Microgrid Design Considerations

Home , Circuit breaker, Low voltage ride through

Dr. Arindam Maitra, EPRI September 8, 2016

Time Topics 14:30-15:00 Design analysis • Needs and Key Interconnection Issues (Arindam Maitra) 15:30-17:30 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

.Optimization of microgrid design is challenging and inherently contains many unknowns…

Regulatory Issues Value of Resiliency

System Design Challenges Engineering Studies Costs

Customer Utility Assets Assets

Micro Grid Controller SCADA/DMS/ / DERMS* Enterprise Integrate d Grid Energy Storage*

Isolating Device*

Distribution Transformer *New assets

.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

.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.

Circuit Breaker Isolating Device – when open the system operates as micro-grid “Islanded” Facility Utility Source Trip Signal

Islanding Control (opens/closes breaker as needed to facilitate independent operation – must provide synchronization)

Electrical Island DG DG Able to Carry Load on Island and Provide Proper Voltage and Frequency

“Islanded” campus area during utility system outages

Building Load

13.2 kV Feeder Building Load Utility Substation

Building Load Utility System Interface Breaker

D D Building Building G G Load Load

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

House 1 House 2 House 3 Distribution Transformer Isolating Power System Device Secondary Utility System (120/240 V) Primary (13.2 kV)

Utility System 50 KVA House 4 House 5 House 6 Interface & Inverter Controller (Synchronization, fault protection, islanding DC Bus detection, etc.) Fuel Cell Charge Regulator

Thermal Energy Storage Storage Heat Distribution

Serves as Isolation Point Utility System Interface AC Bus & Protection Control for Micro-grid mode of operation Utility Building Source Electrical Circuit Loads Breaker Circuit 20 kW Status/control Breaker signals paths to/from Wind electrical loads Energy Master Source System INVERTER Controller Status/control signal Rectification paths to/from thermal and Filtering DC Bus loads

Charge/Discharge Regulator Building 200 kW Heat Energy Recovery Thermal Storage Fuel Cell Loads

Dormitory A Dormitory B Administrative Isolating Device (opens during micro-grid mode) Building Campus Owned 500 kVA 500 kVA 300 kVA Distribution (13.2 kV) Utility System Primary Connection (13.2 kV)

Voltage Utility System To Other 75 kVA Interface Control Regulator Generator Campus (Synchronization, fault protection, islanding detection, Step Up Loads Academic etc.) Transformer Student Heat Distribution Union Building B Paralleling Bus (4.8 kV) Communication & Control Signal Path Generator 1.75 Academic Building A Protection 1.75 1.75 300 and Control MVA MVA MVA 800 kVA kVA Gen Gen Gen Load control

Heat Recovered Heat Distribution from ICE Units

Urban Rural Non-Utility Remote / Utility Utility Microgrids Island . Number of customers served Microgrids Microgrids Microgrids

Commercial / Remote . Physical length of circuits and types Industrial Clusters Planned Communities

of loads to be served Downtown Islanding and Loads Application University Campus Areas

Load Support Geographical Residential . Voltage levels to be used Islands Development

. Feeder configuration (looped, Reliability and Improved Reliability; Power Quality Electrification of Main Drivers Outage Management; networked, radial) Enhancement; Remote Areas Renewable and CHP Integration Energy Efficiency; . Types of distributed energy Improved Reliability; Premium Power Supply resources utilized Fuel Diversity; Quality; Availability Congestion Management; Benefits CHP Integration; Greenhouse Gas Reduction; Demand Response Integration of . AC or DC microgrid Upgrade Deferral; Management Renewables Ancillary Services . Heat-recovery options Grid- Primary Mode of Primary Mode of Operation Never Connected Operation . Desired power quality and reliability Nearby faults or levels System Disturbances Nearby faults or System

Intentional Disturbances Times of Peak Always Islanded Islanding . Methods of control and protection Energy Prices Approaching Storms . Controllers Approaching Storms Source: Johan Driesen and Farid Katiraei, “Design for Distributed Energy Resources,” IEEE Power & Energy Magazine, May/June 2008

• Are the fault contributions from • Are DERs able to regulate the voltage and DERs sufficient to allow frequency within the island? satisfactory operation of • Any issues with parallel grid operation? protection systems? • How is re-synchronization checked • Are existing protection schemes against criteria such as out-of-phase, large adequate? change in voltage?

Microgrids

Need a microgrid controller

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

Site Descriptions

Microgrid Project Objectives

Design Basis and Rationale

Performance Criteria • Electrical & Thermal Needs • Generation Assets • Critical Load Needs • Power Distribution Equip.

DER & Microgrid Controller Control Needs Communication Needs Codes & Standards

Renewables Fossil Fuels Tech ▪ Solar Photovoltaics ▪ Boiler Electric Storage ▪ Solar Thermal ▪ Fuel Cell Microturbine • AggregateSolar capacity Photovoltaics of all units (kwh) ▪ Wind ▪ Microturbine• Maximum charge rate • Max Power (kW) NG• # Genset of modules ▪ (fraction of total capacity charge in one hour) • Sprint capacity (% of power) ▪ Diesel• Module (backup) rating (kW DC)Electric Vehicles • Maximum discharge rate • # of sprint hours (hours) • Module •SizeMultiple (m2) locations (fraction of total capacity discharge per hour) • Fuel type • Efficiency• (%)Min connect/disconnect SOC Energy Storage • MinimumThermal state Tech of charge • Efficiency (ratio) • Inverter• sizeMax (kW charge AC) hours ▪ Electrical (Power, Energy) ▪ Heat• Charge Pump efficiency • CHP capable? (yes/no) • Total land• areaBattery (m2) size ▪ Thermal (Chiller, Refrig.) ▪ CHP• Discharge efficiency • Alpha (power to heat ratio) ------• Efficiency ▪ HVACR• Decay/self-discharge (fraction of total capacity per • NOx emissions rate (kg/hr) • Capital •costDecay ($) ▪ Solarhour) Thermal • etc. • Maximum annual operating hours (hours) • ------Lifetime (years) • Minimum loading (% of power) • O&M fixed costs ($/year) • Fixed cost ($) SOC ------• • O&MVariable variable Cost costs ($/kw ($/year/kW) or $/kwh) Other • Capital cost ($) • Lifetime (years) • Lifetime (years) ▪ Electric Vehicles Disconnect • O&M fixedConnect costs ($/year) • O&M fixed costs ($/year) • O&M variable costs ($/year/unit) • NOx treatment costs ($/kg) t

Variable Distributed Energy Assets within Microgrid Source: PNNL Source:

. 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 - 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. 19 © 2015 Electric Power Research Institute, Inc. All rights reserved. Controller Integration

. 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

8.0 kWmax 10.7 kWmax 85.1 kWh 85.1 kWh

44% Load factor 33%

14.8 kWmax 26.2 kWmax 85.1 kWh 85.1 kWh

24% 14%

.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

. 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 24 to trip © 2015 Electric Power Research Institute, Inc. All rights reserved. Dynamic Models and Controls

From Utility From Utility Typical Main Switch 12 kV Typical Main Switch 12 kV MV-CB MV-CB

Point Of Control JC Jn. Box 12 kV 12 kV

Service 12 kV/ Service 12 kV/ Xfmr 208V Xfmr 208V

LV-CB LV-CB Point Of Control Building Building Building Load Load PV

From Utility Approach: Typical Main Switch 12 kV . Circuit breakers are available only at 12kV main ring. No 12kV circuit breakers downstream. MV-CB . Each circuit breaker controls a group of Point Of transformers/buildings. Control . Control is at the group level. No individual Jn. Box 12 kV 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 Service 12 kV/ during islanded operation. Xfmr 208V . This design necessitates permanently assigning buildings as critical and non-critical. It is not possible to reassign them later. Building . 12KV switching could cause high transformer Load inrush currents during black start. Mitigating equipment may be required if storage inverters are not able to handle this high inrush current.

From Utility Approach: Typical Main Switch 12 kV . Control is shifted to the Low Voltage side. MV-CB . Transformers are connected to buildings through Low Voltage distribution boards. . This creates the ability to separately control loads JC and generation within the buildings. 12 kV Consequences: . No loss of generation (PV on non critical buildings) when loads are disconnected during islanded operation. Service 12 kV/ Xfmr 208V . Ability to reassign buildings as critical / non- critical as and when needed. LV-CB LV-CB . As loads are disconnected from the LV side it is Point Of Control possible to reestablish the MV ring through soft Building Building start with all transformers connected. This could Load PV reduce inrush current significantly.

. 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.

The short-circuit strength of the circuit determines the magnitude of the inrush current during transformer energizing.

휕l(푖, 푡) 휕푖(푡) In differential equation: 푣 푡 = 푍 푖 푡 + 푋 푖 푡 + 푠 푠 푙푘 휕푖(푡) 휕푡 l(푖, 푡) = the total magnetic flux linkage 푖 푡 = inrush current when energized

In a strong system, 푍푠 is small. The inrush current 푖 푡 will be larger. In a weak system, 푍푠 is large. The inrush current 푖 푡 will be smaller.

31 © 2015 Electric Power Research Institute, Inc. All rights reserved. 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) Short-circuit capacity at 12.47 kV bus = 300 MVA Short-circuit capacity at 12.47 kV bus = 30 MVA .Rated transformer current = 70 Arms = 98 Apk 4.6x 3.5x

32 © 2015 Electric Power Research Institute, Inc. All rights reserved. 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)

Short.Rated-circuit capacity transformer at 12.47 kV bus current = 300 MVA = 70 ShortArms-circuit = capacity 98 Apk at 12.47 kV bus = 30 MVA

20x

unacceptable overvoltage Microgrid Controller DER Sizing & Design voltage limits Architecture & Design

Load Only time  Watts

Load and PV Design Analysis Impedance  Approach

Location √ no impact • Steady State load flow Relay desensitization

unserved energy • System Dynamic

Energy • Harmonics

case by case Current look needed Energy exceeding normal • Flicker

Time  Location X • Controls Potential risk • Operation seq. Impedance  Distribution System Modeling, • Fault Current Simulation & Optimization • Black Start Protection & Reliability

Commissioning Data Collection Modeling Impact Studies & Operation

o Network models o Scenarios o Steady state o Model validation •Load types o Model validation o Fault analysis o Real time ops & •DER types o Grid impact o Protection monitoring •Operation o Stability studies o Protection info

Load flow

• Is the micro grid gen(s) is enough to support the islanded load? • Verify compliance to planning & voltage stability requirements

Protection analysis

• Is existing protection adequate? • If not, try various options

Dynamic studies

• Events (loss of large load, load step & fault clearing capabilities) • Fault Ride Through capabilities of various inverter-based DERs

Source: LBNL Paper LBNL-6708E

A variety of MC capabilities requires a variety of models to understand • Performance • Grid interaction • System Protection Scheme Impact

OpenDSS/Grid Lab D/DEW

PSCAD/EMTP-RV/MATLAB DesignBase

DIGSILENT All PSS/SINCAL

CYMDIST Need to apply a consistent modeling framework SynerGEE

Allow existing models to feed new analysis Time-Series Time-Series Transient Dynamic Analysis/Slow Analysis/SS Steady State Dynamics Steps

Microseconds Milliseconds Seconds Minutes Hours Days

37 © 2015 Electric Power Research Institute, Inc. All rights reserved. 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 Techno-economic tool for microgrid design and Laboratory (LBNL) 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 Power system dynamics simulation; full range of Suez transient, mid- and long-term stability; steady-state load flow computation. GridLAB-D Pacific Northwest National Distribution system simulation and analysis. Laboratory (PNNL) HOMER Homer Energy LLC, National Techno-economic tool for microgrid design and Renewable Energy operation. Laboratory (NREL) OpenDSS Electric Power Research Distribution system simulation and analysis. Institute (EPRI) PowerFactory DIgSILENT GmbH Power system analysis tool for load flow and harmonics in transmission, distribution, and industrial networks. PSCAD Manitoba HVDC Research Power system transient simulation, load flow Center simulation. PSS/E Siemens Power Technologies Load flow, dynamic analysis, and harmonic analysis of International (Siemens PTI) utility and industrial networks. 38 © 2015 Electric Power Research Institute, Inc. All rights reserved. Simulation Tools - Comparison

Power Study Power Flow, Short Relay Arc Harmonic Transient Dynamic Quasi Steady- Flow, unbalanced Circuit Coordination Flash Analysis Analysis Analysis State Analysis Tool balanced 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

Renewable Based Microgrids

3.25MW of Load 6.5MW of DG

Plant Load: 5MW 4.8 KV

Plant Load: 1MW

Plant Load: 1.8MW Wind plant : 6.6 MW

Sync DG: 0.416 MW

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

Fault Exposure Scenario #1 . Electricity customers in rural areas Proposed Existing Proposed Existing 34.5 KV Reclosure of NY have been experiencing Reclosure Reclosure Reclosure 34.5 KV power outages lasting 10 hours & longer, which far exceeds the Plant Load: 5MW Customer Average Interruption 4.8 KV Proposed Proposed 2 MWHR Energy Duration Index (CAIDI) targets Plant Load: 1MW PQ Meter Storage Plant Load: 1.8MW

Proposed 1 MWHR Energy Storage Wind plant : 6.6 MW

Microgrid 1 . Average statewide CAIDI target is Sync DG: 0.416 MW ~ 2 hours Fault Exposure Scenario #2

Proposed Existing Proposed Existing 34.5 KV Reclosure Reclosure Reclosure Reclosure 34.5 KV

. This problem is due, in part, to the

Plant Load: 5MW fact that many remote areas of 4.8 KV Proposed New York State are fed radially Proposed 2 MWHR Energy Plant Load: 1MW PQ Meter Storage and have only a single Plant Load: 1.8MW

Proposed transmission or sub-transmission 1 MWHR Energy supply line that feeds these areas Storage Wind plant : 6.6 MW Microgrid 2 Sync DG: 0.416 MW

. 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

−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

. 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

Fault Condition # 1: – Grid Connected Mode: Fault Exposure Scenario #1

Proposed . For a permanent fault between Existing Proposed Existing 34.5 KV Reclosure Attica and Orangeville, recloser Reclosure Reclosure Reclosure 34.5 KV R55 will open. Since R55 is the

Plant Load: 5MW only upstream recloser both 4.8 KV Proposed circuits with be out of service Proposed 2 MWHR Energy Plant Load: 1MW PQ Meter Storage . Need for local generation Plant Load: 1.8MW Proposed 1 MWHR Energy . Important to isolate the fault Storage Wind plant : 6.6 MW Microgrid 1 Sync DG: 0.416 MW – 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 48 © 2015 Electric Power Research Institute, Inc. All rights reserved. Technical Limitations with Current Protection System (cont.)

Fault Condition # 2: Fault Exposure Scenario #2

Proposed Existing Proposed Existing 34.5 KV Reclosure – Grid Connected Mode: Reclosure Reclosure Reclosure 34.5 KV . Permanent fault between

recloser R173 and Plant Load: 5MW Wethersfield, recloser R173 4.8 KV Proposed will open to save Wetherfield Proposed 2 MWHR Energy Plant Load: 1MW PQ Meter Storage Plant Load: 1.8MW

. Isolate the 4.8KV system in Proposed 1 MWHR Energy Wethersfield to prevent back Storage Wind plant : 6.6 MW feed from Wind farm (& Microgrid W Energy storage system Sync DG: proposed as part of the 0.416 MW 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”)

1 1 3 Wind Farm R173 (Form 6) New relay 3 - set of 3 wye-gnd 2.5MVA connected VTs 34.5kV:4.8kV X 1 – single VT

Wethersfield R199 (new) storage 1 battery 1 500kVA 3

Beckwith M-3410A Y Boxler Farm storage battery 2