Calculation Method And Protection Scheme Of Open-phase Operation In Power Plant

Open-phase operation is a common mode for non-normal operation for power plants.The open-phase operation on the breaker at high voltage side of the main transformer may lead to generator failure and power network incident.Therefore,finding an accurate method for calculating sequence current has important meaning for open-phase study.The current protection scheme of open-phase protection of generator is not mature enough.The protection scheme is lack of basis for the principle of setting,and the site applications are not uniform.Improving the open-phase protection scheme of power plants is of great significance for the safe operation of generators and power grids.This paper focuses on a series of researches on the calculation of open-phase sequence current of power plants,open-phase simulation of power plants and open-phase protection schemes of power plants,which is of guiding significance to the stable operation of power plants.Based on the existing symmetrical component method,this paper presents a new method for accurate calculation of sequence current in open-phase operation of power plants.According to the wiring diagram of general power plant,the situation that the main transformer and the auxiliary transformer high-voltage side circuit breaker are in open-phase operation under different operating conditions is calculated.The sequence current at the high voltage side of the transformer after open-phase operation has occurred can be accurately calculated,the calculated negative sequence current and zero sequence current have important reference value for the research of open-phase protection scheme of power plants.Using the electromagnetic transient simulation software PSCAD/EMTDC simulation platform,this paper sets up an analytical model according to the possible operating conditions of the open-phase operation of the high-voltage side circuit-breaker of the transformer,and respectively obtain the electrical quantities of open-phase operation under different loads.The simulation results are compared with the theoretical calculation results to verify the correctness of each other.Based on the analysis of the shortcomings of existing open-phase protection schemes,this paper presents a unified scheme of phase protection.The program sets the sequence current setting,and meet the sensitivity requirements;and can suit all the conditions mentioned above with the best performance across different connection types of transforms.