principle of tan delta test

8/16/2019 Principle of Tan Delta Test

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Principle of Tan Delta Test

A pure insulator when is connected across line and earth, it behaves as a capacitor. In an ideal insulator, as

the insulating material which acts as dielectric too, is 100 % pure, the electric current passing through theinsulator, only have capacitive component. There is no resistive component of the current, flowing fromline to earth through insulator as in ideal insulating material, there is zero percent impurity.

In pure capacitor, the capacitive electric current leads the applied voltage by 0!.

In practice, the insulator cannot be made 100% pure. Also due to the ageing of insulator the impurities li"edirt and moisture enter into it. These impurities provide the conductive path to the current. #onse$uently,

lea"age electric current flowing from line earth through insulator has also resistive component.

ence, it is needless to say that, for good insulator, this resistive component of lea"age electric current is$uite low. In other way the healthiness of an electrical insulator can be determined by ratio of resistive

component to capacitive component. &or good insulator this ratio would be $uite low. This ratio is

commonly "nown as tan' or tan delta. (ometimes it is also referred as dissipation factor.

In the vector diagram above, the system voltage is drawn along )*a)is. #onductive electric current i.e.resistive component of lea"age current, I+ will also be along )*a)is.

As the capacitive component of lea"age electric current I# leads system voltage by 0!, it will be drawn

along y*a)is.

ow, total lea"age electric current I-Ic / I+ ma"es an angle ' say with y*a)is.

ow, from the diagram above, it is cleared, the ratio, I+ to I# is nothing but tan' or tan delta.

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*a" the a%%lied hih voltae is V and corres%ondin current throuh the insulator is

I.

Hence as %er +hm,s law the value of insulation resistance is

This test is enerall" done #" means of meer.

-eer ives reuired direct (') voltae across the insulator an it also shows the

resistive value of insulator directl" in -ohm rane.The meer are enerall" of /00

V& 1./ 2V an / 2V.

/00 V meer are used for insulation test u%to 3.3 2V rated insulation. 4or hih

voltae transformer& other HV eui%ment and machines& 1./ or / 2V meer are

used.

5s all insulators are dielectric in nature the" have alwa"s a ca%acitive %ro%ert". 'ue

to that& durin a%%lication of voltae across the electrical insulator& initiall" there will

#e a charin current. But after some time when the insulator is totall" chared& the

ca%acitive chanin current #ecomes zero and then onl" resistive conductive

current %resents in the insulator. That is wh" it is alwa"s recommended to do

insulation resistance test at least for 3 minute as it is %roved that charin current

totall" #ecomes zero after 3 minute.

+nl" measurin insulation resistance #" meer for 3 minute does not alwa"s ive

relia#le result. 5s the resistive value of an electrical insulator also varies with

tem%erature.

This di6cult" is %artiall" solved #" introducin %olarit" index test or in short PI value

test. The %hiloso%h" #ehind PI test is discussed #elow.

5ctuall" when a voltae is a%%lied across an insulator there will #e a lea!ae currentfrom line to round.

5lthouh this lea!ae current is ver" small is in millam%ere or sometimes in micro

am%ere rane& #ut it has mainl" four com%onents.

3. a%acitive com%onent.

1. Resistive or conductive com%onent.

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It ta!es around 30 minutes to alin the %olar molecules alon electric eld and that

is wh" if we ta!e meer result for 30 minutes& there would #e no e$ect of %olarizin

in meer result.

*o when we ta!e meer value of an insulator for 3 minute& the results re=ects& the

IR value which is free from e$ect of ca%acitive com%onent of lea!ae current. 5ain

when we ta!e meer value of an insulator for 30 minutes& the meer result showsthe 31 value& free from a$ects of #oth ca%acitive com%onent and %olarization

com%onent of lea!ae current.

Polarization index is the ratio of meer value ta!en for 30 minutes to the meer

value ta!en for 3 minute.

The sinicance of %olarization index test.

9et I is the total initial current durin %olarization index test or PI test.

I is the ca%acitive current.

IR is resistive or conductive current.

I* is surface lea!ae current.

IP is %olarization current of the insulator.

Value of insulation resistance test or IR value test& i.e. value meer readin ?ust

after 3 minute of the test& is@

-eer value of 30 minute test& is

Therefore& result of %olarization index test& is

4rom the a#ove euation it is clear that& if the value of (I R A I*) IP& the PI of

insulator a%%roaches to 3. 5nd lare IR or I* or #oth indicate unhealthiness of theinsulation.

Th value of IP #ecomes hih if (IR A I*) is ver" small com%ared to IP. This euation

indicates that hih %olarization index of an insulator im%lies healthiness of insulator.

4or ood insulator resistive lea!ae current I9 is ver" tin".

It is alwa"s desired to have %olarization index of an electrical insulator more than 1.

It is hazardous to have %olarization index less than 3./.

TAN-DELTA TEST SETS DOWNLOAD

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+eatures

uilt!in protection 0 *nstrument is provided with built in high voltage protection device which protects the instrument

operator against failure of test ob1ect or standard capacitor.

2ull "etector 0 uilt!in battery operated null detector is provided which is most suitable for quick balancing of the inst

gives high sensitivity and accuracy.

*%3 0 *nterference compensation #unit$ is useful only in the case of heavy induction area so the to get the correct rea

Te"hni"al s%e"ifi"ation ,

Ca%a"itan"e ange , 4 to 4.4+" in three or four ranges depend upon capacitor and can be extended further #

external current transformer$.

esolution , C. multi%lying fa"tor esolution5.54 5.4

5.4 4

4 45

45 455

A""ura"y , 6 5.47 of reading.

Tan-Delta ange , 5.5554 to 44.4 in three ranges.

esolution , Tan-Delta fa"tor esolution

5.4 4 x 45 !8

4 4 x 45 !9

45 4 x 45 !:

A""ura"y , 6 47 of reading 6 4 to ; x 45 !9.

/igh 0oltage Power our"e '(oel /-)1*

The instrument is used to get the high voltage 5 to 4;


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+eatures

>ero start control, external interlock, open ground indicating lamp, 'T cut!off on overload.

Instrument "an #e use in three ifferent moes2

3T '3ngroune s%e"imen test*,

3sed when the ob1ect under test is not grounded. This mode provides most accurate results.

4T '4roune s%e"imen test*,

3sed when the ob1ect under test is permanently grounded. This mode often used for outdoor installed power systems.

4Tg '4roune s%e"imen test with guar*,

3sed to measure the stray capacitances and separating them from basic measurement in ?/T mode.

Te"hni"al %e"ifi"ation

Test 0oltage 0 5 to 45


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+eatures

ush button controls for rapid testing.

ully protected against all overload and short!circuits.

"rift free operation.

?uard terminal and built!in EA)T'.

ush button self indicating controls for charge, measure & discharge operations.

+aximum output current is made limited to safe value to eliminate the risk of serious shocks.

/uitable for testing resistivity of the insulating liquids when used with oil cell as per */.

Te"hni"al %e"ifi"ations

D2C2 Test 0oltages , 455(, ;85(, 855(, 4


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+eatures

"irect digital reading of dissipation factor #Tan!"elta$.

ower supply sufficient to create required stress voltage.

'igh testing speed as measurements are carried out under actual working conditions and no turning is necessary pr

single reading.

Te"hni"al s%e"ifi"ation

Dissi%ation ange 0 4C.CC7 /" with resolution of 5.547

4CC.C7 /" with resolution of 5.47

Diele"tri" "onstant range 0 5.; to 45

Test 8oltage 0 5 to =5!5 (A% continuously

Ini"ation of Null 0 : B "igit "+.

Ini"ation of Tan-Delta 0 : B "igit "+

Ini"ation of tress 0oltage 0 : B "igit "+

A""ura"y 0 6 47 of reading 6 5.5554 Tan!delta.

Power u%%ly 0 ;:5 (A% 6 457 85 '@.

Warm u% time 0 8 minutes.

/eating Cham#er '7/C* with three terminal oil "ell

'eating chamber is designed to heat the insulating liquid #oil$ up to elevated temperature 5!485F% in short time of 48;

potentiometer is provided for setting of temperature at required level. 'eating chamber with oil cell for easier testing at

temperature fitted with thermostat and protection device to prevent shock ha@ards. Three terminal oil cell is designed t

dissipation factor #Tan!"elta$ and resistivity of the insulation liquids.


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Tem%erature range 0 5 to 485F%

Ini"ation 0 : B "igit "+

/eating element 0 'eating coil

Power sour"e 0 ;:5 (A%85 '@

ensing %ro#e 0 T 455


(ae u% of 0 // & Teflon spacers

Cell Ca%a"itan"e 0 88 6 4

0olume '7il* 0 85 ml.

Cell Constant 0 =;5 2ominal

Ele"troes Distan"e 0 ; mm

principle of tan delta test

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