Session 10: General Overview of Interconnection Standards & Grid Codes for High Penetration PV October 21, 2015 Santiago, Chile Michael Coddington National Renewable Energy Laboratory Golden, Colorado, U.S.A.
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Putting the Pieces Together for Sound Grid Codes! Codes and standards for Generation Systems are Critical to Safety, Reliability, Power Quality and Cost. They help define exactly how things are to be properly designed, built, and operated.
Interconnection Standards & Grid Codes
Codes & Standards Will Differ by Location, but Should be Avaiable Utility Safety and Clearance Standards Interconnection Standards Building Electrical Codes, DG & Inverter Standards
North American Standards & Codes Critical Codes & Standards ANSI C84.1 (Voltage Limits) NESC (Utility Safety & Clearances) NEC (Electrical Building Code) UL 1741 (Inverter Safety Standard) IEEE 1547 (Interconnection @ PCC)
Interconnection Standards & Grid Codes Utility Standard for Voltage Service Limits
NESC is an International IEEE Standard NESC Requirements for De-energized Work Section 444 of the NESC details De-energizing equipment of lines to protect employees Isolate - operate switches, disconnects and lock-out / tag-out Test for Voltage Install protective grounds on each side of the work location Utility Safety and Clearances Standard
Interconnection Standards & Grid Codes National Electrical Code - NEC NFPA 70 Applies to Residential, Commercial and Industrial facilities Often used in utility power plants, service centers Articles 690 (PV systems) & 705 Interconnected Electric Power Production Sources Most countries have an electrical code for building National Code for Safe Building Wiring
Interconnection Standards & Grid Codes UL 1741 Inverters, Converters, Controllers and Interconnection System Equipment for Use with Distributed Energy Resources Applies to the Inverter and interconnection equipment Inverters should be listed to this standard Harmonized with IEEE 1547 Underwriters Laboratories Standard for Safety UL Develops Codes for ALL Countries, Regions Inverter Safety Standard (Harmonized)
IEEE 1547 Standard for Interconnection Purpose Provides a uniform standard for interconnection of DR with EPS Provides requirements relevant to the performance, operation, testing, safety considerations, and maintenance of the interconnection Planned to harmonize with IEC Interconnection Standard at Point of Common Coupling
IEEE 1547 Clause 4 - Specifications 1. General Requirements (details on next slide) 2. Response to Area EPS Abnormal Conditions (v or f )* 1. Area EPS Faults (cease operation during faults) 2. Recloser Coordination (must clear before reclose) 3. Voltage Ranges (clearing times 2 Sec.) * 4. Frequency Ranges (clearing times 2 Sec.) * 3. Power Quality 1. DC injection (<0.5% of full rating at POI) 2. Flicker (no objectionable flicker, see IEEE 519) 3. Harmonics (THD <5%, see table 3) 4. Islanding 1. Unintentional Islands 2. Planned Island Systems
IEEE 1547 General Requirements Active voltage regulation allowed with Utility Coordination Grounding scheme shall not cause overvoltages DR shall not cause voltage fluctuations > ±5% typical Secondary Network requirements* NP shall not be used to isolate network from DR DR shall not cause operation of NP or prevent reclosing of NP >50% of NP must be energized No equipment shall be overloaded DR shall not energize a de-energized circuit DR must have provisions for monitoring Interconnection system must withstand: Electromagnetic Interference (EMI) Voltage or Current surges
Power Quality Topics for Standards & Codes These Power Quality Issues Should be Addressed by Interconnection Standards and Codes Transients Impulsive Oscillatory Short-Term Variations Interruption Sags Swells Long-term Variations Sustained Interruptions Under-voltage Overvoltage Voltage Imbalance Waveform Distortion DC Injection Harmonics Inter-harmonics Sub-harmonics Notching Noise Flicker Ferro-resonance Anti-Islanding Reactive power support
DG Potential Effects on Power Quality Variability in solar or wind resource causes sudden changes in generation, which can lead to flicker and hunting in utility voltage regulation system Examples Cloud passage for solar Rapidly-changing shading from nearby objects (e.g. blowing tree) for solar Irregular and turbulent wind patterns Rhythmic variations from when wind turbine blade passes tower
IEEE 1547 Limits on Harmonics When the DR is serving balanced linear loads, harmonic current injection into the Area EPS at the PCC shall not exceed the limits stated below in Table 3. The harmonic current injections shall be exclusive of any harmonic currents due to harmonic voltage distortion present in the Area EPS without the DR connected
voltage [pu] Harmonics Limiting Harmful Harmonics Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the fundamental system supply The voltage distortion created by nonlinear loads may create voltage distortion beyond the premise s wiring system, through the utility, to another user. 3 2 Voltage with Harmonic Distortion Fundamental 5th order harmonic 7th order harmonic Total Waveform 1 0-1 -2 0 0.005 0.01 0.015 0.02 0.025 0.03 time [s]
IEEE Power Quality Standards IEEE SCC-22: Power Quality Standards Coordinating Committee IEEE 1159: Monitoring Electric Power Quality IEEE P1564: Voltage Sag Indices IEEE 1346: Power System Compatibility with Process Equipment IEEE P1100: Power and Grounding Electronic Equipment (Emerald Book) IEEE 1433: Power Quality Definitions IEEE P1453: Voltage flicker IEEE 519: Harmonic Control in Electrical Power Systems IEEE P519A: Guide for Applying Harmonic Limits on Power Systems IEEE P446: Emergency and standby power IEEE P1409: Distribution Custom Power IEEE P1547: Distributed Resources and Electric Power Systems Interconnection
IEC Power Quality Standards 61000-1-X - Definitions and methodology 61000-2-X - Environment 61000-3-X - Limits 61000-4-X - Tests and measurements (e.g. 61000-4-30 is power quality measurements) 61000-5-X - Installation and mitigation 61000-6-X - Generic immunity & emissions standards E.g.: IEC 61000-4-11 - voltage sag immunity - 16 amps or less IEC 61000-4-34 - voltage sag immunity - more than 16 amps IEC 61000-4-30 - Power quality measurement methods IEC SC77A: Low frequency EMC Phenomena - essentially equivalent of "power quality
Harmonics from DG and other Generation Inverters Older line-commutated inverters had significant harmonic issues Newer inverters have negligible harmonics (often < 2% THD) Synchronous Machines High impedance relative to utility system (e.g. sub-synchronous reactance seen by harmonics is ~15%) harmonic voltage distortion is often intolerable when supplying VFDs Islanding, Fault current contribution Certain designs supply significant triplen harmonics Asynchronous (Induction) Machines VAR Support required PFC: can cause resonance, self-excitation (overvoltage, ferroresonance) Unbalanced fault contribution
Unintentional Islands
Overview of the German PV Experience and Inverter Firmware Modifications
WHY SMART GRIDS? German PV Capacity ~45 GW in 2015 German goal of 66 GW of PV by 2030 U.S installed more PV than Germany in 2013 U.S. PV Capacity is nearly 20 GW today U.S. expected to add 6 GW PV in 2014 Over 350,000 U.S. homes now have PV U.S. Goal of 100-300 GW PV by 2030 (DOE)
Germany
Distributed, But Not Integrated German PV Deployment driven by policies that commanded widespread political support Policies drove Feed-In Tariffs (FIT) that were VERY generous (70 /kwh for 20 Years) backed by the German Renewable Energy Sources Act (EEG) Large FIT are no longer needed to promote new renewables Electric rates have more than doubled since 2000 (currently 40 /kwh) Today, PV self-generators pay 6 /kwh to use their own generation in order to support the grid
Germany Exports PV Power Some Days!
The Germany Frequency Problem PV in Germany was initially installed with inverters that disconnect at 50.2 Hertz Retrofits were necessary to mitigate this issue All inverters greater than 3.68 kva must be retrofitted with the Droop Function so they do not trip offline at the 50.2 Hertz level Estimated cost for this solution has been over 300,000,000
The Frequency Droop Function Source: EPRI The Integrated Grid 2014
Other PV Issues in Germany Significant and common overvoltage or loading issues on distribution feeders Most PV connected to low-voltage circuits, and PV capacity can triple or quadruple peak load Risk of massive disconnection of PV systems due to frequency events Lack of stabilizing inertia from large rotating machine generation has raised concern of properly maintaining frequency and voltage on the grid All Countries should adopt Standards based on the lessons from Germany to avoid similar challenges!
Gracias