Aurora were appointed by Prescient Power to investigate a series of protection mal-operation trips on a new 500kW Solar Farm that has recently been installed. The G59 relay appeared to be tripping for no discernible reason, leading to frequent outages and lost revenue for the end customer. Matters were further complicated as the site only had a HV circuit breaker, instead of a LV breaker and this was causing a lot of additional costs to the client to arrange for an SAP to come and re-close the system manually.

Aurora recognised the urgent priority of this job and gave it immediate priority, beginning a wide range investigation into all the potential sources that could be leading to the protection mal-operation. This began by undertaking an  evaluation of the system configuration and the reviewing the possibility of an uncleared / intermittent fault in the equipment causing the trip. Once this had been ruled out, Aurora suggested installation of data loggers on the system, so that we could build up a picture of the system behaviour prior to the trip.

After several days worth of data, Aurora managed to identify that the cause of the fault was a local factory on the same system, that had a heavily unbalanced lighting system. Once the main factory production systems had gone off line in the evening and all the lights were on, this was causing a noticeable voltage unbalance of nearly 4%, which was causing the G59 relay to trip on unbalance / vector shift.

Once the problem was identified, Aurora alerted Prescient Power to the issue, and advised them to request permission from the DNO to increase the vector shift settings on the G59 relay as an interim solution, whilst discussions were held with the factory to get them to address their load balancing problem.