PV interconnection requirements for mid-sized and large PV systems may be revised by utilities based on new draft guidance from the North American Electric Reliability Corporation (NERC).
That’s because the guidance is intended to help utilities and other transmission owners “develop more comprehensive interconnection requirements.” The guidance was prepared partly in response to questions from utilities and other transmission owners regarding how to translate previous guidance, regarding performance of inverter-based resources, into interconnection requirements. The guidance document is entitled Reliability Guideline: Improvements to Interconnection Requirements for BPS-Connected Inverter-Based Resources.
The guidance addresses all inverter-based resources connecting to the bulk power system (i.e., the transmission grid), including mid-sized PV systems “not subject to NERC Reliability Standards since they do not meet the size criteria as defined by the bulk electric system definition.” This includes mid-sized PV facilities that are connecting to the bulk power system “either at voltages less than 100kV or with capacity less than 75 MVA.”
The guidance indicates that the majority of generating resources newly interconnecting to the bulk power system are below that NERC size threshold.
The guidelines are intended to encompass mid-sized PV facilities connecting to the transmission grid because “while each individual resource may not have a substantial impact to the BPS (bulk power system), the overall response, behavior, and controls of these resources does have an impact on overall BPS reliability and stability.”
“Therefore,” the guidance adds, “it is critical to have some degree of consistency across the generating fleet, and this guideline serves as a reference in this regard.”
NERC explains the need for the guidance as follows:
“Unlike synchronous generation, whose response to grid events is predominantly driven by classical mechanics, inverter-based resource response is driven by advanced controls. These controls are configurable and capable of providing similar essential reliability services (ERSs) as synchronous generating resources; however, industry is faced with providing sufficient guidance during the interconnection process to clearly describe what capabilities and control settings are desired.”
The new draft guidance follows NERC’s September 2018 guidance addressing how inverter-based resources connected to the transmission grid should handle fault conditions, entitled Reliability Guideline: BPS-Connected Inverter-Based Resource Performance.
While that 2018 guidance addressed the performance of inverter-based resources, the new guidance advises utilities and other transmission entities on how to translate those performance standards for inverter-based resources into interconnection requirements.
Distributed resources—defined as those not directly connected to the bulk power system—are not addressed in the new draft guidance; NERC has previously recommended the use of IEEE Standard 1547-2018 for distributed inverter-based resources. (IEEE is a global association of engineers that develops global standards.)
NERC intends its new draft guidance to be a bridging reference document until an IEEE P2800 standard development process comes to fruition. That process will develop “a detailed performance standard that addresses all relevant performance aspects of inverter-based resources connected to the BPS,” NERC’s guidance says. NERC projects that the IEEE P2800 standard will “likely take multiple years to develop, approve, and [be adopted by] local transmission owners.”
NERC’s new draft guidance recommends improvements to interconnection requirements in 18 areas:
- Momentary Cessation
- Phase Jump Immunity
- Capability Curve
- Active Power-Frequency Controls
- Fast Frequency Response
- Reactive Power-Voltage Control
- Reactive Current-Voltage Control
- Reactive Power at No Active Power Output
- Inverter Current Injection during Fault Conditions
- Return to Service Following Tripping
- Operation in Low Short Circuit Strength Systems
- Fault Ride Through Capability
- Grid Forming
- System Restoration and Blackstart Capability
- Protection Settings
- Power Quality.
The guidance recommends improvements to modeling requirements in 6 areas:
- Timing and Quality of Modeling Data Submittals during Interconnection Process
- Steady-State Modeling
- Positive Sequence Dynamics Modeling
- Short-Circuit Modeling
- Electromagnetic Transient Modeling
- Benchmarking Positive Sequence and EMT Models.