Electrical Interview Questions & Answers

Electrical engineering includes an extensive range of sub-fields like electronics, computers, control systems, digital computers, power, robotics, instrumentation, telecommunications, radio, signal processing & microelectronics. In electrical engineering, there are a lot of jobs like control electrical engineer, assistant engineer, trainee mechanical, room operator, junior engineer maintenance, electrical design engineer, etc. An electrical engineering company asks a lot of interview questions in the technical round. So one should brush up and update their technical knowledge by knowing the latest updates in the electrical field by knowing Interview Questions on Electrical. Here we have listed some of the interview questions on electrical engineering with answers that may be asked in a job interview.

Electrical Interview Questions and Answers

The following interview questions on electrical with answers are very helpful for electrical students to clear the technical round in an interview. These electrical interview questions are collected from different fields in electrical engineering.

1). What is electricity?

A). A type of energy that can be caused through electric charge whether in motion otherwise static.

2). What are the different types of electricity?

A). There are two types like static and current electricity.

3). What is static electricity?

A). Static electricity can be defined as an electric charge imbalance on the material or on the material surface. This charge stays until it is freely flowing away through electric current otherwise electrical discharge.

4). What is current electricity?

A). Current electricity can be defined as when the electricity is in motion because of the electrons flow in a conductor.

5). What are the different kinds of current electricity?

A). There are two types such as DC (Direct current) & AC (Alternating current).

6). What are the different methods of producing electricity?

A) The methods are –

• By means of frictions- Static electricity is produced.
• By means of chemical action in cells and batteries.
• By means of mechanical driving- The generator produces electricity in two dissimilar methods.
• By means of heat – Thermal electricity is produced.
• By means of lighting effect – Electricity is produced in a photoelectric cell.

7). What are the sources of electricity?

A). Battery, Generator, and Thermocouple.

8). What are the applications of electricity?

A). Heating, Lighting, Welding, Running of Motors, Battery charging, Electroplating, Relays, telephones, Electronic Equipment, etc.

9). What are the effects of electricity?

A). The physiological effect, Heating effect, Magnetic effect, Chemical effect, and X-Ray effect.

10). What are A.C. and D.C.?

A). A.C is an alternating current that flows in the alternate direction whereas D.C. is a direct current that flows only in one direction.

11). Where is D.C. used?

A). Battery charging, Electroplating, Electrolysis, Relays, traction motors, Cinema projector.

12). Where is A.C. used?

A) Household appliances, Fan, Refrigerators, Power driving motors. Radio and T.V, etc.

13). How will you judge whether the supply is A.C. or D.C. on-premises?

A). By checking the connection of a fan & tube light.

14. What is a conductor?

A). The conductor is a metallic substance that has a number of free electrons and offers less resistance to the electricity flow through them.

15). What is an insulator?

A). The insulator is a nonmetallic substance which has comparatively less free electrons & offers huge resistance that they do not let electricity practically to supply through them.

16). What materials are normally used like conductors?

A). They are Copper, Aluminium, Brass, Iron, Phosphor Bronze, Silver, Zinc, Tungsten, Nickel, etc.

17). What materials are normally used like insulators?

A). Mica, Oil impregnated paper, Vulcanised rubber, Glass, Bakelite, Porcelain, Varnished Cotton, Wood, etc.

18). What term is used in comparing the materials of insulation?

A). Dielectric Strength.

19). What is “Dielectric strength”?

A). Dielectric strength is the highest kilovolts per millimeter which an insulating medium can withstand without breakdown.

20. What are the factors on which the dielectric strength depends?

A). The dielectric strength depends on the following factors

• The thickness of the specimen,
• Size and shape of electrodes used in applying stress,
• Form or distribution of the field of electric stress in the material,
• Frequency of the applied voltage,
• Rate and duration of voltage application,
• Fatigue with repeated voltage application,
• Temperature,
• Moisture content and
• Possible chemical changes under stress.

21). What is a System?

A). When a number of elements are connected in a series to execute a specific function, the group of elements will make a System

22). What is a Control System?

A). The inputs & outputs are interrelated within a System in such a way that the o/p quantity otherwise variable can be controlled through input quantity is known as Control System. The input quantity is an excitation whereas the output quantity is a response.

23). What is the feedback in Control System?

A).  The Feedback in Control System in one in which the o/p is sampled & the proportional signal is given to the input like feedback for automatic error correction to get back the required output.

24). Why Negative Feedback is preferred in the Control System?

A). The Feedback role in the control system is to get back the sampled output from the input & evaluate the output signal through the input signal for error. This feedback will result in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems, negative feedback is considered.

25). What is the effect of positive feedback on the stability of the system?

A). Positive feedback is not used generally in the control system because it increases the error signal and drives the system to instability. But positive feedbacks are used in minor loop control systems to amplify certain internal signals and parameters

26). What is Latching current?

A). When the Gate signal is applied to the thyristor for activating in safe mode. Once the thyristor gets start conducting then the forward current above the minimum value is known as latching current. So to keep the thyristor ON, the gate signal is not required for longer.

27). What is holding current?

A). When SCR is conducting current in forwarding conduction state, SCR will return to forward blocking state when the anode current or forward current falls below a low level called Holding current

Note: Latching current & Holding current is not similar. Latching current can be associated by activating the SCR whereas holding current can be associated with the turn-off process. Generally, the holding current will be slightly lesser than the latching current.

28). Why thyristor is considered as a Charge controlled device?

A). During the thyristor triggering process from forward blocking state to conduction state using the gate signal, the minority carrier density will increase within the P-layer & thus facilitate the reverse break over the J2 junction and the thyristor starts conducting. When the gate current pulse magnitude is higher, then the required time to inject the charge & activating the SCR. When the sum of charge is controlled then the time taken to run On the SCR will be controlled.

29). What are the different losses that occur in thyristor while operating?

A). Different losses that occur are

• Forward conduction losses during conduction of the thyristor
• Loss due to leakage current during forward and reverse blocking.
• Power loss at gate or Gate triggering loss.
• Switching losses at turn-on and turn-off.

30). What is meant by knee point voltage?

A). Knee point voltage is an essential factor to select a current transformer. The knee point voltage is the voltage where a current transformer gets saturated.

31). What is a reverse power relay?

A). A reverse power relay is used for protecting the generating stations. These stations provide power to the grid when generating units are not available, because there is no generation within the plant so the plant uses the power from the power grid. A reverse power relay can be used to stop the power flow from the grid toward the generator.

32). When the DC supply is provided to the primary of a transformer then what will happen?

A). The transformer includes less resistance and high inductance. When the DC supply is given, then there is only resistance but there is no inductance in the electrical circuit. So, the flow of electrical current will be there on the primary transformer, so due to this reason, the insulation and coil will burn out.

33). What is the main difference between isolators & electrical circuit breakers? What is the bus-bar?

A). The isolator is mainly used for switching purposes in normal conditions. However, they cannot work in fault conditions. Generally, these are used for isolating the circuit breakers for maintenance. Circuit breakers will be activated in fault conditions based on the fault detected. The bus bar is nothing but a junction where the power is getting distributed for independent loads.

34). What are the benefits of the freewheeling diode within a Full Wave rectifier?

A). This diode will reduce the harmonics, sparking & arching across the mechanical switch so that the voltage spike can be reduced in an inductive load.

35). What are the different methods to start an induction motor?

A). The various methods to start an induction motor are

• DOL: direct online starter
• Star delta starter
• Autotransformer starterfcircuit
• Resistance starter
• Series reactor starter

36). At no-load condition, what is the PF (power factor) of an alternator?

A). At no-load condition, the alternator is accountable to create angle difference. So the PF must be zero lagging similar to an inductor.

37). What is the main role of anti-pumping within the circuit breaker?

A). When the circuit breaker is closed by using the push button, then an anti-pumping contactor prevents the breaker by closing the push button.

38). What is a stepper motor & its uses?

A). The Stepper Motor is the electrical machine which runs in steps in either direction instead of running in a complete cycle once the input pulse is applied. So, it is used in automation parts.

39). In a Transformer and an induction machine, which device has a maximum load current? and why?

A). The motor has max load current as compared with the transformer because the motor uses real power & the transformer generates the working flux & it is not consuming. Hence the load current within the transformer is due to core loss so it is less.

40). What is SF6 Circuit Breaker?

A). SF6 is Sulpher Hexa Fluoride gas, which is used as an arc quenching medium within a Circuit breaker.

41). What is the frantic effect?

A). The output voltage is higher as compared with the input voltage otherwise the receiving end voltage is higher compared with the sending end voltage.

42). What is the insulation voltage within cables?

A). It is the property of a cable by virtue of it can withstand the applied voltage without rupturing it is known as the insulation level of the cable.

43). What is the difference between MCB & MCCB, Where it can be used?

A).MCB (miniature circuit breaker) is thermal operated & used for short circuit protection in a small current rating circuit. MCCB (molded case circuit breaker) is thermal operated used for overload current & magnetic operation for an instant trip within short circuit conditions. It can be designed under-voltage & under frequency. Normally, it is used wherever the normal current is maximum than 100A.

44). In distribution lines, where should the lighting arrestor is arranged?

A). The lightning arrestor is arranged Near distribution transformers, outgoing feeders of 11kv, incoming feeder of 33kv & near power transformers within sub-stations.

45). What is the IDMT relay?

A). It is an inverse definite minimum time relay where its operating is inversely proportional & also a characteristic of minimum time once this relay works. Once the magnitude of fault current increases then tripping time will be decreased.

46). What are the losses in a transformer?

A). Transformer losses are two types like copper loss and magnetic loss. Copper loss can be caused due to the resistance of the wire (I2R) whereas the magnetic loss can be caused due to the eddy currents as well as hysteresis within the core. Copper loss is stable once the coil has been wound & thus a measurable loss. Hysteresis loss is constant for a particular voltage & current. Eddy-current loss is dissimilar for eery frequency flow through the transformer.

47). What is the full form of KVAR?

A).KVAR stands for Kilo Volt Amps with a Reactive component.

48). Two bulbs of 100w & 40w are connected in series across a 230v supply, then which bulb will glow bright and why?

A). When two bulbs are connected in series then they will get an equivalent amount of electrical current however when the supply voltage is stable across the bulb (P=V^2/R). So the 40W bulb resistance is higher & the voltage across this is more so the 40W bulb will glow brighter.

49). Why in bus bars & isolators, the temperature rise is conducted?

A). These are rated for continuous supply, which means they use heavy currents to increase their temperature. So it is required to test the device for temperature rise.

50). What is the difference between the synchronous & asynchronous generator?

A). The synchronous generator provides both active & reactive power whereas the asynchronous generator provides simply active power & observes reactive power to magnetize. This kind of generator is mainly used in windmills.

51). What is the AVR (Automatic Voltage regulator)?

A). The term AVR stands for the Automatic Voltage Regulator, which is an essential part of Synchronous Generators. It is used to control the o/p voltage of the generator through controlling its excitation current. Therefore,  it controls the generator’s o/p Reactive Power.

52). Difference between a four-point starter & three-point starter?

A). The shunt connection of the 4-point stator can be provided separately using the line whereas in the 3-point stator, it is connected through a line which is the disadvantage of 3-point stater

53). Why does the capacitor work on only AC?

A). Generally, the capacitor provides infinite resistance to dc components & allows the AC components to flow through it.

55). What is a 2 phase motor?

A). A two-phase motor that has the starting winding & the running winding with a phase split. In a servo motor, the auxiliary winding & the control winding includes a 90 degrees phase split.

56). What is the motor principle?

A). Once a current-carrying conductor is arranged within a magnetic field, then it generates the movement of turning or twist is known as torque.

57). What is the armature reaction?

A). The effect of flux from armature to the main is known as armature reaction. This flux gives support to the main flux otherwise opposes the main flux.

58). What is MARX CIRCUIT?

A). Marx circuit is used along with generators to charge the number of capacitors in parallel & discharge them in series. This circuit is used whenever the voltage necessary to test is maximum as compared with available voltage.

60). What are the benefits of speed control using thyristor?

A). Fast Switching Characteristics than MOSFET, BJT, IGBT, Low cost, Higher Accurate.

61). What is ACSR cable and where we use it?

A). ACSR stands for Aluminum conductor steel reinforced, which is used in transmission as well as distribution.

62). What is the difference between UPS & inverter?

A). UPS is mainly used for backup in less time and these are two types like online & offline. Online ups have high voltage and amp for a long time backup using high dc voltage. UPS work with 12v dc & 7 amp. Whereas the inverter works with 12v & 24v dc – 36v dc & 120amp – 180amp battery by long time backup.

63). What will happen once the PF (power factor) is leading in the distribution of power?

A). If there is a high power factor, then

• Losses within the heat form will be decreased.
• Cable becomes less bulky, simple to carry & less cost to afford
• It decreases the overheating in transformers.

64). What are the benefits of a star-delta starter using an induction motor?

A). The main benefit of using the star delta starter is a current reduction when the motor starts. The starting current can be decreased to 3 to 4 times of Direct online starting current. So, the starting current can be decreased; the voltage reduction will be there throughout the motor starting within systems are decreased.

65). Why delta-star Transformers are applicable for Lighting Loads?

A). The neutral conductor is essential in lighting loads & therefore the secondary should be star winding. This kind of lighting load is unbalanced always within all 3-phases. So to decrease the current unbalance within the primary, this connection is used in the primary.

66). In the HT transmission line, why computer humming sound occurred?

A). The sound of computer humming occurs because of the ionization of air in the region of the transmission conductor. So this kind of effect is also known as the Corona effect & it is considered as a power loss.

67). What is rated speed?

A). The rated speed is nothing but when the motor uses normal current, then the motor speed is known as rated speed. This speed is used where the system uses a small current to generate maximum efficiency.

Thus, this is all about job interview questions on electrical. These interview questions on electrical are very useful for electrical graduates to clear the technical round for an interview.