Ans: The HV side of the transformer must be able to withstand the voltage of the line in which it is to be connected, the LV side must have a Voltage of approximately the value by which the line voltage is to be boosted up, and the low voltage side must also have carrying capacity that is sufficient to carry the line current.
2. What special precaution must be taken when using a booster transformer ?
Ans: There must
be no fuse on the HV side , or primary side ; since the booster transformer is similar to a current transformer, if the fuse should blow, Very high voltage produced on secondary side of booster transformer.
3. How are CT's rated ?
Ans: CT's are rated as 100/5 or 50/5 A. the first number is the total current that the CT is supposed to handle, and the second number is the current on the secondary when the full load current is flowing through the primary.
4. What is the general safety practice in use of instrument transformers ?
Ans: The secondary circuit (one side of secondary winding) should be earthed so that potential of the instrument never rise above that of the secondary voltage.
5. What is mean by rated burden of an instrument transformer ?
Ans: The amount of power in volt amperes which an instrument transformer handles at maximum loading is called the rated burden of the instrument transformer.
6. What is the usual secondary ratting of a PT ?
Ans: 110 V
7. How ratio error is compensated in case of a PT ?
Ans: Ratio error in case of a PT can be compensated for by increasing the turns on the secondary by appropriate small amount.
8. How is a transformer rated ?
Ans: A transformer is specified by its KVA(or MVA) output , voltage (primary/secondary) and frequency rating.
9. How does Transformer oil appear when it is new ?
Ans: The transformer oil appear clear light colour with faint characteristic smell.
10. What change will occurs in color of silica gel crystals when they absorb moisture from atmosphere.
Ans: The color of silicagel crystal changes from blue to pink when they absorb moisture from atmosphere.
11. A 2 winding transformer is used to stepdown the voltage from 220V to 110V. If an auto transformer is used for the same purpose, what would be the ratio of copper weights in them ?
Ans: 0.5
12. What is use of Potential transformer ?
Ans: The potential transformers are used for measurement of High voltages by means of low range voltmeters or for energizing the potential coils of watt meters and energy meters. These are also used for energizing relays and other protective devices.
Potential transformer operates on the same potential as a power transformer. Both Primary and secondary winding are wound on a high grade steel - low voltage winding is kept next to the earth core and the high voltage winding is on the outside. The potential transformers are always step down transformers, since they are meant for reducing the voltage to a reasonable operating value.