stitch intime- insulation

8/14/2019 Stitch InTime- insulation

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A STITCH IN TIME

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A Stitch i Time...US $9.95GBP 5.95

The C mp eteG i e t E ectricaI s ati Testi g


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A STITCH IN TIME A STITCH IN TIME

A Stitch I TimeThe C mp ete G i e t

E ectrica I s ati Testi gCop right 2006

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WHAT IS Good InSulATIon?

Ever e ectric wire i our p a t whether its i a motor, ge erator, cab e,switch, tra s ormer, etc. is care u covere with some orm o e ectricai su atio . The wire itse is usua copper or a umi um, which is ow tobe a goo co uctor o the e ectric curre t that powers our e uipme t. Thei su atio must be just the opposite rom a co uctor: it shou resist curre ta eep the curre t i its path a o g the co uctor.

To u ersta i su atio testi g ou rea o t ee to go i to themathematics o e ectricit , but o e simp e e uatio Ohms aw ca be verhe p u i appreciati g ma aspects. Eve i ouve bee expose to this awbe ore, it ma be a goo i ea to review it i the ight o i su atio testi g.

The purpose o i su atio arou a co uctor is much i e that o a pipe

carr i g water, a Ohms aw o e ectricit ca be more easi u erstoo ba compariso with water ow. I Fig. 1 we show this compariso . Pressure owater rom a pump causes ow a o g the pipe (Fig. 1a). I the pipe were tospri g a ea , ou waste water a ose some water pressure.

With e ectricit , vo tage is i e the pump pressure, causi g e ectricit to owa o g the copper wire (Fig. 1b). As i a water pipe, there is some resista ceto ow, but it is much ess a o g the wire tha it is through the i su atio .

Fig re 1C mparis water w (a) with e ectric c rre t (b).

ConTEnTS PAGE

WHAT IS GOOd InSUlATIOn? ........................................................................3

WHAT MAkES InSUlATIOn GO BAd? ................................................................4

HOW InSUlATIOn RESISTAnCE IS MEASUREd .................................................. 5

HOW TO InTERPRET RESISTAnCE REAdInGS .................................................... 6

FACTORS 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................................2 1

EFFECTS OF HUMIdITy ...................................................................................... 23

PREPARATIOn OF APPARATUS TO TEST ........................................................... 2 4

SAFETy PRECAUTIOnS ...................................................................................... 2 6

COnnECTIOnS FOR TESTInG InSUlATIOn RESISTAnCE OFElECTRICAl 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? ....................................................................6 0

MEGGER 5 And 10 kV InSUlATIOn TESTERS ..................................................6 2

MEGGER 1 kV InSUlATIOn TESTERS................................................................6 4


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O ce starte , the i ere t e emies te to ai each other, permitti gexcessive curre t through the i su atio .

Sometimes the rop i i su atio resista ce is su e , as whe e uipme tis oo e . Usua , however, it rops gra ua , givi g p e t o war i g,i chec e perio ica . Such chec s permit p a e reco itio i g be oreservice ai ure. I there are o chec s, a motor with poor i su atio , orexamp e, ma ot o be a gerous to touch whe vo tage is app ie ,but a so be subject to bur out. What was goo i su atio has become apartia co uctor.

HoW InSulATIon RESISTAnCE IS MEASuREd

you have see that goo i su atio has high resista ce; poor i su atio ,re ative ow resista ce. The actua resista ce va ues ca be higher or ower,

epe i g upo such actors as the temperature or moisture co te t o thei su atio (resista ce ecreases i temperature or moisture). With a itt erecor - eepi g a commo se se, however, ou ca get a goo picture othe i su atio co itio rom va ues that are o re ative.

The Megger i su atio tester is a sma , portab e i strume t that gives oua irect rea i g o i su atio resista ce i ohms or megohms. For gooi su atio , the resista ce usua rea s i the megohm ra ge.

The Megger i su atio tester is esse tia a high-ra ge resista ce meter(ohmmeter) with a bui t-i irect-curre t ge erator. This meter is o speciaco structio with both curre t a vo tage coi s, e ab i g true ohms to berea irect , i epe e t o the actua vo tage app ie . This metho is o -

estructive; that is, it oes ot cause eterioratio o the i su atio .

Fig re 2Typica Megger test i str me t h - p t meas re i s ati resista ce.

Commo se se te s us that the more vo tage we have, the more curre tthere be. A so, the ower the resista ce o the wire, the more curre t orthe same vo tage.

Actua , this is Ohms aw, which is expresse this wa i e uatio orm:

E = I x Rwhere, E = vo tage i vo ts

I = curre t i amperes

R = resista ce i ohms

note, however, that o i su atio is per ect (that is, has i f ite resista ce) sosome e ectricit oes ow a o g the i su atio or through it to grou . Sucha curre t ma o be a mi io th o a ampere (o e microampere) but it is

the basis o i su atio testi g e uipme t. note a so that a higher vo tagete s to cause more curre t through the i su atio . This sma amou t ocurre t wou ot, o course, harm goo i su atio but wou be a prob emi the i su atio has eteriorate .

now, to sum up our a swer to the uestio what is goo i su atio ?We have see that, esse tia , goo mea s a re ative high resista ceto curre t. Use to escribe a i su atio materia , goo wou a somea the abi it to eep a high resista ce. So, a suitab e wa omeasuri g resista ce ca te ou how goo the i su atio is. A so, i outa e measureme ts at regu ar perio s, ou ca chec tre s towar its

eterioratio (more o this ater).

WHAT MAkES InSulATIon Go BAd?

Whe our p a t e ectrica s stem a e uipme t are ew, the e ectricai su atio shou be i top otch shape. Furthermore, ma u acturers o wire,cab e, motors, a so o have co ti ua improve their i su atio s orservices i i ustr . neverthe ess, eve to a , i su atio is subject to mae ects which ca cause it to ai mecha ica amage, vibratio , excessiveheat or co , irt, oi , corrosive vapors, moisture rom processes, or just thehumi it o a mugg a .

I various egrees, these e emies o i su atio are at wor as time goeso combi e with the e ectrica stresses that exist. As pi ho es or crac s

eve op, moisture a oreig matter pe etrate the sur aces o thei su atio , provi i g a ow resista ce path or ea age curre t.


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Whether ou test mo th , twice a ear, or o ce a ear epe s upo thet pe, ocatio , a importa ce o the e uipme t. For examp e, a smapump motor or a short co tro cab e ma be vita to a process i our p a t.Experie ce is the best teacher i setti g up the sche u e perio s or oure uipme t.

you shou ma e these perio ic tests i the same wa each time. That is,with the same test co ectio s a with the same test vo tage app ie orthe same e gth o time. A so ou shou ma e tests at about the sametemperature, or correct them to the same temperature. A recor o there ative humi it ear the e uipme t at the time o the test is a so he p ui eva uati g the rea i g a tre . later sectio s cover temperaturecorrectio a humi it e ects.

I summar , here are some ge era observatio s about how ou ca i terpretperio ic i su atio resista ce tests, a what ou shou o with the resu t:

C iti What T d

(a) Fair t high a es n ca se r c cer .a we mai tai e .

(b) Fair t high a es, l cate a reme y the ca se ab t sh wi g a chec the w war tre .c sta t te e cyt war s wer a es.

(c) l w b t we mai tai e . C iti is pr bab y a right, b tca se w a es sh bechec e .

( ) S w as t be sa e. C ea , ry t, r therwise raise thea es be re p aci g e ipme t i

ser ice. (Test wet e ipme t whi eryi g t.)

(e) Fair r high a es, Ma e tests at re e t i ter a s tipre i s y we the ca se w a es is catemai tai e b t sh wi g a reme ie ; r ti the a ess e weri g. ha e bec me stea y at a wer

e e b t sa e r perati ; r tia es bec me s w that it is sa e

t eep the e ipme t i perati .

The ge erator ca be ha -cra e or i e-operate to eve op a highdC vo tage which causes a sma curre t through a over sur aces o thei su atio bei g teste (Fig. 2). This curre t (usua at a app ie vo tageo 500 vo ts or more) is measure b the ohmmeter, which has a i icati gsca e. Fig. 3 shows a t pica sca e, which rea s i creasi g resista ce va ues

rom e t up to i f it , or a resista ce too high to be measure .

Fig re 4Typica rec r i s ati resista ce a mi m t r. C r e A sh ws test a es asmeas re ; C r e B sh ws same a es c rrecte t 20C (see page 22), gi i g a ef ite w wartre t war a sa e c iti . Re erse si e car (at right) is se t rec r the test ata.

Fig re 3Typica sca e the Megger i s ati tester.

HoW To InTERPRET RESISTAnCE REAdInGS

As previous me tio e , i su atio resista ce rea i gs shou be co si erere ative. The ca be uite i ere t or o e motor or machi e teste three

a s i a row, et ot mea ba i su atio . What rea matters is the trei rea i gs over a time perio , showi g esse i g resista ce a war i go comi g prob ems. Perio ic testi g is, there ore, our best approach topreve tive mai te a ce o e ectrica e uipme t, usi g recor car s as showi Fig. 4.


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Fig re 5C r es sh wi g c mp e ts c rre t meas re ri g dC testi g i s ati .

note a so i Fig. 5 that the chargi g curre t isappears re ative rapias the e uipme t u er test becomes charge . larger u its with morecapacita ce wi ta e o ger to be charge . This curre t a so is the storee erg i itia ischarge a ter our test, b short-circuiti g a grou i gthe i su atio . AlWAYS TAkE THIS SAFETY MEASuRE.

you ca see urther rom Fig. 5 that the absorptio curre t ecreases at are ative s ow rate, epe i g upo the exact ature o the i su atio . Thisstore e erg , too, must be re ease at the e o a test, a re uires a

o ger time tha the capacita ce chargi g curre t about our times as o gas the vo tage was app ie .

With goo i su atio , the co uctio or ea age curre t shou bui up to astea va ue that is co sta t or the app ie vo tage, as show i Fig. 5. Ai crease o ea age curre t with time is a war i g o troub e, as iscusse ithe tests escribe i the o owi g sectio .

FACToRS AFFECTInG InSulATIon RESISTAnCE REAdInGS

Remember that the measure resista ce (o the i su atio ) wi beetermi e b the vo tage app ie a the resu ta t curre t (R = E/I).

There are a umber o thi gs that a ect curre t, i c u i g temperatureo the i su atio a humi it , as me tio e i the previous sectio .Right ow, ets just co si er the ature o curre t through i su atioa the e ect o how o g vo tage is app ie .

Curre t through a a o g i su atio is ma e up part o a re ativestea curre t i ea age paths over the i su atio sur ace. E ectricita so ows through the vo ume o the i su atio . Actua , as show iFig. 5, our tota curre t comprises three compo e ts:

1. Capacita ce Chargi g C rre tCurre t that starts out high a rops a ter the i su atio has beecharge to u vo tage (much i e water ow i a gar e hose whe

ou frst tur o the spigot).

2. Abs rpti C rre t A so a i itia high curre t which the rops ( or reaso s iscusseu er the sectio Time-Resista ce Metho ).

3. C cti r lea age C rre t A sma esse tia stea curre t both through a over thei su atio .

As show i Fig. 5, the tota curre t is the sum o the three compo e tsa it is this curre t that ca be measure irect b a microammeter,or i terms o megohms at a particu ar vo tage b mea s o a Meggeri strume t (ohmmeter). Because the tota curre t epe s upo thetime that the vo tage is app ie , ou ca see ow wh Ohms law R = E/Io ho s, theoretica , at a i f ite time (that is, ou have to wait

orever be ore ta i g a rea i g). I practice, as ou wi see i the test metho s escribe be ow, ourea a va ue that is the appare t resista ce a use u va ue to iag osetroub es, which is what ou wa t to o.


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0 A STITCH IN TIME A STITCH IN TIME

I the apparatus ou are testi g has ver sma capacita ce, such as ashort ru o house wiri g, the spot rea i g test is a that is ecessar .However, most e uipme t is capacitive a so our ver frst spot rea i go e uipme t i our p a t, with o prior tests, ca be o a rough gui eas to how goo or ba the i su atio is. For ma ears, mai te a cepro essio a s have use the o e-megohm ru e to estab ish the a owab e

ower imit or i su atio resista ce. The ru e ma be state :

Insulation resistance should be approximately one megohm for each 1,000volts of operating voltage, with a minimum value of one megohm.

For examp e, a motor rate at 2,400 vo ts shou have a mi imum i su atioresista ce o 2.4 megohms. I practice, megohm rea i gs orma areco si erab above this mi imum va ue i ew e uipme t or whe

i su atio is i goo co itio .B ta i g rea i gs perio ica a recor i g them, ou have a better basiso ju gi g the actua i su atio co itio . A persiste t ow war treis usua air war i g o troub e ahea , eve though the rea i gs ma behigher tha the suggeste mi imum sa e va ues. E ua true, as o g as

our perio ic rea i gs are co siste t, the ma be o , eve though owertha the recomme e mi imum va ues. The curves o Fig. 7 show t picabehavior o i su atio resista ce u er var i g p a t operati g co itio s.The curves were p otte rom spot rea i gs ta e with a Megger i strume tover a perio o mo ths.

With a bac grou ow o how time a ects the mea i g o i strume trea i gs, ets co si er three commo test metho s: (1) short-time or spotrea i g; (2) time-resista ce; a (3) step or mu ti-vo tage tests.

TYPES oF InSulATIon RESISTAnCE TESTSSh rt-Time r Sp t-Rea i g Test

I this metho , ou simp co ect the Megger i strume t across thei su atio to be teste a operate it or a short, specifc time perio(60 seco s is usua recomme e ). As show schematica i Fig. 6,

ouve simp pic e a poi t o a curve o i creasi g resista ce va ues;uite o te the va ue wou be ess or 30 seco s, more or 60 seco s.

Bear i mi a so that temperature a humi it , as we as co itio oour i su atio a ect our rea i g.

Fig re 6Typica c r e i s ati resista ce (i meg hms) with time r the sh rt time rsp t-rea i g test meth .


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Time-Resista ce Meth

This metho is air i epe e t o temperature a o te ca giveou co c usive i ormatio without recor s o past tests. It is base o

the absorptio e ect o goo i su atio compare to that o moist orco tami ate i su atio . you simp ta e successive rea i gs at specifc timesa ote the i ere ces i rea i gs (see curves, Fig. 8). Tests b this methoare sometimes re erre to as absorptio tests.

note that goo i su atio shows a co ti ua i crease i resista ce ( esscurre t see curve A) over a perio o time (i the or er o 5 to 10 mi utes).This is cause b the absorptio curre t we spo e o ear ier; goo i su atioshows this charge e ect over a time perio much o ger tha the timere uire to charge the capacita ce o the i su atio .

I the i su atio co tai s much moisture or co tami a ts, the absorptioe ect is mas e b a high ea age curre t which sta s at a air co sta tva ue, eepi g the resista ce rea i g ow (remember: R = E/I).

Fig re 8Typica c r es sh wi g ie ectric abs rpti e ect i a time-resista ce test, ma e capaciti e e ipme t s ch as a arge m t r wi i g.

The time-resista ce test is o va ue a so because it is i epe e t oe uipme t size. The i crease i resista ce or c ea a r i su atio occursi the same ma er whether a motor is arge or sma . you ca , there ore,compare severa motors a estab ish sta ar s or ew o es, regar ess otheir horsepower rati gs.

Fig re 7Typica beha i r i s ati resista ce er a peri m ths er aryi g perati gc iti s, (c r es p tte r m sp t rea i gs with a Megger i str me t).


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die ectric Abs rpti Rati

The ratio o two time-resista ce rea i gs (such as a 60-seco rea i givi e b a 30-seco rea i g) is ca e a ie ectric absorptio ratio. It is

use u i recor i g i ormatio about i su atio . I the ratio is a 10-mi uterea i g ivi e b a 1-mi ute rea i g, the va ue is ca e the po arizatioi ex.

With ha -cra e Megger i strume ts, its a ot easier or ou to ru thetest or o 60 seco s, ta i g our frst rea i g at 30 seco s. I ou have a

i e-operate Megger i strume t, ou get best resu ts b ru i g the test10 mi utes, ta i g rea i gs at 1- a at 10-mi utes, to get the po arizatioi ex. Tab e I gives va ues o the ratios a correspo i g re ativeco itio s o the i su atio that the i icate.

Fig. 9 shows how a 60-seco test wou appear or goo a perhaps bai su atio . Whe the i su atio is i goo shape, the 60-seco rea i g ishigher tha the 30-seco rea i g.

Fig re 9Typica car p t a time-resista ce r b e-rea i g test.

A urther a va tage o this oub e-rea i g test, as it is sometimes ca e ,is that it gives ou a c earer picture, eve whe a spot rea i g sa s thei su atio oo s f e.

For examp e, ets sa the spot rea i g o a s chro ous motor was 10megohms. now, ets assume that the oub e-rea i g chec shows that thei su atio resista ce ho s stea at 10 megohms whi e ou ho vo tage upto 60 seco s. This mea s there ma be irt or moisture i the wi i gs thatbears watchi g. O the other ha , i the poi ter shows a gra ua i creasebetwee the 30-seco a the 60-seco chec s, the oure reaso ab

sure the wi i gs are i goo shape.

Time-resista ce tests o arge rotati g e ectrica machi er especia withhigh operati g vo tage re uire high i su atio resista ce ra ges a a verco sta t test vo tage. A heav - ut Megger test set, i e-operate , servesthis ee . Simi ar , such a i strume t is better a apte or arge cab es,bushi gs, tra s ormers a switchgear.

InSUlATIOnCOndITIOn

60/30-SECOndRATIO

10/1-MInUTE RATIO(POlARIZATIOn IndEX)

da gerous

questio ab e

Goo

Exce e t

1.0 to 1.25

1.4 to 1.6

Above 1.6**

less tha 1

1.0 to 2***

2 to 4

Above 4**

*These va ues must be co si ere te tative a re ativesubject to experie ce with the time-resista ce methoover a perio o time.**I some cases, with motors, va ues approximate 20%higher tha show here i icate a r britt e wi i gwhich wi ai u er shoc co itio s or uri g starts. Forpreve tive mai te a ce, the motor wi i g shou bec ea e ,treate , a rie to restore wi i g exibi it .***These resu ts wou be satis actor or e uipme t withver ow capacita ce such as short ru s o house wiri g.

TABLE ICondition of Insulation Indicated byDielectric Absorption Ratios*


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AC TESTInG vS. dC

Up to ow, weve ta e about testi g with dC vo tage, but ou wi hearo AC testi g a ee to ow the i ere ce. Remember that we spo eo the i s o curre t pro uce i i su atio b dC? (The i itia surge ochargi g curre t, the rop with time to absorptio curre t, a the , a termore time, the stea co uctio curre t.) We saw that i i su atio testi g,the co uctio or ea age curre t is the o e that gives us the i ormatiowe ee .

I co trast, testi g with AC gives a chargi g curre t that is extremearge compare to the other i s; ea age curre t is re ative mi or. ACre ue t is use or high-pote tia testi g; vo tage is i crease to some

specife poi t to see i the i su atio ca sta that particu ar vo tage. Itis a GO/nO-GO t pe o test a ca cause eterioratio o the i su atio , ico trast to the dC test which is basica o - estructive.

I a AC test vo tage has bee use a ou wa t to use dC tests asa a ter ative, ou wi ee to i crease the maximum dC test vo tagesomewhat to obtai e uiva e t resu ts.

I some cases, AC testi g ma be more suitab e or proo testi g oe uipme t (that is, seei g that the e uipme t meets prescribe sta ar s).you ru the vo tage up to the se ecte va ue a the e uipme t eitherpasses or oes t pass the test. With the dC test, ou get a more ua itativepicture; ou ca meter the ea age curre t as ou i crease the vo tage aobtai specifc va ues o i su atio resista ce.

As the size o our e uipme t i creases, there are a so mar e eco omica va tages i dC over AC testi g. As the test vo tage i creases, both thecost a weight o AC e uipme t go up much aster tha with comparab edC test e uipme t. This is because the AC test set must supp the chargi g

curre t which becomes a remai s ver high i the arger machi es. Asexp ai e previous , i dC testi g, this curre t rops rapi a ter the i itiachargi g perio .

TEST volTAGE vS. EquIPMEnT RATInG

Commo use dC test vo tages or routi e mai te a ce are as o ows:

E ipme t AC Rati g dC Test v tage

up to 100 vo ts 100 a 250 vo ts

440 to 550 vo ts 500 a 1,000 vo ts2,400 vo ts 1,000 to 2,500 vo ts

or higher

4,160 vo ts a above 1,000 to 5,000 vo ts,or higher

Test vo tages use or proo testi g o e uipme t are co si erab highertha those use or routi e mai te a ce. A though there are o pub ishei ustr sta ar s or dC maximum proo test vo tages to be use withrotati g e uipme t, the sche u e give be ow is customari use . Forspecifc recomme atio s o our e uipme t, ou shou co su t thema u acturer o the e uipme t.

Pr Test v tages r R tati g E ipme t:

Factor AC Test = 2 x namep ate Rati g + 1000 vo ts

dC Proo Test o I sta atio = 0.8 x Factor AC Test x 1.6

dC Proo Test A ter Service = 0.6 x Factor AC Test x 1.6

Examp e:

Motor with 2,400 VAC amep ate rati gFactor AC Test = 2(2,400) +1,000 = 5,800 VAC

Max. dC Test o I sta atio = 0.8(5,800)1.6 = 7,424 VdC

Max. dC Test A ter Service = 0.6(5,800)1.6 = 5,568 VdC


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There are various wa s to r out e ectrica e uipme t, epe i g upoits size a portabi it . you ca use a b ast o hot air, a ove , circu atioo curre t through co uctors, or a combi atio o tech i ues. loca p a tco itio s a aci ities, together with i ormatio rom the e uipme tma u acturers, ca serve as a gui e to the best metho or our particu are uipme t.

I some cases, or with certai e uipme t, r i g out ma ot be ecessar .you ca chec this b i su atio resista ce tests, i ou have recor s oprevious tests o the apparatus. Whe r i g out is re uire , such recor sare a so he p u to etermi e whe the i su atio is ree o moisture.

noTE: Wet e ipme t is s sceptib e t tage brea w . There re, ysh se a w- tage Megger tester (100 r 250 vdC), at east

i the ear y stages a ryi g- t r . I a w- tage i str me tis t rea i y a ai ab e, s w cra i g a 500- t tester may bes bstit te .

Ma y testers ha e a a iti a test ra ge meas ri g i i hms( W). This meas reme t is typica y ma e at y a ew ts, ais the i ea i itia meas reme t t be ma e e e ipme t.This ra ge meas res be w the Meg hm ra ge, a ca , there re,pr i e a act a meas reme t t se as a be chmar i m it ri gthe ryi g pr cess. I a i hm meas reme t is btai e , i s atihas bee th r gh y sat rate , b t may be rec aimab e. A ter ate ytest a ry, watchi g the rea i gs rise ti they reach the Meg hmra ge, at which time higher tage tests ca be sa e y emp ye .

As a examp e o how importa t past rea i gs are, ets oo at a 100-hpmotor thats bee oo e . A ter a c ea -up, a spot rea i g with the Meggertester shows 1.5 megohms. O ha , ou probab sa this is o . Whats

more, i past recor s showe the i su atio resista ce to ru betwee 1 a2 megohms, ou be sure.

O the other ha , i past recor s showe the orma resista ce va ues toru 10 or 20 megohms, the ou wou ow that water was sti i themotor wi i gs.

I summar , dC test sets are emp o e a most exc usive or high-vo tagemai te a ce a fe testi g or the o owi g reaso s:

1. lower cost2. lighter weight3. Sma er size4. no - estructive5. Better i ormatio , both i ua it a ua tit

uSE oF dC dIElECTRIC TEST SET

The Megger i strume t, rea i g irect i ohms a megohms oi su atio resista ce, is our best bet or routi e i -p a t mai te a ce.However, some p a ts, particu ar with higher vo tage rati gs i e uipme t,use a other Megger pro uct the ie ectric test set. So, ou shou beaware o this i strume t a its use i i su atio resista ce measureme ts.

The ie ectric test set ca be use to etermi e i su atio resista ce b thesame test metho s as out i e or the Megger i strume t; that is, the short-time, time-resista ce a step-vo tage tests. It is esig e or other uses, too,but or i su atio testi g it provi es: (1) a a justab e output vo tage a(2) a mo itori g o the resu ta t curre t i micro-amperes. The Megger dCdie ectric Test Sets are avai ab e with vo tage outputs ra gi g rom 5 V upto 160 V.

The curves o Fig. 5 are p otte as curre t versus time, as are curves ori su atio measureme ts o t pica e uipme t give ear the e o thisma ua . Megger supp ies graph paper which ma es it eas to p ot megohmso i su atio resista ce rom our vo tage a curre t rea i gs.

TESTS duRInG dRYInG ouT oF EquIPMEnT

Wet e ectrica e uipme t is a commo hazar ace b a mai te a cee gi eers. I the e uipme t is wet rom resh water, ou go right ahea

r i g it out. However, i ouve got sa t water, ou must frst wash awa thesa t with resh water. Otherwise, ou eave ver corrosive eposits o sa to meta a i su ati g sur aces as we as i crevices o the i su atio . Withmoisture, such eposits orm a ver goo co uctor o e ectricit . A so, oushou remove oi or grease rom the i su atio , usi g a suitab e so ve t.


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EFFECT oF TEMPERATuRE on InSulATIon RESISTAnCE

The resista ce o i su ati g materia s ecreases mar e with a i crease itemperature. As weve see , however, tests b the time-resista ce a step-vo tage metho s are re ative i epe e t o temperature e ects, givi gre ative va ues.

I ou wa t to ma e re iab e compariso s betwee rea i gs, ou shoucorrect the rea i gs to a base temperature, such as 20C, or ta e a ourrea i gs at approximate the same temperature (usua ot i fcu t to o).We wi cover some ge era gui es to temperature correctio .

O e thumb ru e is:For every 10C increase in temperature,

halve the resistance;

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

For examp e, a two-megohm resista ce at 20C re uces to 1 / 2 megohmat 40C.

Each t pe o i su ati g materia wi have a i ere t egree o resista cecha ge with temperature. Factors have bee eve ope , however, tosimp i the correctio o resista ce va ues. Tab e II gives such actors orrotati g e uipme t, tra s ormers a cab e. you mu tip the rea i gs ouget b the actor correspo i g to the temperature (which ou ee tomeasure).

For examp e, assume ou have a motor with C ass A i su atio a ou get area i g o 2.0 megohms at a temperature (i the wi i gs) o 104F (40C).From Tab e II ou rea across at 104F to the ext co um ( or C ass A) aobtai the actor 4.80. your correcte va ue o resista ce is the :

2.0 megohms x 4.80 = 9.6 megohms(rea i g (correctio (correcteat 104F) actor or rea i g or

C ass A 68F or 20C)i su atioat 104F)

Fig re 10-Typica ryi g c r e where e-mi te rea i gs i s ati resista ce are ta e e eryr h rs.

The t pica r i g-out curve or a dC motor armature (Fig. 10) shows howi su atio resista ce cha ges. duri g the frst part o the ru , the resista ce

actua ecreases because o the higher temperature. The it rises at aco sta t temperature as r i g procee s. Fi a , it rises to a high va ue, asroom temperature (20C) is reache .

note that i ou co uct i su atio resista ce tests uri g r i g, a ouhave rea i gs o previous tests o the r e uipme t, ou ow whe

ouve reache the sa e va ue or the u it. you ma pre er to use a time-resista ce test, ta e perio ica (sa , o ce a shi t), usi g the ie ectricabsorptio ratio or po arizatio i ex to o ow r -out progress ( o ee tocorrect or temperature).


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nomograph o temperature correctio va ues or Megger rea i gs(correcte to 25C). For rotati g machi er with C ass B i su atio .

EFFECTS oF HuMIdITY

We have spo e at various poi ts i this ma ua about the prese ce omoisture i i su atio a its ver mar e e ect upo resista ce va ues. youmight expect, there ore, that i creasi g humi it (moisture co te t) i thesurrou i g (ambie t) air cou a ect i su atio resista ce. A it ca to

var i g egrees.I our e uipme t operates regu ar above the ew-poi t temperature (thetemperature at which the moisture vapor i air co e ses as a i ui ), thetest rea i g orma wi ot be a ecte much b the humi it . Eve i thee uipme t to be teste is i e, the same is true so o g as its temperature is

ept above the ew poi t.

note that the resista ce is a most fve times greater at 68F (20C), ascompare to the rea i g ta e at 104F. The re ere ce temperature orcab e is give as 60F (15.6C), but the importa t poi t is to be co siste ta correct to the same base.

TABlE II-Temperat re C rrecti Fact rs*

TEMP. CABlESROTATInGEqUIP.

C

F C

l A S S A

C l A S S B

O I l - F

I l l E d

T R A n S F O R M E R S

C O d E

n A T U R A l

C O d E

G R - S

P E R F O R M A n C E

n A T U R A l

H E A T R E S I S T

.

n A T U R A l

H E A T R E S I S T

. &

P E R F O R M

. G R - S

O Z O n E R E S I S T

.

n A T U R A l G R - S

V A R n I S H E d

C A M B R I C

I M P R E G n A T E d

P A P E R

05

1015.6

20253035

40455055

60657075

32415060

68778695

104113122131

140149158167

0.210.310.450.71

1.001.482.203.24

4.807.10

10.4515.50

22.8034.0050.0074.00

0.400.500.630.81

1.001.251.582.00

2.503.153.985.00

6.307.90

10.0012.60

0.250.360.500.74

1.001.401.982.80

3.955.607.85

11.20

15.8522.4031.7544.70

0.250.400.611.00

1.472.273.525.45

8.4513.1020.00

0.120.230.461.00

1.833.677.32

14.60

29.2054.00

116.00

0.470.600.761.00

1.241.582.002.55

3.264.155.296.72

8.58

0.420.560.731.00

1.281.682.242.93

3.855.086.728.83

11.6215.4020.3026.60

0.220.370.581.00

1.532.484.036.53

10.7017.1027.8545.00

73.00118.00193.00313.00

0.140.260.491.00

1.753.296.20

11.65

25.0041.4078.00

0.100.200.431.00

1.944.088.62

18.20

38.5081.00

170.00345.00

775.00

0.280.430.641.00

1.432.173.204.77

7.1510.7016.0024.00

36.00

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


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Megger i strume t i use, i which case othi g wou be gai e bseparati g the compo e ts, because the i su atio resista ce o each partwou be sti higher.

For a i itia test, it ma be ecessar to separate the compo e t parts, evethough abor a expe se are i vo ve , a test each o e separate . A soma e a test o a the compo e ts co ecte together. With this i ormatioo recor , it ma ot be ecessar to separate the compo e ts o uturetests u ess u accou tab ow rea i gs are observe .

3. discharge Capacita ce

It is ver importa t that capacita ce be ischarge , both be ore a a tera i su atio resista ce test. It shou be ischarge or a perio about ourtimes as o g as test vo tage was app ie i a previous test.

Megger i strume ts are re ue t e uippe with ischarge c ircuits or thispurpose. I a ischarge u ctio is ot provi e , a ischarge stic shou beuse . leave high capacitive apparatus (i.e., capacitors, arge wi i gs, etc.)short circuite u ti rea to re-e ergize.

4. C rre t lea age at Switches

Whe apparatus is shut ow or the i su atio resista ce test, ma e surethat the rea i gs are ot a ecte b ea age over or through switches or

use b oc s, etc. Such ea age ma mas the true i su atio resista ce o theapparatus u er test. See Use o a G ar Termi a , page 50.

Or, what ma be more serious, curre t rom a e ergize i e ma ea i tothe apparatus a cause i co siste t rea i gs, particu ar i the ive i e isdC. However, such ea age usua ca be etecte b watchi g the poi tero the Megger i strume t at the mome t the test ea s are co ecte tothe apparatus a be ore the i strume t is operate . Be ore ma i g these

observatio s, be sure that a capacita ce is ischarge b short circuiti g orgrou i g the apparatus.

CAUTION: Never connect a Megger insulation tester to energizedlines or equipment. Never use the tester or any of its leads oraccessories for any purpose not described in this book.

The aforementioned statement assumes that the insulation surfacesare free of contaminants, such as certain lints and acids or salts,which have the property of absorbing moisture (theyre calledhygroscopic or deliquescent materials by chemists). Theirpresence could unpredictably affect your readings; they should beremoved before tests are made.

I e ectrica e uipme t were co cer e primari with the co itio s othe expose sur aces where moisture co e ses a a ects the overaresista ce o the i su atio . Stu ies show, however, that ew wi orm i thecrac s a crevices o i su atio be ore it is visib evi e t o the sur ace.dew-poi t measureme ts wi give ou a c ue as to whether such i visib eco itio s might exist, a teri g the test resu ts.

As a part o our mai te a ce recor s, there ore, its a goo i ea to ma eote at east o whether the surrou i g air was r or humi whe thetest was ma e. A so, whether the temperature was above or be ow theambie t. Whe ou test vita e uipme t, recor the ambie t wet a rbu b temperatures, rom which ew-poi t a perce t re ative or abso utehumi it ca be obtai e .

PREPARATIon oF APPARATuS To TEST1. Ta e o t Ser ice

Shut ow the apparatus. Ope switches. de-e ergize. disco ect romother e uipme t a circuits, i c u i g eutra a protective (wor me stemporar ) grou co ectio s. See Sa ety Preca ti s , page 26.

2. Ma e S re J st What is I c e i the Test

I spect the i sta atio ver care u to etermi e just what e uipme tis co ecte a wi be i c u e i the test, especia i it is i fcu t or

expe sive to isco ect associate apparatus a circuits. Pa particu aratte tio to co uctors that ea awa rom the i sta atio . This is verimporta t, because the more e uipme t that is i c u e i a test, the owerthe rea i g wi be, a the true i su atio resista ce o the apparatus i

uestio ma be mas e b that o the associate e uipme t.

It is a wa s possib e, o course, that the i su atio resista ce o the comp etei sta atio (without isco ecti g ever thi g) wi be satis actori high,especia or a spot chec . Or, it ma be higher tha the ra ge o the


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Slight sparking may be encountered:

(1) Whe attachi g the test ea s to e uipme t i which the capacita cehas ot bee comp ete ischarge

(2) duri g a test, arci g through or over au t i su atio

(3) Fo owi g a test whe capacita ce is ischarge

CAUTION:

Do not use the instrumentin an explosive atmosphere.

S ggesti s:

For (1) a (3): Arra ge perma e t i sta e grou i g aci ities atest ea s to a poi t where i strume t co ectio s ca be ma e i a sa eatmosphere.

For (2): Use ow-vo tage testi g i strume ts, or a series resista ce.

For (3): do ot isco ect the test ea s or at east 30 to 60 seco so owi g a test, a owi g time or capacita ce ischarge.

ConnECTIonS FoR TESTInG InSulATIon RESISTAnCEoF ElECTRICAl EquIPMEnT

The o owi g iagrams show how to co ect a Megger i su atio tester tovarious t pes o e ectrica e uipme t. The iagrams a so show i pri cip ehow e uipme t must be isco ecte rom other circuits be ore thei strume t is co ecte .

These i ustratio s are t pica a wi serve as gui es or testi g i su atio

resista ce o practica a t pes o apparatus a co uctors.Be ore procee i g with tests, rea the artic e o Preparati Apparat s

r Test , page 24.

REMEMBER!The Megger i s ati resista ce tester meas reswhate er resista ce is c ecte betwee its termi a s. This mayi c e series r para e ea age paths thr gh i s ati r erits s r ace.

SAFETY PRECAuTIonS

Observe a ru es or sa et whe ta i g e uipme t out o service. B oc outisco ect switches. Test or oreig or i uce vo tages. App wor me s

grou s.

Remember that whe wor i g arou high vo tage e uipme t there isa wa s a possibi it o vo tages bei g i uce i apparatus u er testor i es to which it is co ecte , because o proximit to e ergize highvo tage e uipme t. There ore, rather tha removi g a wor me s grou ior er to ma e a test, it is more a visab e to isco ect the apparatus, suchas a tra s ormer or circuit brea er, rom the expose bus or i e, eavi g the

atter grou e . Use rubber g oves whe co ecti g the test ea s to theapparatus a whi e operati g the Megger i strume t.

Apparatus Under Test Must Not Be Live!

See page 24 o Preparati Apparat s r Test.

I eutra or other grou co ectio s have to be isco ecte , ma e surethe are ot carr i g curre t at the time, a that whe isco ecte oother e uipme t wi ac ecessar protectio .

Pa particu ar atte tio to co uctors that ea awa rom the circuit bei gteste a ma e sure the have bee proper isco ecte rom a sourceo vo tage.

Sh c Hazar r m Test v tage

Observe the vo tage rati g o the Megger i strume t a regar it withappropriate cautio . large e ectrica e uipme t a cab es usua havesu fcie t capacita ce to store up a a gerous amou t o e erg rom the

test curre t. Ma e sure this capacita ce is ischarge a ter the test abe ore ha i g the test ea s. See a so discharge Capacita ce , page 25.

Exp si a Fire Hazar

So ar as is ow , there is o fre hazar i the orma use o a Meggeri su atio tester. There is, however, a hazar whe testi g e uipme t

ocate i i ammab e or exp osive atmospheres.


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17/35


I6. P wer Cab es

Co ectio s or testi g the i su atio resista ce o a power cab e. Whetesti g cab e, it is usua best to isco ect at both e s i or er to testthe cab e b itse , a to avoi error ue to ea age across or throughswitchboar s or pa e boar s. See a so use G ar Termi a , page 50.

Fig re 17

Fig re 18

Co ectio s at the mai power boar , rom which poi t the e tires stem ca be teste to grou at o e time, provi i g a switches i the

istributio pa e are c ose .

4. App ia ces, Meters, I str me ts & Misce a e s E ectrica Apparat s

Fig re 15

Co ectio s or testi g a app ia ce. The test is ma e betwee theco uctor (the heati g u it, motor, etc.) a expose meta parts. Theapparatus must be isco ecte rom a source o power a p ace osome i su ati g materia .

5. C tr , Sig a i g & C mm icati Cab es

Fig re 16

Co ectio s or testi g i su atio resista ce o o e wire i a mu ti-co uctor cab e agai st a other wires a sheath co ecte together.


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AddITIonAl noTES ABouT uSInG A MEGGER InSulATIon TESTERTesti g lea s

I erior or e ective testi g ea s wi cause erro eous a mis ea i g resu tso i su atio resista ce tests. Ta e care i this respect.

u i s ate lea s

To avoi error ue to the i su atio o ea s, p ace the Megger i strume tc ose to the u grou e termi a or co uctor o the apparatus u er testa co ect a short piece o ight bare wire irect rom the li e termi ao the i strume t to the apparatus. I the Guar termi a is use , it ma betreate simi ar . no. 18 or 20 gauge, so i wire wi su fce. Support the eao b its co ectio s to the i strume t a the apparatus.

With this metho o co ecti g rom the li e termi a , the ua it o thei su atio , i a , o the Earth or Grou ea becomes u importa t.

I s ate lea s

Where epe e ce is p ace o the i su atio o ea s, the must beurab e a o the best ua it i su ati g materia . Oi resista t, s thetic,

rubber-i su ate , si g e-co uctor no. 14 stra e wire is recomme e .The outer jac et shou be smooth, with o outer brai . lugs shou beftte or attachi g to the i strume t termi a s, a stout spri g c ips arerecomme e or co ecti g to the apparatus or circuit u er test. Aco ve ie t e gth o ea ma be use . Joi ts are to be avoi e .

A ter co ecti g the ea s to the i strume t, a just be ore co ecti gthem to the apparatus, ma e sure there is o ea rom ea to ea . do thisb operati g the i strume t, which shou rea I f it . do ot correct s ight

ea ea age b attempti g to reset the I f it A juster o a high-ra gei strume t. The touch the test e s o the ea s together to ma e sure

the are ot isco ecte or bro e .

Curre t testi g with the high-ra ge (50,000 megohms) Megger i su atiotesters re uires that the li e test ea be mai tai e at a high va ue so thatit wi ot e ter i to the measureme t. The shie e test ea , with the shieco ecte to Guar , preve ts a ea ages over its termi atio s or throughthe ea i su ati g materia , rom bei g measure .

7. P wer Tra s rmers

Fig re 19

Co ectio s or testi g i su atio resista ce o a tra s ormer high vo tagewi i g a bushi gs, a the high te sio isco ect switch, i para e ,with re ere ce to the ow vo tage wi i g a grou . note that the owvo tage wi i g is grou e or this test.

8. AC Ge erat rs

Fig re 20

With this co ectio , the i su atio resista ce wi be that o the ge eratorstator wi i g a co ecti g cab e combi e . To test either the statorwi i g or the cab e itse , the cab e must be isco ecte at the machi e.


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Sh rt-Time Rea i gs

For short-time rea i gs o i su atio resista ce, operate the i strume t ora ef ite e gth o time, either 30 seco s or 1 mi ute, a rea at the eo that time. Co ti ue c ra i g stea i at s ip spee u ti the rea i g hasbee ta e . Ma e uture tests with the same e gth o operati g time.

Time-Resista ce Meth

Whe usi g a ha -cra e i strume t, operate co ti uous or 1 mi ute.Ta e a rea i g at the e o the frst 30 seco s a a other rea i g at thee o the mi ute.

Whe usi g a motor- rive or rectifer-operate i strume t, the timei terva s are usua 1 mi ute a 10 mi utes rom the time the testi gvo tage is app ie . Or, time-resista ce curves ma be ta e over a perio o10 to 30 mi utes or o ger.

v tage Sca es

Some i su atio testers ma be supp ie with a vo tage sca e to chec orthe abse ce o vo tage be ore i su atio testi g. As exp ai e i the Sa etyPreca ti s sectio , however, i su atio testers shou ever be co ecteto e ergize i es or e uipme t whe operate i a o the I su atio Testor Resista ce Test mo es.

I str cti s r use

The u tagge e o the shie e ea is to be co ecte to the li e aGuar termi a s o the Megger i strume t the e termi a to li e athe si e (shie ) termi a to Guar . The c ip o the li e ea is co ecte tothe apparatus u er test i the regu ar wa . The outboar Guar termi ama be co ecte to that part o the apparatus u er test which the userwishes to guar . The co uctor emp o e i ma i g this co ectio must bei su ate or the vo tage rati g o the Megger i strume t use .

E ect Capacita ce

Capacita ce i apparatus u er test must be charge up to the rate dCvo tage o the Megger i su atio tester, a mai tai e or 30 to 60 seco sbe ore a f a rea i g is ta e . Ma e sure that capacita ce is ischarge ,

b short circuiti g a grou i g the apparatus be ore co ecti g the testea s. See discharge Capacita ce , page 25.

noTE: Capacita ce ca ses the p i ter t swi g t war s zer whi e thei str me t is bei g br ght p t spee , a t swi g sca e beyi f ity whe the ge erat r is s wi g w . This is simp y the charge

wi g i t a t the capacita ce a thr gh the e ecti g c i the hmmeter.

Capacita ce e ects are most oticeab e i arge ge erators, i power acommu icatio cab e more tha a ew hu re eet i e gth, a icapacitors. I ge era , these e ects are sma with capacita ce o ess tha0.01 F. It becomes more oticeab e as capacita ce a /or the se sitivito the i strume t i creases. The heav - ut series o Megger i su atiotesters ca be use o arge capacitors with goo resu ts, particu ar wheoperate rom the power i e rather tha the ha cra .

operati g Time

A ver importa t co si eratio i ma i g i su atio resista ce tests is thetime re uire or the rea i g o i su atio resista ce to reach a maximum.The time re uire to charge the geometric capacita ce is ver short usua

o more tha a ew seco s a that which causes urther e a ireachi g u charge is a ie ectric absorptio e ect. It ma be a matter omi utes or eve hours or this e ectrifcatio time to be comp ete , a orthe poi ter to reach a abso ute maximum.


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There ore, it is stro g recomme e that recor s o perio ic tests be ept,because persiste t ow war tre s i i su atio resista ce usua give airwar i g o impe i g troub e, eve though the actua va ues ma be highertha the suggeste mi imum sa e va ues.

Co verse , a owa ces must be ma e or e uipme t i service showi gperio ic test va ues ower tha the suggeste mi imum sa e va ues, so

o g as the va ues remai stab e or co siste t. I such cases, a ter ueco si eratio has bee give to temperature a humi it co itio s at thetime o test, there ma be o ee or co cer . This co itio ma be causeb u i orm istribute ea ages o a harm ess ature, a ma ot be theresu t o a a gerous oca ize wea ess.

Here agai , recor s o i su atio resista ce tests over a perio o time revea

cha ges which ma justi i vestigatio . The tre o the curve ma be moresig ifca t tha the umerica va ues themse ves.

The o e-Meg hm R e

For ma ears o e megohm has bee wi e use as a air a owab e owerimit or i su atio resista ce o or i ar i ustria e ectrica e uipme t

rate up to 1000 vo ts, a is sti recomme e or those who ma ot betoo ami iar with i su atio resista ce testi g practices, or who ma ot wishto approach the prob em rom a more tech ica poi t o view.

For e uipme t rate above 1000 vo ts the o e megohm ru e is usuastate as a mi imum o o e megohm per thousa vo ts. A though thisru e is somewhat arbitrar , a ma be criticize as ac i g a e gi eeri g

ou atio , it has stoo the test o a goo ma ears o practicaexperie ce. It gives some assura ce that e uipme t is ot too wet or irta has save ma a u ecessar brea ow .

More rece t stu ies o the prob em, however, have resu te i ormu asor mi imum va ues o i su atio resista ce that are base o the i oi su ati g materia use a the e ectrica a ph sica ime sio s o thet pes o e uipme t u er co si eratio .

InTERPRETATIon-MInIMuM vAluES

I su atio resista ce o e ectrica e uipme t is a ecte b ma variab essuch as the e uipme t esig ; the t pe o i su ati g materia use , i c u i gbi ers a impreg ati g compou s; the thic ess o the i su atio aits area; c ea i ess, moisture a temperature. For i su atio resista cerea i gs to be a co c usive measure o the co itio o the e uipme tbei g teste , these variab es must be ta e i to co si eratio .

A ter the e uipme t has bee put i to service, actors such as the esig othe e uipme t, the i o i su ati g materia use , a its thic ess aarea cease to be variab es, a owi g mi imum i su atio resista ce va uesto be estab ishe withi reaso ab e to era ces. The variab es that must beco si ere a ter the e uipme t ha bee put i to service, a at the time

that the i su atio resista ce measureme ts are bei g ma e, are c ea i ess,moisture, temperature a mecha ica amage (such as ractures).

G H se eepi g

The most importa t re uireme ts i the re iab e operatio o e ectricae uipme t are c ea i ess, a the e imi atio o moisture pe etratioi to the i su atio . This ma be co si ere as goo house eepi g, ais esse tia i the mai te a ce o a t pes o e ectrica e uipme t. Thever act that i su atio resista ce is a ecte b moisture a irt, with

ue a owa ces or temperature, ma es the Megger i su atio tester theva uab e too that it is i e ectrica mai te a ce. It is at o ce a gauge oc ea i ess a goo house eepi g as we as a etector o eterioratioa impe i g troub e.

What Rea i gs t Expect Peri ic Tests

Severa criteria or mi imum va ues o i su atio resista ce have beeeve ope a are summarize here. The shou serve as a gui e or

e uipme t i service. However, perio ic tests o e uipme t i service wiusua revea rea i gs co si erab higher tha the suggeste mi imumsa e va ues.


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A compo e ts which are superfcia c ea a r a have va ues esstha 10,000 megohms are usua eteriorate i ter a , b the prese ce omoisture or carbo ize paths, to such a exte t that the are ot re iab e

or goo service u ess reco itio e . This is particu ar so whe operati gu er surge co itio s such as uri g ight i g isturba ces. I the case othe strippe bushi g itse , the ower stem a upper weather shie mustbe either per ect c ea or guar e be ore it is co em e as u re iab ebecause o a i su atio resista ce va ue ess tha 10,000 megohms.

What has bee sai or strippe oi circuit brea er bushi gs a so app iesto bushi gs or other e uipme t, such as tra s ormers. Si ce bushi gsa other associate members have ver high i su atio resista ce va ues

orma , a Megger i su atio tester havi g a ra ge o at east 10,000megohms is ecessar to test such e uipme t. Megger i strume ts havi g

ra ges up to 50,000 megohms wi permit observatio o eteriorati gtre s i bushi gs be ore the reach the uestio ab e va ue o 10,000megohms.

Cab e a C ct rs

Cab e a co uctor i sta atio s prese t a wi e variatio o co itio srom the poi t o view o the resista ce o the i su atio . These co itio s

resu t rom the ma i s o i su ati g materia s use , the vo tagerati g or i su atio thic ess, a the e gth o the circuit i vo ve i themeasureme t. Furthermore, such circuits usua exte over great ista ces,a ma be subjecte to wi e variatio s i temperature, which wi have ae ect o the i su atio resista ce va ues obtai e . The termi a s o cab esa co uctors wi a so have a e ect o the test va ues u ess the arec ea a r , or guar e .

The I su ate Cab e E gi eers Associatio (ICEA) gives mi imum va ueso i su atio resista ce i its specifcatio s or various t pes o cab es aco uctors. These mi imum va ues are or ew, si g e-co uctor wire acab e a ter bei g subjecte to a AC high vo tage test a base o a dCtest pote tia o 500 vo ts app ie or o e mi ute at a temperatureo 60F.

MInIMuM vAluES FoR InSulATIon RESISTAnCER tati g Machi ery

The IEEE gui e, Recomme e Practices or Testi g I su atio Resista ce oRotati g Machi er , ea s with the prob em o ma i g a i terpreti gi su atio resista ce measureme ts or rotati g machi er . It reviews the

actors which a ect or cha ge i su atio resista ce characteristics, out i esa recomme s u i orm metho s or ma i g tests, a prese ts ormu as

or the ca cu atio o approximate mi imum i su atio resista ce va ues orvarious t pes o AC a dC rotati g machi er . The gui e states:

The recomme e mi imum i su atio resista ce R m or a ter ati g-curre ta irect-curre t machi e armature wi i gs a or fe wi i gs oa ter ati g-curre t a irect-curre t machi es ca be etermi e b :

Rm = V + 1where:

Rm = recomme e mi imum i su atio resista ce i megohmsat 40C o the e tire machi e wi i g

V = rate machi e termi a to termi a pote tia , i i ovo ts

I app icatio s where the machi e is vita , it has bee co si ere goopractice to i itiate reco itio i g shou the i su atio resista ce, havi gbee we above the mi imum va ue give b E 2, rop appreciab to earthat eve .

It is rec mme e that th se wh perate a mai tai r tati g machi erybtai c pies the IEEE p b icati , Rec mme e Practices r Testi g

I s ati Resista ce R tati g Machi ery, which ca be btai e bywriti g the IEEE at 345 East 47th St., new Y r , nY, 10017.

B shi gsI the case o out oor oi circuit brea er bushi gs, experie ce has showthat a bushi g, with its assemb e associate i su ati g members,shou , or re iab e operatio , have a i su atio resista ce va ue above10,000 megohms at 20C. This assumes that the oi withi the ta is igoo co itio , that the brea er is separate rom its exter a co ectio sto other e uipme t, a that the porce ai weather shie is guar e .This mea s that each compo e t such as the strippe bushi g itse ,cross-member, i t ro , ower arci g shie , etc., shou have a i su atioresista ce i excess o that va ue.


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The i su atio resista ce o o e co uctor o a mu tico uctor cab e to aothers a sheath is:

R = k og10 d /

where:

d = iameter over i su atio o e uiva e t si g e-co uctor cab e= + 2c + 2b

= iameter o co uctor ( or sector cab es e ua s iametero rou co uctor o same cross-sectio )

c = thic ess o co uctor i su atio

b = thic ess o jac et i su atio

(a ime si s m st be expresse i same its)

Tra s rmers

Acceptab e i su atio resista ce va ues or r a compou -f etra s ormers shou be comparab e to those or C ass A rotati g machi er ,a though o sta ar mi imum va ues are avai ab e.

Oi -f e tra s ormers or vo tage regu ators prese t a specia prob em i thatthe co itio o the oi has a mar e i ue ce o the i su atio resista ceo the wi i gs.

I the abse ce o more re iab e ata the o owi g ormu a is suggeste :

R = CE VA

R = mi imum 1-mi ute 500-vo t dC i su atio resista ce i megohmsrom wi i g to grou , with other wi i g or wi i gs guar e ,

or rom wi i g to wi i g with core guar e

C = a co sta t or 20C measureme ts

E = vo tage rati g o wi i g u er test

VA = rate capacit o wi i g u er test

For tests o wi i g to grou with the other wi i g or wi i gsgrou e , the va ues wi be much ess tha that give b the ormu a.R i this ormu a is base o r , aci - ree, s u ge- ree oi , a bushi gsa termi a boar s that are i goo co itio .

These sta ar mi imum va ues ( or si g e-co uctor cab e) are base othe o owi g ormu a:

R = k og10 d /

where:

R = megohms per 1000 eet o cab e

k = co sta t or i su ati g materia

d = outsi e iameter o co uctor i su atio

= iameter o co uctor

Mi im m va es k at 60 F.

I su atio T peImpreg ate Paper ................................................................... 2,640Var ishe Cambric .................................................................... 2,460Thermop astic-Po eth e e ........................................ above 50,000Composite Po eth e e ......................................................... 30,000Thermop astic-Po vi :

Po vi Ch ori e 60C ........................................................ 500Po vi Ch ori e 75C ..................................................... 2,000

Gra e natura Rubber S thetic Rubber

Co e ...............................................................................................950

Per orma ce ....................................... 10,560 ............................2,000

Heat Resista t..................................... 10,560 ............................2,000

Ozo e Resista t...................... 10,000 (But ) ............................2,000

kerite ..........................................................................................4,000

See pages 44 a 45 or Tab es o log 10 d /


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va es C at 20C

60-Hertz 25-Hertz

Ta e oi -f e t pe 1.5 1.0U ta e oi -f e t pe 30.0 20.0dr or compou -f e t pe 30.0 20.0

This ormu a is i te e or si g e-phase tra s ormers. I the tra s ormeru er test is o the three-phase t pe, a the three i ivi ua wi i gs arebei g teste as o e, the :

E = vo tage rati g o o e o the si g e-phase wi i gs(phase to phase or e ta co ecte u its a phase to

eutra or star co ecte u its)

VA = rate capacit o the comp ete three-phase wi i g u er testTESTS uSInG MulTI-volTAGE MEGGER InSulATIon TESTERS

Mai te a ce practice tre s i icate the va ue o testi g i su atio withdC vo tages at eve s somewhat higher tha the pea va ue o the rate ACvo tage o the e uipme t bei g teste . Such dC tests have i some casesbee show to revea o - estructive i cipie t wea esses i i su atiowhich cou ot otherwise be ou , except possib b partia ischarge

etectio at o - estructive AC test vo tage eve s.

The tech i ue i vo ves the app icatio o two or more dC vo tages, acritica observi g a re uctio o i su atio resista ce at the highervo tage. A mar e or u usua re uctio i i su atio resista ce or aprescribe i crease i app ie vo tage is a i icatio o i cipie t wea ess.

It is importa t to me tio that the merits o this tech i ue arise rom morerece t i vestigatio s which i icate that rather high dC vo tage ca be use

to etect wea esses without amagi g the i su atio . The maximum va ueo vo tage which shou be use wi epe arge o the c ea i ess ar ess o the i su atio to be teste .

I ma i g tests o i su atio at such dC vo tages, the ohmmeter methohas at east two a va tages. First, prescribe fxe vo tages are switchei to use, a o e i strume t measureme t ma e with the irect rea i gohmmeter. This is a simp e a repro ucib e metho compare to o e iwhich ma choices o vo tage are avai ab e. A other importa t a va tage

o the ohmmeter ca be exp ai e b re erri g to Fig. 21. I this fgure, thecha ge which ma occur i ea age curre t a ter the absorptio curre t has

isappeare is show p otte i terms o i su atio resista ce agai st threei ere t vo tages. note that there is o cha ge i resista ce show i the

fgure betwee 500 a 1000 vo ts, i icati g o cha ge i the i su atioas a resu t o app i g these two vo tages. This is a assumptio , but is aco itio which is ot u commo i practice. I the i su atio co ti ues tobe stab e at 2500 vo ts, there wi be o cha ge i the i su atio resista ceva ue obtai e , which is show b the otte exte sio o the horizo ta

i e i the fgure. Whe o - i ear co itio s appear at a higher vo tage, thevo tage resista ce curve revea s this ver c ear b a ower resista ce va ue,i icate b the ow war curve i the fgure. The fgure, there ore, revea sthe simp icit o etermi i g the cha ge i i su atio stabi it b usi g threefxe vo tages which are easi repro ucib e whe ma i g three-vo tage testso a routi e basis.

Fig re 21

We wish to emphasize that the curve i Fig. 21 i icates the resista cecha ge ue to ea age curre t o , a ot the absorptio curre t whichma appear or a perio o time with each cha ge i vo tage. It ma be

ecessar to wait a appreciab e amou t o time a ter each vo tage cha geor the absorptio curre t to isappear be ore ta i g a rea i g.


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prese ce o moisture. I the i su atio resista ce is frst teste o the short-time rea i g basis (frst at o e vo tage eve a the at a higher pote tia ),a ower va ue o i su atio resista ce at the higher dC test vo tage usuai icates the prese ce o moisture. The app ie vo tages shou pre erab bei the ratio o 1 to 5. Experie ce has i icate that a cha ge o 25% i thei su atio resista ce va ue, with a 1 to 5 ratio i test vo tages, is usua ueto the prese ce o a excessive amou t o moisture.

This metho is ot base o a ie ectric absorptio phe ome a, but it oesre ate to the Evershe E ect. As with time-resista ce measureme ts, themu ti-vo tage metho o testi g i su atio resista ce has i crease va uewhe ma e o a perio ic or sche u e basis.

Fig re 22-Time Resista ce Test F rms

To better u ersta the tech i ue o ma i g i su atio resista ce tests attwo or more vo tages, the o owi g steps are suggeste , usi g a i ustriaor tractio motor c asse i the 300- to 1000-vo t ra ge as a examp e:

1. Ma e a o e-mi ute Megger i strume t test at 500 vo ts to serve as a basiso compariso or subse ue t steps.

2. A ter a care u c ea i g operatio ma e a seco 500-vo t test toetermi e the e ective ess o the c ea i g.

3. I the o e-mi ute i su atio resista ce va ue is sub orma , or i the 60seco /30 seco i su atio resista ce ratio is o greater tha o e at thispoi t the a r i g operatio ma be esirab e be ore usi g a highertest vo tage. However, ma i g a other test at 1000 vo ts a compari gthese rea i gs with those rom the 500-vo t test wi he p i etermi i g

the ee or r i g. I the 1000-vo t test va ue is appreciab ess thathat at 500 vo ts, the a r i g operatio shou be per orme . O theother ha , i the 1000-vo t a 500-vo t test va ues are approximatethe same, it is reaso ab e to assume that the ecisio to per orm a r i goperatio ca be e erre u ti a ter the ext step.

4. Ma e a Megger i strume t test at 2500 vo ts. I there is o appreciab ei ere ce i the 500- a 2500-vo t test va ues, goo evi e ce exists that

the motor i uestio is i re iab e co itio as ar as its i su atio isco cer e . O the other ha , i there is a appreciab e i ere ce i thetwo, there is goo evi e ce that more thorough reco itio i g is ca e

or. I the i su atio ai s u er the 2500-vo t test, a ter o owi g steps 1,2 a 3, we be ieve there is a i e ihoo that the motor i uestio wou

ai i service eve though a attempt were ma e to reco itio it o thebasis o ow-vo tage tests o .

The mu ti-vo tage metho ca a so be he p u i etermi i g the prese ceo excessive moisture i the i su atio o e uipme t rate at vo tagese uiva e t to or greater tha the highest vo tage avai ab e rom the mu ti-vo tage Megger i strume t bei g use . I other wor s, eve though thehighest Megger i strume t vo tage avai ab e oes ot stress the i su atiobe o its rati g, a two-vo tage test ca , everthe ess, o te revea the


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now, whe the vo tage is i crease i steps to pro uce e ectrica stresseswhich approach or excee those e cou tere i service, the oca weaspots i ue ce the overa i su atio resista ce more a more. Theresista ce o such oca au ts ge era ecreases rapi as the e ectricastress i them i creases be o a certai imit. The p ot o co secutiveMegger i strume t rea i gs c ear shows the sharp rop whe this occurs(see Fig. 24).

Fig re 24-Test c r es by the step- tage meth , c mpari g res ts with g a ba i s ati .C r e 1 ( wer p t) sh ws ef ite r p i resista ce with i creasi g tage, i icati g a pr b em.C r e 2 ( pper p t) sh ws c iti s i the same m t r wi i g a ter c ea i g, ba i g aimpreg ati g perati .

STEP-volTAGE METHod

I this metho , ou ee a mu ti-vo tage Megger i strume t to app twoor more vo tages i steps, i e 500 vo ts a the 1000 vo ts. you oo ora re uctio o i su atio resista ce at the higher vo tage. I the resista ceis ower, its a sig o a i su atio wea ess that shows up o at thehigher vo tage. Fig. 23 shows a examp e i which, i stea o progressivei creasi g the vo tage, ou frst test at a ow vo tage (such as 500 vo ts) athe , a ter ischargi g the samp e, ou test agai at a higher vo tage (suchas 2500 vo ts). A i ere ce i the two tests i terms o megohms wi showsig s o wea ess at the higher vo tage a war i g to i vestigate urther.As the co itio s withi the samp e eteriorate, the higher-vo tage p ot, asshow i Fig. 23, wi re uce i megohms compare to the ower-vo tageo e, a its upwar s ope wi be ess.

Fig re 23-Typica c r es with the step- tage test.

The theor behi the step-vo tage tech i ue is a bit comp ex, but we trto eep it simp e. Moisture a irt i i su atio are usua revea e b testsat vo tages ar be ow those expecte i service. However, e ects o agi g ormecha ica amage i air c ea a r i su atio ma ot be revea e atsuch ow stress.


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The i su atio o a e ectrica apparatus has two co ucti g or ea agepaths o e through the i su ati g materia a the other over its sur aces.B provi i g a thir test termi a i the path o the sur ace ea age, it isseparate i to two parts, ormi g a three-termi a etwor as show iFig. 25a. I practice, this thir termi a ma be provi e as show iFigures 26 to 38.

Fig re 25a

Fig re 25b

Fig re 26-Sh wi g h w t se the G ar termi a t e imi ate the e ects s r ace ea age acr ssexp se i s ati at e e a cab e. See a s Fig res 28, 30 a 31.

you o ee to eep the test vo tage co sta t betwee steps or about60 seco s. This short perio wi ot a ect the tre i resista ce cha ge.The time perio , however, shou a wa s be the same or a give pieceo e uipme t. A the absorptio curre t ma ot have isappeare i thistime, but our resista ce measureme ts wi be ma e o the same basis athere ore wi be mea i g u . your resu ts are i epe e t o the i su atiomateria a its temperature because oure oo i g at the cha ge iresista ce ot the abso ute resista ce va ues.

As is true with the spot-rea i g a time-resista ce measureme ts, thestep-vo tage metho is more va uab e to ou whe repeate o a perio ic,sche u e basis.

The step-vo tage metho is particu ar use u i etermi i g the prese ceo excessive moisture or other co tami a ts i the i su atio o e uipme tthat is rate at vo tages e uiva e t to or greater tha the highest vo tageavai ab e i our mu ti-vo tage Megger i strume t. I other wor s, evethough our highest vo tage oes ot stress the i su atio be o its rati g,a two-vo tage test ca , everthe ess, o te revea the prese ce o suchco tami a ts.

For examp e, assume that ou frst test i su atio resista ce o a short-timerea i g basis at a vo tage o 500 V dC, a the at a higher pote tia o ,sa , 2500 VdC. Eve though the atter vo tage ma be omi a i re atio tothe vo tage rati g o our e uipme t, a ower va ue o i su atio resista ceat the higher test vo tage usua i icates the prese ce o co tami ate

ractures or other ea age paths through the i su atio to grou .

The app ie vo tages shou pre erab be i the ratio o 1 to 5 or greater(500 a 2500, or examp e). Resu ts to ate show that a cha ge o 25%i the i su atio resista ce va ue, with a 1 to 5 ratio i test vo tages, isusua ue to the prese ce o a excessive amou t o moisture or otherco tami a t.

uSE oF A GuARd TERMInAl

A Megger i su atio testers havi g ra ges o 1000 megohms a higherare e uippe with Guar termi a s. The purpose o this termi a is toprovi e aci ities or ma i g a three-termi a etwor measureme t, so thatthe resista ce o o e o two possib e paths ca be etermi e irect . Ithas the urther or seco ar purpose o provi i g a source o dC vo tage ogoo regu atio a o imite curre t capacit .


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Fig re 28-Sh wi g se the G ar c ecti t e imi ate the e ect ea age t gr , as iFig re 26, a a s the e ect ea age t a jace t c ct rs. n te that the G ar wire is wrappear the exp se i s ati a a s is c ecte t the a jace t c ct rs.

d t c se this iagram with Fig re 26, where the G ar wire g es y t the exp se

i s ati , a the a jace t c ct rs are gr e .

Fig re 29-T e imi ate the e ect s r ace ea age i meas ri g the tr e resista ce a i s ati gmember, s ch as a i t r i a circ it brea er.

There are a so cases, such as ou i two wi i g tra s ormers or mu ti-co uctor cab es, where a three-termi a etwor is orme as show iFig. 25b. Figures 30 a 33 a others show practica app icatio s o this

orm o three-termi a etwor .

I ma i g a three-termi a test i vo vi g o o e measureme t, the li etermi a o the Megger i strume t is co ecte to Termi a 1, Fig. 25a, theGuar termi a to Termi a 3, a the Earth termi a to Termi a 2. This wigive the true va ue o r 12, provi e r 23 a r 13 are ot too ow i va ue. The

eg r23, which is co ecte across the Megger i strume t ge erator, shoube about 1 megohm or higher to preve t excessive oa o the ge erator,a mai tai satis actor ge erator vo tage.

I usi g the Guar termi a , particu ar i the case o motor- rive or

rectifer-operate Megger i strume ts, a so ma e certai that there is ocha ce o a arc-over betwee the guar e termi a o the samp e agrou . Such a arc-over ma cause u esirab e arci g at the commutator othe i strume t ge erator.

The eg r13, which shu ts the Megger e ecti g coi , shou be at east 100megohms or a measuri g accurac o approximate 1%. The 1% accuracfgure is base o the R' ba ast resistor bei g 1 megohm, which is t pica .For more precise etermi atio s o accurac , obtai the exact va ue o R' bwriti g to Megger a givi g the seria umber o the i strume t i use.

Fig re 27-Sh wi g h w t se the G ar c ecti t e imi ate the e ects s r ace ea ageacr ss exp se i s ati at b th e s a cab e whe a spare c ct r i the cab e is a ai ab e rc mp eti g the G ar c ecti .


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Fig re 31-C ecti s r testi g i s ati resista ce betwee e wire a a ther wiresc ecte , with t bei g a ecte by ea age t gr .

Fig re 32-Sh wi g se spri g c ar as a G ar c ecti t e imi ate the e ects s r aceea age. The e ice er test m st be isc ecte r m a ther e ipme t.

The highest accurac is esire i cases as show i Fig. 25a, or wherethe true resista ce o each eg is wa te as i the case o Fig. 25b, threemeasureme ts are re uire a the o owi g e uatio s are use :

r12 = R12 R13 (R')2

R13 + R'

r23 = R12 R23 (R')2

R12 + R'

r13 = R12 R13 (R')2

R12 + R'

where R 12, R23 a R13 are the actua rea i gs i megohms measure acrossthe termi a s o the etwor which are co ecte to the li e a Earthtermi a s o the Megger i strume t with Termi a s 3, 1 a 2 respectiveco ecte to the i strume t Guar termi a . R' is the va ue o the ba astresista ce i megohms o the i strume t i use. I ma i g these threemeasureme ts, o o co ect the li e termi a o the i strume t to thegrou e termi a o the etwor , as a ea age over the i strume t casebetwee the Earth termi a a grou wi shu t the resista ce bei gmeasure .

BuSHInGS, PoTHEAdS And InSulAToRS

Fig re 30-C ecti s r testi g i s ati resista ce betwee e wire a gr , with t bei ga ecte by ea age t ther wires. n te se G ar c ecti .


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ouTdooR oIl CIRCuIT BREAkERS

The our i ustratio s (Fig. 35 through 38) show the usua metho s o testi gbushi gs a associate parts o a out oor oi circuit brea er, a theaccompa i g tab e i icates the test proce ure b steps.

I the test va ues are be ow 10,000 megohms i a o the our steps, theta shou be owere or rai e so that the excessive osses ca beiso ate b urther tests a i vestigatio s. I the test va ues are be ow50,000 megohms i test #1, the tre o the co itio o the particu arbushi g i vo ve shou be watche b ma i g more re ue t tests.

Test Brea erPositioBushi g

E ergizeBushi gGuar e

Bushi gGrou e

PartMeasure

1

2

3

4

ope

ope

ope

c ose

1 (2 toguar )

1

1 & 2

1 & 2

1

1

1 & 2

1 & 2

2

Bushi g 1

Bushi g 1 i para ewith cross member

Bushi g 1 & 2 ipara e

Bushi g 1 & 2 ipara e with i t ro

Fig re 33-C ecti s r testi g i s ati resista ce a tra s rmer high tage wi i g ab shi gs, a the high te si isc ect switch i para e with re ere ce t gr b t with tbei g a ecte by ea age betwee the high a w tage wi i gs thr gh se the G arc ecti .

Fig re 34-C ecti s r testi g i s ati resista ce betwee high a w tage wi i gswith t bei g a ecte by ea age t gr .


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Fig re 37-Step 3

Fig re 38-Step 4Fig re 36-Step 2

Fig re 35-Step 1


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SETTInG uP A MAInTEnAnCE PRoGRAM

To start i su atio testi g there is o e ge era ru e: Put frst thi gs frst.That is, review a the e ectrica e uipme t a c assi it as to re ativeimporta ce. For examp e, i that AC motor ai e i epartme t A, howwou it a ect overa p a t pro uctio ? your pro uctio peop e cacertai he p i this a shou be vita i tereste i the i ea.

I time permits at the start, test ever piece o e ectrica e uipme t ama e out a recor car . Possib at frst ou wi have to combi e severau its but it wi pa i the o g ru to have test recor s or each i ivi uau it. The , i i su atio wea esses o show up, our job o trac i g owthe o e i g part wi be easier.

Show i Fig. 40 is o e orm o test recor car , which is avai ab e rom

Megger. Fo owi g is the t pe o i ormatio , which becomes more va uab eto ou as tests are repeate at i terva s:

1. name a ocatio o the e uipme t2. dates a va ues o test resu ts (recor actua rea i g at the time

o test)3. Ra ge, vo tage, a seria umber o the Megger i strume t use4. Temperature o the apparatus (a so, particu ar or arge u its,

wet a r bu b temperatures or humi it a ew-poi tetermi atio s)

5. I su atio resista ce measureme t correcte or temperature6. A p ot o co secutive rea i gs to show tre a e ab e ou to

a ticipate ai ures

Fig re 40

HoW oFTEn SHould You TEST?

That epe s upo the size a comp exit o our p a t. Eve i e ticau its ca i er i the re uire chec perio s; experie ce is our best gui e.I ge era , however, wor i g apparatus motors, ge erators etc. are more

i e to eve op i su atio wea esses, as compare to wiri g, i su atorsa the i e. A test sche u e or wor i g e uipme t shou be estab ishe ,var i g rom ever 6 to 12 mo ths, epe i g o the size o e uipme ta severit o the surrou i g atmospheric co itio s. For wiri g a the

i e, tests o ce a ear are ge era su fcie t, u ess the p a t co itio s areu usua severe.


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The ew 10 V i su atio resista cetesters rom Megger are a so esig especifca to assist ou with the testi ga mai te a ce o high vo tage e ectricae uipme t.

A cases are rugge a eas to carr ,bei g ma e o tough po prop e e aachievi g a i gress protectio rati go IP65.

n Mai s or batter poweren digita /a a og bac it isp an Variab e test vo tage rom 50 V to 10 Vn Automatic IR, PI, dAR, SV a dd testsn Measures to 15 T W (5 V) a 35 TW (10 V)

The ew 5 V i su atio resista ce testers rom Megger are esig especifca to assist ou with the testi g a mai te a ce o high vo tagee ectrica e uipme t.

MEGGER 5 v & 10 v InSulATIon TESTERS

Where critica , high-capita e uipme t is i vo ve , the i tro uctioo ew a improve i su ati g materia s is re-writi g the boo oi su atio testi g. E uipme t with operati g vo tages above 1 V re uirescomme surate higher test vo tages. Mo er materia s, whe ew orear i their i e c c es, ca have i su atio va ues i to ra ges that wereprevious u measure . your o i su atio tester ma ot be u a e uateto meet the ema s o a rigorous a thorough program o preve tive/ pre ictive mai te a ce o mo er e uipme t.

To be u i co orma ce with the most mo er testi g re uireme ts,Megger o ers a ami o the highest ua it i su atio testers at vo tagesabove 1 V. At the core o high-vo tage testi g...5 V...the MIT510 aMIT520 a or the highest eve o ua it testi g a o g with prime sa et ,co ve ie ce a portabi it . MIT510 o ers se ectab e test vo tages at250, 500, 1000, 2500, a 5000 V, thereb ma i g the tester suitab e orapp icatio s otherwise per orme with a sta ar ha he mo e , ia itio to the more ema i g high-vo tage app icatio s. The MIT520i creases the u ctio a it b permitti g test vo tage to be set i a10 V i creme t rom 50 V to 1 V, the i 25 V steps a the wa to 5 V.The testers measure to 15 Tera-ohms, thereb ma i g them u suitab e

or critica i sta atio tests a estab ishme t o re iab e base ata or ewhigh-capita e uipme t. Test resu ts are isp a e o Meggers pate tee ectro ic igita /a a og arc, thereb a or i g the precisio a assura ceo a igita rea i g combi e with the te -ta e poi ter trave ormareserve or mecha ica moveme ts.

n Mai s or batter poweren digita /A a og bac it isp an Se ectab e test vo tage rom 250 to 5000Vn Automatic IR testn Measures to 15 T Wn Comp ete with ca ibratio certifcate

Megger MIT1020

Megger MIT510


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MEGGER MIT200 SERIESnee o basic 1 V i su atio a co ti uit testi g,with eco om a paramou t co si eratio ? no eeto sacrifce! Megger o ers the o top ua it i e oi expe sive testers o the mar et...the MIT200 Series.Though esig e with eco om i mi , these testerso er o oss o the ua it a re iabi it that the

ame Megger imp ies. Furthermore, there has beeo sacrifce o sa et , which is a serious prob em with

i expe sive testers that have cut cost at the ris o arcash a operator error.

Four mo e s are avai ab e, i eri g o i the testvo tages o ere : MIT200 is a 500 V mo e or sta arapp icatio s; MIT210 is a 1 V mo e where higher testvo tage is i or er; MIT220 o ers two vo tages, 250a 500, or more se sitive app icatio s where a 1 Vtest is to be avoi e ; or u -spectrum app icatio s,MIT230 o ers a three vo tages, 250, 500 a 1 V.

Megger MIT230

MEGGER MIT300 SERIESThe MIT300 Series is esig e a o g Meggers ami iar pri cip e o asce i g

eatures with o oss o basic ua it . Five mo e s comprise the ami , eachbui t o a basic esig e suri g the ua it a re iabi it that are Meggerstra emar s. MIT300 is the simp est mo e , o eri g core u ctio s o highest

ua it but o a itio a eatures that ma prove re u a t i basicapp icatio s. For app icatio s where a 1 V test must be avoi e , the MIT300o ers a 250 a 500 V test o . Combi e with co ti uit a vo tagewar i g, p us a the co ve ie ce a sa et eatures that isti guish the

ami , this is the mo e o choice or the simp est app icatio s.

I basic u ctio is stithe goa but a 1 V testre uire , the MIT310 isthe per ect ft. With thepossibi it o wor i gat higher vo tages, sa eoperatio has bee urthere ha ce b the i c usio oa e au t vo tmeter.

Megger MIT410

MEGGER MIT400 SERIESA ew i e o high per orma ce testers rate to CAT IV600 V provi es greater sa et whe testi g at highervo tage eve s.

The MIT400 Series o er test vo tages rom 10 to 1000V,a i c u es a specia user-se ectab e 10 V to 100 V i1 V i creme ts tester or ow vo tage i su atio testi gre uireme ts. The u its i c u e a exceptio a i su atioresista ce measureme t ra ge that exte s rom 20Gigohms to 200 Gigohms, with the optio to isp athe i su atio test vo tage or ea age curre t o theseco ar isp a .

Time i su atio testi g or PI a dAR testi g isavai ab e o certai mo e s. A 200 mA co ti uit

measureme t is avai ab e with a 0.01-ohm reso utio or ast accurate cab eresista ce measureme t. This ca be set to 20 mA where co ormit toe ectrica testi g regu atio s is ot re uire , exte i g batter i e.

For those who pre er the tra itio a mecha ica a a og t pe o i strume t,the MIT310A o ers ever thi g i the MIT310, but with a movi g coi isp a .The a a og isp a is e ha ce b b ac eca s o a white bac grou , togive high co trast a improve visibi it .

The ami is comp ete b the u - eature MIT320 a MIT330. Theormer a s a i ohm ra ge or measureme ts betwee the extremes o

co ti uit a high vo tage. With this eature, measureme ts ca be ma eco ti uous rom 0.01 W to 999 M W. A bac it isp a is urther e ha ceb bac it se ectio s, to ma e both the setup a resu ts visib e i poor ight.The MIT320 a so o ers au ib e a arms o both the co ti uit a megohmra ges, a justab e across the e tire ra ge.

Fi a , the MIT330 o ers ever thi g escribe i the MIT320, p us storage oup to 1000 resu ts, ow oa i g through a USB port via i c u e so tware,

a a isp a i icatio o remai i g memor .

Megger MIT300 Series


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ME

G-4 8

6 / MI

Megger makes more than justinsulation resistance testersMegger also makes high quality instruments for the following electricaltesting applications:

n Earth/Ground Testing n Battery Testingn Relay Testing n Watthour Meter Testingn

Oil Testingn

Transformer Testingn Circuit Breaker Testing n Cable Fault Testingn Power Quality Analysis n Power Factor Testingn Low Resistance Testing n Hi Pot Testing

Megger manufactures electrical test and maintenance instruments forelectric power, process manufacturing, building wiring, engineering

services and communications.

Visit our website for local assistance worldwide at www.megger.com.

Megger4271 Bronze WayD ll TX 75237

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