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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