Study on Electromagnetic Characteristics of Interturn Short Circuit of Single-phase Transformer

Aiming at the problem of internal current surge and excitation saturation caused by transformer interturn short circuit, we investigated the characteristics of current, magnetic flux and the working principle of transformer interturn short circuit. The time domain differential circuit equation of transformer interturn short circuit mode is established, and the winding current is calculated based on the principle of energy disturbance. The winding current, core flux and leakage flux of the primary and secondary windings with different interturn short circuit ratios and different loads are simulated, respectively. The variation law of current and flux is studied, the main factors affecting the change are analyzed, and the core flux is used to characterize transformer excitation saturation state. The results show that when inter-turn short circuit occurs in primary winding (the turn ratio is 0~10%) of rated operation of transformer, the current of primary side port increases to 0~4.0 times, the short-circuit current suddenly increases to 23 times of the current of primary side port, and the current of secondary side port almost remains unchanged. When inter-turn short circuit occurs in the secondary side winding, the current of primary side port increases to 0~3.0 times, and the short-circuit current suddenly increases to 14 times of the current of secondary side port. At the same time, the core excitation is locally saturated. The magnetic flux leakage of winding increases. When the load ratio decreases, the saturation degree of core excitation deepens. When the short circuit ratio increases, the leakage flux of winding will increase. A test platform for transformer inter-turn short circuit is built to measure current parameters and to verify the correctness of the conclusions by comparing with the current data obtained by simulation, thus providing a basis for the protection design and setting of transformer inter-turn short fault. © 2020, High Voltage Engineering Editorial Department of CEPRI. All right reserved.