19-02-2013, 10:22 AM
LIGHTNING IMPULSE TEST
LIGHTNING IMPULSE.ppt (Size: 588.5 KB / Downloads: 41)
Purpose of test:
The purpose of the test is to secure that the transformer insulations withstand the lightning overvoltages which may occur in service.
METHOD OF TESTING:
The testing is conducted by artificial generation of
lightning impulse using IMPULSe GENERATORS.(FIG 1)
Capacitor banks are charged in parallel from a d.c source and is discharged in series to create impulse voltage of wave front 1.2micro seconds&tail of 50 micro seconds.(FIG 2)
There are 20 capacitors of 150 kv each &together they produce 3 million volts.(shown only 4 capacitors in fig)
procedure
The impulse voltage wave form is obtained at reduced level from the potential divider by polishing its front & tail using Rs and Rp.
The sphere is calibrated to know the voltage to be applied or
can be checked using analyser.
All winding except the test winding is earthed .
The calibrated impulse wave is applied to the test windings.
Its response is recorded using impulse analyser.