University of Illinois Urbana-Champaign 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

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

Electrical power system – renewable generation Residential

Future electric distribution systems – a scenario

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

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

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) 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

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

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

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

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

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 T3 R7 cb7 L3 DG1 DG2 T2 HV S cb TL

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

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)

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

DG variables monitored – multivariable approach

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

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

Real Time Simulator set up – basic relay testing Distribution system Part 1 Distribution system Part 2 Islanding relay

Decision trees – typical results

Comparative performance – relay settings

Dependability indices – comparative evaluation

Security indices – comparative evaluation

Non detection zones – comparative evaluation

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

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

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

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

Isolated/autonomous grids – applying DER Isolated Microgrid Solar Wind Battery storage Synchronous generator Distributed Energy Resources Conventional Generation

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

Electrical storage technologies 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

Storage vs demand response – interchangeable? 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

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

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 loading