Lightning Surge Protection Of Generator Transformer

A lightning impulse is generated and applied to the transmission line. The surge arrester protects the generator transformer.

A medium voltage (13.8 kV) generator is connected to a short transmission line (500 kV) via a generator transformer (13.8 kV to 500 kV). The other end of the line is terminated at a 500 kV transmission substation. Lightnng strikes on the transmission line can damage the generator transformer which in turn can cause blackout. The repair/ replacement cost of the generator transformer is also very high.

The project deals with the protection of the generator transformer by means of a 500 kV surge arrester and simulating lightning surge voltage. The voltage at various points are measured with multi-channel scope.

A lightning surge voltage (> 2000 kV_peak / microsecond) is generated in a single stage impulse generator and applied to the remote end of the transmission line. The surge voltage travels along the 500 kV transmission towards the generatng station and hits the 500 kV surge arrester which clamps down the voltage to a low level (about 837 kV_peak). The clamped voltage travels along the 500 kV conductor to the high voltage terminal of the generator transformer (981 kV). The lightning impulse withstand (basic insulation) level of 1550 kV_peak of the generator transformer is greater than the lightning surge voltage (981 kV) appearing on the high voltage terminal of the generator transformer. Hence the generator transformer is protected.