integration and interconnection of distributed energy...

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


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

McGill University G. Joos

Electrical power system – renewable generation

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Conventional

Renewables

TransmissionGeneration

Industry Transpor-tation Commercial

Storage

DistributionFACTS

Custom Power

HVDC

Residential


Future electric distribution systems – a scenario

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(Microgrid)(Microgrid)


Distributed generation – definition – classification

A subset of Distributed Energy Resources (DER), comprising electrical generators and electricity storage systems

Size – from the kW (1) to the MW (10-20) range

Energy resource Renewables – biomass, solar (concentrating and photovoltaic), wind,

small hydro Fossil fuels – microturbines, engine-generator sets Electrical storage – batteries (Lead-Acid, Li-Ion) Other – fuel cells (hydrogen source required)

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


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


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)


Distributed generation – drivers

Promoting the use of local energy sources –wind, solar, hydro, biomass, biogas, others

Creating local revenue streams (electricity sales)

Creating employment opportunities (manufacturing, erection, maintenance, operation)

Responding to public interest and concerns about the environment – public acceptance can be secured

Green power – Greenhouse Gas (GHG) reduction

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Distributed generation – technical benefits

Enhanced reliability – generation close to the load

Peak load shaving – reduction of peak demand

Infrastructure expansion deferral – local generation

Distribution (and transmission) system loss reduction – generation close to load centers

Lower grid integration costs – local generation reduces size of connection to the main grid

Distribution voltage connection (rather than transmission) – ease of installation and lower cost

Voltage support of weak distribution grids

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Distributed generation – typical installations

Typical power plant types Hydraulic, 5-10 MW Biomass, 5-10 MW Biogas, 5-10 MW Wind, 10-25 MW

Total installed power (2011): 61 plants, 350 MW

Connection: MV grid (25 kV, nominal 10 MW feeders typical for Canadian utilities)

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Ref: Presentation Hydro-Quebec Distribution, 2011


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


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


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)


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


Protection functions of a DG interconnection

-

cb1

~

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


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


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


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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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


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


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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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

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