INSTRUCTIONS

DIFFERENTIAL VOLTAGE RELAYS TYPES

PVD21A PVD21B PVD21C PVD21D

GENERAL ELECTRIC

GEK-45405G

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DESCRIPTION

APPLICATION

GEK-45405

C O NTENT S P A GE

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CONSTRUCTION • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 6

RANGES • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

H I- SEISMIC TA R GET A ND SEA L - IN U NIT • . . . . . . . . . . . . . . . . •

7 8

BURDENS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 9

OPERATING PRINCIPLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 V O L TAGE U NIT ( 8 7 L ) - P V D 2 1 A , P V D 2 1 B , P V D 2 1 C , P V D 2 1 D .. 9 O V ER C U R R ENT U NIT ( 8 7 H ) - P V D 2 1 B , P V D 2 1 D . . . . • . . . . . . . . 1 1

CALCULATION OF S ETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 SET T ING O F H IGH IMP EDA NC E U NIT , 8 7 L . • • . . . . . . . . . . . . . . 1 2 SET T ING O V ER C U R R E NT U NIT , 8 7 H • . . . . . • . . . . . . . . • . . . • . . . 1 4 SA MP L E CA L C U L A T IO N . . . . . • • . . . . . . . . . . . . . . . . • • • • . . • . . • . 1 4

RECEIVING, HANDLING AND STORAGE ....................... 1 6

ACCEPTANCE TESTS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 1 6 V ISUA L INSP EC T IO N • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 1 7 MEC H A NICA L INSP EC T IO N • . . . • . . • . . . . . . . . . . . . . . • • • . . • . . . 1 7 EL EC T R IC A L SET T ING A ND INSP EC T IO N • . . . . . . . . . . . . . • • • . . 1 7

INSTALLATION PROCEEDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 9 L O CA T IO N A ND MO U NT ING . . . • . . . . . . . . . . . . . . . • . . . . . • . . . • . 1 9 C O NNEC T IO NS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 9 V ISUA L INSP EC T IO N • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 2 0 MEC H A NICA L INSP EC T IO N A ND A D JU ST MENT S • . . . . . • • • • . . . . . 2 0 T A R GET A ND SEA L - IN U NIT • • • . • . . . . . . . . . . . . . • . . • . . . . . • . 2 0 8 7 H A ND 8 7 L U NIT S • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 2 0

PERIODIC CHECK S AND ROUTINE MAINTENANCE . . . . . . . . . . . . . . .

C O NTA C T C L EA NING • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

P ER IO D IC T EST EQU IP MENT . . . . . . . . . . . . . . • • . . . . . . • • . . . • .

EL EC T R I.,.C.A L T EST S • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

T H YR IT � U NIT . . . . . . . . . . . . . . • . . . . . . . . . . . . • • . . • . . . . . . .

H I- SEISMIC INST ANTANEO U S U NIT , 8 7 H . • . . • • • • • . . . . • • . . .

H I- SEISMIC TAR GET A ND SEA L - IN U NIT . . . • . • . . . . . . . • • . . .

2 1 2 1 2 1 2 1 2 1 2 2 2 2

RENEWAL PARTS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 2 2

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GEK-45405

DIFFERENTIAL VOLTAGE RELAYS

TYPES:

PVD21A PVD218 PVD21C PVD21D

DESCRIPTION

All the the Type PVD21 relays are single phase, high speed, high impedance, voltage operated relays that are designed to provide protection in bus differential schemes when used in conjunction with suitable current transformers. Typical operating times are shown in Figure 15 . Three PVD relays and a lockout relay are required for combined phase and ground fault protection of a three phase bus. Four models of the relay are available as listed in Table 1 .

TABLE I

VOLTAGE CURRENT NO. OF THYRITE® UNIT (87L) UNIT (878) STACKS

PVD21A Yes No 1 PVD21B Yes Yes 1 PVD21C Yes No 2 PVD21D Yes Yes 2

The PVD21C and PVD21D models of the relay include two paralleled voltage limiting Thyrite® stacks as opposed to the single stack included in the PVD21A and PVD21 B models. This feature makes the PVD21C and PVD21D models better suited to those applications where high internal fault currents can be encountered. This is discussed in detail in the section on APPLICATION in this instruction book.

The PVD21 B and PVD21D models of the relay include a high speed overcurrent unit (87H) in addition to the voltage operated unit (87L). This unit may be used to supplement the high speed voltage unit, and/or when provided with a suitable external timing device and auxiliaries, it may be used to implement breaker failure protection. This is also discussed in detail in the APPLICATION section.

The PVD relays are mounted in a single-end M1 size drawout case, and are provided with a single seal-in and separate targets for each unit. Outline and panel dri 11 ing dimensions for the relays are illustrated in Figure 1 . Internal connections for the various models are illustrated in Figures 2 and 3 .

® Registered trademark of General Electric Co.

These instructions do not purport to cover all details or variations in equipment nor provide for every possible contingency to be met in connection with installation, operation or maintenance. Should further information be desired or should particular problems arise which are not covered sufficiently for the purchaser's purposes, the matter should be referred to the General Electric Company.

To the extent required the products described herein meet applicable ANSI, IEEE and NEMA standards; but no such assurance is given with respect to local codes and ordinances because they vary greatly.

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The exter n a l connect i ons for the PVD2 1A and PVD2 1 C re l ays are i l l u strated i n F i gure 4; those for the PVD2 1 B and PVD2 1 D re l ays are s hown i n F i gure 5 .

APPLICATION

The fo l l owi ng comments on the ap p l i c at i ons of the Types PVD21A, PVD2 1 B , PVD2 1C a nd PVD2 1 D re l ays may be better apprec i ated i f t he deta i l ed sec t i on on OPERATING PRINCIPLES i s rev i ewe d before proceedi ng . The Type PVD2 1 re l ays can be appl i e d for b u s protect i on i n most cases where CT s hav i ng neg l i g i b l e l eakage reactance are u sed. Th i s genera l l y i nc l u des any ki nd of c urrent transformer wi th a toroi dal core i f the wi n di n gs ( on the �. t ap u s ed) are comp l ete l y di str i b uted about t he core . The e l ementary di agram of t he exter n a l connect i ons for a typ i c a l ap p l i c at i on i s shown i n F i g ures 4 and 5 .

A b u s di fferent i a l s cheme u t i l i zi ng Type P V D re l ays h a s cert a i n advant ages that s i mp l i fy ap p l i c at i on cons i derat i o n s :

1 St andar d re l ayi ng- type bus h i ng current transformers m a y be u s ed 1 P erf orm ance for spec i f i c app l i cat i on s i s subject to s i mp l e c a l c u l at i on s 1 P rotect i on i s eas i l y extended i f t he number of , connect i on s t o t he bus i s

i n creased.

The fo l l ow i ng poi nts must be cons i dered bef ore a part i cu l ar app l i c at i on i s attempted:

A l l CT s i n the bus di fferent i a l c i rcu i t shou l d have the s ame rat i o. When addi ng to an ex i s t i ng b u s , at l e ast one CT i n t he new breaker shou l d be ordered wi th the s ame r at i o as the bus di fferent i a l CTs i n the ex i st i ng breakers . If the di fferent i a l c i r c u i t unavo i dab ly i nc l u des di fferent r at i o CTs , the ap p l i c at i on may s t i l l be pos s i b l e , but spec i a l attent i on mus t be g i ven to protect aga i nst overvo l tage condi t i ons dur i n g i nternal f au l ts .

If one or more of the CTs i n F i gures 4 or 5 are a di fferent rat i o than the others , i t wou l d appear that the s i mp l e so l ut i on wou l d be to use the f u l l wi n di ng of the l ower r at i o CTs an d a match i ng t ap on the h i gher rat i o CT s . The h i gh peak vo l tages that occur dur i ng an i ntern al fau l t wi l l be magn i f i ed by the autotran sformer acti on of the t ap pe d h i gher rat i o C T s , a n d t h e peak vo l tages across the f u l l wi ndi ng of t he h i gher rat i o CTs may exceed the capab i l i ty of the i ns u l at i on in t h at c i r c u i t . R efer ap p l i c at i ons i n vol v i ng di fferent rat i o CTs to the l oc a l General El ectr i c Sal es off i ce .

Wh en al l current transformers are of the s ame rati o , f u l l wi n di n gs , i ns tead of t aps , s hou l d be u sed. Th i s w i l l i ns ure max i mum sen s i t i v i ty to i nternal fau l ts i n addi ti on to l i m i t i ng peak vo l t ages . In any c ase , CT secondary l eakage re actance must be neg l i g i b l e .

It may be pos s i b l e , a l though not des i rabl e , to u s e the di fferent i a l c i rcu i t CTs joi n t l y for other funct i ons . The performance of the system under these con di tons can be ca l culated by i nc l udi ng the added burden as part of the CT l ead res i s t ance.

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However, con s i derat i on must be g i ven to the hazards of f a l se oper ati on due to extra connect i on s and errors i n test i ng t he added dev i ce s . Note t hat the re l ays may tr i p if a CT secondary i s open c i rc u i ted dur i ng norma l operat i on of the as soc i ated b u s .

T hyr i te� a non- l i near res i stance, i s u s ed i n t he r e l ays t o l i m i t t h e vo l tages t h at c an be devel oped acros s t he re l ay dur i ng an i nternal fau l t to s afe v a l ues . The m agn i tude of t he vo l tage t hat c an be deve l oped wi l l be a f unct i on of the tot a l i ntern a l f au l t c urrent and the c har acter i s t i cs of t h e CT s used i n t h e di fferent i a l c i rc u i t . F i gure 9 i l l ustr ates t he s af e app l i cat i on l im i ts for the PVD21A and PVD2 1 B re l ays a s a func t i on of the tot al fau l t c urrent and the knee poi nt v o l t age ( Es ) of the poorest CT i n t he c i rcu i t. If t he f au l t c urrent and knee po i nt vo l t age are s uch t hat t he i ntersect i on of t hese two poi nts p l ots b e l ow the curve, then the app l i c ati on wi l l be s afe wi t h respect to the vo l t age l i m i t s . Note that t�s curve app l i es for t he PVD21A and PVD2 1 B re l ays wh i ch h ave a s i ng l e stack of Thyr i t gY. If the app l i c at i on of these re l ays does not appear to be perm i s s i b l e on the bas i s of F i gure 9 , i t may st i l l be perm i s �b l e i f the PVD2 1C o r PVD2 1 D re l ay i s used . These re l ays have two stacks of T hyr i t� connected i n paral l e l so t hat s i gn i f i cant l y greater i nterna l f au l t currents can be accomod ated. F i gure 10 may be used to determ i ne the s afe appl i c at i on l i m i t s for t he PVD21C and PVD2 1 D re l ays .

Dur i ng a n i nterna l f au l t, c urrent wi l l �l ow i n t he Thyr i t� s t ac k, caus i ng energy to be d i s s i p ated. To protect the Thyr i t eti' from therma l d amage, a contact of t� l ockout re l ay must be connected as s hown i n F i gures 4 and 5 t�s hort out the Thyr i t� dur i ng an i ntern al fau l t . The thermal l im i ts of the Thyr i t� wi l l not be exceeded provi ded the re l ay t i me, p l u s l oc kout re l ay t i me, i s l es s than four cyc l es .

An i nst antaneous overcurrent u n i t, 87H , i s connected i n ser i es wi th the Thyr i t� i n PVD2 1 B and PVD2 1 D mode+s. The 87 H un i t, when set wi th t he proper p i c kup , may be used to sup p l ement t he vo l tage un i t, 8 7 L, and/or imp l ement breaker f ai l ure protecti on when a s u i tab l e t i m i ng re l ay and other aux i l i ary dev i ces are prov i ded by the u s er . The requ i red sett i ng of the 87H u n i t i s re l ated to the actu al s et t i ng of the 8 7 L u n i t .

F i gure 8 i l l ustrates the sett i ng to be made on 87H as a funct i on of the 87L sett i ng . Thus , once the vo l tage u n i t set t i ng h as been c a l c u l ated, the c urrent u n i t s ett i ng i s eas i l y determ i ned.

F i gure 5, wh i ch app l i es to the PVD21B and P�21D re l ays , s hows the contact of the l oc kout re l ay connected to s hort out the Thyr i t� on l y. However, the 87H u n i t i s not s horted so that the re l ay can con t i nue to operate as an overcurrent funct i on , becau se i t wi l l stay p i c ked up unt i l the fau l t i s c l eared. The 87H u n i t may be used to imp l ement breaker fa i l ure protect i on . Dev i ce 6 2 X c a n b e connected a s s hown i n F i gure SA to i n i t i ate oper ati on of the breaker fai l ure t i mer.

The curve of F i gure 8 , wh i ch i l l ustrates the 87H sett i ng as a funct i on of the 87L setti ng, i n c l udes s uff i c i ent marg i n to i n sure that the overc urrent u n i t wi l l not operate dur i ng an externa l f au l t . F or th i s reason, the 87H un i t wi l l be l es s sens i t i ve than the 87L u n i t , and i t may not operate for al l i ntern al fau l ts . Howe ver, i t wi l l p i ck up as soon as the l oc kout re l ay operates , prov i ded the fau l t current i s above the p i c kup setti ng . In t hose c as es where the 87H u n i t does not p i ck up unt i l the l oc kout re l ay oprates , t he dropout t i me of 87L i s s uff i c i ent to over l ap the p i ckup t i me of 87H, so that a cont i nuous i nput wi l l be provi ded to dev i ce 62X.

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If any of the bus di fferent i al CTs are protected by pr i mary an d/or s econ dary vo l tage l i m i t i ng dev i ces, s uc h as vacu um gaps, wh i ch m i ght be the c ase i f the bus di fferen t i a l zone i nc l u ded shunt capaci tor ban ks , addi t i ona l cons i derat i ons are necess ary to ens ure a re l i ab l e app l i cat i on . Some means must b e i ncorporated t o prevent t h i s protect i ve e qu i pment from short i ng the operat i ng coi l s of the PVD dur i n g i nter n a l f au l ts . S u c h app l i cat i on s may be referred t o the l oc a l Genera l El ectr i c S a l es Off i ce .

The extern a l connect i on di agrams of F i gures 4 and 5 i n di c ate t h at the di fferen t i a l junct i on po i nts for t he re l ays are l ocated i n the swi tchyard. F or outdoor i ns t al l at i ons where t here i s a gre at di stance between the breaker and the re l ay pane l , i t may be des i rab l e to l oc ate the di fferent i a l junct i on i n the swi tchyard, s i nce the �, res i stance of the f au l t CT l oop may otherwi se be too l arge ( r efer to the sect i on, CALCULATI ON OF SETTINGS). Note that the cab l e res i st ance from the junct i on po i nt to the re l ay i s n ot i nc l u ded as part of the f au l t CT l oop res i stance. It i s perm i s s i b l e to l oc ate junct i on po i nts at the pane l , prov i di ng that the resu l t i ng re l ay sett i n g g i ves the des i red sens i t i v i ty.

The 87L un i t shou l d be s et no h i gher t han 0. 67 t i mes t he secondary exc i t at i on vo l t age at ten amperes s econdary exc i t at i on c urrent ( ev a l u ated for the poorest CT i n the di fferent i a l c i rcu i t ) .

When c i rcu i t breakers are to be bypassed for ma i ntenance purposes, or when any other atyp i c al setup i s to be made, other means than s i mp l y open i ng the PVD contact c i rcu i t s hou l d be u s ed to avoi d i ncorrect tr i pp i ng . Vo l t ages t hat exceed t he con t i n uous r at i ng of the PVD may be deve l oped wi th the h i gh i mpedanc e operat i ng coi l s t i l l connected i n the di fferent i a l c i rcu i t . Th i s c an be avo i de d by remov i ng the connec t i on p l u g , or i f externa l means are requ i red, by short c i rc u i t i n g stu ds 4 and 5 to stud 6.

The fo l l ow i ng i nformat i on must be obta i ned before sett i ngs are determ i ned for a part i c u l ar ap p l i c at i on :

• Determ i ne t he secondary wi ndi ng res i st an ce for a l l t he CTs i nvol ved • Obta i n the s econdary exc i t at i on c ur ves f or a l l the CTs i nvo l ved • Determ i ne t he res i stance of the c ab l e l eads from the CT s to the di fferent i a l

junct i on poi nt .

CONS TRUCTION

The Type P VD re l ays are assemb l e d i n the me di um s i ze s i n g l e-end ( M1 ) drawout c ase h avi ng studs at one end i n t he rear for extern a l connect i on s . The e l ectr i c a l connec t i ons between t he re l ay a n d c a s e studs are t hrough stat i onary mol ded i nner a n d outer b l ocks , between wh i ch nests a removab l e connect i ng p l u g . T h e i nner b l oc k h a s the term i n al s for t he i ntern a l connecti on s .

Every c i rcu i t i n t he drawout c a s e has a n aux i l i ary brus h, as s hown i n F i gure 13 , to provi de adequ ate over l ap when the connect i ng p l u g i s wi thdr awn or i nserted. Some c i rcu i ts are equ i pped wi th s hort i ng b ars ( s ee i nternal connect i ons , F i gures 2 and 3 ) , and i t i s espec i a l l y import ant that the auxi l i ary br ush make cont act on t hose c i rc u i t s w i th ade qu ate pres s ure to prevent the open i ng of important i nter l ocki ng c i rcu i ts , as i ndi cated i n F i gure 13 .

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The r el ay mechan i sm i s mounted i n a s teel framewor k c a l l ed the cradle and i s a compl ete un i t wi th a l l leads term i nated at the i nner block. Th i s crad le i s h eld f i rmly i n the case wi th a l atch at both top and bottom and by a gu i de p i n at the back of the cas e. The connect i n g p l u g, bes i des maki ng the electr i ca l connect i on s between the r espect i ve b l ocks of the cradle and case, also loc ks t h e l atch i n plac e. The cover , wh i c h i s dr awn t o t h e c as e by thumbscrews, holds t h e connect i n g p lu gs i n p lace. The t ar get r es et mechan i sm is a part of the cover as s embly .

The rel ay cas e i s s u i tabl e for ei ther s em i f lu s h or surface mount i n g on a l l panel s up to two i nc h es th i ck, and appropri ate hardware i s av ai l ab l e; however , pan el th i c kn es s must b e i ndi cated o n t h e r el ay order t o i nsure t hat t h e proper h ardware wi ll b e i nc luded . Out l i ne and panel dri l l i ng d imen s i ons are s hown i n F i gure 1.

A s eparate test i n g p lug can b e i n s erted i n p l ace of the connect i n g p l u g to tes t the r el ay i n p l ace o n the panel, ei ther from i ts own source of current a n d vo l t age, o r from other sources . T h e rel ay also c an be drawn out and replaced by anot her wh i ch has been t ested in the l abor atory.

The r el ays covered by thes e i n struct i on s i nc l ude two h i n ged armature type oper at i n g u n i t s : a 11l ow- s et 11 voltage u n i t , dev i c e 8 7 L, and a 11h i gh- s et 11 c urrent u n i t, d ev i ce 87 H .

D ev i c e 87L i s an i nstant aneous t el ephone-type vo l t age un i t havi n g i ts co i l conn ected across the DC term i n al of a f u l l wave r ecti f i er . In turn, the r ect i f i er i s connected to a h i gh pass f i l ter t hrough an attenuator n etwork. The 87L un i t has two normal ly open contacts. One s et of contacts i s connected between t erm i n a l s 7 and 8 , a n d the other s et i s connected i n parall el w i t h the contacts of the s ea l - i n un i t .

Dev i c e 87H i s an i nstantaneous overcurrent u n i t , ).Rounted i n the upper r i ght hand c orner , wi th i ts co i l connected in s er i es wi th Thyr i t� r es i stor d i s c s . A s i n gle s et of normal ly open cont acts i s con n ected between termi n a l s 9 and 10.

H i -Sei sm i c Sea l -i n Un i t

A s ea l - i n un i t i s mounted i n the upper lef t corner of the rel ay ( s ee F i gure 3 ) . The u n i t h as i t s coi l i n s er i es and i ts contacts i n paral l el wi th a s et of normally open contacts of the 87L u n i t . When the s eal- i n un i t p i c ks up, i t ra i s es a tar get i nto v i ew. The t ar get l atches up and r emai ns expos ed unt i l i t i s r el eas ed by man u a l oper at i on of the res et button, wh i ch i s located at the lower lef t corner of the relay.

RANGES

Thes e r el ays are av ai l ab l e for 60 h ertz. The standard oper at i n g ran ges avai l able are gi ven i n the t ab l e bel ow. F actors wh i ch i nf lu ence the s elect i on of the operat i ng r an ge are cover ed i n the s ect i on on CALCULATION OF SETTINGS.

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TABLE 2

87L UNIT LINK RANGE CONTINUOUS RANGE POSITION VOLTS RATING VOLTS

75-500 L 75 - 220 150 H 200 - 500 150

TABLE 3

87H HI-SEISMIC CONTINUOUS **ONE SECOND INSTANTANEOUS LINK **RANGE RATING RATING

UNIT (AMPS ) POSITION (AMPS) (AMPSJ (AMPSl

2-50 L 2 - 10 3.7 130 H 10 - 50 7.5

**The range is approximate, which means that the 2-10, 10-50 ampere range may be 2-8, 7-50 amperes. There will always be at least one ampere overlap between the maximum L setting and the minimum H setting. Select the higher range whenever poss i b 1 e, s i nee it has the higher continuous rating.

For other ranges, consult the local General Electric Sales Office.

87L Continuous Rating

The voltage circuit included in the 87L unit has a continuous voltage rating of 150 volts RMS. Refer to the ACCEPTANCE TESTS section for precautions that should be taken during testing.

Contacts

The current c 1 os i ng rating of the contacts is 30 amperes for voltages not exceeding 150 volts. The current carrying rating is limited by the seal-in unit rating.

HI-SEISMIC TARGET AND SEAL IN UNIT

The Type PVD relay is provided with a universal target and seal in unit having 0.2 and 2.0 ampere taps as indicated in the following tabulations.

If the tripping current exceeds 30 amperes, an auxiliary relay should be used. Its connections should be such that the tripping current does not pass through the contacts or the target and seal-in coils of the protective relay.

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TABLE 4 RATINGS OF THE SEAL-IN UNIT C OIL

0.2

DC Res i st ance +10% ( ohms ) 8.0 Mi n i mum Operat i ng ( amperes ) 0.2 +0%, -25% C arry Cont i nuou s ( amperes ) 0.3 C arry 30 Amperes ( seconds ) 0.03 C arry 10 Amperes ( seconds ) 0.2 5 60 Hertz Imped ance ( ohms ) 52

BURDENS

The burdens of the 87L c i rcu i t at f i ve amperes are:

87L C i rcu i t :

Z (term. 5-6) Ang_l e R

1 678 ohms - 240 1 534

OPERATING PRINCIPLES

TAP 2.0

0.24 2.0 3.0 4.0

30.0 0.5 3

- jX

680

All of the Type PVD re lays i nclude a h i g h i mpedance voltage sens i ng u n i t ( 87L ) t h at operates from the volt age produced by the d i fferent i ally connected CTs dur i rm. an i nternal fau lt. The relays are also prov i ded w i th e i ther one or two Thyr i te ® stacks ( see Table 1 ) connected i n parallel w i th t h e 8 7 L u n i t t o li m i t t h e volt age acros s the r£!lay to s afe v alues dur i ng i nternal fault s. In li m i t i ng the volt age , t he Thyr i te � wi ll p a s s s i gn i f i cant current dur i ng i nternal fault s , but very li ttle current dur i ng normal operat i ng cond i t i on s or exter n al f au lts. The PV D21B and PVD21D relays are prov i ded wi th an i n st antaneous overcurrent u n i t ( 87H ) connected i n ser i es w i th the Thyr i te UP. The 87H u n i t i s set so that i t w i ll not operate for the maxi mum external fault , but wi ll operate for heavy i nternal fault s.

The d i agrams of F i gures 4 and 5 i llus trate typ i cal external connect i ons to the relays for use i n a bus d i fferent i al scheme. A convent i onal d i fferent i al c i rcu i t i s ut i li zed , that i s , the CTs assoc i ated w i t h all of the c i rcu i ts off the bus are connected i n wye and p ar a 1 1 e 1 ed on a per-phase bas i s. One PVD re 1 ay per p h ase i s requ i red t o prov i de complete protect i on for the bu s.

V OLTAGE UNIT (87L ) - PVD21A , PVD21B , PVD21C, PVD21D

If a protect i on scheme ut i li zi ng a PVD relay i s to perform sat i sfactor i ly, i t must not tr i p for faults external to the zone of protect i o n , s u ch as at F 1 i n F i gure 6. Si nce the PVD relay i s a h i gh i mpedance dev i ce , con s i der the effect of an

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external single line to ground fault. Figure 6 illustrates this condition for the faulted phase only. Each of the CTs associated with an infeeding circuit will produce the secondary voltage necessary to drive its secondary current through its winding and leads. The CT in the faulted circuit will produce the voltage necessary to drive the total secondary fault current through its winding and leads. If all of the CTs were to perform ideally, there would be negligible voltage developed across junction points A and D , and hence across the PVD relay. Incidentally, load flow across the bus is similar in effect to an external fault, so there will also be little voltage developed across the relay during normal operating conditions. Unfortunately, during fault conditions CTs do not always perform ideally, because core saturation can cause a breakdown in CT ratio. Such core saturation is generally accentuated by DC transients in the primary current. Any residual flux left in the core may also add to the tendency to saturate.

In the example of Figure 6 , the worst condition would be realized if the CT associated with the faulted circuit saturated completely, thus losing its ability to produce a secondary voltage, while the other CTs did not saturate at all. When a CT saturates completely, its secondary impedance approaches the secondary winding resistance, provided the secondary leakage reactance is negligible. This will be the case when CTs wound on a toroidal core with completely distributed windings are used. The CTs in the infeeding circuits would then be unassisted by the fault CT and would have to produce enough voltage to force their secondary currents through their own windings and leads, as well as the windings and leads of the CT associated with the faulted circuit. As a result, a voltage will be developed across the junction points, A and D , and hence across the PVD relay. The magnitude of this voltage will simply be equal to the product of the total resistance in the CT loop circuit and the total fault current in secondary amperes, that is,

IF VR = ( Rs + 2RL ) (1) N

where: VR = voltage across PVD relay Rs = CT secondary winding and lead resistance RL = one way cable resistance from junction point to CT IF = RMS value of primary fault current N = CT ratio

Note that the factor of two, appearing with the RL term, is used to account for the fact that all of the fault current will flow through both the outgoing cable and the return cable for single line to ground faults. If the CTs are connected as shown in Figures 4 or 5, no current wi 11 flow in the return lead for three phase faults, thus the maximum voltage developed across the PVD relays for three phase faults can be calculated as follows:

IF VR = ( Rs + RL ) --N-- ( 2 )

Equations (1) and (2) can be consolidated and written as follows:

VR = ( Rs + PRL ) � N

(3)

where: P = 1 for three phase faults, and 2 for single line to ground faults.

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For the conditions in question, this voltage, VR, is the maximum voltage that could possibly be developed across the PVD relay. Obviously, the CT in the faulted circuit will not lose all of its ability to produce an assisting voltage, and the CTs in the infeeding circuits may tend to saturate to some degree. In practice, the voltage developed across the relay will be something less than that calculated from equation (3) above. The effect of CT saturation is accounted for by the CT performance factor, K, used in the equation for calculating the actual voltage setting, and it is discussed further in the section CAlCUlATION OF SETTINGS.

Now consider the effect of an internal fault. In this case, all of the infeeding CTs will be operating into the high impedance PVD in parallel with any idle CTs. The voltage developed across the junction points A and D will now approach the open circuit secondary voltage that the CTs can produce. Even for a moderate internal fault, this voltage will be in excess of the value calculated for the maximum external fault as described above. Therefore, the high impedance voltage sensing unit, 87L, can be set with a pickup setting high enough so that it will not operate as the result of the maximum external fault, but will still pick up for moderate and even s 1 i ght i nterna 1 faults. Consequently, the re 1 ay will be selective between internal faults and external faults or load flow.

The actual equation for calculating the 87L voltage unit setting, taking CT performance and margin into account, is as follows:

where: K = CT performance factor (see Figure 7) 1. 6 = margin factor

All other terms are as described above.

OVERCURRENT UNIT (87H) - PVD21B, PVD21D

( 4)

The PVD21B and PVD21D re 1 ays are similar to the PVD21A and PVD21C re 1 ay..s_, respectively, except for the addition of the 87H unit in series with the Thyrite�. The 87H unit is set so that it will not operate on the current passed by the Thyrite® during external faults, but so that it will operate on the current passed during heavy internal faults.

During normal operating conditions, there will be little voltage deveJoped across the PVD relay, and hence across the series combination of the ThyriteUP and 87H. During external faults, the same would be true if the CTs did not saturate. Even if the CT in the fault circuit saturated completely, the maximum voltage that could be developed across the relay would be limited to the drop in the CT resistance plus the associated cable resistance. Because 87L is set at some value above the maximum expected drop, it is possible to determine the current through the ThyriteUP at the 87L setting, and so determine a suitable setting for 87H to insure that it does not operate for the maximum external fault. Figure 8 illustrates the minimum safe pickup setting to be made as a function of the 87L setting with suitable margin included. Thus, once the 87L setting has been calculated, the 87H setting can be easily determined from Figure 8.

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During internal faults, the CTs will attempt to drive all of the fault current through the high impedance PVD relay. As a result, the voltage will build UP. quite rapidly across the relay. As the voltage builds up, the nonlinear Thyrite R will exhibit a declin�ng�esistance characteristic, so that significant current will flow through the Thyr l te U9 and so cause 87H to operate. Because of the margin involved in setting the 87H unit, it will not be qu1te as sensitive as the 87L unit and it may not operate for some low level faults. It is not possible to predict at exactly what fault level the 87H unit will operate because of the numerous factors involved. However, 87H still may be used to supplement tripping by 87L with the assurance that it will at least operate for heavy internal faults. The 87H unit may also be used to implement breaker failure protection, as described in the APPLICATION section.

CALCULATION OF SETTINGS

The formulas and procedures described in the following paragraphs for determining relay settings assume that the relay is connected to the full windings of differentially connected CTs. Further, they assume that the secondary winding of each CT has negl i gi b 1 e leakage reactance, and that a 11 of the CTs have the same ratio. If these are not the conditions that exist in your application, please contact the nearest General Electric District Sales Office.

SETTING OF THE HIGH IMPEDANCE UNIT, 87L

Assuming that an external fault causes complete saturation of the CT in the faulted circuit, the current forced through this secondary by the CTs in the infeeding circuits will be impeded only by the resistance of the winding and leads. The resulting IR drop will be the maximum possible voltage which can appear across the PVD relay for that external fault. The setting of the high impedance 87L unit was described in OPERATING PRINCIPLES . It is expressed as follows:

VR = (K) (1.6) (Rs + PRL) � (5)

where: VR = pickup setting of 87L unit Rs = DC resistance of faulted CT secondary windings and leads to

housing terminal RL = single conductor DC resistance of CT cable for one way run from

CT housing terminal to junction point (at highest expected operating temperature)

P = 1 for three phase faults, 2 for single phase to ground faults If = external fault current, primary RMS value

N = CT ratio 1. 6 = margin factor

K = CT performance factor from Figure 7.

The calculations only need to be made with the maximum value of If for single phase and three phase faults. If the relay is applicable for these conditions, it will perform satisfactorily for all faults.

As previously noted in OPERATING PRINCIPLES , the pessimistic value of voltage determined by equation (5) for any of the methods outlined is never realized in practice. The CT in the faulted circuit will not saturate to the point where it

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produces no assisting voltage. Furthermore, the condition which caused the faulted CT core to saturate a 1 so tends to saturate the cores of the CTs in the i nfeedi ng circuits, resulting in a further decrease in voltage across the PVD relay. These effects are not readily calculated; however, extensive testing under simulated fault conditions on bushing CTs similar to those supplied in most circuit breakers manufactured in the United States, has resulted in the establishment of a so-called .. performance factor, .. which can be determined for each application. The performance factor, K, is not a constant for a given bushing CT, but varies for each installation, depending on the value of (Rs + PRL) IF/N. K is readily determined from the curve of Figure 6, which is based on test data. The use of this curve is explained in SAMPLE CALCULATIONS.

The value of the 87L unit setting established by equation (5) is the m1mmum safe setting. Higher settings will provide more safety margin, but will result in somewhat reduced sensitivity.

The methods of utilizing equation (5) are outlined below:

Method I - Exact Method:

( 1 )

(2)

(3)

(4)

Determine the maximum three phase and single phase to ground fault currents for faults just beyond each of the breakers. The value RL is the one way cable DC resistance from the junction point to the faulted CT being considered. For each breaker in turn, calculate VR separately utilizing the associated maximum external three phase fault current, with P = 1 , and the maximum external single phase to ground fault current, with P = 2. Use the highest of the values of VR obtained in (3) above.

Method II - Simplified Conservative Method:

( 1 ) Use the maximum interrupting rating of the circuit breaker as the maximum external single phase to ground fault current.

(2) The value RL is based on the distance from the junction point to the most distant CT.

(3) Calculate a value for VR using P = 2. (4) This value of VR becomes the pickup setting.

Begin with Method II. The calculated value of VR is determined as outlined in the paragraph, 11Minimum Fault to Trip 87L. 11 If the sensitivity resulting from the value calculated is not adequate, then Method I should be used. When the 87L pickup from Method II proves to yield an adequate sensitivity, a unique advantage is realized, since the 87L pickup setting will not require recalculation following changes in system configuration, which would result in higher bus fault magnitudes.

It is desirable for the pickup voltage of the 87L unit to plot below the knee point of the excitation curve (that is, the point on the excitation curve where the slope is 45 degrees) of all the CTs in use. However, it is permissible for the 87L pickup voltage to be higher than the knee point voltage. The maximum setting for the 87L unit is equal to the secondary excitation voltage at ten amperes secondary excitation current (evaluated for the poorest CT in the differential circuit) , multiplied by 0.67.

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Minimum Fault to Trip 87L Unit

After the pickup setting of the 87L unit has been established for an application, a check should be made to determine the minimum internal fault current which will just cause the unit to operate. If this value is less than the minimum internal fault current expected, the pickup setting is suitable for the application. The following expression can be used to determine the minimum internal fault current required for a particular 87L unit pickup setting:

Imi n = [ � (I) X + IR + I 1] N ( 6) X = 1

where: Imin = m1n1mum internal fault current to trip 87L n = number of breakers connected to the bus, (i.e., number

of CTs per phase) I = secondary excitation current of individual CT at a

voltage equal to the pickup of 87L IR = current in 87L unit at pickup voltage = VR/1700 I1 = current in the Thyrite R unit at 87L pickup voltage (see

Figure 11) N = CT ratio

The values of I1, I2, etc., are obtained from the secondary excitation characteristics of the respective CTs. The first term in equation (6) reduces to NI if it is assumed that all CTs have the same excitation characteristic. The relay current, IR, can be determined from the impedance of the 87L circuit, assumed to be � constant at 1700 ohms. That is: #

IR = VR/1700 (7)

The current drawn by the Thyrite® unit, I1, can be obtained from that curve in Figure 11 that applies to the relay being used.

SETTING OVERCURRENT UNIT, 87H

The required setting for the overcurrent unit, 87H, is dependent on the actual setting of the voltage unit, 87L. Figure 8, which is a plot of the 87H setting in RMS amperes versus the 87L setting in RMS volts, illustrates the relationship between these two settings. In order to determine the required 87H setting, it is only necessary to calculate the 87L setting and then enter the curve of Figure 8 at that value of voltage to read the 87H setting directly. ��

SAMPLE CALCULATION

The various steps for determining the settings of the PVD relay in a typical app 1 i cation will be exp 1 a i ned with the aid of a worked ex amp 1 e. Method I I will be used with the following assumed parameters:

Number of breakers: five Maximum breaker interrupting rating: 40,000 amperes Cable resistance for longest run: 0.50 ohms at 25oc CT Ratio: 1200/5

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The characteristics for the 1200/5 CT are shown in Figure 12. The value of Rs from this figure is:

Rs = (0.0029) (240) + 0.113 = 0.809 ohms

The cable resistance for the longest CT run is given at 25°C. If higher operating temperatures are expected, this must be taken into account in determining the maximum expected resistance. Resistance values of wire at 25°C, or at any temperature, t1, may be corrected to any other temperature, t2, as follows:

Rt2 = [1 + P1 (t2 - t1)] Rt1

where: Rt1 = resistance in ohms at t1, degrees Centigrade Rt2 = resistance in ohms at t2, degrees Centigrade P1 = temperature coefficient of resistance at t1

For standard annealed copper, P1 = 0.00385 at t1 = 250C; therefore the value of RL at sooc is:

RL = [1 + 0.00385 (50 - 25)] 0.5 = 0.548 ohms

The CT performance factor, K, must next be determined. calculate:

(R8 + PRL) (1� <Es) (N)

To do this, first

Because Method II was selected, use P = 2. From Figure 12, Es = 300 volts

[(0.809) + (2) (0.548)] (40,000) ---------- = 1.06

(300) (240)

From Figure 7, K = 0.7.

Using Equation (5), the appropriate relay setting is:

(1.6) (0.7) [0.809 + (2) (0.548)] (40,000) v = ---------------R 240 VR = 355 volts

This value is just above the knee point (300 volts) of the CT characteristic, and well below 67 % of the voltage at ten amperes excitation, (0.67)x{590)=395 so the application is satisfactory in that respect.

Next it is necessary to determine whether the PVD21A or PVD21B, or the PVD21C or PVD210 (one versus two Thyrite® stacks) should be used. First determine the knee point voltage, Es, for the poorest CT in the circuit. From Figure 12, Es = 300 volts {all CTs are assumed to be identical). Assume that the maximum internal fault current is 45,000 amperes primary, which is equivalent to 188 amperes secondary. The curve of Figure 10, when entered at these coordinates (300 volts and 188 amperes), shows that the application is safe for either the PVD21C or PV021D relays (two Thyrite® stacks). If Figure 9 were entered at the same coordinates, it would show that PV021A or PVD21B would not be applicable.

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The next step in the calculation is to determine the sensitivity of the relay to internal faults. This may be done using equation (6) as follows:

From the excitation curve of Figure 12, I at 355 volts: 0.07 amperes

From the Thyrite® curve of Figure 11, I at 355 volts: 1.1 amperes (use curve for two Thyrite® stacks)

From equation (7):

From equation (6):

IR = 355/1700 = 0.209 amperes

Imin = [5(0.07) + 1.1 + 0.209] 240

Imin = 398 amperes primary

If the minimum internal primary fault current is above 398 amperes, the pickup setting of 355 volts is adequate.

If the instantaneous overcurrent unit will be included in the relay, then the PVD21D must be used. To determine the 87H setting, enter the curve of Figure 8 at the calculated 87L setting of 355 volts. Read the 87H setting from the scale for the PVD21D relay. For the 355 volt setting of 87L, the appropriate setting for 87H is 11.8 amperes.

RECEIVING. HANDLING AND STORAGE

These relays, when not included as part of a control panel will be shipped in cartons designed to protect them against damage. Immediately upon receipt of a relay, examine it for any damage sustained in transit. If damage resulting from rough handling is evident, file a damage claim at once with the transportation company and promptly notify the nearest General Electric Apparatus Sales Office.

Reasonable care should be exercised when unpacking the relay in order that none of the parts are damaged nor the adjustments disturbed. If the relays are not to be installed immediately, they should be stored in their original cartons in a place that is free from moisture, dust and metallic chips. Foreign matter collected on the outside of the case may find its way inside when the cover is removed, and cause trouble in the operation of the relay.

ACCEPTANCE TESTS

Invnediately upon receipt of the relay, an inspection and acceptance test should be made to insure that no damage has been sustained in shipment and that the re 1 ay ca 1 i brat ions have not been disturbed. These tests may be performed at the discretion of the user, since most operating companies use different procedures for acceptance and installation tests. The following section includes all applicable tests that may be performed on these relays.

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VISUAL INSPECTION

Check the nameplate stamping to insure that the model number, rating and calibration range of the relay received agree with the requisition.

Remove the re 1 ay from its case and check that there are no broken or cracked molded parts, or other signs of physical damage, and that all screws are tight.

MECHANICAL INSPECTION

Cradle and Case Blocks

Check that the fingers on the cradle and case agree with the internal connection diagram. Check that the shorting bars are in the correct position, and that each finger with a shorting bar makes contact with the shorting bar. Deflect each contact finger to insure that there is sufficient contact force available, and check that each auxiliary brush is bent high enough to contact the connection plug.

Contact 87L

The following mechanical adjustments must be checked:

1. The armature and contacts of the seal-in unit, as well as the armature and contacts of the instantaneous unit, should move freely when operated by hand. There should be at least 0.015 inch wipe on the seal-in contacts.

2 . The targets in the seal-in and the instantaneous unit must come into view and latch when the armatures are operated by hand, and they should unlatch when the target release button is operated.

3 . The brushes and shorting bars should agree with the internal connections diagram.

4. With the telephone relays in the de-energized position, all circuit closing contacts should have a gap of 0.015 inch, and all circuit opening contacts should have a wipe of 0.005 inch. The gap may be checked by inserting a feeler gage. Wipe can be checked by observing the amount of deflection on the stationary contact before parting the contacts. The armature should then be operated by hand, and the gap and wipe again checked as described above.

ELECTRICAL SETTING AND INSPECTION

Hi-Seismic Instantaneous Unit, 87H

Make sure the instantaneous unit link is in the correct position for the range in which it is to operate. See internal connections diagram, Figures 3 and 4, and connect as indicated in the test circuit of Figure 14A. Use the higher range whenever possible, since the higher range has a higher continuous rating.

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Setting the Hi-Seismic Instantaneous Unit

The instantaneous unit has an adjustable core located at the top of the unit. To set the instantaneous unit to a desired pickup, loosen the locknut and adjust the core. Turning the core clockwise decreases the pickup; turning it counterclockwise increases it. Bring the current up slowly until the unit picks up. It may be necessary to repeat this operation until the desired pickup value is obtained. Once the desired pickup value is reached, tighten the locknut.

CAUTION: Refer to the RATINGS section for continuous and one second ratings of the instantaneous unit. Do not exceed these ratings when applying current to the instantaneous unit.

The range of the instantaneous unit (±10% of minimum and maximum current value) must be obtained between one-eighth (1/8) and 20 counterclockwise turns of the core from the fully clockwise position.

Hi-Seismic Target and Seal-in Unit

The target and seal-in unit has an operating coil tapped at 0. 2 and 2. 0 amperes. The re 1 ay is shipped from the factory with the tap screw in the 1 ower ampere position. The tap screw is the screw holding the right had stationary contact. To change the tap setting, first remove one screw from the left-hand stationary contact and place it in the desired tap. Next remove the screw from the undesired tap and place it on the left- hand stationary contact where the first screw was removed. This procedure is necessary to prevent the right-hand stationary contact from getting out of adjustment. Screws should never be left in both taps at the same time.

87L Unit

TAP

0. 2 2. 0

TABLE 5

PICKUP CURRENT

0. 15 - 0. 1 95 1 . 50 - 1 . 95

DROPOUT CURRENT

0.05 or more 0. 50 or more

The 87L unit can be adjusted at any voltage within the range shown on its calibration plate. Four specific calibration values, for both the high and low voltage range are shown on the plate, which correspond to the values stamped on the nameplate. The 87L unit, unless otherwise specified on the requisition, will be set at the factory to operate at its minimum pickup voltage. If the unit is to be set at some other point, the calibration marks should be used as a guide in making a rough adjustment, and the test circuit of Figure 14B should then be used to make an exact setting.

When the test plug is inserted in the relay, as depicted in Figure 148, the current transformer secondaries are shorted by means of the link between the outer terminals 5 and 6. The adjustable test voltage is applied across terminals 5 and 6 of the relay; that is, across the voltage circuit which includes the 87L unit. Since the continuous voltage rating of the resonant circuit is only 1 50 volts, it is recommended that a hand-reset lockout relay be used in the test setup if the desired 87L setting is to be above this figure.

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The following procedure should be followed in checking pickup of the 87L unit. Start with a test voltage considerably higher than the expected operating point. Lower the test voltage by successively smaller increments, closing the test switch at each point. The lockout relay will operate each time, protecting the resonant circuit. Eventually, a point will be reached where the 87L unit will just fail to operate. The preceding voltage value, therefore, is the pickup value of the 87L unit (within reasonable accuracy).

At the point where the 87L unit fai 1 s to pick up, the test voltage must be removed at once to prevent damage to the relay.

If the 87L unit setting is to be less than the 150 volt continuous rating, it will not be necessary to use the lockout relay. The voltmeter used must have high internal impedance.

The 87L unit operating time can be checked by using the test circuit shown in Figure 148 and measuring the time elapsed between application of the input voltage and the operation of the 87L output contacts. The times measured should be within plus three and minus seven milliseconds of the time shown in Figure 15.

Thyrite® Unit

Apply 120 volts direct current to studs 3 and 6. The current should be between 0.005 and 0.012 amperes for a single stack, and between 0.008 and 0.024 amperes for a double stack of Thyrite®. Any meter error in the voltmeter will be magnified four to five times, for example, a 3% meter error will have an effect on the current of from 12 to 15%.

INSTALLATION PROCEDURE

LOCATION AND MOUNTING

The relay should be mounted on a vertical surface in a location reasonably free from excessive heat, moisture, dust and vibration. The relay case may be grounded using at least #12 AWG gage copper wire. The outline and panel drilling dimensions for Type PVD relays are shown in Figure 1.

CONNECTIONS

Internal connections diagrams for the Type PVD21A and PVD21C, and the Type PVD21B and PVD21D relays, are shown in Figures 2 and 3, respectively. The elementary diagram of the external connections for a typical application is shown in Figure 4.

Note in Figure 4 that when the relay is installed, a connecting jumper should be placed between terminals 3 and 5, and that terminals 5 and 6 are then connected across differential junction points A and B of the several current transformers. In Figure 5, a connecting jumper should be placed across terminals 4 and 5 when the relay is installed. A shorting bar is provided between terminals 5 and 6 so that if the connection plug of the relay is withdrawn, the differential circuit will not be opened.

The midpoint between the Thyrite® stack and unit 87H is connected to terminal 3. This makes it possible to test or calibrate unit 87H without the necessity of passing

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high current through the Thyrit�, and makes it possible to short out the 87H coil when its operation is not necessary.

The external connections in Figure 4 indicate that the differential junction, points A and B, should be located in the switchyard. This is important in outdoor installations where the distance between the breaker and relay panel may be great, since the resistance through the fault CT loop may otherwise be too large. The junction points can be located at the panel, provided that the necessary relay setting gives the desired sensitivity.

There should be only one ground connection in the secondary circuit. When the junction points are located in the switchyard, the ground connection should be made there rather than at the panel.

The voltage limiting Thyrit@ is short-time rated. The contacts of the auxiliary relay device 86 short circuits the differential circuit to protect it.

CAUTION: UNDER NO CIRCUMSTANCES SHOULD THE RELAY BE PLACED IN SERVICE WITHOUT THE THYRITE VOLTAGE LIMITING CIRCUIT CONNECTED; THAT IS, WITHOUT A JUMPER BETWEEN TERMINALS 4 AND 5. OTHERWISE, THE RELAY AND SECONDARY WIRING WILL NOT BE PROTECTED FROM HIGH CREST VOLTAGES WHICH RESULT FROM AN INTERNAL FAULT.

VISUAL INSPECTION

Repeat the items described under ACCEPTANCE TESTS, VISUAL INSPECTION.

MECHANICAL INSPECTION AND ADJUSTMENTS

Repeat the items described under ACCEPTANCE TESTS, MECHANICAL INSPECTION.

TARGET/SEAL-IN UNIT

Set the target/seal-in unit tap screw in the desired position. The contaCt adjustment will not be disturbed if a screw is first transferred from the left contact to the desired tap position on the right contact, and then the screw in the undesired tap is removed and transferred to the left contact.

87H AND 87L UNITS

Refer to the appropriate descriptions in ACCEPTANCE TESTS for the proper method of setting the 87L and 87H units.

The external trip circuit wiring to the relay, as well as the relay itself, should be checked by operating one of the relay units by hand and allowing it to trip the breaker or lockout relay. Observe that the target operates upon manual operation of the re 1 ay unit.

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PERIODIC CHECKS AND ROUTINE MAINTENANCE

In view of the vital role of protective relays in the operation of a power system, it is important that a periodic test program be followed. The interval between periodic checks will vary depending upon environment, type of relay and the user's experience with periodic testing. Until the user has accumulated enough experience to select the test interval best suited to his individual requirements, it is suggested that the points listed under INSTALLATION PROCEDURE be checked at

� an interval of from one to two years.

Check the items described in ACCEPTANCE TESTS, both VISUAL and MECHANICAL INSPECTION. Examine each component for signs of overheating, deterioration, or other damage. Check that all connections are tight by observing that the lockwashers are fully collapsed.

CONTACT CLEANING

Examine the contacts for pits, arc or burn marks, corrosion and insulating films. A flexible burnishing tool should be used for cleaning relay contacts. This is a flexible strip of metal with an etch-roughened surface, which in effect resembles a superfine file. The polishing action of this file is so delicate that no scratches are left on the contacts, yet it cleans off any corrosion thoroughly and rapidly. The flexibility of the tool insures the cleaning of the actual points of contact. Relay contacts should never be cleaned with knives, files, or abrasive paper or cloth.

PERIODIC TEST EQUIPMENT

* A test set is available for periodic testing of PVD relays. It is intended to be mounted on the panel adjacent to the relays, and in addition to testing, it can also be used to check current transformers for open or short circuits, and incorrect wiring. This test set is more fully described in instruction book GEK-65521.

ELECTRICAL TESTS

Pickup of the 87L and 87H units should be measured and the results compared against the desired setting. If a measured value is slightly different from that measured previously, it is not necessarily an indication that the relay needs readjustment. The errors in all the test equipment are additive, and the total error of the present setup may be of opposite sign from the error present during the previous periodic test. Instead of readjusting the relay, if the test results are acceptable, no adjustment should be made. Note the deviation on the relay test record. After sufficient test data has been accumulated, it will become apparent whether the measured deviations in the setting are due to random variations in the test conditions, or are due to a drift in the relay characteristics.

THYRITE® UNIT

Repeat the test described in ACCEPTANCE TESTS, ELECTRICAL INSPECTION.

* Indicates revision

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HI-SEISMIC INSTANTANEOUS UNIT, 87H

Check for the following:

GEK-45405

1. Both contacts should close at the same time.

2. The backing should be so formed that the forked end (front) bears against the molded strip under the armature.

3. With the armature against the pole piece, the cross member of the 11 T" spring should be in a horizontal plane, and there should be at least 0.015 inch wipe on the contacts. Check by inserting a 0.010 inch feeler gage between the front half of the shaded pole with the armature held -closed. The contacts should close with the feeler gage in place.

HI-SEISMIC TARGET AND SEAL-IN UNIT

Check steps 1 and 2 as described in the paragraph above for the instantaneous unit. To check the wipe of the seal-in unit, insert a 0.010 inch feeler gage between the plastic residual bump of the armature and the pole piece with the armature held closed. The contacts should close with the feeler gage in place.

RENEWAL PARTS

Sufficient quantities of renewal parts should be kept in stock for the prompt replacement of any that are worn, broken or damaged.

When ordering renewal parts, address the nearest Sales Office of the General Electric Company. Specify the name of the part wanted, quantity required, and catalog numbers as shown in Renewal Parts Bulletin GEF-4543.

Since the last edition, the paragraph on the Thyrite® unit in the ACCEPTANCE TEST ELECTRICAL SETTING AND INSPECTION section has been revised.

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6.625 168MM

0/' ,p

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GEK-45405

PANEL LOCATION SEMI-FLUSH SURFACE

�MTG. MTG� I

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384MM (6) 10-32 X 3/8

MTG. SCREWS 10-32 STUDS

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FRONT VIEW

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VIEW SHOWING ASSEMBLY OF HARDWARE FOR SURFACE MTG. ON STEEL PANELS

F ig u re 1 (K-6209273-5 ) Outline and Panel D rilling D imensions for an Ml Case

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LOW

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Figure 3 (0257A8387-3) Internal Connections for Type PV021B and Type PV0210 Re l ays

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zF= RMS VAL UE OF PRIHARY CI/RRENT N = C T RA TIO VR = VOL TAG£ ACROSS P VO

Figure 6 (0257A.8389 -0) Simplified Circuit Illustrating the Effect of Sing 1 e Line to Ground Faults on the Type PVD Re 1 ay

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F i gure 7 ( 0257A8586-l ) CT Performance Factor, K, for Type PVD21 Re 1 ays

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GEK-45405

' r-�r--1�'�1---+---+---r---r---r---r--1---1--� � \ ' ��--�-\++--�--1---��--�--1---��---+ � \ ' r---�--���--r---+---�--�--�--+---�--+---+ � �

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F i gure 8 ( 0257A8587-1 ) Curve for Obta i n i ng 87H Sett i n g as a Fu nc t i on o f 8 7 L Sett i ng

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(AR E A OF SAFE APPUCATI� N IS BElOW A N D LEFT OF THE CURV E

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F i gure 1 2 ( 0246A3799-l ) Typ i c a l Secondary Exc i tat i o n Character i st i c for B u s h i ng Type Current Transformer

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GEK-45405

CON N ECTI NG PLUG B LOCK

A U X I L I ARY B R U S H ---'

S HORT I N G B A R --­

N OT E : A F T E R E N G A G I NG A U X I L I AR Y B R U S H CO N N ECTIN G P L U G

T R AV E LS Y4 I N C H B E FO R E E N G A G l NG T H E M A I N B R U S H O N

T H E T E R M I N AL B LO C K

F i gure 1 3 ( 802503 9 ) Cros s Sec t i o n of Drawou t Case Show i ng Pos i t i on of Aux i l i ary Brush and Short i ng B ar

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GEK-45405

� �--------------------------�

T EST C I RC U I T F O R SETT I N G 8 7 H

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H IG H - 2

W A R N I N G - W HEN U S I N G A X L A I 2 A T E S T P L U G , I N S T A L L S H O R T I N G B A R AC R O SS T ER MINA L S 5 A ND 6 BE FORE I N SE R T ING T ES T PL UG.

N O T E - A B O VE T E ST F IG U R E S S H O W X L AI 2 T E S T PLUG

F i gure 1 4 (0269A3025-0 ) Test C i rcu i t Connec t i o n s

38

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(8/94) (3000)

Protection and Control GE Technology Center 205 Great Valley Parkway Malvern, Pennsylvania 19355-1 337

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