A Method to Evaluate the Safety Margin for Setting Value of the Transformer Protection Device with Domestic Chips and Analyze the Influencing Factors

To ensure the reliable operation of UHV transformer, which is an important equipment in transmission network, a high margin longitudinal differential protection (LDP) is used as one of its main protection. However, after the adoption of domestic chips in the UHV LDP for relay of transformer (LDPRT), the performance changes of chips make the quantization process deteriorate under extreme conditions, resulting in the risk of insufficient safety margin for the setting value. In order to quantify the risks, this paper proposes the safety margin for the setting value of LDP-RT, and an evaluation method to the safety margin of the setting value considering the ADC chip and CT transmission. Specifically, Firstly, based on transformer sensitivity coefficient and error sources, the safety margin for the setting value of LDP-RT is defined. Secondly, the calculation method to the extreme safety margin for the setting value of the LDP-RT is presented, and the assessment based on the safety margin is proposed. Finally, the characteristic of the safety margin for the setting value of the LDP for UHV transformer with domestic chips is evaluated and analyzed with Matlab[R] Simulink, and the influence of the braking coefficient is also quantitatively analyzed.