New Techniques for the Monitoring of Transformer … Techniques for the Monitoring of Transformer Condition. Agenda ... • On-line monitoring as future trend • C/DF monitoring –The

Thomas Prevost – OMICRON electronics USA

IEEE T&D Conference

Chicago, Illinois April 17, 2014

New Techniques for the Monitoring of

Transformer Condition

Agenda

• Monitoring Expectations & Needs

• Bushing Monitoring

– Capacitance

– Power Factor

• Transformer Monitoring

– Partial Discharge

– Voltage Transients

• Summary & Conclusions

Scope of Monitoring – Expectations and Needs

Continuous Diagnostics

Condition based maintenance

Full utilization of life span

Fa

ilure

Ra

te

time / a 0 10 20

Classical

Diagnostics

Temporary

Monitoring

Permanent

Monitoring

5a

3a

Scope of Monitoring – Expectations and Needs

Arguments and user expectations

> Continuous monitoring under service conditions

Reliable measurement data

> Diagnostic of errors before they appear

Condition based maintenance

> Knowledge about historical use

Fully utilize life span of equipment

Transformer Failure Statistics

[Viereck, Hillinger, Transform 2011]

Agenda



– Capacitance

– Power Factor





• According to the data from various researches and

electric power utilities, bushings failures make 5 to

50 %, or in average, one quarter of the total

number of transformer failures .These failures most

commonly cause transformer fires which may result

in huge collateral damages of switchyard.

Reference [3] indicates that 30 % of generator

step-up transformer failures are caused by a

bushing malfunction, and that they also cause

56 % of failures accompanied by fire.

Failure Mechanisms and Diagnostics

• Partial breakdowns

– Capacitance

– Partial discharges

Voltage

[kV]

No. of

layers

%

change

123 14 7.1

245 30 3.3

420 40 2.5

550 55 1.8

A

Emax= high

Emax= low

A

without

layers

with layers

Failure Mechanisms and Diagnostics

• Voids, cracks

– Partial discharges

– Capacitance

• Ageing by-products, moisture

– Dissipation factor / power factor

0,0

0,2

0,4

0,6

0,8

1,0

Dis

sip

atio

n F

acto

r (%

)

typ: 0,25

OIP

typ: 0,35

IEC60137 max: 0,7 %

RIP 0,0

0,2

0,4

0,6

0,8

1,0

Po

wer

Fac

tor

(%)

typ: 0,25

OIP

typ: 0,35

max: 0,85

RIP

max: 0,5

IEEE C57.19.01

Where Can I Get the Reference from?

• Off-line test: Reference from HQ capacitor

• On-line test: Reference?

u

U X (t) U R (t) Z 1

Z 2

C X, C R

0 (t)

Reference Measurement path

I R I X

Im

j

d

Uo

IX IR

Relative C/DF Measurement

> Sum of the bushing currents

> Three phase vectors are added up

> Bushing-to-bushing comparison

> Vectors of bushings in same phase are

compared

L1

L2 L3

from 2011-02-13 to 2011-02-15

[P. Picher “Integration of New Transformer Monitoring Technologies ...”

TechCon Asia-Pazific 2011]

Systematic error

0.65 %

plus instrument

inaccuracy 0.5 %

Capacitance?

DF impossible!

0,0

0,2

0,4

0,6

0,8

1,0

DF

(%)

typ: 0,25

OIP

typ: 0,35

Systematic error

RIP

•PAGE 12

VT Bushing

Data Storage and

Analysis Unit

Connection Diagram VT Reference

j

d

IB UVT+

90°

TanDelta Measurement Phase U

Comparison to accurate

off-line tests:

DF 2.701 E-3

C (pF) 467.1

C/DF Measurement over 1.75 Years

0,0

0,2

0,4

0,6

0,8

1,0

DF

(%)

typ: 0,25

OIP RIP

400

467 +/- 2 pF Measurement

478 pF Warning

500

Cap

acit

ance

(p

F)

0,27 +/- 0,05 % Measurement

0.7 % IEC Warning

DF Temperature Correction

[ABB Guide for Bushing diagnostics and conditioning, Ludvika 2000]

Agenda



– Capacitance

– Power Factor





Reasons and Effects of Partial Discharges

Reasons

• Failures of design or during manufacturing process

• Aging of equipment

– Electrical stress

– Thermal stress

– Mechanical stress

Effects of PDs:

• Heating

• Creeping destruction of the insulation material

• Treeing, chain reaction

• Insulation breakdown, short circuit

Treeing in polyethylene

PD Activity

over 4 Days

10

1

0.1

0.01

00:00:00 01:00:00 02:00:00 03:00:00 04:00:00 05:00:00

Q in

nC

t in dd:hh:min

L1L2L3

Fighting PD Noise: UHF Gating

Electr. PD

UHF PD

Internal

PD

Corona

EM Field

Combination of the Methods

IEC PD Measurement

Corrected IEC PD Measurement

& UHF PD Measurement

IEC

UHF

3PARD: PD Discrimination by Amplitude

MPD1

Internal

PD

Corona

EM Field

MPD2 MPD3

1

2 3

3PARD and Back Transformation

3FREQ: PD Discrimination by Spectrum

MPD1

Internal

PD

Corona

EM Field

0.5M

2M 8M

f

A

0.5M 2M 8M

PD Risk Assessment

Noise rejection

Source separation

Pattern classification

PD localization

• Galvanic

decoupling

• Gating

• UHF

• RTD

• 3 PARD

• 3 FREQ

• Manual

• Automatic

• Asset

• Phase

• Acoustic

localization

Agenda



– Capacitance

– Power Factor





Switching Transients

Dr. Robert Degenneff

IEEE PES Transformers

Committee

Tutorial – March 2014

Switching Transients

0

Vo

lta

ge

in

kV

t in ms 80 40 0

200

-200

24 17 t in ms

0

Vo

lta

ge

in

kV

t in ms 100 50 0

200

-200

29 15 t in ms

G

Grid400 kV

GSU1100 MVA

Generator900 MW

21 kVTransmission line

400 kV6 km

Substation

Transformer 2Transformer 1

ca. 10 m

UMTS

Generator

OMS843- PD- Transients- C/DF

UHF620 + UVS


Voltag Transformers

OMS843- C/DF

(Reference)

UHF620 + UVS

PDM600

Case Study: Combined Generator and

Transformer Monitoring

C/DF and PD Couplers

Generator:

Capacitive couplers

Transformer:

Capacitive bushing

adapters and UHF

drain valve sensor

Transformer 2Transformer 1

ca. 10 m

UMTS

Generator


UHF620 + UVS


Voltage Transformers

OMS843- C/DF

(Reference)

UHF620 + UVS

PDM600

Monitoring Results

20 10 0 t in ms

1

0.1

0.01

QIE

C in

nC

10

20 10 0 t in ms

100

1

0.001

U in µ

V

1000 500 0 f in MHz

P in d

Bm

-120

-100

-60

0,0%

0,2%

0,4%

0,6%

0,8%

1,0%

11-20-2012 11-25-2012 11-30-2012

DF

/ %

U

V

W

Influence of Environmental Conditions

0 5 10 15 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1 d

issip

ation

fa

cto

r in

%

0

5

10

15

20

25

30

35

40

tem

pe

ratu

re in

C°

V-phase

U-phase W-phase

IEC60137 max: 0,7 %

time / days

G

Grid400 kV

GSU1100 MVA

Generator900 MW

21 kVTransmission line

400 kV6 km

Substation

0

Vo

lta

ge

in

kV

18 t in ms 12 6 0

200

-400

400

-200

C Phase

B Phase

A Phase

BAT20

BAT10

0

Vo

lta

ge

in

kV

200

-400

400

-200

Transient Over-Voltages

> Oszillation frequency 10 kHz,

beat frequency 600 Hz

> Several times a day

t in ms 12 6 0

BAT10

18 t in ms 12 6 0

Agenda



– Capacitance

– Power Factor





Summary

• On-line monitoring as

future trend

• C/DF monitoring

– The reference problem

– Solution: VT reference

– Accuracy +/- 2pF

• On-line PD monitoring

– The noise problem

– Possible solutions:

• UHF-gating

• Software separation

• Pattern recognition

• Voltage Transients

Questions??

Thomas Prevost

[email protected]

Documents

New Techniques for the Monitoring of Transformer … Techniques for the Monitoring of Transformer Condition. Agenda ... • On-line monitoring as future trend • C/DF monitoring –The