Development of Voltage Sag Metric for Large Meshed Transmission Systems and Stochastic Fault Data Sensitivity Analysis

This paper describes an approach to determine the impact zone and voltage sag metric for delivery points (DP) in large meshed transmission systems. The metric is to quantify the severity and frequency of voltage sag (VS) experienced at particular DPs. The network model of the system is developed and verified for voltage sag calculation using fault data captured by the power quality (PQ) meters installed across the system. The validated model is used to form the impact zone in terms of the circuit length causing the voltage sag event. Having the impact zones, stochastic fault data is used to create the voltage sag metric. To show the sensitivity of voltage sag metric to different treatment of stochastic fault data, the voltage sag metric is obtained with two sets of data: individual circuit outage frequency and zonal average outage frequency. The approach is implemented on Hydro One Ontario Transmission system. The results are examined to correlate the system behavior with network configuration, voltage level, and proximity to major stations with auto transformers. The results are validated using the data collected over 3 to 5 years by the PQ meters installed in the system. At utility-scale, the approach is used to proactively predict the impact of new planning projects, the retirement of big generation units, and major system reconfiguration on the voltage sag performance of major stations. Additionally, for customers connected on the low voltage (LV) side of transformer stations, the proposed metric can be used to differentiate the impact of transmission system from the events caused by faults on distribution feeders.