Transformer Principles Questions and Answers For Engineering Students and Workers

QUESTIONS:

1. What is the difference between the primary and the secondary of a transformer?
2. What is an oil-immersed transformer?
3. What is a transformer?
4. What factors affect the amount of induced electromotive force emf in a transformer?
5. Why is oil used in a transformer?
6. Is it possible to connect two single-phase transformers to secure a three-phase output from a three-phase input?
7. What is an air-core transformer?
8. What are eddy currents?
9. What means can be taken to keep eddy currents at a minimum?
10. Is hysteresis objectionable?
11. Are transformers normally considered to be efficient devices?
12. What factors constitute the major losses produced in transformers?
13. There are two basic types of transformers. What are they?
14. Is there a definite relationship between the number of turns and voltages in transformers?
15. What are instrument transformers?
16. Ordinarily, what is the phase relationship between the primary and secondary voltages of a transformer?
17. Is it possible to have the primary and secondary of a transformer in phase?
18. How are the leads of a transformer marked, according to ANSI (American National Standards Institute)?
19. What is mutual inductance?
20. What is a booster transformer?

ANSWERS:

1. The primary of the transformer is the input side of the transformer and the secondary is the output side of the transformer. On a step-down transformer, the high-voltage side is the primary and the low-voltage side is the secondary; on a step-up transformer, the opposite is true
2. The core and coils are immersed in a high-grade mineral oil, which has high dielectric qualities.
3. A device that transforms electrical energy from one or more circuits to one or more other circuits at the same frequency but usually at a different voltage and current. It consists of a core of soft-iron laminations surrounded by coils of copper-insulated wire.
4. The strength of the magnetic field, the speed at which the conductors are cut by the magnetic field, and the number of turns of wire being cut by the magnetic field.
5. To increase the dielectric strength of the insulation, to keep down the possibility of arcing between coils, and to dissipate heat to the outer case so that the transformer can carry heavier loads without excessive overheating.
6. Yes, they would have to be connected in an open delta.
7. A transformer that does not contain oil or other dielectric
compositions but is insulated entirely by the winding insulations and air.
8. Circulating currents induced in conductive materials (usually
the iron cores of transformers or coils) by varying magnetic
fields.
9. The iron used in the core of an alternation-current transformer
is laminated, or made up of thin sheets or strips of iron,
so that eddy currents will circulate only in limited areas.
10. Yes, it is a loss and affects the efficiency of transformers.
11. Yes, they have one of the highest efficiencies of any electrical device.
12. Power loss of the copper I2R losses, eddy currents, and hysteresis losses.
13. The isolation type, in which the two windings are physically isolated and electrically insulated from each other, and the autotransformer type, in which there is only one coil with a tap or taps taken off it to secure other voltages the primary is part of the secondary and the secondary is part of the primary.
14. Yes, the voltage varies in exact proportion to the number of turns connected in series in each winding.
15. In the measurement of current, voltage, or kilowatt-hours on systems with high voltage or high current, it is necessary to use a device known as an instrument transformer, which reproduces in its secondary circuit the primary current or voltage while preserving the phase relationship to measure or record at lower voltages
or lower amperages, and then to use a constant to multiply the readings to obtain the actual values of voltage or current. Current transformers CTs are used to measure the current, and potential transformers PTs are used to register the potential.
16. They are 180º out of phase.
17. Yes, by changing the connections on one side of the transformer.
18. The high side of the transformer is marked H1, H2, etc. The low side of the transformer is marked X1, X2, etc.
19. The linkage of flux between two coils or conductors, caused by the current flowing within one or both of the coils or conductors.
20. A transformer arrangement that is often used toward the end of a power line in order to raise the voltage to its desired value. These are often called “Buck-boost” transformers.