Aspects of partial discharge measurement

Prof .Dr.-Ing.habil. Rainer Haller Electrical Power & Environmental Engineering University of West Bohemia Pilsen/ Czech Republik

1 Introduction2 Historical overview

3 Digital measuring techniques

4 Future trends

5 Summary

Aspects of partial discharge measurement


1 Introduction



why it´s necessary to know more about partial discharges (pd)?


For avoiding outages of electri-cal power supply the measure-ment of pd´s seems to be neces-sary


pd´s can be an indicator for „weak points“ into the electrical insulation !

pd might be caused by

poor design of the insulation

failures during manufacturing or assembling

failures by electrical, thermal, mechanical, …

overstress in operation

normal ageing or degradation processes


the pd- measurement as an important tool for quality control is used not only in the electrical power engineering, but more and more in other application fields of electrical insulation

low voltage power devices

(motors, transformers, .. )

electronic devices

…


typical quality defects in MV- GIS

- particle on the insulators

-missing bolts or bad contacts

on conductor- connections

- free potential components

- microvoids into insulators

- . . .


protrusions on conductive sheets

microvoids

cracks(conductive, insulated)

typical quality defects in power cables



water tree (wt)

wt + electrical tree



oil- paper cable connectors


basic questions for pd measurement

how pd´s can be measured ? principles sensitivity

kind of failure („weak points“) ? identification dangerousness where pd´s (weak points) are located ? localization





Historical overview

[G.C.Lichtenberg, 1777)]


Historical overview

detection of failures on overhead lines and power transformers

(B.Koske 1939)


measurement principles

1:Tp / T2 = 1 µs / 5 µs2:Tp / T2 = 5 ns / 50 ns3:Tp / T2 = 5 ns / 20 ns

dtetitiFjF tj )()}({)(

)()( 0FjFq

apparent charge q


first devices


narrowband measuring devices

less disturbances

easy handling

no special experiences


broadband measuring devices

more suszeptibly to noise, disturbances

special knowledge is requested

more information about the pd- processes


first devices


measurement principles

[IEC 60270]


real pd spectra


Standardized measuring circuit

[IEC 270, 60270]


How dangerous are pd´s ?

%

80

60

40

20

kV/mm

10-3

10-2

10-1

100

10-3 10-2 10-1 100 101

50 Hz / 20 °C

50 Hz / 20 °C

moisture of paper wV

erl

us

tfa

kto

r ta

n

Qkrit = ? more informations about the pd- processes

were necessary !

Is there any correlation between the measured charge and the lifetime ?



[Izeki, Tatsuta, 1984]







typical PRPP






digital measurement techniques













recognition

diagnosis

1

2

n

data acquisition

analysis,

model

database

action

cbm, service,

risk assess-ment

sensors




statistical parameters of pd´s

[see also Gulski, 1991]



statistical data of typical pd- sources stored in a database

diagnostic (expert) system



measured pd - pattern

typical pd- reference -data -base

of available pd- systems

?

product- specifical- pd- data

must be obtained !



high measuring sensitivity

high susceptibility to noise, disturbances, …


Sources of electromagnetic disturbances

1 net connection

2, 11 power supply

3 hv- transformer

4 low pass filter

5 hv leads

6 coupling cap.

7 free potential obj.

8 stochastic disturb.

9 periodic disturb.

10 ground


suppression of disturbances

[Lemke, 1981]

radio/HF- suppression impuls- suppression

reflection- suppression

amplifyer processingelectronic integrator





screening of the testroom



noise signals, caused by SFC- generator, located in the same testroom

new methods for suppression of disturbances are requested


localization of the pd- producing „weak points“ ?

classical method (reflectrometry)

non electrical (classical) methods

(acoustical, optical, …)

ultra- high- frequency method (UHF)

(electromagnetic field , combined with

acoustic measurement)


(classical) principle of reflectrometry


1

2 3

A B C D

Richtkoppler Richtkoppler

Signal an Kopplerausgang Impulsherkunft / -Nr. A B C D Muffe / 1 – X X – Kabel links / 2 X – X – Kabel rechts / 3 – X – X

methods of failure localizationin cable- joints -1


methods of failure localizationin cable- joints -2

1‘1‘

1

1‘‘

2‘

2‘

2

3‘

3‘

3

+ –

1 2 3

1‘ 2‘ 3‘

1‘‘ 2‘‘ 3‘‘

2‘‘ =0 3‘‘ =0

RogowskispuleRogowskispule

Muffe

Signal- summierer

DisplayOriginalimpulse

Impulse nach Durchlaufen der Rogowskispulen

Impulse nach Durchlaufen des Signal-Summierers


methods of failure localization(classical acoustic method)




4 Future trends



future trends

measuring sensitivity vs noise, disturbances

(digital procedures, neuronal networks)

interpretation of pd- parameter

(identifying, correlation to the lifetime)

localization of defects on site testing


spectral analyzing of pd


spectral analyzing of pd

zero span

pd source


digital de- noising


digital de- noising

[Kranz, 1996]


identification of pd sources












multichannel pd measurement


multichannel pd measurement


dangerousness of pd


dangerousness of pd

for better understanding the physical processes of damaging or deterioration of insulation more/ other informations about the pd- processes seem to be necessary

- Δupd

- Δwpd

- …


new parameters of pd- processes


new parameters of pd- processes


new methods of failure localization


new methods of failure localization


new methods of failure localization(combined UHF - acoustic method)

[Markalous, 2006]

acoustic measurement will be triggered by UHF- signal




4 Future trends

5 Summary



summary

pd measurements are up to now an essen-

tial tool for quality testing of electrical insulation

and diagnostic purposes

progress in digital techniques makes it possible

getting more informations about pd`s at

increased sensitivity


summary

basic investigations of insulation materials for

finding a correlation between pd- parameters

and lifetime

increasing measuring sensitivity for diagnostic

measurements even under on- site conditions

(new methods of filtering, neuronal networks, ..)

using combined techniques for improved

localization


Thank you

Questions ?

& Answers !

Documents

Aspects of partial discharge measurement