A new wind turbine transformers protection method against high du/dt switching transients taking place during a wind turbine operation is described. High-frequency transients, characterized by a high rate of voltage rise (du/dt) and overvoltage at the wind turbine transformer high-voltage terminals may be a result of operations of the turbine switchgear typically comprising a vacuum circuit breaker. The protection concept described in this paper is a follow up of research activities on a transients suppressing method dedicated for distribution transformers. The principle of operation of the protective device proposed and parameters optimization procedures for windmill transformers are provided in this paper. The performance of the device was verified by means of Alternative Transients Program-Electromagnetic Transients Program simulations. The physical device was built and experimentally verified by full-scale functional tests reflecting a real wind turbine power network.

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The paper presents a procedure for measuring and analyzing the switching arc parameters occurring in air-insulated low voltage (LV) relays operating in distorted supply voltage conditions. The main purpose of the research was the analysis of the switching arc duration and its energy affecting the current breaking capacity of the selected LV current interrupters (CI). The performed study and simple statistical analysis enabled the determination of the main factors and their impact level on parameters of the switching arc that comes about during switching-off operation. Experimental tests executed for various shapes of the supply voltage but similar RMS (Root Mean Square) and THD (Total Harmonic Distortion) values and for various breaking moments of the load current allowed recognition of the decisive factors for estimating the tested relay’s switching-off capacity. Tests stand combined with dedicated software developed in the frame of the research, permiting fast calculation of the arc parameters based on a large number of recorded diagrams.

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