Question 1:
- Describe how the Schering Bridge is balanced when measuring the loss angle tan-delta and capacitance of an unknown dielectric. (Do not exceed 200 words)
- Derive an expression for tan-delta and capacitance in terms of the known values of R and C of the other branches of the bridge.
- Explain the role of "Wagner Earth" in balancing the bridge. (Do not exceed 100 words)
Question 2:
- Describe how discharges in a void inside a solid dielectric is detected using the PD test circuit. Also, explain how the measured apparent charge can be related to the actual discharges in the void. (Do not exceed 200 words)
- Analyze the following insulation systems using partial discharge patterns. In all cases assume that the test object is a solid insulation of thickness much larger than the depth of the cavity (defect). The insulation is stressed with power frequency AC voltage of magnitude much higher than the PD inception levels. Illustrate the patterns on an elliptical display of the discharge activities in each case. Provide your justifications in terms of influence of the electric field and the physics of discharge activities. (Do not exceed 200 words)
