Estimation Based Protection of Three-Phase Saturable Core Transformer for Cross-Country Fault Detection

Despite decades-old research in the area of power system protection, situations where traditional protection schemes might not operate effectively still exist. Such gaps in the protection capabilities of traditional relays must be addressed to ensure the safe and secure operation of the power grid. The focus of this paper is on cross-country faults. Specifically, we are interested in accurately detecting an internal fault in the presence of an external fault close to our protection zone. This is an important problem, because the external disturbance may have two adverse effects. First, it may cause relays that monitor nearby zones to issue a trip command, as if the fault was within their protection zones. Second, schemes that guard against this problem may desensitize the relay and fail in detecting a fault that may happen inside the protection zone during the external fault. Our approach is model-based. The dynamic models of the protected and measuring devices are utilized alongside the obtained measurements to verify that the measurements are consistent with the devices operating normally. The performance of our approach is tested with an external fault, a difficult case of an internal fault, namely a transformer inter-turn fault, and a combination of the two previous cases. Results are provided showing that our approach works correctly in all three cases.