BESS – EREC P28 Voltage Fluctuations Assessment
Northern Powergrid is starting to connect Battery Energy Storage Systems (BESS), generally sized between 10 and 100MW, to its EHV network (or connected at the HV busbars of EHV/HV substations). We consider EHV to be 132kV, 66kV and 33kV and HV to be 20kV, 11kV and 6.6kV. BESS connections are typically designed so that the operator can enter into frequency response services with the Electricity System Operator (ESO) where fast changes in active power output or input are required. The same BESS may also be used to provide other services such as commercial energy arbitrage.
During the initial connection assessment Northern Powergrid use simple and conservative step voltage calculations to determine the maximum active power swing that a BESS should be limited to in order to be compliant with EREC P28. EREC P28 prescribes the voltage fluctuation planning limits that customers must adhere to. BESS developers sometimes carry out their own EREC P28 studies which are usually delivered close to the date of first energization of the project. These studies often result in different maximum active power swings to those determined by Northern Powergrid during the initial connection assessment. Reactive power also has a significant effect on system voltages and consequently voltage fluctuations. Changes in reactive power can either worsen or improve voltage fluctuations associated with the changes in active power swings depending upon how the BESS control system is configured. Reactive power considerations are not mentioned in EREC P28. GB DNOs have different policies for assessing BESS against P28. Developers may wish to operate their BESS to manage reactive power in order to maximise the permissible active power swing whilst ensuring that the voltage fluctuations are minimised and within the requirements of EREC P28. There is a need to establish i) a common method that can be applied by DNOs and developers for calculating voltage fluctuations to ensure compliance with EREC P28, ii) a set of solutions acceptable to the BESS developer and the DNO to manage voltage fluctuations and iii) determine an appropriate operating regime and control system for managing the active and reactive power input and output of a BESS.
BESS are becoming a significant tool for the ESO to use to manage system frequency as the electricity generation portfolio transitions to low carbon generation. This is an opportune moment to study how BESS operation effects system voltage, how the functions of BESS control systems can be utilised to minimize voltage fluctuations, and to consider whether EREC P28 together with DNO policies associated with assessing EREC P28 compliance of the connection of BESS need updating.
The project’s primary objectives are to:
- Develop simplified and advanced methodologies for assessing the effects of BESS connection and operation on voltage fluctuations on distribution systems operating at EHV or HV where the BESS is connected at the HV busbars of an EHV/HV substation;
- Examine optimal BESS active and reactive power control modes and setpoints to minimise voltage fluctuations associated with BESS operation and the operation of the distribution network;
- Provide material that can be disseminated to NPg staff and included in updates to NPg policies, as required, to facilitate the assessment of voltage fluctuations from BESS connections taking into account active and reactive power flows that are expected to be seen from commercial service operation;
- Feedback to the DCRP EREC P28 workgroup on the project findings.
Timescales: November 2023 - December 2024
Associated documents:
