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

1. For voltage above 100 kV a _____  potential transformer is used.

  1. Resistive
  2. Capacitive
  3. Inductive
  4. Normal

Answer.2. Capacitive

Explanation:

For the voltage above 100 kV, the conventional type of potential transformer becomes extremely expensive. For voltage above 100 kV, a capacitor potential transformer is used. It is a combination of a capacitor potential divider and a magnetic potential transformer of a relatively small ratio is used. A magnet potential transformer is also known as an intermediate transformer.

 

2. Electromagnetic type Potential Transformer is also called as ________

  1. High Voltage PT
  2. Low Voltage PT
  3. Medium Voltage PT
  4. Power PT

Answer.1. High Voltage PT

Explanation:

Electromagnetic type Potential Transformer is also called high voltage (HV) PTs and is used for voltages at 100 kV and above. They are very large and costly due to very strict insulation requirements. PTs operating at 110 kV are giants at 7.5 m in height and weigh nearly 5 tonnes.

 

3. Electromagnetic type potential transformer is used upto

  1. 50 kV
  2. 200 kV
  3. 10 kV
  4. 132 kV

Answer.4. 132 kV

Explanation:

Electromagnetic type potential transformer is conveniently used up to 132 kV. It is similar to a conventional wound-type transformer with additional features to minimize errors. As its output is low, it differs from power transforımers in physical size and cooling techniques.

 

4. For lower voltages, up to 3.3 kV _____ type potential transformer is used.

  1. Capacitive
  2. Electromagnetic
  3. Dry
  4. Electrostatic

Answer.1. Dry

Explanation:

For lower voltages, up to 3.3 kV, dry-type potential transformers with varnish impregnated and taped windings are used.

A dry-type transformer is a type of transformer that never uses any insulating liquid where its winding or core are immersed in liquid. Rather, the windings and core are kept within a sealed tank that is pressurized with air.

For higher voltages, oil-immersed VTs are used. Recently VTs with windings impregnated and encapsulated in synthetic resins have been developed for higher voltages. This technique has made it possible to use dry-type VTs for system voltages up to 66 kV.

5. Which type of bushing is used in the potential transformer?

  1. Shell Type
  2. Paper Type
  3. Oil-filled
  4. Varnish type

Answer.3. Oil filled

Explanation:

Oil-filled bushings are used to connect the high voltage potential transformers (above 7KV) to the main lines. The primary winding of a potential transformer has a large number of turns whereas secondary winding has fewer turns.

For oil-filled potential transformers, bushings are also oil-filled to minimize the overall dimensions of the transformer. When neither side of the potential transformer is at ground potential, two bushings are used. But when connected from line to neutral in grounded neutral systems, only one high voltage bushing is provided.

 

6. Outdoor potential transformers type are available in ___

  1. Single Phase
  2. Three Phase
  3. Both single-phase and Three-phase
  4. None of the above

Answer.3. Both single-phase and Three-phase

Explanation:

Outdoor potential transformers types are available in three-phase and single-phase upto 33 KV and are magnetic type. Above 33 kV outdoor potential transformers are single-phase and available in two types: the magnetic type and the capacitor voltage transformer (CVT).

 

7. The coupling capacitor type potential transformer is connected in series with ______

  1. Current Transformer
  2. Magnetic voltage transformer
  3. Auto Transformer
  4. Power Transformer

Answer.2. Magnetic voltage transformer

Explanation:

The coupling capacitor type potential transformer consists of two capacitors made of oil-impregnated paper and aluminum foil. A magnetic voltage transformer is connected in series with an inductance (CI). A damping impedance is provided in the secondary circuit to avoid Ferro-resonance.

 

8. In bushing type potential transformer the _____ type bushings is used.

  1. Condenser
  2. Synchronous
  3. Iron
  4. Non-condenser

Answer.1. Condenser

Explanation:

In bushing type potential transformer the condenser-type bushings can be provided with tapping, which can be used for voltage measurement.

The output voltage is proportional to the line-to-ground system voltage and is in phase with it. The output voltage (by suitable tap) can be 63.5 V or 110V and the burden is 5-30 VA. Therefore, this is used only for voltage indication and synchrocheck. The accuracy is not adequate for revenue metering.

 

9. Indoor potential transformers type are available in ___

  1. Single Phase
  2. Three Phase
  3. Both single-phase and Three-phase
  4. None of the above

Answer.3. Both single phase and Three phase

Explanation:

Indoor potential transformers are the molded, magnetic type, and are available in single-phase or three-phase.  The mounting mechanism can be the draw out or the fixed type (to suit the type of board).

Line side fixed type potential transformers are either directly connected to the outgoing cable or fuses are provided on the transformer body on the primary side. Bus potential transformers can have either fuses or a load break switch and fuses.

 

10. The optoelectronic Voltage transformer is also known as ________

  1. Capacitive transformer
  2. Auto Transformer
  3. Power Transformer
  4. Electronic Transformer

Answer.4. Electronic Transformer

Explanation:

  • The optoelectronic Voltage transformer is also known as an electronic Transformer.
  • The operation of an optoelectronic potential transformer is based on the fact that the voltage difference between the conductor and the ground manifests in an electric field between the two electrodes.
  • The optoelectronics send a circularly polarized light beam that travels through an optical fiber up the column.
  • The light beam passes through three strategically placed Pockels cells on the return path. The circular polarization changes to elliptical polarization as the light passes through a cell.
  • The elliptically polarized lights from each cell are sent back to the opto-electronics at the ground level. The weighted measurements of the change of polarization in the three cells is used to determine the voltage difference between the conductor and the ground.

 

11.  _____ is a type of potential transformer whose primary winding (or windings) is (are) ‘not intended to be earthed’.

  1. Underground
  2. Outdoor
  3. Indoor
  4. Unearthed

Answer.4. Unearthed

Explanation:

Unearthed Voltage Transformer is a potential transformer whose primary winding (or windings) is (are) ‘not intended to be earthed’. In such a potential transformer, the entire primary winding(s), including the terminal(s) is (are) insulated from the ‘Earth’ to a level that corresponds to the system’s rated insulation.

 

12. Medium type voltage Transformer is mainly used in

  1. Indoor only
  2. Outdoor Only
  3. Both indoor and Outdoor
  4. Underground location

Answer.3. Both indoor and Outdoor

Explanation:

  1. The potential transformer in the range of 3.3 to 11 kV is normally indoor type while those for 22 kV and 33 kV may be indoor or outdoor.
  2. Presently, indoor VTs are cast resin or resin encapsulated type; the oil-filled ones being extinct. The manufacturing process is the same as that for CTs for both indoor and outdoor types.
  3. The primary windings are ‘fully’ insulated from both the secondary ones and the core.
  4. Link-type fuses are normally used on both primary and secondary sides.
  5. The VT’s for connection between phases and neutral are ‘single pole’ insulated while those to be connected between two phases must have ‘double pole’ insulation.
  6. The outdoor type VTs are housed inside hollow porcelain insulators and their construction, in principle is the same as that of the HV-PT.

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