Author S Prepared Contribution for the Paper

Author’s prepared contribution for the paper:

INFLUENCE OF FAULTS IN DISTRIBUTION NETWORK ON BEHAVIOR OF ASYNCHRONOUS GENERATORS IN SMALL HYDROELECTRIC POWER PLANTS

In some mountainous regions in Slovenia the production of electrical energy from small hydro-electric power plants covers almost 50% of power demand. A three phase asynchronous machines are normally used as generators. In this networks there are a large number of short circuit faults and line interruptions each year. Each fault represent a disturbance to the generators.

The observed network operates on 20 kV voltage level. In the network there are 50 small hydroelectric power stations, more than 30 of which are normally in operation. Most of them have one or two asynchronous generators. The total average active power generation is around 45% of the load demand.

With the help of dynamic simulation a different short-circuit faults were simulated in the network and the generators responses were observed. We focused on two main subjects:

• the increase in speed of generators and

• the increase in the short circuit power by the generators in the network.

The speed of asynchronous generators during the fault increases far beyond their nominal speed. According to results, the most dangerous fault is near the generator. With a normal fault clearing times, faults with a residual voltage of less than 20% will result in a speed twice as fast as synchronous speed.

TABLE 1 - Increase in speed of asynchronous generators at different residual voltages and fault durations on a 20 kV bus-bar in TSS Sentjanz

Simulations of short-circuit fault in a network with and without the consideration of generators were also made. The aim was to determine the influence of generators on the amplitude of short-circuit currents in the network. The results show that generators increase the short circuit power in the network for over 25%.

TABLE 4 - Three-phase short-circuit fault currents in a network with and without the contribution from the generators in SHPP

After the results were obtained, the generators’ protection devices were checked, as well as the circuit breaker capacities in the substations. In the period since most of the power plants were put into operation, no serious problems have occurred in the network.