Burden of Instrument Transformers MCQ || Burden of Instrument Transformers Questions and Answers

1. The burden of the instrument transformer is considered when instruments are ______

  1. Connected internally
  2. Connected externally
  3. Both 1 and 2
  4. Out of phase

Answer.2. Connected externally

Explanation:

The burden of the instrument transformer is considered to be everything connected externally to its terminals, such as monitoring devices, relays, and pilot wiring. The impedance values of each component, which can be obtained from manufacturer data sheets, should be added algebraically to determine the total load.

 

2. The burden value in Potential Transformer (PT) should be ______ to achieve low errors in PT.

  1. Low
  2. Medium
  3. Infinite
  4. High

Answer.4. High

Explanation:

The burden is the greatest VA load at which the PT will operate contınuously without Overheating its windings beyond the permissible limits. . Burden must be high of a potential transformer to achieve low errors.

 

3. The potential transformer is always a ______

  1. Step-up transformer
  2. Step-down transformer
  3. Auto-transformer
  4. Power Transformer

Answer.2. Step-down transformer

Explanation:

The Primary winding of the potential transformer consists of large numbers of turns while the secondary has less number of turns. The primary is connected across the high voltage line while the secondary is connected to the low range voltmeter coil. The potential transformer is always a step-down transformer.

 

4. The Burden of protective Current Transformer (CT) is specified in

  1. Percentage of load current
  2. Percentage Ratio error
  3. Volt-Ampere
  4. Percentage Phase error

Answer.3. Volt-Ampere

Explanation:

  • The burden of CT is the maximum load (in VA) that can be applied to the CT secondary.
  • The burden can be expressed in two ways.
  • The burden can be expressed as the total impedance in ohms of the circuit or the total volt-amperes (VA) and power factor at a specified value of current or voltage and frequency.

 

5. The potential transformer is always a ______

  1. Step-up transformer
  2. Step-down transformer
  3. Auto-transformer
  4. Power Transformer

Answer.2. Step-down transformer

Explanation:

In the current transformer, the primary winding of the transformer is connected in series with the line carrying a high current. The secondary of the transformer is made up of a large number of turns of fine wire having a small cross-section area. This transformer is basically a step-up transformer, it’s step-up a voltage from primary to secondary. Thus it reduces current from primary to secondary.

 

6. The ratio of transformation in the case of potential transformers

  1. Increases with increases in power factor of secondary burden
  2. Remains constant irrespective of the power of secondary burden
  3. Decreases with increases in power factor of Secondary burden
  4. None of the above

Answer.3. Decreases with increases in power factor of Secondary burden

Explanation:

The burden across the secondary of an instrument transformer is specified as V2/I2

The ratio of transformation in the case of potential transformers decreases with increases in power factor of Secondary burden.

 

7. If the secondary burden of potential transformer  increases, the secondary current will ______

  1. Decrease
  2. Increase
  3. Remain Same
  4. Become Negative

Answer.2. Increase

Explanation:

If the secondary burden of the potential transformer increases, the secondary current will increase proportionately, and therefore, the primary current will also increase causing both the primary and secondary voltage drops to increase.

 

8. An ammeter of 0.1 Ω resistance is connected across the secondary of a 400 / 5A current transformer (CT). The CT burden is

  1. 0.5 VA
  2. 2.5 VA
  3. 5.0 VA
  4. 25 VA

Answer.2. 2.5 VA

Explanation:

Given that

Rs = 0.1 Ω, Is = 5 A

Vs = Secondary voltage of CT.

Rs = Ammeter resistance which is connected in the CT secondary

Is = CT rated secondary current

Secondary voltage of CT = CT rated secondary current x Ammeter resistance which is connected in the CT secondary

Vs = Is × Rs

= 5 × 0.1

⇒ Vs = 0.5 V.

CT burden = CT rated secondary current x CT secondary Voltage

= 5 × 0.5

 = 2.5 VA

 

9. If the secondary burden of a current transformer is 20 VA, and the secondary current is 8 A, the impedance of the connected load will be

  1. 0.50 ohms
  2. 0.25 ohm
  3. 0.13 ohms
  4. 0.31 ohms

Answer.4. 0.31 ohms

Explanation:

Secondary burden of a C.T. = I2R

⇒ (8)2(R) = 20

⇒ R = 0.3125 Ω

 

10. What are the advantages of instrument transformers?

  1. Cheap
  2. High voltage insulation is not required
  3. Low power consumption
  4. All of the above

Answer.4. All of the above

Explanation:

Advantages of Instrument Trasnformer

  1. A single range instrument can be used for the measurement of currents or voltages of various ranges simply by using a multi-range current or voltage transformer or several single-range transformers.
  2. When the measurement is to be done on a high-tension circuit (transmission line), the instrument can be located at some distance from the circuit, thus giving great safety to the control room operator.
  3. As the measuring instrument is isolated from a high-tension circuit, it need not be insulated for high voltage.
  4. With the help of a current transformer with a suitably split and hinged core, the current in a heavy current bus bar can be measured without breaking the current circuit. T
  5. When a.c. indicating instruments are used in conjunction with instrument transformer, their readings do not depend upon their constants viz. R, L, and C as is the case with shunts and multipliers.
  6. It is a very cheap and moderate rating instrument that can be used to measure large currents and high voltages.
  7. There is low power consumption in the metering circuit.
  8. With the standardization of C.T. and P.T. secondary winding ratings, it is possible to standardize instruments around these ratings and, therefore, there is a great reduction in the costs of instrument transformers and instruments.
  9. Replacement of instruments is easy on account of the standardization of the ratings.
  10. Several instruments can be operated from a single instrument transformer.

 

11. Which of the following are the main disadvantages of an Instrument transformer?

  1. High power consumption
  2. Can be used only for AC circuit
  3. Very Expensive
  4. All of the above

Answer.2. Can be used only for AC

Explanation:

The only disadvantage of these instrument transformers is that they can be used only for a.c. circuits and not for d.c. circuits.

 

12. Which of the following are applications of instrument transformers?

  1. Range extension
  2. Isolate measuring Instrument
  3. Used for routing Measurement
  4. All of the above

Answer.4. All of the above

Explanation:

Applications of Instrument Transformers

  1. Extend the range of the a.c. measuring instrument (similar to that of the multiplier used to extend the range of a d.c. meter).
  2. Isolate the measuring instrument from the high-voltage power line.
  3. Widely used for very precise measurements as well as routine measurements.

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