tan delta / dissipation factor as an effective tool in ... educational program spring 2001. benefits...

ICC Educational Program Spring 2001.

Tan Delta / Dissipation Factor As AnEffective Tool In Determining The

Insulation Condition Of Power CablesUsing The BAUR PHG VLF System.

Craig Goodwin, HV Diagnostics Inc. GA, USAe-mail: [email protected]


Summary of Presentation

• Theory / Background

• Description of Diagnostic Method/s

• Field Examples


Benefits of Voltage Testing with VLFSinusoidal Waveforms in the field.

� Low Power Requirement for on site testing. � Compact portable design of test equipment.� Easier diagnosis of water tree deteriorated insulation at low frequencies compared to higher frequencies such as 60Hz using TD.� Easier to integrate Cable diagnostic interfaces such as TD and PD etc.


"WATER TREEING" in polymeric insulation(schematic layout)

● electrical field conditions for possible● water water development of● disturbance field "water trees"● time

outer semiconductinglayer

insulation

inner semiconductinglayer

conductor

"bow-tie trees"

"vented trees"

ICC Educational Program Spring 2001.ICC Educational Program Spring 2001.

Vented- tree growing from the inner semiconVented- tree growing from the inner semiconlayer of a 30 kV- PE- cable


Dielectric Failure of insulation originating from a watertree


What is Dissipation Factor ( tan δ) ??

time/sec0 10

voltage

current

= U RU C

²/².ω

1ωCR.

dissipation factor tan δ = true power reactive power

=


Simplified Dielectric Equivalent Circuit of aWater Tree

w t

R1C1

R2 C2

>>


AC Pure Sinewave Output Voltage andCurrent.


Do I have a DF dependancy regarding thetotal length or the amount of joints in acable?

NO!

Q & AQ & A


Voltage Dependence of 0,1 Hz Tan Delta on Newand Service-aged XLPE-insulated Medium Voltage

Cables.

0

1

2

3

4

5

6

7

8

9

1 0

0 0 .5 1 1 .5 2 2 .5 3

V /V 0 (A p p lie d V o lta g e )

0.1

Hz

Dis

sip

ati

on

Fa

c

G ood c ab le S ligh tly s e rvic e -aged (1 ) Mode ra te ly s e rvic e -a ged (2 )

Mode ra te ly s e rvic e -a ged (3 ) S trong ly s e rv ic e -aged (4 )

Ta nD e lta . (1 0 - 3)


Cables are still in good condition, if :

tan δ (2 Uo) < 1,2 ‰ and

[tan δ (2 Uo) - tan δ (Uo)] < 0,6 ‰

Cables in bad condition (or to be replaced immediately ) if :

tan δ (2 Uo) ≥ 2,2 ‰ or

[tan δ (2 Uo) - tan δ (Uo)] ≥ 1,0 ‰

EPR and TR - XLPE cables have higher absolute values of TanDelta than the above XLPE values, however the change in TanDelta is still the important criteria to take note of.

Criteria For tan Criteria For tan δδ – for PE or XLPE – for PE or XLPE


Field Test Result for an 1974 XLPE Cable

Good Resultfor an old Cable.


Field Test Result for an 1984 XLPE Cable

Nominal OperatingVoltage: Vo = 14kV

PDIV: only at 19kV

Note: TD values are poor even at Vo.


Comparison of Cable Diagnostic SystemsIR C R e c o v e r y D is s . F a c to r S p e c tr o s c o p y

A n a ly s is V o lta g e V L F ta n d V L F ta n d

D ia g no s is s t ro n g ly a g e d c a b le s 0 - + +

In f lue nc e o f d is tu rb a n c e s - 0 + +

R e pro du c ib i li ty o f m e a s u re m e n ts - + + +

D ia g no s t ic te s t t im e - - + +

In f lue nc e o f T e m p e ra tu re + - + -

R E F .: R E F .: I P H B e r lin

S IN T E F R e p o rt, N 7 4 6 5 T ro n d h e im D r. I n g . R . P la th T U B e r lin

S . H v id s te n , J .T . B e n ja m in s e n P ro f . D r. W . K a lk n e r V E W E U R O T E S T

T R A 5 0 7 2 , A u g . 2 0 0 0 D ip l. I n g . I . K ra g e

Key:0 OK+ Pos. - Neg.


Other Applications and Techniques available using theTan Delta measurement:

● Measurement of TD and Capacitance with respect to

Frequency ( Dielectric Spectroscopy).

● Application of TD as a reference signature andmethod

for determining moisture ingress for PILC cables.


Conclusions of Tan Delta Diagnostics

● A TD cable assessment system can clearlydistinguish between new, medium and strongly aged extruded

cable insulation.

● Water trees which are a major original source of insulation failures in aged extruded cables can be detected in a non-destructive manner.

● Excellent Field Results.

● To detect singular defects, a combined assessment system including the application of partial discharge measurement and location in addition to TD is necessary.

tan delta / dissipation factor as an effective tool in ... educational program spring 2001. benefits...

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