Generator modeling for transformer transfer voltage study

This paper is focused to hydraulic generator modeling in a transient simula tion for a transformer transfer voltage due to a lightning surge on a trans mission line from the viewpoint of the insulation design of a hydraulic gen erator station. The transfer voltage of a generator step-up transformer is measured. Three generator models are investigated in comparison with the me asured result. A conventional surge impedance model gives a satisfactory re sult of a calculated peak voltage, but a oscillating frequency disagrees wi th the measured one. A sub-transient reactance model composed of inductance elements and capacit ance elements representing a generator subtransient reactance and an armatu re winding capacitance can produce a transfer voltage oscillation. However, it can not simulate the crest value and the oscillating frequency of the m easured voltage. A new model proposed in the paper is based on the subtransient reactance mo del. The inductance is modified by taking into account the frequency charac teristic of a transfer voltage. And resistance elements are added in parall el with reactance elements to represent the damping of the voltage oscillat ion. The accuracy of the proposed model is confirmed to be satisfactory in both transfer voltage crest value and oscillating frequency in comparison w ith the measured results.