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.

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

• 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

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)

24

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