Assessment of Power Swing Blocking Functions

Power swings and loss of synchronism are complex events which occur during power system faults, line switching, generator disconnection, and the loss or application of large loads. As generators have different frequencies for a duration following the event, this results in power swings which cause voltages and currents in different parts of the network to swing in amplitude and phase angle. Power swing blocking (PSB) is a vital security feature in distance protection relays for preventing unnecessary tripping during temporary power system oscillatory events. A case study is taken as an example, which following a system disturbance on the Irish transmission system, there was a subsequent power swing event on a part of a 110 kV network. DigSilent PowerFactory was used to perform dynamic time-domain simulations of the event. A COMTRADE file is generated from simulations and can be "played back" to a relay to verify how the relay responds to various stable and unstable power swing. The paper also outlines a utility's experience in analysing PSB algorithms on distance protective relays in use on a transmission system. Finally, an overview of the methods used in developing a systematic and practical approach to testing and mitigating the effects of the disturbance on the network is investigated.