Electrical Engineering Interview Questions and Answer for MNCs (Written Test/Interview) Company_01

Company_01 Based on Power Plant Engineering 

1) Full Form: 

a) IEEE      : Institute of Electrical and Electronics Engineers

b) SCADA : Supervisory Control and Data Acquisition

c) PLC       : Programmable Logic Controller

d) IEC        : International Electrotechnical Commission

2) Difference between Earthing and Neutral.

Earthing : The primary purpose of earthing (also known as grounding) is to provide a safe path for electrical faults or surges to dissipate into the ground, thereby reducing the risk of electrical shock, fires, and equipment damage.

Neutral : The neutral wire in an electrical system is designed to provide a return path for current from the load back to the source. It ensures that the voltage across electrical devices remains at a safe and consistent level.

3) How we can Change the rotation of  3-phase and 1-phase Induction Motor ?

A) For 3-Phase Induction Motor:

1. Swap Any Two Phase Leads: To change the rotation of a 3-phase motor, you need to interchange any two of the three phase leads. This reversal of the phase sequence will reverse the direction of rotation.

Example: If you have the following connections: A-B-C (clockwise rotation), you can change it to A-C-B (counterclockwise rotation) by swapping phases B and C. 

B) For 1-Phase Induction Motor:

1. Swap Start and Run Windings: 1-phase induction motors have two windings: the start winding and the run winding. To change the rotation of a 1-phase motor, you can swap the connections of either the start winding or the run winding.

Example: If the motor is wired as A-Start and B-Run (clockwise rotation), you can change it to A-Run and B-Start (counterclockwise rotation) by swapping the start and run winding connections.

4) What is the phase angle of Three phase supply.

120 Degree.

5) Faraday's Law of Electromagnetic.

Faraday's First Law : It states that whenever there is a change in magnetic flux associated with a coil, EMF is induced in that coil.

Faraday's Second Law : It states that the magnitude of EMF induced in the coil is directly proportional to the rate of change of magnetic flux associated with that coil.

6) OR and NOR Boolean Expression.

7) What is Residual Voltage Transformer.

In the context of transformers, residual voltage refers to the small amount of voltage that may be present in the secondary winding of a transformer when there is no primary voltage applied. This residual voltage can result from magnetization or remanence in the transformer's core material.

8) Define Slip.

A rotor of a three-phase induction motor rotates at a speed close to the synchronous speed but not equal to the synchronous speed. The difference between the synchronous speed and the rotor speed is known as slip speed. It is given by. Slip speed = Ns - Nr.

9) What is the actual speed of motor if 50Hz frequency, Pole 6, Voltage 440V and %slip 6.

10) What is the secondary voltage if the transformer turns ratio 6% and V1=1200.

Turns Ratio (N2/N1) = (V2/V1)

Given:

- Turns Ratio (N2/N1) = 6

- Primary Voltage (V1) = 1200 volts

Now, rearrange the formula to solve for V2:

                V2 = Turns Ratio (N2/N1) x V1

                V2 = 6 x 1200 volts

                V2 = 7200 volts

So, the secondary voltage (V2) of the transformer is 7200 volts.

11) Difference Between Timer and Counter.

Timers : It count elapsed time from a specific starting point (usually when they are activated) until a predetermined endpoint is reached. 

- They can operate in various modes, such as one-shot (generating a single pulse or delay), periodic (repeating at regular intervals), or pulse width modulation (PWM) for controlling the duty cycle of a signal.

Counters : It increment or decrement a numerical value (count) based on incoming pulses or events. 

- They can count up (increment) or count down (decrement) and can be programmed to reset when a specific count is reached.

12) Define All Day Efficiency of Transformer.

All day efficiency means the power consumed by the transformer throughout the day. It is defined as the ratio of output power to the input power in kWh or Wh of the transformer over 24 hours. Mathematically, it is represented as.

13) Symbol : 

            a) Transformer                        b) Motor                      c) Battery                        d) Earthing

14) How Induction Motor Start.

In an induction motor, the stator winding is fed with an AC supply. This causes the stator winding to develop an alternating flux. We call this rotating flux “Rotating Magnetic Field (RMF).

According to Faraday’s Law of Electromagnetic Induction, the relative speed between the stator RMF and the rotor RMF causes an induced EMF in the rotor conductors. Rotor conductors are short-circuited, and a rotor current is produced due to induced EMF.

This induced current produces alternating flux around it. It should be noted that the stator flux lags behind the rotor flux.

Due to the relative velocity between the rotating stator flux and the rotor, the rotor rotates in the same direction as that of the stator flux to minimize the relative velocity. This is the basic working principle of the induction motor

15) Material Use for slip Ring and Brush.

Copper and Carbon.

16) What is Transposition in Transmission Line.

Transposition in a transmission line refers to the deliberate and systematic swapping or repositioning of the phase conductors (wires or cables) within a multi-conductor transmission line system. The primary purpose of transposition is to balance the electrical and electromagnetic characteristics of the conductors, especially in three-phase transmission lines.

17) Circuit Breaker and Their type.

A circuit breaker is an electrical switching device designed to protect an electrical circuit from damage caused by excessive current or a short circuit. Its primary function is to interrupt or open the circuit when it detects an abnormal current condition, thereby preventing electrical fires, equipment damage, and electrical hazards.

*Low Voltage : 

a) MCB    : Miniature Circuit Breaker

b) MCCB : Molded Case Circuit Breaker

c) RCCB  : Residual Current Circuit Breaker 

*High Voltage : 

a) ACB : Air Circuit Breaker

b) VCB : Vacuum Circuit Breaker

c) SF6 : Sulfur hexafluoride

d) OCB : Oil Circuit Breaker

18) What is the reason of arc formation in Circuit breaker.

Arc formation in a circuit breaker occurs primarily due to the interruption of electric current when the circuit breaker's contacts open. Then, the ionization of air occurs between the two contacts, leading to the formation of an electrical arc.

19) Selection of cable depend on voltage or current? Justify.

In cable selection, both voltage and current are pivotal considerations, and they go hand in hand. Voltage determines the cable's insulation requirements and safety, ensuring that it can handle the electrical potential without breakdown. Current, on the other hand, is essential to size the cable appropriately, preventing overheating and ensuring efficient power transmission. Neglecting either voltage or current can lead to safety hazards, equipment damage, and inefficient electrical systems. Therefore, a thorough assessment of both factors is fundamental in cable selection to ensure safe and reliable electrical installations, complying with industry standards and regulations.

20) Who can justify the which is step up and which one is step down transformer.

Step-up       :  Secondary turns is more than primary turns.

Step-Down :  Primary Turns is more than secondary.

Best Of LUCK.......!