Interview Questions.

Question 1. What Are The Functions Of Protective Relays?

Answer :To stumble on the fault and provoke the operation of the circuit breaker to isolate the faulty detail from the rest of the machine, thereby protective the gadget from damages consequent to the fault.

Question 2. Give The Consequences Of Short Circuit?

Answer :

Whenever a brief-circuit happens, the cutting-edge flowing via the coil will increase to an large price. If protective relays are present , a heavy cutting-edge also flows thru the relay coil, causing it to perform with the aid of remaining its contacts.The experience circuit is then closed , the circuit breaker opens and the fault is remoted from the rest of the gadget. Also, a low voltage may be created which may harm structures linked to the deliver.

Electronics and Communications Engineering Interview Questions
Question 3. Define Protected Zone?

Answer :

Are the ones which might be without delay included by way of a shielding gadget together with relays, fuses or switchgears.If a fault taking place in a sector can be straight away detected and or remoted by using a protection scheme committed to that unique area.

Question 4. What Are Unit System And Non Unit System?

Answer :

A unit protective machine is one wherein best faults happening within its blanketed region are remoted.Faults going on some place else in the system haven't any impact on the operation of a unit system.A non unit machine is a protecting system that is activated even if the faults are outside to its blanketed quarter.

Question five. What Is Primary Protection?

Answer :

Is the safety in which the fault happening in a line may be cleared by way of its own relay and circuit breaker.It serves because the first line of defence.

Electronic Circuits Interview Questions
Question 6. What Is Back Up Protection?

Answer :

Is the second line of defence , which operates if the primary safety fails to set off within a particular time postpone.

Question 7. Name The Different Kinds Of Over Current Relays?

Answer :

Induction type non-directional over cutting-edge relay,Induction type directional over cutting-edge relay & present day differential relay.

Electrical Engineering Interview Questions
Question 8. Define Energizing Quantity?

Answer :

It refers back to the contemporary or voltage which is used to set off the relay into operation.

Question 9. Define Operating Time Of A Relay?

Answer :

It is defined because the term prolonged from the incidence of the fault through the relay detecting the fault to the operation of the relay.

Electronic Communications Interview Questions
Question 10. Define Resetting Time Of A Relay?

Answer :

It is defined as the time taken through the relay from the on the spot of separating the fault to the moment whilst the fault is eliminated and the relay can be reset.

Question eleven. What Are Over And Under Current Relays?

Answer :

Overcurrent relays are those that function while the present day in a line exceeds a predetermined price. (eg: Induction type non-directional/directional overcurrent relay, differential overcurrent relay)while undercurrent relays are those which operate every time the contemporary in a circuit/line drops underneath a predetermined fee.(eg: differential over-voltage relay)

ELECTRONICS & INSTRUMENTATION Engineering Interview Questions
Question 12. Mention Any Two Applications Of Differential Relay?

Answer :

Protection of generator & generator transformer unit; protection of huge vehicles and busbars .

Electronics and Communications Engineering Interview Questions
Question thirteen. What Is Biased Differential Bus Zone Reduction?

Answer :

The biased beam relay is designed to reply to the differential modern-day in terms of its fractional relation to the cutting-edge flowing via the protected sector. It is largely an over-modern balanced beam relay kind with an additional restraining coil. The restraining coil produces a bias force inside the contrary route to the working force.

Question 14. What Is The Need Of Relay Coordination?

Answer :

The operation of a relay have to be speedy and selective, ie, it have to isolate the fault in the shortest possible time causing minimum disturbance to the system. Also, if a relay fails to function, there must be sufficiently short backup protection so that the rest of the machine is included. By coordinating relays, faults can constantly be isolated speedy without serious disturbance to the relaxation of the gadget.

Question 15. Mention The Short Comings Of Merz Price Scheme Of Protection Applied To A Power Transformer?

Answer :

In a electricity transformer, currents in the primary and secondary are to be as compared. As these two currents are commonly one of a kind, the use of identical transformers will give differential modern-day, and operate the relay below no-load circumstance. Also, there is often a phase difference between the primary and secondary currents of 3 phase transformers. Even CT’s of proper turn-ratio are used, the differential modern may additionally glide thru the relay underneath everyday circumstance.

Electrical Machines Interview Questions
Question sixteen. What Are The Various Faults To Which A Turbo Alternator Is Likely To Be Subjected? Failure Of Steam Supply; Failure Of Speed; Overcurrent; Over Voltage; Unbalanced

Answer :

loading; stator winding fault 

Question 17. What Is An Under Frequency Relay?

Answer :

An underneath frequency relay is one which operates when the frequency of the system (normally an alternator or transformer) falls under a sure value.

Electronic Devices and Circuits Interview Questions
Question 18. Define The Term Pilot With Reference To Power Line Protection.

Answer :

Pilot wires refers back to the wires that connect the CT’s located on the ends of a electricity transmission line as a part of its protection scheme. The resistance of the pilot wires is generally much less than 500 ohms.

Electronic Circuits Interview Questions
Question 19. Mention Any Two Disadvantage Of Carrier Current Scheme For Transmission Line Only.

Answer :

The application time (ie, the time taken by using the service to reach the opposite cease-upto .1% mile); the response time of band skip filter out; capacitance phase-shift of the transmission line .

Question 20. What Are The Features Of Directional Relay?

Answer :

High pace operation; excessive sensitivity; ability to operate at low voltages; ok brief-time thermal ratio; burden should not be excessive.

Electrical Power System Interview Questions
Question 21. What Are The Main Types Of Stator Winding Faults?

Answer :

Fault among phase and floor; fault between stages and inter-flip fault related to turns of the same phase winding.

Question 22. Give The Limitations Of Merz Price Protection?

Answer :

Since neutral earthing resistances are regularly used to guard circuit from earth-fault currents, it becomes not possible to guard the whole of a celebrity-related alternator. If an earth-fault takes place near the impartial factor, the voltage may be inadequate to perform the relay. Also it is extremely difficult to locate  equal CT’s. In addition to this, there always an inherent phase distinction among the primary and the secondary portions and a possibility of cutting-edge thru the relay even when there may be no fault.

Question 23. What Are The Uses Of Buchholz’s Relay?

Answer :

Bucholz relay is used to give an alarm in case of incipient( slow-growing) faults within the transformer and to connect the transformer from the deliver within the event of excessive internal faults. It is generally used in oil immersion transformers with a score over 750KVA.

Question 24. Why Neutral Resistor Is Added Between Neutral And Earth Of An Alternator?

Answer :

In order to restriction the flow of modern through impartial and earth a resistor is brought between them.

Electrical Engineering Interview Questions
Question 25. What Is The Backup Protection Available For An Alternator? Overcurrent And Earth Fault Protection Is The Backup Protections. What Are Faults Associated With An Alternator?

Answer :

External fault or thru fault

Internal fault

1. Short circuit in transformer winding and connection

2.Incipient or slow growing faults

Question 26. What Are The Main Safety Devices Available With Transformer?

Answer :

Oil degree guage, surprising stress postpone, oil temperature indicator, winding temperature indicator .

Question 27. What Are The Limitations Of Buchholz Relay?

Answer :

Only fault below the oil stage are detected.

Mercury switch setting have to be very accurate, otherwise even for vibration, there can be a fake operation.

The relay is of sluggish running kind, that is unsatisfactory.

Electronic Communications Interview Questions
Question 28. What Are The Problems Arising In Differential Protection In Power Transformer And How Are They Overcome?

Answer :

Difference in lengths of pilot wires on either aspects of the relay. This is triumph over with the aid of connecting adjustable resistors to pilot wires to get equipotential points at the pilot wires.

Difference in CT ratio mistakes distinction at high values of short circuit currents that makes the relay to operate even for external or through faults. This is triumph over through introducing bias coil.

Tap converting alters the ratio of voltage and currents among HV and LV sides and the relay will experience this and act. Bias coil will remedy this.

Magnetizing inrush modern seems anywhere a transformer is energized on its primary facet producing harmonics. No contemporary could be seen by the secondary. CT’s as there's no load within the circuit. This difference in contemporary will actuate the differential relay. A harmonic restraining unit is introduced to the relay so that you can block it when the transformer is energized.

Question 29. What Is Ref Relay?

Answer :

It is confined earth fault relay. When the fault happens very near to the neutral point of the transformer, the voltage to be had to pressure the earth circuit could be very small, which might not be sufficient to prompt the relay, except the relay is about for a totally low modern. Hence the sector of safety inside the winding of the transformer is constrained to cover only round eighty five%. Hence the relay is referred to as REF relay.

Question 30. What Is Over Fluxing Protection In Transformer?

Answer :

If the turns ratio of the transformer is extra than 1:1, there will be higher center loss and the functionality of the transformer to face up to this is restrained to a few minutes most effective. This phenomenon is referred to as over fluxing.

Question 31. Why Busbar Protection Is Needed?

Answer :

Fault degree at busbar is excessive.

The balance of the machine is tormented by the faults inside the bus sector.

A fault within the bus bar reasons interruption of supply to a big portion of the machine community.

Question 32. What Are The Merits Of Carrier Current Protection?

Answer :

Fast operation, car re-final feasible, easy discrimination of simultaneous faults .

Question 33. What Are The Errors In Ct?

Answer :

Ratio mistakes

Percentage ratio errors = [(Nominal ratio – Actual ratio)/Actual ratio] x 100 The cost of transformation ratio is not equal to the turns ratio.

Phase attitude blunders:

Phase perspective       =one hundred eighty/π[(ImCos δ-I1Sin δ)/nIs]

ELECTRONICS & INSTRUMENTATION Engineering Interview Questions
Question 34. What Is Field Suppression?

Answer :

When a fault takes place in an alternator winding despite the fact that the generator circuit breaker is tripped, the fault maintains to fed because EMF is induced inside the generator itself. Hence the field circuit breaker is opened and stored power inside the area winding is discharged via any other resistor. This method is called discipline suppression.

Question 35. What Are The Causes Of Bus Zone Faults?

Answer :

Failure of support insulator ensuing in earth fault
Flashover across support insulator during over voltage Heavily polluted insulator causing flashover Earthquake, mechanical harm etc.
Question 36. What Are The Problems In Bus Zone Differential Protection?

Answer :

Large wide variety of circuits, one of a kind cutting-edge levels for different circuits for outside faults.
Saturation of CT cores because of dc aspect and ac aspect in quick circuit currents. The saturation introduces ratio mistakes.
Sectionalizing of the bus makes circuit complicated.
Setting of relays need a trade with massive load changes.
Electrical Machines Interview Questions
Question 37. What Is Static Relay?

Answer :

It is a relay in which measurement or contrast of electrical quantities is made in a static community that's designed to present an output sign while a threshold circumstance is exceeded which operates a tripping device.

Question 38. What Is Power Swing?

Answer :

During switching of strains or wrong synchronization surges of actual and reactive strength flowing in transmission line causes intense oscillations inside the voltage and present day vectors. It is represented with the aid of curves originating in load areas and travelling towards relay characteristics.

Question 39. What Is A Programmable Relay?

Answer :

A static relay may have one or more programmable devices including microprocessors or microcomputers in its circuit.

Question 40. What Is Cpmc?

Answer :

It is blended protection, monitoring and manipulate device included inside the static device.

Electronic Devices and Circuits Interview Questions
Question 41. What Are The Advantages Of Static Relay Over Electromagnetic Relay?

Answer :

Low energy consumption as little as 1mW
No transferring contacts; as a result related troubles of arcing, touch soar, erosion, replacement of contacts
No gravity effect on operation of static relays. Hence may be used in vessels ie, ships, aircrafts and so on.
A single relay can carry out numerous features like over modern-day, below voltage, single phasing safety with the aid of incorporating respective useful blocks. This is not feasible in electromagnetic relays
Static relay is compact
Superior running characteristics and accuracy
Static relay can assume , programmable operation is viable with static relay
Effect of vibration is nil, subsequently may be utilized in earthquake-inclined regions o Simplified testing and servicing. Can convert even non-electric quantities to electrical at the side of transducers.
Question 42. What Is Resistance Switching?

Answer :

It is the approach of connecting a resistance in parallel with the touch space(arc). The resistance reduces the restriking voltage frequency and it diverts a part of the arc modern. It assists the circuit breaker in interrupting the magnetizing modern-day and capability modern.

Electrical Power System Interview Questions
Question 43. What Do You Mean By Current Chopping?

Answer :

When interrupting low inductive currents inclusive of magnetizing currents of the transformer, shunt reactor, the rapid deionization of the contact space and blast effect might also cause the cutting-edge to be interrupted earlier than the herbal current 0. This phenomenon of interruption of the modern before its natural 0 is called current chopping.

Question forty four. What Are The Methods Of Capacitive Switching?

Answer :

Opening of unmarried capacitor bank
Closing of one capacitor bank against every other
Question 45. What Is An Arc?

Answer :

Arc is a phenomenon going on when the 2 contacts of a circuit breaker separate underneath heavy load or fault or short circuit circumstance.

Question forty six. Give The Two Methods Of Arc Interruption?

Answer :

High resistance interruption:-the arc resistance is improved with the aid of elongating, and splitting the arc so that the arc is fully extinguished

Current zero technique:-The arc is interrupted at cutting-edge zero role that occurs100 instances a 2d in case of 50Hz power gadget frequency in ac.

Question forty seven. What Is Restriking Voltage?

Answer :

It is the transient voltage performing across the breaker contacts at the immediately of arc being extinguished.

Question 48. What Is Meant By Recovery Voltage?

Answer :

The strength frequency rms voltage performing across the breaker contacts after the arc is extinguished and temporary oscillations die out is known as recovery voltage.

Question forty nine. What Is Rrrv?

Answer :

It is the price of upward thrust of restriking voltage, expressed in volts in step with microsecond. It is closely related to herbal frequency of oscillation.

Question 50. What Is Circuit Breaker?

Answer :

It is a chunk of gadget used to interrupt a circuit automatically beneath fault situations. It breaks a circuit both manually or by way of far off manage below normal situations and beneath fault conditions.

Question 51. Write The Classification Of Circuit Breakers Based On The Medium Used For Arc Extinction?

Answer :

Air smash circuit breaker Oil circuit breaker
Minimum oil circuit breaker Air blast circuit breaker
SF6 circuit breaker
Vacuum circuit breaker
Question fifty two. What Is The Main Problem Of The Circuit Breaker?

Answer :

When the contacts of the breaker are separated, an arc is struck between them. This arc delays the present day interruption technique and also generates sizeable warmth which can also cause harm to the gadget or to the breaker itself. This is the main hassle.

Question fifty three. What Are Demerits Of Mocb?

Answer :

Short contact existence

Frequent renovation Possibility of explosion

Larger arcing time for small currents Prone to restricts

Question fifty four. What Are The Advantages Of Oil As Arc Quenching Medium?

Answer :

It absorbs the arc energy to decompose the oil into gases, which have awesome cooling residences

It acts as an insulator and allows smaller clearance among line conductors and earthed components

Question fifty five. What Are The Hazards Imposed By Oil When It Is Used As An Arc Quenching Medium? There Is A Risk Of Fire Since It Is Inflammable. It May Form An Explosive Mixture?

Answer :

with arc. So oil is favored as an arc quenching medium.

Question 56. What Are The Advantages Of Mocb Over A Bulk Oil Circuit Breaker?

Answer :

It requires lesser quantity of oil
It calls for smaller space
There is a discounted risk of fireplace
Maintenance hassle are decreased
Question 57. What Are The Disadvantages Of Mocb Over A Bulk Oil Circuit Breaker?

Answer :

The degree of carbonization is improved because of smaller amount of oil
There is difficulty of disposing of the gases from the touch area in time
The dielectric strength of the oil deteriorates swiftly because of excessive degree of carbonization.
Question 58. What Are The Types Of Air Blast Circuit Breaker?

Answer :

Arial-blast type
Cross blast Radial-blast
Question 59. What Are The Advantages Of Air Blast Circuit Breaker Over Oil Circuit Breaker?

Answer :

The danger of fire is faded
The arcing time may be very small due to fast buildup of dielectric power among contacts
The arcing merchandise are completely removed through the blast whereas oil deteriorates with successive operations
Question 60. What Are The Demerits Of Using Oil As An Arc Quenching Medium?

Answer :

The air has enormously inferior arc quenching residences

The air blast circuit breakers are very sensitive to versions within the rate of rise of restriking voltage

Maintenance is needed for the compression plant which substances the air blast

Question sixty one. What Is Meant By Electro Negativity Of Sf6 Gas?

Answer :

SF6 has excessive affinity for electrons. When a unfastened electron comes and collides with a impartial fuel molecule, the electron is absorbed with the aid of the neutral gasoline molecule and terrible ion is formed. This is referred to as as electro negativity of SF6 gasoline.

Question sixty two. What Are The Characteristic Of Sf6 Gas?

Answer :

It has top dielectric energy and amazing arc quenching property. It is inert, non-poisonous, noninflammable and heavy. At atmospheric stress, its dielectric strength is 2.Five times that of air. At three times atmospheric stress, its dielectric power is identical to that of the transformer oil.

Question 63. Write The Classifications Of Test Conducted On Circuit Breakers?

Answer :

Type test
Routine take a look at Reliability take a look at
Commissioning take a look at
Question sixty four. What Are The Indirect Methods Of Circuit Breaker Testing?

Answer :

Unit take a look at
Synthetic test
Substitution checking out o Compensation trying out o Capacitance checking out
Question sixty five. What Are The Advantages Of Synthetic Testing Methods?

Answer :

The breaker can be tested for desired transient healing voltage and RRRV.
Both test modern and check voltage can be independently varied. This offers flexibility to the check
The technique is straightforward With this technique a breaker ability (MVA) of 5 time of that of the capacity of the test plant may be examined.
Question 66. How Does The Over Voltage Surge Affect The Power System?

Answer :

The over voltage of the electricity device ends in insulation breakdown of the equipments. It causes the road insulation to flash over and may also harm the close by transformer, turbines and the opposite device linked to the road.

Question sixty seven. What Is Pick Up Value?

Answer :

It is the minimum modern within the relay coil  at which the relay starts to function.

Question sixty eight. Define Target?

Answer :

It is the indicator used for showing the operation of the relay.

Question sixty nine. Define Reach?

Answer :

It is the space upto which the relay will cowl for protection.

Question 70. Define Blocking?

Answer :

It way stopping the relay from tripping because of its very own characteristics or because of additional relays.

Question 71. Define A Over Current Relay?

Answer :

Relay which operates while the modern ia a line exceeds a predetermined cost.

Question seventy two. Define An Under Current Relay?

Answer :

Relays which operates on every occasion the current in a circuit drops under a predetermined fee.

Question 73. Mention Any 2 Applications Of Differential Relays?

Answer :

Protection of generator and generator-transformer unit: protection of large motors and bus bars

Question seventy four. Mention The Advantages Of Field Tests?

Answer :

The circuit breaker is tested below actual conditions like those who occur inside the community. Special events like breaking of charging currents of long strains ,very brief line faults ,interruption of small inductive currents and so on. May be tested by using direct checking out simplest.

Question seventy five. State The Disadvantages Of Field Tests?

Answer :

The circuit breaker can be tested at simplest a given rated voltage and network potential.
The necessity to break the regular offerings and to test handiest at light load conditions.
Extra inconvenience and fees in set up of controlling and measuring system within the field.
Question 76. Define Composite Testing Of A Circuit Breaker?

Answer :

In this approach the breaker is first examined for its rated breaking capacity at a reduced voltage and afterwards for rated voltage at a low modern.This approach does now not provide a right estimate of the breaker performance.

Question seventy seven. State The Various Types Of Earthing?

Answer :

Solid earthing, resistance earthing , reactance earthing , voltage transformer earthing and zig-zag transformer earthing.

Question 78. What Are Arcing Grounds?

Answer :

The presence of inductive and capacitive currents inside the isolated impartial device results in formation of arcs known as as arcing grounds.

Question 79. What Is Arc Suppression Coil?

Answer :

A technique of reactance grounding used to suppress the arc due to arcing grounds.

Question 80. State The Significance Of Single Line To Ground Fault?

Answer :

In unmarried line to ground fault all the sequence networks are linked in series. All the series currents are same and the fault current significance is 3 instances its sequence currents.

Question eighty one. What Are Symmetrical Components?

Answer :

It is a mathematical tool to solve unbalanced additives into balanced components.

Question 82. State The Three Sequence Components?

Answer :

Positive series additives, bad collection components and 0 sequence additives.

Question eighty three. Define Positive Sequence Component?

Answer :

has 3 vectors equal in magnitude and displaced from each other via an perspective a hundred and twenty degrees and having the segment series as original vectors.

Question eighty four. Define Zero Sequence Component?

Answer :

They has 3 vectors having same magnitudes and displaced from each other by using an perspective 0 degees.

Question 85. State The Significance Of Double Line Fault?

Answer :

It has no zero series element and the high-quality and negative sequence networks are linked in parallel.

Question 86. Define Negative Sequence Component?

Answer :

It has 3 vectors same in significance and displaced from each other by way of an attitude a hundred and twenty tiers and has the segment sequence in contrary to its unique phasors.

Question 87. State The Different Types Of Faults?

Answer :

Symmetrical faults and unsymmetrical faults and open conductor faults. 92. State the various forms of unsymmetrical faults.

Line to ground ,line to line  and double line to ground faults

Question 88. Mention The Withstanding Current In Our Human Body?

Answer :

9mA

Question 89. State The Different Types Of Circuit Breakers?

Answer :

Air ,oil,vacuum circuit breakers.

Question 90. Define Per Unit Value?

Answer :

It is defined as the ratio of real cost to its base price. 96. Mention the inductance price of the peterson’s coil.

L=1/3ωc2

Question 91. Define Single Line Diagram?

Answer :

Representation of diverse strength device additives in a single line is described as unmarried line diagram.

Question 92. Differentiate Between A Fuse And A Circuit Breaker?

Answer :

Fuse is a low present day interrupting tool. It is a copper or an aluminium cord.Circuit breaker is a excessive modern interrupting device and it act as a transfer underneath ordinary working conditions.

Question ninety three. How Direct Tests Are Conducted In Circuit Breakers?

Answer :

Using a short circuit generator because the supply.
Using the electricity utility system or network as the source.
Question 94. What Is Dielectric Test Of A Circuit Breaker?

Answer :

It includes overvoltage withstand check of energy frequency lightning and impulse voltages.Testa are carried out for both inner and external insulation with transfer in each open and closed situations.