IEEE PES Swiss Chapter Workshop: Microgrids Evolution and Integration in Modern Power Systems

Transcription

1 Alexandre Oudalov, ABB Switzerland Ltd., Corporate Research, Microgrid Protection IEEE PES Swiss Chapter Workshop: Microgrids Evolution and Integration in Modern Power Systems

2 Microgrid Protection Outline What is a microgrid? Traditional distribution grid protection Problems caused by DER and islanded operation Potential solutions Adaptive protection concept Hailuoto microgrid Distributed adaptive protection approach May 2, 2014 Slide 2

3 Microgrids Expected evolution of distribution system Central generation including renewables MW HV grid a backbone for long distance bulk power transmission at kv (AC or DC) MV grid for a local power distribution at 6-69 kv Distributed generation including renewables 1-25 MW LV grid for the last mile power distribution at V Sub-utility generation including renewables MW May 2, 2014 Slide 3

4 Microgrids Expected evolution of distribution system Microgrids are electricity distribution systems containing loads and distributed energy resources, (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled, coordinated way either while connected to the main power network or while islanded. CIGRE C6.22 working definition Central generation including renewables MW HV grid a backbone for long distance bulk power transmission at kv (AC or DC) MV grid for a local power distribution at 6-69 kv Distributed generation including renewables 1-25 MW LV grid for the last mile power distribution at V Sub-utility generation including renewables MW May 2, 2014 Slide 4

5 Microgrids Expected evolution of distribution system Microgrids are electricity distribution systems containing loads and distributed energy resources, (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled, coordinated way either while connected to the main power network or while islanded. CIGRE C6.22 working definition Central generation including renewables MW HV grid a backbone for long distance bulk power transmission at kv (AC or DC) MV grid for a local power distribution at 6-69 kv Distributed generation including renewables 1-25 MW LV grid for the last mile power distribution at V Sub-utility generation including renewables MW May 2, 2014 Slide 5

6 Microgrids Global markets Navigant Research says: There are >400 projects currently in operation or under development worldwide The global market may reach MW of deployed annual capacity and B$40 in annual revenue by 2020 May 2, 2014 Slide 6

7 Microgrid protection Grid connected and islanded modes Protection must respond to both utility grid and microgrid faults utility grid faults: protection isolates the microgrid from the utility grid as rapidly as necessary to protect the microgrid loads. microgrid faults: protection isolates the smallest possible section of the feeder. May 2, 2014 Slide 7

8 Microgrid protection Grid connected and islanded modes Protection must respond to both utility grid and microgrid faults utility grid faults: protection isolates the microgrid from the utility grid as rapidly as necessary to protect the microgrid loads. microgrid faults: protection isolates the smallest possible section of the feeder. May 2, 2014 Slide 8

9 Faults in traditional distribution networks Causes and damages Initiated by: Lightning Dirt/salt on insulators Flashover lineline (wind) Flashover to tree Tower/pole or conductor falls Objects fall on conductors Cable insulation failure Excavation work Unintentional short circuits may occur between phases, phase(s) and neutral/earth and are usually caused when a wire's insulation breaks down, or when another conducting material is introduced A large current causes: rapid buildup of heat, potentially resulting in overheat and damage to the wire's insulation, or a fire vibration due to magnetic forces, deformation of busbars May 2, 2014 Slide 9

10 Protection devices used in distribution networks Fuses and Circuit Breakers Unit protection protects generator, line, transformer but weakens system when tripping CB System protection acts to avoid system blackouts e.g. sacrifice some load to save the rest All protections are based on knowledge about normal and abnormal operation and limits of the system Objectives of unit protection: Protect faulted part from damage: Detect fault Selectively isolate faulted component Continued supply for rest of system Apparatuses Fuses Circuit breakers CBs (operated by relays) May 2, 2014 Slide 10

11 Digital protection relays Solutions for MV and LV networks May 2, 2014 Slide 11 Control the tripping of CBs surrounding the faulted part of the network Large variety of protection functions: Over-current (OC) Directional over current Earth fault Under/over voltage Under/over frequency Reverse power flow Phase unbalance etc. Remote configuration, monitoring and control via a communication link

12 Protection settings Over-current protection Measured values are compared with precalculated settings and relay generates a tripping command when the measured value exceeds the thresholds Settings are usually calculated at the design/planning stage either manually or with software tools based on standards, e.g. IEC60909 Usually settings are not touched afterwards Multiple setting groups are possible today (switching by means of an external command) but not actively used May 2, 2014 Slide 12

13 Protection settings Over-current protection Measured values are compared with precalculated settings and relay generates a tripping command when the measured value exceeds the thresholds Settings are usually calculated at the design/planning stage either manually or with software tools based on standards, e.g. IEC60909 Usually settings are not touched afterwards Multiple setting groups are possible today (switching by means of an external command) but not actively used May 2, 2014 Slide 13

14 Protection settings Coordination between multiple protection devices Selective operation is when only the CB immediately on the supply side of the fault is tripped and continuity of service for the rest of the system is ensured It requires a coordination of protection devices between the source and the fault. The selectivity is obtained by current and/or tripping time discriminating CB A CB B CB C Load A Load B Load C May 2, 2014 Slide 14

15 Protection settings Coordination between multiple protection devices Selective operation is when only the CB immediately on the supply side of the fault is tripped and continuity of service for the rest of the system is ensured It requires a coordination of protection devices between the source and the fault. The selectivity is obtained by differentiating the current values and the trip times CB A Blocking signal Blocking signal No signal CB B CB C out in out in out in Load A Load B Load C May 2, 2014 Slide 15

16 Microgrid Protection Main challenges DERs and isolated operation from main grid imposes new challenges for the traditional distribution grid protection Changes in the magnitude and direction of short circuit currents Reduction of fault detection sensitivity and speed in tapped DER connections Unnecessary tripping of utility breaker for faults in adjacent lines due to fault contribution of the DER Auto-reclosing of the utility line breaker policies may fail May 2, 2014 Slide 16

17 Microgrid Protection Main challenges In the grid connected mode the utility provides a significant fault current during the fault After isolation from the utility grid the local generator (DG) is the only fault current source in the island Fault current level depends on type, size and location of DG but it is lower than the fault current from the utility grid CB1 operation will be delayed and if the time delay exceeds a limit of DG under voltage protection CB2 will disconnect DG unit and the island will be shut down Utility grid CB1 DG Fault CB2 May 2, 2014 Slide 17

18 Microgrid Protection Main challenges In the grid connected mode the utility provides a significant fault current during the fault After isolation from the utility grid the local generator (DG) is the only fault current source in the island Fault current level depends on type, size and location of DG but it is lower than the fault current from the utility grid CB1 operation will be delayed and if the time delay exceeds a limit of DG under voltage protection CB2 will disconnect DG unit and the island will be shut down Utility grid CB1 DG Fault CB2 May 2, 2014 Slide 18

19 Microgrid Protection Main challenges In the grid connected mode the utility provides a significant fault current during the fault After isolation from the utility grid the local generator (DG) is the only fault current source in the island Fault current level depends on type, size and location of DG but it is lower than the fault current from the utility grid CB1 operation will be delayed and if the time delay exceeds a limit of DG under voltage protection CB2 will disconnect DG unit and the island will be shut down Utility grid CB1 DG Fault CB2 May 2, 2014 Slide 19

20 Microgrid protection New Strategies Microgrid protection strategies ideally should be generic such that they could be: Applicable for both grid and islanded operation Adapted to any DER type Scalable so that the strategy does not need to be redefined with each new DER connection May include requirements for: Modifying/replacing protection devices Use of advanced protection functions Add new/upgrade existing fault current sources Dynamic protection settings management May 2, 2014 Slide 20

21 Fault Current Source Ensure fault level in inverter dominated microgrids Do not enforce sophisticated protection in customer s premises. Use classical fuses At least one resource must deliver a fault current high enough to ensure operation and selectivity of protections High-power storage is an ideal candidate for a Fault Current Source (FCS) An FCS is connected to the main LV bus in parallel to the network and contains: A slow-charge, rapid-release electricity storage An inverter in idle mode, rated to deliver a high current for a few seconds A short-circuit detection unit (measure local voltage) A charging circuit to restore the status of energy storage device

22 Microgrid protection Dynamic protection settings management Adapt protection settings to the actual state of the microgrid based on the preset logic Accomplished by monitoring of actual protection settings and DER/network connectivity information A programmable logic application is called to perform after changes in CB status. No on-line setting calculations are needed in this application. Suggestions for practical implementation: Use of IEDs with directional over-current protection function and with multiple setting groups Use of communication infrastructure and standard protocols to exchange information between IEDs and a central setting coordination unit (e.g. substation computer or RTU) May 2, 2014 Slide 22

23 Centralized microgrid adaptive protection example Grid connected mode Utility Grid Load Load CB IED Active Setting Group DG Central controller Communication Network May 2, 2014 Slide 23

24 Centralized microgrid adaptive protection example Transition to islanded mode Utility Grid DG 1. Data (CB status) are transmitted from the end devices using unsolicited messages as conditions change. The central controller also polls each end device periodically to ensure that the end device is still healthy May 2, 2014 Slide 24

25 Centralized microgrid adaptive protection example Transition to islanded mode Utility Grid DG 1. Data (CB status) are transmitted from the end devices using unsolicited messages as conditions change. The central controller also polls each end device periodically to ensure that the end device is still healthy 2. The central controller analyzes the network state and if necessary adapts protection settings to fit the new network configuration May 2, 2014 Slide 25

26 Centralized microgrid adaptive protection example Islanded mode Utility Grid DG May 2, 2014 Slide Data (CB status) are transmitted from the end devices using unsolicited messages as conditions change. The central controller also polls each end device periodically to ensure that the end device is still healthy 2. The central controller analyzes the network state and if necessary adapts protection settings to fit the new network configuration 3. The central controller sends control messages (to switch settings) to the field devices

27 Centralized microgrid adaptive protection example Islanded mode Utility Grid DG May 2, 2014 Slide Data (CB status) are transmitted from the end devices using unsolicited messages as conditions change. The central controller also polls each end device periodically to ensure that the end device is still healthy 2. The central controller analyzes the network state and if necessary adapts protection settings to fit the new network configuration 3. The central controller sends control messages (to switch settings) to the field devices

28 Microgrid protection Centralized adaptation scheme lab tests Centralized approach has been tested in the lab (focus on data exchange) with a realization for MV (IEC61850) and LV (Modbus) grids In addition a real-time HIL simulations have been conducted for the MV case Adaptation process is limited by communication system/protocol capability and takes <100 ms in the MV case and ~700 ms (per circuit breaker) in the LV case Both systems have demonstrated good performance and operated properly in different conditions (including situation when settings have been forced manually to the wrong setting group) May 2, 2014 Slide 28

29 Hailuoto microgrid Practical demonstration of adaptive protection Hailuoto is the Finnish island in the Northern Gulf of Bothnia in the Baltic Sea. It has ~1000 regular inhabitants and 600 holiday houses Goal is to develop and demonstrate in the field an active microgrid management Active management functionalities include: Protection settings changing based on microgrid topology (e.g. grid connected ó island) Transition between grid connected and islanded operation modes: Unintentional islanding via black-start Intentional islanding via SCADA Re-synchronization to the utility grid May 2, 2014 Slide 29

30 Hailuoto microgrid System configuration May 2, 2014 Slide 30

31 Hailuoto microgrid System configuration May 2, 2014 Slide 31

32 Hailuoto microgrid System configuration May 2, 2014 Slide 32

33 Hailuoto microgrid Automation system configuration Off-line process Trusted settings are uploaded to IEDs as multiple setting groups IEC is used as a master protocol for communications with the IEDs IEC programming languages are used in the PLC application which allows easy cross-platform transfer of the application May 2, 2014 Slide 33

34 Hailuoto microgrid On line operation and control logic OPC Data Access mechanism provides a way to supply the IED data received from the field devices to the IEC Logic Processor OPC Client/Server architecture allows feeding the control actions back to the IEDs Additional OPC server instance can be used to map and broadcast the IED data upstream to the distribution network control center via SCADA May 2, 2014 Slide 34

35 Microgrid protection Distributed adaptation scheme Aimed to simplify an implementation for a microgrid with a large number of circuit breakers Protected system is split into small areas being delimited by the adjacent switching devices coordinated by local logic units (LL) Each LL communicates with units in directly adjacent areas and exchange information on local short circuit levels (SCL) May 2, 2014 Slide 35

36 Microgrid protection Distributed adaptation scheme MVA method: each network component is replaced by a block representing the contribution or the reduction of the SCL expressed in MVA Configuration change in an area triggers re-evaluating of a local SCL using the MVA method Each protection setting group corresponds to a specific range of available SCLs LL decides on switch/keep an active setting group SCL information is sent to neighbouring areas where it is further used to re-evaluate local SCLs The adaptation process progressively advances through the microgrid May 2, 2014 Slide 36

37 Microgrid Protection Key take away points High penetration level of DER and islanded operation mode pose main protection challenges in microgrids Ideally protection system must follow microgrid configuration changes Adaptive protection may increase availability of local generation and reduces customer outages At the moment it looks like a switching between the precalculated trusted setting groups is a preferred solution Centralized adaptive protection scheme based on full connectivity model can be suitable for small scale microgrids For large scale microgrids a distributed adaptive protection scheme with a limited connectivity model can be more pertinent May 2, 2014 Slide 37

38 Microgrid Protection Further reading A. Oudalov, A. Fidigatti, Adaptive Network Protection in Microgrids, International Journal of Distributed Energy Resources, Vol.5, No.3, pp , July-September 2009 W. Zhao, A. Oudalov, B. Su, Y. Chen, Research on Close-Loop Simulation for Centralized Coordination of Protection Settings, in Proc. of China International Conference on Electricity Distribution, Shanghai, 2012 A. Oudalov, L. Milani, E. Ragaini, A. Fidigatti, Sample Implementation of Adaptive Protection for LV Networks, PAC World Magazine, Vol.20, pp.28-33, June 2012 D. Ishchenko, A. Oudalov and J. Stoupis, "Protection Coordination in Active Distribution Grids with IEC 61850," in Proc. of IEEE T&D conference, 2012, Orlando, FL, USA. H. Laaksonen, D. Ishchenko, A. Oudalov, Adaptive Protection and Microgrid Control Design for Hailuoto island, IEEE Trans on Smart Grids, March, 2014 May 2, 2014 Slide 38

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