microgrid design considerations - integrated...

© 2015 Electric Power Research Institute, Inc. All rights reserved.

Dr. Arindam Maitra, EPRI

September 8, 2016

Microgrid Design

Considerations

Part 3 of 3

2


Outline – Microgrid Design and Analysis Tutorial

Part II

Time Topics

14:30-15:00

15:30-17:30

Design analysis• Needs and Key Interconnection Issues (Arindam Maitra)

Design analysis (cont.)• Methods and Tools

• Case Studies

#1: Renewable Rich Microgrids - Protection Case Studies

(Mohamed El Khatib)

#2: Rural radial

#3: Secondary n/w

17:00-17:30 Q&A

17:30 Adjourn

3© 2015 Electric Power Research Institute, Inc. All rights reserved.

Microgrids

Optimization of microgrid design is challenging and

inherently contains many unknowns…

Regulatory Issues

Costs

Value of Resiliency

System Design

Challenges

Engineering Studies


Integrating Customer DER with Utility Assets

Distribution Transformer

Energy Storage*

Micro Grid Controller/ DERMS*

Customer

Assets

Utility Assets

Isolating Device*

Integrate

d Grid

SCADA/DMS/Enterprise

*New assets

5


Microgrid Types

Commercial/Industrial Microgrids: Built with the goal of reducing demand and costs

during normal operation, although the operation of critical functions during outages is

also important, especially for data centers.

Community/City/Utility and Network Microgrids: Improve reliability of critical

infrastructure, deferred asset investment, emission and energy policy targets and also

promote community participation.

University Campus Microgrids: Meet the high reliability needs for research labs,

campus housing, large heating and cooling demands at large cost reduction

opportunities, and lower emission targets. Most campuses already have DG resources,

with microgrid technology linking them together. They are usually large and may be

involved with selling excess power to the grid. Some of these facilities typically serve

as emergency shelters for surrounding communities during extreme events

Public Institutional Microgrids: Improve reliability and lower energy consumptions at

facilities impacting public health and safety, including hospitals, police and fire stations,

sewage treatment plants, schools, public transport systems, and correctional facilities.

Additional requirement of uninterrupted electrical and thermal service increases

attractiveness of CHP-based district energy solutions

6


Microgrid Types

Military Microgrids: Military microgrids focus on high reliability for mission-critical loads,

strong needs for cyber and physical security, DoD energy cost reduction, and

greenhouse gas emission reduction goals at the operating bases.

Rural Microgrid Communities: Remote microgrid communities are typically connected

to rural distribution system where it is prohibitive due to the distance or a physical

barrier to bring in new transmission service for backup. Many already use diesel

generation. They microgrids offer best candidate to incorporate renewable energy,

improve system reliability targets, and defer investment and reduce supply chain risk.


Microgrid Configurations Depending on Location and Purpose


Micro-grid: Operating as an “Island” Isolated from the

Bulk Supply

Utility

Source

“Islanded” Facility

DG

Trip

Signal

Circuit Breaker Isolating Device

– when open the system

operates as micro-grid

Islanding Control

(opens/closes breaker as needed to

facilitate independent operation –

must provide synchronization)

Electrical Island

DG Able to Carry Load on

Island and Provide Proper

Voltage and Frequency


Utility System

Interface Breaker

Utility Substation

Building

Load

Building

Load

Building

Load

Building

Load

Building

Load

13.2 kV Feeder

“Islanded” campus area

during utility system outages

DG trip settings for DG coordinated to allow

utility system interface breaker to trip during

utility faults so that stable transition to

islanded state is achieved for the campus

without interruption of DG service

“Islanding” for Reliability Enhancement

D

G

D

G


Distribution

Transformer

Utility System

Primary (13.2 kV)

50 KVA

Inverter

Utility System

Interface &

Controller (Synchronization, fault

protection, islanding

detection, etc.)

Power System

Secondary

(120/240 V)

Charge

Regulator

Energy

Storage

Isolating

Device

Heat

Distribution

DC Bus

Thermal

Storage

House 1 House 2 House 3

House 4 House 5 House 6

Fuel

Cell

A Six Home Microgrid


Utility

Source

INVERTER

Utility System Interface

& Protection Control

Energy

Storage

Building

Thermal

Loads

Heat

Recovery

Rectification

and Filtering

20 kW

Wind

Energy

Source

Circuit

Breaker

Circuit

Breaker

Status/control

signals paths to/from

electrical loads

Status/control signal

paths to/from thermal

loads

Master

System

Controller

Building

Electrical

Loads

200 kW

Fuel Cell

DC Bus

AC BusServes as Isolation Point

for Micro-grid mode of

operation

A Single Building

Multiple Sources, Storage, and Heat Recovery

Charge/Discharge

Regulator


A Campus Microgrid System

Utility System

Primary Connection

(13.2 kV)

Utility System Interface Control(Synchronization, fault

protection, islanding detection, etc.)

Campus Owned

Distribution (13.2 kV)

Isolating Device (opens

during micro-grid mode)

Heat Distribution

Academic Building A

Dormitory B Administrative

Building

Dormitory A

Student

Union

Academic

Building B

To Other

Campus

Loads

500 kVA 500 kVA 300 kVA

75 kVA

800 kVA

300

kVA

Generator

Step Up

Transformer

GenGenGen

Generator

Protection

and Control

Paralleling Bus (4.8 kV)

Voltage

Regulator

Heat Distribution

1.75

MVA

1.75

MVA1.75

MVA

Heat Recovered

from ICE Units

Load

control

Communication & Control Signal Path


Microgrid Design Parameters

Number of customers served

Physical length of circuits and types of loads to be served

Voltage levels to be used

Feeder configuration (looped, networked, radial)

Types of distributed energy resources utilized

AC or DC microgrid

Heat-recovery options

Desired power quality and reliability levels

Methods of control and protection

Controllers

Urban Utility

Microgrids

Rural Utility

Microgrids

Non-Utility Microgrids

Remote / Island

Microgrids

Application Downtown

Areas

Planned

Islanding

Load Support

Commercial /

Industrial Clusters

University Campus

Residential

Development

Remote

Communities

and Loads

Geographical

Islands

Main Drivers

Improved Reliability;

Outage Management;

Renewable and CHP Integration

Reliability and

Power Quality

Enhancement;

Energy Efficiency;

Electrification of

Remote Areas

Benefits

Improved Reliability;

Fuel Diversity;

Congestion Management;

Greenhouse Gas Reduction;

Upgrade Deferral;

Ancillary Services

Premium Power

Quality;

CHP Integration;

Demand Response

Management

Supply

Availability

Integration of

Renewables

Grid-

Connected Primary Mode of Operation

Primary Mode of

Operation Never

Intentional

Islanding

Nearby faults or System

Disturbances

Approaching Storms

Nearby faults or

System Disturbances

Times of Peak

Energy Prices

Approaching Storms

Always Islanded

Source: Johan Driesen and Farid Katiraei, “Design for Distributed Energy Resources,” IEEE Power & Energy Magazine,

May/June 2008


Microgrid Design Elements

• Are DERs able to regulate the voltage and

frequency within the island?

• Any issues with parallel grid operation?

• How is re-synchronization checked

against criteria such as out-of-phase, large

change in voltage?

Need a microgrid controller

• Are the fault contributions from

DERs sufficient to allow

satisfactory operation of

protection systems?

• Are existing protection schemes

adequate?

Plan, design, operate, control, monitor and optimize seamlessly

Microgrids


Microgrid Detailed Technical Design

Microgrid Project Objectives

Design Basis and Rationale

Performance Criteria

Site Descriptions

• Electrical & Thermal Needs• Generation Assets

• Critical Load Needs• Power Distribution Equip.

DER & Microgrid Controller

Codes & Standards

Control NeedsCommunication Needs


DER Characterization

Renewables

Solar Photovoltaics

Solar Thermal

Wind

Fossil Fuels Tech

Boiler

Fuel Cell

Microturbine

NG Genset

Diesel (backup)

Energy Storage

Electrical (Power, Energy)

Thermal (Chiller, Refrig.)

Thermal Tech

Heat Pump

CHP

HVACR

Solar Thermal

Other

Electric Vehicles

Electric Storage

• Aggregate capacity of all units (kwh)

• Maximum charge rate

(fraction of total capacity charge in one hour)

• Maximum discharge rate

(fraction of total capacity discharge per hour)

• Minimum state of charge

• Charge efficiency

• Discharge efficiency

• Decay/self-discharge (fraction of total capacity per

hour)

----------------------------------

• Fixed cost ($)

• Variable Cost ($/kw or $/kwh)

• Lifetime (years)

• O&M fixed costs ($/year)

Solar Photovoltaics

• # of modules

• Module rating (kW DC)

• Module Size (m2)

• Efficiency (%)

• Inverter size (kW AC)

• Total land area (m2)

----------------------------------

• Capital cost ($)



• O&M variable costs ($/year/kW)

Microturbine

• Max Power (kW)

• Sprint capacity (% of power)

• # of sprint hours (hours)

• Fuel type

• Efficiency (ratio)

• CHP capable? (yes/no)

• Alpha (power to heat ratio)

• NOx emissions rate (kg/hr)

• Maximum annual operating hours (hours)

• Minimum loading (% of power)

----------------------------------

• Capital cost ($)



• O&M variable costs ($/year/unit)

• NOx treatment costs ($/kg)

Electric Vehicles

• Multiple locations

• Min connect/disconnect SOC

• Max charge hours

• Battery size

• Efficiency

• Decay

• etc.

t

Connect

Disconnect

SOC


Variable Distributed Energy Assets within Microgrid

Sourc

e: P

NN

L


Key Considerations in Design for Energy Storage

Standby Power Loss

– Storage is primarily needed

when the microgrid is islanded

– Standby power loss will reduce

the efficiency of the microgrid

• Response time

– For seamless transition, response

time must be very fast

– This is more than just battery

response time – communications

latency and control functions also

play a role


Isochronous / Droop Modes of Operation

Isochronous - Isochronous control mode means that the frequency (and voltage) of the electricity generated is held constant, and there is zero generator droop.

Droop Control Mode - strategy commonly applied to generators for frequency control (and occasionally voltage control) to allow parallel generator operation (e.g. load sharing).

For grid-tied microgrids – all the DG and storage resources operate in droop mode and the utility is the isochronous generator reference.

For off-grid microgrids – one generating unit is designated to run in isochronous mode and all other follow in droop mode. Larger units and higher inertia prime movers are normally the reference machine. PV inverters are nearly always operating in droop mode. Battery inverters may operate either way when generating.


Controller Integration

Source: EPRI DOE SHINES Project


Microgrid Technical Challenges : Protection

Not enough short-circuit current in Microgrid mode for

protection to sense and operate

– Voltage-based protection was recommended : No

need for multiple settings group to support grid or

islanded operation

May require additional equipment and change in

protection settings.

Insulation coordination could be an issue

Microgrid operation may result in loss of effective ground

reference

Keeping protection scheme simple translates into improved

dependability as well as much simpler analysis in the event of

misoperation


For a small microgrid: need to understand the load Daily, from hourly to cycles in single family residence Knoxville, TN

8.0 kWmax

85.1 kWh

44% Load factor

10.7 kWmax

85.1 kWh

33%

26.2 kWmax

85.1 kWh

14%

14.8 kWmax

85.1 kWh

24%


PQ Enhancements Possible

Instant Islanding to mitigate campus interruptions caused by feeder faults

Proactive islanding due to “expected” feeder interruption or voltage sag (e.g. approaching lightning storm)

Partial voltage sag mitigation by means of DG voltage support during fault!

Improved local voltage flicker and regulation due to lower impedance of power system


Low Voltage Ride-Through

No low voltage ride-through requirements in the current IEEE

Std1547-2003 version (or the amendments)

A full revision of the 1547 is under way – inclusion of ride-through

requirements is considered

The CA Rule 21 ride-through requirements will likely inform the IEEE

Std 1547 ride-through requirements

The inverter must stop

producing power but be ready

to produce power again if the

voltage starts to normalize

before the inverter is allowed

to trip


Dynamic Models and Controls


Micro-Grid Switching - MV vs LV

Typical Main Switch

Jn. Box

12 kV

12 kV

Service

Xfmr

12 kV/

208V

MV-CB

From Utility

Building

Load

Point Of

Control

JC12 kV

Service

Xfmr

12 kV/

208V

MV-CB

LV-CB

Point Of

Control

Building

Load

LV-CB

Building

PV

Typical Main Switch 12 kV

From Utility


Micro-Grid Switching at MV Level

Approach:

Circuit breakers are available only at 12kV main

ring. No 12kV circuit breakers downstream.

Each circuit breaker controls a group of

transformers/buildings.

Control is at the group level. No individual

control at building level

Consequences:

Switching OFF a transformer on 12kV side

disconnects both building loads and connected

PV. This results in loss of generation (PV on non

critical buildings) when resources are needed

during islanded operation.

This design necessitates permanently assigning

buildings as critical and non-critical. It is not

possible to reassign them later.

12KV switching could cause high transformer

inrush currents during black start. Mitigating

equipment may be required if storage inverters

are not able to handle this high inrush current.

Typical Main Switch

Jn. Box

12 kV

12 kV

Service

Xfmr

12 kV/

208V

MV-CB

From Utility

Building

Load

Point Of

Control


Micro-Grid Switching at LV

Approach:

Control is shifted to the Low Voltage side.

Transformers are connected to buildings through

Low Voltage distribution boards.

This creates the ability to separately control loads

and generation within the buildings.

Consequences:

No loss of generation (PV on non critical

buildings) when loads are disconnected during

islanded operation.

Ability to reassign buildings as critical / non-

critical as and when needed.

As loads are disconnected from the LV side it is

possible to reestablish the MV ring through soft

start with all transformers connected. This could

reduce inrush current significantly.

JC12 kV

Service

Xfmr

12 kV/

208V

MV-CB

LV-CB

Point Of

Control

Building

Load

LV-CB

Building

PV

Typical Main Switch 12 kV

From Utility


Transformer inrush current and its impact

Inrush current during the energizing could be much higher than

the full rated current. It is short lived – a few cycles only.

Inrush currents can be as high as 6 and 18 times the rated

current. Magnitude of inrush current depends on several factors –

e.g.

– Primary voltage

– Transformer saturation curve

– Short circuit capacity of the network – lower the short circuit level, lower

the inrush current

Impact

– Inrush currents are reactive and can cause voltage drops

– Inrush currents do not normally pose any challenge in grid connected

mode as rotary generators are designed to handle these high currents

– However inverters are not designed to carry these. Typically they can

handle up to 2 to 3 times their rated current but not more.


Transformer Energizing: Equivalent Circuit

The short-circuit strength of the circuit determines the

magnitude of the inrush current during transformer energizing.

𝑣𝑠 𝑡 = 𝑍𝑠𝑖 𝑡 + 𝑋𝑙𝑘𝑖 𝑡 +𝜕l(𝑖, 𝑡)

𝜕𝑖(𝑡)

𝜕𝑖(𝑡)

𝜕𝑡

In a strong system, 𝑍𝑠 is small. The inrush current 𝑖 𝑡 will be larger.

In a weak system, 𝑍𝑠 is large. The inrush current 𝑖 𝑡 will be smaller.

l(𝑖, 𝑡) = the total magnetic flux linkage

𝑖 𝑡 = inrush current when energized

In differential equation:


Transformer Core Saturation Characteristics: I-V


Transformer Energizing: Full-Voltage Energizing

With a Typical Saturation Curve

Transformer is unloaded energized at bus full voltage. Short-

circuit strength is x

1.5 MVA, 12.47 kV/480V, 5.07% (for now - Ygnd Ygnd)

Rated transformer current = 70 Arms = 98 ApkShort-circuit capacity at 12.47 kV bus = 300 MVA Short-circuit capacity at 12.47 kV bus = 30 MVA

4.6x

3.5x


Transformer Energizing: Full-Voltage Energizing

With a Very Flat Saturation Curve

Transformer is unloaded energized at bus full voltage.

1.5 MVA, 12.47 kV/480V, 5.07% (for now - Ygnd Ygnd)

Rated transformer current = 70 Arms = 98 ApkShort-circuit capacity at 12.47 kV bus = 300 MVA Short-circuit capacity at 12.47 kV bus = 30 MVA

20x

9x


Design Analysis

volt

age

time

limits

unacceptableovervoltage

Cu

rren

t

Impedance

Relay desensitization

Wat

ts

Impedance

Load Only

Load and PV

Ener

gy

Time

unserved energy

Energy exceedingnormal

Design Analysis Approach

Load Analysis

Protection & Reliability

DER Sizing & Design

Distribution System Modeling, Simulation & Optimization

Microgrid Controller Architecture & Design

case by case look needed

Location √no impact

Location XPotential risk

• Steady State load flow• System Dynamic• Harmonics• Flicker• Controls• Operation seq.• Fault Current• Black Start


Data Collection Modeling Impact StudiesCommissioning

& Operation

Microgrid Design Analysis

o Model validation

o Real time ops &

monitoring

o Network models•Load types

•DER types

•Operation

o Protection info

o Scenarios

o Model validation

o Grid impact

o Steady state

o Fault analysis

o Protection

o Stability studies


Key interests

• Is the micro grid gen(s) is enough to support the islanded load?

• Verify compliance to planning & voltage stability requirements

Load flow

• Is existing protection adequate?

• If not, try various options

Protection analysis

• Events (loss of large load, load step & fault clearing capabilities)

• Fault Ride Through capabilities of various inverter-based DERs

Dynamic studies


Detailed Design Analysis – Tools Source: LBNL Paper LBNL-6708E

Need to apply a consistent modeling

framework

Allow existing models to feed new analysis

PSCAD/EMTP-RV/MATLAB DesignBase

DIGSILENT

PSS/SINCAL

CYMDIST

SynerGEE

Transient Dynamic

Time-Series

Analysis/Slow

Dynamics

Time-Series

Analysis/SS

Steps

Steady State

All

OpenDSS/Grid Lab D/DEW

Microseconds Milliseconds Seconds Minutes Hours Days

A variety of MC capabilities

requires a variety of models to

understand

• Performance

• Grid interaction

• System Protection Scheme

Impact


Available Tools

Software Tool Affiliated Org. Tool Type

CYMDIST CYME International T&D Inc. Planning and simulation of distribution networks,

including load flow, short-circuit, and network optimization analysis.

DER-CAM Lawrence Berkeley National Laboratory (LBNL)

Techno-economic tool for microgrid design and operation.

DesignBase Power Analytics Broad platform for electrical system design, simulation, and optimization.

EMTP-RV POWERSYS Solutions Power system transients simulation, load flow, harmonics.

EUROSTAG Tractebel Engineering GDF Suez

Power system dynamics simulation; full range of

transient, mid- and long-term stability; steady-state load flow computation.

GridLAB-D Pacific Northwest National Laboratory (PNNL)

Distribution system simulation and analysis.

HOMER Homer Energy LLC, National

Renewable Energy Laboratory (NREL)

Techno-economic tool for microgrid design and operation.

OpenDSS Electric Power Research Institute (EPRI)

Distribution system simulation and analysis.

PowerFactory DIgSILENT GmbH Power system analysis tool for load flow and

harmonics in transmission, distribution, and industrial networks.

PSCAD Manitoba HVDC Research Center

Power system transient simulation, load flow simulation.

PSS/E Siemens Power Technologies International (Siemens PTI)

Load flow, dynamic analysis, and harmonic analysis of utility and industrial networks.


Simulation Tools - Comparison

Power

Flow,

balanced

Power Flow,

unbalanced

Short

Circuit

Relay

Coordination

Arc

Flash

Harmonic

Analysis

Transient

Analysis

Dynamic

Analysis

Quasi Steady-

State Analysis

EMTP-RV,

Simulink,

PSCAD

Aspen, Cape

DesignBase,

PowerFactory

PSLF, PSS/E

OpenDSS

GridLAB-D

Best choice

Can be done, but not preferred choice

Cannot be done

Tool

Study


Case # 1:Protection Case Studies

(Mohamed El Khatib)

Renewable Based Microgrids


Case # 2: Rural Radial Community

(Arindam Maitra)


Case Study: Two Remote Rural Communities

3.25MW of Load

6.5MW of DG


One-line diagram of the 34.5-kV

34.5 KVExisting

Recloser

Existing

Recloser 34.5 KV

Plant Load: 5MW

Wind plant : 6.6 MW

Plant Load: 1MW

4.8 KV

Plant Load: 1.8MW

Sync DG:

0.416 MW

R55 R173

Wind Turbine: Type 2 induction generator with rotor resistor control.

This type of turbine needs a stiff transmission grid and a strong synchronous source for stable

operation and can introduce oscillations if it remains connected during islanded operation.

They require external reactive support to maintain voltage, which is typically provided by static

or/and dynamic compensation


Case Study: Reliability Assessments In Rural Areas of

New York

Microgrid 1

34.5 KVExisting

Reclosure

Existing

Reclosure

Proposed

PQ Meter

Proposed

Reclosure 34.5 KV

Plant Load: 5MW

Wind plant : 6.6 MW

Plant Load: 1MW

4.8 KV

Plant Load: 1.8MW

Sync DG:

0.416 MW

Proposed

Reclosure

Proposed

2 MWHR Energy

Storage

Proposed

1 MWHR Energy

Storage

Fault Exposure Scenario #1

Microgrid 2

34.5 KVExisting

Reclosure

Existing

Reclosure

Proposed

Reclosure 34.5 KV

Plant Load: 5MW

Wind plant : 6.6 MW

Plant Load: 1MW

Plant Load: 1.8MW

Proposed

Reclosure

Proposed

2 MWHR Energy

Storage

Proposed

1 MWHR Energy

Storage


Proposed

PQ Meter

Sync DG:

0.416 MW

4.8 KV

Electricity customers in rural areas

of NY have been experiencing

power outages lasting 10 hours &

longer, which far exceeds the

Customer Average Interruption

Duration Index (CAIDI) targets

Average statewide CAIDI target is

~ 2 hours

This problem is due, in part, to the

fact that many remote areas of

New York State are fed radially

and have only a single

transmission or sub-transmission

supply line that feeds these areas


Design Study

Rural electrification in areas with otherwise poor reliability is the key driver to evaluate microgrid as a possible solution

– Many remote communities are situated in locations without a backup transmission or sub-transmission connection

– Restoration time is quite high

– Microgrids can play a role in reducing fault investigation time, shorter outage duration and lower costs for first responders

– Operating remote communities as a microgrid

Complete transition from grid-connected operation to micro-grid operation within 15 minutes following the loss of the supply line

Supply at least 50% of the customers in the Wethersfield and 50% customers in Orangeville area for at least (8) hrs


Case Study: Focus Areas

−Define the Modes of Operations – Based on a permanent fault location

on 34.5 kV supply line and system protection requirements, different microgrid

scenarios are identified. Additional equipment or changes in the circuit

configuration to facilitate stable operation of the microgrids is proposed

−System Protection Study – Identify the required enhancements to

protections system for the area under study during microgrid conditions.

− A high-level protection system design (relay types, communication needs, etc.) that

are needed to accommodate normal and microgrid operation

−Fault Location Study – Develop improved fault locating algorithms for a

utility-supplied distribution circuit

− Emphasis was on 34.5 kV line and underlying 4.8 kV system as well to evaluate the

possible local microgrid effects at the 4.8 kV side.

− Develop improved fault locating algorithms in PSCAD

−


Possible Microgrid Configurations

Microgrid “OW”: both circuits

operate as a unified microgrid

Microgrid “W”: Circuit operates as

a standalone microgrid

Microgrid “O”: Circuit operates as

a standalone microgrid


Technical Limitations with Current Protection

Fault Condition # 1:

– Grid Connected Mode:

For a permanent fault between

Attica and Orangeville, recloser

R55 will open. Since R55 is the

only upstream recloser both

circuits with be out of service

Need for local generation

Important to isolate the fault

– EPRI proposes a new recloser

at Exchange St Rd P122. This

will allow Orangeville and

Wethersfield to be served as

microgrid (“OW”) with energy

storage while the fault is being

cleared

Microgrid 1

34.5 KVExisting

Reclosure

Existing

Reclosure

Proposed

PQ Meter

Proposed

Reclosure 34.5 KV

Plant Load: 5MW

Wind plant : 6.6 MW

Plant Load: 1MW

4.8 KV

Plant Load: 1.8MW

Sync DG:

0.416 MW

Proposed

Reclosure

Proposed

2 MWHR Energy

Storage

Proposed

1 MWHR Energy

Storage



Technical Limitations with Current Protection System

(cont.)

Fault Condition # 2:

– Grid Connected Mode:

Permanent fault between recloser R173 and Wethersfield, recloser R173 will open to save Wetherfield

Isolate the 4.8KV system in Wethersfield to prevent back feed from Wind farm (& Energy storage system proposed as part of the microgrid mode)

In this scenario, Orangeville and Boxler plant remain connected to the Attica substation in “grid-tie” mode.

– EPRI proposes a new recloser at J197/J199. Wethersfield will operate as a standalone microgrid (“W”)

34.5 KVExisting

Reclosure

Existing

Reclosure

Proposed

Reclosure 34.5 KV

Plant Load: 5MW

Wind plant : 6.6 MW

Plant Load: 1MW

Plant Load: 1.8MW

Proposed

Reclosure

Proposed

2 MWHR Energy

Storage

Proposed

1 MWHR Energy

Storage


Proposed

PQ Meter

Sync DG:

0.416 MW

4.8 KV

Microgrid W


Attica 34.5kV

R55

Boxler Farm

2.5MVA

34.5kV:4.8kV

500kVA

Wind Farm

Wethersfield

Beckwith M-3410A

R122 (new)

R199 (new)

X

storage

battery 1

New relay

Y

storage

battery 2

R173 (Form 6)

3 - set of 3 wye-gnd

connected VTs

3

1 – single VT

11

3

1

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173

Scenario - permanent fault between R55 and R122

X

Permanent fault occurs here

open

closed

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


X

open

closed

• X and Y opened by 34.5kV voltage protection before first reclose of R55

• R55 in reclosing cycle

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


X

open

closed

• R55 locks out

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


X

open

closed

• R122, R173, and R199 open

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


X

open

closed

• Both battery systems come back online and close X & Y

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


X

open

closed

• R199 will close using hot bus – dead line

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


X

open

closed

• R173 will close using sync-check

• Complete island established

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


open

closed

• Fault is removed and R55 manually closed

in reclosing

cycle

Orangeville Tap


R55

Boxler Farm

500kVA

Wind Farm

Wethersfield

R122

R199

X

Y

R173


open

closed

• R122 closes sync-check

• System normal

in reclosing

cycle

Orangeville Tap


Recommendations - Protections

• 34.5kV protection and control of micro grid scheme is voltage based

• Voltage protection disconnects energy storage batteries prior to entering

microgrid operation

• Voltage protection detects and clears 34.5kV faults that occur during microgrid

operation

• Ferroresonance suppression is prudent for 34.5kV wye-grounded VTs

as well as using VTs with high saturation knee point (e.g. 2.0 per unit)

• Low voltage current based protection (e.g. 4.8kV feeders) will have to be

evaluated based on energy storage devices capability to source fault current

or alternative protection should be investigated – not addressed in this section

• Setting and reclosing setting changes needed on R55 and R173 as well as the

additional protection & control described in this section for microgrid operation


Proposed Protection, Monitoring, & Control

Modifications

1.12 mi

AtticaSTA. 12

34.5 kV

Attica PrisonSTA.

Orangeville STA. 1934.5 kV

R55

J192

Boxler Farm480V, 416 kW

6.3 mi 0.2 mi 6.1 mi Vestas TAP34.5 kV

0.1

mi

Wethersfield STA. 23 34.5 kV

R122 R173

R1

99

4.0

mi

PQ48V

PQ48B

WNY Wind Corp. 6.6 MW

Thevenin equivalent source for

Attica substation



Attica Prison

Wethersfield 4.8-kV circuit and load

Orangeville 4.8-kV circuit and load

Boxler DG4.8 kV


34.5 KVExisting

recloser

Existing

recloser

Proposed

PQ Meter

Proposed

recloser 34.5 KV

Plant Load: 5MW

Wind plant : 6.6 MW

Plant Load: 1MW

4.8 KV

Plant Load: 1.8MW

Sync DG:

0.416 MW

Proposed

recloser

Proposed

2 MWHR Energy

Storage

Proposed

1 MWHR Energy

Storage

Microgrid OW –

Orangeville & Wethersfield

Proposed System Level Modifications – Energy Storage

System

• 2 Separate ES systems proposed.

− Closer to the Loads at Orangville and Wethersfield

− Valid for independent operations of Orangville and

Wethersfield

− Smaller Systems are more reliable


Fault Location Analysis

Number of

events

Monitor Samples/cycle Voltage level Actual Fault

location

Circuit

model

Data useful for

fault location

12 R55 4 34.5 kV Unknown ASPEN

OneLiner

Yes

10 R173 16 Limited

1.12 mi

AtticaSTA. 12

34.5 kV

Attica PrisonSTA.


R55

J192



0.1

mi


R122 R173

R1

99

4.0

mi

PQ48V

PQ48B



Attica substation



Attica Prison



SEL PG10Cooper Form

Type 6


Line Exposed to Faults in Grid Connected Mode

Scenario G1: Multiple single line-to-ground faults applied in Line Section 1, between reclosers R55 and R122

Scenario G2: Multiple single line-to-ground faults applied in Line Section 2, between reclosers R173 and R199

Scenario G3: Multiple line-to-line faults applied in Line Section 3, between PQ48V and PQ48B

1.2 mi

AtticaSTA. 12

34.5 kV

Attica PrisonSTA.


R55

J192



0.1

mi


R122 R173

R1

99

4.0

mi

PQ48V

PQ48B



Attica substation



Attica Prison



Boxler DG4.8 kV

L i n e S e c t i o n 1 L i n e S e c t i o n 2

Line

Section

3


Line Exposed to Faults in Microgrid Operation

Scenario OW1: Multiple line-to-line faults applied in Line Section 2, between reclosers R173 and R199 (in

Microgrid OW operation)

Scenario OW2: Multiple line-to-line faults applied in Line Section 3, between PQ48V and PQ48B (in Microgrid

OW operation)

Scenario O1: Multiple line-to-line faults applied in Line Section 3, between PQ48V and PQ48B (in Microgrid O

operation)

“Microgrid O”“Microgrid OW”

Line Sectio

n 3


J192


0.2 mi 6.1 mi Vestas TAP34.5 kV

0.1

mi

R122 R173

4.0

mi

PQ48V

PQ48B



Boxler DG4.8 kV

OrangevilleEnergy Storage


R1

99


Wethersfield 4.8-kV circuit and load Wethersfield

Energy Storage

L i n e S e c t i o n 2

Line Sectio

n 3


4.0

mi

PQ48V

PQ48B



Boxler DG4.8 kV

OrangevilleEnergy Storage


Fault Location Algorithms Applied in “Grid Connected” Mode

1.12 mi

AtticaSTA. 12

34.5 kV

Attica PrisonSTA.


R55

J192



0.1

mi


R122 R173R

19

9

4.0

mi

PQ48V

PQ48B



Attica substation



Attica Prison



Line Section 1 Line Section 2

Lin

e S

ec

tio

n 3

Scenario Algorithms to be Applied during SLG Faults

Line Section 1 One-ended methods (R55) Simple reactance, Takagi, Novosel et al.

Two-ended method (R55, R122) Two-terminal negative-sequence

Line Section 2 One-ended methods (R173) Simple reactance, Takagi, Novosel et al.

Line Section 3 One-ended methods (PQ48B) Simple reactance, Takagi, Eriksson

Two-ended methods (PQ48B, PQ48V) Two-terminal negative-sequence


Case # 3: Secondary Network

(Arindam Maitra)


Case Study #3: Secondary Network

Models developed in

OpenDSS, EMTP-RV, &

Power Factory

Microgeneration types: CHP

behind inverter and PV

Scenario tested: Small-scale

Distributed CHP units (small

synchronous machine

behind an inverter) + small

scale PV


One Line Diagram


Scenarios

1. Small-scale Distributed CHP units

(small synchronous machine behind

an inverter) + small scale PV

2. Small-scale Distributed CHP units

(small synchronous machine behind

an inverter) + small scale PV +

small scale distributed storage

3. Large-scale Central CHP unit (large

synchronous machine) + small

scale PV

4. Large-scale Central CHP unit (large

synchronous machine) + small

scale PV + Large-scale central

storage

5. 100% Large CHP unit (large

synchronous machine)

6. 100% Large CHP unit (large

synchronous machine behind an

inverter)

VS8360(44X_VS8360)

10

38

4(4

4X

_1

03

84

) M1049(44X_M1049)

BLDG 7(5917.44X_10384)

kVA = 314.794

M1047(44X_M1047)

10385(44X_10385)

BLDG 5(5829.44X_10385)

kVA = 182.114

M1

04

8(4

4X

_M

10

48

)

BLDG 6(5877.44X_M1048)

kVA = 222.239

BC3998(44X_BC3998)

VS4007(44X_VS4007)

VS3998(44X_VS3998)

0.05 MVA 0.05 MVA 0.05 MVA

0.025 MVA

303 Vernon Ave(5916.44X_BC3998)

kVA = 310.728

0.025 MVA

303 Vernon Ave(5766.44X_BC3998)

kVA = 140.5

0.3 MVA 0.3 MVA 0.3 MVA

0.15 MVA 0.15 MVA

Inverter

Inv

ert

er

Inverter Inverter

Inv

erte

r

Inverter Inverter Inverter

Inv

ert

er In

ve

rter


Assumptions

The LV system is solidly grounded via a dedicated ground link at:

– Distribution supply transformer LV (transformers are Delta-Wye, directly

connected to ground on the secondary side)

– Each LV generator (generators are Y connected to ground)

– LV network protection vaults

System impedance to ground is maintained at less than 5 ohms

as specified by Client

The DERs are assumed:

– 3-phase YN connected and the neutral is solidly grounded

– Provide up to 1.8 per unit fault current

– Can sustainably provide fault current, including earth fault current until

fault is cleared or isolated


General philosophy used

Determine the required level of selectivity for different fault scenarios. Generally, this

can be determined by considering the impact to the customers for different grid faults.

Group parallel cables connecting common LV nodes together into single ’branches’

Split the Microgrid into separate regions/zones which with appropriate protection

grading will achieve the desired selectivity.

Ensure LV grid relays protecting branches directly connected to customers trip first to

remove the fault from the remaining healthy grid as quickly as possible

Ensure some time delay between tripping of customer branches and any

interconnector circuits connecting together main LV nodes

Ensure customer relays trip last to ensure healthy generation remains in service post

fault


High selectivity protection zones


Grid Connected Mode – Summer Peak Steady

State Branch Currents and Bus Voltages

74

Line IDFrom

BusTo Bus

Current

(A)

Loading

(%)

sec_6643_1

10385 M1047

143 17%

sec_6643_2 143 17%

sec_6644_1 159 20%

sec_6644_2 159 20%

sec_6645_1

M1047 M1048

129 16%

sec_6645_2 129 16%

sec_6646_1 115 14%

sec_6646_2 115 14%

sec_6646_3 115 14%

sec_6649_1

M1048 10384

213 25%

sec_6649_2 213 25%

sec_6650_1 239 29%

sec_6651_1 M1049 10384 0 0%

sec_6751_1

M1048BC399

8

249 29%

sec_6751_2 249 29%

sec_6751_3 249 29%

sec_6751_4 249 29%

sec_6754_1

VS8360 M1048

244 29%

sec_6754_2 244 29%

sec_6754_3 244 29%

sec_6754_4 244 29%

Bus IDPhase A

(pu)

Phase B

(pu)

Phase C

(pu)

M1048 0.98 0.98 0.98

10384 0.96 0.96 0.96

10385 0.97 0.97 0.97

BC3998 0.99 0.99 0.99

M1049 0.96 0.96 0.96

M1047 0.97 0.97 0.97

VS8360 0.98 0.98 0.98

VS4007 0.99 0.99 0.99

VS3998 0.99 0.99 0.99


Summer Peak Steady State and Fault Induced Bus Voltages –

Grid Connected & Islanded

75

Bus ID

Summer Load Fault @ 10384 Fault @ BC3998 Fault @ M1048

Phase

A

Phase

B

Phase

C

Phase

A

Phase

B

Phase

C

Phase

A

Phase

B

Phase

C

Phase

A

Phase

B

Phase

C

M1048 1.00 1.00 1.00 0.13 0.13 0.13 0.05 0.05 0.05 0.00 0.00 0.00

10384 1.00 1.00 1.00 0.00 0.00 0.00 0.09 0.09 0.09 0.05 0.05 0.05

10385 1.01 1.01 1.01 0.15 0.15 0.15 0.07 0.07 0.07 0.03 0.03 0.03

BC3998 1.00 1.00 1.00 0.14 0.14 0.14 0.00 0.00 0.00 0.02 0.02 0.02

M1047 1.00 1.00 1.00 0.14 0.14 0.14 0.06 0.06 0.06 0.01 0.01 0.01

VS8360 1.00 1.00 1.00 0.13 0.13 0.13 0.05 0.05 0.05 0.00 0.00 0.00

VS4007 1.00 1.00 1.00 0.14 0.14 0.14 0.00 0.00 0.00 0.02 0.02 0.02

VS3998 1.00 1.00 1.00 0.14 0.14 0.14 0.00 0.00 0.00 0.02 0.02 0.02

Bus ID

Summer Load Fault @ 10384 Fault @ BC3998 Fault @ M1048

Phase

A

Phase

B

Phase

C

Phase

A

Phase

B

Phase

C

Phase

A

Phase

B

Phase

C

Phase

A

Phas

e B

Phas

e C

M1048 0.98 0.98 0.98 0.69 0.69 0.69 0.37 0.37 0.37 0.00 0.00 0.00

10384 0.98 0.98 0.98 0.00 0.00 0.00 0.66 0.66 0.66 0.47 0.47 0.47

10385 0.99 0.99 0.99 0.79 0.79 0.79 0.59 0.59 0.59 0.35 0.35 0.35

BC3998 0.98 0.98 0.98 0.79 0.79 0.79 0.00 0.00 0.00 0.32 0.32 0.32

M1047 0.99 0.99 0.99 0.74 0.74 0.74 0.48 0.48 0.48 0.17 0.17 0.17

VS8360 0.99 0.99 0.99 0.73 0.73 0.73 0.46 0.46 0.46 0.14 0.14 0.14

VS4007 0.99 0.99 0.99 0.86 0.86 0.86 0.33 0.33 0.33 0.55 0.55 0.55

VS3998 0.99 0.99 0.99 0.80 0.80 0.80 0.04 0.04 0.04 0.35 0.35 0.35

When islanded

the bus voltages

are close to zero

and inadequate

for fault location

determination

In grid connected

mode the bus

voltages of un-

faulted buses are

non-zero


Changes from Grid Connected Mode to Islanded Mode in

Summer Peak Steady State and Fault Induced Phase A Branch

Currents

Line ID From Bus To BusSummer

LoadFault @ 10384

Fault @

BC3998Fault @ M1048

sec_6643_1

10385 M1047

78% -75% -87% -92%

sec_6643_2 78% -75% -87% -92%

sec_6644_1 78% -75% -87% -92%

sec_6644_2 78% -75% -87% -92%

sec_6645_1

M1047 M1048

78% -75% -87% -92%

sec_6645_2 78% -75% -87% -92%

sec_6646_1 78% -75% -87% -92%

sec_6646_2 78% -75% -87% -92%

sec_6646_3 78% -75% -87% -92%

sec_6649_1

M1048 10384

-31% -82% -85% -90%

sec_6649_2 -31% -82% -85% -90%

sec_6650_1 -31% -82% -85% -90%

sec_6751_1

M1048 BC3998

279% -86% -88% -95%

sec_6751_2 279% -86% -88% -95%

sec_6751_3 279% -86% -88% -95%

sec_6751_4 279% -86% -88% -95%

Total Fault Current at the Fault Location (%) -89% -93% -93%

When islanded

line loading

increases for

most line

sections

When islanded

fault currents

decrease for all

3-phase faults


Modeling Existing Protection

Used representative curves Curve in power factory

Typical TCC for a

current-limiting fuse


Findings and recommendations: Current-Limiting Protection

Normally the Current limiter (CL) fuse will “melt” when the

current in the fuse element exceeds the current specified by

the fuse’s melt characteristic.

No enough fault currents from the inverter based gens;

hence there is no compliance to protection standards and

performance metrics during island mode

Clearly, this type of protection in utilizing current limiters isn’t

sufficient

Another set of protection strategies need to be adopted


Small-scale Distributed CHP units (small

synchronous machine behind an inverter) + small

scale PV

79

• The overcurrent modules and circuit breakers tip-times

depend on the fault-current amplitude

• The appropriate directional modules were set to trip

slightly after the overcurrent models

Circuit breakers

Directional-

Overcurrent


3 Phase Fault @ 10384

80



81

1. D/O module between 10384 and M1048 trips on overcurrent

2. Circuit breaker at 10384 PCC trips on overcurrent

1

2



82

Isolated

Loads and generators at bus 10384 are

isolated



83

After fault is cleared bus voltages

recover to normal values



84



85



1

2



86

Isolated


isolated



87




1 Phase Fault (46.6 mΩ) @ 10384

88


1 Phase Fault (46.6 mΩ) @ 10384

89



1

2


1 Phase Fault (46.6 mΩ) @ 10384

90

Isolated


isolated


1 Phase Fault (46.6 mΩ) @ 10384

91




Phase-Phase Fault @ 10384

92



93



2

1



94

Isolated


isolated



95




Phase-Phase-Ground Fault @ 10384

96



97



2

1



98

Isolated


isolated



99




3 Phase Fault @ M1048

100



101

1. D/O module between 10384 and M1048 trips on directional

2. D/O module between BC3998 and M1048 trips on directional

3. D/O module between M1047 and M1048 trips on overcurrent

4. Circuit breaker at M1048 PCC trips on overcurrent

1

2

3

4



102

Isolated

Loads and generators at all buses are

isolated

Isolated Isolated

Isolated



103

After fault is cleared bus voltages:

1. at 10385 and M1048 are elevated

2. at BC3998 are bellow normal

values

3. at 10384 recover to normal values


3 Phase Fault @ BC3998

104



105

1. D/O module between BC3998 and M1048 trips on

overcurrent

2. Circuit breaker at BC3998 PCC trips on

overcurrent

1

2



106

Loads and generators at bus BC3998

are isolated

Isolated



107


1. at 10384, 10385 and M1048 are

elevated

2. at BC3998 are bellow normal

values



108



109

1. D/O module between 10385 and M1048 trips on

directional


1

2



110


isolated

Isolated



111


1. at 10385 are elevated

2. at 10384, M1048, and BC3998 are

bellow normal values


Summary

“Microgrids” brings many technical needs: Good PSA tools available

No one-size fits all protection scheme works for all microgrids

Action planContinue testing various protection schemes

Level of dynamic studies details depends on so many

factors i.e. gen types, operation philosophy etc.

Best protection scheme depends on microgrid objective

• Network

• Objective

• Scenarios

• Modeling

Grid requirements

Controllability

Monitoring

Reliability


Together…Shaping the Future of Electricity

microgrid design considerations - integrated...

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