Grid Management Voltage ControlDistribution Grid Voltage Regulation

with DERMichael 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

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.

Voltage Regulation on Distribution Circuit

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 inANSI C84.1 Table 1.

IEEE 1547 Requirements (Section 4.1.1; 4.2.3)

ANSI C84.1 Range A Voltage Limits (120-Volt Base)

IEEE 1547.7 Check List Criteria P5.- P5.5

• 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.

Distribution Feeder Voltage Regulation

DER Impacts to a Distribution Feeder

From Robert Broderick Sandia

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

Voltage Regulation Issues

From Robert Broderick Sandia

Technical Analysis of Prospective Photovoltaic Systems in UtahSandia & 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 shoulddisconnect 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 anti-islanding 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.

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

Possible Solution/Options Grid Management

Dynamic Volt-Var Mode with Deadband and/or Hysteresis

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.

Draft California Smart Inverter Working Group (SIWG) Volt/VAR Function

Questions/Follow-Up

• California Smart Inverter WG Rule 21

• Time Series Analysis Power Flow

• Fixed Power Factor Solution

• IEEE 1547 Update