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Electrical and Electronic Engineering Interview Questions
1 .
What is the difference between generator and alternator?
Both generator and alternator work on the same principle they convert mechanical energy into electrical energy.

Generator : It converts induced emf (Electro Motive Force) into direct current, where it based on stationary magnetic field and revolving conductor which rolls on the armatures with slip rings and brushes riding against each other.

Alternator : It has rotating magnetic and stationary armature for high voltage and stationary magnetic field and a rotating armature for low voltage
2 .
What do you understand by the RLC current?
RLC stands for Resistor (R), Inductor (which is denoted by L), and Current (C). The word RLC is made of three elements of the circuit which are Resistor (R), Inductor (L), and Current (C). This circuit can provide direct current flowing throughout the circuit.

This ability is characterized by a differential equation of the second order. That's why it is also known as a second-order circuit.
3 .
What do you understand by the term electrical engineering? What are its different applications?
Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics, and electromagnetism.

* Electrical engineering generally deals with high voltage, especially AC above the range of 110 or 220V.

* Electrical machines, components, and devices use alternating current (AC) / Voltages and tend to be larger and require 230V (In UK) and 110V (In the US) single-phase ac voltages.

* In industries and power stations, it may require up to 11kV, and for transmission, it may be higher than 400kV.
The different applications of electrical engineering are as follows :

* Electrical Power Systems
* Electrical Control Systems
* Diodes, Rectifiers, and Transformers
* Digital Circuits
* AC and DC Motors
* AC and DC Generators
* Instrumentation Systems
* Communication Systems
* Digital and Analog Electronics etc.
4 .
What are the different colors on wires indicates?
Black wire : This wire is used for power supply in all circuits. Any circuits with this color is considered hot or live. It is never used for a neutral or ground wire.

Red wire : This color wire is a secondary live wire in a 220 volt circuit and used in some types of interconnection. You can join the red wire to another red wire or to a black wire

Blue and Yellow wire : These wires are also used to carry power but are not wiring the outlets for common plug-in electrical devices. They are used for the live wire pulled through the conduct. You will see yellow wire in the fan, structure lights, and switched outlets.

White and Gray : This color wire is used as a neutral wire. It carries the current (unbalanced load) to the ground. You can join white and gray only to other white and gray wires

Green : It is connected to the grounding terminal in an outlet box and run from the outlet box to the ground bus bar within an electric panel
5 .
Define the principle of motors?
The principle of an electric motor is situated on a conductor that carries current and produces a magnetic field surrounding it. The placement of a conductor perpendicular to a magnetic field leads to rotatory movements (known as torque).
6 .
What are the primary responsibilities of an electrical engineer?
The primary responsibilities of an electrical engineer are to create, design, test, and observe the electrical components of a project.

This is a vast field, and projects within this field can vary from manufacturing products to designing power grids. Due to its vast field, the responsibilities can vary from position to position.

The key responsibilities of an electrical engineer are as follows :

* Fixing and troubleshooting electronic devices.
* Conducting the functionality tests.
* Analyzing current trends and information.
* Developing manufacturing processes for building and assembling electrical components etc.
7 .
What are the critical skills required to become an electrical engineer?
The main task of an electrical engineer is to take care of the components of the electrical system. To prevent and troubleshoot such failures, a skilled electrical engineer must do the following things :

* Analyze data to get top trends.
* Communicate clearly with supervisors and clients to get the decision efficiently.
* Keep up to date on emerging trends within the industry.
* Adhere to strict safety codes.
* Work in tandem with supervisors and management.
8 .
What are the fundamental components of electrical circuits?
Following are the fundamental components of electrical circuits :

Active Circuits : Active Circuits are the elements used to generate energy from within their system as a form of source.

Passive Circuits : Passive circuits are the elements that allow the electric current to pass through it and do not generate any energy from it.

AC or DC Circuits : AC stands for Alternating Current, and DC stands for Direct Current. AC always produces some fluctuating current, whereas DC always produces a stable current in a constant source.

Series Circuits : When the electrical components are connected in series within a circuit, it is known as a series circuit.

Parallel Circuits : When the electrical components are connected in parallel within a circuit, it is known as a parallel circuit.
9 .
What are the Different kind of Cables Used for Transmissions?
Cables are categorized into three forms according to its thermal capacity

Low tension cables : Transmits voltage upto 1000 volts

High tension cables : Transmits voltage up to 23000 volts

Super tension cables : Transmits voltage up to 66kv to 132kv
10 .
What is the difference between the term Capacitance and Inductance?
Difference between Capacitance and Inductance :

Capacitance : The term capacitance can be specified as an amount of charge stored inside a capacitor at a specifically given voltage.

Inductance : Inductance is the property of a coil to resist any changes in the electric current flowing through it. Mutual inductance happens when a secondary coil opposes the current change in the primary coil.
11 .
Define electrical engineering and explain its applications
Electrical engineers who want to join your organization should know that electrical engineering deals with electrical circuits, the application of electrical elements and electricity, and electromagnetism.

Interviewees should know that the field deals with alternating current, high voltage, and current in different industries.
12 .
Explain Norten's theorem in one or two sentences.
Norton's theorem is the most famous electrical engineering theorem and is widely used by engineers in every sector.

Example : “Norten's theorem states that regardless of the complexity of a circuit, you can simplify it into an equivalent linear circuit with a parallel resistance connected to a load and single current source."
13 .
Give two reasons that may cause a transformer humming.
* One reason could be the magnetostriction effect of alternating currents that flow through the coil of the transformer.

* Another reason could be the breaking of the core adhesive part and laminated layers.
14 .
Can you change a 35 V 100 microfarad capacitor with a 50 V 100 microfarad capacitor?
No, you cannot change a 35V 100 microfarad capacitor with a 50V 100 microfarad capacitor. It's because the voltage written on a capacitor shows the highest voltage a capacitor can bear
15 .
What would happen when two positively charged materials are placed together?
As we know that the positives repel and opposites attract. So, if you place two positively charged materials next to each other, the two materials will repel and move away.
16 .
What is the difference between a Capacitor, Resistor, and Inductor?
Capacitor : A capacitor is an electrical component that opposes the current flow and acts as a passive element. It also stores some form of electrical charge when a potential is applied.

Resistor : A resistor is an electrical component that opposes the flow of current. It is a two-terminal component and is mainly used to reduce the flow of current.

Inductor : An inductor is an electrical component used to build electrical circuits and store the energy in the form of a magnetic field. It is also called a choke or a coil.
17 .
What is the definition of an ideal transformer?
A transformer is called an ideal transformer if there no losses happen at all. In other words, we can say that, in an ideal transformer, the transformer input authority should be equivalent to the output authority of the transformer, i.e., they have 100% competence.

Transformer Input Power = Transformer Output Power PIN = POUT. ​
18 .
Mention how NPN and PNP transistor works?
When we use NPN transistor in a circuit :

* No current flowing from A to D = No flow from X to Z Current flowing from A to D = Current allowed to flow from X to Z


When we use PNP transistor in a circuit :

* No current flowing from A to D = Current is allowed to flow from X to Z Current flowing from A to D = No current flow from X to Z
19 .
What is meant by reverse polarity and how it can be fixed?
Reverse polarity is referred in a condition where one or more of your receptacles are connected incorrectly. To fix the reverse polarity, check the wire connection at the outlet and inspect your receptacle.

A receptacle with reverse polarity will have the white wire screwed to the hot side and the black wire will be connected to the neutral side, if that the case swap the wires and it will resolves the problem. If it persists, a licensed electrician will be needed.
20 .
Explain what rectifiers is and what are the types of rectifiers?
A rectifier is an electrical device that transforms A.C  or alternating current into direct current (D.C), which flows in only one direction. The types of rectifiers are

Half wave rectifier : It uses one p-n junction

Full wave rectifier : It uses two p-n junction
21 .
What are the different types of networks used to build an electrical circuit?
There are mainly two types of networks used to build an electrical circuit called Passive or Active Networks.

A Passive network is a network that contains passive elements in its network, such as Resistance, Capacitance, or Inductance.

On the other hand, an Active Network is a network that contains active elements in its network, such as Current or Voltage Sources.
22 .
How a tube light circuit is connected, and how does it work?
In a tube light circuit, a choke is linked to one end of the tube light, and a starter is in sequence with the circuit. When we supply the current, the starter breaks off the supply cycle of AC. Due to this unexpected change in supply, the chock makes around 1000 volts.

This voltage is enough to break the electrons within the tube to make the electrons flow. Once the accessible voltage passes through the pipe, the appetizer circuit will be out of the part. Now, no supply transform makes the choke voltage normal and diminishes the current.
23 .
What are the main advantages of speed control using thyristor?
Following are some main advantages of speed control using thyristor :

* It reduces the cost.
* It is highly accurate.
* It provides fast switching characteristics than BJT and IGBT.
24 .
What are some essential tools used for the measurement of electrical parameters in an electrical circuit?
Following is the list of some measuring tools used for the measurement of electrical parameters :

* Voltmeter
* Ammeter
* Ohmmeter
* Multi-meter
* Power meter
* Microwave meter
* Cathode Ray Oscilloscope
* Signal Generators and Analyzers
* Wattmeter
* Sweep Generator etc.
25 .
Explain what is laser diodes?
Laser diodes are compact transistor like packages with two or more electrical leads. Lasing occurs when stimulated emission results into the amplification of photon confined to the lasing mode.  These photons hit back and forth between the back and front mirror, and hence a diverging beam emits from the laser diode packages.
26 .
Explain what is Zener diode?
Zener diode is a type of seme-conductor diode that allows current to flow in the opposite direction when exposed to enough voltage.
27 .
What is Armature Reaction?
The armature reaction is the effect of the armature field on the main field. In other words, we can say that the armature reaction specifies the impact of the armature flux on the main field flux. The armature field is produced by the armature conductors when we flow the current through them.
28 .
What are the different criteria you should keep in mind while selecting a type of wire?
We should select the wire based on several factors such as wire capacity, a gauge of the different wires, etc. If you use larger and heavier products, such as electrical heaters or furnaces, you should choose a smaller wire gauge. Gauge 6 wire may be perfect for this purpose.

It has a higher capacity to carry and handle the current. On the other hand, if you choose the wire for household objects such as lamps and lights, which require a low voltage, you should choose the wires with higher gauge values. Gauge 12 wire may be perfect for this purpose.
29 .
What are the different types of coupling mechanisms in an electric circuit?
There are mainly three different types of coupling mechanisms used in an electric circuit :

* Conductive Coupling : In conductive coupling, we have to give the power supply simultaneously to both the sensor and the load.

* Inductive Coupling : In Inductive coupling, an electric field is a leading cause for the noise.

* Capacitive Coupling : In Capacitive coupling, a magnetic field is a leading cause of the current flows' noise.
30 .
Why is SF6 gas used in circuit breakers?
The SF6 gas is used in circuit breakers due to its low gaseous viscosity. The SF6 gas can efficiently transfer heat by convection. Due to this unique property, the SF6 gas is used as a circuit breaker in a complete range of medium voltage and high voltage electrical power systems.
31 .
What is SF6 gas? Why is it Used?
SF6 gas is known as Sulphur Hexafluoride gas. This gas is used to extinguish the arc because it is an excellent dielectric, arc quenching, and has chemical and other physical properties, making it superior to other arc quenching mediums such as oil or air. Due to this reason, it is called a circuit breaker.

The SF6 circuit breaker is mainly divided into three types :

* Non-puffer piston circuit breaker.
* Single-puffer piston circuit breaker.
* Double-puffer piston circuit breaker.
32 .
What do you understand by a transistor?
A transistor is a semiconducting device that is made up of semiconducting materials. Transistors are used to interpret electrical signals and powers. A transistor should be connected to at least three terminals through an external circuit. It is also known as a combination of many n-type and p-type semiconductors.
33 .
What are the main usages of a transistor?
The primary usage of a transistor is to increase the input current, which ultimately increases the output. In other words, we can say that transistors are used to increase electric and electrical power.
34 .
What do you understand by AVR or automatic voltage regulator?
AVR is a short-term that stands for Automatic Voltage Regulator. It is a central part of Synchronous Generators and is used to regulate the voltage. It gets the fluctuation in the voltage and changes them into a constant voltage.

The fluctuation in the voltage generally occurs due to the variation in load on the supply system, which can damage the equipment of the power system. To control the voltage, we have to install the voltage control equipment at several places such as near the transformers, generator, feeders, etc.
35 .
What are the main differences between an Analogue and a Digital circuit?
Differences between an Analogue and a Digital circuit :

Analogue Circuit Digital Circuit
The Analogue circuits operate on continuous-valued signals. The Digital circuits operate on the signal, which exists at two levels 0's and 1's.
This circuit doesn't require conversion of the input signal before transmitting the signals. This circuit directly executes various logical operations and produces an analog output. This circuit requires the conversion of the input signal before transmitting the signals. Before the signal is transmitted, it is converted into digital form.
This circuit is more precise because there is no probability of losing any information as there is no conversion. This circuit is less precise because, during signal conversion, some amount of information can be lost.
The Analogue circuit lacks flexibility. The Digital circuits provide a high range of flexibility to offer to its users.
36 .
What do you understand by a two-phase motor?
A two-phase motor is an electrical system (motor) with two voltages 90 degrees apart.

The alternator is composed of two windings placed at 90 degrees from each other.

They require two live and one ground wire that works in two phases. These types of motor are no longer in use nowadays.
37 .
What do you understand by reverse polarity, and how can you fix it?
The reverse polarity is a condition where one or more receptacles are misconnected. You should check the wire connection at the outlet and inspect the receptacle to fix the reverse polarity. A receptacle with reverse polarity connects the white wire to the hot side and the black wire to the neutral side. You can swap the wires to resolve the problem efficiently.
38 .
What is the full form of FPGA, and why is it used?
The full form of the term FPGA stands for Field Programmable Gate Array. It is one type of semiconductor logic chip programmed to become almost any kind of system or digital circuit such as PLDs. The only difference between PLD and FPGA is that PLDS are limited to hundreds of gates, but FPGAs support thousands of gates. The FPGA architecture's configuration is generally specified using a language known as HDL (Hardware Description language).
39 .
What do you understand by ASCR cable, and where is it used?
ACSR cable stands for Aluminum Conductor Steel-Reinforced cable. It is a type of high-capacity, high-strength stranded conductor wire typically used in overhead power lines. It is also used in broadcast & distribution. It is best suited for broadcast & distribution because of its good conductivity, low weight, low cost, resistance to corrosion, and decent mechanical stress resistance.
40 .
What is the Control System, and what are its different types?
A Control System is a system where the output and inputs are interrelated so that the input parameters control the output parameters. There are mainly two types of Control Systems, i.e., Open-loop Control systems and Closed Loop Control Systems.

* Open-loop Control System : In Open-Loop Control Systems, there is no feedback from the output-input for correction.

* Closed-Loop Control Systems : In Closed Loop Control Systems, there is feedback from the output to input for correction to control the desired output quantities.
41 .
What is a transformer and what are its applications?
A Transformer is an electrical device used to convert the electric voltage from smaller to larger quantities and vice versa. In other words, we can say that a transformer is a device that transfers electric energy from one alternating-current circuit to one or more other circuits. It is either used to increase (step-up) or reduce (step down) the voltage.

Following are the main applications of a transformer :

* The main task of a transformer is to step up or step down voltages.
* A transformer can be used to match impedance.
* It can be used as a rectifier.
* It acts as a voltage rectifier or stabilizer also.
* It is also used in voltmeter or ammeter applications.
* It is also used for the isolation of electrical circuits.
42 .
What is the primary usage of a transistor in an electric circuit?
Transistors are mainly used to amplify the current to make the output power higher than the input power.
43 .
What is the usage of a string of resistors in a series?
When we add a string of resistors in a sequence, they split the source voltage into the amount to their values.
44 .
What would happen if the series current gets double?
If the series current gets double, then the confrontation will half.
45 .
What are the different types of semiconductors?
There are mainly two types of semiconductors used in electronics, i.e., intrinsic and extrinsic semiconductors. The extrinsic semiconductors can be categorized into N-type semiconductors and P-type semiconductors.
46 .
What do you understand by Alternator and Generator? What are the main differences between them?
The Alternator and Generator are both used for power generation. An Alternator generates the power on a small scale, whereas the Generator generates electricity by converting one form of energy to another.

Alternator Generator
An Alternator is used to generate power on the small-scale requirement. A Generator is used to generate electricity for large-scale requirements or supplies.
In Alternator, electricity is produced by spinning the magnetic field inside the windings of the copper wire. A generator uses dynamo to convert mechanical energy to electrical energy. It works on the principle of electromagnetic induction.
Alternators use only the required amount of energy. So, they conserve more energy. Generators use all the energy that is produced. So, they conserve less energy.
An alternator always induces an alternating current (AC). A generator can generate either alternating (AC) or direct current (DC).
Alternators are considered very efficient. Generators are considered less efficient.
It doesn't require polarization in the case of alternators. Polarization is required after installation in the case of generators.
In Alternator, the magnetic field is rotating inside the stator. In Generator, the magnetic field is stationary or fixed, and the armature winding spins.
The armature of an alternator is always stationary. The armature of the Generator is rotating.
The Alternator receives the input supply from the stator. The Generator receives the input supply from the rotor.
Alternators generate voltage only when needed. Generators produce voltage at all times.
Alternators run on a high range of RPM. Generators run on a high range of RPM.
Alternators are generally smaller in size. Generators are generally larger and require more space to fit in.
Alternators can never charge a dead battery. A generator can be used to charge a dead battery.
The brushes of alternators are long-lasting. The brushes of generators are lesser long-lasting when compared to an alternator.
Alternators are mainly used in the automobile industry as a charging system for the battery. Generators are mainly used to produce large-scale electricity.
47 .
How can you start-up the 40w tube lite with 230v AC/DC without using any choke/Coil?
It’s possible by means of Electronic chokes,otherwise it’s not possible to ionize the particles in tube light with normal voltage.
48 .
3. What is "pu" in electrical engineering?
Pu stands for per unit and this will be used in single line diagram of power distribution and it is like a huge electrical circuit with no of components (generators, transformers, loads) with different ratings (in MVA and KV). To bring all the ratings into common platform we use pu concept in which, in general largest MVA and KV ratings of the component is considered as base values, then all other component ratings will get back into this basis.Those values are called as pu values. (p.u=actual value/base value).
49 .
Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?
Link is provided at a Neutral common point in the circuit from which various connection are taken for the individual control circuit and so it is given in a link form to withstand high Amps. But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e load) only.So if any malfunction happen the fuse connected in the particular control circuit alone will blow off.
50 .
Whats is MARX CIRCUIT?
It is used with generators for charging a number of capacitor in parallel and discharging them in series.It is used when voltage required for testing is higher than the available.
51 .
What is the difference between MCB & MCCB, Where it can be used?
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.
52 .
Why use the VCB at High Transmission System ? Why can’t use ACB?
Actually the thing is vacuum has high arc quenching property compare to air because in VCB ,the die electric strengths equal to 8 times of air . That y always vacuum used as inHT breaker and air used as in LT .
53 .
What does the KVAR means?
The KVAR indicates the electrical power. KVAR means “Kilo Volt Amperes with Reactive components”
54 .
What is the difference between electronic regulator and ordinary electrical rheostat regulator for fans?
The difference between the electronic and ordinary electrical regulator is that in electronic regulator power losses are less because as we decrease the speed the electronic regulator gives the power needed for that particular speed but in case of ordinary rheostat type regulator, the power wastage is same for every speed and no power is saved.In electronic regulator, triac is employed for speed control by varying the firing angle speed and it is controlled but in rheostatic ,control resistance is decreased by steps to achieve speed control.
55 .
What is a differential amplifier? Also, explain CMRR.
Differential Amplifier : The amplifier, which is used to amplify the voltage difference between two input-lines neither of which is grounded, is called differential amplifier. This reduces the amount of noise injected into the amplifier, because any noise appearing simultaneously on both the input-terminals as the amplifying circuitry rejects it being a common mode signal.

CMRR :  It can be defined as the ratio of differential voltage-gain to common made voltage gain. If a differential amplifier is perfect, CMRR would be infinite because in that case common mode voltage gain would be zero.
56 .
Explain thin film resistors and wire-wound resistors
* Thin film resistors - It is constructed as a thin film of resistive material is deposited on an insulating substrate.

Desired results are obtained by either trimming the layer thickness or by cutting helical grooves of suitable pitch along its length. During this process, the value of the resistance is monitored closely and cutting of grooves is stopped as soon as the desired value of resistance is obtained.


* Wire wound resistors – length of wire wound around an insulating cylindrical core are known as wire wound resistors. These wires are made of materials such as Constantan and Manganin because of their high resistivity, and low temperature coefficients. The complete wire wound resistor is coated with an insulating material such as baked enamel
57 .
Compare JFET's and MOSFET's.
Comparison of JFET’s and MOSFET’s :

* JFET’s can only be operated in the depletion mode whereas MOSFET’s can be operated in either depletion or in enhancement mode. In a JFET, if the gate is forward-biased, excess-carrier injunction occurs and the gatecurrent is substantial.

* MOSFET’s have input impedance much higher than that of JFET’s. Thus is due to negligible small leakage current.

* JFET’s have characteristic curves more flat than that of MOSFET is indicating a higher drain resistance.

* When JFET is operated with a reverse-bias on the junction, the gate-current IG is larger than it would be in a comparable MOSFET.
58 .
Why, when birds sit on transmission lines or current wires doesn't get shock?
Its true that if birds touch the single one line (phase or neutral) they don’t get electrical shock… if birds touch 2 lines than the circuit is closed and they get electrical shock.. so if a human touch single one line(phase) then he doesn’t get shock if he is in the air (not touching – standing on the ground if he is standing on the ground then touching the line (phase) he will get a shock because the ground on what we standing is like line (ground bed – like neutral)? and in the most of electric lines the neutral is grounded..so that means that human who touch the line closes the circuit between phase and neutral.
59 .
What is vacuum circuit breaker.define with cause and where be use it Device?
A breaker is normally used to break a circuit. while breaking the circuit, the contact terminals will be separated.

At the time of separation an air gap is formed in between the terminals. Due to existing current flow the air in the gap is ionized and results in the arc. various mediums are used to quench this arc in respective CB’s. but in VCB the medium is vacuum gas. since the air in the CB is having vacuum pressure the arc formation is interrupted. VCB’s can be used up to kv.
60 .
Whats the one main difference between UPS & inverter ? And electrical engineering & electronics engineering ?
Uninterrupt Power Supply (UPS) is mainly use for short time . means according to ups VA it gives backup. ups is also two types : online and offline.

online ups having high volt and amp for long time backup with with high dc voltage.but ups start with 2v dc with 7 amp. but inverter is start with 2v,24,dc to 36v dc and 20amp to 80amp battery with long time backup.
61 .
What is the difference between synchronous generator & asynchronous generator?
In simple, synchronous generator supply’s both active and reactive power but asynchronous generator(induction generator) supply’s only active power and observe reactive power for magnetizing.This type of generators are used in windmills.
62 .
1 ton is equal to how many watts?
1 ton = 12000 BTU/hr and to convert BTU/hr to horsepower, 12,000 * 0.000929 = 4.715 hp therefore 1 ton = 4.715*.746 = .5 KW.
63 .
What is Automatic Voltage regulator(AVR)?
AVR is an abbreviation for Automatic Voltage Regulator. It 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.
64 .
How many types of colling system it transformers?
* ONAN (oil natural,air natural)
* ONAF (oil natural,air forced)
* OFAF (oil forced,air forced)
* ODWF (oil direct,water forced)
* OFAN (oil forced,air forced)
65 .
Tell me in detail about CT and PT?
The term CT means Current Transformer, and the term PT means Potential Transformer. In circuit where measurements of high voltage and high current is involved they are used there.Particularly when a measuring device like voltmeter or ammeter is not able to measure such high value of quantity because of large value of torque due to such high value it can damage the measuring device.so, CT and PT are introduced in the circuits.

They work on the same principle of transformer, which is based on linkage of electromagnetic flux produced by primary with secondary.They work on the ratio to they are designed.E.g if CTis of ratio 50005A and it has to measure secondary current of 8000A.then ANS=8000*55000=8Aand this result will be given to ammeter .and after measuring 8A we can calculate the primary current.same is the operation of PT but measuring voltage.
66 .
Define IDMT relay?
It is an inverse definite minimum time relay.In IDMT relay its operating is inversely proportional and also a characteristic of minimum time after which this relay operates.It is inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase.
67 .
What is the count of hvdc transmission lines in India?
Resolution : At present there are three hvdc transmission lines in india

* chandrapur to padghe(mumbai)–(100 MW at ±00 kV DC)
* rehand to delhi (100 MW at ±00 kV DC)
* talchal to kolar (200 MW)
68 .
Why is the starting current high in a DC motor?
Resolution : In DC motors, Voltage equation is V=Eb-IaRa (V = Terminal voltage,Eb = Back emf in Motor,Ia = Armature current,Ra = Aramture resistance).At starting, Eb is zero. Therefore, V=IaRa, Ia = V/Ra ,where Ra is very less like 0.01ohm.i.e, Ia will become enormously increased.
69 .
Why ELCB can't work if N input of ELCB do not connect to ground?
ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an ELCB, the current will flow through phase and that much current will have to return neutral so resultant current is zero. Once there is a ground fault in the load side, current from phase will directly pass through earth and it will not return through neutral through ELCB. That means once side current is going and not returning and hence

because of this difference in current ELCB wil trip and it will safe guard the other circuits from faulty loads. If the neutral is not grounded, fault current will definitely high and that full fault current will come back through ELCB, and there will be no difference in current.
70 .
How electrical power is generated by an A.C Generator?
For the generation of elect power we need a prime mover which supplies mechanical power input to the alternator, can be steam turbines,or hydro turbines.

When poles of the rotor moves under the armature conductors which are placed on the stator ,field flux cut the armature conductor ,therefore voltage is generated and is of sinusoidal in nature…due to polarity change of rotor poles(i,e) N-S-N-S.
71 .
What is the difference between earth resistance and earth electrode resistance?
Only one of the terminals is evident in the earth resistance. In order to find the second terminal we should recourse to its definition: Earth Resistance is the resistance existing between the electrically accessible part of a buried electrode and another point of the earth, which is far away.

The resistance of the electrode has the following components :

(A) the resistance of the metal and that of the connection to it.

(B) the contact resistance of the surrounding earth to the electrode.
72 .
Why most of analog o/p devices having o/p range 4 to 20 mA and not 0 to 20 mA?
4-20 mA is a standard range used to indicate measured values for any process. The reason that 4ma is chosen instead of 0 mA is for fail safe operation .For example- a pressure instrument gives output 4mA to indicate 0 psi, up to 20 mA to indicate 100 psi, or full scale. Due to any problem in instrument (i.e) broken wire, its output reduces to 0 mA. So if range is 0-20 mA then we can differentiate whether it is due to broken wire or due to 0 psi.
73 .
What are the advantage of free wheeling diode in a Full Wave rectifier?
It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load.
74 .
What is the different between digital phase converter and ordinary phase converter?
Digital phase converter are a recent development in phase converter technology that utilizes proprietary software in a powerful microprocessor to control solid state power switching components. This microprocessor, called a digital signal processor (DSP), monitors the phase conversion process, continually adjusting the input and output modules of the converter to maintain perfectly balanced three-phase power under all load conditions.
75 .
Use of switch mode power converter in real-time basis?
Switch mode power converter can be used in the following 5 different ways :

* step down an unregulated dc input voltage to produce a regulated dc output voltage using a circuit known as Buck Converter or Step-Down SMPS,

* step up an unregulated dc input voltage to produce a regulated dc output voltage using a circuit known as Boost Converter or Step-Up SMPS,

* step up or step down an unregulated dc input voltage to produce a regulated dc output voltage,

* invert the input dc voltage using usually a circuit such as the Cuk converter, and

* produce multiple dc outputs using a circuit such as the fly-back converter.
76 .
Why electricity in India is in the multiples of 11 like 11kv, 22kv, 33kv?
Transformer Induced voltage equation contains 4.44 factor.

E=4.44*f*T*phi
E -Induced emf per phase
T -number of turns
f -frequency
phi -maximum flux per pole
From the equation we see that E is proportional to 4.4 and it is in turn multiple of 11.

So always transmission voltage is multiple of 11
77 .
What are the advantages of VSCF wind electrical system?
Advantages of VSCF wind electrical system are :

* No complex pitch changing mechanism is needed.
* Aero turbine always keeps going at maximum efficiency point.
* Extra energy in the high wind speed region of the speed – duration curve can be extracted
* Significant reduction in aerodynamic stresses, which are associated with constant – speed operation.
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