Grid Management Voltage Control
Distribution Grid Voltage Regulation
with DER
Michael Sheehan, P.E.
IREC
Pacific Northwest Solar Partnership
Overview of Grid Management – Distribution Voltage Control
• Grid Management Renewable Portfolio Standards
• Example EPS Voltage Regulation Philosophy
• Distribution Feeder Voltage Regulation
• Voltage Drop/Rise on Line Transformers, Services and
Secondaries
• Voltage at the Meter and at the Inverter
• Smart Inverter Features & Time Series Power Flow Analysis
Electric Grid Symbols
Grid Management Functions
CAISO October Profile
CAISO December Profile
CAISO Amount of PV will Challenge Grid Management
CAISO Amount of PV will Challenge Grid Management
Voltage Regulation on Distribution Circuit
The EPS is designed to operate within set ranges of voltage (C84.1).
Most customers depend on their voltage to be maintained within
their applicable voltage limits to protect their equipment from
excessive voltage or overheating. Voltage regulation throughout the
EPS may be accomplished in various ways, such as using bus
capacitors and load tap changers at substations and with line
capacitor banks and voltage regulators installed on the distribution
circuits.
IEEE 1547 Requirements (Section 4.1.1; 4.2.3)
The DR shall not actively regulate the voltage at the PCC. The DR
shall not cause the Area EPS service voltage at other Local EPSs to
go outside the requirements of ANSI C84.1, Range A.
4.2.3 Voltage defines the maximum allowable operating voltage to by
110% of the nominal system voltage as defined in
ANSI C84.1 Table 1.
ANSI C84.1 Range A Voltage Limits (120-Volt Base)
IEEE 1547.7 Check List Criteria P5.- P5.5
Distribution Feeder Voltage Regulation
• Utilities regulate the voltage on the distribution feeders so that the
delivery voltage at the customers meter will stay within +/- 5% of
nominal (ie. 120 V +/- 5% or 126-114V). The national standard
related to this is ANSI C84.1 In some states, rules are slightly more
stringent and may allow a smaller bandwidth.
• Voltage regulators raise or lower the voltage in very small steps,
typically 5/8% per step for up to 10% raise or lower.
DER Impacts to a Distribution Feeder
Voltage Regulation
•Ability to maintain customer voltage within range
• Wear-and-tear on voltage control equipment (e.g., tap operations) due to variable output
Power Quality
• Flicker, harmonics
Protection
• Performance of relays and other protection equipment
• Risk of unintentional islanding
System planning and operations
• Feeder load switching, maintenance, outage management
• Controllability and visibility of distributed resources
• Possible impact on bulk system
From Robert Broderick Sandia
Voltage Regulation Issues
From Robert Broderick Sandia
Technical Analysis of Prospective Photovoltaic Systems in Utah
Sandia & Rocky Mountain Power Time Series Analysis
Toquerville Feeder 11
2-MWAC nameplate
Toquerville 11 2010 Average Load Amps
Toquerville Peak PV Penetration period maximum voltage profiles – with and without PV.
Toquerville Peak PV Penetration period minimum voltage profiles – with and without PV.
Toquerville 11 Results Summary.
Two Issues Overvoltage at the Inverter
The level of local voltage rise is directly related to the impedance or strength of the network (stiffness ratio).
If the distribution feeder to which the inverter is connected is weak (i.e. high impedance) the voltage at the
inverter connection point will begin to rise. This has two potential consequences. The first impact is that once
the voltage at the inverter connection point rises to the inverter pre-set overvoltage limit as prescribed in IEEE
1547 , the inverter will disconnect from the grid. If this occurs, no power can be exported and no income can
be generated.
The second issue is that if the overvoltage limit on the inverter is set too high, the connection point voltage
may exceed the allowed maximum feeder voltage. Many utilities have specified that inverters should
disconnect from the grid when the inverter connection point voltage exceeds 126 V (1.05 pu). However, either
by design, or other adjustment by installers, some inverters are not configured in this fashion and inverter
connection point voltages of up to 132 V (maximum inverter voltage according to IEEE 1547 before antiislanding protection operates) have been observed. These voltage levels are outside ANSI C84.1 standard
voltages and will likely damage or significantly reduce the lifespan of equipment connected at or near the
inverter connection point.
Possible Solution/Options Grid Management
California Rule 21 Smart Inverter Working Group
California Rule 21
http://www.cpuc.ca.gov/PUC/energy/rule21.htm
Hawaiian Electric Company New LVRT LFRT
Dynamic Volt-Var Mode with Deadband and/or Hysteresis
Draft California Smart Inverter Working Group (SIWG) Volt/VAR Function
The SIWG proposes establishing that the I-DER system shall be
capable of providing dynamic reactive power compensation (dynamic
volt/var operation) within the following constraints:
•The volt/var function shall not cause the line voltage at the point
of common coupling to go outside the requirements of the latest
version of ANSI C84.1, Range A.
•The full Range A should be allowed for distribution feeders with
customer generation.
•Suggested range: Autonomous operations described above may be
superseded by an external signal issued by the Area EPS operator.
Questions/Follow-Up
• California Smart Inverter WG Rule 21
• Time Series Analysis Power Flow
• Fixed Power Factor Solution
• IEEE 1547 Update