Type of Current Transformer MCQ || Type of Current transformer Questions and Answers

1. According the classification based on technology the type of current transformer are

  1. Protective current transformer
  2. Electromagnetic Current transformer
  3. Opto-electronic transformer
  4. Both 2 and 3

Answer.4. Both 2 and 3

Explanation:

Classification of CTs Based on Technology:

CTs can be broadly classified into the following categories, depending on the technology they use for their construction and operation

  1. Electromagnetic CTs
  2. Opto-electronic CTs
  3. Rogowski Coil

 

2. A ________ is a transformer with separate primary and secondary windings wrapped around a laminated core.

  1. Wound Current Transformer
  2. Window current transformer
  3. Bushing Current transformer
  4. Ring current transformer

Answer.1. Wound Current Transformer

Explanation:

  1. A wound current transformer is a transformer with separate primary and secondary windings wrapped around a laminated core.
  2. For this type of transformer, the primary winding of more than one turn are wound upon the core and provides the primary section of the transformer.
  3. Such primary winding is so designed that it could be able to carry the short-circuit current of the system.
  4. According to the design and turn-ratio requirement, the secondary winding is accordingly wound to provide the required current on the secondary circuit of the system.

 

3. Wound type current transformer can measure the current upto

  1. 50 A
  2. 150 A
  3. 100 A
  4. 200 A

Answer.1. Wound Current Transformer

Explanation:

  1. A wound current transformer is a transformer with separate primary and secondary windings wrapped around a laminated core.
  2. There are designed to measure currents from 1 amp to 100 amps. The wound type provides excellent performance under a wide operating range.
  3. Typically, the wound type is insulated to only 600 volts.

 

4. For Bar Type Current Transformer the primary winding consists of a _______ of suitable size.

  1. Circular Conductor
  2. Bar Conductor
  3. Parallel Conductor
  4. No conductor

Answer.2. Bar Conductor

Explanation:

In Bar Type Current Transformer the primary winding consists of a bar conductor of suitable size and passes from one side of the CT to the other side.

This conductor becomes an integral part of the current transformer. The primary winding is regarded as a conductor of a single primary turn and the secondary winding in the form of a toroid, occupies over the primary conductor, with proper insulation between primary and secondary winding.

 

5. Which current transformer does not have primary winding and insulation

  1. Bushing current transformer
  2. Bar current transformer
  3. Wound current transformer
  4. Ring current transformer

Answer.1. Bushing current transformer

Explanation:

Bushing current transformer is similar to the bar type transformer. But in such type of CT neither any primary winding nor any insulation for such winding is provided. Normally the bushing of the circuit breaker or the power transformer is used as a centrally placed primary winding for such CT.

The necessary winding and the insulation provided over the winding, plays the role of primary part of the CT. Moreover the secondary winding being wound over the bushing primary provides necessary secondary current to the circuit.

 

6. _____ current transformer is used to monitor residual current in the system.

  1. Bushing
  2. Bar
  3. Wound
  4. Core-Balance

Answer.4. Core-Balance

Explanation:

  • Core-Balance Current Transformer  is also similar to the bushing type and bar type CT.
  • The core-balance CT is normally of the ring type, through the centre of which the three-core cable or three single core cables of three phases system is passed.
  • The basic use of such CT is to monitor the residual current in the system.
  • The sensitive earth fault relay is used on the secondary of this CT to operate for the unbalanced current in the system either due to the fault or unbalanced load in the system.
  • Core-balance transformers are normally mounted over a cable at a point near to the cable gland for the electrical equipments.

 

7. Ring type current transformer is also called as _______

  1. Wound Current Transformer
  2. Window current transformer
  3. Bushing Current transformer
  4. Core-balance transformer

Answer.2. Window current transformer

Explanation:

  • Ring type current transformer has no primary winding and looks like a toroidal ring that contains only secondary winding being wound over a core.
  • The open space in the centre allows the active conductor to pass through the CT, i.e., this CT is taken through the primary conductor.
  • This type of CT is also called window type current transformer.
  • This CT has only one core and has only one CTR (current transformation ratio) and is generally used for small voltage rating system.

 

8. _______ current transformer is basically applied to supply the current to the indicating instruments.

  1. Protection CT
  2. Measuring CT
  3. Both 1 and 2
  4. Window CT

Answer.2. Measuring CT

Explanation:

  • Measuring current transformer is basically applied to supply the current to the indicating instruments like ammeters, integrating meters ike wattmeters, energy meters, etc.
  • The windings and design of the cores for this CT are considered on the basis of the requirement of the circuit.
  • Metering circuit needs better accuracy performance, than the knee-point voltage margin.
  • So the windings, that are used for this purpose should have better steady state accuracy factor, as compared to the transient accuracy factor.

 

9. _____  Current Transformer is applied to supply the current to the protective relays in the circuit.

  1. Protection CT
  2. Measuring CT
  3. Both 1 and 2
  4. Window CT

Answer.2. Measuring CT

Explanation:

  • Protection Current Transformer is applied to supply the current to the protective relays in the circuit like current activated relays, power relays and impedance relays, etc.
  • For such transformer, the design of winding and core is considered on the basis of knee point voltage and excitation current at this knee point voltage.
  • The accuracy limit factor of the CT is not that important as compassed to the metering class.
  • But the action and response of this winding for both in transient and steady state condition should be active and ready to take action for operation of the relays in the circuit.

 

10. Dual Purpose Current Transformer is used as ____

  1. Protection CT
  2. Measuring CT
  3. Both 1 and 2
  4. Residual CT

Answer.2. Measuring CT

Explanation:

  • Dual Purpose Current Transformer is used for connection to the secondary having both metering circuit and protection scheme in the system.
  • The design of the winding and core is decided in such a way, so that the accuracy factor renmains within the specification limit for all the stages of current loading on the CT.
  • To maintain such accuracy limit, the relevant factors like design, cost, space and withstanding capability of the instrument (CT) are accordingly considered and becomes more in comparison.

 

11. ______ current transformer is also called transactors.

  1. Dry type
  2. Ring type
  3. Oil Insulated
  4. Air Support

Answer.4. Air Support

Explanation:

Air Support Current Transformer are small current transformers in which a small air gap is included in the core to produce a secondary voltage output proportional in magnitude to current on the primary winding. Sometimes they are termed as “transactors” or “quadrature CT”. Such type of CT is rarely used in main power system circuit, because of its limitations.

 

12. The insulation used in dry type current transformer is

  1. Epoxy Resin
  2. Polycrete
  3. Paper
  4. All of the above

Answer.4. Air Support

Explanation:

  • Dry Type Current Transformer is used for this type of transformer is of solid and dry nature.
  • It does not require the use of any liquid or semi-liquid material as the insulation of the CT.
  • The solid insulation may be of epoxy resin bound material or polycrete type material.
  • But polycrete instruments have better strength in comparison to other solid insulations.
  • For the case of few small voltage rating transformers, paper insulation is also provided as the solid insulation and the range of such class is restricted to 13 kV range.
  • The epoxy resin-filled bound and polycrete instruments have ranges even up to 72 kV class and the performance is well within the satisfactory limit.

 

13. The feature/advantage of  Dry current transformer is

  1. High Mechanical strength
  2. Low Maintenance
  3. Environment Friendly
  4. All of the above

Answer.4. All of the above

Explanation:

Dry current transformer provide the following features.

  1. Compact and solid insulation design.
  2. High mechanical strength.
  3. Excellent outdoor performance under extreme ambient conditions.
  4. Maintenance-free and longer life.
  5. Simplified transport and erection.
  6. Environment-friendly.

 

14. The dielectric strength of  oil in oil insulated current transformer is _____

  1. High
  2. Low
  3. Either high or Low
  4. None of the above

Answer.1. High

Explanation:

In oil insulated current transformer oil is used as the insulation between primary and secondary Winding. In practice high dielectric strength oll-impregnated paper being dried and degassed is used as the insulation material.

The oil is filled over to this paper insulation. Because of this design insulation, it is called paper-oil insulated CT To protect the paper oil insulation from ambient temperature, maximum CIs are hermitically sealed by bellows arrangement.

 

15. CTs designed for mounting inside metal cubicles are known as ______

  1. Insulated Transformer
  2. Outdoor Transformer
  3. Indoor Transformer
  4. Wound Transformer

Answer.1. High

Explanation:

CTs designed for mounting inside metal cubicles are known as indoor CTs. Depending upon the method of insulation, these can be further classiied as (a) tape insulated, and (b) cast resin (epoxy, polyurethene or polycrete).

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