L & T Interview Questions
1)What is Ferranti Effect?
a)The effect in which the voltage at the receiving end of the transmission line is more than the sending voltage is known as Ferranti Effect.
b)Such type of effect mainly occurs because of light load (or) open circuit at the receiving end.
c)Ferranti Effect is due to the charging current of the line.
2)How do you Overcome Ferranti Effect?
a)Ferranti Effect can be reduced by installing shunt compensation devices at receiving end .
b)The compensation devices is a shunt reactor which is connected in parallel with the transmission line.
c)It reduces the voltage level by absorbing the reactive power.
d)Running the transmission line with higher load.
3)What is Charging Current in Transmission line?
When the voltage is applied across the sending end of the transmission line,current starts flowing between the conductors.This current is called the charging current in the transmission line.
4)What is Skin Effect?
a)Accumulation of current on the surface of conductor is called Skin Effect.
b)Due to skin Effect the effective area of current flowing path is reduced causes Increased
Resistance.
c)The effect becomes more and more apparent as the frequency increases.
5)How can you reduce Skin Effect?
a)ACSR bundled Conductor is used to reduce to skin effect.
b)Use cable material with less magnetic permeability.
c)Reduce the size of conductor.
d)Increasing the volatge by reducing the current which decreases the skin effect in the same conductor.
6)What is ohm's law?
a)Ohm's law states that the current through a conductor between two points is directly
Proportional to the volatge across two points.
b)Ohm's law states the volatge (or) potential difference between two points is directly
Proportional to the current (or) electricity passing through resistance .
7)What is Lenz's law?
a)A law stating that the direction of an induced current is always such as to oppose the change in the circuit (or) the magnetic field that produces it.
b) It states that when a volatge is created by a change in magnetic flux ,the induced volatge must create a current whose magnetic field is in opposition to the change which produces it.
8)What is Faraday's law of mutual Induction?
a)When an emf is produced in a coil because of the change in current in a coupled coil,the
effect is called mutual Inductance.
9)What is Faraday's First Law?
a)Any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil.
This emf is called induced emf and if the conductor circuit is closed,the current will also circulate through the circuit and this current is called induced current.
10)What is Faraday's Second Law?
a)It states that the magnitude of emf induced in the coil is equal to the rate of change of flux
that linkages with coil.The flux linkage of the coil is the product of the number of turns in the
coil and flux associated with the coil.
11)What is Coulomb's First Law?
a)If two electrically charged bodies are placed near by each other there will be an attraction
(or) a repulsion force acting on them depending up on nature of the charge of the bodies.
b)Like charged objects repel each other
c)Unlike charged objects attract each other
12)What is Coulomb's Second Law?
a)The force of attraction (or) repulsion between two electrically charged objects is directly
Proportional to the magnitude of their charge and inversely proprotional to the square of the
distance between them.
13) What is Gauss's law?
a)Gauss's law states that the net flux of an electric field through a closed surface is proportional
to the enclosed electric charge.
b)The electric flux is defined as the electric field passing through a given area multiplied by the
area of the surface in a plane perpendicular to the field.
14)What is Zone of Protection?
a)Protection Zone is defined as the part of the power system which is protected by a certain
Protective Scheme.It is established around each power system equipment.When the fault
occurs on any of the protection zones then only the circuit breakers within that zone will
be opened.
15)Difference between Current Transformer and Potential Transformer ?
a)Transform the current from high value to the low value.
Transform the volatge from high value to the low value.
b)Usally built up with lamination of silicon steel.
It is made up of with high quality steel operating at low flux densities.
c) It carries the current which is to be measured.
It carries the voltage which is to be measured.
d) Connected in Series with the instrument.
Connected in Parallel with the instrument.
e)High Transformation ratio
Low Transformation ratio.
f)Low Impedance
High Impedance.
g)Constant Current.
Constant Voltage.
i)Measuring Current and power,monitoring the power grid operation,for operating protective relay.
Measurement,power source,operating protective relay.
16)What is a Relay?
a)The Relay is the device that open (or) closes the contacts to cause the operation of the other
electric control.
b)It detects the intolerable (or) undesirable condition with an assigned area and gives the
commands to the circuit breaker to disconnect the affected area.Thus protects the
system from damage.
17)What is Working Principle of Relay?
a)It works on the principle of an electromagnetic attraction.
b)When the circuit of the relay senses the fault current,it energises the electromagnetic field
which produces the temporary magnetic field.
c)This magnetic field moves the relay armature for opening (or) closing the connections.
18)What are the Different types of Relays?
a)Based on Characteristic the Protection relay can be categorized as:
1)Definite Time relays
2)Inverse Time relays with definite minimum time
3)Instantaneous realys.
4)IDMT with inst.
5)Stepped Charcteristic
6)Programmed Switches
7)Voltage restraint over current relay.
b)Based on of logic the Protection relay can be categorized as:
1)Differential
2)Unbalance
3)Neutral Displacement
4)Directional
5)Restricted earth fault
6)Over Fluxing
7)Distance Schemes
8)Bus bar Protection
9)Reverse power relays
c)Based on actuating parameter the protection relay can be categorized as
1)Current relays
2)Volatge relays
3)Frequency relays
4)Power relays
d)Based on application the protection relay can be categorized as
1)Primary relay
2)Backup relay
19) )What is a Starter and its Types?
a)A starter is a device that reduces initial high current of the motor by reducing the supply volatge applied to the motor.Such reduction is applied for very short duration and once the
motor accelerates,slip value decreases and hence a normal voltage is then applied.
b)1)Direct Online Starters
2)Star-Delta Starters
3)Autotransformers starters
4)Soft starters
5)VFD starters
6)Resistance stator starters
7)Slip ring motor starters
20)What are the major equipment of a Sub Station?
1)Lightning Arrestor
2)Power Transformer
3)Instrument Transformer
4)Bus-Bar
5)Wave Trapper
6)Isolator
7)Circuit Breaker
8)Relay
9)Battery
10)Capacitor bank
11)Switch Yard
12)Insulator
21)What is Drift Velocity?
a)Drift Velocity is defined as the average velocity with the free electrons get drifted towards the
positive end of the conductor under the influence of an external electric field applied.
22)What is Luminous Efficacy?
a)It is a measure of how well a light source produces visible light.
b)It is the ratio of luminous flux to power measured in lumens per watt .
23)What is Transformer?
Transformer is a static device which convert electrical power from one circuit to another without
changing the its frequency.It step up (or) step down the level of Ac volatge and Current.
24)Explain Working Principle of Transformer?
1)The main principle of operation of Transformer is mutual Inductance between two circuits which is linked by a common magnetic flux.
2)A basic Transformer consists of two coils that are electrically separate and inductive,but are magnetically, linked through a path of reluctance.
25)What are the major parts of the Transformer?
a)Laminated Core.
b)Windings
c)Insulating Materials
d)Transformer Oil
e)Tap Changer
f)Oil Conservator
g)Breather
i)Cooling Tubes
j)Buchholz Relay
k)Explosion Vent
26)What Use of Conservator Tank in Transformer?
When Transformer is loaded and when ambient Temperature rises,the volume of oil
Inisde the Transformer Increases.A Conservator Tank o Transformer Provides adequate Space
to this exapnded Transformer oil.It also acts a Reservoir for Transformer insulating oil.
27)What is the Use of Breather in Transformer?
29)Difference between Eddy Current Loss and Hysteresis Loss?
a)The loss occur because of the relative motion between the core and the magnetic flux.
The losses which occur because of the reversal of the magnetism is known as the hysteresis loss.
b)Interaction of the magnetic flux and Conductor.
Because of reversal of flux
c)By making the core of thin lamination
By Using Silicon steel Material.
30)What are the types of starter used for induction motor?
a)Star delta starter
b)Direct Online Starter
c)Auto Transformer motor starting
d)Rotor Resistance Starting
31)What is PWM and How it works?
In short, PWM operates like a switch which constantly cycles on and off, thereby regulating the amount of power the fan or pump motor gains. The PWM system that is used for controlling fans and pumps works with the motor, either getting +12V (full power) or 0V (no power). ... So, the motor is being fed impulses of power.
32)What is Power factor?
In electrical engineering, the power factor (PF or cosĪ) is the ratio between thepower that can be used in electric circuit (real power, P) and the power from the result of multiplication between the current and voltage circuit (apparent power, S). The power factor is defined as: PF ranges from zero to one.
33)What is Admittance in Ac Circuit?
Admittance is the reciprocal of impedance, Z and is given the symbol Y. In AC circuits admittance is defined as the ease at which a circuit composed of resistances and reactances allows current to flow when a voltage is applied taking into account the phase difference between the voltage and the current.
34)What is Impedance?
Impedance, denoted Z, is an expression of the opposition that an electronic component, circuit, or system offers to alternating and/or direct electric current.Impedance is a vector (two-dimensional)quantity consisting of two independent scalar (one-dimensional) phenomena: resistance and reactance.
35)What is Power system?
The power system is a network which consists generation, distribution and transmission system. ... The power system includes the devices connected to the system like the synchronous generator, motor, transformer, circuit breaker, conductor, etc.
36)
1)What is Ferranti Effect?
a)The effect in which the voltage at the receiving end of the transmission line is more than the sending voltage is known as Ferranti Effect.
b)Such type of effect mainly occurs because of light load (or) open circuit at the receiving end.
c)Ferranti Effect is due to the charging current of the line.
2)How do you Overcome Ferranti Effect?
a)Ferranti Effect can be reduced by installing shunt compensation devices at receiving end .
b)The compensation devices is a shunt reactor which is connected in parallel with the transmission line.
c)It reduces the voltage level by absorbing the reactive power.
d)Running the transmission line with higher load.
3)What is Charging Current in Transmission line?
When the voltage is applied across the sending end of the transmission line,current starts flowing between the conductors.This current is called the charging current in the transmission line.
4)What is Skin Effect?
a)Accumulation of current on the surface of conductor is called Skin Effect.
b)Due to skin Effect the effective area of current flowing path is reduced causes Increased
Resistance.
c)The effect becomes more and more apparent as the frequency increases.
5)How can you reduce Skin Effect?
a)ACSR bundled Conductor is used to reduce to skin effect.
b)Use cable material with less magnetic permeability.
c)Reduce the size of conductor.
d)Increasing the volatge by reducing the current which decreases the skin effect in the same conductor.
6)What is ohm's law?
a)Ohm's law states that the current through a conductor between two points is directly
Proportional to the volatge across two points.
b)Ohm's law states the volatge (or) potential difference between two points is directly
Proportional to the current (or) electricity passing through resistance .
7)What is Lenz's law?
a)A law stating that the direction of an induced current is always such as to oppose the change in the circuit (or) the magnetic field that produces it.
b) It states that when a volatge is created by a change in magnetic flux ,the induced volatge must create a current whose magnetic field is in opposition to the change which produces it.
8)What is Faraday's law of mutual Induction?
a)When an emf is produced in a coil because of the change in current in a coupled coil,the
effect is called mutual Inductance.
9)What is Faraday's First Law?
a)Any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil.
This emf is called induced emf and if the conductor circuit is closed,the current will also circulate through the circuit and this current is called induced current.
10)What is Faraday's Second Law?
a)It states that the magnitude of emf induced in the coil is equal to the rate of change of flux
that linkages with coil.The flux linkage of the coil is the product of the number of turns in the
coil and flux associated with the coil.
11)What is Coulomb's First Law?
a)If two electrically charged bodies are placed near by each other there will be an attraction
(or) a repulsion force acting on them depending up on nature of the charge of the bodies.
b)Like charged objects repel each other
c)Unlike charged objects attract each other
12)What is Coulomb's Second Law?
a)The force of attraction (or) repulsion between two electrically charged objects is directly
Proportional to the magnitude of their charge and inversely proprotional to the square of the
distance between them.
13) What is Gauss's law?
a)Gauss's law states that the net flux of an electric field through a closed surface is proportional
to the enclosed electric charge.
b)The electric flux is defined as the electric field passing through a given area multiplied by the
area of the surface in a plane perpendicular to the field.
14)What is Zone of Protection?
a)Protection Zone is defined as the part of the power system which is protected by a certain
Protective Scheme.It is established around each power system equipment.When the fault
occurs on any of the protection zones then only the circuit breakers within that zone will
be opened.
15)Difference between Current Transformer and Potential Transformer ?
a)Transform the current from high value to the low value.
Transform the volatge from high value to the low value.
b)Usally built up with lamination of silicon steel.
It is made up of with high quality steel operating at low flux densities.
c) It carries the current which is to be measured.
It carries the voltage which is to be measured.
d) Connected in Series with the instrument.
Connected in Parallel with the instrument.
e)High Transformation ratio
Low Transformation ratio.
f)Low Impedance
High Impedance.
g)Constant Current.
Constant Voltage.
i)Measuring Current and power,monitoring the power grid operation,for operating protective relay.
Measurement,power source,operating protective relay.
16)What is a Relay?
a)The Relay is the device that open (or) closes the contacts to cause the operation of the other
electric control.
b)It detects the intolerable (or) undesirable condition with an assigned area and gives the
commands to the circuit breaker to disconnect the affected area.Thus protects the
system from damage.
17)What is Working Principle of Relay?
a)It works on the principle of an electromagnetic attraction.
b)When the circuit of the relay senses the fault current,it energises the electromagnetic field
which produces the temporary magnetic field.
c)This magnetic field moves the relay armature for opening (or) closing the connections.
18)What are the Different types of Relays?
a)Based on Characteristic the Protection relay can be categorized as:
1)Definite Time relays
2)Inverse Time relays with definite minimum time
3)Instantaneous realys.
4)IDMT with inst.
5)Stepped Charcteristic
6)Programmed Switches
7)Voltage restraint over current relay.
b)Based on of logic the Protection relay can be categorized as:
1)Differential
2)Unbalance
3)Neutral Displacement
4)Directional
5)Restricted earth fault
6)Over Fluxing
7)Distance Schemes
8)Bus bar Protection
9)Reverse power relays
c)Based on actuating parameter the protection relay can be categorized as
1)Current relays
2)Volatge relays
3)Frequency relays
4)Power relays
d)Based on application the protection relay can be categorized as
1)Primary relay
2)Backup relay
19) )What is a Starter and its Types?
a)A starter is a device that reduces initial high current of the motor by reducing the supply volatge applied to the motor.Such reduction is applied for very short duration and once the
motor accelerates,slip value decreases and hence a normal voltage is then applied.
b)1)Direct Online Starters
2)Star-Delta Starters
3)Autotransformers starters
4)Soft starters
5)VFD starters
6)Resistance stator starters
7)Slip ring motor starters
20)What are the major equipment of a Sub Station?
1)Lightning Arrestor
2)Power Transformer
3)Instrument Transformer
4)Bus-Bar
5)Wave Trapper
6)Isolator
7)Circuit Breaker
8)Relay
9)Battery
10)Capacitor bank
11)Switch Yard
12)Insulator
21)What is Drift Velocity?
a)Drift Velocity is defined as the average velocity with the free electrons get drifted towards the
positive end of the conductor under the influence of an external electric field applied.
22)What is Luminous Efficacy?
a)It is a measure of how well a light source produces visible light.
b)It is the ratio of luminous flux to power measured in lumens per watt .
23)What is Transformer?
Transformer is a static device which convert electrical power from one circuit to another without
changing the its frequency.It step up (or) step down the level of Ac volatge and Current.
24)Explain Working Principle of Transformer?
1)The main principle of operation of Transformer is mutual Inductance between two circuits which is linked by a common magnetic flux.
2)A basic Transformer consists of two coils that are electrically separate and inductive,but are magnetically, linked through a path of reluctance.
25)What are the major parts of the Transformer?
a)Laminated Core.
b)Windings
c)Insulating Materials
d)Transformer Oil
e)Tap Changer
f)Oil Conservator
g)Breather
i)Cooling Tubes
j)Buchholz Relay
k)Explosion Vent
26)What Use of Conservator Tank in Transformer?
When Transformer is loaded and when ambient Temperature rises,the volume of oil
Inisde the Transformer Increases.A Conservator Tank o Transformer Provides adequate Space
to this exapnded Transformer oil.It also acts a Reservoir for Transformer insulating oil.
27)What is the Use of Breather in Transformer?
The function of breather in transformer is to filter out the moisture from air. Breather consist of silica gel which absorbs the moisture from air. When there is overloading on transformer, the winding of transformer gets heated so the oil in main tank of transformer also get heated. The hot oil started expanding.
28)What is the Use of Buchholz Relay?
Buchholz relay is a safety device which is generally used in large oil immersed transformers (rated more than 500 kVA). ... It is used for the protection of a transformer from the faults occurring inside the transformer, such as impulse breakdown of the insulating oil, insulation failure of turns etc29)Difference between Eddy Current Loss and Hysteresis Loss?
a)The loss occur because of the relative motion between the core and the magnetic flux.
The losses which occur because of the reversal of the magnetism is known as the hysteresis loss.
b)Interaction of the magnetic flux and Conductor.
Because of reversal of flux
c)By making the core of thin lamination
By Using Silicon steel Material.
30)What are the types of starter used for induction motor?
a)Star delta starter
b)Direct Online Starter
c)Auto Transformer motor starting
d)Rotor Resistance Starting
31)What is PWM and How it works?
In short, PWM operates like a switch which constantly cycles on and off, thereby regulating the amount of power the fan or pump motor gains. The PWM system that is used for controlling fans and pumps works with the motor, either getting +12V (full power) or 0V (no power). ... So, the motor is being fed impulses of power.
32)What is Power factor?
In electrical engineering, the power factor (PF or cosĪ) is the ratio between thepower that can be used in electric circuit (real power, P) and the power from the result of multiplication between the current and voltage circuit (apparent power, S). The power factor is defined as: PF ranges from zero to one.
33)What is Admittance in Ac Circuit?
Admittance is the reciprocal of impedance, Z and is given the symbol Y. In AC circuits admittance is defined as the ease at which a circuit composed of resistances and reactances allows current to flow when a voltage is applied taking into account the phase difference between the voltage and the current.
34)What is Impedance?
Impedance, denoted Z, is an expression of the opposition that an electronic component, circuit, or system offers to alternating and/or direct electric current.Impedance is a vector (two-dimensional)quantity consisting of two independent scalar (one-dimensional) phenomena: resistance and reactance.
35)What is Power system?
The power system is a network which consists generation, distribution and transmission system. ... The power system includes the devices connected to the system like the synchronous generator, motor, transformer, circuit breaker, conductor, etc.
36)
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