McGill University G. Joos 1 Integration and Interconnection of Distributed Energy Resources Geza Joos, Professor Electric Energy Systems Laboratory Department of Electrical and Computer Engineering McGill University 4 November 2013 University of Illinois Urbana-Champaign
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McGill University G. Joos1
Integration and Interconnection of Distributed Energy Resources
Geza Joos, Professor
Electric Energy Systems LaboratoryDepartment of Electrical and Computer EngineeringMcGill University
4 November 2013
University of Illinois Urbana-Champaign
McGill University G. Joos2
Overview and issues addressed
Background Distributed generation and resources – definition and classification Benefits and constraints
Grid integration issues
Grid interconnection and relevant standards Distribution systems standards Steady state and transient operating requirements
Protection requirements General requirements – types of protection Islanding detection
Concluding comments Distributed energy resources – microgrids and isolated systems Future scenarios
Connection Grid connected – distribution grid, dispersed or embedded generation,
may be connected close to the load center, voltage and frequency st by the electric power system
Isolated systems – voltage and frequency set by a reference generator
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Distributed generation – definition – features
Not centrally planned (CIGRE) – is often installed, owned and operated by an independent power producer (IPP)
Not centrally dispatched (CIGRE) – IPP paid for the energy produced and may be required to provide ancillary services (reactive power, voltage support, frequency support and regulation)
Connection – at any point in the electric power system (IEEE) Interconnection studies required to determine impact on the grid May modify operation of the distribution grid
Types of distributed generation Dispatchable (if desired) – engine-generator systems (natural gas,
biogas, small hydro) Non dispatchable (unless associated with electricity storage) – wind,
solar
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Distributed generation – installations
Typical installations, from large to small Industrial – Generating plants on industrial sites, high efficiency, in
combined heat and power (CHP) configurations Commercial Residential installations, typically solar panels (PV)
Features of smaller power dispersed generation Can typically be deployed in a large number of units Not necessarily integrated in the generation dispatch, not under the
control of the power system operator (location, sizing, etc)
McGill University G. Joos
Distributed generation – drivers
Promoting the use of local energy sources –wind, solar, hydro, biomass, biogas, others
Creating local revenue streams (electricity sales)
Connection: MV grid (25 kV, nominal 10 MW feeders typical for Canadian utilities)
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Ref: Presentation Hydro-Quebec Distribution, 2011
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Hydro-Quebec – on-going projects 2011-2015
Biomass 4 plants 25 MW on MV grid Commissioning 2012-2013
Small hydro 8 plants 54 MW on MV grid Commissioning 2010-2013
Wind power plants 5 plants 125 MW on MV grid Commissioning 2014-2015
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DG connection to the grid – options
Connection options Distribution network – low (LV), typically 600 V, and up to 500 kW Distribution network - medium voltage (MV), up to 69 kV, typically 25
kV, up to 10-20 MW Transmission network – aggregated units, typically 100 MW or more
Power system impacts Distribution – local, typically radial systems Transmission – system wide, typically meshed systems
Differing responsibilities and concerns Distribution – power quality (voltage), short circuit levels Transmission – stability, voltage support, generation dispatch
Integration constraints – in relation to the electric power grid Power quality – should not be deteriorated Power supply reliability and security – should not be compromised
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Integration and interconnection issues
Integration of the generation into existing grids – constraints Operating constraints – maximum power (IPP paid for kWh produced),
desired operation at minimum reactive power (unity power factor) Dealing with variability and balancing requirements (if integrated into
generation dispatch) – characteristic of wind and solar installations Integration into the generation dispatch – requires monitoring, energy
production forecasting
Interconnection into the existing grid – constraints Connection to legacy systems – protection coordination, transformer
and line loading, impact on system losses Reverse power flow – from end-user/producer to substation Increased short circuit current – DG contribution Operational issues – grid support requirements and contribution
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Specific DG interconnection issues
Generation power output variability Short term fluctuations – flicker (wind, solar) Long term fluctuations – voltage regulation, voltage rise at connection
Reactive power / Voltage regulation – coordination Reactive compensation – interaction with switched capacitor (pf) Voltage regulation – impact on tap-changing transformer operation Impact on Volt/Var compensation – interference
Harmonics and static power converter filter interaction Voltage distortion produced by power converter current harmonics Resonances with system compensating capacitors
Islanding and microgrid operation Operation in grid connected and islanded modes – transfer Microgrids – possibility of islanded operation – aid to system restoration
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DG interconnection and control requirements
Reactive power and power factor control – required
Voltage regulation – may be required (using reactive power)
Synchronization – to the electric power system
Response to voltage disturbances – steady state and transient
Response to frequency disturbances – steady state and transient
Anti-islanding – usually required (to avoid safety hazards)
Fault, internal and external – overcurrent protection
Power quality – harmonics, voltage distortion (flicker)
Grounding, isolation
Operation and fault monitoring
Grid support – larger units
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General DG standards
Distributed resources (DR) standards IEEE 1547, Standard for Interconnecting Distributed Resources with
Electric Power Systems and applies to DR less than 10 MW
Generally applicable standards for the connection of electric equipment to the electric grid. IEEE in North America and IEC in Europe, cover harmonic interference
and electrical impacts on the grid. Most commonly used are the IEEE 519 and the IEC 61000 series.
Utility interconnection grid codes and regulations – issued by regional grid operators as conditions for connecting DGs to the electric grid
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Operational requirements – larger installations
Based in part on conventional generation (synchronous) – may apply to DGs connected to the distribution grid
Voltage regulation – may be enabled
Frequency regulation – may be required
Low voltage ride through (LVRT) – may be required
Power curtailment and external tripping control – may be required
Control of rate of change of active power – ramp rates
Other features – typically required for large wind farms (> 100 MW, transmission connected), may be required for farms > 5-25 MW control of active power on demand reactive power on demand inertial response for short term frequency support Power System Stabilization functions (PSS) – special function
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DG protection issues – general considerations
Operational requirements Distribution system – must be protected from influences caused by DG
during faults and abnormal operating conditions DG – must be protected from faults within DG and from faults and
abnormal operating conditions caused by distribution circuits
Specific considerations Impact of different DG technologies on short circuit contribution and
voltage support under faults – induction generators, synchronous generators, static power converters (inverters)
Impact of power flow directionality (reversal) on existing distribution system protection
Instantaneous reclosing following temporary faults Utility breaker reclosing before DG has disconnected – may lead to out-
of-phase switching – avoided by disconnecting the DG during the auto-reclosing dead time (as low as 0.2 s)
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Protection system – role and requirements
Role – to detect and isolate only the faulty section of a system so that to maintain the security and the stability of the system
Abnormal conditions – include effect of short circuits, over-frequency, overvoltages, unbalanced currents, over/under frequency, etc.
Protection system requirements rated adequately selective – will respond only to adverse events within their zones of
protection dependable – will operate when required secure – will not operate when not required
Faults seen by the DG Short circuits on the feeder Loss of mains – feeder opening and islanding
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Protection functions of a DG interconnection
-
cb1
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T1 PCC -LV bus
cb2
L1
Line1
L2
cb5
cb4
Line2 Line3
L4
cb8
T3R7
cb7
L3
DG1 DG2
T2R7
PCC -HV bus
S
cb
TL
PCC ‐ HV side PCC ‐ LV side DG ‐ LV side
Distance Automatic recloser Frequency (over and under frequency)Pilot differential Fuses Voltage (over and under voltage)Phase directional overcurrent Voltage (over and under voltage) Overcurrent (instantaneous and delayed)Ground directional overcurrent Overcurrent (instantaneous) Loss of mains (islanding)Automatic recloser Underfrequency SynchronizationUndervoltage Phase directional overcurrent Loss of earth (grounding)Overvoltage Ground directional overcurrent Neutral overcurrent
Transformer differential Negative sequence (voltage, current)Directional overcurrent Reverse power flowZero sequence Generator (loss of excitation, differential)
Distance relay
McGill University G. Joos
DG islanding detection – requirements
Unintentional islanding defined as DG continuing to energize part of distribution system when connection(s) with area-EPS are severed (also referred to as “loss of mains”)
IEEE 1547 - the DG shall cease to energize the Area EPS circuit to which it is connected prior to reclosure by the Area EPS
Repercussions of an island remaining energized include: Personnel safety at risk Poor power quality within the energized island Possibility of damage to connected equipment within the island,
including DG (due to voltage and frequency variations)
Utility grid codes may allow islanded operation during major outages – may help restore service in distribution system
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Islanding detection techniques – passive
Passive approaches Frequency relays (Under/Over-frequency) - use of the active power
mismatch between island load and DG production levels Voltage relays (Under/Over Voltage) - based on voltage variations
occurring during islanding, resulting from reactive power mismatch ROCOF relays (Rate Of Change Of Frequency – resulting from real
power mismatch in the case an island is created Reactive power rate of change – resulting from reactive power
mismatch in the case an island is created
Other approaches Active protection – based on difference in area-EPS response at DG
site when islanded; injection of signature signals at specific intervals Communication-based protection – using a communication link
between DG and area EPS (usually at the substation level) to convey info on loss of mains (and possibly activate a transfer-trip)
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Alternative approach – intelligent relays
Alternative (intelligent) proposed approach – passive, using only measured signals (current, voltage and derived signals)
Use of a multivariate approach to develop a data base of islanding patterns
Use of data mining to extract features from the running of a large number of operating conditions (normal) and contingencies (faults)
Use of extracted features to develop decision trees that define relay settings
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DG variables monitored – multivariable approach
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Feature extraction – methodology
Data Mining – a hierarchical procedure that has the ability to identify the most critical DG variables for islanding pattern detection, or protection handles
Decision Trees – define decision nodes; every decision node uses different DG variables to proceed with decision making on identifying the islanding events
Training data set – islanding (contingencies) and non-islanding events
Time dependent decision trees generated – extracted at different time steps up to the maximum time considered/allowable
Choice of decision tree for relay setting (best) – based on Dependability (ability to detect an islanding event as such) and Security (ability to identify a non-islanding event as such) indices
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Performance requirements – islanding detection
Requirements - defining maximum permissible islanding detection time (typically 0.5 to 2 s)
Performance indices Dependability and Security indices Speed of response, or detection time Existence of non detection zones
Constraints accounting for Interconnection Protection response times (reclosers) detection of islanding and tripping before utility attempts reclosing (out
of phase reclosing may be damageable)
Nature of relay and impact on performance requirements – short circuit detection needs to be faster that islanding detection – allows additional to refine the decision tree
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Real Time Simulator set up – basic relay testing
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Distribution systemPart 1
Distribution systemPart 2
Islanding relay
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Decision trees – typical results
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Comparative performance – relay settings
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Protective Device Setting Time delay
Intelligent Decision Tree 100 ms Under Frequency 59.7 Hz 100 ms Over Frequency 60.5 Hz 100 ms
ROCOF 0.1,0.25,0.5 Hz/s 0ms, 50ms
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Dependability indices – comparative evaluation
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Security indices – comparative evaluation
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Non detection zones – comparative evaluation
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Feasibility and performance of intelligent relays
The proposed data mining approach is capable of Identifying the DG variables that capture the signature of islanding
events, in any given time interval Recommending variables and thresholds for protection relay setting
The islanding intelligent relay Operates within prescribed time requirements (or faster) Can be configured for delayed operation possible Dependability and security indices typical better than existing passive
techniques Offers improved performance, including smaller non detection zones Can be configured for different types of DG (rotating and power
converters based), multiple DG systems and mixed DG type systems Can also be used for short circuit detection (including high impedance
faults) and other types of faults
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Impact of DG technology on protection design
DG operation dependent upon the type of generator used Rotating converters: synchronous and induction generators Static power converter interfaces (inverter based): wind turbine (Type
4), solar power converters Mixed: doubly-fed induction generators (wind turbine, Type 3)
Impact of the type of generator connected to the grid on protection design Short circuit level – typically lower in inverter based systems (1-2 pu) Transients – fully controlled in inverter based systems, dependent on
controller settings Speed of response of real and reactive power injection – typically much
faster in inverter based systems Real and reactive power capability and control – independent control in
inverter based systems
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McGill University G. Joos
DER integration – opportunities in microgrids
DER integration into distribution systems As individual systems, either generation or storage, connected to a
feeder or in a substation Integrated into a self managed system, or microgrid Aggregated to form a Virtual Power Plant
Microgrid definition – a distribution system featuring Sufficient local generation to allow operation in islanded mode A number of distributed generators and storage systems, including
generation based on renewable energy resources A local energy management system A single connection to the electric power system, with possibility of
islanded operation The controllers required to allow connection and disconnection and
interaction with the main
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Microgrid – types and uses
Microgrid deployment drivers – general and current Increasing the resiliency and reliability of critical infrastructure and
specific entities, in the context of exceptional events (storms) –reducing dependence on central generation and the transmission grid
Facilitating the integrating renewable energy resources – managing variability locally
Taking advantage of available local energy resources – renewables and fossil fuels (shale gas)
Reducing greenhouse gases and reliance on fossil fuels – costs
Types, applications and loads Military bases – embedded or remote Large self managed entities – university campuses, prisons Industrial and commercial installations Communities – managing storage and generation locally
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Isolated/autonomous grids – applying DER
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GridInterfaceESS Community
loads
Windgenerator(s)
Diesel plant
Dumpload
PCSPhoto-voltaics
Synchronous generator
Solar
Wind
Batterystorage
Distributed Energy
ResourcesConventional
Generation
Isolated Microgrid
McGill University G. Joos
Benefits of storage and demand response
In conjunction with renewable DG Reducing power variations in variable and intermittent generation Ability to provide voltage support and voltage regulation Enabling operation of DG at peak power and efficiency Power quality – voltage sag and flicker mitigation Possibility of islanded operation – microgrid operation
Distribution system benefits Ability to dispatch/store energy and manage peak demand Reduced line loading – managing line congestion Frequency regulation, black start, reactive power Ability to provide other ancillary services Ability to perform arbitrage on electricity prices – market context
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Electrical storage technologies
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Source: Fraunhofer UMSIGHT
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Demand response – characteristics
Available loads Electric hot water heaters – thermal storage Other curtailable loads – on critical Electric vehicle battery storage systems
Features of loads Dispersed – low power, large numbers are required Availability – short duty cycles Controllability – usually only in curtailment, possibly as additional laod Duration of service – limited curtailment
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Storage vs demand response – interchangeable?
Demand response Benefits: instantaneous response Drawbacks: unavailability, discrete control, requires a large number of
loads (stochastic behavior) Others: no power quality issues, but discrete steps Operational: energy restoration time management Implementation, hardware: minimal
Electrical storage Benefits: fully controllable, can inject energy into the system Drawbacks, implementation: complex, requires power electronic
converters, life expectancy, maintenance Other: losses (standby), energy efficiency Operational: recharging management
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McGill University G. Joos
Distributed energy reources – scenarios 2020
Scenario 1 – Low DG penetration (<10 %), connection mostly to the MV grid – business as usual Reduction of impact on existing grid – power quality (flicker, voltage
variation) Source of power (MW) – limited contribution to voltage and frequency
regulation Islanding required in case of loss of mains
Scenario 2 – Increase in DER penetration (> 20 %?), connection mostly to the MV grid – individual or in microgrids Integration into the generation dispatch – need for monitoring and
forecasting production (wind and solar) Participation in ancillary services – voltage and frequency regulation Requirements to remain connected for temporary loss of mains – low
voltage ride through
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Distributed energy resources – scenarios 2020
Scenario 3 – Increase in the penetration of DER, with connection to the MV grid and the low voltage grid – PV panels, smaller units, controllable loads, including electric vehicles
For MV connections, same considerations as for Scenario 2
For low voltage connections (residential, commercial), with a large number of units, a number of outstanding questions Integration in generation dispatch – included? Participation in ancillary services – frequency/voltage regulation? Role of smart grids in managing a large penetration Financial consideration – generation (feed-in tariffs), ancillary services impacts on the grid – power quality (voltage rise), distribution system