Polarizing Voltage Generating Method for Distance and Directional Protection Elements

Distance and directional elements are widely used in power system protection. One of the used essential signals, having a substantial impact on proper operation, is polarizing voltage. During faults close to a protection relay, memory filters can be used to ensure the availability of this voltage. A basic assumption of these memory filters is that during a fault only an amplitude of a measured voltage changes rapidly and other parameters change very slow. The assumption is correct in power systems with an overwhelming share of traditional rotating generators. However, today, more and more energy sources are connected to power systems through inverters. Algorithms implemented in inverters can control parameters of output voltage so that they can be changed rapidly without any inertia. Therefore, a source of robust polarizing voltage is needed to ensure proper operation of distance and directional elements. The paper presents a method of a reference signal generation based on phase-locked loop (PLL). The algorithm consists of PLL with an adaptive notch filter, and elements adding inertia to the generated signal. The reference signal can be used as a polarizing voltage in protection elements. The paper describes all elements of the algorithm and presets operational tests.