This set of Transformers Multiple Choice Questions & Answers (MCQs) focuses on “Voltage Regulation-1”.
a) 33 kV
b) 66 kV
c) 132 kV
d) 00 kV
Explanation: Transmission voltage in power transfer in India (highest) is 750KV AC and these lines are erected by Power Grid Corporation for interstate connections throughout India. However, work on 800KV is in the progress. DC transmission voltage (highest) in India is 600KV.
2. A transformer can have zero voltage regulation at _______
a) Leading power factor
b) Lagging power factor
c) Unity power factor
d) Zero power factor
Explanation: At leading power factor the voltage regulation is given by I*(Rcosφ- Xsinφ). Thus, at a particular condition of angle φ we may get zero voltage regulation. While in lagging power factor case we have + sign in the above formula.
3. What will happen to a given transformer if it made to run at its rated voltage but reduced frequency?
a) Flux density remains unaffected
b) Iron losses are reduced
c) Core flux density is reduced
d) Core flux density is increased
Explanation: E=4.44fNAB is the emf equation for a transformer, now as E is kept constant we can say frequency is inversely proportional to the B value. Thus, as frequency increases we will get less core flux density and vice-versa.
4. In an actual transformer the iron loss remains practically constant from no load to full load because ___________
a) Value of transformation ratio remains constant
b) Permeability of transformer core remains constant
c) Core flux remains practically constant
d) Primary voltage remains constant
Explanation: The reason behind core-iron loss being constant is that hysteresis loss and eddy current loss both are dependent on the magnetic properties of the material which is used in the construction and design of the core of the transformer.
a) Capacitive loading only
b) Inductive loading only
c) Inductive or resistive loading
d) Cannot be determined
Explanation: The sign -ve arises in the voltage regulation calculations when, the load connected to the transformer is leading in the nature. The only condition when we’ll get negative voltage regulation when second term is higher than first term.
6. When will a transformer have regulation closer to zero?
a) On full-load
b) On overload
c) On leading power factor
d) On zero power factor
Explanation: Since voltage regulation of a transformer in the leading loading condition is not additive in nature, at particular power factor in leading we can get zero voltage regulation. While, in lagging condition we’ll get ultimately non-zero VR.
7. A good voltage regulation of a transformer indicates ______________
a) output voltage fluctuation from no load to full load is least
b) output voltage fluctuation with power factor is least
c) difference between primary and secondary voltage is least
d) difference between primary and secondary voltage is maximum
Explanation: Voltage regulation is defined as rise in the voltage when the transformer is thrown off from full load condition to no-load condition. Thus, least voltage regulation means output fluctuations depending on the load are very less.
8. Which of the following acts as a protection against high voltage surges due to lightning and switching?
a) Horn gaps
b) Thermal overload relays
Explanation: Arcing horns in a transformer form a spark gap across the insulator with a lower breakdown voltage than the air path along the insulator surface, so an overvoltage it will cause the air to break down and the arc to form between the arcing horns, diverting it away from the surface of the insulator.
Explanation: When the leading load is connected to the transformer difference of Rcosφ and Xsinφ is multiplied with the current, thus we may get -ve, zero voltage regulations at this condition. That is minimum voltage regulation.
Sanfoundry Global Education & Learning Series – Transformers.
To practice all areas of Transformers, here is complete set of 1000+ Multiple Choice Questions and Answers.