Facility Rating Methodology
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Facility Ratings Methodology
FAC-008-3 Compliance Document
Establishment Date: December 19, 2016
Effective Date: July 14th, 2017
Approved by:
Job Title Name
Manager, Network & IRP Transmission Planning
Sachin Verma
Version:1 0.5
1 The Facility Ratings Methodology (FRM) was established on December 19, 2016, and is subject to change based on new information and input collected during NV Energy Facility Ratings data collection.
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Contents
Scope ............................................................................................................................................................................. 4
Overview ................................................................................................................................................................... 4
Hierarchy of Reference Sources for Manufacturer/Nameplate Ratings ................................................................... 4
Determination of Most Limiting Facility .................................................................................................................... 4
Jointly-Owned Facility Ratings................................................................................................................................... 5
Procedures for Ring and Breaker-and-a-Half Bus Configurations ............................................................................. 5
Procedures for Non-standard Bus Configurations .................................................................................................... 5
Methodology ................................................................................................................................................................. 6
Transmission Line Conductor - [TRANSMISSION PLANNING].................................................................................... 6
Underground Cable Ratings .................................................................................................................................. 8
Transformers – [TRANSMISSION PLANNING] .......................................................................................................... 10
Shunt Compensation Devices [SUBSTATION DESIGN] ............................................................................................ 12
Series Compensation Devices [SUBSTATION DESIGN] ............................................................................................ 13
Circuit Breakers/Circuit Switchers [SUBSTATION DESIGN]...................................................................................... 14
Bus [SUBSTATION DESIGN] ...................................................................................................................................... 15
Jumpers [SUBSTATION DESIGN] .............................................................................................................................. 17
Disconnect Switches [SUBSTATION DESIGN] .......................................................................................................... 18
Line Switches [TRANSMISSION ENGINEERING] ....................................................................................................... 19
Current Transformers (CTs) [SUBSTATION DESIGN & SYSTEM PROTECTION] ........................................................ 20
Control Cables and Wiring [SUBSTATION DESIGN] ................................................................................................. 21
Protective Relay Devices [SYSTEM PROTECTION] ................................................................................................... 22
Wave Traps [SUBSTATION DESIGN] ........................................................................................................................ 24
Facility Rating Communication ................................................................................................................................... 25
Reliability Coordinator Communication .................................................................................................................. 25
Neighboring Entities ................................................................................................................................................ 25
Communication of Thermal Rating Incursions ........................................................................................................ 25
Change Control Process .............................................................................................................................................. 26
Facility Ratings Methodology .................................................................................................................................. 26
Facility Ratings Data/Spreadsheet .......................................................................................................................... 26
Facility Ratings Updates – SharePoint Workflow .................................................................................................... 30
Example Workflow .............................................................................................................................................. 31
Version History ............................................................................................................................................................ 33
Appendix A - Analysis of Weather Assumptions .......................................................................................................... 34
Appendix B - Standard Conductor Ratings................................................................................................................... 37
Appendix C – NV Energy MOT Conductor Ratings ....................................................................................................... 41
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Appendix D – Aluminum Conductor Bus Ratings (Classes AA and A) .......................................................................... 42
Appendix E - Standard Bus Ratings .............................................................................................................................. 44
Appendix F – Control Cable Ratings ............................................................................................................................. 45
Appendix G – NVE Jointly-owned Facility Rating Data Request .................................................................................. 46
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Scope Overview This document provides NV Energy’s methodology for developing and communicating Facility Ratings of its solely
and jointly-owned Facilities. This document defines the basis for the calculation of normal and emergency ratings
of NV Energy Bulk Electric System (BES) Facilities, to comply with the requirements of NERC Reliability Standard FAC-
008-3.
NV Energy’s Transmission Planning department has primary responsibility for developing and maintaining the Facility
Ratings and methodology, beyond the Generator Step-up (GSU) Transformer high-side bushings2. Facility Ratings
collection is a collaborative effort between multiple NV Energy departments: Substation Construction and
Maintenance, Substation Design, System Protection, Transmission Civil Engineering and Construction, and
Transmission Planning. The NV Energy Generation department maintains primary responsibility for developing
Facility Ratings for Generation Facilities and equipment up to the high-side bushings of the GSU3.
NV Energy’s transmission system is designed such that the high-side bushings of the GSU are the point of
interconnection between the Generator Owner and the Transmission Owner. Given that there are no Facilities
between the generation Facilities and the point of interconnection with the Transmission Owner, NV Energy, by
definition does not own or operate Facilities addressed under Requirement 2. Procedural documents and Element
data association with Generation Facilities are owned and maintained by the NV Energy Generation department.
Hierarchy of Reference Sources for Manufacturer/Nameplate Ratings Several reference sources will be used to establish equipment ratings based on manufacturer or nameplate ratings. The following list establishes a hierarchy of reference sources used when establishing equipment nameplate or manufacturer ratings. 1) Manufacturer data or correspondence 2) Nameplate drawing or image 3) Engineering single line diagram 4) Other engineering drawings (plan view, section views, bill of materials, etc.) 5) Purchase Orders The highest ranked resource known at the time the rating is established will be used in establishing the equipment
rating.
Determination of Most Limiting Facility The NERC defined term, Facility, is “a set of electrical equipment that operates as a single Bulk Electric System
Element.” In addition, the NERC defined term, Element, is “any electrical device with terminals that may be
connected to other electrical devices such as a generator, transformer, circuit breaker, bus section, or transmission
line. An Element may be comprised of one or more components.”
Elements in series, which make up a Facility (line section, substation transformer circuit, shunt reactive device), will
be reviewed to determine which Element(s) have the most limiting rating. NV Energy’s Facility Rating shall respect
the most limiting applicable Equipment Rating of the individual equipment that comprises that Facility4.
2 FAC-008-3 R6 3 FAC-008-3 R1 4 FAC-008-3 R3.3
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If information is received suggesting that a more limiting Element exists on a Facility, NV Energy will take steps to
verify the information, which may include field inspections. Once review and field verification, (if applicable) is
complete, NV Energy will take steps to mitigate any differences identified for either the Facility normal rating or
Facility emergency rating.
Jointly-Owned Facility Ratings In cases where a BES Facility is shared with an external entity (such as a line terminal being owned by one party
and the line conductor by another party), NV Energy takes into account rating data provided by the owner(s) of the
segment(s) of the Facility and applies the most limiting rating as the rating of the Facility. The communication
process for requesting these ratings can be found in the Establishment and Communication of Facility Ratings
section of this Methodology.
In cases where a Facility is jointly owned (such as two owners each owning an undivided 50% ownership interest in
a Facility), the operator of the Facility determines the Facility rating and shares this rating information with the
other joint owners.
Procedures for Ring and Breaker-and-a-Half Bus Configurations In the event that a line section or bulk power transformer terminates on a substation configured as a ring bus or a
breaker-and-half, the facility rating for long-range planning models will be determined assuming a closed ring bus
or closed breaker-and-a-half. The most limiting facility rating of the entire ring bus or the most limiting facility
rating of the breaker positions adjacent to the line section or bulk power transformer in a breaker-and-a-half
scheme are considered in determining the rating of the line section or bulk power transformer. In order to account
for the flow split when entering a closed ring or closed breaker-and-a-half, a multiplier is used to adjust the ratings
of the ring bus or breaker-and-a-half facilities. The multiplier assumes a split of 50%-50%, meaning that 50% of the
line section flow or bulk transformer flow is assumed to be transferred onto one leg of the ring bus or breaker-and-
a-half. This results in the ring bus or breaker-and-a-half limit (including breakers, switches, and jumpers) being
adjusted by 200% to account for the flow split of a closed ring or a closed breaker-and-a-half.
Procedures for Non-standard Bus Configurations In the event that a bulk power transformer terminates on a substation not configured in a ring bus or a breaker-
and-half, the facility rating for long-range planning models will still be determined assuming a configuration with
all breakers closed. In order to account for the flow split when entering, the non-standard configuration, a
summation of the connected breaker ratings (Breaker A + Breaker B….+ Breaker N = Facility Rating) multiplied by a
safety factor of .75, is used to adjust the ratings of transformer facilities.
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Methodology5 Transmission Line Conductor - [TRANSMISSION PLANNING]
Background
NV Energy’s original “Legacy” ratings for Northern Transmission Lines were based on values in the Westinghouse
Transmission & Distribution Reference books.
For the Northern system, lines will keep their “Legacy” ratings until Maximum Operating Temperatures (MOTs) are
known (pending completion of LiDAR analysis). Once MOTs are known, the ratings will be re-calculated based on
the IEEE 738 assumptions in this report.
Most of the lines in Southern Nevada have LiDAR verified MOT information available. In absence of LiDAR MOT or
verified DOT information, it is assumed that the line meets clearance requirements, and can operate up to the
maximum conductor temperature. The ratings for these lines are determined based on RateKit IEEE738
calculations using standard weather assumptions for that region, and the conductor’s MOT.
In the Northern System, NV Energy previously had the underground cable manufacturer perform the design based
on information provided to them. The manufacturer then provided NV Energy a rating for the complete line design
as it was to be constructed in the field.
Lead lines connected from the high-side bushing of the GSU, are designed not to be limiting Elements for the
operation of the GSU or the Transmission Line Facility.
Procedure
NV Energy uses the following procedure to determine ratings on overhead conductors.
LiDAR MOT?
Confirmed DOT?
Is there a Westinghouse Rating available for the conductor?
Run Ratekit with Conductor MOT
No
NoNo
Westinghouse Ratings
Yes
Is this line on an exception list in NVE’s FAC-008-3 Policy?
No
Yes
Run RateKit with the Exception Weather Parameters in the Policy.
Run Ratekit with the Standard North or South rating parameters.
No Yes
Yes
North or South?
North
Run Ratekit with Conductor MOT
South
NOTE: If the LiDAR Clearance MOD or DOT is above the Conductor
MOT, the lower is used.
Figure 1: Conductor Rating Procedure
5 FAC-008-3 R3
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Switches are included in the line facility rating if they meet the below flow-chart criteria.
Is the switch connected to any bus-work?
Yes
Include in Line Listing
No
Addressed in FAC-008-3 Ratings Spreadsheet
Figure 2: Procedure to Determine Switch Inclusion in Line Ratings
Normal & Emergency Current Ratings
The ratings calculated by RateKit using the weather assumptions (Appendix A) result in the “Continuous Current
Rating” of the conductor. NV Energy uses an emergency rating for conductor equal to the normal rating.
Within the NV Energy system, there are instances where dynamic ratings are used for transmission lines.
Protection of these locations are done through thermal-loading protective relaying schemes. Dynamic ratings of
transmission lines are not a common practice in NV Energy. The following lines are identified with dynamic ratings:
Line #118: Eagle – Oreana 120kV Line
Line #173: Mira Loma – Airport 120kV Line
Standard Weather Assumptions
Below are the standard weather assumptions for use in RateKit IEEE738 conductor rating calculations. Under
certain conditions, NV Energy may monitor ambient temperature and dynamically rate lines for operational
purposes.
Figure 3: RateKit Parameters
North South Laughlin
Air Temperature (°C) 40 (104F) 44.4 (112F) 48.9 (120F)
Wind Speed (Ft/Sec) 2 2 2
Wind Angle relative to conductor 90 90 90
Elevation (Ft) 5500 2000 800
Latitude (Deg N) 39 36 35
Date (Month/Day) 4-Jul 4-Jul 4-Jul
Solar Time (Hr) 17 17 17
Coefficient of Emissivity 0.7 0.7 0.7
Coefficient of Solar Absorptivity 0.8 0.8 0.8
Conductor Orientation (North=0) 0 0 0
Atmosphere
Conductor Type
Diameter (In)
Conductor Resistance (ohms/mi) @ 25°C
Conductor Resistance (ohms/mi) @ 75°C
MOT (°C)
Actual
Actual (or DOT)
IEEE 738 Steady State Thermal Rating Calculation Parameters
Clear
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Westinghouse & RateKit Engineering Reference
Appendix C is a list of all conductor types that NV Energy owns on 55kV or above facilities. For each conductor, the
Westinghouse Legacy Rating is included (if available). Additionally, the conductor code-name used for RateKit is
included, and RateKit ampacity ratings are calculated using the standard weather assumptions plus the conductor’s
MOT.
Laughlin Weather Assumptions (Exception)
The Laughlin Area subjects NV Energy’s lines to different conditions than those present in Vegas. For Laughlin, the
same assumptions are used as in Vegas, except for the following alterations:
Ambient Temperature: 48.9°C
Altitude: 800 feet
Latitude: 35°
This exception applies to the following list of lines:
Laughlin - Mohave 500kV #1
Laughlin - Mohave 500kV #2
Laughlin - Southpoint 69kV
Laughlin - River Road 69kV
Laughlin - Big Bend 69kV
River Road - Kidwell 69kV
Southpoint – Big Bend 69kV
Kidwell – Searchlight 69kV
Underground Cable Ratings For NV Energy, the normal rating will be ampacity that produces a conductor temperature of 90⁰C. A four hour
emergency rating may be applied if needed to meet contingencies; the emergency rating shall be equal to the
ampacity that will produce a conductor temperature of 105⁰C.
NV Energy designs and constructs the underground cable system duct-bank around physical space constraints such
as highways, parallel transmission lines sewer and water lines, or other subsurface utilities. The rating may be
calculated using a program called Cymcap or may be based on outside consultant’s engineering study, or cable
manufacturer provided data.
Initial design takes into account the ampacity requirement, and what short circuit ratings are necessary
from the underground cable system.
If necessary, parallel cables may be placed in the same duct bank.
CYMCAP is then used to rate the ampacity of the cable using:
o Cable system design and/or “As Built” conditions.
o Cable information from manufacturer.
o Concrete thermal data.
o PVC pipe thermal data.
o NV Energy utilizes thermal conductivity of the soil for ampacity calculations. If unavailable,
typical data may be utilized.
o The software considers crossover points for underground mutual heating.
o 90⁰C/105 ⁰C Normal/Emergency is the maximum operating temperature assumed for
underground cable.
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If necessary, outside consultants may be engaged to conduct an ampacity study for a specific cable
installation. This study may use CYMCAP software, or other software that may be proprietary to the
consultant.
Assumptions
Conductor Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used 1) Industry Standard 2) Equipment Manufacturers
FAC-008 R3.2.1 Standard Used ANSI/IEEE Standard 738 Method of Calculation
FAC-008 R3.2.2 Manufacturers Ratings Westinghouse Ratings (See Appendix B)
FAC-008 R3.2.4 Ambient Conditions See ‘Standard Weather Assumptions’ above
FAC-008 R3.2.4 Operating Limitations N/A
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Transformers – [TRANSMISSION PLANNING]
Procedure
NV Energy will use the manufacturer’s transformer nameplate rating to determine normal and emergency current
ratings.
Normal Ratings
For each winding on a transformer, NV Energy uses the maximum nameplate MVA rating as the Normal rating for
that particular winding, unless a detailed engineering study has shown that the transformer needs to be de-rated
below this value.
Emergency Ratings
In general, NV Energy utilizes the following priority list for selecting transformer ratings:
1. Manufacturer provided 2-hour thermal MVA ratings.
2. 2-hour thermal ratings based on a detailed engineering study, as detailed in the following section:
Emergency Load Rating Methodology.
3. In the absence of other information, NV Energy will use a default 2-hour rating equal to 120% of the
maximum nameplate value.
In situations where known operational response time is shorter than 2-hours (for example 30-minutes) such
ratings may be used with comments indicating the timeframe in the Facility Ratings spreadsheet.
The default emergency 2-hour rating of 120% is based on ANSI C57.92-1981, Tables 3(m)(n)(p). The emergency
rating assumes 70% initial load or lower (see Figure below).
Legacy Transformer Emergency Ratings
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Application of Transformer Facility Ratings (For System Modeling Purposes)
A Target Operational Nominal kV Base (for example 525kV) is provided in the Facility Ratings Spreadsheet.
Two categories of ratings are considered for each winding when applying Transformer Facility Ratings to models:
Transformer Rating o Transformers in NV Energy’s system will be rated in terms of MVA (as opposed to Amps).
Connected Equipment Rating o All connected amp-limited equipment will be identified with a rating in Amps. o The minimum Amp rating is the total rating of the Connected Equipment. o The Amp rating, on the Operational kV Base, provides an MVA rating for the Connected
Equipment. The minimum MVA rating of these two is the total Facility Rating for a Transformer Winding.
Emergency Load Rating Methodology
For detailed engineering studies on transformer ratings, the loading capability will be calculated utilizing the EPRI
PTLOAD (Version 6.1) computer program which models/simulates the electrical and thermal properties of the
transformer. The calculations are based on a 113 degree maximum 24 hour ambient temperature provided by
weather service hourly data and typical 24 hour load cycle profiles provided by Transmission and Distribution
Planning and System Operations with all existing cooling fans or pumps in continuous operation.
For each calculation, the maximum allowable values of winding temperature (hot spot), top oil temperature, and
Acceptable Loss of (transformer) Life of insulation were specified. Specific test parameters associated with each
transformer were used, including heat run (temperature rise data), load and no load losses, core and coil weight,
gallons of oil, etc.
Emergency rating limitations are based upon a 2 hour period: Hot Spot and Top Oil temperature limitations of
140C and 110C respectively in addition to other limiting parameters described below. Acceptable Loss of Life of
0.04% is considered along with a typical 24 hour load cycle preload.
Assumptions
Transformer Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Manufacturer’s nameplate and Engineering Analysis
FAC-008 R3.2.1 Standard Used IEEE C57.91 – 2011 IEEE C57.92 - 1981
FAC-008 R3.2.2 Manufacturers Ratings Nameplate rating
FAC-008 R3.2.4 Ambient Conditions 65 Degree C Rise
FAC-008 R3.2.4 Operating Limitations N/A
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Shunt Compensation Devices [SUBSTATION DESIGN]
Background
NV Energy has Shunt Reactors and Shunt Capacitors within its system.
Procedure
The normal rating shall be the continuous rating provided by the equipment manufacturer or obtained from
manufacturer specifications such as the top nameplate rating of the capacitor, reactor, or that of the most limiting
device (e.g., a disconnect switch) in the series circuit for series compensation or in the shunt circuit for shunt
compensation.
Normal & Emergency Current Ratings
Normal and Emergency current ratings are equivalent.
Assumptions
Shunt Devices Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Manufacturer’s Nameplate Rating
FAC-008 R3.2.1 Standard Used N/A
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer’s Nameplate Rating
FAC-008 R3.2.4 Ambient Conditions N/A
FAC-008 R3.2.4 Operating Limitations N/A
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Series Compensation Devices [SUBSTATION DESIGN]
Background
NV Energy only has Series Capacitors within its system. NV Energy does not have Series Reactors within its system.
Procedure
The normal rating shall be the continuous rating provided by the equipment manufacturer or obtained from
manufacturer specifications such as the top nameplate rating of the capacitor, reactor, or that of the most limiting
device (e.g., a disconnect switch) in the series circuit for series compensation or in the shunt circuit for shunt
compensation.
Normal & Emergency Current Ratings
Normal and Emergency current ratings are equivalent.
Assumptions
Series Capacitor Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Manufacturer’s Nameplate Rating
FAC-008 R3.2.1 Standard Used N/A
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer’s Nameplate Rating
FAC-008 R3.2.4 Ambient Conditions N/A
FAC-008 R3.2.4 Operating Limitations N/A
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Circuit Breakers/Circuit Switchers [SUBSTATION DESIGN]
Background
In some locations in Northern Nevada and Southern Nevada, Power Circuit Breakers have breaker bypass switches
installed. These switches are designed for providing a current path during maintenance of the circuit breaker.
Operationally, NV Energy will only use breaker bypass switches in as-needed emergencies. Bypass switches are
rated at the same current as the connected circuit breaker, unless otherwise noted in the Facilities Rating
spreadsheet.
Procedure
Nameplate Ratings are used for circuit breakers and circuit switchers, unless the manufacturer provides specific calculations. These are based on the current ANSI, NEMA, and IEEE Standards. Circuit breakers in the SPPC system are rated at 40° C ambient temperature as per the latest version of IEEE C37.04. Circuit breakers in the NEVP system are designed to have a continuous current rating at 50° C ambient temperature.
Normal & Emergency Current Ratings
Normal and Emergency ratings are equivalent to nameplate unless the manufacturer provides specific normal and
emergency ratings.
Assumptions
Circuit Breaker Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Manufacturer’s nameplate rating
FAC-008 R3.2.1 Standard Used IEEE C37.04
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer’s nameplate rating
FAC-008 R3.2.4 Ambient Conditions 40° C for SPPC; 50°C for NEVP
FAC-008 R3.2.4 Operating Limitations N/A
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Bus [SUBSTATION DESIGN]
Background
Presently for Transmission Line conductors, for SPPC, lines will keep their “Legacy” ratings until Maximum
Operating Temperatures (MOTs) are known (pending completion of LiDAR analysis). Once MOTs are known, the
ratings will be re-calculated based on the IEEE 738 assumptions in this report.
Most of the lines in NEVP have LiDAR verified MOT information available.
In order to maintain consistency with similar conductor types used for lines, substation bus conductor ratings will
be the same as transmission line conductors.
Procedure
Bus Conductor
Bus conductor located in SPPC substations will use the Westinghouse ratings located in Appendix B as an initial
rating.
Bus Conductor located in NEVP substation will use ratings based on Conductor MOT’s, calculated from IEEE 738
calculations and weather assumptions for the South. These values are shown in Appendix C.
Bus Conductor used in NEVP substations that do not have a Conductor MOT listed in Appendix C, will use ratings
from Standard Handbook for Electrical Engineers (13th Ed.), D. Fink &H.W. Beaty Eds., McGraw-Hill, Aluminum
Conductor – Physical Characteristics, Classes AA and A, Table 4-22, (Appendix D)
Aluminum Bus
Bus Ratings for both NEVP and SPPC shall be based on Table 13-27 from Aluminum Electrical Conductor Handbook
(3rd Ed.), L. Kirkpatrick. The current ratings selected should use the values for Schedule 40 pipe for Aluminum
6063-T6 Temper located in Appendix E6.
GIS Bus
Bus Ratings for both NEVP and SPPC shall be based on Manufacturer’s Specifications.
Normal & Emergency Current Ratings
NV Energy uses an emergency rating for all bus types equal to the normal rating.
6 http://www.aflglobal.com/productionfiles/resources/catalogs/afl-substation-bus-conductors
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Assumptions
Bus Conductor
Weather assumptions used for IEEE738 Transmission Line Conductor calculations are the same assumptions used
for Bus Conductors.
For bus conductors used in NEVP substations that do not have a Conductor MOT listed in Appendix C, The
following conditions will be assumed: 40°C Rise over 40°C Ambient with 2.0 ft/sec crosswind, 0.5 emissivity factor,
without sun.
Jumper Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used 1) Equipment Manufacturers 2) Industry Standard
FAC-008 R3.2.1 Standard Used ANSI/IEEE Standard 738 Method of Calculation
FAC-008 R3.2.2 Manufacturers Ratings Westinghouse Ratings (See Appendix B)
FAC-008 R3.2.4 Ambient Conditions See Transmission Line Conductors Ambient Conditions
FAC-008 R3.2.4 Operating Limitations Not Applicable
Aluminum Bus
Per NV Energy’s Substation Material Standard SB-6, Aluminum Bus shall be designed to meet standard ASTM
B241/B241M using a material of Seamless Aluminum 6063-T6 temper, produced from hollow extrusion ingrot and
extruded by use of the die and mandrel method. Weather assumptions match the assumptions used by AFL
Global: 30 degree C rise over 40 degree C ambient, horizontally mounted conductors, with spacing sufficient to
eliminate proximity effects, 2 ft./sec crosswind, nominal oxidized surface (e=0.50).
Bus Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Manufacturers Rating
FAC-008 R3.2.1 Standard Used Not Applicable
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer’s Specifications provided by AFL Global
FAC-008 R3.2.4 Ambient Conditions 30 degree C rise over 40 degree C ambient, horizontally mounted conductors, with spacing sufficient to eliminate proximity effects, 2 ft./sec crosswind, nominal oxidized surface (e=0.50).
FAC-008 R3.2.4 Operating Limitations Not Applicable
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Jumpers [SUBSTATION DESIGN]
Background
Currently at SPPC, Transmission Line conductors, will keep their “Legacy” ratings until Maximum Operating
Temperatures (MOTs) are known (pending completion of LiDAR analysis). Once MOTs are identified, the conductor
ratings will be re-calculated based on the IEEE 738 assumptions in this report.
The majority of the lines owned by NEVP have LiDAR-verified MOT information available.
In order to maintain consistency with similar conductor used for lines, substation jumper ratings will be identified
as the same as transmission line conductors.
Procedure
As an initial rating, jumpers located in SPPC substations will use the Westinghouse ratings located in Appendix B.
Jumpers located in NEVP substations, will use ratings based off of Conductor MOT’s, calculated from IEEE 738
calculations and weather assumptions for the South. These values are shown in Appendix C.
Jumpers used in NEVP substations that do not have a Conductor MOT listed in Appendix C, will use ratings from
Standard Handbook for Electrical Engineers (13th Ed.), D. Fink &H.W. Beaty Eds., McGraw-Hill, Aluminum
Conductor – Physical Characteristics, Classes AA and A, Table 4-22, , Pg. 4-59
Normal & Emergency Current Ratings
NV Energy uses an emergency rating for jumpers equal to the normal rating.
Assumptions
Weather assumptions used for IEEE738 Transmission Line Conductors calculations are the same assumptions used
for jumpers.
Jumper Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used 1) Equipment Manufacturers 2) Industry Standard
FAC-008 R3.2.1 Standard Used ANSI/IEEE Standard 738 Method of Calculation
FAC-008 R3.2.2 Manufacturers Ratings Westinghouse Ratings (See Appendix B)
FAC-008 R3.2.4 Ambient Conditions See Transmission Line Conductors Ambient Conditions
FAC-008 R3.2.4 Operating Limitations Not Applicable
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Disconnect Switches [SUBSTATION DESIGN]
Procedure
For switches manufactured under the ANSI standards, the normal rating shall be the rating provided by the
manufacturer or obtained from the manufacturer specifications such as the nameplate rating of the switch.
The ANSI temperature rise is based on the allowable temperature rise in ANSI C37.37 for the specific switch
contact material utilized in the switch (e.g., copper/copper alloy or aluminum).
In some instances, if no manufacturer’s drawing(s) or nameplate information was available, an assumed rating of
600 amps for the disconnect switch was used for these instances. This assumption is based on the known
information for existing disconnect switch ratings offered by NVE vendors, and manufacturers.
Normal & Emergency Current Ratings
Normal and Emergency current ratings are equivalent.
Assumptions
Substation Disconnect Switch Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Equipment manufacturer
FAC-008 R3.2.1 Standard Used ANSI IEEE C37.37
FAC-008 R3.2.2 Manufacturers Ratings Nameplate rating
FAC-008 R3.2.4 Ambient Conditions 40°C
FAC-008 R3.2.4 Operating Limitations N/A
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Line Switches [TRANSMISSION ENGINEERING]
Background
NV Energy has transmission line switches in operation from several manufactures with widely varying
manufacturer dates, configuration types, voltage classes and current ratings. In general, NV Energy has required
the switch manufacturers to provide switches that been rated by applicable ANSI and IEEE standards. Therefore,
NV Energy uses the current rating provided on the final drawings or nameplate.
Procedure
For switches manufactured under the ANSI standards, the normal rating shall be the rating provided by the
manufacturer or obtained from the manufacturer specifications such as the nameplate rating of the switch.
For the Northern System, if no nameplate is available then the switches should be assumed to be rated for 600
amps, which is the lowest rating that is available in a line switch.
Normal & Emergency Current Ratings
Normal and Emergency ratings are equivalent.
Assumptions
Transmission Line Switch Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Ratings provided by equipment manufacturers through drawings or nameplates. NV Energy requires to manufacturers to determine rating based on several ANSI/IEEE standards.
FAC-008 R3.2.1 Standard Used ANSI C29.8, ANSI C29.9, IEEE C37.30, ANSI C37.32, IEEE C37.37
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer’s Information
FAC-008 R3.2.3 Ambient Conditions -40°C to 50°C based on current specification.
FAC-008 R3.2.4 Operating Limitations N/A.
Facility Rating Methodology
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Current Transformers (CTs) [SUBSTATION DESIGN & SYSTEM PROTECTION]
Background
The standard nominal rating of all CTs in the NVE system is 5 A secondary. The primary CT rating is part of the
major equipment specifications of which the CTs are a part. For example, a 2000 A rated circuit breaker would
typically include 2000:5 multi-ratio bushing CTs, unless specified otherwise. Multi-ratio CTs use standard tap
ratios, as listed in IEEE C57.13-2016, Table 11 (or its successor).
Continuous overload thermal rating factors will be applied to tapped windings per manufacturer’s data and
recommendations. The thermal rating factor (TRF) allows multiplication of secondary current rating by the
specified value (1.0, 1.33, 1.5, 2.0, 3.0, or 4.0).
Procedure
For calculation of CT ratings, if the thermal rating factor is available, NVE will use this value. If a CT rating factor is
unknown, NVE will assume a TRF = 1.0.
For CTs, with tapped windings not set on the highest available tap, a continuous overload rating will be calculated
based on the methodology created by PJM Interconnection, and documented within PJM article VI.C “Circuit
Breakers” and PJM article VI.F “Current Transformers”.
Itap = Adjusted rated continuous current of specific current transformer tap under consideration
Ir = Rated continuous current (current transformer nameplate rating)
Itapr = Rated continuous current of specific current transformer tap under consideration
RF = Continuous thermal current rating factor
n = 2; NV Energy will always use the more conservative value of “2” (Circuit Breaker “n” equals 1.8) for rating CTs
Auxiliary CT’s
For those instance where auxiliary CT’s are used, the auxiliary CT will always be rated at TRF = 1.0
Normal & Emergency Current Ratings
Normal and Emergency ratings are equivalent.
Assumptions
Current Transformer Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used PJM Method, see above Engineering Analysis
FAC-008 R3.2.1 Standard Used N/A
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer’s Specifications
FAC-008 R3.2.4 Ambient Conditions See Standard Weather Assumptions under T-Line Conductor
FAC-008 R3.2.4 Operating Limitations N/A
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Control Cables and Wiring [SUBSTATION DESIGN]
Background
NV Energy substation design recommended practices specify installation of 12 AWG through 8 AWG for control
leads and current transformer secondary leads.
Procedure
The smallest CT cable from the CT through the CT circuit will be used as the limiting rating for the CT cable. In
instances where the CT cable is unknown, 12AWG will be assumed.
Ratings of the cable type can be determined by the NEC Table 310.15(B)(16) Allowable Ampacities of Insulated
Conductors… (Appendix F).
In instances where there is an auxiliary CT in a CT circuit, if the auxiliary CT ratio decreased the current then the
cable rating will be determined by multiplying the cable rating by the primary CT ratio. If the auxiliary CT ratio
increases the current, then the rating of the cable should be adjusted by multiplying the cable rating by the
auxiliary CT ratio and the primary CT ratio.
Normal & Emergency Current Ratings
Normal and Emergency current ratings are equivalent.
Assumptions
CT Cable Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Industry Standard
FAC-008 R3.2.1 Standard Used NEC Table 310.15(b)(16) Allowable Ampacities of Insulated Conductors
FAC-008 R3.2.2 Manufacturers Ratings N/A
FAC-008 R3.2.4 Ambient Conditions N/A
FAC-008 R3.2.4 Operating Limitations N/A
Facility Rating Methodology
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Protective Relay Devices [SYSTEM PROTECTION]
Background
NV Energy System Protection maintains a philosophy for new protective relay installations, or revisions to existing
protective relaying packages, to use Schweitzer Engineering Laboratories (SEL) microprocessor relays. The model of
the SEL relay selected is based on the specific application requirements.
Previous protective relaying philosophy, required installation of various relay equipment types and manufacturers,
based on precedence, education, and technology available. Regardless of philosophy, Substation relays and
protection control equipment match or exceed the 5A secondary current transformer Ratings used by NV Energy.
Procedure
NV Energy uses the manufacturer’s standard equipment ratings for relays that require AC current to operate.
Additionally, NV Energy System Protection personnel will determine the specific relay AC current ratings by
referencing the manufacturer’s instruction manuals, or by using a conservative assumption of 10 A. For instances
where currents from multiple CT’s are summed together and then go to a relay (such as for a high impedance
differential relay), the current seen by the relay during load conditions would nominally be zero. As such, the
ratings for these relays should not be considered.
In instances where there is an auxiliary CT in a CT circuit, if the auxiliary CT ratio decreased the current then the
relay rating will be determined by multiplying the relay rating by the primary CT ratio. If the auxiliary CT ratio
increases the current, then the rating of the relay should be adjusted by multiplying the relay rating by the
auxiliary CT ratio and the primary CT ratio.
For facilities subject to NERC Standard PRC-023, Criteria 1 may be used to ensure adequate margin between the
facility rating and the relay trip setting. For facilities subject to NERC Standard PRC-023 which are using a different
Criteria or facilities not subject to NERC Standard PRC-023, best efforts are made to set the trip points above the
facility ratings. In instances where this is not possible, the relay trip setting will be the new limiting factor.
Normal & Emergency Current Ratings
Normal and emergency ratings are the same.
Example Data Entry
To simplify the data entry process, the following process has been implemented:
Engineers first enter:
o Lowest Tapped CT Ratio
o Lowest Relay Rating
o Blank entry for “Relay CT Ratio”
By default, the spreadsheet will make the conservative assumption that the “Relay CT Ratio” is the Lowest
Tapped CT. If this causes a system limitation on the facility, the following investigation must be
performed:
o For each CT connected, multiply the CT Ratio (as found at actual tap) by the Relay Rating.
o Select the lowest multiplied value, and enter the “Relay CT Ratio” and “Relay Rating” based on
this final, lowest rated value.
Below is an example for properly entering the Relay Rating.
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Assumptions
Protective Relay Rating Methodology Summary Table
Equipment Thermal Rating Relay Settings
FAC-008 R3.1 Methodology Used Manufacturer Ratings NA
FAC-008 R3.2.1 Standard Used NV Energy purchase specifications NA
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer Specifications NA
FAC-008 R3.2.4 Ambient Conditions NA NA
FAC-008 R3.2.4 Operating Limitations NA PRC-023, when applicable
Facility Rating Methodology
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Wave Traps [SUBSTATION DESIGN]
Background
Transmission line wave traps are designed to meet ANSI and IEEE Standards, as well as other international
standards. Terminals are supplied to meet the applicable IEEE standards.
Wave trap Ratings assume a 40° C rise over a 24-hour mean ambient temperature as per the latest version of
IEEE/ANSI Standards.
Procedure
For wave traps manufactured under the ANSI standards, the normal rating shall be the rating provided by the
manufacturer or obtained from the manufacturer specifications such as the nameplate rating of the wave trap.
In some instances, if no manufacturer’s drawing(s) or nameplate information was available, an assumed rating of
800 amps for the wave trap was used for these instances. This assumption is based on the known information for
existing wave traps and the similarities to the known wave traps with ratings and the wave traps without ratings.
Normal & Emergency Current Ratings
Normal and Emergency current ratings are equivalent.
Assumptions
Wave Trap Rating Methodology Summary Table
FAC-008 R3.1 Methodology Used Manufacturer’s Rating
FAC-008 R3.2.1 Standard Used Not Applicable
FAC-008 R3.2.2 Manufacturers Ratings Manufacturer’s Ratings
FAC-008 R3.2.4 Ambient Conditions 40° C rise over a 24-hour
FAC-008 R3.2.4 Operating Limitations Not Applicable
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Facility Rating Communication NV Energy Transmission Owner (and each Generator Owner subject to Requirement R2) shall provide requested
information as specified below (for its solely and jointly owned Facilities that are existing Facilities, new Facilities,
modifications to existing Facilities and re-ratings of existing Facilities) to our Reliability Coordinator, and neighboring
Planning Coordinator(s), Transmission Planner(s), Transmission Owner(s) and Transmission Operator(s).
Reliability Coordinator Communication NV Energy’s communication of Facility Ratings to the Reliability Coordinator (PeakRC) consists of coordination of
System Operating Limits (SOLs) per FAC-014, and then communication to PeakRC, our internal Transmission,
Distribution, and Network Operations groups.
The following process is to occur after revisions to Facility Ratings:
Collected Facility Ratings will be used to establish NV Energy SOLs based upon NVE’s SOL methodology
NVE will ensure that NVE established SOLs are consistent with PeakRC’s SOL methodology7
Update NVE SOLs documentation accordingly
Communicate any newly established SOL’s to PeakRC8
Communication to NVE Operations personnel of any newly established SOL’s
Updated NVE EMS to account for newly established SOL’s
Neighboring Entities NV Energy has multiple Facilities that are jointly-owned with a neighboring entity. These Facilities may also have
different ownership percentages associated with Elements that make up the Facility. Regardless of ownership
percentage, NV Energy will provide Facility Rating data upon request of the neighboring entity9.
NV Energy will also have the obligation to submit Facility Rating requests to an Entity that shares ownership of a
Facility. The NVE Transmission Planning department will be the conduit for NV Energy to request Facility Ratings
from jointly-owned Facilities. Transmission Planning will maintain a NV Energy Interconnection spreadsheet that
will contain the locations of the jointly-owned Facilities, as well as the communication information of the
personnel at the Entity that will receive the data request. Transmission Planning will submit (through electronic
mail) a request (see Appendix G), to the identified point of contact (POC) of the Entity, for ratings of the Entity-
owned Element(s) that make up the shared Facility.
Communication of Thermal Rating Incursions NV Energy will provide the information described in R8.1 within 30 calendar days (or a later date if specified by the
requester), for any requested Facility with a Thermal Rating that limits the use of Facilities under the requester’s
authority by causing any of the following:
1) An Interconnection Reliability Operating Limit
2) A limitation of Total Transfer Capability
3) An impediment to generator deliverability
4) An impediment to service to a major load center
7 FAC-011-2, FAC-014-2 8 FAC-014-2 R5.2 9 FAC-008-3 R8.1
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In addition to providing the Thermal Rating that limits the use of Facilities under the requestor’s authority by causing
any of the limitations described in 1-4 above, NV Energy will provide the identity of the next most limiting equipment
(R8.2.1) and the thermal rating (R8.2.2) of the Facility.
Change Control Process
Facility Ratings Methodology
Documentation Location
The Facility Ratings Methodology will be located on the Transmission Planning department’s SharePoint site,
within the Facility Ratings library.
Users will be granted access permissions based on need (read/write requirements), by the owner of the SharePoint
site, Manager of Network & IRP Transmission Planning and/or delegated Transmission Planning Engineer.
Review Process
This document will be reviewed by the NV Energy Transmission Planning department every 12 calendar months.
Revisions to the document can occur during the review process, or through communication of methodology
changes for Element rating data collection by Element owners. All revisions to this document will require approval
by the Manager, Network & IRP Transmission Planning.
Document Revision Notification
Upon completion of revisions to the Facility Ratings Methodology, notification of the revisions will be required to
be delivered to management personnel of the following Facility Ratings stakeholders:
Compliance & Standards
Substation Design
Substations & Technical Operations
Transmission & Distribution Operations
Transmission Planning
Transmission Civil Engineering & Construction
Facility Ratings Data/Spreadsheet
Documentation Location
The Facility Ratings spreadsheet will be located on the Transmission Planning department’s SharePoint site, within
the Facility Ratings library.
Users will be granted access permissions based on need (read/write requirements), by the owner of the SharePoint
site, Manager of Network & IRP Transmission Planning and/or delegated Transmission Planning Engineer.
Review Process
This spreadsheet will be reviewed annually as part of the Technical Assessment, conducted by the Senior
Compliance Engineer in Compliance & Standards. Findings from the review will be delivered to the Manager,
Network & IRP Transmission Planning, and a corrective action plan and timeline will be requested for any findings
that require revisions to the spreadsheet.
Additionally, it is the responsibility of the Element owners to review this spreadsheet at their own discretion.
Ongoing review by the Element owners will ensure the spreadsheet will contain correct Facility Rating data.
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Revision Notification Process
Revisions to the Facility Ratings spreadsheet will be required in the following scenarios:
Installation of a new Facility
Modifications to an existing Facility
Modifications in the Element owners methodology for establishing Rating
Modifications to an existing jointly-owned Facility
To ensure that all Element ratings are accounted for during the aforementioned scenarios, it will require the
diligent effort of all Element owners to maintain consistent communication with Transmission Planning on the
occurrence of these scenarios.
Installation of a New Facility
The process for data collection for new predicted installations of Elements will begin and close with Transmission Planning. Transmission Planning will be the single point of data entry for Facility Ratings for new installations. Transmission Planning personnel will update the Facility Ratings spreadsheet, upon receipt of a completed Facility Ratings installation form (referred to as the “Form”). Upon completion of revisions, identified NV Energy Facility Ratings stakeholders will be notified of the changes. The Form will live throughout the lifetime of a project, and all document-required data will be completed by project stakeholders (if necessary) at the close of the project. Data entry and management roles and responsibilities are as follows:
1. Initial data entry would be completed by Transmission Planning, on what the existing Facility Ratings are for projected connections, and what the Facility must be rated for
2. The Project Manager’s responsibility is to verify that stakeholders have provided Element data to Transmission Planning by the close of a capital project.
3. Data should be communicated to Transmission Planning through a completed Form(s), or other mutually agreed upon format, by close of pre-energization meeting(s) by the Project Manager or Facility Rating stakeholder.
4. Project Managers also have the responsibility of notifying EIM and/or Transmission Technology Engineers of projected Facility ratings. Information is required for updates to NVE EMS network model, and quarterly CAISO model updates.
5. It is the responsibility of the Facility Rating stakeholders to verify that data provided is correct within the Form(s), or other mutually agreed upon format, to the Project Manager and/or Transmission Planning.
6. Substation Design will then fill in the Form with their ratings, as determined by procured material for the project. This will include the majority of elements within the Form.
7. System Protection will provide tapped CT Ratio, Relay Thermal Rating, and Loadability to the Form 8. Transmission Engineering will provide transmission line parameters to the Form. Line parameter data will be
used for MOT calculations completed by Transmission Planning, prior to data entry in the Facility Ratings spreadsheet.
9. Substation Construction & Maintenance will provide the final verification of the data on the Form. Substation Construction will verify that installed equipment matches the equipment identified within the Form. Any incorrect information will be identified, and revised on the document by Substation Construction & Maintenance personnel.
10. If Transmission Planning identifies any issues with the data in the Form, they will provide corrective action requests to identified stakeholder personnel
Modifications to an Existing Facility
The assumption is that instances of “modifications” to existing Facilities would occur due to an unpredictable
occurrence (i.e. identified while doing maintenance, an outage, or other emergencies). For all modifications to
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Facilities conducted through planned and managed scheduled projects, please refer to the processes in the
Installation of a New Facility.
The key to capturing necessary data through an unpredictable occurrence is to document the occurrence and necessary processes required for the installation. The identified responsible parties for data collection are Substation Construction & Maintenance, System Protection, and Transmission Lines, as their equipment and field personnel would be more than likely affected by unpredictable events and immediate Element installation. Field personnel from these departments would be required to document the ratings (and other identifying data) of the equipment that is being installed. This ratings information should be entered directly into the Form, or through another mutually agreeable format.
For unplanned equipment installation, Substation Construction & Maintenance and System Protection personnel will replace the equipment with similar equipment; however, in the event that similar equipment is unavailable, it is the responsibility of field personnel to document the installation of unlike equipment for delivery to Transmission Planning for entry into the Facility Ratings spreadsheet. For unplanned maintenance of transmission lines, personal will repair the equipment with the same size conductor however, in the event that a similar conductor is unavailable and another conductor must be used in the replacement/repair, it is the responsibility of field personnel to provide the new conductor information to Transmission Engineering. Transmission Engineering will use this information to update the NV Energy PLS-CADD model (if available), and then Transmission Engineering will deliver the Element ratings to Transmission Planning. To track and process Facility Rating updates, Facility Rating stakeholders will submit their rating changes, and justification, through the Transmission Planning SharePoint site. Stakeholders will upload documentation of necessary Facility Rating changes to the Facility Ratings Update library. Manager of IRP Transmission Planning will delegate (through SharePoint work task) Transmission Planning Engineering personnel to review the rating change and justification prior to updating the Facility Ratings spreadsheet and model. Upon completion of review, the Engineer has completed his SharePoint work task, and upon closing the item out, a subsequent work task will be delivered to the Manager of Network Engineering & EIM Market Operations for review. Manager of Network Engineering & EIM Market Operations will delegate (through the same SharePoint work task) Network Engineering personnel to review the rating change and justification prior to requesting updates to the NVE EMS model.
Modifications to Element Ratings Methodology
All modifications to an Element Ratings Methodology must follow the procedures listed above in the Review
Process section of the Facility Ratings Methodology.
Any modifications to Element Ratings Methodologies that effect the rating values of the Element itself (based upon
changes in calculations, analysis, etc.), will require the associated Element owner to provide updated ratings to the
Facility Ratings spreadsheet. The notification system within SharePoint will provide other Element owners
awareness of the revisions to the spreadsheet, as well as the revisions to the Facility Ratings Methodology. In
addition, all revisions to the spreadsheet, and Methodology, must be completed with a detailed description of the
revisions with in the versioning history of the spreadsheet and Word document.
Modifications of a Jointly-Owned Facility by the Non-NVE Owner
These modifications will be initiated based upon communication from the external party that shares ownership
with NV Energy of a Facility. NV Energy will provide third-party communication of NV Energy Facility Ratings
modifications through the Transmission Planning department; however, it cannot be assumed that all Facility
modifications will be communicated from third-parties through Transmission Planning. It will be the responsibility
of all Element owners to provide communication to the Manager of Network & IRP Transmission Planning of third-
party Facility modifications that would require adjustments to currently maintained Facility Ratings.
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Upon notification of third-party Facility modifications, Transmission Planning will be the point of contact for NV
Energy for retrieving all necessary Element ratings data to update the NV Energy Facility Ratings spreadsheet.
Additional Element Owner Responsibilities
It is the responsibility of all Element owners to provide appropriate training and education on the change control
processes listed in the Methodology.
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Facility Ratings Updates – SharePoint Workflow A “Facility Ratings Updates” SharePoint library is being maintained to:
1. Store detailed documentation for every Facility Rating Update
2. Provide document versioning (e.g. for spreadsheets that get regular updates and impact ratings)
3. Give managers flexibility in tracking assignments
4. Improve transparency for compliance purposes
When a document is uploaded to the “Facility Ratings Updates” library, a SharePoint Workflow will automatically
initiate an “Approval” process on the uploaded document.
1. A task is created and an email is sent to a manager in Transmission Planning to review the item.
(A manager may complete the task, or re-assign the task)
Transmission Planning must do the following, then mark the item as “Approved”:
a. Implement the rating in the Master.SAV PSLF case, and create a “Change Log” to include in the
Master Case Corrections folder.
b. Modify the Facility Ratings spreadsheet to reflect the update.
2. Once TP marks the item as “Approved”, the task is assigned to Operations, and an email is sent to a
manager in Operations.
Operations must do the following, then mark the item as “Approved”:
a. Review & implement changes to operational SOLs (if necessary)
b. Review & implement the rating in their alarm settings (if necessary)
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Example Workflow
Figure 4: Facility Rating Update Submittal Process (Users submitting ratings changes are done at this point)
Figure 5: Automatic Email Received by Manager
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Figure 6: Task Review & Approval Process
Figure 7: Compliance Monitoring of Updates (Clicking the “In Progress” button will show full detail of task timeline)
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Version History Version
No. Issue Date Name Description or reason for revision
0.0 12/19/2016 Salsbury Initial version
0.1 12/21/2016 Salsbury Multiple revisions
0.2 12/29/2016 Salsbury Revision to Change Control Process to incorporate Sub Construction &
Maint., Major Projects
0.3 1/27/2017 Salsbury Revised to include dynamic line ratings; Updated Change Control
Process; Rating appropriation for ring and breaker-and-a-half scheme
0.4 6/20/2017 Ben Multiple revisions
0.5 7/14/2017 Ben Underground Cable methodology revisions
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Appendix A - Analysis of Weather Assumptions The IEEE 738 standard discusses how to rate Transmission Lines, and it includes thermal models to determine an
Amp rating based on Maximum Operating Temperature (MOT) and weather assumptions. The RateKit software
package is used to perform these calculations based on the below parameters.
Air Temperature
Ratings should use 40C (104F) ambient air temperature conditions for Northern Nevada based on the temperature
data below. This is a conservative value, since the temperature is below 40C for 99.99% of the recorded values. For
Southern Nevada, ratings would use 44.4C (112F). The historical temperature in Las Vegas was below this value for
99.94% of the recorded values.
Figure 8: Ambient Air Temperature
Wind Speed
In reference to CIGRE TB299, IEEE 738 says the following:
“In the absence of data from field rating studies, the use of certain worst-case weather conditions including
a 2 ft./s (0.61 m/s) perpendicular wind speed and an air temperature near the seasonal maximum should be
used.”10
10 IEEE Std 738-2012, Page 30
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Due to the sparse nature of NV Energy’s transmission system and the variety of weather conditions to which our
lines may be subject, ratings should use a 2 ft./s perpendicular Effective Wind Speed11 assumption per IEEE 738.
Emissivity & Absorptivity
Emissivity (ε) and absorptivity (α) are addressed in IEEE 738 and CIGRE TB299.
“For sag-limited lines, the JTF recommends that base ratings be calculated for an effective wind speed of 0.6
m/s, an ambient temperature close to the maximum annual value along the line route and a solar radiation
of 1000 W/m2. When combined with an assumed conductor absorptivity of no less than 0.8 (Conductor
emissivity should be chosen to be 0.1 less than absorptivity), this combination can be considered safe for
thermal rating calculations without field measurements.”12
Based on the above references, ratings should use: α = 0.8 ε = 0.7
Elevation
NV Energy uses the average elevation of Nevada for Northern Nevada rating calculations, which is 5500 ft. per a
book entitled “The Average Elevation of the United States” by Henry Gannett, Department of the Interior – US
Geological Survey.
For Southern Nevada, the elevation of Las Vegas is used (2,000 ft.).
Latitude
Carson City (Nevada’s Capital) is located at approximately 39° Latitude in Northern Nevada. This is used as the
reference Latitude for the rest of Northern Nevada’s transmission system.
For Southern Nevada, the latitude of Las Vegas is used (36°).
Date & Solar Time
NV Energy uses July 4th @ 1700 as its Date & Solar Time assumption.
MOT13
A line’s Maximum Operating Temperature is determined on a case-by-case basis, and is either limited either by line
clearance or by the temperature at which the conductor begins to anneal (whichever is lowest).
Clearance
Where LiDAR data is available, the MOT is calculated based on NEC14 & NESC15 clearance limitations.
11 Per CIGRE TB299, August 2006, Page 10: “Most transmission lines consist of multiple line sections, each line section being terminated by strain structures. Wind speed and direction (and thus conductor temperature) may vary along each line section but the sags depend on the average conductor temperature in the line section. The effective wind speed is that perpendicular wind speed which yields the same average conductor temperature along the line section as the actual variable wind. 12 CIGRE TB299 2006, Page 14-15 13 Maximum Operating Temperature (MOT): Means the maximum temperature at which an aerial conductor may continuously operate with the conductor clearance meeting or exceeding the minimum National Electrical Safety Code (NESC) clearance requirements applicable at the time of construction, and the maximum temperature at which an aerial conductor may continuously operate that will not cause permanent damage to the conductor, whichever is more limiting. 14 National Electrical Code 15 National Electrical Safety Code
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Conductor Annealing
On lines with abundant clearance, the next most limiting factor is the temperature at which there would be loss of
life due to annealing of the conductor as follows:
AA 95C
ACSR 100C
ACCC 180C
ACSS 200C
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Appendix B - Standard Conductor Ratings The table below includes Westinghouse conductor ratings, Manufacturer Ratings,
ACSR Conductor Data from “Westinghouse – Electrical Transmission & Distribution Reference Book”
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Copperweld Conductor Data from “Westinghouse – Electrical Transmission & Distribution Reference Book”
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Copper Conductor Data from “Westinghouse – Electrical Transmission & Distribution Reference Book”
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Aluminum Conductor Data from “Westinghouse – Electrical Transmission & Distribution Reference Book”
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Appendix C – NV Energy MOT Conductor Ratings
Conductor Rating Reference (Westinghouse Ratings and RateKit IEEE738 Ratings with Standard Weather Assumptions + Conductor MOT)
Unique ID Size TypeConductor
MOT (°C)
Conductor
MOT (°F)
RateKit IEEE738
Wire Name
Legacy Wire
Ratings
(Westinghouse)
North
IEEE738
Calc
South
IEEE738
Calc
Laughlin
IEEE738
Calc
Manufacturer
Ratings
2011 NEC
Table 310.15(B)(16)
4 / 0 CU I-Beam 4 / 0 CU IB 75 167Copper Twisted I-Beam
Use: CU4/0AWG-7520 371 358 329 - -
2A Copperweld 2A Copperweld 125 2572A Copperweld
Use: CU2AWG-7240 287 289 284 - -
721 ACAR 721 ACAR 95 203CURTIS
Use: ORCHID
776
(For ORCHID)777 771 741 - -
1272 ACSS 1272 ACSS 200 392 BITTERN/ACSS - 2173 2198 2188 - -
1272 ACSS, Old 1272 ACSS 200 392 PHEASANT/ACSS - 2149 2173 2164 - -
954 ACSS 954 ACSS 200 392 CARDINAL/ACSS - 1772 1792 1785 - -
1949 ACCC 1949 ACCC 180 356 LAPWING/ACCC/TW - 2599 2626 2610 - -
1026 ACCC 1026 ACCC 180 356 DRAKE/ACCC/TW - 1713 1732 1722 - -
431 ACCC 431 ACCC 180 356 LINNET/ACCC/TW - 968 979 973 - -
4 / 0 CU 4 / 0 CU 75 167 CU4/0AWG-7 480 371 358 329 - -
2 / 0 CU 2 / 0 CU 75 167 CU2/0AWG-7 360 279 269 247 - -
1 / 0 CU 1 / 0 CU 75 167 CU1/0AWG-7 310 241 233 214 - -
#4 CU #4 CU 75 167 CU4AWG-7 180 136 131 121 - -
#2 CU #2 CU 75 167 CU2AWG-7 230 181 175 161 - -
#1 CU #1 CU 75 167 CU1AWG-7 270 209 202 186 - -
250 CU 250 CU 75 167 CU250-37 540 413 398 365 - -
350 CU 350 CU 75 167 CU350-37 670 508 490 449 - -
2156 ACSR 2156 ACSR 100 212 BLUEBIRD - 1776 1768 1708 - -
1590 ACSR 1590 ACSR 100 212 LAPWING 1380 1474 1468 1418 - -
1272 ACSR 1272 ACSR 100 212 BITTERN 1200 1283 1277 1234 - -
954 ACSR, North 954 ACSR 100 212 RAIL 1010 1072 1067 1032 - -
954 ACSR, South 954 ACSR 100 212 CARDINAL 1010 1084 1080 1043 - -
795 ACSR 795 ACSR 100 212 TERN 900 955 951 919 - -
795 ACSR, Old 795 ACSR 100 212 DRAKE 900 973 969 936 - -
636 ACSR 636 ACSR 100 212 GROSBEAK 780 843 839 812 - -
556.5 ACSR 556.5 ACSR 100 212 DOVE 730 773 770 744 - -
477 ACSR 477 ACSR 100 212 HAWK 670 700 696 673 - -
397.5 ACSR 397.5 ACSR 100 212 IBIS 590 622 619 599 - -
397.5 ACSR, Old 397.5 ACSR 100 212 LARK 600 631 628 607 - -
336.4 ACSR 336.4 ACSR 100 212 LINNET 530 559 556 538 - -
4 / 0 ACSR 4 / 0 ACSR 100 212 PENGUIN 340 371 369 357 - -
3 / 0 ACSR 3 / 0 ACSR 100 212 PIGEON 300 322 320 310 - -
2 / 0 ACSR 2 / 0 ACSR 100 212 QUAIL 270 284 282 273 - -
1 / 0 ACSR 1 / 0 ACSR 100 212 RAVEN 230 249 248 240 - -
#2 ACSR #2 ACSR 100 212 SPARROW 180 188 187 181 - -
4 / 0 AAC 4 / 0 AAC 95 203 OXLIP 380 383 380 366 - -
2 / 0 AAC 2 / 0 AAC 95 203 ASTER 282 286 283 273 - -
1 / 0 AAC 1 / 0 AAC 95 203 POPPY 242 246 244 235 - -
#2 AAC #2 AAC 95 203 IRIS 180 184 182 175 - -
2500 AAC 2500 AAC 95 203 LUPINE - 1772 1758 1689 - -
2250 AAC 2250 AAC 95 203SAGEBRUSH
Use: BLUEBIRD- 1681 1668 1602 - -
2000 AAC 2000 AAC 95 203 COWSLIP - 1569 1557 1496 - -
1590 AAC 1590 AAC 95 203 COREOPSIS 1380 1371 1361 1307 - -
1272 AAC 1272 AAC 95 203 NARCISSUS 1210 1197 1188 1142 - -
954 AAC, North 954 AAC 95 203 GOLDENROD 1000 1005 998 959 - -
954 AAC, South 954 AAC 95 203 MAGNOLIA 1000 999 992 953 - -
795 AAC 795 AAC 95 203 ARBUTUS 897 895 889 854 - -
636 AAC 636 AAC 95 203 ORCHID 776 777 771 741 - -
556.5 AAC 556.5 AAC 95 203 DAHLIA 710 712 706 679 - -
477 AAC 477 AAC 95 203 COSMOS 646 646 641 616 - -
397.5 AAC 397.5 AAC 95 203 CANNA 575 574 570 548 - -
336.4 AAC 336.4 AAC 95 203 TULIP 514 518 513 494 - -
NV Energy Conductor RatingsRating (Amps)
Facility Rating Methodology
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Appendix D – Aluminum Conductor Bus Ratings (Classes AA and A)
Facility Rating Methodology
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Facility Rating Methodology
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Appendix E - Standard Bus Ratings The table below shows manufacturer ratings provided by AFL Global. Current ratings used should be for 6063-T6,
Schedule 40 Pipe.
Facility Rating Methodology
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Appendix F – Control Cable Ratings
Facility Rating Methodology
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Appendix G – NVE Jointly-owned Facility Rating Data Request The following text contains language designed to be a template for requesting Element ratings from multiple Entities.
TO: [Enter Interconnection Entity Contact Name]
DATE:
RE: Request to provide Element Ratings for [Enter Interconnection Name]
Per FAC-008-3, NV Energy needs to identify all Elements ratings associated with the requested Facilities below, at
the location listed above. This will allow NV Energy to identify the most limiting element of our jointly-owned
Facility. Additionally, if you require any Element information from NV Energy, please request as needed.
For Transmission Lines – Provide ratings for associated circuit breakers, switches, wavetraps (if applicable), relays
and current transformer ratings that are in conjunction with the circuit breakers as well as any shunt or series
compensation devices associated with the transmission line.
For Transformers – Provide ratings for associated circuit breakers, switches, relays and current transformers in
conjunction with those circuit breakers or the transformer. Also provide transformer normal and emergency
rating.
Please respond to this request within 30 calendar days. If you are unable to provide NV Energy with the
aforementioned information in the timeline requested, please feel free to contact us with a more agreeable
timeframe for submitting the data
Contact Sachin Verma with NV Energy for any questions regarding this request.
Sachin Verma
Manager, Network & IRP Transmission Planning
775-834-4878, [email protected]