Model-based power system protection – benefits and drawbacks

Conventional protection schemes must evolve to accommodate the increasing number of inverter-based distributed energy resources (DERs) and the associated variation in power system operating conditions. The adoption of standards like IEC 61850 and the increased communication capabilites of digital substations have led to an increase in available measurement data, which, unlike conventional approaches, can be effectively utilized by model-based protection schemes for not just individual power system components but entire power system areas. In addition the model-based protection paves the way for centralised protection solutions. This paper investigates the security and dependability of a model-based protection scheme based on a Kalman filter. Contrary to conventional protection schemes, this approach uses a sample based algorithm that compares the estimated state-space vector, of voltages and currents, with the measured equivalent at the system boundaries. By benchmarking the model-based protection scheme against a conventional differential protection scheme it becomes possible to identify similarities and differences in the resulting protection functionality. The benefits of model-based protection over conventional protection are faster tripping time and the independence from distorted and unknown inverter infeeds. The need for further research on the Kalman filter in the context of protection technology is clearly demonstrated.