TRANSFORMERS EXAM

1. Transformers are used extensively for AC power transmissions and for various control and indication circuits.

2. The ratio between the primary and secondary impedances is referred to as the impedance ratio.

3. In a delta connection, all three phases are connected in series.

4. In a wye connection, three common ends of each phase are connected together at a common terminal, and the other three ends are connected to a three-phase line.

5. If the secondary of a transformer has no load, the primary has high current.

6. Core losses are caused by two factors:

7. Copper loss is power lost in the primary and secondary windings of a transformer due to the ohmic resistance of the windings.

8. In the delta connection, all three phases are connected in series to form a closed loop.

9. The current in the windings of a transformer is directly proportional to the voltage in the windings.

10. The voltage of the windings in a transformer is directly proportional to the number of turns on the coils.

11. The ratio of primary voltage to secondary voltage is known as the voltage ratio.

12. The coil of a transformer that is energized from an AC source is called the secondary winding , and the coil that delivers this AC to the load is called the primary winding.

13. A transformer works on the principle that energy can be transferred by magnetic induction from one set of coils to another set by means of a varying magnetic flux.

14. Efficiency of a transformer is the ratio of the output power to the input power .

15. Maximum power is transferred from one circuit to another through a transformer when the impedances are unequal.

16. The turns ratio is defined as the ratio of turns of wire in the primary winding to the number of turns of wire in the secondary winding.

17. Transformers are constructed so that their characteristics match the application for which they are intended.

18. Electronics or power transformers are sometimes considered to be those with ratings of                 volt-amperes and below.

19. Some commonly used methods of cooling distribution transformers are using oil or some other heat-conducting material.

20. The auto transformer is generally used in low power applications where a variable current is required.

21. Isolation transformers are normally low power transformers used to isolate noise from or to ground electronic circuits.

22. Control transformers are generally used in circuits that require constant voltage or constant current with a low power or volt-amp rating.

23. Instrument potential and instrument current transformers are used for operation of instruments such as ammeters, voltmeters, watt meters, and relays used for various protective purposes.

24. A current transformer should always be short-circuited when not connected to an external load.