Planning a successful microgrid

www.trcsolutions.com

Planning a Successful MicrogridJanuary 22, 2015

Bill Moran, Senior Electrical EngineerMark Lorentzen, Vice President, Energy Efficiency

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Today’s Grid

Source: http://peswiki.com/index.php/Directory:Smart_Grid

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Tomorrow’s Microgrids

Georgia Tech, Climate and Energy Policy Labhttp://www.cepl.gatech.edu/drupal/

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TRC Microgrid Team

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A pioneer in groundbreaking scientific and engineering developments since 1969, TRC is a national engineering, consulting and construction management firm that provides integrated services to three primary markets:

Energy | Environmental | Infrastructure

Expert problem solvers

100+ U.S. offices London office

3,000+ employees

NYSE: TRR

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Company Profile

TRC’s Guiding Principles

Our Mission ’ creativity, experience, integrity and dedication to deliver superior solutions to ’ f .

Our Vision We will solve the challenges of making the Earth a better place to live –community by community and project by project.

ENR Top 500 Design Firms

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"The energy market growth is inevitable and one of the largest sectors for capital investment. Any design firm working and supporting that market will have a bright future.“

Chris Vincze, CEO, TRC Companies Inc.

E32 36 TRC Cos. Inc., Lowell, Mass.

Rank

2013 2012

Firm Firm Type

Growth Drivers

Reliability | Power Supply | Aging Generation Assets | Regulatory

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Electrical Transmission, Distribution & Substation Engineering

Energy Efficiency, Demand Response, Renewable Energy, CHP

Communications Engineering

Transformation

High-Profile Private Sector Clients

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Working With All Levels of Government

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State and Local Federal

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Speaker Highlights

Bill Moran has over 35 years' experience in electrical power generation and distribution with a focus on the design, construction and operation of large campus type power distribution systems. Bill is the lead technical consultant supporting the development of f ’ Microgrid Grant and Loan Pilot Program.

He is a key member of the TRC MicrogridTeam, a multidiscipline team of experts assembled to help clients plan, design and build microgrids.

William Moran Senior Electrical EngineerTRC Companies, Inc.

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• Microgrid development – where to start

• Site selection and types of distribution

• Load management

• Generation sources

• Microgrid protection and controls

• Grounding

Overview

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• Multiple critical facilities

• Physical location – Critical Facilities and generation all within reasonable walking distance; voltage drop and cost of distribution feeders are considerations

• Widely spaced facilities with numerous non-critical sites between will greatly increase cost of microgrid; separating critical and non critical facilities require additional switching equipment and possibly a dedicated circuit

• Are all microgrid facilities within a campus, or will power have to cross public roads?

• What does the microgrid look like?

Microgrid Development – Site Selection

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Campus Microgrid

Typical campus system has a single owner of all facilities, and is often served from a single utility meter.

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Lateral Island Microgrid

LEGEND

CF = CRITICAL FACILITYNC = NON-CRITICAL FACILITY

Fed from a single utility distribution feeder, which also feeds non-critical facilities that are not included in microgrid.

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Dedicated Circuit Microgrid

LEGEND

CF = CRITICAL FACILITYNC = NON-CRITICAL FACILITY

Expensive – redundant distribution circuit to connect critical facilities with microgrid generation.

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Meet with the utility

• Identify feeder(s) to be incorporated into microgrid

• Identify primary system voltage and grounding method

• Identify critical facilities to be included in microgrid

• Obtain DG interconnection requirements

• Discuss system hardening and reliability improvements

– Undergrounding, loop feeds, automatic sectionalizing

Steps to Project Development

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Loop Feed Distribution

Features

• Redundant circuit path to each facility

• Protective relay functionality to isolate system faults

• Communication with other loop switches for coordinated operation

• Establishes self-healing distribution

• Minimizes outages to individual facility

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Underground Loop Distribution Switch

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Meet with Engineering consultants – establish scope of services

• Load Study Prerequisite: upgrade metering to provide real time demand data

(1 minute interval ideal), 12 months data preferred

On Peak: 6AM – 8PM average load

Peak load and duration of peak

Off Peak: 8PM – 6 AM average load

Identify loads that can be time-shifted to off peak

• Motor starting study Inventory motors over 1 HP

Size of largest motor

Motors over 10 HP: consider soft start or at a minimum wye-delta starting (mandatory for inverter based systems)

Calculate starting currents for large motors

Know expected motor operating schedule and what motors operate concurrently

Steps to Project Development

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• Load shedding study

– Tier 1 Loads (must run, most critical)

– Tier 2 Loads – less critical, to be shed short term to preserve spinning reserve capacity

– Tier 3 Loads – emergency load reduction to avoid blackout

• Short circuit study

– Calculate available fault current when grid connected

– Calculate available fault current when islanded

Engineering Studies

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• ANSI/IEEE standard symbols

• Point(s) of common coupling shown

• Location and type of isolation switch and circuit breaker shown

• All protective relay functions shown

• Transformer grounding shown

• Transformer impedances shown

• Meters and metering connections shown

One-Line Electrical Diagram

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Typical One-Line

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Generation selection

• Land availability

• Environmental considerations

• Energy resources

– Wind

– Solar

– River or tidal flow

– Fossil fuels

• Effect of uncontrolled renewables (wind and solar) de-stabilizes islanded microgrid and creates need for energy storage

Steps to Project Development

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• Generation must match the load – exactly– Overload= under frequency trip (0.16 seconds response time)

– High speed load shedding a necessity

• Provisions for peaks (spinning reserve)– Normally 15-20% of operating load

– Depends on system load profile

• Surge capacity (motor starting) – Reactive power requirements

– Voltage control

Powering a Microgrid

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Generator types

• Synchronous– Voltage and current source

– Can supply or absorb reactive power

• Induction– Current source only

– Requires system source of excitation voltage

– No voltage control

• Inverter– Current source, externally commutated (UL-1741)

– Current and voltage source, self commutated

– Limited fault current

– Limited reactive power capability

Powering a Microgrid

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Generator characteristics

• Base load – slowly changing or fixed output (slow ramp rate)– Lean burn natural gas

– Fuel cell

– Gas turbine (large) > 5MW

– Hydro

• Peaking – rapid response to follow system loads– Diesel

– Rich burn natural gas

– Inverters

– Small gas turbines < 2MW

Powering a Microgrid

Fuel Cells

7 MW Gas Turbine

Diesel Generator

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Energy Storage

• Load and generation smoothing

– Short term 0-15 minutes

– Flywheel

– Battery & inverter

• Time shifting

– Reserve energy for peaking

– Transferring PV generation to dark hours

Powering a Microgrid

Flywheel

1 MW Battery & Inverter

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Operation when grid connected

• Frequency controlled by grid

• Voltage controlled by grid

• Reactive power (VAR) demand supplied by grid

• Distributed generation controlled to maintain desired power output (kW)

• Higher available fault current, Utility source + Generation

Microgrid Controls

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Islanded Operation

• Frequency must be controlled by microgrid generation

• Microgrid must be able to absorb swings in load

• Ramp rate of generators becomes an issue

• How is load shared among multiple generators?

• Isochronous vs. droop governing

• Lower available fault current (generator only)

– Will likely require different settings for protective relays

– Different short circuit coordination requirements

– Potentially greater arc-flash requirements (longer clearing times)

Microgrid Controls

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Protection

• Grid connected– Higher available fault currents

– Need to identify external vs. internal faults to prevent false tripping

– Fast break away from grid on external fault

– Tight control of short time frequency and voltage tripping

– Provide for low generation voltage and frequency ride through; keep generation on line as long as possible to support grid

– Separate from utility to preserve microgrid and generation

Protection and Controls

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Protection

• Island Mode– Lower fault currents may require separate settings

– Wider tolerances on frequency and voltage tripping of generation

– Coordinate settings with load management controls to shed Tier 2 loads before frequency degrades on overload

– Look at downstream devices, may not properly coordinate tripping with lower fault current

Protection and Controls

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Controls

• Grid connected– Generation dispatch – maximize economics, use historical data

– Load management – maintain preplanned load preservation scheme using real-time data; always ready for transition to island mode

• Island Mode– Generation dispatch

• Establish base load capacity

• Establish peaking capacity (load following) (frequency regulation)

• Start additional generation as needed

• Maintaining spinning reserve

Protection and Controls

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Controls

• Island Mode - Load management

– Shed Tier 2 (and Tier 3 if required) on transfer to island mode

– Restore loads when sufficient generation capacity is on line

– Maintain real time list of Tier 2 loads to be shed to preserve microgrid

– Activate load shed during system disturbance, restore loads when able

Protection and Controls

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Controls

• Synchronization - Closed transition

– Shift generation to frequency and voltage control upon separation from utility

– Monitor external grid voltage and frequency for return of normal service (IEEE-1547 five minute delay of retransfer after stabilization)

– When ready, adjust microgrid voltage and frequency to match utility source

– Close utility tie breaker

– Transition generation to grid paralleled mode

– Shut down excess generation

Protection and Controls

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• Primary system grounding when islanded

– Delta system

• Grounding transformer

– Wye system

• Generator Grounding

– Ground fault current islanded vs. grid parallel

– Grounding resistor vs. reactor

– Generator step-up transformer – Wye-Wye?

• Ground fault currents grid connected vs. island mode

Grounding

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Microgrid Development

• Identify facilities to be served

• Consult with utility for feasibility

• Identify facility loads

• Define physical and electrical boundaries and ownership of distribution and generation

Design

• Design interconnection and physical layout of Microgrid

• Select and locate appropriate generation sources

• Design protection system for grid parallel and island modes

• Configure load management controls

• Obtain Interconnection Agreement with host utility

Conclusion

Questions?

Mark LorentzenP: 607.330.0322 | E: [email protected]

Bill MoranP: 774.235.2602 | E: [email protected]

www.trcsolutions.com