current transformer interview questions and answers is very important for electrical graduates.
Here we are going to discuss some very important current transformer interview questions with proper answers which are mostly asked with Electrical Graduates in every industrial interview as well as in university exam viva. So please go through all these CT interview questions with their appropriate answers to improve your subject knowledge.
What is Transformer?
It works on the principle of electromagnetic induction. The transfer of electrical energy from one circuit to another takes place with the help of mutual induction. It is most commonly used to step up or step down the voltage of Electrical Power.
It transfers the electrical power from one place to another without any variation in their frequency. It is also a static device which maintains constant flux throughout its operation.
[ ##eye## Different Parts of transformer and their functions]
What is Instrument Transformer?
In Electrical power system, the level of currents and voltages are very high, therefore the direct measurement of these electrical quantities is not possible practically. In such a case, the instrument transformer is being used to step down the voltage and current within the range of the existing measuring instrument.
- Current Transformer (CT)
- Potential Transformer (PT)
What is Current Transformer?
What are types of current transformer?
- Ring type CT
- Core type CT
- Shell type CT
[ ##eye## Construction
and Working of LVDT]
Why Current transformers are used for measurement?
- To extend the range of the existing measuring instrument (Ammeter).
- To isolate the circuit of measuring instruments from a high voltage line.
What is turns ratio of current transformer?
What is burden on C.T?
The burden of CT is the maximum load (in VA) that can be applied to the secondary of CT. It can be expressed in two ways. The burden is expressed as the total impedance (in ohm) of the circuit. It can also be expressed as total volt-ampere (VA) and power factor at a certain value of voltage or current and frequency.Is current transformer a step-up transformer?
[ ##eye## Power Factor Correction techniques]
What are the basic differences between CT and PT?
- C.T is connected in series with HT line whereas P.T is connected in parallel in HT line.
- In C.T, the no. of turns become inversely proportional to current whereas in P.T no. if turns become directly proportional to the voltage.
- In CT the primary has one or more turns of thick conductor and the secondary has large no of turns of the thin conductor whereas in PT the primary has large no. of turns of thin conductors and secondary has few no. of turns of thick wires.
- C.T is step-up instrument transformer which steps down the current whereas P.T is a step down instrument transformers which step down the voltage up to measuring range.
Why the secondary terminal of CT should not be left open-circuited?
If the secondary winding of CT is kept open then secondary current will be zero while the primary current of CT will remain the same. Therefore the opposing MMF in secondary winding will no longer exist. Hence the net MMF due to primary current only which is very large. This large MMF will produce huge flux in the core of CT. Hence it will saturate the core of CT. Again, due to huge flux in the core, the flux linkage of secondary winding will be large which in turn will produce a very large amount of voltage across the secondary terminal of the CT. Hence the large voltage across the secondary of CT will be very dangerous which will lead to insulation failure. There is a chance that the person who is opening the secondary winding of CT while the primary is energized will die due to electrical shock.
What is knee point voltage of CT?
How to calculate knee point voltage of CT?
[ ##eye## Transformer interview questions with answer]
What are errors in C.T?
- Ratio error:- The ratio error is the amount by which secondary current differs from the exact proportionality of the primary current of CT. It is expressed in percentage of rated secondary current.
- Phase difference error:- The phase difference error is the angle by which the secondary current differs in phase from the primary current of CT. It is expressed in minutes of arc.
At what load the phase angle error of CT will be negative?
If the core of CT is permanently magnetized then how will you demagnetize it?
What is meant by turn compensation?
What materials are used for the core of C.T and why?
What is effect of saturation on performance of C.T?
The increase in excitation current of CT causes the reduction in secondary output which reduces the speed of over-current relays. The saturation of CT also disturbs the balance in differential relays thus affecting the stability of protection. Therefore the effect of saturation makes the operation of CT unsatisfactory.
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