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?**

**[ ##eye## Different
Parts of transformer and their functions]**

##
**What is the Instrument Transformer?**

- Current Transformer (CT)
- Potential Transformer (PT)

##
**What is Current Transformer?**

##
**What are the 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 the turns ratio of current
transformer?**

_{P}/ N

_{S}= I

_{S}/ I

_{P}. A CT of turns ratio 100:5 would mean the primary current of 100 amperes would produce a secondary current of 5 amperes in the Ammeter connected.

## What is the 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?**

##
**What is
the knee point voltage of CT?**

##
**How to calculate the knee point voltage of CT?**

**[ ##eye## Transformer interview questions with answer]**

##
**What
are the 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?**

^{2}with the phase difference error limited to 1.5 to 2⁰. A nickel-iron alloy (Mu-metal) which contains the small amount of copper having the maximum permeability of 80000 at flux density near about 3500 lines/cm

^{2}with phase difference error below 0.5⁰ is also used for the core of CT. As the nickel-iron alloy (Mu-metal) reduces the magnetizing current and core losses up to 10% as compared to corresponding silicon steel material. Hence Nickel-iron alloy is the best suitable material for the core of C.T. where a high degree of accuracy is required.

##
**What is the effect of saturation on the 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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