Question

1. What do you mean by ‘Intrinsic strength’ of a solid dielectric?

2. What are the drawbacks of single stage circuit for the generation of very high impulse voltage?

3. What is a cascaded transformer?

4. What is the effect of nearby earthed objects on the measurements using sphere gaps?

Answer 1

1. intrinsic strength of a solid dielectric is the maximum electric field a material that can withstand without breaking down independent of the size or the shape of the material.

3.when the required test voltages are greater than 300kv then single transformer cannot be used because the construction of a single transformer becomes very difficult and the process is costly. moreover, even after constructing those big transformers transporting and assembling those transformers become very diffcult. that is why it is not feasible to build huge transformers. to overcome this problem we use cascaded transformer. cascaded transformer is a transformer in which several identical units single stage transformers are connected in series. all the high voltage windings of units are connected in series.

2. the drawback of single stage circuit for generation of very high impulse voltage. Basically, in the single stage generator, the generator capacitance C1 is to be charged and then discharged into the wave shaping circuits. this single stage generator can be used to generate voltages upto 200kV only. for values above 200kV it is not feasible. this is because i) first designing such a huge capacitor itself is very difficult as size becomes very huge

ii) even if we design such a big capacitor charging unit becomes very costly.

these are the drawbacks in single stage generator.