Handbook - Megger

8/3/2019 Handbook - Megger

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The CmpeteGie t EectricaIsati Testig


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A Stitch I Time

The Cmpete Gie t

Eectrica Isati Testig

Cpright 2006


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ConTEnTS PAGE

WHAT IS Good InSUlATIon? ........................................................................ 3

WHAT MAkeS InSUlATIon Go BAd? ................................................................ 4

HoW InSUlATIon ReSISTAnCe IS MeASURed .................................................. 5

HoW To InTeRPReT ReSISTAnCe ReAdInGS .................................................... 6FACToRS AFFeCTInG InSUlATIon ReSISTAnCe ReAdInGS .............................. 8

TyPeS oF InSUlATIon ReSISTAnCe TeSTS ....................................................... 10

TeST VolTAGe VS. eqUIPMenT RATInG .......................................................... 16

AC TeSTInG VS. dC ............................................................................................ 17

USe oF dC dIeleCTRIC TeST SeT ...................................................................... 18

TeSTS dURInG dRyInG oUT oF eqUIPMenT .................................................. 18eFFeCT oF TeMPeRATURe on InSUlATIon ReSISTAnCe................................ 21

eFFeCTS oF HUMIdITy ...................................................................................... 23

PRePARATIon oF APPARATUS To TeST ........................................................... 24

SAFeTy PReCAUTIonS ......................................................................................26

ConneCTIonS FoR TeSTInG InSUlATIon ReSISTAnCe oF

eleCTRICAl eqUIPMenT ..................................................................................27

AddITIonAl noTeS ABoUT USInG A MeGGeR InSUlATIon TeSTeR ........... 33

InTeRPReTATIon-MInIMUM VAlUeS .............................................................. 36

MInIMUM VAlUeS FoR InSUlATIon ReSISTAnCe .......................................... 38

TeSTS USInG MUlTI-VolTAGe MeGGeR InSUlATIon TeSTeRS ...................... 42

STeP-VolTAGe MeTHod ..................................................................................48

USe oF A GUARd TeRMInAl ............................................................................50

BUSHInGS, PoTHeAdS And InSUlAToRS ....................................................... 54

oUTdooR oIl CIRCUIT BReAkeRS ................................................................... 57

SeTTInG UP A MAInTenAnCe PRoGRAM ....................................................... 60

HoW oFTen SHoUld yoU TeST? .................................................................... 60

MeGGeR 5 And 10 kV InSUlATIon TeSTeRS.................................................. 62


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WHAT IS Good InSulATIon?

evr ctric wir i ur pat whthr its i a mtr, gratr, cab,

switch, trasrmr, tc. is caru cvr with sm rm ctrica

isuati. Th wir its is usua cppr r aumium, which is w t

b a g cuctr th ctric currt that pwrs ur uipmt. Th

isuati must b just th ppsit rm a cuctr: it shu rsist currta p th currt i its path ag th cuctr.

T ursta isuati tstig u ra t t g it th

mathmatics ctricit, but simp uati ohms aw ca b vr

hpu i apprciatig ma aspcts. ev i uv b xps t this aw

br, it ma b a g ia t rviw it i th ight isuati tstig.

Th purps isuati aru a cuctr is much i that a pip

carrig watr, a ohms aw ctricit ca b mr asi urst ba cmparis with watr w. I Fig. 1 w shw this cmparis. Prssur

watr rm a pump causs w ag th pip (Fig. 1a). I th pip wr t

sprig a a, u wast watr a s sm watr prssur.

With ctricit, vtag is i th pump prssur, causig ctricit t w

ag th cppr wir (Fig. 1b). As i a watr pip, thr is sm rsistac

t w, but it is much ss ag th wir tha it is thrugh th isuati.

Figre 1Cmparis water w (a) with eectric crret (b).


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Cmm ss ts us that th mr vtag w hav, th mr currt

thr b. As, th wr th rsistac th wir, th mr currt r

th sam vtag.

Actua, this is ohms aw, which is xprss this wa i uati rm:

e = I x Rwhr, e = vtag i vts

I = currt i amprs

R = rsistac i hms

nt, hwvr, that isuati is prct (that is, has ifit rsistac) s

sm ctricit s w ag th isuati r thrugh it t gru. Such

a currt ma b a miith a ampr ( micrampr) but it is

th basis isuati tstig uipmt. nt as that a highr vtagts t caus mr currt thrugh th isuati. This sma amut

currt wu t, curs, harm g isuati but wu b a prbm

i th isuati has trirat.

nw, t sum up ur aswr t th usti what is g isuati?

W hav s that, sstia, g mas a rativ high rsistac

t currt. Us t scrib a isuati matria, g wu as

ma th abiit t p a high rsistac. S, a suitab wa

masurig rsistac ca t u hw g th isuati is. As, i u

ta masurmts at rguar pris, u ca chc trs twar its

trirati (mr this atr).

WHAT MAkES InSulATIon Go BAd?

Wh ur pat ctrica sstm a uipmt ar w, th ctrica

isuati shu b i tp tch shap. Furthrmr, mauacturrs wir,

cab, mtrs, a s hav ctiua imprv thir isuatis r

srvics i iustr. nvrthss, v ta, isuati is subjct t macts which ca caus it t ai mchaica amag, vibrati, xcssiv

hat r c, irt, i, crrsiv vaprs, mistur rm prcsss, r just th

humiit a mugg a.

I varius grs, ths mis isuati ar at wr as tim gs

cmbi with th ctrica strsss that xist. As pi hs r cracs

vp, mistur a rig mattr ptrat th suracs th

isuati, prviig a w rsistac path r aag currt.


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oc start, th irt mis t t ai ach thr, prmittig

xcssiv currt thrugh th isuati.

Smtims th rp i isuati rsistac is su, as wh uipmt

is . Usua, hwvr, it rps graua, givig pt warig,

i chc priica. Such chcs prmit pa rcitiig br

srvic aiur. I thr ar chcs, a mtr with pr isuati, rxamp, ma t b agrus t tuch wh vtag is appi,

but as b subjct t bur ut. What was g isuati has bcm a

partia cuctr.

HoW InSulATIon RESISTAnCE IS MEASuREd

yu hav s that g isuati has high rsistac; pr isuati,

rativ w rsistac. Th actua rsistac vaus ca b highr r wr,

pig up such actrs as th tmpratur r mistur ctt th

isuati (rsistac crass i tmpratur r mistur). With a itt

rcr-pig a cmm ss, hwvr, u ca gt a g pictur

th isuati citi rm vaus that ar rativ.

Th Mggr isuati tstr is a sma, prtab istrumt that givs u

a irct raig isuati rsistac i hms r mghms. Fr g

isuati, th rsistac usua ras i th mghm rag.

Th Mggr isuati tstr is sstia a high-rag rsistac mtr

(hmmtr) with a buit-i irct-currt gratr. This mtr is spcia

cstructi with bth currt a vtag cis, abig tru hms t b

ra irct, ipt th actua vtag appi. This mth is -

structiv; that is, it s t caus trirati th isuati.

Figre 2Typica Megger test istrmet h-p t measre isati resistace.


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Th gratr ca b ha-cra r i-prat t vp a high

dC vtag which causs a sma currt thrugh a vr suracs th

isuati big tst (Fig. 2). This currt (usua at a appi vtag

500 vts r mr) is masur b th hmmtr, which has a iicatig

sca. Fig. 3 shws a tpica sca, which ras icrasig rsistac vaus

rm t up t ifit, r a rsistac t high t b masur.

Figre 4Typica recr isati resistace a mi mtr. Crve A shws test vaes as

measre; Crve B shws same vaes crrecte t 20C (see page 22), givig a efite wwar

tre twar a sae citi. Reverse sie car (at right) is se t recr the test ata.

Figre 3Typica scae the Megger isati tester.

HoW To InTERPRET RESISTAnCE REAdInGS

As prvius mti, isuati rsistac raigs shu b csir

rativ. Th ca b uit irt r mtr r machi tst thr

as i a rw, t t ma ba isuati. What ra mattrs is th tr

i raigs vr a tim pri, shwig ssig rsistac a warig

cmig prbms. Priic tstig is, thrr, ur bst apprach t

prvtiv maitac ctrica uipmt, usig rcr cars as shw

i Fig. 4.


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Whthr u tst mth, twic a ar, r c a ar ps up th

tp, cati, a imprtac th uipmt. Fr xamp, a sma

pump mtr r a shrt ctr cab ma b vita t a prcss i ur pat.

expric is th bst tachr i sttig up th schu pris r ur

uipmt.

yu shu ma ths priic tsts i th sam wa ach tim. That is,with th sam tst cctis a with th sam tst vtag appi r

th sam gth tim. As u shu ma tsts at abut th sam

tmpratur, r crrct thm t th sam tmpratur. A rcr th

rativ humiit ar th uipmt at th tim th tst is as hpu

i vauatig th raig a tr. latr sctis cvr tmpratur

crrcti a humiit cts.

I summar, hr ar sm gra bsrvatis abut hw u ca itrprtpriic isuati rsistac tsts, a what u shu with th rsut:

Citi What T d

(a) Fair t high vaes n case r ccer.a we maitaie.

(b) Fair t high vaes, lcate a remey the case abt shwig a chec the wwar tre.cstat teecy

twars wer vaes.

(c) lw bt we maitaie. Citi is prbaby a right, btcase w vaes sh bechece.

() S w as t be sae. Cea, ry t, r therwise raise thevaes bere pacig eipmet iservice. (Test wet eipmet whie

ryig t.)

(e) Fair r high vaes, Mae tests at reet itervas tiprevisy we the case w vaes is catemaitaie bt shwig a remeie; r ti the vaesse werig. have becme steay at a wer

eve bt sae r perati; r tivaes becme s w that it is saet eep the eipmet i perati.


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FACToRS AFFECTInG InSulATIon RESISTAnCE REAdInGS

Rmmbr that th masur rsistac ( th isuati) wi b

trmi b th vtag appi a th rsutat currt (R = e/I).

Thr ar a umbr thigs that act currt, icuig tmpratur

th isuati a humiit, as mti i th prvius scti.

Right w, ts just csir th atur currt thrugh isuati

a th ct hw g vtag is appi.

Currt thrugh a ag isuati is ma up part a rativ

sta currt i aag paths vr th isuati surac. ectricit

as ws thrugh th vum th isuati. Actua, as shw i

Fig. 5, ur tta currt cmpriss thr cmpts:

1. Capacitace Chargig Crret

Currt that starts ut high a rps atr th isuati has b

charg t u vtag (much i watr w i a gar hs wh

u frst tur th spigt).

2. Absrpti Crret

As a iitia high currt which th rps (r rass iscuss

ur th scti Tim-Rsistac Mth).

3. Ccti r leaage CrretA sma sstia sta currt bth thrugh a vr th

isuati.

As shw i Fig. 5, th tta currt is th sum th thr cmpts

a it is this currt that ca b masur irct b a micrammtr,

r i trms mghms at a particuar vtag b mas a Mggr

istrumt (hmmtr). Bcaus th tta currt ps up th

tim that th vtag is appi, u ca s w wh ohms law R = e/I

hs, thrtica, at a ifit tim (that is, u hav t waitrvr br taig a raig).

I practic, as u wi s i th tst mths scrib bw, u

ra a vau that is th appart rsistac a usu vau t iags

trubs, which is what u wat t .


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Figre 5Crves shwig cmpets crret measre rig dC testig isati.

nt as i Fig. 5 that th chargig currt isappars rativ rapi

as th uipmt ur tst bcms charg. largr uits with mrcapacitac wi ta gr t b charg. This currt as is th str

rg iitia ischarg atr ur tst, b shrt-circuitig a gruig

th isuati. AlWAYS TAkE THIS SAFETY MEASuRE.

yu ca s urthr rm Fig. 5 that th absrpti currt crass at a

rativ sw rat, pig up th xact atur th isuati. This

str rg, t, must b ras at th a tst, a ruirs a

gr tim tha th capacitac chargig currt abut ur tims as g

as th vtag was appi.

With g isuati, th cucti r aag currt shu bui up t a

sta vau that is cstat r th appi vtag, as shw i Fig. 5. A

icras aag currt with tim is a warig trub, as iscuss i

th tsts scrib i th wig scti.


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With a bacgru w hw tim acts th maig istrumt

raigs, ts csir thr cmm tst mths: (1) shrt-tim r spt

raig; (2) tim-rsistac; a (3) stp r muti-vtag tsts.

TYPES oF InSulATIon RESISTAnCE TESTS

Shrt-Time r Spt-Reaig Test

I this mth, u simp cct th Mggr istrumt acrss th

isuati t b tst a prat it r a shrt, spcifc tim pri

(60 scs is usua rcmm). As shw schmatica i Fig. 6,

uv simp pic a pit a curv icrasig rsistac vaus;

uit t th vau wu b ss r 30 scs, mr r 60 scs.

Bar i mi as that tmpratur a humiit, as w as citi

ur isuati act ur raig.

Figre 6Typica crve isati resistace (i meghms) with time r the shrt time r

spt-reaig test meth.


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I th apparatus u ar tstig has vr sma capacitac, such as a

shrt ru hus wirig, th spt raig tst is a that is cssar.

Hwvr, mst uipmt is capacitiv a s ur vr frst spt raig

uipmt i ur pat, with prir tsts, ca b a rugh gui

as t hw g r ba th isuati is. Fr ma ars, maitac

prssias hav us th -mghm ru t stabish th awab

wr imit r isuati rsistac. Th ru ma b stat:

Insulation resistance should be approximately one megohm for each 1,000

volts of operating voltage, with a minimum value of one megohm.

Fr xamp, a mtr rat at 2,400 vts shu hav a miimum isuati

rsistac 2.4 mghms. I practic, mghm raigs rma ar

csirab abv this miimum vau i w uipmt r wh

isuati is i g citi.B taig raigs priica a rcrig thm, u hav a bttr basis

jugig th actua isuati citi. A prsistt wwar tr

is usua air warig trub aha, v thugh th raigs ma b

highr tha th suggst miimum sa vaus. eua tru, as g as

ur priic raigs ar csistt, th ma b , v thugh wr

tha th rcmm miimum vaus. Th curvs Fig. 7 shw tpica

bhavir isuati rsistac ur varig pat pratig citis.

Th curvs wr ptt rm spt raigs ta with a Mggr istrumtvr a pri mths.


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Figre 7Typica behavir isati resistace ver a peri mths er varyig peratig

citis, (crves ptte rm spt reaigs with a Megger istrmet).


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Time-Resistace Meth

This mth is air ipt tmpratur a t ca giv

u ccusiv irmati withut rcrs past tsts. It is bas

th absrpti ct g isuati cmpar t that mist r

ctamiat isuati. yu simp ta succssiv raigs at spcifc tims

a t th ircs i raigs (s curvs, Fig. 8). Tsts b this mthar smtims rrr t as absrpti tsts.

nt that g isuati shws a ctiua icras i rsistac (ss

currt s curv A) vr a pri tim (i th rr 5 t 10 miuts).

This is caus b th absrpti currt w sp arir; g isuati

shws this charg ct vr a tim pri much gr tha th tim

ruir t charg th capacitac th isuati.

I th isuati ctais much mistur r ctamiats, th absrpti

ct is mas b a high aag currt which stas at a air cstat

vau, pig th rsistac raig w (rmmbr: R = e/I).

Figre 8Typica crves shwig ieectric absrpti eect i a time-resistace test, mae

capacitive eipmet sch as a arge mtr wiig.

Th tim-rsistac tst is vau as bcaus it is ipt

uipmt siz. Th icras i rsistac r ca a r isuati ccurs

i th sam mar whthr a mtr is arg r sma. yu ca, thrr,

cmpar svra mtrs a stabish staars r w s, rgarss thir hrspwr ratigs.


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Fig. 9 shws hw a 60-sc tst wu appar r g a prhaps ba

isuati. Wh th isuati is i g shap, th 60-sc raig is

highr tha th 30-sc raig.

Figre 9Typica car pt a time-resistace r be-reaig test.

A urthr avatag this ub-raig tst, as it is smtims ca,

is that it givs u a carr pictur, v wh a spt raig sas th

isuati s f.

Fr xamp, ts sa th spt raig a schrus mtr was 10

mghms. nw, ts assum that th ub-raig chc shws that th

isuati rsistac hs sta at 10 mghms whi u h vtag up

t 60 scs. This mas thr ma b irt r mistur i th wiigs that

bars watchig. o th thr ha, i th pitr shws a graua icras

btw th 30-sc a th 60-sc chcs, th ur rasab

sur th wiigs ar i g shap.

Tim-rsistac tsts arg rtatig ctrica machir spcia with

high pratig vtag ruir high isuati rsistac rags a a vr

cstat tst vtag. A hav-ut Mggr tst st, i-prat, srvs

this . Simiar, such a istrumt is bttr aapt r arg cabs,

bushigs, trasrmrs a switchgar.


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dieectric Absrpti Rati

Th rati tw tim-rsistac raigs (such as a 60-sc raig

ivi b a 30-sc raig) is ca a ictric absrpti rati. It is

usu i rcrig irmati abut isuati. I th rati is a 10-miut

raig ivi b a 1-miut raig, th vau is ca th parizati

ix.

With ha-cra Mggr istrumts, its a t asir r u t ru th

tst r 60 scs, taig ur frst raig at 30 scs. I u hav a

i-prat Mggr istrumt, u gt bst rsuts b ruig th tst

10 miuts, taig raigs at 1- a at 10-miuts, t gt th parizati

ix. Tab I givs vaus th ratis a crrspig rativ

citis th isuati that th iicat.

InSUlATIonCondITIon

60/30-SeCondRATIo

10/1-MInUTe RATIo(PolARIZATIon IndeX)

dagrus

qustiab

Gexct

1.0 t 1.25

1.4 t 1.6Abv 1.6**

lss tha 1

1.0 t 2***

2 t 4Abv 4**

*Ths vaus must b csir ttativ a rativsubjct t xpric with th tim-rsistac mthvr a pri tim.**I sm cass, with mtrs, vaus apprximat 20%highr tha shw hr iicat a r britt wiigwhich wi ai ur shc citis r urig starts. Fr

prvtiv maitac, th mtr wiig shu bca,trat, a ri t rstr wiig xibiit.***Ths rsuts wu b satisactr r uipmt withvr w capacitac such as shrt rus hus wirig.

TABLE ICondition of Insulation Indicated by

Dielectric Absorption Ratios*


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TEST VolTAGE VS. EquIPMEnT RATInG

Cmm us dC tst vtags r ruti maitac ar as ws:

Eipmet AC Ratig dC Test Vtage

up t 100 vts 100 a 250 vts

440 t 550 vts 500 a 1,000 vts2,400 vts 1,000 t 2,500 vts

r highr

4,160 vts a abv 1,000 t 5,000 vts,

r highr

Tst vtags us r pr tstig uipmt ar csirab highr

tha ths us r ruti maitac. Athugh thr ar pubish

iustr staars r dC maximum pr tst vtags t b us with

rtatig uipmt, th schu giv bw is custmari us. Fr

spcifc rcmmatis ur uipmt, u shu csut th

mauacturr th uipmt.

Pr Test Vtages r Rtatig Eipmet:

Factr AC Tst = 2 x nampat Ratig + 1000 vts

dC Pr Tst Istaati = 0.8 x Factr AC Tst x 1.6

dC Pr Tst Atr Srvic = 0.6 x Factr AC Tst x 1.6

Exampe:

Mtr with 2,400 VAC ampat ratig

Factr AC Tst = 2(2,400) +1,000 = 5,800 VAC

Max. dC Tst Istaati = 0.8(5,800)1.6 = 7,424 VdC

Max. dC Tst Atr Srvic = 0.6(5,800)1.6 = 5,568 VdC


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ASTITCHINTIME

AC TESTInG VS. dC

Up t w, wv ta abut tstig with dC vtag, but u wi har

AC tstig a t w th irc. Rmmbr that w sp

th is currt pruc i isuati b dC? (Th iitia surg

chargig currt, th rp with tim t absrpti currt, a th, atr

mr tim, th sta cucti currt.) W saw that i isuati tstig,th cucti r aag currt is th that givs us th irmati

w .

I ctrast, tstig with AC givs a chargig currt that is xtrm

arg cmpar t th thr is; aag currt is rativ mir. AC

rut is us r high-pttia tstig; vtag is icras t sm

spcif pit t s i th isuati ca sta that particuar vtag. It

is a Go/no-Go tp tst a ca caus trirati th isuati, i

ctrast t th dC tst which is basica -structiv.

I a AC tst vtag has b us a u wat t us dC tsts as

a atrativ, u wi t icras th maximum dC tst vtag

smwhat t btai uivat rsuts.

I sm cass, AC tstig ma b mr suitab r pr tstig

uipmt (that is, sig that th uipmt mts prscrib staars).

yu ru th vtag up t th sct vau a th uipmt ithr

passs r st pass th tst. With th dC tst, u gt a mr uaitativ

pictur; u ca mtr th aag currt as u icras th vtag a

btai spcifc vaus isuati rsistac.

As th siz ur uipmt icrass, thr ar as mar cmic

avatags i dC vr AC tstig. As th tst vtag icrass, bth th

cst a wight AC uipmt g up much astr tha with cmparab

dC tst uipmt. This is bcaus th AC tst st must supp th chargig

currt which bcms a rmais vr high i th argr machis. Asxpai prvius, i dC tstig, this currt rps rapi atr th iitia

chargig pri.


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ASTITCHINTIME

I summar, dC tst sts ar mp amst xcusiv r high-vtag

maitac a f tstig r th wig rass:

1. lwr cst

2. lightr wight

3. Smar siz

4. n-structiv

5. Bttr irmati, bth i uait a uatit

uSE oF dC dIElECTRIC TEST SET

Th Mggr istrumt, raig irct i hms a mghms

isuati rsistac, is ur bst bt r ruti i-pat maitac.

Hwvr, sm pats, particuar with highr vtag ratigs i uipmt,

us athr Mggr pruct th ictric tst st. S, u shu b

awar this istrumt a its us i isuati rsistac masurmts.

Th ictric tst st ca b us t trmi isuati rsistac b th

sam tst mths as uti r th Mggr istrumt; that is, th shrt-

tim, tim-rsistac a stp-vtag tsts. It is sig r thr uss, t,

but r isuati tstig it prvis: (1) a ajustab utput vtag a

(2) a mitrig th rsutat currt i micr-amprs. Th Mggr dC

dictric Tst Sts ar avaiab with vtag utputs ragig rm 5 V up

t 160 V.

Th curvs Fig. 5 ar ptt as currt vrsus tim, as ar curvs r

isuati masurmts tpica uipmt giv ar th this

maua. Mggr suppis graph papr which mas it as t pt mghms

isuati rsistac rm ur vtag a currt raigs.

TESTS duRInG dRYInG ouT oF EquIPMEnT

Wt ctrica uipmt is a cmm hazar ac b a maitac

girs. I th uipmt is wt rm rsh watr, u g right aha

rig it ut. Hwvr, i uv gt sat watr, u must frst wash awa th

sat with rsh watr. othrwis, u av vr crrsiv psits sat

mta a isuatig suracs as w as i crvics th isuati. With

mistur, such psits rm a vr g cuctr ctricit. As, u

shu rmv i r gras rm th isuati, usig a suitab svt.


20/67

ASTITCHINTIME

Thr ar varius was t r ut ctrica uipmt, pig up

its siz a prtabiit. yu ca us a bast ht air, a v, circuati

currt thrugh cuctrs, r a cmbiati tchius. lca pat

citis a aciitis, tgthr with irmati rm th uipmt

mauacturrs, ca srv as a gui t th bst mth r ur particuar

uipmt.

I sm cass, r with crtai uipmt, rig ut ma t b cssar.

yu ca chc this b isuati rsistac tsts, i u hav rcrs

prvius tsts th apparatus. Wh rig ut is ruir, such rcrs

ar as hpu t trmi wh th isuati is r mistur.

noTE: Wet eipmet is ssceptibe t vtage breaw. Therere, y

sh se a w-vtage Megger tester (100 r 250 VdC), at east

i the eary stages a ryig-t r. I a w-vtage istrmetis t reaiy avaiabe, sw craig a 500-vt tester may be

sbstitte.

May testers have a aitia test rage measrig i ihms

(W). This measremet is typicay mae at y a ew vts, a

is the iea iitia measremet t be mae e eipmet.

This rage measres bew the Meghm rage, a ca, therere,

prvie a acta measremet t se as a bechmar i mitrig

the ryig prcess. I a ihm measremet is btaie, isatihas bee thrghy satrate, bt may be recaimabe. Ateratey

test a ry, watchig the reaigs rise ti they reach the Meghm

rage, at which time higher vtage tests ca be saey empye.

As a xamp hw imprtat past raigs ar, ts at a 100-hp

mtr thats b . Atr a ca-up, a spt raig with th Mggr

tstr shws 1.5 mghms. oha, u prbab sa this is . Whats

mr, i past rcrs shw th isuati rsistac t ru btw 1 a

2 mghms, u b sur.

o th thr ha, i past rcrs shw th rma rsistac vaus t

ru 10 r 20 mghms, th u wu w that watr was sti i th

mtr wiigs.


21/67

0 ASTITCHINTIME

Figre 10-Typica ryig crve where e-mite reaigs isati resistace are tae every

r hrs.

Th tpica rig-ut curv r a dC mtr armatur (Fig. 10) shws hw

isuati rsistac chags. durig th frst part th ru, th rsistac

actua crass bcaus th highr tmpratur. Th it riss at a

cstat tmpratur as rig prcs. Fia, it riss t a high vau, as

rm tmpratur (20C) is rach.

nt that i u cuct isuati rsistac tsts urig rig, a u

hav raigs prvius tsts th r uipmt, u w wh

uv rach th sa vau r th uit. yu ma prr t us a tim-

rsistac tst, ta priica (sa, c a shit), usig th ictric

absrpti rati r parizati ix t w r-ut prgrss ( t

crrct r tmpratur).


22/67

ASTITCHINTIME

EFFECT oF TEMPERATuRE on InSulATIon RESISTAnCE

Th rsistac isuatig matrias crass mar with a icras i

tmpratur. As wv s, hwvr, tsts b th tim-rsistac a stp-

vtag mths ar rativ ipt tmpratur cts, givig

rativ vaus.

I u wat t ma riab cmpariss btw raigs, u shu

crrct th raigs t a bas tmpratur, such as 20C, r ta a ur

raigs at apprximat th sam tmpratur (usua t ifcut t ).

W wi cvr sm gra guis t tmpratur crrcti.

o thumb ru is:

For every 10C increase in temperature,

halve the resistance;

or, for every 10C decrease,double the resistance.

Fr xamp, a tw-mghm rsistac at 20C rucs t 1/2

mghm

at 40C.

each tp isuatig matria wi hav a irt gr rsistac

chag with tmpratur. Factrs hav b vp, hwvr, t

simpi th crrcti rsistac vaus. Tab II givs such actrs r

rtatig uipmt, trasrmrs a cab. yu mutip th raigs ugt b th actr crrspig t th tmpratur (which u t

masur).

Fr xamp, assum u hav a mtr with Cass A isuati a u gt a

raig 2.0 mghms at a tmpratur (i th wiigs) 104F (40C).

Frm Tab II u ra acrss at 104F t th xt cum (r Cass A) a

btai th actr 4.80. yur crrct vau rsistac is th:

2.0 mghms x 4.80 = 9.6 mghms

(raig (crrcti (crrct

at 104F) actr r raig r

Cass A 68F r 20C)

isuati

at 104F)


23/67

ASTITCHINTIME

nt that th rsistac is amst fv tims gratr at 68F (20C), as

cmpar t th raig ta at 104F. Th rrc tmpratur r

cab is giv as 60F (15.6C), but th imprtat pit is t b csistt

a crrct t th sam bas.

TABlE II-Temperatre Crrecti Factrs*

TeMP. CABleSRoTATInG

eqUIP.

C

F C

lASSA

ClASSB

oIl-FIlled

TRAnSFoRMeRS

Code

nATURAl

Code

GR-S

PeRFoRMAnCe

nATURAl

HeATReSIST.

nATURAl

HeATReSIST.&

PeRFoRM.GR-S

oZoneReSIST.

nATURAlGR-S

VARnISHed

CAMBRIC

IMPReGnATed

PAPeR

0

5

10

15.6

20

25

30

35

40

45

50

55

60

65

7075

32

41

50

60

68

77

86

95

104

113

122

131

140

149

158167

0.21

0.31

0.45

0.71

1.00

1.48

2.20

3.24

4.80

7.10

10.45

15.50

22.80

34.00

50.0074.00

0.40

0.50

0.63

0.81

1.00

1.25

1.58

2.00

2.50

3.15

3.98

5.00

6.30

7.90

10.0012.60

0.25

0.36

0.50

0.74

1.00

1.40

1.98

2.80

3.95

5.60

7.85

11.20

15.85

22.40

31.7544.70

0.25

0.40

0.61

1.00

1.47

2.27

3.52

5.45

8.45

13.10

20.00

0.12

0.23

0.46

1.00

1.83

3.67

7.32

14.60

29.20

54.00

116.00

0.47

0.60

0.76

1.00

1.24

1.58

2.00

2.55

3.26

4.15

5.29

6.72

8.58

0.42

0.56

0.73

1.00

1.28

1.68

2.24

2.93

3.85

5.08

6.72

8.83

11.62

15.40

20.3026.60

0.22

0.37

0.58

1.00

1.53

2.48

4.03

6.53

10.70

17.10

27.85

45.00

73.00

118.00

193.00313.00

0.14

0.26

0.49

1.00

1.75

3.29

6.20

11.65

25.00

41.40

78.00

0.10

0.20

0.43

1.00

1.94

4.08

8.62

18.20

38.50

81.00

170.00

345.00

775.00

0.28

0.43

0.64

1.00

1.43

2.17

3.20

4.77

7.15

10.70

16.00

24.00

36.00

*Corrected to 20 C for rotating equipment and transformers; 15.6 C for cable.


24/67

ASTITCHINTIME

nmgraph tmpratur crrcti vaus r Mggr raigs(crrct t 25C). Fr rtatig machir with Cass B isuati.

EFFECTS oF HuMIdITY

W hav sp at varius pits i this maua abut th prsc

mistur i isuati a its vr mar ct up rsistac vaus. yu

might xpct, thrr, that icrasig humiit (mistur ctt) i th

surruig (ambit) air cu act isuati rsistac. A it ca t

varig grs.

I ur uipmt prats rguar abv th w-pit tmpratur (th

tmpratur at which th mistur vapr i air css as a iui), th

tst raig rma wi t b act much b th humiit. ev i th

uipmt t b tst is i, th sam is tru s g as its tmpratur is

pt abv th w pit.


25/67

ASTITCHINTIME

The aforementioned statement assumes that the insulation surfaces

are free of contaminants, such as certain lints and acids or salts,

which have the property of absorbing moisture (theyre called

hygroscopic or deliquescent materials by chemists). Their

presence could unpredictably affect your readings; they should be

removed before tests are made.

I ctrica uipmt wr ccr primari with th citis

th xps suracs whr mistur css a acts th vra

rsistac th isuati. Stuis shw, hwvr, that w wi rm i th

cracs a crvics isuati br it is visib vit th surac.

dw-pit masurmts wi giv u a cu as t whthr such ivisib

citis might xist, atrig th tst rsuts.

As a part ur maitac rcrs, thrr, its a g ia t mat at ast whthr th surruig air was r r humi wh th

tst was ma. As, whthr th tmpratur was abv r bw th

ambit. Wh u tst vita uipmt, rcr th ambit wt a r

bub tmpraturs, rm which w-pit a prct rativ r absut

humiit ca b btai.

PREPARATIon oF APPARATuS To TEST

1. Tae ot Service

Shut w th apparatus. op switchs. d-rgiz. discct rm

thr uipmt a circuits, icuig utra a prtctiv (wrms

tmprar) gru cctis. S Saety Precatis, pag 26.

2. Mae Sre Jst What is Ice i the Test

Ispct th istaati vr caru t trmi just what uipmt

is cct a wi b icu i th tst, spcia i it is ifcut r

xpsiv t iscct assciat apparatus a circuits. Pa particuar

attti t cuctrs that a awa rm th istaati. This is vr

imprtat, bcaus th mr uipmt that is icu i a tst, th wr

th raig wi b, a th tru isuati rsistac th apparatus i

usti ma b mas b that th assciat uipmt.

It is awas pssib, curs, that th isuati rsistac th cmpt

istaati (withut iscctig vrthig) wi b satisactri high,

spcia r a spt chc. or, it ma b highr tha th rag th


26/67

ASTITCHINTIME

Mggr istrumt i us, i which cas thig wu b gai b

sparatig th cmpts, bcaus th isuati rsistac ach part

wu b sti highr.

Fr a iitia tst, it ma b cssar t sparat th cmpt parts, v

thugh abr a xps ar ivv, a tst ach sparat. As

ma a tst a th cmpts cct tgthr. With this irmati rcr, it ma t b cssar t sparat th cmpts utur

tsts uss uaccutab w raigs ar bsrv.

3. discharge Capacitace

It is vr imprtat that capacitac b ischarg, bth br a atr

a isuati rsistac tst. It shu b ischarg r a pri abut ur

tims as g as tst vtag was appi i a prvius tst.

Mggr istrumts ar rut uipp with ischarg circuits r this

purps. I a ischarg ucti is t prvi, a ischarg stic shu b

us. lav high capacitiv apparatus (i.., capacitrs, arg wiigs, tc.)

shrt circuit uti ra t r-rgiz.

4. Crret leaage at Switches

Wh apparatus is shut w r th isuati rsistac tst, ma sur

that th raigs ar t act b aag vr r thrugh switchs r

us bcs, tc. Such aag ma mas th tru isuati rsistac th

apparatus ur tst. S Us a Gar Termia, pag 50.

or, what ma b mr srius, currt rm a rgiz i ma a it

th apparatus a caus icsistt raigs, particuar i th iv i is

dC. Hwvr, such aag usua ca b tct b watchig th pitr

th Mggr istrumt at th mmt th tst as ar cct t

th apparatus a br th istrumt is prat. Br maig ths

bsrvatis, b sur that a capacitac is ischarg b shrt circuitig rgruig th apparatus.

CAUTION: Never connect a Megger insulation tester to energized

lines or equipment. Never use the tester or any of its leads or

accessories for any purpose not described in this book.


27/67

ASTITCHINTIME

SAFETY PRECAuTIonS

obsrv a rus r sat wh taig uipmt ut srvic. Bc ut

iscct switchs. Tst r rig r iuc vtags. App wrms

grus.

Rmmbr that wh wrig aru high vtag uipmt thr is

awas a pssibiit vtags big iuc i apparatus ur tst

r is t which it is cct, bcaus prximit t rgiz high

vtag uipmt. Thrr, rathr tha rmvig a wrms gru i

rr t ma a tst, it is mr avisab t iscct th apparatus, such

as a trasrmr r circuit brar, rm th xps bus r i, avig th

attr gru. Us rubbr gvs wh cctig th tst as t th

apparatus a whi pratig th Mggr istrumt.

Apparatus Under Test Must Not Be Live!

S pag 24 Preparati Apparats r Test.

I utra r thr gru cctis hav t b iscct, ma sur

th ar t carrig currt at th tim, a that wh iscct

thr uipmt wi ac cssar prtcti.

Pa particuar attti t cuctrs that a awa rm th circuit bigtst a ma sur th hav b prpr iscct rm a surc

vtag.

Shc Hazar rm Test Vtage

obsrv th vtag ratig th Mggr istrumt a rgar it with

apprpriat cauti. larg ctrica uipmt a cabs usua hav

sufcit capacitac t str up a agrus amut rg rm th

tst currt. Ma sur this capacitac is ischarg atr th tst a

br haig th tst as. S as discharge Capacitace, pag 25.

Expsi a Fire Hazar

S ar as is w, thr is fr hazar i th rma us a Mggr

isuati tstr. Thr is, hwvr, a hazar wh tstig uipmt

cat i iammab r xpsiv atmsphrs.


28/67

ASTITCHINTIME

Slight sparking may be encountered:

(1) Wh attachig th tst as t uipmt i which th capacitac

has t b cmpt ischarg

(2) durig a tst, arcig thrugh r vr aut isuati

(3) Fwig a tst wh capacitac is ischarg

CAUTION:

Do not use the instrument

in an explosive atmosphere.

Sggestis:

Fr (1) a (3): Arrag prmat ista gruig aciitis atst as t a pit whr istrumt cctis ca b ma i a sa

atmsphr.

Fr (2): Us w-vtag tstig istrumts, r a sris rsistac.

Fr (3): d t iscct th tst as r at ast 30 t 60 scs

wig a tst, awig tim r capacitac ischarg.

ConnECTIonS FoR TESTInG InSulATIon RESISTAnCEoF ElECTRICAl EquIPMEnT

Th wig iagrams shw hw t cct a Mggr isuati tstr t

varius tps ctrica uipmt. Th iagrams as shw i pricip

hw uipmt must b iscct rm thr circuits br th

istrumt is cct.

Ths iustratis ar tpica a wi srv as guis r tstig isuati

rsistac practica a tps apparatus a cuctrs.

Br prcig with tsts, ra th artic Preparati Apparats

r Test, pag 24.

REMEMBER! The Megger isati resistace tester measreswhatever resistace is cecte betwee its termias. This mayice series r parae eaage paths thrgh isati r verits srace.


29/67

ASTITCHINTIME

1. AC Mtrs & Startig Eipmet

Figre 11

Cctis r tstig th isuati rsistac a mtr, startig

uipmt a cctig is, i para. nt that th startr switch is

i th psiti r th tst. It is awas prrab t iscct th

cmpt parts a tst thm sparat i rr t trmi whr

wasss xist.

2. dC Geeratrs & Mtrs

Figre 12

With th brushs rais as iicat, th brush riggig a f cis ca b

tst sparat rm th armatur. liwis th armatur ca b tst b

its. With th brushs wr, th tst wi b that brush riggig, fcis a armatur cmbi.


30/67

ASTITCHINTIME

3. Wirig Istaati

Figre 13

Cctis r tstig t gru ach circuit sparat, wrig rm th

istributi pa.

Figre 14


31/67

0 ASTITCHINTIME

Cctis at th mai pwr bar, rm which pit th tir

sstm ca b tst t gru at tim, prviig a switchs i th

istributi pa ar cs.

4. Appiaces, Meters, Istrmets & Misceaes Eectrica Apparats

Figre 15

Cctis r tstig a appiac. Th tst is ma btw th

cuctr (th hatig uit, mtr, tc.) a xps mta parts. Th

apparatus must b iscct rm a surc pwr a pac

sm isuatig matria.

5. Ctr, Sigaig & Cmmicati Cabes

Figre 16

Cctis r tstig isuati rsistac wir i a muti-

cuctr cab agaist a thr wirs a shath cct tgthr.


32/67

ASTITCHINTIME

I6. Pwer Cabes

Cctis r tstig th isuati rsistac a pwr cab. Wh

tstig cab, it is usua bst t iscct at bth s i rr t tst

th cab b its, a t avi rrr u t aag acrss r thrugh

switchbars r pabars. S as use Gar Termia, pag 50.

Figre 17

Figre 18


33/67

ASTITCHINTIME

7. Pwer Trasrmers

Figre 19

Cctis r tstig isuati rsistac a trasrmr high vtag

wiig a bushigs, a th high tsi iscct switch, i para,

with rrc t th w vtag wiig a gru. nt that th w

vtag wiig is gru r this tst.

8. AC Geeratrs

Figre 20

With this ccti, th isuati rsistac wi b that th gratr

statr wiig a cctig cab cmbi. T tst ithr th statr

wiig r th cab its, th cab must b iscct at th machi.


34/67

ASTITCHINTIME

AddITIonAl noTES ABouT uSInG A MEGGER InSulATIon TESTER

Testig leas

Irir r ctiv tstig as wi caus rrus a misaig rsuts

isuati rsistac tsts. Ta car i this rspct.

uisate leasT avi rrr u t th isuati as, pac th Mggr istrumt

cs t th ugru trmia r cuctr th apparatus ur tst

a cct a shrt pic ight bar wir irct rm th li trmia

th istrumt t th apparatus. I th Guar trmia is us, it ma b

trat simiar. n. 18 r 20 gaug, si wir wi sufc. Supprt th a

b its cctis t th istrumt a th apparatus.

With this mth cctig rm th li trmia, th uait thisuati, i a, th earth r Gru a bcms uimprtat.

Isate leas

Whr pc is pac th isuati as, th must b

urab a th bst uait isuatig matria. oi rsistat, sthtic,

rubbr-isuat, sig-cuctr n. 14 stra wir is rcmm.

Th utr jact shu b smth, with utr brai. lugs shu b

ftt r attachig t th istrumt trmias, a stut sprig cips ar

rcmm r cctig t th apparatus r circuit ur tst. A

cvit gth a ma b us. Jits ar t b avi.

Atr cctig th as t th istrumt, a just br cctig

thm t th apparatus, ma sur thr is a rm a t a. d this

b pratig th istrumt, which shu ra Ifit. d t crrct sight

a aag b attmptig t rst th Ifit Ajustr a high-rag

istrumt. Th tuch th tst s th as tgthr t ma sur

th ar t iscct r br.

Currt tstig with th high-rag (50,000 mghms) Mggr isuati

tstrs ruirs that th li tst a b maitai at a high vau s that

it wi t tr it th masurmt. Th shi tst a, with th shi

cct t Guar, prvts a aags vr its trmiatis r thrugh

th a isuatig matria, rm big masur.


35/67

ASTITCHINTIME

Istrctis r use

Th utagg th shi a is t b cct t th li a

Guar trmias th Mggr istrumt th trmia t li a

th si (shi) trmia t Guar. Th cip th li a is cct t

th apparatus ur tst i th rguar wa. Th utbar Guar trmia

ma b cct t that part th apparatus ur tst which th usrwishs t guar. Th cuctr mp i maig this ccti must b

isuat r th vtag ratig th Mggr istrumt us.

Eect Capacitace

Capacitac i apparatus ur tst must b charg up t th rat dC

vtag th Mggr isuati tstr, a maitai r 30 t 60 scs

br a fa raig is ta. Ma sur that capacitac is ischarg,

b shrt circuitig a gruig th apparatus br cctig th tstas. S discharge Capacitace, pag 25.

noTE: Capacitace cases the piter t swig twars zer whie the

istrmet is beig brght p t spee, a t swig scae bey

ifity whe the geeratr is swig w. This is simpy the charge

wig it a t the capacitace a thrgh the eectig ci

the hmmeter.

Capacitac cts ar mst ticab i arg gratrs, i pwr acmmuicati cab mr tha a w hur t i gth, a i

capacitrs. I gra, ths cts ar sma with capacitac ss tha

0.01 F. It bcms mr ticab as capacitac a/r th ssitivit

th istrumt icrass. Th hav-ut sris Mggr isuati

tstrs ca b us arg capacitrs with g rsuts, particuar wh

prat rm th pwr i rathr tha th ha cra.

operatig Time

A vr imprtat csirati i maig isuati rsistac tsts is th

tim ruir r th raig isuati rsistac t rach a maximum.

Th tim ruir t charg th gmtric capacitac is vr shrt usua

mr tha a w scs a that which causs urthr a i

rachig u charg is a ictric absrpti ct. It ma b a mattr

miuts r v hurs r this ctrifcati tim t b cmpt, a r

th pitr t rach a absut maximum.


36/67

ASTITCHINTIME

Shrt-Time Reaigs

Fr shrt-tim raigs isuati rsistac, prat th istrumt r

a fit gth tim, ithr 30 scs r 1 miut, a ra at th

that tim. Ctiu craig stai at sip sp uti th raig has

b ta. Ma utur tsts with th sam gth pratig tim.

Time-Resistace Meth

Wh usig a ha-cra istrumt, prat ctiuus r 1 miut.

Ta a raig at th th frst 30 scs a athr raig at th

th miut.

Wh usig a mtr-riv r rctifr-prat istrumt, th tim

itrvas ar usua 1 miut a 10 miuts rm th tim th tstig

vtag is appi. or, tim-rsistac curvs ma b ta vr a pri

10 t 30 miuts r gr.

Vtage Scaes

Sm isuati tstrs ma b suppi with a vtag sca t chc r

th absc vtag br isuati tstig. As xpai i th Saety

Precatis scti, hwvr, isuati tstrs shu vr b cct

t rgiz is r uipmt wh prat i a th Isuati Tst

r Rsistac Tst ms.


37/67

ASTITCHINTIME

InTERPRETATIon-MInIMuM VAluES

Isuati rsistac ctrica uipmt is act b ma variabs

such as th uipmt sig; th tp isuatig matria us, icuig

birs a imprgatig cmpus; th thicss th isuati a

its ara; caiss, mistur a tmpratur. Fr isuati rsistac

raigs t b a ccusiv masur th citi th uipmtbig tst, ths variabs must b ta it csirati.

Atr th uipmt has b put it srvic, actrs such as th sig

th uipmt, th i isuatig matria us, a its thicss a

ara cas t b variabs, awig miimum isuati rsistac vaus

t b stabish withi rasab tracs. Th variabs that must b

csir atr th uipmt ha b put it srvic, a at th tim

that th isuati rsistac masurmts ar big ma, ar caiss,

mistur, tmpratur a mchaica amag (such as racturs).

G Hseeepig

Th mst imprtat ruirmts i th riab prati ctrica

uipmt ar caiss, a th imiati mistur ptrati

it th isuati. This ma b csir as g huspig, a

is sstia i th maitac a tps ctrica uipmt. Th

vr act that isuati rsistac is act b mistur a irt, with

u awacs r tmpratur, mas th Mggr isuati tstr th

vauab t that it is i ctrica maitac. It is at c a gaug

caiss a g huspig as w as a tctr trirati

a impig trub.

What Reaigs t Expect Periic Tests

Svra critria r miimum vaus isuati rsistac hav b

vp a ar summariz hr. Th shu srv as a gui r

uipmt i srvic. Hwvr, priic tsts uipmt i srvic wiusua rva raigs csirab highr tha th suggst miimum

sa vaus.


38/67

ASTITCHINTIME

Thrr, it is strg rcmm that rcrs priic tsts b pt,

bcaus prsistt wwar trs i isuati rsistac usua giv air

warig impig trub, v thugh th actua vaus ma b highr

tha th suggst miimum sa vaus.

Cvrs, awacs must b ma r uipmt i srvic shwig

priic tst vaus wr tha th suggst miimum sa vaus, sg as th vaus rmai stab r csistt. I such cass, atr u

csirati has b giv t tmpratur a humiit citis at th

tim tst, thr ma b r ccr. This citi ma b caus

b uirm istribut aags a harmss atur, a ma t b th

rsut a agrus caiz wass.

Hr agai, rcrs isuati rsistac tsts vr a pri tim rva

chags which ma justi ivstigati. Th tr th curv ma b mrsigifcat tha th umrica vaus thmsvs.

The oe-Meghm Re

Fr ma ars mghm has b wi us as a air awab wr

imit r isuati rsistac riar iustria ctrica uipmt

rat up t 1000 vts, a is sti rcmm r ths wh ma t b

t amiiar with isuati rsistac tstig practics, r wh ma t wish

t apprach th prbm rm a mr tchica pit viw.

Fr uipmt rat abv 1000 vts th mghm ru is usua

stat as a miimum mghm pr thusa vts. Athugh this

ru is smwhat arbitrar, a ma b criticiz as acig a girig

uati, it has st th tst a g ma ars practica

xpric. It givs sm assurac that uipmt is t t wt r irt

a has sav ma a ucssar braw.

Mr rct stuis th prbm, hwvr, hav rsut i rmuas

r miimum vaus isuati rsistac that ar bas th i

isuatig matria us a th ctrica a phsica imsis th

tps uipmt ur csirati.


39/67

ASTITCHINTIME

MInIMuM VAluES FoR InSulATIon RESISTAnCE

Rtatig Machiery

Th Ieee gui, Rcmm Practics r Tstig Isuati Rsistac

Rtatig Machir, as with th prbm maig a itrprtig

isuati rsistac masurmts r rtatig machir. It rviws th

actrs which act r chag isuati rsistac charactristics, utisa rcmms uirm mths r maig tsts, a prsts rmuas

r th cacuati apprximat miimum isuati rsistac vaus r

varius tps AC a dC rtatig machir. Th gui stats:

Th rcmm miimum isuati rsistac Rm

r atratig-currt

a irct-currt machi armatur wiigs a r f wiigs

atratig-currt a irct-currt machis ca b trmi b:

Rm

= V + 1

whr:

Rm

= rcmm miimum isuati rsistac i mghms

at 40C th tir machi wiig

V = rat machi trmia t trmia pttia, i ivts

I appicatis whr th machi is vita, it has b csir g

practic t iitiat rcitiig shu th isuati rsistac, havigb w abv th miimum vau giv b e 2, rp apprciab t ar

that v.

It is recmmee that thse wh perate a maitai rtatig machiery

btai cpies the IEEE pbicati, Recmmee Practices r Testig

Isati Resistace Rtatig Machiery, which ca be btaie by

writig the IEEE at 345 East 47th St., new Yr, nY, 10017.

BshigsI th cas utr i circuit brar bushigs, xpric has shw

that a bushig, with its assmb assciat isuatig mmbrs,

shu, r riab prati, hav a isuati rsistac vau abv

10,000 mghms at 20C. This assums that th i withi th ta is i

g citi, that th brar is sparat rm its xtra cctis

t thr uipmt, a that th prcai wathr shi is guar.

This mas that ach cmpt such as th stripp bushig its,

crss-mmbr, it r, wr arcig shi, tc., shu hav a isuatirsistac i xcss that vau.


40/67

ASTITCHINTIME

A cmpts which ar suprfcia ca a r a hav vaus ss

tha 10,000 mghms ar usua trirat itra, b th prsc

mistur r carbiz paths, t such a xtt that th ar t riab

r g srvic uss rciti. This is particuar s wh pratig

ur surg citis such as urig ightig isturbacs. I th cas

th stripp bushig its, th wr stm a uppr wathr shi must

b ithr prct ca r guar br it is cm as uriab

bcaus a isuati rsistac vau ss tha 10,000 mghms.

What has b sai r stripp i circuit brar bushigs as appis

t bushigs r thr uipmt, such as trasrmrs. Sic bushigs

a thr assciat mmbrs hav vr high isuati rsistac vaus

rma, a Mggr isuati tstr havig a rag at ast 10,000

mghms is cssar t tst such uipmt. Mggr istrumts havig

rags up t 50,000 mghms wi prmit bsrvati triratigtrs i bushigs br th rach th ustiab vau 10,000

mghms.

Cabe a Cctrs

Cab a cuctr istaatis prst a wi variati citis

rm th pit viw th rsistac th isuati. Ths citis

rsut rm th ma is isuatig matrias us, th vtag

ratig r isuati thicss, a th gth th circuit ivv i thmasurmt. Furthrmr, such circuits usua xt vr grat istacs,

a ma b subjct t wi variatis i tmpratur, which wi hav a

ct th isuati rsistac vaus btai. Th trmias cabs

a cuctrs wi as hav a ct th tst vaus uss th ar

ca a r, r guar.

Th Isuat Cab egirs Assciati (ICeA) givs miimum vaus

isuati rsistac i its spcifcatis r varius tps cabs a

cuctrs. Ths miimum vaus ar r w, sig-cuctr wir acab atr big subjct t a AC high vtag tst a bas a dC

tst pttia 500 vts appi r miut at a tmpratur

60F.


41/67

0 ASTITCHINTIME

Ths staar miimum vaus (r sig-cuctr cab) ar bas

th wig rmua:

R = k g10

d/

whr:

R = mghms pr 1000 t cab

k = cstat r isuatig matria

d = utsi iamtr cuctr isuati

= iamtr cuctr

Miimm Vaes k at 60 F.

Isuati TpImprgat Papr ................................................................... 2,640

Varish Cambric .................................................................... 2,460

Thrmpastic-Pth ........................................abv 50,000

Cmpsit Pth ......................................................... 30,000

Thrmpastic-Pvi:

Pvi Chri 60C ........................................................ 500

Pvi Chri 75C ..................................................... 2,000

Gra natura Rubbr Sthtic Rubbr

C ...............................................................................................950

Prrmac ....................................... 10,560 ............................2,000

Hat Rsistat..................................... 10,560 ............................2,000

oz Rsistat...................... 10,000 (But) ............................2,000

krit ..........................................................................................4,000

S pags 44 a 45 r Tabs lg10

d/


42/67

ASTITCHINTIME

Th isuati rsistac cuctr a muticuctr cab t a

thrs a shath is:

R = k g10

d/

whr:

d = iamtr vr isuati uivat sig-cuctr cab

= + 2c + 2b

= iamtr cuctr (r sctr cabs uas iamtr

ru cuctr sam crss-scti)

c = thicss cuctr isuati

b = thicss jact isuati

(a imesis mst be expresse i same its)

Trasrmers

Accptab isuati rsistac vaus r r a cmpu-f

trasrmrs shu b cmparab t ths r Cass A rtatig machir,

athugh staar miimum vaus ar avaiab.

oi-f trasrmrs r vtag rguatrs prst a spcia prbm i that

th citi th i has a mar iuc th isuati rsistac

th wiigs.

I th absc mr riab ata th wig rmua is suggst:

R = Ce

VA

R = miimum 1-miut 500-vt dC isuati rsistac i mghms

rm wiig t gru, with thr wiig r wiigs guar,

r rm wiig t wiig with cr guar

C = a cstat r 20C masurmts

e = vtag ratig wiig ur tst

VA = rat capacit wiig ur tst

Fr tsts wiig t gru with th thr wiig r wiigs

gru, th vaus wi b much ss tha that giv b th rmua.

R i this rmua is bas r, aci-r, sug-r i, a bushigs

a trmia bars that ar i g citi.


43/67

ASTITCHINTIME

Vaes C at 20C

60-Hrtz 25-Hrtz

Ta i-f tp 1.5 1.0

Uta i-f tp 30.0 20.0

dr r cmpu-f tp 30.0 20.0

This rmua is it r sig-phas trasrmrs. I th trasrmr

ur tst is th thr-phas tp, a th thr iiviua wiigs ar

big tst as , th:

e = vtag ratig th sig-phas wiigs

(phas t phas r ta cct uits a phas t

utra r star cct uits)

VA = rat capacit th cmpt thr-phas wiig ur tst

TESTS uSInG MulTI-VolTAGE MEGGER InSulATIon TESTERS

Maitac practic trs iicat th vau tstig isuati with

dC vtags at vs smwhat highr tha th pa vau th rat AC

vtag th uipmt big tst. Such dC tsts hav i sm cass

b shw t rva -structiv icipit wasss i isuati

which cu t thrwis b u, xcpt pssib b partia ischarg

tcti at -structiv AC tst vtag vs.Th tchiu ivvs th appicati tw r mr dC vtags, a

critica bsrvig a ructi isuati rsistac at th highr

vtag. A mar r uusua ructi i isuati rsistac r a

prscrib icras i appi vtag is a iicati icipit wass.

It is imprtat t mti that th mrits this tchiu aris rm mr

rct ivstigatis which iicat that rathr high dC vtag ca b us

t tct wasss withut amagig th isuati. Th maximum vau vtag which shu b us wi p arg th caiss a

rss th isuati t b tst.

I maig tsts isuati at such dC vtags, th hmmtr mth

has at ast tw avatags. First, prscrib fx vtags ar switch

it us, a istrumt masurmt ma with th irct raig

hmmtr. This is a simp a rprucib mth cmpar t i

which ma chics vtag ar avaiab. Athr imprtat avatag


44/67

ASTITCHINTIME

th hmmtr ca b xpai b rrrig t Fig. 21. I this fgur, th

chag which ma ccur i aag currt atr th absrpti currt has

isappar is shw ptt i trms isuati rsistac agaist thr

irt vtags. nt that thr is chag i rsistac shw i th

fgur btw 500 a 1000 vts, iicatig chag i th isuati

as a rsut appig ths tw vtags. This is a assumpti, but is a

citi which is t ucmm i practic. I th isuati ctius t

b stab at 2500 vts, thr wi b chag i th isuati rsistac

vau btai, which is shw b th tt xtsi th hrizta

i i th fgur. Wh -iar citis appar at a highr vtag, th

vtag rsistac curv rvas this vr car b a wr rsistac vau,

iicat b th wwar curv i th fgur. Th fgur, thrr, rvas

th simpicit trmiig th chag i isuati stabiit b usig thr

fx vtags which ar asi rprucib wh maig thr-vtag tsts

a ruti basis.

Figre 21

W wish t mphasiz that th curv i Fig. 21 iicats th rsistac

chag u t aag currt , a t th absrpti currt which

ma appar r a pri tim with ach chag i vtag. It ma b

cssar t wait a apprciab amut tim atr ach vtag chag

r th absrpti currt t isappar br taig a raig.


45/67

ASTITCHINTIME

VAluESoFloG

10

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Vaescntinednnextpage.

.G.W.A

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46/67

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47/67

ASTITCHINTIME

T bttr ursta th tchiu maig isuati rsistac tsts at

tw r mr vtags, th wig stps ar suggst, usig a iustria

r tracti mtr cass i th 300- t 1000-vt rag as a xamp:

1. Ma a -miut Mggr istrumt tst at 500 vts t srv as a basis

cmparis r subsut stps.

2. Atr a caru caig prati ma a sc 500-vt tst t

trmi th ctivss th caig.

3. I th -miut isuati rsistac vau is subrma, r i th 60

sc/30 sc isuati rsistac rati is gratr tha at this

pit th a rig prati ma b sirab br usig a highr

tst vtag. Hwvr, maig athr tst at 1000 vts a cmparig

ths raigs with ths rm th 500-vt tst wi hp i trmiig

th r rig. I th 1000-vt tst vau is apprciab ss thathat at 500 vts, th a rig prati shu b prrm. o th

thr ha, i th 1000-vt a 500-vt tst vaus ar apprximat

th sam, it is rasab t assum that th cisi t prrm a rig

prati ca b rr uti atr th xt stp.

4. Ma a Mggr istrumt tst at 2500 vts. I thr is apprciab

irc i th 500- a 2500-vt tst vaus, g vic xists that

th mtr i usti is i riab citi as ar as its isuati is

ccr. o th thr ha, i thr is a apprciab irc i thtw, thr is g vic that mr thrugh rcitiig is ca

r. I th isuati ais ur th 2500-vt tst, atr wig stps 1,

2 a 3, w biv thr is a iih that th mtr i usti wu

ai i srvic v thugh a attmpt wr ma t rciti it th

basis w-vtag tsts .

Th muti-vtag mth ca as b hpu i trmiig th prsc

xcssiv mistur i th isuati uipmt rat at vtags

uivat t r gratr tha th highst vtag avaiab rm th muti-

vtag Mggr istrumt big us. I thr wrs, v thugh th

highst Mggr istrumt vtag avaiab s t strss th isuati

b its ratig, a tw-vtag tst ca, vrthss, t rva th


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prsc mistur. I th isuati rsistac is frst tst th shrt-

tim raig basis (frst at vtag v a th at a highr pttia),

a wr vau isuati rsistac at th highr dC tst vtag usua

iicats th prsc mistur. Th appi vtags shu prrab b

i th rati 1 t 5. expric has iicat that a chag 25% i th

isuati rsistac vau, with a 1 t 5 rati i tst vtags, is usua u

t th prsc a xcssiv amut mistur.

This mth is t bas a ictric absrpti phma, but it s

rat t th evrsh ect. As with tim-rsistac masurmts, th

muti-vtag mth tstig isuati rsistac has icras vau

wh ma a priic r schu basis.

Figre 22-Time Resistace Test Frms


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STEP-VolTAGE METHod

I this mth, u a muti-vtag Mggr istrumt t app tw

r mr vtags i stps, i 500 vts a th 1000 vts. yu r

a ructi isuati rsistac at th highr vtag. I th rsistac

is wr, its a sig a isuati wass that shws up at th

highr vtag. Fig. 23 shws a xamp i which, ista prgrssivicrasig th vtag, u frst tst at a w vtag (such as 500 vts) a

th, atr ischargig th samp, u tst agai at a highr vtag (such

as 2500 vts). A irc i th tw tsts i trms mghms wi shw

sigs wass at th highr vtag a warig t ivstigat urthr.

As th citis withi th samp trirat, th highr-vtag pt, as

shw i Fig. 23, wi ruc i mghms cmpar t th wr-vtag

, a its upwar sp wi b ss.

Figre 23-Typica crves with the step-vtage test.

Th thr bhi th stp-vtag tchiu is a bit cmpx, but w tr

t p it simp. Mistur a irt i isuati ar usua rva b tsts

at vtags ar bw ths xpct i srvic. Hwvr, cts agig r

mchaica amag i air ca a r isuati ma t b rva at

such w strss.


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nw, wh th vtag is icras i stps t pruc ctrica strsss

which apprach r xc ths cutr i srvic, th ca wa

spts iuc th vra isuati rsistac mr a mr. Th

rsistac such ca auts gra crass rapi as th ctrica

strss i thm icrass b a crtai imit. Th pt cscutiv

Mggr istrumt raigs car shws th sharp rp wh this ccurs

(s Fig. 24).

Figre 24-Test crves by the step-vtage meth, cmparig rests with g a ba isati.

Crve 1 (wer pt) shws efite rp i resistace with icreasig vtage, iicatig a prbem.

Crve 2 (pper pt) shws citis i the same mtr wiig ater ceaig, baig a

impregatig perati.


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yu t p th tst vtag cstat btw stps r abut

60 scs. This shrt pri wi t act th tr i rsistac chag.

Th tim pri, hwvr, shu awas b th sam r a giv pic

uipmt. A th absrpti currt ma t hav isappar i this

tim, but ur rsistac masurmts wi b ma th sam basis a

thrr wi b maigu. yur rsuts ar ipt th isuati

matria a its tmpratur bcaus ur ig at th chag i

rsistac t th absut rsistac vaus.

As is tru with th spt-raig a tim-rsistac masurmts, th

stp-vtag mth is mr vauab t u wh rpat a priic,

schu basis.

Th stp-vtag mth is particuar usu i trmiig th prsc

xcssiv mistur r thr ctamiats i th isuati uipmt

that is rat at vtags uivat t r gratr tha th highst vtag

avaiab i ur muti-vtag Mggr istrumt. I thr wrs, v

thugh ur highst vtag s t strss th isuati b its ratig,

a tw-vtag tst ca, vrthss, t rva th prsc such

ctamiats.

Fr xamp, assum that u frst tst isuati rsistac a shrt-tim

raig basis at a vtag 500 VdC, a th at a highr pttia ,

sa, 2500 VdC. ev thugh th attr vtag ma b mia i rati tth vtag ratig ur uipmt, a wr vau isuati rsistac

at th highr tst vtag usua iicats th prsc ctamiat

racturs r thr aag paths thrugh th isuati t gru.

Th appi vtags shu prrab b i th rati 1 t 5 r gratr

(500 a 2500, r xamp). Rsuts t at shw that a chag 25%

i th isuati rsistac vau, with a 1 t 5 rati i tst vtags, is

usua u t th prsc a xcssiv amut mistur r thr

ctamiat.

uSE oF A GuARd TERMInAl

A Mggr isuati tstrs havig rags 1000 mghms a highr

ar uipp with Guar trmias. Th purps this trmia is t

prvi aciitis r maig a thr-trmia twr masurmt, s that

th rsistac tw pssib paths ca b trmi irct. It

has th urthr r scar purps prviig a surc dC vtag

g rguati a imit currt capacit.


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Th isuati a ctrica apparatus has tw cuctig r aag

paths thrugh th isuatig matria a th thr vr its suracs.

B prviig a thir tst trmia i th path th surac aag, it is

sparat it tw parts, rmig a thr-trmia twr as shw i

Fig. 25a. I practic, this thir trmia ma b prvi as shw i

Figurs 26 t 38.

Figre 25a

Figre 25b

Figre 26-Shwig hw t se the Gar termia t eimiate the eects srace eaage acrss

expse isati at e e a cabe. See as Figres 28, 30 a 31.


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Thr ar as cass, such as u i tw wiig trasrmrs r muti-

cuctr cabs, whr a thr-trmia twr is rm as shw i

Fig. 25b. Figurs 30 a 33 a thrs shw practica appicatis this

rm thr-trmia twr.

I maig a thr-trmia tst ivvig masurmt, th li

trmia th Mggr istrumt is cct t Trmia 1, Fig. 25a, thGuar trmia t Trmia 3, a th earth trmia t Trmia 2. This wi

giv th tru vau r12

, prvi r23

a r13

ar t t w i vau. Th

g r23

, which is cct acrss th Mggr istrumt gratr, shu

b abut 1 mghm r highr t prvt xcssiv a th gratr,

a maitai satisactr gratr vtag.

I usig th Guar trmia, particuar i th cas mtr-riv r

rctifr-prat Mggr istrumts, as ma crtai that thr is chac a arc-vr btw th guar trmia th samp a

gru. Such a arc-vr ma caus usirab arcig at th cmmutatr

th istrumt gratr.

Th g r13

, which shuts th Mggr ctig ci, shu b at ast 100

mghms r a masurig accurac apprximat 1%. Th 1% accurac

fgur is bas th R' baast rsistr big 1 mghm, which is tpica.

Fr mr prcis trmiatis accurac, btai th xact vau R' b

writig t Mggr a givig th sria umbr th istrumt i us.

Figre 27-Shwig hw t se the Gar cecti t eimiate the eects srace eaage

acrss expse isati at bth es a cabe whe a spare cctr i the cabe is avaiabe r

cmpetig the Gar cecti.


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Figre 28-Shwig se the Gar cecti t eimiate the eect eaage t gr, as i

Figre 26, a as the eect eaage t ajacet cctrs. nte that the Gar wire is wrappe

ar the expse isati a as is cecte t the ajacet cctrs.

d t cse this iagram with Figre 26, where the Gar wire ges y t the expse

isati, a the ajacet cctrs are gre.

Figre 29-T eimiate the eect srace eaage i measrig the tre resistace a isatig

member, sch as a it r i a circit breaer.


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Figre 31-Cectis r testig isati resistace betwee e wire a a ther wires

cecte, witht beig aecte by eaage t gr.

Figre 32-Shwig se sprig car as a Gar cecti t eimiate the eects srace

eaage. The evice er test mst be iscecte rm a ther eipmet.


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Figre 33-Cectis r testig isati resistace a trasrmer high vtage wiig a

bshigs, a the high tesi iscect switch i parae with reerece t gr bt witht

beig aecte by eaage betwee the high a w vtage wiigs thrgh se the Gar

cecti.

Figre 34-Cectis r testig isati resistace betwee high a w vtage wiigs

witht beig aecte by eaage t gr.


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ouTdooR oIl CIRCuIT BREAkERS

Th ur iustratis (Fig. 35 thrugh 38) shw th usua mths tstig

bushigs a assciat parts a utr i circuit brar, a th

accmpaig tab iicats th tst prcur b stps.

I th tst vaus ar bw 10,000 mghms i a th ur stps, th

ta shu b wr r rai s that th xcssiv sss ca b

isat b urthr tsts a ivstigatis. I th tst vaus ar bw

50,000 mghms i tst #1, th tr th citi th particuar

bushig ivv shu b watch b maig mr rut tsts.

Tst BrarPsiti

Bushigergiz

BushigGuar

BushigGru

PartMasur

1

2

3

4

p

p

p

cs

1 (2 tguar)

1

1 & 2

1 & 2

1

1

1 & 2

1 & 2

2

Bushig 1

Bushig 1 i parawith crss mmbr

Bushig 1 & 2 ipara

Bushig 1 & 2 ipara with it r


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Figre 36-Step 2

Figre 35-Step 1


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Figre 37-Step 3

Figre 38-Step 4


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SETTInG uP A MAInTEnAnCE PRoGRAM

T start isuati tstig thr is gra ru: Put frst thigs frst.

That is, rviw a th ctrica uipmt a cassi it as t rativ

imprtac. Fr xamp, i that AC mtr ai i partmt A, hw

wu it act vra pat pructi? yur pructi pp ca

crtai hp i this a shu b vita itrst i th ia.

I tim prmits at th start, tst vr pic ctrica uipmt a

ma ut a rcr car. Pssib at frst u wi hav t cmbi svra

uits but it wi pa i th g ru t hav tst rcrs r ach iiviua

uit. Th, i isuati wasss shw up, ur jb tracig w

th ig part wi b asir.

Shw i Fig. 40 is rm tst rcr car, which is avaiab rm

Mggr. Fwig is th tp irmati, which bcms mr vauabt u as tsts ar rpat at itrvas:

1. nam a cati th uipmt

2. dats a vaus tst rsuts (rcr actua raig at th tim

tst)

3. Rag, vtag, a sria umbr th Mggr istrumt us

4. Tmpratur th apparatus (as, particuar r arg uits,

wt a r bub tmpraturs r humiit a w-pittrmiatis)

5. Isuati rsistac masurmt crrct r tmpratur

6. A pt cscutiv raigs t shw tr a ab u t

aticipat aiurs

Figre 40


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ASTITCHINTIME

HoW oFTEn SHould You TEST?

That ps up th siz a cmpxit ur pat. ev itica

uits ca ir i th ruir chc pris; xpric is ur bst gui.

I gra, hwvr, wrig apparatus mtrs, gratrs tc. ar mr

i t vp isuati wasss, as cmpar t wirig, isuatrs

a th i. A tst schu r wrig uipmt shu b stabish,varig rm vr 6 t 12 mths, pig th siz uipmt

a svrit th surruig atmsphric citis. Fr wirig a th

i, tsts c a ar ar gra sufcit, uss th pat citis ar

uusua svr.


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MEGGER 5 V & 10 V InSulATIon TESTERS

Whr critica, high-capita uipmt is ivv, th itructi

w a imprv isuatig matrias is r-writig th b

isuati tstig. euipmt with pratig vtags abv 1 V ruirs

cmmsurat highr tst vtags. Mr matrias, wh w r

ar i thir i ccs, ca hav isuati vaus it rags that wrprvius umasur. yur isuati tstr ma t b u auat

t mt th mas a rigrus a thrugh prgram prvtiv/

prictiv maitac mr uipmt.

T b u i crmac with th mst mr tstig ruirmts,

Mggr rs a ami th highst uait isuati tstrs at vtags

abv 1 V. At th cr high-vtag tstig...5 V...th MIT510 a

MIT520 ar th highst v uait tstig ag with prim sat,

cvic a prtabiit. MIT510 rs sctab tst vtags at

250, 500, 1000, 2500, a 5000 V, thrb maig th tstr suitab r

appicatis thrwis prrm with a staar hah m, i

aiti t th mr maig high-vtag appicatis. Th MIT520

icrass th uctiait b prmittig tst vtag t b st i a

10 V icrmt rm 50 V t 1 V, th i 25 V stps a th wa t 5 V.

Th tstrs masur t 15 Tra-hms, thrb maig thm u suitab

r critica istaati tsts a stabishmt riab bas ata r w

high-capita uipmt. Tst rsuts ar ispa Mggrs pattctric igita/aag arc, thrb arig th prcisi a assurac

a igita raig cmbi with th t-ta pitr trav rma

rsrv r mchaica mvmts.


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Th w 10 V isuati rsistactstrs rm Mggr ar as sig

spcifca t assist u with th tstig

a maitac high vtag ctrica

uipmt.

A cass ar rugg a as t carr,

big ma tugh pprp a

achivig a igrss prtcti ratig

IP65.

nMais r battr pwr

ndigita/aag bacit ispa

nVariab tst vtag rm 50 V t 10 V

nAutmatic IR, PI, dAR, SV a dd tsts

nMasurs t 15 TW (5 V) a 35 TW (10 V)

Th w 5 V isuati rsistac tstrs rm Mggr ar sigspcifca t assist u with th tstig a maitac high vtagctrica uipmt.

nMais r battr pwr

ndigita/Aag bacit ispa

nSctab tst vtag rm 250 t 5000VnAutmatic IR tst

nMasurs t 15 TW

nCmpt with caibrati crtifcat

Megger MIT1020

Megger MIT510


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MEGGER MIT300 SERIES

Th MIT300 Sris is sig ag Mggrs amiiar pricip ascigaturs with ss basic uait. Fiv ms cmpris th ami, achbuit a basic sig surig th uait a riabiit that ar Mggrstramars. MIT300 is th simpst m, rig cr uctis highstuait but aitia aturs that ma prv ruat i basicappicatis. Fr appicatis whr a 1 V tst must b avi, th MIT300rs a 250 a 500 V tst . Cmbi with ctiuit a vtagwarig, pus a th cvic a sat aturs that istiguish thami, this is th m chic r th simpst appicatis.

I basic ucti is sti thga but a 1 V tst ruir,th MIT310 is th prctft. With th pssibiit wrig at highr vtags,sa prati has burthr hac b thicusi a autvtmtr.

Fr ths wh prr thtraitia mchaicaaag tp istrumt,th MIT310A rs vrthig i th MIT310, but with a mvig ci ispa.Th aag ispa is hac b bac cas a whit bacgru, tgiv high ctrast a imprv visibiit.

Th ami is cmpt b th u-atur MIT320 & MIT330. Thrmr as a ihm rag r masurmts btw th xtrms ctiuit a high vtag. With this atur, masurmts ca b mactiuus rm 0.01 W t 999 MW. A bacit ispa is urthr hacb bacit sctis, t ma bth th stup a rsuts visib i pr ight.Th MIT320 as rs auib aarms bth th ctiuit a mghmrags, ajustab acrss th tir rag.

Fia, th MIT330 rs vrthig scrib i th MIT320, pus strag up t 1000 rsuts, waig thrugh a USB prt via icu stwar,a a ispa iicati rmaiig mmr.

Megger MIT Series


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MEGGER MIT200 SERIES

n basic 1 V isuati a ctiuittstig, with cm a paramut csirati?n t sacrifc! Mggr rs th tpuait i ixpsiv tstrs th mart...th MIT200 Sris. Thugh sig with cmi mi, ths tstrs r ss th uaita riabiit that th am Mggr impis.Furthrmr, thr has b sacrifc sat,which is a srius prbm with ixpsiv tstrsthat hav cut cst at th ris arc ash apratr rrr.

Fur ms ar avaiab, irig i thtst vtags r: MIT200 is a 500 V mr staar appicatis; MIT210 is a 1 V mwhr highr tst vtag is i rr; MIT220 rstw vtags, 250 a 500, r mr ssitivappicatis whr a 1 V tst is t b avi; ru-spctrum appicatis, MIT230 rs a thrvtags, 250, 500 a 1 V.

Megger MIT230


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Megger maes mre tha jst

isati resistace testersMggr as mas high uait istrumts r th wig ctricatstig appicatis:

n earth/Gru Tstig n Battr Tstign Ra Tstig n Watthur Mtr Tstign

oi Tstign

Trasrmr Tstign Circuit Brar Tstig n Cab Faut Tstign Pwr quait Aasis n Pwr Factr Tstign lw Rsistac Tstig n Hi Pt Tstig

Mggr mauacturs ctrica tst a maitac istrumts rctric pwr, prcss mauacturig, buiig wirig, girig

srvics a cmmuicatis.

Visit ur wbsit r ca assistac at www.BiddleMggr.cm.

Handbook - Megger

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