Learnings

Outcomes

A critical assessment has been made of EREC P28 in relation to BESS operation. This provides clarity around the three assessment areas of P28 namely: voltage step, rapid voltage change and flicker. The work is feeding into the development of an ENA Engineering Report (EREP) currently being drafted by the DCRP P28 Working Group.  

BESS should be operated and assessed at unity power factor. Whilst this is not ideal for system losses it allows more BESS to be connected and avoids large voltage disturbances when ramping power, helping to maintain P28/2 limits.  

A methodology for assessing voltage step changes and rapid voltage changes has been developed and an associated tool in DIgSILENT PowerFactory has been developed. This has been tested against some existing BESS projects that have been or will be connected to NPg’s network and where some power swing restrictions exist under non intact system conditions. The tool has shown that voltage fluctuations are within limits but uncertainty remains surrounding the treatment of co-incident BESS swings. 

Lessons Learnt

The use of voltage control to manage local voltage oscillations could be trialled on a real world BESS to alleviate local voltage disturbance issues. It is suggested that this is implemented slowly on a single BESS connected to the 132kV network.   

The role of ANM could be expanded for multiple BESS units based on actual performance. Where coincident swings are occurring and P28 limits may be breached, a Last In First Out (LIFO) queue could be explored.  

Where co-incident effects of generating unit and/or BESS operation needs assessing, ways of sharing this information between parties without compromising confidentiality on technical models needs to be examined and recommendations proposed. A move towards generic models such as those developed by WECC rather vendor specific models would facilitate this. 

How to treat co-incident power swings from multiple BESS units remains a challenge. It has been suggested that the 3% step change limit is retained and a move towards using weighting factors should be used, and that for the short-term that weighting factor should be 1.0 with further work required to determine a methodology to develop less conservative weightings. Whether only the PCC for newly connecting BESS or whether PCCs for existing BESS needs consideration will need to be considered by the DCRP P28 Working Group.