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iagnostic Measurements on Powerransformers

Michael Krger e Marcelo Paulino - Soaulo maio/2010 1

INTRODUCTION INTO PARTIAL DISCHARGE (PD)PHENOMENA AND PD MEASUREMENT

Dr. Michael Krger

May 10 PAGE 2

Introduction

Partial Discharges (PD)

"localized electrical discharges that only partially

bridge the insulation between conductors" [IEC 60270:2000]

can harm insulation systems generate electromagnetic signals

PD Measurement

General specifications: IEC 60270:2000o Transformers: IEC 60076 (and others)

detection of critical defects

recognition of defects

assessment of risk

measurable

May 10 PAGE 3

PD Inception and Extinction Voltage

Internal PD hashystersis

External coronahas normally nohysteresis

IEC 60034-27

May 10 PAGE 4

PD Classification

a) corona discharge b) surface discharges

c) discharge in laminated material d) cavity discharge

e) treeing

May 10 PAGE 5

Electrical Treeing in PE

May 10 PAGE 6

Electrical Treeing in PE


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May 10 PAGE 7

Chemical (DGA)

Optical (e.g. UV camera for corona)

Electrical (narrow band or wide band)according to IEC 60270

Acoustical

UHF

Detection of PD

May 10 PAGE 8

Equivalent Circuit Diagram

Uz

U1(t)

Ut(t)

U'1(t)-Uz

tUL-UL

FCUq .1=

I1(t)

t

B

A

CP

CS

CF

R1

SI1(t)

Ut

U1

Is(t)

I2(t)I3(t)

B

A

r0CP/2 CP/2

2CS

2CS

CF

= dttiq ).(1

May 10 PAGE 9

Apparent Charge

Apparent charge q, of a pulse is that charge

which, if injected between the terminals of the

test object, would give the same reading on

the measuring instrument as the PD current

pulse itself.

Expressed usually in pC.

The apparent charge is not equal to theamount of charge locally involved at the site

of the discharge, which can not measured

directly.

May 10 PAGE 10

When to measure?

Factory test:

Standard measurement during the AC withstand testfor every new (or repaired) transformer. Usually lowground noise level.

On-site test:

After indication of DGA results.

Usually high ground noise level and other disturbances.

May 10 PAGE 11

The classical visualization

May 10 PAGE 12

PRPD Phase Resolved Histogram


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May 10 PAGE 13

Calibration of the PD Instrument

CK

Z

CtU ~A

B

I(t)

U0

C0

Calibrator

Cc

ZmUmMeasuringImpedanc

e

M

Amp. Filter

qks .max

=

Smax

Q = C * U

May 10 PAGE 14

Transformerunder test

Couplingcapacitor

Conventional Coupling of the MeasuringDevice

Testingtransformer

IPD

PD

Fault (discharge)

May 10 PAGE 15

Typical PD Measurement in a Test Lab

Testing transformer

Test object

Coupling capacitor

Faraday cage

PD instrument

May 10 PAGE 16

NoiseFiltering

- High bandwidth desirable for sensitive measurement andhigh pulse repetition rates

- Low bandwidth improves interference rejection

- Always use the highest possible bandwidth

- Only a variable filter is suitable for on-site measurements

May 10 Page: 17

Analogue and Digital PD measuring instruments

PD systems

Analogue PD measuringinstrument

May 10 PAGE 18

Traditional PD Measurement


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May 10 PAGE 19

"Digital" PD Measurement withAnalogue Filter

May 10 PAGE 20

"Digital" PD Measurement with Multi-Channels and MUX

May 10 PAGE 22

MPD 600 True Digital Measurement withDigital Filtering

May 10 Page: 24

Synchronous Multi-Channel PD MeasurementSystem MPD600

May 10 PAGE 26

Synchronous multi-channel

measurement

May 10 PAGE 27

Separation of PD and Corona Sources at

Different Locations with 3PARD

3PARD = Three Phase Amplitude Relation Diagram


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May 10 PAGE 28

Inner PD source in L1 in 3PARD

L1

L2

L3

L1

L2

L3

Inner PD SourceL1>L2>L3

3PARD

timeframe1 s

Inner PD Source in

L1

5


May 10 PAGE 29

L2

L3

3PARD

L1

L1

L2

L3

Outer NoiseL1 L2 L3

timeframe1 s

Outer Noise

6

Outer noise in 3PARD


May 10 PAGE 30

3PARD

May 10 PAGE 31

Back Transformation

May 10 PAGE 32

PD source 1 PD source 2 PD source 3

FFT pulse 1

FFT pulse 2

FFT pulse 3

FFT of all three impulses

MPD600

Frequency 2

Frequency 1Frequency 3

PD source 2

PD source 3

PD source 1Frequency 3F re qu en cy 1 F re qu en cy 2

3CFRD 3 Center Frequency

Relation Diagram

May 10 PAGE 33

Measurement at Three Different Frequencies

with 3CFRD

Faulty joint

Needle

Surfacedischarge

22kV_Corona_Surface_Joint


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May 10 PAGE 34

Case Studies

PD Measurements on Power Transformers

Coupling of the Measuring System

May 10 PAGE 37

Coupling of the PD Measurement Instrumentto the HV Bushing Measuring Tap

MPD600

May 10 PAGE 38

Power Transformer 132kV/32kV inthe Factory

May 10 PAGE 39

PD Decoupling at the Measuring Tap ofthe HV Bushing

May 10 PAGE 40

PD Decoupling at the Measuring Tap

of the HV Bushing

Advantage

Little constructive effort

No coupling capacitors necessary

Drawback

Measuring tap not always

accessible / existing

May 10 PAGE 41

PD Decoupling by Coupling

Capacitors

MPD600


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May 10 PAGE 42

PD Decoupling by CouplingCapacitors

May 10 PAGE 43

PD Decoupling by CouplingCapacitors

May 10 PAGE 44

HV Connections PD free!

May 10 PAGE 45

Inductive PD Decoupling at Cable Screen

May 10 PAGE 46

Capacitive Sensors

Sensor for capacitive coupling(Patented by the University of Hannover)

MPD 600

MPD 600

MPD 600

May 10 PAGE 47

Practical Examples

PD Measurements on Power Transformers

Measuring Results


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May 10 PAGE 48

Measuring Results

30 MVA Transformer, 115 kV / 11.3 kV

May 10

Page 49

Synchronous Multi-Channel PD Measurementon a 30MVA 115 / 11.3 kV Transformer

May 10 PAGE 50

Decoupling of PD at the Neutral

May 10 PAGE 51

Measuring Results

30 MVA Transformer, 115 kV / 11.3 kV

Statistical Noise

External Disturbance

PD Fault

May 10

Page 52

Transformer with Coupling Capacitors,

Step-up Transformer and Diesel Generator

Coupling capacitorwith MPD 600 on U

Step-up transformer400V / 21kV

DieselGenerator

Transformer

UVW

May 10

Page 53

Simultaneous PD Measurement on

3 Phases

without 3PARDfiltering

with3PARD

filtering

U

V

W


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May 10

Page 54

PD source 1 PD source 2 PD source 3

FFT pulse 1

FFT pulse 2

FFT pulse 3

FFT of all three impulses

MPD600

Frequency 2

Frequency 1Frequency 3

PD source 2

PD source 3

PD source 1Frequency 3F re qu en cy 1 F re qu en cy 2

3CFRD 3 Center FrequencyRelation Diagram

May 10

Page 55

Simultaneous PD Measurement at 3Different Center Frequencies, Phase U

3MHz

300kHz10MHz

withoutfiltering

withfiltering

3MHz

300kHz

10MHz

May 10

Page 56

Decrease of the PD Amplidude withIncreasing Frequencies

PD is not close to themeasurement point (bushing)

10MHz3MHz

May 10 PAGE 6114.05.2010OMICRON Energy Page 61

Combined UHF and IEC Measurements


Connection to

the MeasuringTap of theBushing


UHF Sensor at the Main Valve


10/10


Michael Krger e Marcelo Paulino - So

May 10 PAGE 64

The OMICRON mtronix Solution

May 10 PAGE 65

The OMICRON mtronix Solution

May 10 PAGE 66

Combined UHF and IEC measurement

IEC PD Measurement UHF PD Measurement

Corrected IEC PD Measurement

+

May 10 PAGE 67

Summary

Partial Discharges (PD) can lead to outages

PD measurement is reasonable tool for

diagnosis and quality control

Sensitive PD measurements: High demands on

PD measuring system

MPD600: a variable tool for all kind of

application electrical equipment (cable, transformer, rot.

machines, )

measuring condition (laboratory, factory, on-site)

May 10 PAGE 68

T

hankYouforYourkind

a

ttention!

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