Automatic Reclosing of Distribution and Transmission Line Circuit ...

MULTILINGER-2540A

Automatic Reclosing ofDistribution and Transmission

Line Circuit Breakers

GE Power Management

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CONTENTS

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INTRODUCTION

APPLICATION CONSIDERATIONS – GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

TYPE NLR RECLOSING RELAYSGENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Distribution Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Transmission Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

PRINCIPLES OF OPERATIONGENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Timing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Stepping Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Telephone-Type Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

DISTRIBUTION CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Reclosing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Delayed Initial Reclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Reset Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8AC Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Special Contact Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Special Connections and Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

TRANSMISSION LINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21High Speed Reclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Delayed Reclosures Following Immediate Reclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24Delayed Initial Reclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24Out-of-Step Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24General Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Remote Breaker Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

TYPE NSR RECLOSING RELAYSGENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

PRINCIPLES OF OPERATIONGENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26TYPICAL CONNECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Initiation by 52/b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30AC Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

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INTRODUCTION

The primary purpose of this paper is to describethe operating principles of the General ElectricTypes NLR and NSR reclosing relays, and todiscuss their application with distribution ortransmission line circuit breakers. Both relaysare designed to perform the same basic function– to automatically reclose a circuit breakerwhich has been tripped by protective relaying.

Generally speaking, the Type NLR relay, which isa multi-shot reclosing relay, is most frequentlyapplied to circuit breakers in the distributionarea; and the Type NSR relay, which is a single-shot reclosing relay, is usually applied on high-voltage transmission lines. There are, however,many exceptions to this general rule. The TypeNLR relay, for example, is being increasinglyused with transmission line breakers in a"selective reclosing" scheme. This arrangementinitiates an immediate reclosure followinginstantaneous trips by primary relaying, butinitiates delayed reclosures with synchronismcheck following delayed trips or unsuccessfulinitial immediate reclosures. The Type NSR relayhas been applied in the distribution area wherespecial circumstances dictate that only a singleinstantaneous reclosure is wanted. Ondistribution breaker applications, however, it isusually preferable to use the Type NLR relayeven though only a single high-speed reclosureis initially desired, since this provides the meansof adding delayed reclosures at a later date.

APPLICATION CONSIDERATIONS –GENERAL

The following general factors should beconsidered in the application of any automaticreclosing relay:

1. Interrupting Rating of Power Circuit Breaker –The derating factor applying to theinterrupting rating of the power circuitbreaker should be checked prior to theapplication of a reclosing relay or theselection of a reclosing cycle.

2. Closing Control Circuits – When automaticreclosing is used, it is essential that theclosing circuits with solenoid mechanismensure complete closure of the breaker eventhough the auxiliary switch on the breakermechanism opens before the closure iscomplete.

3. Latch-checking Switches – In order to ensuresuccessful operation of a breaker reclosed bya Type NSR relay, or by a Type NLR relay setfor immediate initial reclosure, it is necessarythat the breaker mechanism be equippedwith a latch-checking switch if themechanism is trip-free. This switch ensuresthat the mechanism latch is properly set forreclosure before the closing circuit iscompleted. Latch-checking switches are notrequired for non-trip-free mechanisms.

4. Control Switches – A control switch (typicallyModel 16SB1B9) should be provided with

Automatic Reclosing of Distribution and Transmission Line Circuit Breakers

L. E. GoffPower Systems Management

General Electric Company6901 Elmwood Avenue

Philadelphia, Pennsylvania 19142

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automatic reclosing schemes using the TypeNLR or Type NSR reclosing relays. This switchincludes contacts to prevent the breaker frombeing automatically reclosed after it has beentripped by the control switch. The breakermust be reclosed by means of the switchbefore the automatic reclosing feature will berestored.

5. Undervoltage Devices – Where undervoltagedevices are involved on the circuit fed by thebreaker, it is usually necessary to coordinatethe reclosing time and the trip time of theundervoltage device to ensure that thedesired results are obtained. Where the UVDis involved in a throwover scheme, the initialreclosure usually should be faster. Wheremotor control is involved, it may or may notbe desirable for the initial reclosure to befaster. Each application should be checked todetermine the required coordination.

6. Associated Protective Relays – If high-speedreclosing is to be successful, the protectiverelays that tripped the breaker obviouslymust reopen their contacts before the breakerrecloses. Some of the superseded types ofinduction time-overcurrent relays are notsuitable for use with high-speed reclosing. Ifdistance relays are supplied from line-sidepotential, their contacts should be supervisedby contacts of instantaneous fault detectorsto ensure that the trip circuit is open beforethe breaker recloses.

In addition to the above general applicationconsiderations, there are a number of specificrequirements which must be considered whenapplying the Type NLR or NSR relays in variousreclosing schemes. These are described in thesections which follow.

TYPE NLR RECLOSING RELAYS

GENERAL

The Type NLR reclosing relay is designed to initiatemultiple reclosures of a circuit breaker which hasbeen tripped by protective relaying. It is essentiallya timing device, with a heavy-duty stepping switchoperating contacts in response to impulses from asolid-state electronic timing circuit. The basic relayis designed for dc operation from the stationbattery. Models are available, however, with aninternally mounted full-wave bridge rectifier foroperation from an ac source.

The Type NLR reclosing relays are designed toprovide a variety of reclosure combinations, fromsingle-shot, either immediate or delayed, toimmediate plus two delayed reclosures (or threedelayed reclosures for some models). The totalreclosing cycle is adjustable from 18 to 180seconds. Delayed reclosure intervals can beconveniently set by means of cams. An optionalreset feature, set by means of a movable link,provides three choices of reset following asuccessful reclosure; (1) reset occurs two stepsafter the reclosure; (2) reset occurs at the nextreclose point; or (3) reset occurs one time stepafter the lockout position.

The NLR relays include a number of otherfeatures to meet requirements peculiar tocertain specific areas of application. These arediscussed in detail in the following paragraphs.

APPLICATION

The Type NLR family of reclosing relays findsapplication in two major areas of powersystems:

1. Distribution area on radial circuits.

2. Transmission lines where generation isusually present at both ends of the line.

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Although the general requirements of the Type NLRrelay are the same in both areas, each imposes certainspecific requirements which must be considered inthe design of the Type NLR relay or in the associatedreclosing scheme. Models now in general use in thetwo areas are listed in Table I. Refer to the GeneralElectric Handbook on Protective Relays for completemodel numbers for the typical voltage ratings listed.

The Type NLR21E relay is designed specifically forapplication with transmission line circuit breakersand would not be used in any other area. Theremaining relays in Table I are intended primarily foruse in the distribution area, as indicated in the table.However, these relays have been utilized withtransmission line circuit breakers in somecircumstances. The specific applicationrequirements and relay features peculiar to eacharea are discussed in the following paragraphs.

Table ITYPE NLR RELAYS

Gen AC Typical NumberApplic or Voltage of Re-

Type Area* DC Ratings closures RemarksNLR21A D DC 48,125 3

or 250NLR21B D AC 120 or 3

240V,60 Hz

NLR21C D DC 48, 125 4 Initial reclosureor 250 fixed instan-

taneousNLR21D D AC 120 or 4 Initial reclosure

240V, fixed instan-60 Hz taneous

NLR21E T DC 48, 125 4 Initial reclosureor 250 fixed instan-

taneousNLR21G D DC 48 or 3 Fast lockout

125NLR21M D DC 48/125 4 Dual ratedNLR21U D DC 48/125 3NLR21P D AC 120V 3

60 HzNLR21T D DC 125 3

*D = Distribution circuits;

T = Transmission lines.

Distribution Circuits

1. Coordination with Branch Fuses – The TypeNLR reclosing relays are frequently applied ata main feeder breaker supplying a number offused branch feeder circuits. Usual practice isto clear a fault on a branch feeder by firsttripping the feeder breaker by instantaneousrelays, and blocking the instantaneous tripcircuit prior to the initial reclosure. If the faultis still present, it will be cleared the secondtime by the blowing of the branch feeder fuse,with time overcurrent relaying at the feederproviding back-up protection. The timeovercurrent relays must, of course, coordinatewith the branch fuses.

The relays in Table I designated for use ondistribution circuits include means for blockingthe instantaneous trip circuit prior to the initialreclosure, and means for reinstatinginstantaneous trip when the Type NLR relaylocks out, if this is desired.

2. Blocking of Automatic LTC — Many users findit desirable to block operation of theautomatic load tap changing of thesubstation transformer during a reclosingcycle. Means are provided in Type NLR relays,designated for distribution circuit application,to block this circuit at the start of the cycleand to reinstate it at lockout.

3. Selective Reclosing — The relays in Table Idesignated for distribution application areascan be connected to initiate an immediatefirst reclosure or a delayed first reclosuredepending on which protective relays trippedthe breaker. However, these NLR relays do notinclude means for coordinating withsynchronism check relays.

Separatelyadjustabledelay onfirst step

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Transmission Lines

1. Selective Reclosing with Synchronism Check– On transmission line applications, where asource of generation exists at each end of theline, typical practice when multishot reclosingrelays are used is to initiate high-speedreclosing following instantaneous tripping bythe primary pilot relaying, but to block high-speed reclosing and initiate one or moredelayed reclosures, supervised bysynchronism check relays, following a trip bybackup relaying. The NLR21E relays fortransmission line application are designed toaccomplish this.

2. Out-of-Step Blocking of Reclosing — Iftransmission line protective relays areallowed to trip on an out-of-step condition, acommon practice is to block instantaneousreclosing. An out-of-step blocking relay canbe interconnected with the NLR21E relay toaccomplish this.

3. The NLR21A through NLR21D models, andother relays designated in Table I for thedistribution area, are applicable in somecircumstances on transmission line circuitbreakers when the special features of theNLR21E are not required.

PRINCIPLES OF OPERATION

GENERAL DESCRIPTION

Since the basic elements and operatingprinciples of all Type NLR relays are the same,the following general description is given as apreliminary to the more detailed discussions ofthe specific schemes.

Timing Circuit

Relay operation is based on the operation of astatic timing circuit and a heavy-duty steppingswitch, shown schematically in Fig. 1. Theswitch steps once in response to each impulsefrom the static timing circuit. The intervalbetween steps, that is between impulses, iscontrolled by the R-C characteristic of the timingcircuit. The voltage across this circuit isregulated to provide identical step-timeintervals, unaffected by changes in supplyvoltage. The step time interval can be adjustedfrom 0.5 to 5.0 seconds by means of rheostat R1,providing a total timing period from 18-secondsminimum (36 steps of 0.5 seconds) to 180seconds maximum (36 steps of 5 seconds).

Stepping Switch

The stepping switch rotates its shaft through acomplete revolution in 36 equal time steps. Eachstep is initiated by an impulse from the statictiming circuit. This impulse occurs when thetiming capacitor (C1) charges to the turn-onpoint of the unijunction transistor. The output ofthe unijunction in turn fires the SCR whichcauses current to flow through the operatingcoil of the switch (SA).

The physical arrangement of the steppingswitch is shown in Fig. 2. When the armature ofthe switch picks up, it lifts the driving pawl ofthe ratchet wheel to the next tooth and loadsthe main spring. At the same time, the armatureopens an SA contact which interrupts the SCRcurrent, turning off the SCR. The main springthen resets the armature and turns the ratchetwheel one step.

As the ratchet wheel turns the shaft, three camsare also turned. Two of these, the lockout andreset cams, are fixed and have one lobe each.They operate contacts once per revolution. Thethird cam, not shown in Fig. 2, has three

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adjustable lobes. These are the lobes whichinitiate the breaker closing signal. They can beset to initiate a reclosure at any point in thereclosing cycle, including the reset position(high-speed reclosure), as will be described later.

The lockout and reset cams each operate threecontacts, one normally open (NO) and twonormally closed (NC). The adjustable cam alsooperates three contacts, two NO and one NC.Note that the position of a contact (i.e., NO orNC) describes its condition when it is notoperated by a cam of the stepping switch, andnot necessarily its position when the NLR is atreset. This will be apparent in the more detaileddiscussions which follow.

An additional adjustable cam with one lobeoperates the RS switch. This can be optionallyconnected to provide either a NO or NC contact.The lobe can be set to close (or open) thecontact for a six-step interval at any point in theNLR relay cycle.

Telephone-Type Relays

The Type NLR relays listed in Table I, with theexception of the NLR21E and NLR21G, includetwo telephone-type relays mounted at the rear.The "C" unit maintains the closing signal to thecircuit breaker to ensure completion of theclosing operation. The "R" unit maintains thereset signal to the SA coil following a successfulreclosure until the stepping switch has steppedto position 36, the reset position.

The Type NLR21E relays for application ontransmission lines include, in addition to the "C"and "R" units, a CX unit which stops the timer ata delayed reclosure point until the synchronismcheck circuit permits reclosure.

The Type NLR21G relays, in addition to the "C"and "R" units, include an "L" unit which providesa fast lockout function.

A more detailed description of the operation ofthe Type NLR relays is given in the followingsections describing operation of several typicalschemes.

DISTRIBUTION CIRCUITS

The relays most commonly used in thedistribution area are the NLR21A, NLR21C,NLR21M and NLR21U for dc applications, andthe NLR21B or NLR21D for ac applications. Theelementary diagram in Fig. 3 shows typicalconnections for the dc relays with single rating,such as the NLR21A or -21C. Dual rated dc relayssuch as the NLR21M and -21U are covered byFig. 4. The cam-operated contacts SC, SL, andSR are shown as they would be with the relay inits reset position and set for an instantaneousinitial reclosure. For this condition, SC1 and SC3are held closed by a cam lobe, while SR1 andSR2 are held open.

The C unit can be connected to seal-in directlyto the positive bus or through a 52/b contact. InFig. 3 the C1 seal-in contact is shown connecteddirectly to positive which is permissible if thecontrol scheme of the associated breaker isinherently pump-free. Differences in theoperation of the reclosing scheme with the twoconnections of the C1 contact are described inthe following paragraphs.

Reclosing Circuit

The reclosing cycle is initiated by the closure ofthe breaker auxiliary switch 52/b when thebreaker trips. This energizes the C unit coilthrough the closed contacts R1, SL1, and SC1,and also energizes the timing circuit through thediode D1. When the C unit picks up, it seals indirectly to the positive bus through the C1contact, and also energizes the stepping-switchcoil SA through the SA1, C7 and SC3 contacts.This causes the stepping switch to move onestep immediately, as described in the preceding

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GENERAL DESCRIPTION section on theStepping Switch, resulting in the SC and SRcontacts shifting to a position opposite to thatshown in Fig. 3. It also discharges the timingcapacitor C1 when contact SA2 closesmomentarily.

Closure of contact SC2 energizes the breakerclosing circuit through contact C2 and the seal-in contact C1. Note that this seal-in contact willhold the C unit picked up for one time interval,which will maintain the pump-free closingcircuit energized for this period. If the closingcircuit is not inherently pump-free, an alternateconnection must be used as described later.Closure of contact SR1 on the instantaneousstep will keep the timing circuit energized,whether or not the breaker remains closed onthe initial reclosure. Opening of contact SC3prevents a second immediate step when SA1recloses.

If it is assumed that the fault is permanent andthe breaker retrips after the initial (andsubsequent) reclosures, the following sequencewill occur. After the first time interval, the SCRwill be gated. The C unit coil will be shorted bythe SCR and C will reset. There will be no stepafter this time interval since contact C4 wasinitially open preventing operation of SAthrough the SCR, and the opening of contact C3cuts off the SCR before contact C4 closes. Thus,the immediate step, which occurred when Cpicked up, will be regained. The overlappingcontacts C5 and C6 will discharge the timingcapacitor as C drops out.

The timer will continue to run and the steppingswitch will continue to operate, with equalelapsed time intervals between steps, until thepoint of the first delayed reclosure is reached asdetermined by the setting of the adjustablecams. At this point, contacts SC1 and SC3 willclose and SC2 will open. The resulting delayedreclosure sequence is very similar to the

immediate initial reclosure. When SC1 closes, itenergizes the C unit which picks up and seals inand energizes the SA coil through C7 and SC3.The switch will then immediately step again,closing SC2 and initiating the delayed breakerreclosure through C1 and C2. As withinstantaneous reclosure, the C unit will remainsealed up for one time interval, at which pointthe SCR will be gated, resetting the C unit. Theswitch will be prevented from stepping at thispoint by the C4 contacts, so the immediate stepis again recovered.

The relay will continue to step through one ortwo additional delayed reclosure attempts(depending on the relay type) and eventuallywill reach the lockout point where SL1 and SL2will be opened by a cam lobe, and the timingand stepping circuits will be de-energized.

Delayed Initial Reclosure

The immediate initial reclosure described abovewas obtained by setting an adjustable cam lobeso that the SC1 and SC3 contacts are heldclosed in the reset position. If a delayed initialreclosure is preferred, it is merely necessary toset the cam lobes for the desired delayed initialreclosure and for the subsequent delayedreclosure points. In the reset position, contactsSC1 and SC3 will then be open and SC2 closed.Thus, when the 52/b switch closes, the C unitwill not operate but the timing circuit will beenergized through diode D1. The timer will thenrun and the stepping switch will operate withequal time intervals between steps until theinitial delayed reclosure point is reached. Thesequence for the initial and subsequent delayedreclosures will be the same as described in thepreceding section.

Reset Circuits

In the preceding discussions it was assumedthat the fault was permanent, so that the

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breaker retripped following each reclosure andthat the NLR relay consequently steppedthrough its complete cycle until the lockoutposition was reached. A "RESET" selection linkis available which can be set to provide resetfollowing a successful reclosure. There are threechoices of link position: (1) "STEP-2" positionwhich resets the NLR two stop-time intervalsafter any successful breaker reclosure; (2) "NEXTCLOSE" position which initiates reset after asuccessful reclosure when the NLR ratchet hasreached the step where the next reclosing signalwill be given; and (3) the "NONE" position inwhich the rapid reset feature is eliminated andthe NLR will not reset after any successfulreclosure until the relay has stepped through itscomplete time cycle to one time interval afterthe lockout position.

The elementary diagram in Fig. 3 shows theselection link in the "STEP-2" position. Considerthe immediate initial reclosure sequencepreviously described. The reclosure attemptoccurs after the immediate step which takesplace when C picks up and seals in. If thereclosure is successful, breaker auxiliary switch52/a will remain closed which sets up the circuitthrough SR2, the coil of the R unit, and theselection link to contact C4 which will be open.After the first time interval the SCR drops out Cbut, since the SCR cuts off before contact C4closes, there will be no step and unit R will notpick up. On the next time step when the SCRfires, unit R will pick up, seal-in through contactsR2 and R3 and block the reclose circuit atcontact R1. The SA unit will then repetitivelypick up and drop out and the stepping switchwill run without time delay until it "homes" inthe reset position where contacts SR1 and SR2will reopen and the R unit will drop out. The NLRrelay is now reset and all contacts will again bein the position shown in Fig. 3. The same rapidreset sequence will occur after a successfuldelayed reclosure.

With the selection link in the "NEXT CLOSE"position, the R unit will not pick up following asuccessful reclosure until contact SC3 closes at thenext reclose position of the stepping switch. At thatpoint, R picks up and seals-in, and the steppingswitch will run without time delay, as previouslydescribed, until it "homes" in the reset position.

If the selection link is in the "NONE" position,there will be no rapid reset after a successfulreclosure and the NLR relay will run through itsnormal cycle until the lockout position isreached. At this point, contacts SL1 and SL2 willopen, but, if 52/a is closed, the timer will timeout one more interval and the switch will stepone more notch to the reset position.

The preceding paragraphs describe theoperation with the C1 contact connected directlyto positive. The C unit will be held picked up forone time interval after each reclosure, which willmaintain the breaker closing circuit energized forthis period. This is permissible if the closingcircuit is pump-free, which is usually the casewith dc circuits. An advantage of this connectionof the C1 contact is that the immediate stepassociated with each reclosure is regained at theend of the first time interval following thereclosure. Thus, the number of time stepsbetween reclosures will be a direct measure ofthe time interval between reclosures.

If the breaker closing circuit is not pump-free, itwill be necessary to connect the seal-in contactC1 through a 52/b contact rather than directly topositive. This connection of contact C1 is shownas an option in Fig. 3 and results in a lost timestep after each reclosure. The operation of theNLR relay for this connection is described indetail in the following section.

The external connections for the dual-rated dcmodels, NLR21M or NLR21U, are shown in Fig. 4.The operation of the scheme is covered by thepreceding description of the single-rated relays.

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AC Supply Voltage

The timing and stepping circuits of the NLR relayare inherently dc circuits. However, models areavailable (see Table I) which include a full-wavebridge rectifier to adapt the relay for operationfrom ac source. The elementary diagram in Fig. 5shows the recommended connections. Since theac closing circuit of the circuit breaker is notinherently pump-free, the C1 contact must beconnected so that the C unit seals-in through the52/b switch rather than directly to positive. Thisresults in some differences in the reclosing cycle.

The elementary diagram in Fig. 5 again shows thecam-operated contacts SC, SL, and SR as theywould be with the relay in its reset position and setfor an immediate initial reclosure. When 52/bcloses, the C unit picks up and seals-in (through52/b), the SA coil is energized through C7 and SC3,and the stepping switch moves one stepimmediately. This opens SC1 and SC3, and closesSC2, energizing the closing circuit through the C2contact. Thus far the sequence is the same asdescribed for the dc connections with the C1contact sealing in directly to the positive bus.

With the connections of Fig. 5 the C relay will notremain sealed in for one time interval, but will dropout when the 52/b switch opens during the initialreclosure. Consequently, at the end of the first timeinterval when the SCR is gated, C4 will be closedand SA will operate causing the stepping switch tomove another step. Thus, the immediate step willnot be regained and there will be a time step lostbetween successive reclosures. This must be takeninto account when setting the delayed reclosureintervals.

If rapid reset following a successful reclosure isdesired, it is recommended that the selectionlink be placed in the "NEXT CLOSE" position.Use of the "STEP-2" position will provide onlyone time interval between the reclosure andreset of the NLR relay. This results from the "lost

step" after each reclosure, and may beconsidered to be too quick, particularly if thetime step interval has been set below its fivesecond maximum value.

Special Contact Functions

A number of contact functions independent ofthe reclose or reset circuits are shown on theelementary diagram figures for the DistributionCircuit relays:

1. Block Instantaneous Trip – As noted underAPPLICATION, it is sometimes desirable tocoordinate with branch circuit fuses, byblocking the instantaneous trip circuit prior tothe initial reclosure. This can be accomplishedby means of the SR3 contact which is closedwhen the NLR relay is in the reset positionand will open on the immediate step whichoccurs prior to a high-speed initial reclosure.Typical connections of contact SR3 to blockinstantaneous trip are shown in Fig. 6.

It is also possible to reinstate the instantaneoustrip circuit prior to lockout by means of the RSswitch as described below.

The C8 contact associated with the SR3 contactis normally jumpered out. It can, however, bereconnected in parallel with SR3 so thatinstantaneous tripping blocked by SR3 will bereinstated one time interval after the reclosure.With this arrangement, the instantaneous tripcircuit will be blocked for one time interval,usually 5 seconds, after each subsequentdelayed reclosure.

2. Function of the RS Contact — The cam whichoperates the RS contact is dimensioned tohold the switch in the operated position forabout six steps of the stepping switch. Thus,the RS1 contact shown closed on theelementary diagram will be closed for 6 stepsand open for the remaining 30 steps of the

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cycle. There is a green jumper lead connectedto the common point between RS1 and RS2.By shifting this jumper from stud 9 to stud 10,the RS2 contact will become the effective oneand will be open for 6 steps and closed for theremaining 30 steps.

Normally, the jumper is connected to stud 9 andthe cam is set so that RS1 is closed at reset,opens shortly after the start of the NLR cycle,and recloses ahead of lockout. With this normalconnection, the RS1 contact is commonlyconnected in the control circuit of the tapchanger to block automatic load tap changingwhile the NLR relay is operating through itsreclosing cycle, and to reinstate it before therelay reaches the lockout position.

The RS1 contact with normal adjustment can beused in place of the SR3 contact in theinstantaneous trip circuit to blockinstantaneous tripping after the initial reclosure(either immediate or delayed). This providestwo instantaneous tripouts of the breakerbefore shifting to time delay trip to allowclearing by the branch fuse. With thisarrangement, instantaneous tripping will bereinstated at lockout.

Where the SR3 contact is used to blockinstantaneous trip prior to the immediate initialreclosure, the RS1 contact can be used toreinstate instantaneous tripping prior tolockout. To accomplish this, the RS1 contactwould be connected in parallel with SR3, and itsactuating cam would be positioned to close RS1prior to lockout, hold it closed in the lockoutposition, but reopen it when the relay steps tothe reset position.

3. Alarm Circuit – When the relay steps to thelockout position, contact SL3 in the alarmcircuit will close. If the breaker is open, the "b"switch and contact R5 will be closed and thelockout alarm circuit will be completed. The

R5 and "b" contacts prevent an alarm whilethe relay is passing through the lockout toreach the reset position following a successfulreclosure. If the breaker should trip againduring this transition period, the "b" contactwill close but the NLR relay will continue toreset, since the R unit has sealed in, and willthen initiate another cycle of reclosures. TheR5 contact prevents the lockout alarm fromoperating in this situation.

Special Connections and Schemes

A number of additional functions are available,either by means of special connections to theNLR21A, -B, -C, -D, -M or -U relays previouslymentioned, or by using special-purpose NLRrelays as described below:

1. Selective Reclosing—External connectionsare shown in Fig. 7 to initiate either animmediate initial reclosure or a delayed initialreclosure, depending on what protective relaytripped the circuit breaker. The diagram in Fig.7 specifically applies to the NLR21A or -21Crelays operating from a dc control voltage.The scheme requires the use of the RS1-RS2contacts in the instantaneous reclose circuitand the SR3 contact in the stepping circuit.This of course precludes the use of thesecontacts in the LTC control and instantaneoustrip circuits as previously described.

All cam-operated contacts are shown in theircondition with the NLR relay in the resetposition. The RS cam is set so that RS1 is closedand RS2 is open in the reset position, and sothey will reverse position on the first step. Theadjustable SC cams are set so that SC2 is closedand SC1 and SC3 open at reset, and so SC1closes at the desired delayed reclose points.

If the breaker is tripped by relaying with whichimmediate reclosing is desired, the Rl unit willbe picked up and, in turn, will operate C through

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contacts RS1 and SC2. The C unit will seal-inand will also energize the SA coil throughcontacts C2, R1, SL1, diode D1, SA1, C7 andSR3. The stepping switch will move one stepimmediately, and when contact RS2 closes, itwill energize the closing circuit via contacts SC2and C1. After the initial reclosure attempt, theNLR relay will continue to operate in the normalmanner, resetting if the initial reclosure wassuccessful or continuing through the delayedreclosure positions if the breaker retripped.

If the breaker is tripped initially by relayingwhich should not initiate an immediatereclosure, the Rl unit will not operate and theclosure of 52/b will start the timer through R1,SL1, and diode D1. The relay will then proceed

to step and initiate delayed reclosures in thenormal manner. If all reclosures fail, the NLRrelay will lockout in the normal manner.

The cam which actuates the RS contacts is sodesigned that the contact will be held closed forsix steps. Consequently if the cam is set so thatRS1 opens and RS2 closes on the first step, thenRS2 will reopen and RS1 will reclose about foursteps ahead of the lockout position. This limitsthe maximum delayed reclosure time since theRS2 contact is in the delayed reclosing circuit.

On manual closure following lockout, if the firstclose attempt is successful, the NLR relay willstep once to the reset position in the normalmanner previously described. However, if the

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fault is still present and is so located thatprotective relays operate which pick up Rl, thenthe Rl contact will close momentarily. This willcause C to pick up and seal-in, but there will beno immediate step since contacts SC3 and SR3will both be open. However, the C unit willremain sealed up after the breaker retrips. Asubsequent successful manual closure will startthe timer through 52/a, and diode D2. At the endof the step time interval, the SCR will fire, butthere will be no step since contact C4 is open.The gated SCR will cause C to reset, however, sothat at the end of the next step time interval theSCR will operate SA and the relay will step onceto the reset position.

Although this scheme does provide the meansof distinguishing between a breaker trip byprimary pilot relaying or by delayed backuprelaying, and initiating either an immediate or adelayed initial reclosure, it does not includemeans for coordinating with a synchronismcheck scheme. Consequently, the NLR21E relay, which does include such means, is recommended for transmission lineapplications.

2. Two Initial Instantaneous Reclosures – Thediagram in Fig. 8 describes a scheme forobtaining two instantaneous reclosuresfollowed by two (or three} additional delayedreclosures, using the NLR21A (or NLR21C)relays and a special Type NAA auxiliary relay.

On the initial tripout of the breaker, the 52/bcontact will pick up 79X/A which seals in aroundcontact SR3, and picks up the 79X/B unit. The79X/A3 contact will operate SA, initiating animmediate step. This causes SC2 to open andSC1 and SC3 to close. It also results in the SRcontacts reversing position so SR3 will now beopen. The closing of SC1 initiates the first high-speed reclosure through contact 79X/A5.

When 52/b opens during the breaker closing

cycle, 79X/A will drop out, but 79X/B will remainsealed in through contact SC3. If the breakertrips again, the C unit will pick up through SC1and 79X/A4, and another immediate step will beinitiated by contact C7 through SC3. This stepwill open SC1 and SC3, and close SC2 to initiatea second high-speed reclosure through contactsC1, SC2 and C2. The C unit will now remainsealed in for one time interval, as with thestandard NLR21A relay scheme shown in Fig. 3and previously described.

It should be noted that if the second high-speedreclosure is to be realized, the breaker mustretrip within the first time step interval,normally 5 seconds. Otherwise, the SCR willhave initiated a step, reopening SC1 andpreventing the C unit from picking up when 52/bcloses.

The timing circuit will now time out one steptime interval and gate the SCR. This resets C,but there is no step since C4 blocks the circuitthrough the SA coil. The second immediate stepis thus regained and the NLR relay will nowproceed in the normal manner to the firstdelayed reclosure point. If a 15 second initialdelayed reclosure is desired, the second SC camlobe should be set at position 4 to allow for theinitial immediate step which was not regained.

If the breaker stayed closed after either the firstor second high-speed reclosure, the NLR relaywill reset after two step time intervals, which isequivalent to three steps of the stepping switchsince the initial immediate step was notregained. After a successful first immediatereclosure, the 52/b contact will remain open, sowhen 79X/A drops out, the C unit will not pickup. The timer will now time out one interval andgate the SCR. Since contact C4 is closed, thiswill initiate a step. However, the 79X/B unit willstill be sealed up through SC3, so contact79X/B2 will prevent the R unit from operatingand thus block reset at this point. However,

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79X/B will drop out when SC3 opens on thisstep, so after the next step time interval, unit Rwill pick up, if 52/a is still closed, and the NLRwill step to reset in the normal manner.

If it is the second instantaneous reclosure which issuccessful, 79X/B will have dropped out when SC3opens prior to the reclosure, but R is now blockedby the C4 contact on the second step whichpreceded the successful reclosure, and on thefiring of the SCR after the first time interval whichresets C. Reset will be initiated after the secondtime interval or the third step of the switch.

3. Fast Lockout – The Type NLR21G relayincludes an additional telephone-type relay,the L unit, which provides a means ofobtaining fast lockout following the trippingof the associated breaker by certain trippaths, for example a differential relay trip, abreaker failure backup trip, or a supervisorytrip. A typical external connection diagram forthe NLR21G is shown in Fig. 9.

As will be noted in Fig. 9, the L unit is picked upthrough the SL4 contact by the 87, B, F, orSUP/T contact, except when the NLR is alreadyin the locked out position. The L unit is sealed inby the L1 contact, and the SA coil is energizedthrough the SL4 contact, the diode, and thecontact SA1 and L3 causing the stepping switchto step immediately to the locked out position.The L2 contact in the C unit coil circuit preventsthat unit from picking up and attempting areclosure during the fast lockout cycle. The Lunit is de-energized by the SL4 contact when thelockout position is reached.

4. Separately Adjustable First-step Time – TheTypes NLR21P and NLR21T relays aredesigned to initiate up to three independentlyadjustable delayed reclosures of a circuitbreaker, the first of which can be set for ashort delay as determined by a separatelyadjustable first-step time of 4 to 24

milliseconds. The relays are otherwise similarto the NLR21B and NLR21A respectively.

The diagram in Fig. 10 describes typical externalconnections for the NLR21T dc relay. All cam-operated contacts are shown in the position theywill assume with the relay in its reset position.When the relay is to be set for a short-delayinitial reclosure one of the three SC lobes mustbe set in the STEP-1 position so that contactsSC1 and SC3 will be open and SC2 will be closedin the STEP-0 position. When the reclosing cycleis initiated by the closing of the breaker auxiliaryswitch (52/b) the stepping switch will take itsfirst step after a short delay, determined by thesetting of potentiometer R11, causing the SCcontacts to reverse position. Contacts SC1 andSC3 will now be closed and SC2 will be open.The C unit will pick up and seal in, and will closethe C7 contact in the SA coil circuit. This willcause the stepping switch to immediately stepagain initiating the breaker closure through theSC2, C1 and C2 contacts. Note that the SR3contact will open on the first step, opening theR11 circuit so that subsequent delayedreclosures will be determined by the normal stepinterval adjustment. The range of 4 to 24milliseconds on the first-step delay is based on anormal step time interval setting of 5 seconds.

The performance of the NLR21T relay onsubsequent delayed reclosures is the same asthe NLR21A previously described.

5. Cumulative Lockout – The Type NLA15Astepping relay is available for those who wishto incorporate a cumulative lockout featurewith their automatic reclosing scheme. Whenused with the NLR relay, the NLA relay will beconnected to step once for each automaticreclosure, to sound an alarm after apreselected number of operations, and tolockout the automatic reclosing circuit after acertain number of subsequent operationsfollowing the alarm.

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TRANSMISSION LINES

The circuits previously described have beenapplied in some instances with transmission linecircuit breakers. Usually, however, the applicationof multi-shot reclosing relays on transmission linesinvolves special considerations. Since generationis usually present in back of each terminal of theline, a selective reclosing scheme is needed whichinitiates an immediate reclosure or a delayedreclosure depending on protective relay operation.If an immediate reclosure is to be successful, it isessential that the breakers at all terminals of theline be open before any breaker is reclosed.Consequently, some form of pilot relaying isnecessary, with immediate reclosing initiated onlyif the breaker is tripped by the pilot relaying. If thebreaker is tripped by time back-up relays, theinitial reclosure will be delayed, and will usually besupervised by synchronism check or dead-linecheck relays. Furthermore, it is sometimesdesirable to block immediate reclosing if theprimary pilot relaying is allowed to trip on an out-of-step condition.

The Type NLR21E relay is designed specifically forapplication on transmission lines. It includesmeans for achieving immediate initial reclosurefollowing a pilot relay trip, and for coordinating thedelayed reclosure with a synchronism check circuitfollowing a delayed trip by backup relays. It canalso be interconnected with the contacts of theout-of-step blocking auxiliary (OB) of a TypeCEB12B or CEB51A relay to prevent a high-speedreclosure if the primary relays operate on an out-of-step condition. The elementary diagram in Fig.11 shows the recommended connections of theType NLR21E relay.

High Speed Reclosure

All contacts in Fig. 11 are shown as they wouldbe with the NLR relay in its reset position and nofault on the line. Cam-operated contacts SC1,

SC3, and SR3 are held closed by a cam lobe andwill open on the first step of the steppingswitch, while SC2 is held open and will close onthe first step. Contacts RS1 and RS2 are held inthe positions shown by a cam lobe, but will notchange positions until the switch steps thesecond time.

If the primary pilot relays operate, they willenergize Rl and the breaker trip coil at the sametime. Closure of Rl will energize the CX auxiliaryunit through SR3, and will also energize thetiming circuit through diode D2. Operation of CXwill pick up C through contacts CX1 and CX2and diode D2. Contact CX3 will discharge thetiming capacitor. Closure of contact C7 willenergize the SA coil and cause the steppingswitch to step once immediately, closing SC2and setting up the circuit to the breaker closingcircuit. When the "bd" and/or "b" contacts close,the breaker closing circuit will be energizedthrough contacts CX1, C2, SC2, and RS1. Notethat the immediate step also opens SC1, SC3and SR3. However, the RS1 contacts are stillclosed since the cam was set to cause the RScontacts to change position on the second step.

The Rl unit will reset when the fault is clearedand 52/b will reopen during the initial reclosure.Hence, the CX unit will drop out and the path tothe breaker closing circuit will be open if thebreaker should retrip. The C unit will remainsealed in.

When the CX unit drops out, the timingcapacitor will start to charge through SR1 andSL2. At the end of the first time interval, the SCRwill be gated. The C unit will reset, but there willbe no step since C4 was open when the SCR wasgated. This sequence "regains" the immediatestep as described previously for the NLR21Arelay. At the end of the next time interval, thestepping switch will step for the second time,opening RS1 and closing RS2.

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Delayed Reclosures Following ImmediateReclosure

If the fault is permanent, the breaker will beretripped by the primary relaying and the Rlcontact will again close. A second immediatereclosure will be prevented because the CX unithas dropped out, and contact SR3 is open so the Rlcontact cannot pick up CX again. The NLR will nowstep to the first delayed reclosure point where acam will open SC2 and close SC1. The SC1 contactwill pick up CX through the RS2 contact, andclosure of the CX contacts will pick up C whichseals in. The CX3 contact will short out the timingcapacitor thus preventing further operation of thestep timer while CX is up. However, the C7-SC3contact combination will energize SA, causing theswitch to step once more to reclose SC2 and openSC1 and SC3. Closure of SC2 completes the closingcircuit up to the synchronism check circuit (or liveline/dead bus or live bus/dead line check). The NLRrelay will wait at this point because CX will remainpicked up. When the check circuits permit areclosure, the CX unit will drop out permitting thetiming circuit to commence functioning again.

Delayed Initial Reclosure

If the breaker is initially tripped by time-delaybackup relays, the Rl unit will not pick up.Closure of the "b" switch will start the timer, anddiode D2 prevents CX from picking up and inturn operating C. On the first time step, SC1 andSC3 will open and SC2 will close. On the secondtime step, the RS contacts will reverse position.

When the first delayed reclosure position isreached, the cam will open SC2 and close SC1and SC3. Closure of SC1 will pick up CX, sincethe RS2 contact is now closed, and this in turnwill operate C. The sequence will now be thesame as described in the previous sectionheaded "Delayed Reclosures FollowingImmediate Reclosure", with the delayed

reclosure controlled by the synchronism checkcircuit.

Reset

Immediate reset following a successfulreclosure is accomplished in the same manneras previously described for the NLR21A relay.The selection link can be set in either the STEP-2, NEXT CLOSE, or NONE position.

Out-of-Step Blocking

If the primary relays are allowed to trip on an out-of-step condition, many users elect to block high-speed reclosing. This can be accomplished bymeans of contacts of the OB auxiliary unit in theType CEB12B or CEB51A relay (68 device), asshown in Fig. 11.

A normally closed contact of OB is connected inthe CX coil circuit, and a normally open contact ofOB is connected from the Rl contact to the C unitcoil circuit. When a swing enters the 68/MOBcharacteristic, the OB unit will operate, block theCX unit, and set up a circuit from the Rl contact tothe C unit. If the primary relays ultimately trip onout-of-step, the Rl unit will pick up and operate C,which in turn will seal-in. The C7 contact willinitiate an immediate step in the normal manner,opening SC1, SC3 and SR3, and closing SC2. Therewill be no reclosure since SC1 and SR3 will be openbefore SC2 closes, and CX has not operated.

When the line is cleared by the breaker, the OB unitwill reset. However, this unit has a minimumdropout time of 4 cycles so there is ample time forthe immediate step to take place opening SC1 andSR3. When these contacts are open, the CX unit isblocked even though the OB contact has reclosed.

The NLR will now proceed to operate aspreviously described in the sections on delayedreclosures. The delayed reclosure attempts will

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be supervised by the synchronism check or liveline/dead bus live bus/dead line check circuits.

On multi-breaker arrangements, such as ringbus or breaker-and-a-half, there will normally bea single Type OSB relay associated with a line,and separate reclosing relays for each of the twobreakers with that line. There are sufficient OBcontacts in the Type CEB12B or CEB51A toaccomplish the functions shown in Fig. 11 foreach breaker.

General Comments

If it is desired to operate the NLR21E relayscheme with selective reclosing but withoutsynchronism check or live line/dead bus live bus/dead line check, it is merely necessary toconnect terminal 9 of the NLR relay directly tothe breaker closing circuit, omitting the checkcontacts and RS1. A primary trip which operatesRl will then initiate an immediate reclosure,while delayed trips will initiate a delayed initialreclosure.

If it is desired to use the NLR21E relay withoutselective reclosing, omit Rl and jumperterminals 10 and 14. Closure of 52/b will theninitiate an immediate reclosure regardless ofwhether the trip was instantaneous or delayed.Such an arrangement would not normally berecommended on transmission lines, but mightbe needed if the NLR21E relay were to beapplied on a stub-feed circuit.

Remote Breaker Control

When circuit breaker closing and tripping isfrom two or more locations, the use of controlswitch contacts such as 5-5C of 52CS shown inthe various figures would not normally give thedesired results. It is recommended that the 5-5Ccontact of 52CS be replaced by the contact of anauxiliary relay. One commonly used circuit is a

latched-type auxiliary relay which is picked up(and latches) by "trip" contacts of the two ormore circuit breaker control switches and isunlatched by "close" contacts of the two ormore breaker control switches; a contact whichcloses in the unlatched condition is used inplace of 5-5C of 52CS in the circuits coveredherein. Instead of a latched relay, similar resultscan be obtained by a single-coil, non-latchingauxiliary relay which is picked up by an "a"contact of the breaker and seals itself aroundthe breaker "a" contact; any breaker controlswitch operated to the trip position drops outthe auxiliary relay. A normally open contact ofthe relay is used in place of 5-5C of 52CS.

When circuit breaker control is by supervisorycontrol, a time-delay pick-up relay, connected asdescribed above for the non-latching auxiliaryrelay, is recommended. The purpose of the timedelay is to ensure that the breaker has beenclosed into an unfaulted line before setting upautomatic reclosing.

TYPE NSR RECLOSING RELAYS

GENERAL

The Type NSR reclosing relay is designed toinitiate a single high-speed reclosure of a powercircuit breaker which has been tripped byprotective relays. After the relay has initiated asuccessful breaker reclosure it will resetautomatically in a predetermined adjustablereset time. The relay will lock out if the breakershould trip again during the reset time interval.

The basic relay circuit consists of a capacitor-resistor timing scheme with an associatedauxiliary relay; unit. Hence, the relay isinherently suited for dc operation. Models areavailable, however, with an internal rectifier foroperation from an ac source.

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APPLICATION

The Type NSR reclosing relays are usuallyapplied with transmission line circuit breakerswhere a single high-speed reclosure is desired,and where if this single reclosure attempt isunsuccessful, it is desired to lock out thebreaker. The usual application of the relay iswith line protective relays, eitherelectromechanical or static, which include areclosure initiation function (Rl) to initiate thereclosure sequence when the primary protectiverelays operate. Relay models now available arelisted in Table II.

Table IITYPE NSR RELAYS

AC Typical Typicalor Voltage Target

Type DC Ratings Target Ratings RemarksNSR11C AC 120/240, No —

60 HzNSR11D AC 120/240, Yes 0.1, 0.2

60Hz &1.OANSR21E DC 48/125/ No —

250NSR21F DC 48/125/ Yes 0.1, 0.2

250 &1.OANSR21G DC 48/125/ No — Adjustable re-

250 close timeNSR21H DC 48/125/ Yes 0.1, 0.2 Adjustable re-

250 & 1.0A close time

PRINCIPLES OF OPERATION

GENERAL DESCRIPTION

The basic operating elements of the Type NSRrelay are a timing capacitor, a high-resistancerheostat, and a telephone-type relay having twoelectrically separate coils. The operation ofthese basic components to initiate a singleimmediate reclosure is illustrated by thesimplified diagram in Fig. 12. Under normalconditions with the breaker closed, thecapacitor will be fully charged. When the circuitbreaker is tripped, the initiating contact willconnect the operating coil of the telephone-type

relay (79/OC) across the capacitor. The capacitorwill discharge through the operating coil,causing the unit to pick up and seal in by meansof its holding coil (79/HC), and energize thebreaker closing circuit through contact 79-1.Contact 79-2 will completely discharge thecapacitor so that full reset time will be realizedafter each operation. When the breaker recloses,the 52Y contact (or equivalent) associated withthe breaker closing circuit will open the holdingcoil circuit, and the unit will drop out.

If the breaker is reclosed successfully, thecapacitor will immediately start to recharge. Thereset time of the NSR relay is the time requiredfor the capacitor to recharge to the point whereits stored energy will be sufficient to pick up thetelephone-type unit if the capacitor is againdischarged through 79/OC. This reset time isadjustable over a range of 3 to 20 seconds bymeans of the high-resistance rheostat(79/RHEO) which is accessible from the front ofthe relay. If the breaker should retrip prior to thereset time, the stored energy in the capacitorwill not be sufficient to operate the telephone-type unit and the NSR relay will lock out.

TYPICAL CONNECTIONS

The most common applications of the Type NSRrelay is on transmission lines where a singlehigh-speed reclosure is required. Theelementary diagram in Fig. 13 shows typicalexternal connections for such an application ofthe NSR21E or NSR21F with dc control voltage.The basic circuit elements described in theGENERAL section will be recognized. However, anumber of refinements are shown on thedetailed elementary which require explanation.

Under normal conditions, the timing capacitorwill be charged through the 86 and 79 COcontacts. The capacitor voltage, when it is fullycharged, is limited to 30 volts by the Zenerregulator connected across the capacitor and

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the rheostat. The regulator assures that thevoltage across the capacitor-rheostatcombination will be constant, and hence thereset time will be independent of variations inthe supply voltage. In fact, the timing circuit isthe same for dc voltage ratings of 48, 125, or250. A selection link is provided for the holdingcoil circuit, however, to select the proper seriesresistor for 48,125, or 250 volts.

On typical transmission line breakerapplications, high-speed reclosing is initiated bya contact of the reclosure initiating unit (Rl),which in turn is operated by the high-speedprimary pilot relaying. On directionalcomparison carrier schemes or transferred tripschemes, using electromechanical relays, the Rlunit is in the associated Type NAA auxiliaryrelay. On static relay schemes, Rl is in theassociated Type SLA or SLAT auxiliary relay.

Closure of the Rl contact will cause the capacitorto discharge through the operating coil (79/OC),via the CCS and 68/OB contacts and the diode(D2), causing the main closing unit to pick upand seal in by means of its holding coil (79/HC).Closure of the 79 unit contact (studs 1-2) willthen energize the circuit breaker closingscheme, through a 52/b or 52/bd switch notshown on the typical diagram in Fig. 13. Thisarrangement of initiating the single reclosure bymeans of an Rl unit makes it possible todistinguish between tripping by the pilotrelaying, where a reclosure is desired, and by thebackup relaying where a reclosure should not beinitiated. Note that when the NSR21E orNSR21F is applied in this manner the green leadmust be connected to terminal 8.

Another contact of 79 discharges the capacitorthrough the 47-ohm discharge resistor. Aspreviously noted, this ensures that the timingcapacitor will be completely discharged so thatfull reset time will be realized after eachoperation. Note that the 52/b contact also

provides a second discharge path through diodeD3. This ensures that the capacitor will bedischarged when the breaker is manuallytripped, or is tripped by protective relaying thatdoes not initiate a high-speed reclosure. The52/b contact also performs the function of de-energizing the holding coil (79/HC) when thecircuit breaker is reclosed. Some users mayprefer to use a 52Y contact, associated with thebreaker closing circuit, to open the holding coilcircuit. Scheme diagrams covering this optioncan also be furnished.

On some circuit breakers, for example theGeneral Electric Type ATB, the 52/b switchcloses early in the opening stroke. The resistorin the circuit to terminal 8 of the NSR relayensures that the 52/b contact will not dischargethe capacitor before the Rl contact has had achance to operate 79/OC. The resistor has beenselected to assure proper operation of the 79/OCcircuit for an assumed extreme condition of Rland 52/b closing simultaneously.

If a 52Y contact is used to de-energize theholding coil (79/HC) and a 52/b contact is notavailable to discharge the capacitor, a contact ofthe control switch (52CS) should be used for thispurpose. This contact should be closed in theTRIP position of the switch. Use of such acontact will discharge the capacitor following amanual trip of the circuit breaker and thus avoidthe possibility of a close-trip-reclose sequence ifthe breaker is subsequently manually reclosedonto a fault.

On some transmission line applications, it isdesirable to block reclosing in the event that thebreaker is tripped by an out-of-step condition.The diagram in Fig.13 shows the use of contactsof the auxiliary unit OB in the out-of-stepdetecting relay 68 for this purpose. A normallyclosed contact of OB opens the circuit to theoperating coil of the NSR relay, while a normallyopen contact is connected to discharge the

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capacitor in the event that the Rl unit is pickedup by operation of the primary relaying on theout-of-step condition. Note that if the systemrecovers from the swing without the primaryrelaying and Rl operating, the capacitor will notbe discharged, and the high-speed reclosingcircuit will be reinstated as soon as 68/OB dropsout.

Where an Rl function is not included as anintegral part of the primary relaying, selectivereclosing can be realized by using an externallymounted auxiliary unit in combination with atripping rectifier to separate the instantaneousand time delay trip buses. The Type NGA15Drelay, with appropriate pickup and dropouttimes, was designed specifically for thispurpose.

Initiation by 52/b

On applications where a single high-speedreclosure is desired on any trip by protectiverelays, except bus or transformer differential,automatic reclosing should be initiated by a 52/bcontact. The diagram in Fig. 14 shows therecommended connections. Note that withthese connections, the green lead in the NSRrelay internal wiring should be connected toterminal 3. With this connection the closure ofthe 52/b contact when the breaker trips causesthe capacitor to discharge through the operatingcoil (79/OC), causing the main unit to pick upand seal in by: means of the holding coil (79/HC)

via the same 52/b contact. The 52/b contactwhich initiates the reclosure will also ensuredischarge of the capacitor following a manualtrip. The 79/OC coil will be energizedmomentarily, but the 3-5 contacts of the 52CSswitch will be open so reclosing will be blockedand the holding coil will not be energized.

On some applications with transmission linecircuit breakers it may be desirable to introducea slight time delay into the reclosing sequence.The NSR21G relay includes a timer (0.5 to 3 or10 seconds) for this purpose. The diagram in Fig.15 shows typical external connections for theNSR21G when reclosure is initiated by the Rlfunction in the pilot relaying scheme. Theoperation of this scheme is the same asdescribed above for the NSR21E, exceptoperation of the 79 contact now operates atimer, the output contact of which energizes thebreaker closing circuit.

AC Control

The Type NSR11C and NSR11D relays withinternal rectifier are designed for use where onlyac control voltage is available. Typical externalconnections for these relays are shown in Fig.16.

The diagram shows initiation of reclosure bymeans of a 52/b contact since this will usually bethe case in the application area where ac controlvoltage is used.

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