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Eskom <strong>Transmission</strong>’s Current<br />

<strong>Perspec</strong>tive On Power<br />

Transformer and Shunt Reactor<br />

Maintenance<br />

Compiled and presented by<br />

Sidwell Mtetwa (Pr. Eng)


Contents<br />

• Definitions<br />

• <strong>Transmission</strong> Network Overview<br />

• Challenges<br />

• Strategies<br />

• Summary


“The The days of our lives are seventy years; and if by<br />

reason of strength they are eighty years, Yet their<br />

boast is only labour and sorrow; For it is soon cut off<br />

and we fly away.”<br />

Psalms 91:10<br />

Life is finite, no matter what.


“The The days of our lives are forty years; and if by reason<br />

of good maintenance they are fifty years, Yet their<br />

significance is only availability and outage; For it is<br />

soon cut off and we are scrapped.”<br />

Life Cycle Management Plan


Definitions<br />

Maintenance<br />

• The act of keeping an asset in good condition to<br />

perform efficiently and safely the service for<br />

which it is used.<br />

Maintenance Philosophy<br />

• What action to do and when to do it<br />

TMP – <strong>Transmission</strong>’s Maintenance Philosophy


<strong>Transmission</strong> Network’s Overview<br />

• <strong>Transmission</strong> has 155 substations with an incoming<br />

voltage of either 132, 220, 275, 400 or 765 kV<br />

• Substations are grouped in 8 grids / regions<br />

• There are 510 Power Transformers ( >125GVA)<br />

• 135 additional transformers planned ( installed by<br />

2017)<br />

• The present average age of this transformer fleet is<br />

28 years


<strong>Transmission</strong> Network’s Overview<br />

• About 80 Shunt Reactors (> 7 GVAr)<br />

• 45 additional shunt reactors required by 2017<br />

• The average age of <strong>Transmission</strong>’s reactor fleet is<br />

24 years<br />

• 33 different OEMs for transformers and reactors<br />

• 21 different tap changer OEMs


Q u a n t it y<br />

180<br />

160<br />

140<br />

120<br />

100<br />

80<br />

60<br />

40<br />

20<br />

0<br />

<strong>Transmission</strong> Network’s Overview<br />

<strong>Transmission</strong> Tapchangers By Make<br />

ABB<br />

AEG<br />

AEI<br />

Alsthom<br />

Ansaldo<br />

ASEA<br />

Asgen<br />

ATC<br />

D esta<br />

Elin<br />

Eng Elec<br />

Ferranti<br />

Fuji<br />

Fuller<br />

H aw ker Sid<br />

M itsubishi<br />

Osaka<br />

MR<br />

Toshib a<br />

Trafo U nion<br />

U nknown<br />

Manufacturers<br />

Series1


TMP - Challenges<br />

1. Unavailability of plant for long outages.<br />

• Maintenance engineers – ensure LTPH and<br />

safety.<br />

• Plant operators – security of supply and safety.<br />

2. In carrying out maintenance<br />

– Not enough time.<br />

– Lack of skilled people – risk of further outage<br />

– Lack of OEM support on certain old makes


TMP - Challenges<br />

3. On line processes are insufficient to keep the<br />

plant in service for very long time. Offline<br />

interventions are needed


TMP – Plant Availability<br />

• Network was built with redundancy<br />

• Economic growth exceeded the expectations<br />

• Redundancy no longer existing in some<br />

substations<br />

• During outage – increased risk of failure<br />

(loading / age)<br />

• Some units have conditional avail ability<br />

(fixed tap pos.)


TMP - Skills<br />

• Skills are becoming harder to mature and to<br />

retain<br />

• OEM training is expensive (overseas)<br />

• Lack of extensive exposure after training<br />

• OEM trained staff are quickly recruited in the<br />

private sector


TMP – Skills<br />

• Staff not trained by OEM’s, performing intrusive<br />

work - risk of failure<br />

• Wide spectrum of types installed in the network<br />

• OEMs are no longer in business<br />

• OEMs still in business - designs were<br />

discontinued


Incident No.1 – Near Miss<br />

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

for a scheduled tap changer maintenance during a<br />

weekend. When the maintenance was completed, the<br />

transformer was re-commissioned and put back on load.<br />

Minutes after taking load, smoke was seen coming out of<br />

the diverter chamber of the transformer.<br />

• The investigation revealed that the transition resistors<br />

were heating the oil, because the resistors were<br />

continually in the circuit due to incorrect wiring.


Incident No.2 – Reduced Capability<br />

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

service for a scheduled tap changer maintenance over a<br />

weekend. This transformer had a design where the diverter is<br />

physically sitting on top of the 132kV bushing. During<br />

inspection, problems were identified on the diverter switches.<br />

• Instead of removing only the diverter switch, the contractor<br />

removed the complete set of bushing and diverter. In attempting<br />

to re-install, the equipment was mishandled and the bushing got<br />

damaged. No spares could be found for this old design.<br />

• The transformer was then modified to run on a fixed tap<br />

position.


Incident No.3<br />

A 145MVAr 765kV Shunt reactor was taken out of<br />

service for maintenance. A person supposed to<br />

clean the pressure relief valve removed the PRV<br />

and oil gushed out.


TMP - Challenges<br />

• All these bring about a complex situation and<br />

<strong>Transmission</strong> has to manage it for continuity of supply.<br />

• If maintenance is correctly/timeously done – benefits<br />

• If maintenance is incorrectly/not done - consequences


TMP - Challenges


TMP - Challenges<br />

Eskom <strong>Transmission</strong> considers precise<br />

maintenance philosophy combined with proper<br />

strategies is the key in managing all these<br />

challenges


TMP - Strategies<br />

<strong>Transmission</strong> maintenance philosophy is built with<br />

the following strategies<br />

1. Specify and use low maintenance technologies<br />

• Vacuum tap changers – 300 000 ops<br />

• Welded main covers – no gasket leaks<br />

• RIP bushings – no bushing oil leaks<br />

• Online dryers – preserve paper insulation<br />

• Conservator air bags – eliminate oil oxidation.


TMP - Strategies<br />

Oil tap<br />

Conservator with air bag


TMP - Strategies<br />

RIP bushings with SiR sheds OIP bushing with porcelain sheds


TMP - Strategies<br />

Oil leak on main lid gasket<br />

On line moisture remover


TMP - Strategies<br />

2. Maintenance - as per OEM instruction or 6 yearly<br />

(synchronized with breaker maintenance)<br />

3. Only accredited persons to do intrusive work.<br />

4. Only people trained by OEMs and have post<br />

training experience are accredited


TMP - Strategies<br />

5. Standardizing on components e.g. tap changers<br />

(difficult to keep spares for all types)<br />

6. Repair non OEM supported units using existing<br />

classical supplier for parts or use local suppliers<br />

7. Detailed and frequent inspections<br />

8. Inspection and maintenance records are kept in<br />

an electronic database


TMP - Strategies


TMP - Strategies


TMP - Strategies<br />

Experience has shown us that only OEM trained<br />

technicians with suitable post training experience<br />

can be accredited to perform intrusive<br />

maintenance


Summary<br />

• Asset reliability is a function of maintenance<br />

• <strong>Transmission</strong>’s challenges with maintenance are<br />

– Non availability of plant for outage<br />

– Scarcity of skilled people<br />

– Many OEMs are no longer in business – no<br />

spares<br />

– Some old designs have been discontinued –<br />

no support<br />

– Wide spectrum of component types


Summary<br />

• Strategies that have been developed are<br />

– Use of no / low maintenance technologies<br />

– Maintenance as per OEM instruction or 6 yearly<br />

– Only accredited technicians to do intrusive work.<br />

– Only people trained by OEMs and have post training<br />

experience are accredited<br />

– Standardizing on components like tap changers<br />

– Get specs and manufacture components locally – quality<br />

risk. Else do modifications


Maintenance Categories<br />

• <strong>Transmission</strong> maintenance is categorized in<br />

three types<br />

1. Short term maintenance<br />

2. Medium term maintenance<br />

3. Long term maintenance


Thank Thank Thank Thank Thank You You<br />

You<br />

You<br />

You<br />

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