ARRESTERS
Protecting Power Plants Against Lightning
Lightning protection is usually associated mainly with distribution networks or transmission lines and substations. However, another area in the electricity supply paradigm where application of arresters needs to be considered are relatively small power stations, also known as distributed generation( DG) plants. These facilities, located in populated as well as remote locations, typically generate up to 100 MW and are either hydro and wind-powered or rely on a range of fuels from natural gas to methane to diesel.
This article, contributed by INMR Columnist and arrester specialist Jonathan Woodworth, reviews two case histories involving lightning and switching surge protection of such power plants.
had been compromised, since it is well known to have a low impulse withstand capability.
Photos courtesy of Jonathan Woodworth
Diesel Power Generator
A 100 MW diesel power station, located on the southern coast of the Dominican Republic, supplies electricity to an inland mining facility some 50 miles( 80 km) away.
134 20
YEARS
Q2 2013
This facility suffered a major failure that required the complete rebuild of one of its 10 MW generators due to a fault during operation. After initial investigation, it was determined that the likely cause was a lightning or switching surge. Then, within only months, a second generator also failed in a similar manner. Again, it appeared that the stator insulation
Each failure ended up costing more than US $ 200,000 in repairs. To make matters worse, the plant had to operate at lower capacity during the repair period, even as their prime customer was demanding ever more power.
The plant’ s maintenance scheme was good, with generators monitored routinely for partial discharges and balance issues. Moreover, there was no obvious indication or precursor to either failure. Given this, a first step towards understanding and resolving the problem involved surveying the generators, the internal switchgear and the generator step-up transformer( GSU) station.
Figure 1 is a simplified system schematic that shows that the surge arresters in the system are located downstream of the breaker and not on the generator side.