Experiment No: 9
High Voltage AC Test Source
Breakdown studies of uniform field and non-uniform field gaps under A.C. excitation:
A) POINT-PLANE. B) SPHERE-SPHERE.
1. Connect the test gap (A) to the transformer as shown in the circuit diagram.
2. Adjust the gap distance to an initial value of 10mm.
3. Close the circuit breaker S1.
4. Slowly raise the till faint hissing audible sound is heard. Note the reading on the
Analog Multimeter and actual value from the calibration chart provided. This is the
beginning of corona. Hence the Corona Inception Voltage.
5. Raise the Voltage further till such time there is a faint visible glow at the high
voltage electrode. This is the Visible Corona Inception level. Note the value.
6. Then slowly reduce voltage further till such time the hissing sound subside i.e., dies
down or becomes extinct. Note this value as Corona Extinction Voltage.
7. Once again raises the voltage till such time there is a Break Down. Note this value
as break down Voltage.
8. Reduce the voltage completely and open the circuit breaker.
9. Increase the gap distance by 5mm and repeat steps 3 to 8.
10. Repeat step 9 for 6 (six) different gap distances.
11. Repeat the experiment for test Gap (B).
12. Correct the observed values for standard atmospheric conditions and plot the gap
distance Vs Breakdown voltage for each gap.