Asset Management of Power Transformers

TRANSFORM Partner

Asset Management

of Power Transformers

Prof. Dr.-Ing. C. Neumann

Asset Management of Power Transformers

Claus Neumann

Page 2 07.06.2013

Study of electrical engineering at Technical University of Aachen,

Germany

Dr.-thesis at Technical University of Darmstadt, Germany

Till 2010 head of Operative Asset Management at Amprion, former

RWE TSO

Since 2010 active as a freelance Senior Consultant; fields of activities:

network development, asset management, design and diagnostics of

gas-insulated systems

Honorary professor at Technical University of Darmstadt, Germany,

lecture in HV switchgear and substations



1. Introduction

2. Basic tasks and functions of asset management

3. Renovation strategy, life cycle assessment

4. Risk assessment

5. Maintenance, condition monitoring & assessment, life

estimation

6. Design optimization based on evaluation of service

experience

7. Conclusions

Page 3 07.06.2013


Introduction

In the course of liberalisation of the electricity market significant changes in

the regulatory framework strong impact on network business

Intensive efforts of grid operators for optimized exploitation of the system

and the equipment installed with regard to technical and economical

aspects

Introduction of management methods known from property management &

insurance-trade – asset management and risk management

Application of these methods for control of economy & reliability of HV

systems distinct technical aspects modifications necessary

Fundamental functions of asset management duties & tools;

examples, mainly related to power transformers

Page 4 07.06.2013


Fundamental functions of asset management

Preparing of the key decisions for the network business, managing the

relationship with internal and external partners maximising long term

profitability and business success

Revenues in network business mainly grid charges, more or less fixed

optimisation of grid costs, improvements in efficiency, cost reduction

(OPEX, CAPEX)

Development and implementation of strategies guarantee a given

quality of supply at minimised cost expenditure

Ensure the asset rent ability

Preservation of the existing network - maintenance, condition

assessment & life estimation; future network development

Work on technical & management oriented subjects

Page 5 07.06.2013


Relation between costs and quality of supply C

os

ts

Quality of supply

costs in total

costs for quality

of equipment costs for

interruption

of supply

Δ C

Δ Q

Ref.: G. Balzer, C. Schon: AM für Infrastrukturanlagen; Springer Verlag 2011

Page 6 07.06.2013


Asset Owner, Asset Manager, Service Provider

corporate planning

financial responsibility,

legal duties

corporate management

Asset Owner

preservation & extension

of the grid,

preparation of the key decisions

of the grid operator,

optimisation & guarantee

of asset rent ability

Asset Manager

execution of

AM‘s work orders,

erection, assembly,

maintenance

operation

Service Provider

Page 7 07.06.2013


Asset Owner, Asset Manager, Service Provider

Ref.: CIGRE Brochure 309, Dec. 2006

Page 8 07.06.2013


Asset management process

Ref.: G. Balzer, A. Gaul, C. Neumann, C. Schorn: The general AM process….

CIGRE Symposium Osaka, Nov. 2007, Report 212

Business policy, financing

Budget, authorisation

Business development

Regulatory management

Links to authorities, legal rules

Financing management

Links to customers

Maintenance strategies, refurbishment

Risk management

R & D, new technologies

Budget management

Maintenance management

Project realisation

Commissioning, maintenance,

Purchasing, stock management

Operation, service functions

Stand-by duty, fault diagnosis

Page 9 07.06.2013


Technical & management oriented subjects

Replacement, renovation & extension

Risk management

Maintenance, condition monitoring & assessment, life estimation

New technologies

Service experience, reliability

Performance measurements

Environmental interaction

Know-how & skill retention and development

Consideration under technical & economical aspects with special

regard to power transformers

Page 10 07.06.2013


Life cycle cost assessment for finding the most economic solution

Decision making for investment by Life Cycle Cost Assessment:

In the past: Decision making mainly based on

– Investment costs

– Spatial & environmental considerations

Today: Decision making also affected by

– Service costs

– Lifetime considerations

Asset Management of Power Transformers Page 11 07.06.2013

Different shares of LCC over years of service

0 1 2 3 38 39 40 19 20 21 year of service 0 1 2 3 38 39 40 19 20 21

erection,

acquisition

scheduled maintenance, losses

co

sts

renewal

unplanned maintenance

decommiss.,

disposal

All payments in future to be represented as present values to year 0

Discounting interest rate: 10 % / a; inflation rate: 2,0 % / a

Asset Management of Power Transformers 07.06.2013

0%

20%

40%

60%

80%

100%

120%

140%

160%

180%

transformer 350 MVA

LC

C c

os

t s

ha

res

re

late

d

to in

ve

st c

os

ts i

n t

ota

l IC

losses

renewal

unplanned mainten.

scheduled mainten.

balance of plant

equipment


Life Cycle Costs (LCC), 380/110 kV transformer

Page 14

equipment 80% IC

balance of plant 20% IC

scheduled

mainten. per year 0,11% IC

unplanned

mainten. per year 0,36% IC

renewal after 50 a 80% IC

loading 50% Pr

losses 6 ct/kWh

IC investment costs

07.06.2013

0%

20%

40%

60%

80%

100%

120%

cable system

LC

C c

os

t s

ha

res

re

late

d to

inv

es

t c

os

t

losses

renewal

unplanned mainten.

scheduled mainten.

interface structure

cables


LCC: 380 kV transformer – 380 kV cable system

0%

20%

40%

60%

80%

100%

120%

140%

160%

180%

transformer 350 MVA

LC

C c

os

t s

ha

res

re

late

d to

inv

es

t c

os

t

losses

renewal

unplanned mainten.

scheduled mainten.

balance of plant

equipment

Page 15 07.06.2013


LCC: 380 kV transformer – 380 kV GIS, AIS

0%

20%

40%

60%

80%

100%

120%

140%

160%

GIS AIS

LC

C c

ost sh

are

s

rela

ted

to

in

vest.

co

sts

losses

renewal

unplanned mainten.

scheduled mainten.

balance of plant

system, equipment

0%

20%

40%

60%

80%

100%

120%

140%

160%

180%

transformer 350 MVA

LC

C c

os

t s

ha

res

re

late

d to

inv

es

t c

os

t

losses

renewal

unplanned mainten.

scheduled mainten.

balance of plant

equipment

Page 16 07.06.2013


Renovation and equipment end of life

assessment

Page 17

Decision making process using an approach based on condition c and

importance i of the equipment

Maintenance & renovation measures:

sequence depending on urgency d:

Urgency d depending on condition c

and importance i

E. g. renovation measures

equipment 3 first, equipment 2

secondly, equipment 1 depending

on the budget available

E.g. maintenance measures:

equipment 5 will be maintained

prior to equipment 4

c

i

d

region I

region II

region III

high

bad

07.06.2013


Assessment of condition and importance

parameters

Page 18

1. Assessment of condition parameters

• Actual condition quantities: taken from inspection & condition

assessment, interval to next planned maintenance activity

• General condition quantities: service experience (e. g. after-sales

service quality, maintenance costs), type related and individual

failure rates

assessment by school marks

2. Assessment of importance parameter

• Derived from the loading of the transformer in question related to

the nominal power

• Weighted by a factor reflecting the relevance of the station in the

system

3. Condition and importance parameters normalised to 100

07.06.2013


Condition & importance of 110 kV transformers

Page 19

importance

maintenance

replacement

co

nd

itio

n

0

20

40

60

80

100

0 20 40 60 80 100

Population of von 640 transformers

replacement

maintenance

dr2 dr1

dm1

dm2

07.06.2013


Sequence of transformer replacement measures

according to urgency

Page 20

0

20

40

60

80

100

1 4 7 10 13 16 19 22 25 28 31 34

Trafo

Dri

ng

lic

hk

eit

Priorität 1 Priorität 3Priorität 2

transformer

urg

en

cy

Priority 1 Priority 2 Priority 3

07.06.2013




Risk management


New technologies







Page 21 07.06.2013

Risk assessment process

Asset Management of Power Transformers Page 22

Ref.: G. Balzer, C. Neumann, et al. : SELECTION OF AN OPTIMAL MAINTENANCE AND REPLACEMENT

STRATEGY OF H.V. EQUIPMENT BY A RISK ASSESSMENT PROCESS; CIGRE-Report B3-103, 2006

Time after commissioning

respect. service

Result of reliability

calculation

07.06.2013

Conventional risk assessment methods => assessment of risk factors of various

equipment, e. g. different frequencies & consequences of failures, by mean values

Stochastic characteristics of risk factors neglected => risk can be under- or

overestimated

VaR method => risk factors considered as stochastic distribution functions => Fig. a

VaR summarizes the expected maximum (financial) loss within a given confidence

interval over a target horizon => Fig. b

Risk assessment, value at risk (VaR) method


0,04

0,03

0,02

0,01

0,0 0,5 1,00,80,60,40,2 [1/a]

f(t) failure rate

0

a) b)

00

0,05

0,10

0,15

0,20

0,25

f(t)

2 4 106 8 12 14 16 [Mio €] 20

Financial loss per a

Critical value

at confidence

level of 95%

07.06.2013

Example: Population of 110kV/MV transformers


Risk factors to be considered:

Energy costs

Transmitted power

Outage time *

Value of the equipment, investments

Repair costs *

Failure frequency *

Outage

time

Repair

costs

Failure

frequency

Outage time & failure frequency => non-availability =>

costs for repair & corrective maintenance

Ref.: G. Balzer, C. Schon:

AM für Infrastrukturanlagen;

Springer Verlag 2011

* stochastic quantities

07.06.2013

Result of VaR calculation:

Loss costs in the period under consideration


Ref.: G. Balzer, C. Schon: AM für Infrastrukturanlagen; Springer Verlag 2011

Co

sts

re

late

d t

o m

ax

. c

os

ts

100

75

50

25

0

[%]

58%

11%

95% probability

50% probability

probabilty [%]

07.06.2013




Risk management


New technologies







Page 26 07.06.2013


(Transformer) Lifetime model

new condition

age

condition after

refurbishment

minimum strength

maintenance

refurbishment,

corrective maintenance

stress

failure,

outage strength

service life

Maintenance strategy has impact on loss of strength

Refurbishment can compensate loss of strength

Definition of minimum strength

Assessment of actual strength

Page 27 07.06.2013

Maintenance & diagnosis strategy for power

transformers


routine diagnosis

Special diagnostic measurements

inadmissible

impact ?

precautionary withdrawal from service,

repair actions

failure

indication ?

yes

no

no

yes

Stepwise diagnosis*) *) in addition to a quarterly

visual inspection and

periodical servicing

Stepwise diagnosis strategy for power

transformers


comp. diagnosis method online offline off site remark

oil ageing X routine

dissolved gas analysis (DGA) X routine

resistance measurement X after indication (DGA)

PD measurement X after indication (DGA)

imdepance measurement X after short circuit

transfer function measurem. X after short circuit

PDC measurement X condition assessment

furan analysis X condition assessment

DP measurement X condition assessment

capacit. / tan measurem. X routine

DGA X condition assessment

PD measurement X condition assessment

diverter switch inspection X routine

torque measurement X condition assessment

active

part

bushing

tap

changer


transformers

















active

part

bushing

tap

changer

DGA most important diagnostic tool for transformers

In case of larger populations expert system

Classification of DGA results & condition based determination

of sampling intervals

07.06.2013

















active

part

bushing

tap

changer

Short circuits in the vicinity of transformer terminals mecha-

nical impact on windings danger of winding displacements

TF measurements diagnostic tool for detection of winding

displacements


transformers

TF measurements for detection of

winding displacements


Measurements on 12 transformers of the same type

0.0

2.0

4.0

6.0

8.0

10.0

12.0

(k )-1

16.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 MHz 1.0Frequenz f

|TF

1(f

)|

Limburg Trafo 22

Brauweiler Trafo 22

Dauersberg Trafo 21

Kelsterbach Trafo 23A

a.)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Frequenz f

|TF

1(f

)|

Osterath Trafo 22

Walsum Trafo 21

Pfalzdorf Trafo 22

Pfalzdorf Trafo 21

Opladen Trafo 24

Dünnwald Trafo 23

Ibbenbüren Trafo 21

Lüstringen Trafo 23


Mündelheim Trafo 23

Fühlingen Trafo 22

St. Barbara Trafo 21

MHz

(k )-1

b.)

A

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 MHz 1.0Frequenz f

|TF

2(f

)|

Limburg Trafo 22

Brauweiler Trafo 22

Dauersberg Trafo 21

Kelsterbach Trafo 23V

c.)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Frequenz f

|TF

2(f

)|

Osterath Trafo 22

Walsum Trafo 21

Pfalzdorf Trafo 22

Pfalzdorf Trafo 21

Opladen Trafo 24

Dünnwald Trafo 23





Fühlingen Trafo 22


MHz

V

d.)

a.) frequency f

0.0

2.0

4.0

6.0

8.0

10.0

12.0

(k )-1

16.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 MHz 1.0Frequenz f

|TF

1(f

)|Limburg Trafo 22

Brauweiler Trafo 22

Dauersberg Trafo 21


a.)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Frequenz f

|TF

1(f

)|

Osterath Trafo 22

Walsum Trafo 21

Pfalzdorf Trafo 22

Pfalzdorf Trafo 21

Opladen Trafo 24

Dünnwald Trafo 23





Fühlingen Trafo 22


MHz

(k )-1

b.)

A

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 MHz 1.0Frequenz f

|TF

2(f

)|

Limburg Trafo 22

Brauweiler Trafo 22

Dauersberg Trafo 21


c.)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Frequenz f

|TF

2(f

)|

Osterath Trafo 22

Walsum Trafo 21

Pfalzdorf Trafo 22

Pfalzdorf Trafo 21

Opladen Trafo 24

Dünnwald Trafo 23





Fühlingen Trafo 22


MHz

V

d.)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

(k )-1

16.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 MHz 1.0Frequenz f

|TF

1(f

)|

Limburg Trafo 22

Brauweiler Trafo 22

Dauersberg Trafo 21


a.)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Frequenz f

|TF

1(f

)|

Osterath Trafo 22

Walsum Trafo 21

Pfalzdorf Trafo 22

Pfalzdorf Trafo 21

Opladen Trafo 24

Dünnwald Trafo 23





Fühlingen Trafo 22


MHz

(k )-1

b.)

A

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 MHz 1.0Frequenz f

|TF

2(f

)|

Limburg Trafo 22

Brauweiler Trafo 22

Dauersberg Trafo 21


c.)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Frequenz f

|TF

2(f

)|Osterath Trafo 22

Walsum Trafo 21

Pfalzdorf Trafo 22

Pfalzdorf Trafo 21

Opladen Trafo 24

Dünnwald Trafo 23





Fühlingen Trafo 22


MHz

V

d.)

b.) frequency f

Page 33


MHz

m-1

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

frequency f

|TF

I-1N/U-2U (f)|

TF of I-1N/U-2U on 06.10.1999 TF of I-1N/U-2U on 04.07.2005

110 kV windings

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

frequency f

|TF

I-1N

/U-2

V(f

)|

TF of I-1N/U-2V on 06.10.1999

TF of I-1N/U-2V on 04.07.2005

MHz

m-1

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

frequency f|T

FI-

1N

/U-2

W(f

)|

TF of I-1N/U-2W on 06.10.1999

TF of I-1N/U-2W on 04.07.2005

MHz

m-1

measurem. Oct. 1999

measurem. May 2005

phase U

phase V

phase W

TF measurement on a 220/110 kV

transformer after short circuit on May 2005


TF measurement on a 220/110 kV

transformer after short circuit on May 2005

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

frequency f

|TF

I-1N

/U-2

W(f

)|

TF of I-1N/U-2W on 06.10.1999

TF of I-1N/U-2W on 04.07.2005

MHz

m-1

measurem. Oct. 1999

measurem. May 2005

phase W

Winding displacement

















active

part

bushing

tap

changer

Failure statistics on transformers ~15% of all failures caused

by failures on bushings

Measurements of capacitance and dissipation factor tan delta

diagnostic tools to detect ageing phenomena and to prevent

failures

07.06.2013

Page 37

Ageing behavior of resin bonded paper

bushings: Delta C & tan

0

2

4

6

8

10

0 10 20 30 40

age / a

Delta C

/ %

0,0

0,5

1,0

1,5

2,0

0 10 20 30 40

age / a

tan

/

%

capacitance C dissipation factor tan





Risk management


New technologies, e. g. monitoring systems







Page 38 07.06.2013

Basic requirements for monitoring systems


Monitoring systems valuable data and information for

condition assessment of the system and the equipment installed

Variety of data recorded and transmitted may cause problems

when the information has to be evaluated and presented for the

user

Standardisation needed, basic requirements to be defined:

− Autonomous system, no inadmissible interference of the transformer in case of an outage

− Modular structure, which can be updated; monitoring server as well as sensors

− Uniform operator environment, independent from the transformer manufacture and type

07.06.2013

Modular structured sensors


test tap

connector

bushing

coupler

unit

oil level indicator

temperature

measuring

device

transformer

bus link plugs

moisture in oil

measuring

device

gas in oil

measuring

device

gas in oil monitor

(subsystem)

test tap

connector

bushing

coupler

unit

oil level indicator

temperature

measuring

device

transformer

bus link plugs

moisture in oil

measuring

device

gas in oil

measuring

device

gas in oil monitor

(subsystem)

analogue intelligent

intelligent

subsystem

intelligent

analogue intelligent

07.06.2013

test tap

connector

bushing

coupler

unit

oil level indicator

temperature

measuring

device

transformer

bus link plugs

moisture in oil

measuring

device

gas in oil

measuring

device

gas in oil monitor

(subsystem)

test tap

connector

bushing

coupler

unit

oil level indicator

temperature

measuring

device

transformer

bus link plugs

moisture in oil

measuring

device

gas in oil

measuring

device

gas in oil monitor

(subsystem)

adapter

standardised

manufacturer’s

responsibility

Standardised visualisation of power

transformer monitoring data


information for

system management

operation

asset management

07.06.2013




Risk management


New technologies, e. g. monitoring systems

Service experience, reliability => design optimisation






Page 42 07.06.2013

Failures on 220 & 380 kV power transformers


30% 25%

10% 15%

20%

OLTC Carbonized-oil

formation

Displacement by

short circuit stress

Interturn fault

bushing

07.06.2013

Transformer failures: tripping


compon.

18%

main tank

29%

outside of

transf.

53%

other

causes

18%

caused by

animals

82%

cable connection

an

angeschloss.

Komp.

50%

an Trafo-

Klemmen od.

Verschien.

50%

on compon.

connected

50%

on transf.

terminals or bar

connections

50%

07.06.2013

Transformer failures:

Alarm & warning signals


others

17%

Buchholz gas

component.

44%

Buchholz gas

main tank

39%

no

findings

62%

fault gas

34%

miss

signal

4%

dry type

bushing

07.06.2013

Optimized transformer design

250 MVA, 400/120/30 kV


Further features: On load tap changer with vacuum switching device,

maintenance free air drying units

self supporting

natural cooling unit

(maintenance free) monitoring system

resin impregnated paper bushing (RIP)

with composite insulator

(oil free design, no special protection device)

tertiary winding with

cable connection

and plug in arresters

(protection against

external short circuits)

Plug in cables Plug in arresters

No external

condensers !

07.06.2013

Conclusions


Grid operators seek for asset rent ability optimization by an adequate asset management strategies and tools

Technical as well as management oriented tasks, e. g. renovation, risk assessment, maintenance & condition assessment, new technologies, service experience, design optimization

Renovation => LCC assessment, RCM method

Risk assessment => VaR method

Maintenance and condition assessment => multi-stage diagnosis: Basic diagnosis routine measurements; depending on the findings more sophisticated diagnostic investigations

New technologies, e. g. monitoring systems => standardisation & definition of basic requirements

Evaluation of service experience => design optimization, reduction of maintenance expenditure

07.06.2013

Asset Management of Power Transformers 48

Thank you for your

kind attention !

07.06.2013

Documents

Asset Management of Power Transformers