Simulation Analysis And The Protection Design Of The Grounding Transformer

The grounding transformer is intended solely for establishing a neutral connection point on an ungrounded power system, which is connected with the Petersen-coil or the resistance grounded, thousands were put into operation annually in the nation. Ground fault protection schemes that provide selective and reasonably fast tripping are often incorporated with these grounding transformers. In recent two years, several grounding transformers were in failure caused by over-voltage and the other faults of itself. Since the grounding transformers are not encountered on a specific protect theory and device domestic and overseas, the paper makes the fault simulation and the design of the grounding transformer’s protection.A mathematical model of the grounding transformer is first described in the paper that can be used to simulate internal fault waveforms for power system protection studies. In order to effectively implement the internal fault simulation, the architectural characteristic and electromagnetic principle are analyzed. Besides, a method to calculate the three-phase currents and the grounding current is outlined. Then a zigzag grounding transformer is modeled based on the MATLAB simulation platform. Simulation results showing the fault currents, including a single phase to ground fault, an interturn fault of main windings and an interturn fault of phase-shifting windings, are presented. An inrush current simulation model also is built in the software, which simulation was achieved. Comparisons are made between the principle analysis and the simulated waveforms to verify the accuracy of the model.There are some deficiencies in the Grounding transformer protection existing technology on the sensitivity and reliability .With the data generated by this internal fault simulation model, the protection scheme used for the grounding transformer be designed and improved accordingly. The longitudinal differential protection was equipped as the main protection; Backup protection would be provided by a restricted earth fault relay. Provide a theoretical basis for further study on the ground transformer’s protection equipment.Analysis based simulation model is developed in the paper, and different ground faults and load switching operations are investigated. Then an experiment was made to text the simulation model correctly, the protection scheme is simulated by Matlab software. Fault data generated is input into the Matlab simulation program for analysis. The protection performance is assessed. Results show that the protection scheme can remove the influence of the all kinds of the grounding transformer’s faults, which has the broad application prospects.