Power System

12 Most asked Interview Questions in Power System

Q-01: What is the full form of KVAR? 

Ans- We know there are three types of power in Electrical as Active, apparent & reactive. So KVAR is stand for ‘Kilo Volt Amps’ with Reactive component.

Q-02: What is the difference between Isolators and  electrical Circuit Breakers?

Ans – Isolators are mainly for switching purpose under normal conditions but they cannot operate in fault conditions .Actually they used for isolating the CBs for maintenance. Whereas CB gets activated under fault conditions according to the fault detected.

Q-03: What is bus-bar?

Ans – Bus bar is nothing but a junction where the power is getting distributed for independent loads.

Q- 04: Which power plant has high load factor?

AnsAll base load power plants have a high load factor. If we use high efficiency power plants to supply the base load,we can reduce the cost of generation. Hydro power plants have a higher efficiency than thermal & nuclear power plants. 

Q- 05: What are HRC fuses and where it is used?

Ans – HRC stand for “high rupturing capacity” fuse and it is used in distribution system for electrical transformers.

Q- 06: Why in a three pin plug the earth pin is thicker and longer than the other pins?

Ans – It depends upon R=ρ l/a where area(a) is inversely proportional to resistance (R), so if (a) increases, R decreases & if R is less the leakage current will take low resistance path so the earth pin should be thicker. It is longer because the The First to make the connection and Last to disconnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.

Q- 07: Where should the lighting Arrester be placed in distribution lines?

Ans – Near distribution transformers and out going feeders of 11kv and incoming feeder of 33kv and near power transformers in sub-stations.

Q- 08: What is the difference between MCB & MCCB, Where it can be used?

Ans – MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit.

MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition.under voltage and under frequency may be inbuilt. Normally it is used where normal current is more than 100A.

Q- 09: What is Ferrantic Effect?

Ans – Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage.

Q- 10: What is SF6 Circuit Breaker?

Ans – SF6 is Sulpher-hexa Flouride gas.. if this gas is used as arc quenching medium in a Circuit breaker means SF6 CB.

Q- 11: What is Boucholz relay and the significance of it in to the transformer?

Ans – Boucholz relay is a device which is used for the protection of transformer from its internal faults, it is a gas based relay. 

Q- 12: What is power factor? whether it should be high or low? why?

A:Power factor is the ratio of true power to apparent power. it has to be ideally 1.

If it is too low then cable over heating & equipment overloading will occur. If it is greater than 1 then load will act as capacitor and starts feeding the source and will cause tripping. 

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