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World-first transformer testing: More than meets the eye

We’re using a novel approach to assess the condition of vital, and costly, equipment on the electricity grid and it is attracting national and international attention.

High voltage technician, Luke Gerhard, who works in the field and in a lab testing facility set up at our Kewdale Depot, had the initial idea.

He noticed in the software provided by Austrian company Omicron for equipment used to test the condition of transformers that the instruments could potentially be used to test other devices.

So he decided to test it out on a piece of equipment, called a bushing.

Bushings lined up ready for testing in our HV lab

A bushing is a sleeve or barrier that protects high voltage electricity as it travels from large powerlines into a transformer and it is notoriously difficult to very accurately test when one is about to fail.

The point of knowing if a bushing is about to fail is that when they do they burst and the outcome could be significant.

“The transformer itself, you’re talking millions of dollars; generally what happens when a bushing does fail catastrophically is that there’s a fire, and that fire damages the transformer, and all of a sudden this piece of plant that costs, say $50,000,… has failed and all up its cost a couple of million dollars,” said Luke.

The reason a bushing failure is so dramatic is that bushings are typically filled with oil/paper and covered in porcelain, materials which provide heavy protection to the high voltage electricity flowing through them.

When they burst they cause fires, damage nearby equipment, often destroy the bushing next to them, create missiles of the shattered porcelain, interrupt power supplies for lengthy periods, take months to replace if there isn’t an exact match in storage, divert labour from regular maintenance jobs, not to mention damage a company’s reputation.

Being able to more accurately know their condition has a lot riding on it.

Our new method of bushings testing began in 2014 and it is producing very positive and detailed results.

Using high voltage equipment in the lab, Luke and the high voltage lab team are able to test spare bushings by simulating the conditions experienced in the field.

The deterioration of bushings does not occur at a consistent rate. They are affected by a wide range of factors from fluctuations in voltage due to different levels of demand for power on the grid, to lightning or weather conditions that cause metal to expand or contract. Moisture ingress and internal insulation degradation are the two most common causes of bushing failures.

Testing the state of a bushing is no easy task. Determining the condition of the oil or paper within has always been a complex challenge as it’s not possible to simply open them up and have a look.

With the new approach to testing, we are able to much better determine the expected life of a particular bushing.

“The biggest thing we discovered is that we got a much better picture on the overall condition of a bushing,” said Luke.

Western Power still uses the established testing method but now cross-references the results of both tests to provide better asset failure estimations.

This means significant cost savings.

To provide a sense of the investment in this component on the grid, we had a $14m bushing replacement program, a $1m ongoing testing program, a $3.5m testing process, a $1.5m program to install monitors on the insulators and a $200,000 offline testing program.

Any improvements in efficiency are understandably welcome.

The new approach has identified 215 bushings for replacement and another 79 needing close monitoring.

Already the team believes eight transformers, valued at $18.3M, have been spared damage or replacement because bushings at high risk of failure have been replaced.

The data and detailed information gleaned with the new testing approach is allowing us to be more targeted in how we either proactively replace or maintain bushings to prevent asset failure.

Up until now network providers had a less sophisticated pass/fail approach to testing bushings and are recommended to replace them after 25 to 30 years’ service, despite some bushings possibly having a serviceable life of 40 years or more.

“The new testing process gives an earlier indication about which bushings are likely to fail and gives us more time to replace them,” said Christopher Broughton, Technical Team Lead, who oversaw the testing process.

“Now if the test determines that a 25 year old bushing is in good working order it stays in service.”

Conversely if testing reveals the insulating condition of oil or paper, for example, is poor but can last another 6 months then a new one that meets the exact requirements for a particular section of the grid can be ordered.

And with a manufacturing process that can take up to 6 months, the risk of a section of the grid being shut down for that length of time due to a failure, is greatly reduced.

We have now tested more than 120 bushings.

Bushing manufacturer ABB recently asked Western Power to present a joint paper on the testing to an international audience, as they see it as a considerable achievement.

Other Australian utilities have also contacted us to learn about this new testing approach.

It is not surprising that the ground breaking work in our high voltage laboratory is attracting international attention.

Western Power potentially holds the key to multi-million dollar savings for electricity grids worldwide.

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