session 10: general overview of interconnection standards ... · october 21, 2015 – santiago,...
TRANSCRIPT
October 21, 2015 – Santiago, Chile
Michael Coddington
National Renewable Energy Laboratory
Golden, Colorado, U.S.A.
Session 10:
General Overview of Interconnection Standards
& Grid Codes for High Penetration PV
DISCLAIMER
ISGAN is an initiative of the Clean Energy Ministerial (CEM). It is formally
organized as the Implementing Agreement for a Co-operative Programme
on Smart Grids (ISGAN), operating under a framework of the International
Energy Agency (IEA). The views, findings and opinions expressed herein do
not necessarily state or reflect those of any of ISGAN’s participants, any of
their sponsoring governments or organizations, the CEM, the IEA
Secretariat, or any of the IEA’s member countries. No warranty is expressed
or implied, no legal liability or responsibility is assumed for the accuracy,
completeness, or usefulness of any information, apparatus, product, or
process disclosed, and no representation is made that its use would not
infringe privately-owned rights. Reference herein to any specific
commercial product, process, or service by trade name, trademark,
manufacturer, or otherwise does not necessarily constitute or imply its
endorsement, recommendation, or favoring.
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.
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)
NESC is an International IEEE Standard
• 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
NESC Requirements for De-energized Work
Utility Safety and Clearances Standard
Interconnection Standards & Grid Codes
• 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 Electrical Code - NEC NFPA 70
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
• 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
These Power Quality Issues Should be Addressed by Interconnection Standards and Codes
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
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.
0 0.005 0.01 0.015 0.02 0.025 0.03-2
-1
0
1
2
3
time [s]
vo
lta
ge
[p
u]
Voltage with Harmonic Distortion
Fundamental5th order harmonic7th order harmonicTotal Waveform
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
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)
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
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
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!