Testing times

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Regular testing and monitoring of critical equipment can prolong the service life of ageing power assets.

With the liberalisation of energy markets across the world, the issues of safety and reliability have been thrown to the fore as never before. Power providers are having to up their game as customers grow less tolerant of disruptions to electricity supply, whilst at the same time rising energy demand is putting increased pressure on ageing assets.

Systems are regularly being stretched to the limit of their capacity and as equipment ages it becomes more likely to fail. Catastrophic failure can have dire consequences, such as blackouts, injury or even death. And repair work can run into hundreds of millions of dollars.

But frequent testing and monitoring of key equipment, like transformers, cable systems and switchgears, can help to detect faults before they occur and reduce the likelihood of outages.

Oil analysis

Transformers are widely considered as the most critical pieces of equipment inside power plants because of the large quantity of oil in contact with high-voltage elements.

Industry experts estimate that there are on average five transformer explosions worldwide each week, with the majority caused by electrical faults, triggered by the deterioration of the insulating medium.

In most power transformers, the conductor windings are insulated by paper impregnated with mineral insulating oil. A typical transformer contains 10-12 tonnes of cellulose-based paper and 45 tonnes of oil.

Overtime, heat, oxygen and moisture can degrade this insulation and weaken its mechanical strength.

But regular oil checks will highlight any changes in the condition of the insulation and give early warning that invasive maintenance, perhaps a purification treatment, is needed.

"One of the most important indicators of the condition of a transformer is the oil as an insulating material," says Martin Baur, president and CEO of Austrian electrical testing firm, BAUR Pruf- und Messtechnik.

"Oil insulation is an image of the transformer quality and mobile oil testing devices are usually kept by utilities to check the quality annually or every six months."

"If the quality is changing, like humidity is entering the oil, or dust or other contaminants are detected in the oil, the transformer is likely to fail and maybe explode."

Portable oil testers measure the electric breakdown strength of the transformer insulants. Other devices may look for changes in the transformer's chemical characteristics by recording water or hydrogen content.

As with any condition monitoring test, for oil analysis to be effective, a database of previous test results needs to be maintained in order to track changes in its condition.

For an even more comprehensive analysis, utilities can send oil samples to a laboratory for testing. As Alan Roberts, business development manager Middle East at EA Technology explains: "We use our lab in the UK to provide oil analysis on samples that are returned here."

"We look for other things that portable devices don't check for; we are trying to identify the current condition of the transformer and also indicate its remnant life."

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