A new technique for improving stability of distributed synchronous generators during temporary faults in a distribution network

A system is developed for performing coordinated control of operation of distributed synchronous generators during transients caused by disturbances due to faults in the interconnecting network. For this purpose a braking resistor is used where excess electrical energy is dissipated, thus preventing over-speeding and loss of synchronism of the machine during transient processes caused by temporary faults and actions of the protection system together with the system for automatic reclose of the line. In addition to controlling the operation of the braking resistor, the proposed system performs a coordinated control of the excitation of the generator. The coordinated control of the braking resistor and excitation voltage of the generator provides a good fault ride through capacity of the machine even during faults when the generator stays in the island operating mode for some time. The functionality and practical applicability of the developed system have been tested by dynamic simulations carried out on a real model of a hydro-aggregate incorporating a synchronous machine and with real parameters of a distribution network. The simulations were performed by using program package DIgSILENT PowerFactory.