Transmission Perspec..

Transmission Perspec..

Eskom Transmission’s Current

Perspective On Power

Transformer and Shunt Reactor


Compiled and presented by

Sidwell Mtetwa (Pr. Eng)


• Definitions

Transmission Network Overview

• Challenges

• Strategies

• Summary

“The The days of our lives are seventy years; and if by

reason of strength they are eighty years, Yet their

boast is only labour and sorrow; For it is soon cut off

and we fly away.”

Psalms 91:10

Life is finite, no matter what.

“The The days of our lives are forty years; and if by reason

of good maintenance they are fifty years, Yet their

significance is only availability and outage; For it is

soon cut off and we are scrapped.”

Life Cycle Management Plan



• The act of keeping an asset in good condition to

perform efficiently and safely the service for

which it is used.

Maintenance Philosophy

• What action to do and when to do it

TMP – Transmission’s Maintenance Philosophy

Transmission Network’s Overview

Transmission has 155 substations with an incoming

voltage of either 132, 220, 275, 400 or 765 kV

• Substations are grouped in 8 grids / regions

• There are 510 Power Transformers ( >125GVA)

• 135 additional transformers planned ( installed by


• The present average age of this transformer fleet is

28 years

Transmission Network’s Overview

• About 80 Shunt Reactors (> 7 GVAr)

• 45 additional shunt reactors required by 2017

• The average age of Transmission’s reactor fleet is

24 years

• 33 different OEMs for transformers and reactors

• 21 different tap changer OEMs

Q u a n t it y











Transmission Network’s Overview

Transmission Tapchangers By Make









D esta


Eng Elec




H aw ker Sid

M itsubishi



Toshib a

Trafo U nion

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TMP - Challenges

1. Unavailability of plant for long outages.

• Maintenance engineers – ensure LTPH and


• Plant operators – security of supply and safety.

2. In carrying out maintenance

– Not enough time.

– Lack of skilled people – risk of further outage

– Lack of OEM support on certain old makes

TMP - Challenges

3. On line processes are insufficient to keep the

plant in service for very long time. Offline

interventions are needed

TMP – Plant Availability

• Network was built with redundancy

• Economic growth exceeded the expectations

• Redundancy no longer existing in some


• During outage – increased risk of failure

(loading / age)

• Some units have conditional avail ability

(fixed tap pos.)

TMP - Skills

• Skills are becoming harder to mature and to


• OEM training is expensive (overseas)

• Lack of extensive exposure after training

• OEM trained staff are quickly recruited in the

private sector

TMP – Skills

• Staff not trained by OEM’s, performing intrusive

work - risk of failure

• Wide spectrum of types installed in the network

• OEMs are no longer in business

• OEMs still in business - designs were


Incident No.1 – Near Miss

• A 15MVA 132/33kV transformer was taken out of service

for a scheduled tap changer maintenance during a

weekend. When the maintenance was completed, the

transformer was re-commissioned and put back on load.

Minutes after taking load, smoke was seen coming out of

the diverter chamber of the transformer.

• The investigation revealed that the transition resistors

were heating the oil, because the resistors were

continually in the circuit due to incorrect wiring.

Incident No.2 – Reduced Capability

• A 500MVA 275/132/22kV autotransformer was taken out of

service for a scheduled tap changer maintenance over a

weekend. This transformer had a design where the diverter is

physically sitting on top of the 132kV bushing. During

inspection, problems were identified on the diverter switches.

• Instead of removing only the diverter switch, the contractor

removed the complete set of bushing and diverter. In attempting

to re-install, the equipment was mishandled and the bushing got

damaged. No spares could be found for this old design.

• The transformer was then modified to run on a fixed tap


Incident No.3

A 145MVAr 765kV Shunt reactor was taken out of

service for maintenance. A person supposed to

clean the pressure relief valve removed the PRV

and oil gushed out.

TMP - Challenges

• All these bring about a complex situation and

Transmission has to manage it for continuity of supply.

• If maintenance is correctly/timeously done – benefits

• If maintenance is incorrectly/not done - consequences

TMP - Challenges

TMP - Challenges

Eskom Transmission considers precise

maintenance philosophy combined with proper

strategies is the key in managing all these


TMP - Strategies

Transmission maintenance philosophy is built with

the following strategies

1. Specify and use low maintenance technologies

• Vacuum tap changers – 300 000 ops

• Welded main covers – no gasket leaks

• RIP bushings – no bushing oil leaks

• Online dryers – preserve paper insulation

• Conservator air bags – eliminate oil oxidation.

TMP - Strategies

Oil tap

Conservator with air bag

TMP - Strategies

RIP bushings with SiR sheds OIP bushing with porcelain sheds

TMP - Strategies

Oil leak on main lid gasket

On line moisture remover

TMP - Strategies

2. Maintenance - as per OEM instruction or 6 yearly

(synchronized with breaker maintenance)

3. Only accredited persons to do intrusive work.

4. Only people trained by OEMs and have post

training experience are accredited

TMP - Strategies

5. Standardizing on components e.g. tap changers

(difficult to keep spares for all types)

6. Repair non OEM supported units using existing

classical supplier for parts or use local suppliers

7. Detailed and frequent inspections

8. Inspection and maintenance records are kept in

an electronic database

TMP - Strategies

TMP - Strategies

TMP - Strategies

Experience has shown us that only OEM trained

technicians with suitable post training experience

can be accredited to perform intrusive



• Asset reliability is a function of maintenance

Transmission’s challenges with maintenance are

– Non availability of plant for outage

– Scarcity of skilled people

– Many OEMs are no longer in business – no


– Some old designs have been discontinued –

no support

– Wide spectrum of component types


• Strategies that have been developed are

– Use of no / low maintenance technologies

– Maintenance as per OEM instruction or 6 yearly

– Only accredited technicians to do intrusive work.

– Only people trained by OEMs and have post training

experience are accredited

– Standardizing on components like tap changers

– Get specs and manufacture components locally – quality

risk. Else do modifications

Maintenance Categories

Transmission maintenance is categorized in

three types

1. Short term maintenance

2. Medium term maintenance

3. Long term maintenance

Thank Thank Thank Thank Thank You You




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