Aspects of partial discharge measurement

transcript

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 ?

10-3 10-2 10-1 100 101

50 Hz / 20 °C

moisture of paper wV

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

data acquisition

analysis,

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

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‘ 3‘

1‘‘ 2‘‘ 3‘‘

2‘‘ =0 3‘‘ =0

RogowskispuleRogowskispule

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

zero span

pd source

digital de- noising

[Kranz, 1996]

identification of pd sources

multichannel pd measurement

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 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 !

Aspects of partial discharge measurement

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