An Influence of a Current Compounding on the Behavior of a Synchronous Generator With a Brushless Excitation System During a Terminal-voltage Variation

: pp. 35 - 42
Lviv Polytechnic National University
Lviv Polytechnic National University

Brushless excitation systems of synchronous generators provide non-contact transfer of the excitation power to the generator rotor in case absence of a commutation in rotor circuit. Such systems have a long response time of terminal-voltage regulation caused by the additional rotating machine (exciter). Using of fast-acting compound circuit allows improving dynamic parameters of terminal-voltage regulation in modes of sharp voltage variation and short circuit in line.

The brushless excitation system of synchronous generator with current-compound circuit implements a combined approach of the terminal-voltage regulation. A disturbance-compensating control is realized by compound circuit with the current source and error-closing control provides by automatic voltage regulator with the voltage source. In other side, there’s a currents’ redistribution of the brushless excitation system with current-compound circuit in different modes of synchronous generator. The excitation-current increment is not equal to the compound-current increment because the changing the voltage-source current. It’s caused by mutual influences between the voltage source and the current source (compound circuit). The compound current is proportional to the stator current of the synchronous generator.

The influence of the compound circuit is essential in modes of the sharp changes of generator variables. To analyze this effect, the paper investigates the modes of the 10 % terminal-voltage reducing and three-phase short-circuit in line. These researches have obtained for different ratio of current transformers by mathematical modeling method. The influence of the compound-circuit parameters (transformer ratio of current transformer) on the system characteristics and the stability of the generator is analyzed. Therefore, the static error of the voltage regulation is reduced by increasing the coefficient of the compound circuit in the terminal-voltage reducing mode. The reducing the the coefficient of the current- compound circuit can lead to the synchronism loss of a synchronous generator in three-phase short-circuit modes, depending on the distance of the short-circuit point from the generator and the value of the terminal-voltage drop.

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