Gerhard Myburgh Namibian Power Corporation; Namibia

Graduate School of Technology Management, University of Pretoria; South Africa

Establishment of a Life Assessment and Decision

Methodology for Critical Network

Transformers/Reactors

Agenda

• Introduction

• Theory

– Problem Statement and Objective

– Research Study Process Design

• Application

– Development and Testing of the Life Assessment and Decision Methodology

– Implementation results (Year 1&2)

• Benchmarking

– Survey Methodology

– Survey Results

• Conclusion and Recommendations

General Information Area: 825 418 km2

People: 2,324,004

Density: 2.8 people/km2

(South Africa 42.4 people/km2)

Network Lines (Km) TRFRs

400 kV 988 15

350kV 952 10

330 kV 522 9

220 kV 2795 40

132 kV 2006 21

66 kV 3507 111

Introduction

A preliminary investigation suggested that The Namibian Power Corporation’s

(NamPower) maintenance plan lacked

• clear and documented life assessment criteria

• an approved methodology for maintenance strategy selection of critical

network transformers

Problem Statement and Objective

Problem statement

NamPower’s maintenance plan lacked clear

and documented life assessment criteria

and methodology for maintenance strategy

selection of critical network transformers.

Objective

To establish life assessment criteria and a

methodology for integration into a

maintenance strategy selection model in

order to improve system availability and

reliability.

Research Study Process Design

Phase 1

Criteria

development

Weighting and

scoring criteria

Information

sharing and

application

workshop

Final life assessment procedure

Life assessment

model

development

Deductive

reasoning

Deductive

reasoning

Objective

To establish transformer life assessment criteria and a methodology for integration into a maintenance strategy

selection model in order to improve system availability and reliability

Research

Research Study Process Design

Phase 2 & 3

NamPower internal assessments on

targeted critical transformers only

Summarise assessment results

Priority review session

Summarise assessment results

Feedback and benchmark review

session

Publish results

Criteria and maintenance strategy

questionnaire to target technology-

based organisations

Approval and induction of new

transformer life assessment

methodology

Development and Testing of the

Life Assessment and Decision

Methodology

TRFR Technical Condition (Input) Impact/consequence NamPower

Risk Profile (Input)

AHP (Processing)

Strategy

Selection Model

(Output)

Step 1

Step 2

Step 3

Technical Criteria Assessment

Evaluate Transformer Technical

Condition

Main criteria

Sub criteria

Elements

Historical experience

Availability (50%)

2.01 Maintenance/ Failure spare availability

(27%)

2.03 Transformer loading

(17%)

2.04 Transformer fault levels (10%) 2.02 OEM Support

(18%)

2.05 Network redundancy

(27%)

1.01 Age (5%)

1.02 Time in Service (6%)

1.03 Service History (17%)

1.04 Visual inspection (5%)

1.05 Chemical diagnostics (27%)

1.06 Electrical diagnostics (27%)

1.07 Failures (11%)

Product support (20%)

Performance (80%)

Reliability (50%)

Transformer Consequence/Impact A B C D E

Rating Financial Impact People Effect Legal and Compliance Continuity of Supply Environment

5 N$ 20-N$ 50mil

Multiple fatality and/or

Significant irreversible effects

to 10's of people

-Major litigation costing

N$10mil+

-Investigation by regulatory

body resulting in long term

interruption to operations

-Possibility of custodial

sentence

-Regional blackout lasting

<6hrs

-National load shedding

<2weeks

-Loss of critical supply to

critical customer (mines,

towns etc)

- Prolonged environmental

impact

-High profile community

concerns raised - requiring

significant rectification

measures

-Legislation agency enquiry

- Potential for significant legal

sanctions against NamPower

4 N$10 – N$20 mil

Single fatality and/or

irreversible disability or

impairment to one or more

persons

-Major breach of

regulationwith with punitive

fine.

-Significant litigation involving

many weeks of senior

management time

-Regional loss of supply to

large customers or affecting

>10 000 (50MW) customers

for >12hrs

-Loss of supply to major

centre or customer >12hrs

- Measurable environmental

harm - medium term recovery

- High potential for complaints

from stakeholders and

community

- Environmental directives

issued by authorities

3 N$10 – N$20 mil

Extensive injuries or

irreversible disability or

impairment to one or more

persons

-Breach of regulationwith

investigation or report to

authority with prosecution

and/or moderate fine possible

-Local loss of supply to large

customers or affecting >10

000 (50MW) customers for

>8hrs

- Medium term recovery,

immaterial effect on

environment / community

-Required to inform legislative

authority

2 N$ 100 - N$1 mil

- Medium term largely

reversible disability to one or

more persons

- Significant medical

treatment, disabling or lost

time injury <2weeks

-Minor legal issues, non-

compliance and breaches of

regulation

-Loss of supply to large

customers or affecting >5000

customers for <4hrs

Short term transient

environmental or community

impact - some cleanup costs

1 <N$100 000 loss- First Aid treatment or minor

medical treatmentNo breach

-Loss of supply to some

customers (normal

interruption) effects 1 000

customers for <4hrs

Negligible impact on the

environment, little or no

ecological effect and no

measurable impact on human

health

Impact Assessment Criteria

Sheet and Risk Matrix Input

Impact Assessment Criteria

Sheet and Risk Matrix Input Transformer Consequence/Impact

NAMPOWER ASSET MAINTENANCE RISK MATRIX

100 year event years to decades months to years Weeks to months Days to weeks

1 2 3 4 5

A5 B5 C5 D5 E5 5 6 7 8 9 10

A4 B4 C4 D4 E4 4 5 6 7 8 9

A3 B3 C3 D3 E3 3 4 5 6 7 8

A2 B2 C2 D2 E2 2 3 4 5 6 7

A1 B1 C1 D1 E1 1 2 3 4 5 6

>5%

probability

(Rare)

>20%

probability

(Can Happen)

>50%

probability

(Very Likely)

99%

probability

(Will Happen)

SUBSTATION NAME:

TRANSFORMER INSTALLATION DESCRIPTION:

COMPILED BY:

DATE COMPILED:

<5%

probability

(Highly

Unlikely)

FREQUENCY/PROBABILITY OF OCCURRENCE

En

vir

on

me

nt

CO

NS

EQ

UE

NC

ES

(5

CA

TE

GO

RIE

S)

Fin

an

cia

l Im

pa

ct

Pe

op

le E

ffe

ct

Le

ga

l a

nd

Co

mp

lia

nc

e

Co

nti

nu

ity

of

Su

pp

ly

Pairwise comparison scale

A 5-point scale is used

Description Score Process question example

Equal / no difference in importance 1

Moderately more important 2 Main criteria

Strongly more iomportant 3

Significantly more important 4

Extremely more important 5 Sub criteria

G P

1 0.50

1 0.50

G P

0.5 0.20

2 0.80

1.01 1.02 1.03 1.04 1.05 1.06 1.07 G P Lambda 5.9

1.01 1 1/3 1/3 2 1/5 1/5 1/3 0.48 0.05 CI -0.19

1.02 3 1 1/3 1 1/5 1/5 1/3 0.54 0.06 CR -0.13

1.03 3 3 1 2 1 1 1 1.51 0.17

1.04 1/2 1 1/2 1 1/5 1/5 1/2 0.47 0.05

1.05 5 5 1 5 1 1 4 2.43 0.27

1.06 5 5 1 5 1 1 4 2.43 0.27

1.07 3 3 1 2 1/4 1/4 1 1.02 0.11

1.00

2.01 2.02 2.03 2.04 2.05 Geom P

2.01 1 5 1 3 1/3 1.47 0.27 Lambda 7.2

2.02 1/5 1 1 1 5 1.00 0.18 CI 0.56

2.03 1 1 1 3 1/4 0.94 0.17 CR 0.491

2.04 1/3 1 1/3 1 1/3 0.52 0.10

2.05 3 1/5 4 3 1 1.48 0.27

1.00

G P

1 0.17

2.46 0.42

1 0.17

0.407 0.07

1 0.17

1.00

G P

1.414 0.67

0.707 0.33

Reliability Availability

Performance 4 1

Reliability

Availability 1

11

What is the relative importance of Availability compared to Reliability in terms of transformer technical condition based on

increased Risk Exposure ?

What is the relative importance of Product Support compared to Performance w.r.t transformer Availability?

Reliability

1

Product Support 1 1/4

Product Support Performance

3

Financial Impact 1 1/5

Availability

Financial Impact People Effects Legal and Compliance Continuity of Supply Environment

1/2 5 2

People Effects 5

1/3

Continuity of Supply 1/5 1/3 1/3 1 1/2

Legal and Complience

1 2 3

2 1/2 1 3

Technical Condition Consequence/Impact

1Environment 1/2 1/3 3 2

Technical Condition 1 2

Consequence 1/2 1

Technical/Impact Condition

Criteria Weighting

with AHP

Strategy Selection and Decision

Model (Output) Preventative

(TBM)

Predictive

(CBM)

Testing the Strategy Selection

and Decision Model

• Ruacana Generator Transformer (11/330 kV, 90

MVA)

• Auas TX Reactor

(400 kV, 100 MVAr)

• Kokerboom TX Transformer (400/220/132 kV,

315 MVA)

• Omburu TX Transformer

(220/66/22 kV, 40 MVA)

• Rossing TX Transformer

(220/11 kV, 40 MVA)

• Karas T-OFF Reactor/Transformer (220/22 kV

15 MVAr)

Input of Sample

Transformers/Reactors

NamPower Life Assessment and Decision Methodology

Input SheetCriteria

Criteria Weight

Subcriteria

Subcriteria Weight

Total weight 100% 100%

Substation Equipment Name Serial Voltage (kV) MVA/r ManufacturerTechnical

Condition

Impact/

Consequence

Priority

Distance

Ruacana TX Gen TRFR Gen T3 26807 11/330 90 ABB/Powertech 1.65 4.02 4.01

Auas TX Reactor K/B 29986 400 100 ABB/Powertech 1.96 2.57 3.21

Kokerboom TX Transformer T22 29977 400/220/132 315 ABB/Powertech 1.13 2.85 2.81

Omburu TX Transformer T12 H8914 220/66/22 40 GEC 1.75 1.83 2.53

Rossing TX Transformer T2 26676 220/11 40 ASEA 2.38 3.55 4.19

Karas T-Off TX Reactor R1 1447884 220/22 15 Elin 3.50 2.29 4.09

Strategy Selection and Decision

Model (Result)

0

1

2

3

4

5

0 1 2 3 4 5

Ruacana

Kokerboom

Karas T-Off

Rossing

AuasOmburu

Preventative

(TBM)

Predictive

(CBM)

Evaluation of 36 of NamPower’s

66 kV Fleet Transformers (Year 1)

Evaluation of 36 of NamPower’s

66 kV Fleet Transformers (Year 2)

Trending Individual Transformer

Data

3.00

1.00 1.00

3.81

2.55 2.55

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

2010 2011 2012 2013 2014

Omatando TX TRFR 1_66/11 kV

Technical Condition

Priority Distance

1.75

1.5

2.25

3.91

3.81

4.07

3.75

3.80

3.85

3.90

3.95

4.00

4.05

4.10

0.00

0.50

1.00

1.50

2.00

2.50

2010 2011 2012 2013 2014

Onunu TX TRFR 1_66/33 kV

Technical Condition

Priority Distance

Benchmarking Survey

Methodology

The sample reviewed had been allocated as follows: Respondents 63

Companies 39

Objective of the technical questionnaire:

To evaluate and benchmark the research rationale followed

in the study against industry practices for evaluating and

motivating practical implementation by NamPower

Technical criteria responses had been divided as per respondent’s

continent and organisation: Africa 38 Utilities 30

USA 12 Private Companies 20

Europe 7 OEM 7

Benchmarking Survey Results Which of the following maintenance strategies do you believe to be adequate for

integration in a decision model for critical transformer life assessment? (Run To

Failure, Fix Time Maintenance, Design Out Maintenance, Skill Level Upgrade,

Condition-Based Maintenance, All)

Run To Failure6%

Fixed Time Maintenance

23%

Design Out Maintenance

12%

Skill Level Upgrade11%

Condition Base Maintenance

39%

All9%

Benchmarking Survey Results Which of the following transformer risk criteria do you believe to be necessary for

integration in a decision model? Rank 1-6 (Effect on Personnel, Financial Impact,

Environment, Brand Reputation, Legal Compliance, Other)

Survey Respondents NamPower Respondents

Effect On Personnel, 1

Financial Impact, 2

Environment, 4Brand

Reputation, 5

Legal Compliance, 3

Effect On Personnel, 1

Financial Impact, 2

Environment, 2

Legal Compliance, 2

Continuity of Supply, 3

Benchmarking Survey Results

Which of the following transformer technical condition criteria do you believe to be necessary for

integration in an input decision model? Rank 1-14 ( Age, Time in Service, Service History, Network

Criticality, Visual Inspection, Chemical Diagnostics, Electrical Diagnostics, Failures, Spare

Availability, OEM Support, Transformer Loading, Transformer Fault Levels, Network Redundancy,

Other)

Survey Respondents NamPower Respondents

Most Important

Least Important

Most Important

Least Important

Conclusion

It is notable that chemical diagnostics, electrical diagnostic, network

criticality and service history (NamPower’s four main criteria) feature in

the response of the most important criteria from all respondents of all

continents reviewed. The criteria had thus been successfully

benchmarked and found to be valid for implementation against industry

best practices

Recommendations Further testing with the incorporation of a larger sample of transformers

as required data becomes available

Investigation for the re-programming of the current spread sheet

program to integrate and automate the decision methodology with the

current NamPower CMMS program.

A family tree of transformer failures per specific OEM is developed and analysed. The OEM’s rated

with the higher transformer family failing history can then be given higher priority in criticality and

action when referred to transformer technical condition.

Utilise sweep frequency response analysis (SFRA) with electrical diagnostics as baseline data

becomes more available

After final testing, approval and integration of the transformer life assessment and decision

methodology, the framework of the methodology to be utilised for the development of life assessment

and decision methodologies and models for all other NamPower network assets starting with

switchgear

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Gerhard Myburgh

Engineer: CBM and Projects

gerhard.myburgh@nampower.com.na

+264 61 2052024

+264 81 1224802