# Assistant engineer interview questions-8

When the transformer shows the transformer inter trip

Ans:

The inter trip acts when the transformer trips in fault. When the primary breaker tripped on any fault the secondary also tripped immediately and vice versa to protect the transformer.

One an exceptional case is there is breaker trips on over current or earth fault the inter trip will not be enabled.

What will happen if we connect two bulbs is in series with the two phase wire

Ans:

Bulb will be dark because the line to line voltage was same .If we connect the two bulbs in different phase it will bright.

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

Ans:

It depends upon R=ρL/A where area (A) is inversely proportional to resistance (R), so if area (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.

Why humming sound occurred in HT transmission line?

Ans:

This sound is coming due to ionization (breakdown of air into charged particles) of air around transmission conductor. This effect is called as Corona effect, and it is considered as power loss.

Which type of A.C motor is used in the fan?

It is Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

What happen if we give 220 volts dc supply to bulb or tube light?

Ans:

Bulbs or devices for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element.

Why PT is placed before the CT in substation ?

Ans:

To avoid voltage drop

What is the polarity winding

Polarity depends on the entering and leaving of the current. Connect one winding to the supply that time the which terminal the current entering is positive and leaves is negative.

What is the difference between UPS and SMPS?

Ans:

The out put SMPS is DC and output of UPS .The SMPS is switched mod power supply used in computers .The SMPS(Switched Mode Power Supply) input is AC its convert ac to dc .The SMPS also covert the high frequency voltage ac to high frequency low voltage by using the transformer .

In the case UPS (Uninterruptible Power Supply) when there is supply available it gives the direct output and also charge the battery .If the supply is not UPS will invert the DC from battery .

What is the use of NGR in transformer?

NGS is the Neutral Grounding Resistor .its main function to reduce the current during the earth fault.

What is AGC and AVR and which is faster?

Ans:

AGC- Automatic Gain Controller.
AVR- Automatic Voltage Regulation.
AGC will contol the active power by controlling the speed of mechanism by adjusting the inlet valve and blades.
AVR is important part in Synchronous Generators; it controls the output voltage of the generator by controlling its excitation current. Thus it can control the output Reactive Power of the Generator.

What is mean by Hydrothermal scheduling?

Ans:

It is the Scheduling required by the load despatching center to forecast the hydel and thermal generation

Reference

Electrical Notes & Articles

Tony

Hi, Myself Tony George. An Electrical Engineer by Education, a Software Developer by Profession and an Education Blogger by Passion. In the past, I had been working as an Engineer in KSEB. The knowledge that I have acquired I would like to share here with you. I will be happy if these articles can give you a way to your career growth. Feel free to contact me.