1.Explain different types of fault?
There are basically two types of fault.
a)Shunt faults - Basically shunt faults are short circuits.When the path of the load current is cut short because of breakdown of insulation,we say that a ‘short circuit’ has occurred which is nothing but a shunt fault.
b)Series Fault - Series faults are nothing a break in the path of current.It is observed in practice that most of the open conductor faults sooner or later develop into some or other short-circuit fault
2.What are the various states of operation of a power system?
Normal alert,Emergency,In extremis and restorative are various states of operation of power system.
3.Explain the working of current transformer ?
The current transformer has two jobs to do.Firstly,it steps down the current to such a level that it can be easily handled by the relay current coil.Secondly,it isolates the relay circuitry from the high voltage of EHV system. A CT whose primary is in series with the line in which the current is to be measured.
4.Why the secondary of a CT should not be open ?
If the secondary of a CT is open current through it is zero and hence the ampere turns produced by secondary which generally oppose the primary ampere turns becomes zero.As there is no counter m.m.f,primary m.m.f produces high flux in the core which leads to excessive core losses and overheating.
5.Explain the working of a potential transformer ?
The voltage transformer or potential transformer steps down the high voltage of the line to a level safe enough for relaying system and personnel to handle.A PT primary is connected in parallel at the point where a measurement is desired.