR2

1p-WSxfm


No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

1p-RP-BAxfm Stable with voltage violations

1p-BR2 Unstable during recovery

1p-WSxfm


No Disturbance

3p-FW

3p-WW

3p-NB

3p-RW

3p-BR

3p-EP

3pBAxfm

43

1p-RP-BAxfm

1p-BR2 Unstable during recovery

1p-WSxfm



For off-peak conditions with west-to-east transfers on the Blackwater HVDC transmission, there

are no stability or voltage issues for the pre-project configurations. In the post-project cases with

Tres Amigas in operation at 750 MW, however, stability issues occur for the N-2 1p-BR2

contingency. Post fault recovery for this contingency is unstable with Blackwater operating in

either SVC mode or at 200 MW. As noted previously in the steady-state analysis, the powerflow

solution for the post-contingency configuration for this outage would not converge without either

additional reactive compensation on the B-A 345 kV bus, or remedial actions involving the Tres

Amigas HVDC to reduce post-fault loadings on area transmission facilities.

Voltage violations also occur for the N-2 contingency 1p-RP-BAxfm, a single phase, 12 cycle

fault at the B-A 345 kV bus with outages of both the B-A transformer and the Rio Puerco-BA

345 kV circuit. Voltage violations for this case with both Blackwater and Tres Amigas in

operation at a combined loading of 950 MW are listed below in Table 21.

Table 21 - 2013-2014 Off-Peak System Conditions; Case 1p-RP-BAxfm

Bus

Initial

Voltage

(pu)

Voltage Dip

(%)

Time

(sec)

Duration

(cycles)


TAIBANMS 345.0 1.0128 42.421 1.4062 2.5

BLACKWTR 345.0 1.0463 39.404 1.4062 2.5

3AMIGAS 345.0 1.0498 38.918 1.4062 2.5

ARGONNE3 138.0 1.0683 33.070 1.4062 2.5

ARGONNE4 138.0 1.0579 32.467 1.4062 1.3

GUADLUPE 345.0 1.0496 31.055 1.4062 1.3

10.3 Remedial Actions

Remedial actions considered for the stability issues observed for N-2 breaker failure contingency

at the B-A 345 kV bus included the following switching scenarios:

Runback of the Tres Amigas power schedule

Trip the Tres Amigas HVDC transmission and the associated fixed reactive compensation at

the Guadalupe 345 kV station.

Trip both the Tres Amigas and the Blackwater HVDC transmissions and the associated fixed

reactive compensation at the Guadalupe 345 kV station.

A runback of the scheduled power on the Tres Amigas HVDC transmission would be the

preferred option since this leaves the reactive support of the Tres Amigas converters in service

during the post-fault system recovery. However, the PSLF Tres Amigas VSC model used in this

study was very slow in responding to voltage changes at the Tres Amigas 345 kV station,

44

resulting in over voltages in excess of 1.4 pu during the initial post-fault voltage swing. Due to

these issues with the VSC model, alternatives tripping the Tres Amigas facility and tripping both

the Blackwater and Tres Amigas facilities were also considered as part of this study. The results

of the dynamic simulations for each of these scenarios are summarized below in Table 22, with

the description and discussion of each to follow. Detailed results for each case are presented in

Appendix D. Note that only off-peak system conditions with west-to-east transfers on

Blackwater and Tres Amigas were considered in this analysis.

Table 22 - 2013-2014 Off-Peak Stability Results; West-to-East Transfers

Case No. Stable


Notes < 25%1

< 30%2




1p-BR2 Tres Amigas Runback to 100 MW

1p-BR2 Trip Tres Amigas

1p-BR2 Trip Tres Amigas and Blackwater


1p-BR2 Tres Amigas Runback to 200 MW

1p-BR2 Trip Tres Amigas

1p-BR2 Trip Tres Amigas and Blackwater



10.3.1 Tres Amigas DC Power Runback

The initial implementation of the power schedule runback modified the power order variables in

the Tres Amigas user model, vscdc-pnm.p. At the specified time, the power orders for both

converters were set to the desired post fault power order and maintained at that setting for the

duration of the simulation. In addition to the power runback, reactive compensation was

disconnected at the Guadalupe 345 kV station in order to limit the post-fault overvoltages

resulting from the decreased loading on the BB line. Both the runback and the MSSC were

initiated 6 cycles after fault clearing, allowing for a 100 ms communications delay between the

B-A station and the Guadalupe and Tres Amigas stations. Breaker operating time for switching

the MSSC bank was 3 cycles.

The results indicate that a runback to 100 MW does stabilize the system recovery with

Blackwater operating at 200 MW and Tres Amigas initially operating at 750 MW. Voltage

violations for this scenario are listed below in Table 23. It should also be noted that this

switching scenario is the dimensioning case for the dynamic reactive compensation modeled at

the Guadalupe 345 kV station. As indicated in Table 24, the system is unstable at compensation

levels less than ±200 MVar. At ±200 MVar, the system is stable if the 450 MVar Guadalupe

MSSC bank remains in service following fault clearing and unstable when the bank is switched

out of service. With a ±250 MVar SVC at Guadalupe and the 450 MVar MSSC bank switched

out of service as described above, the system is stable with a much improved voltage profile at

the B-A, Guadalupe, and Blackwater 345 kV station.

With Blackwater in SVC mode, a runback to 200 MW is sufficient to stabilize the post-fault

system recovery without additional voltage violations.

45

Table 23 - 2013-2014 Off-Peak System Conditions; Case 1p BR2

Bus

Initial

Voltage

(pu)

Voltage Dip

(%)

Time

(sec)

Duration

(cycles)

Blackwater at 200 MW; Tres Amigas at 750 MW; Runback to 100 MW

ARGONNE4 138 1.0579 60.316 1.4021 11.3

ARGONNE3 138 1.0683 60.122 1.4021 11.3

GUADLUPE 345 1.0496 58.862 1.4021 10.0

B-A 345 0.9861 58.201 1.4021 11.3

NORTON 345 0.9804 53.054 1.4021 11.3

NORTON_1 115 1.0428 47.378 1.4021 10.0

NORTON_2 115 1.0424 47.194 1.4021 10.0

POWRPLNT 115 0.0000 46.853 1.4021 10.0

BUCKMAN 115 1.0410 46.827 1.4021 10.0

MEJIA 115 1.0372 46.794 1.4021 10.0

MEJIA_T 115 1.0378 46.688 1.4021 10.0

SPACHECO 115 1.0367 46.644 1.4021 10.0

MGLLUJAN 115 1.0376 46.628 1.4021 10.0

BECKNER 115 1.0374 46.541 1.4021 10.0

STATEPEN 115 1.0378 46.539 1.4021 10.0

ZIA_2 115 1.0373 46.526 1.4021 10.0

ZIA_1 115 1.0372 46.516 1.4021 10.0

RODEO_T 115 1.0373 46.512 1.4021 10.0

ZAFARANT 115 1.0384 46.326 1.4021 10.0

SCRSTBLT 115 1.0362 45.967 1.4021 10.0

SCRSTBL 115 1.0359 45.974 1.4021 10.0

CDELRIO 115 1.0397 45.943 1.4021 10.0

CUCHILLA 115 1.0433 45.924 1.4021 10.0

SHELLTAP 115 1.0436 45.922 1.4021 10.0

AN_TAP 115 1.0401 45.829 1.4021 10.0

B-A 115 1.0452 45.728 1.4021 10.0

ELDORAD# 115 1.0354 45.409 1.4021 10.0

ELDRADOT 115 1.0356 45.402 1.4021 10.0

COLINAS 115 1.0350 44.745 1.4021 10.0

BUDAGERS 115 0.0000 43.830 1.4021 10.0

WHITEROK 115 1.0299 43.329 1.4021 8.8

ROWE_TAP 115 1.0339 41.363 1.4021 10.0

STA 115 1.0268 41.321 1.4021 8.8

ETA 115 1.0252 40.930 1.4021 8.8

LA-MPF 115 1.0258 40.800 1.4021 8.8

WTA 115 1.0248 40.712 1.4021 8.8

TA-3 115 1.0244 40.394 1.4021 8.8

NO_BERN 115 1.0453 40.294 1.4021 10.0

S_DOMING 115 1.0415 38.824 1.4021 8.8

AVILA 115 1.0455 36.555 1.4021 8.8

AVILA_T 115 1.0456 36.551 1.4021 8.8

LA_JARA 115 1.0429 35.777 1.4021 8.8

TAIBANMS 345 1.0128 35.009 1.4021 6.3

VALENCIA 115 1.0334 34.961 1.4021 8.8

SNYSIDRO 115 1.0410 34.897 1.4021 8.8

ENCHNTED 115 1.0401 34.330 1.4021 7.5

ALGODONE 115 1.0399 34.276 1.4021 7.5

46

Bus

Initial

Voltage

(pu)

Voltage Dip

(%)

Time

(sec)

Duration

(cycles)

ARRIBA 115 1.0311 33.944 1.4021 8.8

GALLINAT 115 1.0313 33.937 1.4021 8.8

ARRIBA_T 115 1.0314 33.927 1.4021 8.8

STORRIE 115 1.0309 33.404 1.4021 7.5

PRGRSS 115 1.0380 31.693 1.4021 6.3

PACHMANN 115 1.0391 31.669 1.4021 6.3

3AMIGAS 399 1.0849 29.858 1.7562 1.3

Table 24 - 2013-2014 Off-Peak Stability Results; Dynamic Compensation Requirements

Case

No. Description

Guadalupe

Dynamic

Compensation

(MVAr)

Post-Fault

Static

Compensation1

(MVAr)

Guadalupe

345 kV

Voltage

(pu)

Blackwater

345 kV

Voltage

(pu)

1p-

BR2

1-Phase fault on BA-Rio

Puerco 345 kV line at BA

345 kV. Trip both BA-Rio

Puerco lines in 12 cycles.

Tres Amigas Runback to

100 MW at 18 cycles.

< ±200 450 Unstable Unstable

0 Unstable Unstable

±200 450 1.6514 1.6699

0 Unstable Unstable

±250 450 1.6867 1.7196

0 1.1376 1.3456

1. 450 MVAr pre-fault static compensation for all cases

47

10.3.2 Tripping Tres Amigas and Guadalupe Fixed Reactive Compensation

Tripping the Tres Amigas HVDC transmission was initiated via the status parameters of the

machine models representing the VSC converters in the powerflow. At the specified time, both

converters were removed from service by setting the power flow machine status of each to 0. In

addition to tripping the converters, fixed reactive compensation was disconnected at the

Guadalupe 345 kV station in order to limit the post-fault overvoltages resulting from the

decreased loading on the BB line. Both the trip and the MSSC switching were initiated 6 cycles

after fault clearing, allowing for a 100 ms communications delay between the B-A station and

the Guadalupe and Tres Amigas stations. Breaker operating time for switching the shunt MSSC

bank was 3 cycles.

The results of the dynamic simulations with Blackwater in SVC mode and Tres Amigas

operating at 750 MW indicate that tripping the Tres Amigas HVDC transmission is sufficient to

stabilize the post fault recovery of the system without voltage violations. With Blackwater

operating at 200 MW, it is unclear as to whether or not tripping Tres Amigas stabilizes the

system recovery. Initially, the system is slow to recover and appears to recover about 6 seconds

after the fault is cleared. However, at about 9 seconds, the Blackwater HVDC transmission

becomes unstable and the transmitted dc power is reduced to zero. This is thought to be the

result of an instability in the PSLF Blackwater HVDC model brought on by the weakened post-

fault system configuration. Additional study is recommended for this scenario when a more

detailed technical study is performed. Voltage violations for the case are listed below in Table

25.

Table 25 -2013-2014 Off-Peak System Conditions; Case 1p BR2

Bus

Initial

Voltage

(pu)

Voltage Dip

(%)

Time

(sec)

Duration

(cycles)

Blackwater at 200 MW; Tres Amigas at 750 MW; Trip Tres Amigas at 18 cycles

3AMIGAS 345 1.0498 81.542 2.8604 8.7

BLACKWTR 345 1.0463 80.623 3.6312 10.0

TAIBANMS 345 1.0128 56.218 1.6937 7.5

ARGONNE3 138 1.0683 40.566 1.6729 8.8

ARGONNE4 138 1.0579 39.969 1.6937 7.5

GUADLUPE 345 1.0496 39.170 1.7146 6.3

10.3.3 Tripping Tres Amigas, Blackwater, and Guadalupe Fixed Reactive Compensation

In addition to tripping the Tres Amigas HVDC transmission as described above, this switching

scenario initiated tripping of the Blackwater HVDC transmission via the status parameters of the

dcc models representing the conventional HVDC converters in the powerflow. At the specified

time, both the Tres Amigas and Blackwater converters were removed from service by setting the

power flow model status for each to 0. In addition to tripping the converters, reactive

compensation was disconnected at the Guadalupe 345 kV station in order to limit the post-fault

overvoltages resulting from the decreased loading on the BB line. Both the trip and the MSSC

switching were initiated 6 cycles after fault clearing. Breaker operating time for switching the

MSSC bank was 3 cycles.

48

With Blackwater at 200 MW and Tres Amigas at 750 MW, the results of the dynamic simulation

indicate that tripping both the Tres Amigas and Blackwater HVDC transmissions is sufficient to

stabilize the post fault recovery of the system. Voltage violations for the case, listed below in

Table 26, were limited primarily to the Blackwater station and vicinity. With Blackwater in

SVC mode, tripping both the Tres Amigas and Blackwater HVDC transmissions stabilized the

post-fault system recovery without any voltage violations.

Table 26 - 2013-2014 Off-Peak System Conditions; Case 1p BR2

Bus

Initial

Voltage

(pu)

Voltage Dip

(%)

Time

(sec)

Duration

(cycles)

Blackwater at 200 MW; Tres Amigas at 750 MW; Trip Tres Amigas & Blackwater at 18 cycles

3AMIGAS 345 1.0498 44.352 1.4021 1.3

BLACKWTR 345 1.0463 44.154 1.4021 1.3

ARGONNE3 138 1.0683 41.295 1.4021 2.5

TAIBANMS 345 1.0128 41.261 1.4021 1.3

ARGONNE4 138 1.0579 39.538 1.4021 2.5

GUADLUPE 345 1.0496 37.389 1.4021 1.3

49

11 PNM Transfer Analysis without Dynamic voltage support

During the course of Phase 1 analysis it was mutually agreed by PNM and Tres Amigas to

evaluate the project without dynamic voltage support at Guadalupe station and the synchronous

condenser at the Tres Amigas station to determine what total transfers could take place absent

network upgrades. This analysis was performed by PNM in parallel to the work being performed

by ABB. This section summarizes the analysis performed and its results.

The analysis reviewed a normal system configuration with all transmission facilities in service

along with the most limiting contingencies for transfers to and from the BB line in northern New

Mexico. Table 27 below lists the scenarios considered for this transfer analysis. These are used

as the metric for determining total transfer capability absent dynamic voltage support.

Table 27 - Scenarios considered for Transfer Analysis

Case Description

All Transmission Facilities in Service

Four Corners-West Mesa 345 kV Outage

Rio Puerco-San Juan 345 kV Outage

BA-Norton 345 kV Outage

11.1.1 Transfer Case development

Four transfer cases were created out of the post project cases that ABB has created for the study:

Case Direction

Blackwater

Schedule

(MW)

2015 Heavy

Summer East-to-West

200

0

2013-14 HW1A

Off-peak West-to-East

200

0

Aragonne Mesa and NM Wind Energy Center wind farms were off-line and not contributing to

reactive power requirements of the B-A – Blackwater line for the purposes of determining total

transfer capability.

11.2 Voltage Stability

PV analysis was performed to determine how much power could be transferred in a steady state

powerflow model. The Tres Amigas project transfer was incremented or decremented in the

analysis to determine when voltage collapse would occur at the Guadalupe 345 kV station for

any of the contingencies listed in Table 27. The limit is established at 5% below the total

transfer at the voltage collapse point based on WECC criteria. Dynamic stability analysis is then

50

performed at the transfer limit to verify a lower dynamic stability limit is not present. The

maximum transfers achieved are plotted in Error! Reference source not found. below for the

ontingencies in Table 27. Table 288 shows the results of this analysis in tabular format.

Figure 14 - PV Analysis Plots

Table 28: Voltage stability limit without dynamic voltage support

Case Type Transfer Direction Tres Amigas

Transfer

Blackwater

Transfer

Total

Transfers

2015 Peak E-W 480 200 680 2015 Peak E-W 676 Off-line 676

2013-14 Off-peak W-E 371 200 571 2013-14 Off-peak W-E 550 Off-line 550

11.3 Stability Analysis

Once the transfer limit was established based on voltage stability, dynamic stability simulations

at the transfer limits were performed to ensure stable operation. Table 2929 below represents the

maximum Tres Amigas Transfers limited by the implied behavior of the dynamic model

provided for the project.

51

Table 29: Stability Analysis Results

Case Type Transfier Direction Tres Amigas

Transfer

Blackwater

Transfer

Total

Transfers

2015 Peak E-W 377 200 577 2015 Peak E-W 450 Off-line 450

2013-14 Off-peak W-E 355 200 555 2013-14 Off-peak W-E 450 Off-line 450

52

12 Conclusions and Recommendations

The purpose of the preceding study was to evaluate the interconnection of the 750 MW Stage 1

Tres Amigas VSC HVDC transmission facility between the PNM transmission system at Clovis,

New Mexico and the SPP transmission system at the Tolk generating station east of Muleshoe,

Texas. The proposed transmission facility is approximately in parallel with the existing PNM

Blackwater HVDC interconnection at Clovis. Due to the lack of available firm transmission

capacity in the vicinity of the Blackwater station, the present study was to evaluate

interconnecting and transferring power in and out of the Project on an “as available” basis only,

using only non-firm transmission capacity. The objectives of the Study included:

1. An assessment of the short circuit capacity at the Blackwater Station to determine if

sufficient system strength is available to support simultaneous operation of the Tres

Amigas and Blackwater facilities.

2. An analysis of the reactive power and AC voltage control strategies of the Tres Amigas

and Blackwater HVDC converters.

3. An assessment of the steady state and dynamic performance of the PNM transmission

system with the addition of Stage 1.

Peak load conditions were considered for east-to-west transfers while only off-peak load

conditions were considered for west-to-east transfers. Base cases included both operation of the

Blackwater converters at rated capacity and in Static Var Compensator (“SVC”) mode. ABB,

Inc. was retained by PNM to perform the analysis with support from PNM.

Short Circuit Capability Assessment

The results of the short circuit capability assessment determined that there is not sufficient short

circuit capability at the Blackwater Station to support the simultaneous operation of the Project

and the existing 200 MW Blackwater Station. The short circuit requirements for the Project

converters are not fully known due to the simplified positive sequence models used for the

Study. To provide enough short circuit capability to support the operation of both the Project

and Blackwater Station, the Study assumed this capacity would be provided by synchronous

condensers Tres Amigas would locate at the Project station. To maintain acceptable dynamic

system performance, the size of the synchronous condenser was established at 250 MVA.

Steady-State Performance

The powerflow analysis shows that substantial additional voltage support will be required to

accommodate the combined total power transfer of the Project and the Blackwater Station. The

total current associated with the full 950 MW westbound power transfer requirement on the BB

line remained below the conductor thermal rating (1076 MVA) but exceeded the BB line

wavetrap rating (717 MVA) and the voltage stability limit of 371 MVA identifyied in the

analysis3. When modeling the full transfer requirement in the eastbound direction, the maximum

transfer that could be accomodated without exceeding the thermal limit was 925 MW. As with

the westbound direction, the maximum transfer was found to be limited to 480 MW without

3 This voltage stability limit was established by powerflow studies. Due to its length, the BB has relatively low

surge impedance loading (426 MVA). Without compensation, it cannot be loaded much more than the surge

impedance loading because angle stability cannot be maintained.

53

substantial additional voltage support along the BB line and to no more than 717 MVA without

replacement of the BB line wavetraps.

The additional voltage support requirements identified along the BB line to support the total

power transfer from west-to-east included the addition of 450 Mvar of MSSC banks at the

Guadalupe 345 kV station in order to maintain stable operation for worst case off-peak system

conditions. Based on requirements for the various system configurations examined, a maximum

step size of 150 Mvar for the MSSCs is recommended. In addition to the MSCCs, the addition

of a ±250 Mvar SVC at Guadalupe is required in order to meet both the dynamic stability

performance requirements and voltage change requirements for switching the MSSC banks.

In addition to the above requirements, an outage of the BB line for the westbound transfers can

cause 115 kV station voltages in the Albuquerque area to rise above acceptable limits. Since

PNM does not currently have automatic voltage-controlled shunt devices on the system in the

Albuquerque area that could be used to limit 115 kV overvoltages, an automatic voltage-

controlled shunt reactor at the BA 115 kV station may be required.

Dynamic Analysis for Small-Signal Disturbances

Dynamic simulations of capacitor/reactor switching scenarios at Blackwater and Guadalupe

345 kV stations were performed to determine the closed-loop dynamic voltage stability of the

combined Blackwater/Tres Amigas systems. All cases are stable and meet the PNM stability

performance criteria with no evidence of control instabilities in either the Blackwater or Tres

Amigas controls.

Dynamic Stability Performance

Dynamic stability violations were identified for off-peak system conditions. The violations

occur for a single line to ground fault with delayed clearing (breaker failure scenario) at the B-A

345 kV station resulting in the double line outage of both BA-Rio Puerco 345 kV circuits. This

contingency is the driver for the size requirements of the 250 Mvar SVC at Guadalupe.

Even with the SVC, remedial actions are required for this contingency. The following scenarios

were considered:

1. Runback of the Tres Amigas power schedule combined with tripping the MSSC banks at

Guadalupe.

2. Tripping Tres Amigas and the Guadalupe MSSC banks

3. Tripping Tres Amigas, the Blackwater Station, and the Guadalupe MSSC banks

The results of the study indicate that either scenario 1 or 2 is sufficient to stabilize the system.

54

Short Circuit Analysis

Short circuit studies were conducted to determine if the existing circuit breakers, particularly at

Blackwater and BA, can handle the increased fault currents associated with the Tres Amigas

project. Based on these results, the existing circuit breakers are adequate.

Blackwater Facilities

The interconnection of the project will require the addition of a 345 kV three breaker ring bus at

Blackwater. The existing station consists of a single breaker for isolating the Blackwater Station

from the BB line.

Conclusions

The results presented in this report show that the Project will require several system

improvements for the “as available” transmission service scenario assumed in the Study. The

minimum system improvements required to support the full 950 MW combined transfer

capability of the Blackwater and Tres Amigas facilities include:

250 MVA synchronous condenser to be located at the Project station.

3 - 150 Mvar MSSC banks to be located at the Guadalupe 345 kV station.

±250 Mvar SVC to be located at the Guadalupe 345 kV station.

Expand the Blackwater Station from a single breaker to a three breaker 345 kV ring bus

station.

Re-conductor the BA-Guadalupe 345 kV line.

Replace the communication wave trap on the BB line.

An automatic voltage-controlled shunt reactor to be located at the BA 115 kV station.

The Study also identified the maximum transfer in or out of the Project absent the system

improvements identified above, excluding the expansion of the Blackwater switchyard. These

maximum transfers are summarized in the table below:

Without System Improvements


East to West 377 / 480 200 577 / 680 East to West 450 / 676 off-line 450 / 676 West to East 355 / 371 200 555 / 571 West to East 450 / 550 off-line 450 / 550

The first number reflects reduced transfer levels to address apparent operational limitations of

the Project likely resulting from the lack of adequate short-circuit capacity at the Blackwater 345

kV switchyard. The limitations are implied by the behavior of the dynamic model provided for

the Project. The second number reflects voltage stability limitations of the BB line.

Discussions with Tres-Amigas have indicated that estimates for the scenario without system

improvements are of primary interest. As a result cost estimates included in the Study are

limited to expansion of the Blackwater 345 kV switching station into a three breaker ring bus.

The cost estimate and schedule are summarized below:

55

Interconnection item Cost

Estimated

Time for construction

Expand the Blackwater Station from a single to three breakers $7 M 18 months

The results of this analysis are preliminary and may be modified based on more detailed

technical study (Phase 2) to analyze the control interactions between devices, temporary over-

voltages, coordination of control and protection, evaluation of single pole switching, low order

harmonic resonance, AC filter performance and dynamic over voltages. Furthermore, future

studies will be required to identify the necessary transmission line and station additions for

utilization of the Project that exceeds the “as available” service limitations assumed in the Study

once users of Tres Amigas make firm point-to-point transmission delivery service requests.

Nothing in this Study is intended to imply any right to receive transmission service from PNM

until such upgrades are defined and in-service.

The results of the Study are based on available data and assumptions made at the time of

conducting the Study. The results provided in this report may not apply if any of the data, models

and/or other assumptions used to perform the Study change.

56

13 References

[1] ABB Technical Report 2010-E3019-1.1.R00, “Blackwater HVDC Upgrade Project

PSLF Powerflow Model”, February 5, 2010.

[2] ABB Technical Report 2010-E3019-2.1.R00, “Blackwater HVDC Upgrade Project

PSLF Dynamics Model”, February 5, 2010.

[3] GE Technical Report, “Voltage Source Converter User Written Model – Final Report”,

October 17, 2011.

[4] Anderson and Fouad, “Power System Control and Stability”, The Iowa State University

Press, 1977

power systems consulting tres amigas interconnection ... · power systems consulting tres amigas...

Documents