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