University of Illinois Urbana-Champaign

1. 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

2. Overview and issues addressed • Background • Distributed generation and resources – definition and classification • Benefits and constraints • Grid integration issues • Grid interconnection and relevant standards • Distribution systemsstandards • 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

3. Electrical power system – renewable generation Residential

4. Future electric distribution systems – a scenario

5. 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

6. 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

7. 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)

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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)

19. 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

20. - Protection functions of a DG interconnection T1 PCC - LV PCC - HV bus bus cb1 Line2 Line3 Line1 ~ cb4 cb7 S cb2 T2 T3 cb R7 R7 L3 cb5 cb8 TL L1 DG1 DG2 L2 L4

21. 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

22. 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)

23. 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

24. DG variables monitored – multivariable approach

25. 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

26. 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

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

28. Decision trees – typical results

29. Comparative performance – relay settings

30. Dependability indices – comparative evaluation

31. Security indices – comparative evaluation

32. Non detection zones – comparative evaluation

33. 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

34. 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

35. 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

36. 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

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

38. 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

39. Electrical storage technologies Source: Fraunhofer UMSIGHT

40. 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

41. 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

42. 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

43. 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