Tuesday, 2 July 2019

Interview Questions Related to Sub-station

Interview Questions Related to Sub-station

Hello guys, in this video i will discuss about interview questions related to sub-station.


Interview Question and Answer

The Engineering Street 


01. What is the importance of sub-stations ?
Ans. Sub-stations are used throughout the electrical power system. Starting with the generating station, a sub-station raises the medium-voltage generated by the alternators to the high-voltage needed to transmit the electrical economically. The high transmission line voltage is again reduced in other sub-stations located close to the power-consuming centres.



02. What is the usual apparatus in a sub-station ?
Ans. A sub-station usually contains the following major apparatus :
a. Transformers
b. Circuit Breaker
c. Horn-gap switches
d. Disconnect switches
e. Grounding switches
f. Surge arresters
g. Current-limiting reactors
h. Instrument transformers



03. What is Circuit Breaker ?
Ans. Circuit Breaker are designed to interrupt either normal or short-circuit currents. They behave like big switches that may be opened or closed either normally or automatically. A circuit breaker will automatically open a circuit whenever the line current exceeds a preset value.



04. Give two principal disadvantages of underground cables ?
Ans. The two principal disadvantages of underground cables are :
a. The capital cost of laying underground cables is very high. Depending upon system voltage, it can be 4 to 8 times that of bare conductor overhead lines.
b. It is true the occurrence of fault in underground cables is very rare. But once it occurs, it is difficult to locate and the repair is expensive.





05. What are the main parts of a distribution system ?
Ans. The main parts of a distribution system are :

a. Secondary sub-station - 33/11KV
b. Primary distribution line (or feeder) - 11KV
c. Distribution sub-station - 11KV/400V
d. Secondary distribution line (or distribution - 400V & 230V.



06. What is the fundamental basis for the selection of conductor size for a feeder ?
Ans. The fundamental basis for the selection of conductor size for a feeder is the current carrying capacity. Voltage drop consideration is not important in a feeder. It is because there are no consumers tapped off from a feeder and the receiving--end voltage can be raised to the desired value.




07. What is the fundamental basis for the selection of conductor size for a distributor ?
Ans. The fundamental basis for the selection of conductor size for a distributor is the voltage drop. It is because according to indian electricity rules, the consumers voltage must be kept within + or - 6% of the declared voltage.




08. What are  low tension cables ?
Ans. The cables rated upto 1100V are called low tension power cables. These are almost invariably PVC cables and find many applications in domestic, commercial and industrial circuits.

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