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1.What are the functions of protective relays

To detect the fault and initiate the operation of the circuit breaker to isolate the defectiveelement from the rest of the system, thereby protecting the system from damages consequent to

the fault.

2.Give the consequences of short circuit.

Whenever a short-circuit occurs, the current floing through the coil increases to an enormous

value. !f protective relays are present , a heavy current also flos through the relay coil, causing

it to operate by closing its contacts.The trip circuit is then closed , the circuit breaker opens and

the fault is isolated from the rest of the system. "lso, a lo voltage may be created hich may

damage systems connected to the supply.

#.$efine protected %one.

"re those hich are directly protected by a protective system such as relays, fuses or

sitchgears.!f a fault occurring in a %one can be immediately detected and or isolated by a

 protection scheme dedicated to that particular %one.

  &.What are unit system and non unit system'

  " unit protective system is one in hich only faults occurring ithin its protected %one are

isolated.(aults occurring elsehere in the system have no influence on the operation of a unitsystem." non unit system is a protective system hich is activated even hen the faults are

e)ternal to its protected %one.

 *.What is primary protection'

 !s the protection in hich the fault occurring in a line ill be cleared by its on relay and

circuit breaker.!t serves as the first line of defence.

 +.What is back up protection'

 !s the second line of defence , hich operates if the primary protection fails to activate ithin a

definite time delay.

.ame the different kinds of over current relays.

!nduction type non-directional over current relay,!nduction type directional over current relay

current differential relay.

/.$efine energi%ing quantity.

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  !t refers to the current or voltage hich is used to activate the relay into operation.

0.$efine operating time of a relay.

!t is defined as the time period e)tendind from the occurrence of the fault through the relay

detecting the fault to the operation of the relay.

 1.$efine resetting time of a relay.

!t is defined as the time taken by the relay from the instant of isolating the fault to the moment

hen the fault is removed and the relay can be reset.

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QUESTION BANK 

UNIT – 01 2 Marks

1. $efine the terms 3urden, 4eset, 5perating time, 678, T78, over reach ,pickup.

  2. What are the advantages of static relay over electromagnetic relay'

  #. What is the need for protective gear in poer system'

  &. What are the different classification of relays'

  *. $efine selectivity of protective relaying.

+. Give at least to merits of resistance grounding system.

. 8ention the various parameters used for discriminating fault location in a poer system.

/. What is backup protection'

0. 9ist the functional characteristics that a protective relay is required to satisfy.

1. What are the desirable qualities of protective relaying'

11. What are the protective %ones of poer system'

12 What are the causes of fault in poer system'

1#. What is the need for protective %ones in poer system'

1&. The 6ositive, egative and :ero sequence reactance of a 28;",1#.2

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1. Give any to application of electromagnetic relays.

11. Give the block diagram of static relay indicating its basic elements.

12. 9ist the various schemes of protection of feeders.

1#. $ifferentiate beteen a poer transformer and a current transformer.

1&. $ra a protection scheme to detect a turn-turn fault in a inding of an alternator'

1*. " #B, *k;",11@.&k; transformer is connected in delta@star. The protection transformer

on the 9; side have turns ratio of *@* hat ill be CT ratio on the A; side of thetransformer'

1+. $ra the schematic diagram for biased differential protection of "lternator.

1. (or the 8er%-pri%e circulating current system for the protection of a 18;", 11k;@.&k;$elta@7tar #phase transformer. (ind the turns ratio of the current transformer for a nominal *"

secondary current'

1/. 9ist the abnormal condition in a transformer against hich protection is necessary.

10. What are the to types of protection given for busbars'

2. What is the meaning of burden on C.T'

21. 3usbar protection need special attention hy'

22. Why the protection of generator is comple)'

2#. What is 3uchhol% relay' 7tate the its important function.

2&. What are the requirements of protective line'

2*. $istinguish beteen primary and secondary protection schemes'

2+. 7tate the application of CT?s@6.T?s in protective schemes.

UNIT – 04 & 05 2 Marks

1. What is meant by arc quenching'

2. $efine current chopping related to arc quenching.

#. What is meant by 4estriking voltage'

&. ame the to theories that are used to describe "rc e)tinction phenomenon.

*. 8ention the different methods of high resistance arc interruption.

+. What are the basic requirements of circuit breakers'

. What are the problems encountered in $C circuit breaking'

/. What is meant by arc interruption in circuit breakers'

0. $efine recovery voltage in circuit breakers.

1. Why $C circuit breaking is difficult compared ith "C circuit breaking.

11 9ist the factors on hich the "C resistance depends .

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12. $efine rate of rise of restriking voltage.

1#. What is the effect of current symmetry on the instantaneous values of recovery voltage'

1&. $ra the 7tatic $ynamic arc characteristics.

1*. $ifferentiate "C $C circuit breaking.

1+. What are the to factors on hich 444; depends upon.

1. Ao is arc intiated across the contacts of C.3'

1/. $ifferentiate beteen a symmetrical assymetrical breaking current.

10. What is the advantage of cross-Det e)plosion pot in C.3'

2. " circuit breaker is rated at 12",1*8;",##

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EiF compare the arc rupture in oil air blast C.3 summari%e their relative merits

demerits

EiiF Ao 7(+ gas is used as a "rc quenching medium in a Aigh ;oltage C 3 for circuit

 breaking '

/. =)plain the Construction, 6rinciples of 5peration, merits, and demerits of "ir 3reak circuit3reaker.

0. EiF Write short notes on breakdon in vacuum. EiiF Compare $ifferent types of Circuit3reakers in detail

UNIT – 02 16 Marks

01. What is meant by directional feature of an directional over current relay' $escribe itsconstruction

  "nd 6rinciple of operation.

02. E)plain ith a aid of neat diagram, the principle of operation of induction type over currentrelay.

"nd also e)plain !$8T characteristics ho they are obtained in an induction type relay'

03. E)plain the orking principle of non-directional directional induction type over currentrelay.

  "nd =)plain the operating characteristics of the directional over current relay'

04. E)plain the principle of operation of E1Fcirculating current differential protection and

E2F 3alanced voltage differential protection compare

them'

05. =)plain ith sketches the !mpedance relay. $ra their 4- diagram.

06. (i) 7ho that the torque on the disc of an induction disc relay is ma)imum hen the phasedifference

 beteen to flu)es is 0H.

  EiiF Describe the operating principle of an attracted armature type relay. What measures aretaken to

minimi%e the noise in it.

07. "n !$8T9 over current relay has a current setting of 1*I has a time multiplier settingof .*. The

  CT ratio is *@*".calculate the time of operation relay if the circuit carries a fault current of 

+ ".  4elay has the folloing characteristics for 1I plug setting.

  678 2 #.+ * / 1 1*

  Time Ein 7ec.F 1 + #.0 #.1+ 2./ 2.2

08. E)plain the construction ,orking principle characteristics of reactance relay typedistance relay.

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10.  With a neat sketch e)plain the orking of a $istance relay ith $irectional feature. =)plain

the merits

"nd demerits of this relay' $ra the relevant 4- $iagram.

11. =)plain the clearly the difference beteen !mpedance, 4eactance, 8A5 relay. Give the

torque equation

  of each type sho their characteristics on 4- diagram .e)plain hat is meant by # %one protection

12 (i)  =)plain ith suitable diagram the principle of orking of Translay relay.  (ii) 9ist the merits and demerits of static relay

1# EiF !llustrate ith a neat sketch and vector diagram of protection using egative phasesequence relays.

  EiiF =)plain earth fault protection and restricted earth fault protection ith a neat sketch

1& 9ist various building blocks that constitute for the static relay give brief description about

each blocks.

UNIT – 03 16 Marks

01. $escribe ith a neat diagram the biased differential protection for star@delta transformersho is the

  machine operation against magneti%ing in rush current avoided'

02EiF With a neat schematic e)plain the construction orking of a buchhol% relay for transformer protection'

  EiiF Ao is J!nverted runningK prevented in a turbo alternator, diesel generator'

03(i). =)plain to protection scheme used for a busbar ith e)ample.  EiiF =)plain Generator-Transformer unit protection using the differential relaying scheme.

04. =)plain the different protection scheme necessary for the protection of a poer transformer.

"lso tabulate

The different types of CT connections used for different types of inding connections.

05. =)plain the folloing protection scheme of alternators.  EiF 7tator inter turn protection EiiF 8er%. price protection

06(i) What are rotor faults in an alternator' for such cases give their causes suggest protective

measures'

  EiiF What is 3urden of a CT' Why the secondary should not be open circuited.

07. Give different protection schemes for protection of transmission line using distance relay.

08 $ra e)plain protection scheme of a "C # phase induction motor in detail'

09. " star connected # phase 128;",+.+

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10.  " generator is protected by restricted earth fault protection .the generator ratings are

1#.2

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2EiF $escribe essential qualities of protective relay

  EiiF $iscuss the symmetrical components method to analy%e an unbalanced system.

#EiF 9ist the causes of faults in different equipment in a sample system.  EiiF =)plain the primary back up protection.

  EiiiF " # phase 11

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  had a natural frequency of 1+