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DER Applications and Testing

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  1. DER Applications and Testing Ben Kroposki, PE Senior Electrical Engineer - National Renewable Energy Laboratory

  2. DER Technology Portfolio Examples Reciprocating Engines Fuel Cells Advanced Turbines Photovoltaics Thermally Activated Technologies Microturbines Wind

  3. Distributed Energy Resources Interconnection Technologies Electric Power Systems Utility Grid • Functions • Power Conversion • Power Conditioning (PQ) • Protection • DER and Load Control • Ancillary Services • Communications • Metering Fuel Cell PV Inverter Utility Grid Simulator Micro Grids Microturbine Wind Loads Energy Storage Local Loads Load Simulators Switchgear, Relays, & Controls Generator DER Grid Interconnection

  4. Residential Applications Fuel Cells or Photovoltaic Systems The CRN Residential Fuel Cell Demonstration Handbook serves as a comprehensive guide to residential fuel cell technology and related issues. http://www.nrel.gov/docs/fy02osti/32455.pdf.

  5. Residential Applications Grid Parallel Power Flow: Power flows from the DER to the customer’s dwelling and to/from the grid, both of which are connected in parallel. Often this arrangement is “net metered”. Interconnect:The DER interconnects with the grid through a fused disconnect, which is accessible to distribution service personnel, and an internal disconnect under control of the power plant. In the event of a short-term grid upset, the inverter typically interrupts or stops commuting. In the event of a longer upset, the inverter opens an internal disconnect and likely goes to idle while monitoring the grid and waiting to reconnect after a preset time delay after the grid returns to normal.

  6. Residential Applications Grid-Independent Power Flow:Power flows only from the DER to the customer’s dwelling. Thus, the DER must meet all dwelling loads. This requires application preplanning and perhaps load monitoring before installation. The DER will likely have a substantial battery storage system charged by the cell stack at night to supplement the cell stack during peak daytime loads. Interconnect: The DER connects to the dwelling through a fused disconnect and perhaps an internal disconnect for certain fault-clearing events.

  7. Residential Applications Dual Mode (Combination Grid Parallel and Grid Independent) Power Flow: Power flows from the DER to the customer’s dwelling and to/from the grid in normal operation. In the event of a grid upset, the power plant interrupts. In the event of a serious grid event, it disconnects itself and the dwelling from the grid and runs independently. After a suitable delay after the grid returns to normal, the inverter interrupts, and grid-parallel operation is restored. Interconnect: The DER interconnects with the grid through a fused disconnect. An internal DER disconnect is provided for certain grid-parallel upsets and may be provided for certain dwelling grid-independent fault-clearing events.

  8. Commercial Applications – Transfer Switch Area Electric Power System (Area EPS) Point of Common Coupling (PCC) PCC PCC Transfer Switch Point of DR Connection Distributed Resource (DR) Unit Load Load Distributed Resource (DR) Unit Local EPS 1 Local EPS 2 Local EPS 3 Note: Dashed lines are EPS boundaries. There can be any number of Local EPSs

  9. Commercial Applications – Parallel Switch Area Electric Power System (Area EPS) Point of Common Coupling (PCC) PCC PCC Parallel Switch Point of DR Connection Distributed Resource (DR) Unit Load Load Distributed Resource (DR) Unit Local EPS 1 Local EPS 2 Local EPS 3 Note: Dashed lines are EPS boundaries. There can be any number of Local EPSs

  10. Commercial Applications – Facility Microgrid Area Electric Power System (Area EPS) Point of Common Coupling (PCC) PCC PCC Point of DR Connection Point of DR Connection Distributed Resource (DR) Unit Load Load Distributed Resource (DR) Unit Local EPS 1 Local EPS 2 Local EPS 3 Note: Dashed lines are EPS boundaries. There can be any number of Local EPSs

  11. Utility Applications – Area EPS Microgrid Area Electric Power System (Area EPS) Point of Common Coupling (PCC) PCC PCC Point of DR Connection Point of DR Connection Distributed Resource (DR) Unit Load Load Distributed Resource (DR) Unit Local EPS 1 Local EPS 2 Local EPS 3 Note: Dashed lines are EPS boundaries. There can be any number of Local EPSs

  12. Utility Applications – Substation DER EPS Source Area Electric Power System (Area EPS) Local EPS 2 PCC Local EPS 4 Point of DR Connection Load Distributed Resource (DR) Unit Load DR Load(s) Local EPS 3

  13. DER Power QualityIssues • Sustained Interruptions – DG can provide backup power if designed to do so. This may improve reliability if designed and operated properly. • Voltage Regulation – DG can provide voltage regulation if allowed. This can also be a limiting factor as to penetration on a feeder. • Harmonics – There are harmonic concerns with both rotating and inverter based DG. • Voltage Sag – DG may be able to help keep voltage up, but only if allowed to do so.

  14. DER Microgrids – for improved reliability

  15. DER-Grid Interconnection Operational Issues • Short circuit contribution • Protection coordination • Voltage regulation • Unintentional islanding • Grounding and overvoltages • --------- ------------------ ------------------- • Interconnection issues are real and resolvable: • e.g., specific to: equipment, design, location, application, etc.

  16. Covers IEEE 1547 Section 4.3.2 Covers IEEE 1547 Section 4.1.4 IEEE 1547 Series Standards 1547-2003Standard for Interconnecting Distributed Resources with Electric Power Systems 1547.1-2005 Conformance Test Procedures for Equipment Interconnecting DR with EPS Current Projects Future Projects P1547.2 Application Guide for IEEE 1547 Standard for Interconnecting DR with EPS DG Specifications and Performance Interconnection System Certification Guide P1547.3 Guide for Monitoring, Information Exchange and Control of DR Guide for Grid/DG Impacts Determination P1547.4 Guide for Design, Operation, and Integration of DR Island Systems with EPS P1547.5 Guidelines for Interconnection of Electric Power Sources Greater Than 10 MVA to the Power Transmission Grid P1547.6 Recommended Practice for Interconnecting DR With EPS Distribution Secondary Networks

  17. IEEE 1547Technical Requirements • General Requirements • Voltage Regulation • Integration with Area EPS Grounding • Synchronization • Secondary and Spot Networks • Response to Area EPS Abnormal Conditions • Voltage Disturbances • Frequency Disturbances • Disconnection for Faults • Power Quality • Limitation of DC Injection • Limitation of Voltage Flicker • Induced by the DR • Islanding • Inadvertent Energizing of the Area EPS • Monitoring • Isolation Device • Loss of Synchronism • Feeder Reclosing Coordination • Immunity Protection • Harmonics • Surge Capability

  18. IEEE 1547.1 Interconnection Tests have been incorporated into UL 1741 for product certification DER Interconnection Equipment Certification Approach • IEEE 1547 • Interconnection System Requirements • Voltage Regulation • Grounding • Disconnects • Monitoring • Islanding • IEEE 1547.1 • Interconnection System Testing • O/U Voltage • and Frequency • Synchronization • EMI • Surge Withstand • DC injection • Harmonics • Islanding • Reconnection • UL 1741 • Interconnection Equipment • Construction • Protection against risks of injury to persons • Rating, Marking • Specific DR Tests for various technologies

  19. NREL DER Test Facility

  20. Testing Interconnection Equipment GE Universal Interconnection Technology (UIT) ASCO – Soft-Load Transfer Switch • Validation of IEEE P1547 Interconnection Standard Tests • Over/Under Voltage and Frequency Response • Unintentional islanding test

  21. Test Results – System Configuration Unit under Test Onan 125kW Generator 200kW Grid Simulator Programmable Load Banks

  22. DR SIZE Frequency Range (Hz) Clearing Time (s) Voltage Range(Based on 480 V) Clearing Time (s) 30 kW >60.5 0.16 V<240 0.16 <59.3 0.16 240V<422.4 2 >30 kW >60.5 0.16 528<V<576 1 <{59.8–57.0} (adjustable setpoint) Adjustable 0.16–300 V576 0.16 <57.0 0.16 Test Results – IEEE 1547 Response Times Response to Abnormal Voltage Response to Abnormal Frequency

  23. V 515 500 480 15 sec 300 sec t Test Results • Testing Results from ASCO SLTS – Overvoltage Magnitude Test

  24. DG Disconnect Exceed Trip Point V 510 500 t =0.2 ms 15 sec 480 60 sec t Test Results • Testing Results from ASCO SLTS – Overvoltage Time Test

  25. Test Results • Testing Results from NPS DER Switch – Synchronization Test Testing synchronization around a specific voltage and frequency window Using secondary injection testing X – shows where equipment does not meet spec This equipment was recalibrated to meet spec.

  26. IEEE 1547 - Islanding • Unintentional Islanding - For an unintentional island in which the DR energizes a portion of the Area EPS through the PCC, the DR interconnection system shall detect the island and cease to energize the Area EPS within two seconds of the formation of an island. • Intentional Islanding - This topic is under consideration for future revisions of this standard. (IEEE 1547.4 covers this topic)

  27. Test Results • Testing Results from ASCO SLTS – Unintentional Islanding • IEEE 1547 requirement is to disconnect within 2 seconds of island formation

  28. Test Results • Testing Results from ASCO SLTS – Unintentional Islanding

  29. IEEE 1547 - Islanding • Limited DR capacity as share of customer load – If the aggregate DR capacity is less than one-third of the minimum load of the Local EPS, it is generally agreed that, should an unintentional island be formed, the DR will be unable to continue to energize the load connected within the Local EPS and still maintain acceptable voltage and frequency. In this case, it is expected that that the DR itself will respond by various means to cease to energize the island. These may include excitation system behavior for synchronous generators, overload or over/underspeed sensing, or the over/undervoltage relays or over/Underfrequency relays which are required elsewhere in IEEE 1547. • Non-Islanding Inverter – Many inverters are designed specifically such that they are unable to supply a load without the presence of the electrical system. The inverter, in many cases, will lock to the Area EPS frequency. The inverter controls may also be equipped with one of several anti-islanding means, which usually continually attempt to force the inverter off the power system frequency, such that, if the power system is unavailable, the inverter voltage and frequency will quickly deviate from nominal ranges to cause under/over voltage or frequency trips. • Reverse Power Protection – If the DR is intended to supply power only to its own Local EPS, and not to provide power to the Area EPS across the PCC, reverse power relays may be installed at the PCC to operate isolating devices. These isolating devices may be the generator isolation device itself, or, if the DR wishes to continue to support the Local EPS as an intentional island, may be at the PCC. • Passive Protection – Passive protection may use voltage and frequency relays as a means of anti-island protection, as detailed above. This passive scheme measures electrical variables at the PCC and detects conditions that indicate an island has been formed. This protection scheme is based on the DR’s inability to satisfy a sudden change in load without a corresponding change in its voltage and/or frequency. In this instance, the voltage or frequency relays will take the unit off line. Besides under/over voltage and frequency relays, several means derived from voltage and frequency changes are also commonly used for anti-islanding detection, for example, phase or vector jump, rate of change of frequency.

  30. IEEE 1547 - Islanding • Synchronous Generator Excitation System Controls – Synchronous generators may also be equipped with excitation system controls that maintain a constant power-factor or constant power, and rely on the under/overvoltage or under/overfrequency relays to operate if the load on the generator does not match the generator output. • For example, power factor control can be used as an anti-islanding method. The DR is set to regulate at a fixed power factor. This power factor should be selected to be intentionally significantly different from the load that would be isolated with the DR. If an island condition develops, the DR will either supply too little or too much VAR support resulting in a high or low voltage condition. For example, if the load power factor is 0.9 and the DR is regulating to a power factor of 1.0, the DR will not provide sufficient VAR support should an island form. This will result in an undervoltage condition which in turn will cause the generator to trip due to low voltage (assuming standard undervoltage protection per IEEE 1547). • Active Protection – Active protection will take a more proactive approach, and attempt to detect an island directly. Anti-islanding controls in an inverter fall into this category. In some cases, passive protection can be fooled if the generator is able to carry the load of the island without a substantial change in voltage or frequency. Some inverter manufacturers have added an additional “active” anti-islanding capability . • One class of active scheme is to use external devices, for example, to actively inject current signal with certain frequencies other than fundamental frequency, and then measure voltage at those frequencies. Islanding will be detected by examining the impedance changes. (e.g. ENS device commonly used in Germany) • Active schemes measure electrical variables at the PCC, but the response of the variables is checked against a deliberate variation in some aspects of the DR output. Active anti-islanding is more robust than passive, but even it cannot guarantee that an island will not develop in some rare cases. Anti-Islanding relays are available which continually monitor for minute momentary changes in the vector relationships of the current of voltage to detect events on the Area EPS which would form an unintentional island. • Direct Transfer Trip – Direct Transfer Trip may also be used, and is a very active and positive approach to assure that the DR ceases to energize an unintentional island. Direct transfer trip involves communication equipment both on the Area EPS and at the DR. The specific events on the Area EPS will be used to send a secure reliable communications signal to the DR to cause the DR to open isolation devices as needed to satisfy this requirement. Implementation of direct transfer trip will be addressed comprehensively in IEEE P1547.3, a recommended practice that is in the early development stages.

  31. References • Basso, T.S. and DeBlasio, R. "IEEE P1547 Series of Standards for Interconnection: Preprint for IEEE Power Engineering Society Transmission and Distribution 2003 Conference and Exhibition" NREL/CP-560-34003. Golden, CO: NREL, May 2003. • Basso T.S. and DeBlasio, R. “IEEE 1547 Series of Standards: Interconnection Issues.” NREL Report No. 34882. September 2003. • Kroposki, B., Basso, T. and DeBlasio, R. “Interconnection Testing of Distributed Resources” Preprint for 2004 PES General Meeting, June 2004, NREL/CP-560-35569. Golden, CO: NREL. • Distributed Energy Resources Interconnection Systems: Technology Review and Research NREL/SR-560-32459 • Universal Interconnection Technology Workshop Proceedings NREL/BK-560-32865 • CRN Residential Fuel Cell Demonstration Handbook, http://www.nrel.gov/docs/fy02osti/32455.pdf. • Ye, Z.; Dame, M.; Kroposki, B. (2005). Grid-Connected Inverter Anti-Islanding Test Results for General Electric Inverter-Based Interconnection Technology. 24 pp.; NREL Report No. TP-560-37200. http://www.nrel.gov/docs/fy05osti/37200.pdf

  32. References • Kroposki, B.; Englebretson, S.; Pink, C.; Daley, J.; Siciliano, R.; Hinton, D. (2003). Validation of IEEE P1547.1 Interconnection Test Procedures: ASCO 7000 Soft Load Transfer System. 52 pp.; NREL Report No. TP-560-34870.http://www.nrel.gov/docs/fy04osti/34870.pdf • Distributed Generation: Opportunities and Challenges for the T&D System, Michael Doyle and Reigh Walling, 2003 IEEE/PES Transmission and Distribution Conference • Interconnection and Integration Studies for Wind Farms, Jeff Smith, 2003 IEEE/PES Transmission and Distribution Conference • Electrical Power Systems Quality- 2nd Edition, Roger Dugan, Mark McGranaghan, Surya Santoso, Wayne Beaty, 2002, Chapter 9 • IEEE 1547-2003 Standard for Interconnecting Distributed Resources with Electric Power Systems • IEEE 1547.1-2005 Standard Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems • Lynch, J.; John, V.; Danial, S. M.; Benedict, E.; Vihinen, I.; Kroposki, B.; Pink, C. (2006). Flexible DER Utility Interface System: Final Report, September 2004--May 2006. 222 pp.; NREL Report No. TP-560-39876. http://www.nrel.gov/docs/fy06osti/39876.pdf