Thomas Marks: How has the supply of formed coils changed over the years?

James Stevens: Today, there's an expectation for assets to last for decades. The various quality measures required to allow for this have changed quite drastically. We are now carrying out thermal cycle and voltage endurance tests to simulate the through-life performance of the coils.

To protect their products from moisture ingress, and in turn, support their longevity, OEMs have typically manufactured rotating machines using vacuum pressure impregnation or VPI technology.

However, there has been some confusion in the repair market around what is better, VPI or resin rich. The OEMs use VPI, so surely, it's better? In fact, particularly in high-voltage applications, VPI isn't always the answer.

If the VPI process is tried and tested and carefully controlled, it can certainly be a good choice. However, in the repair market particularly, resin-rich tends to be preferred. In high-voltage applications, it has various advantages, such as a lower void content where it matters, a lower partial discharge (PD) result and longer service life.

Additionally, you can reach a point where VPI tanks are only so big, and you can only fit a certain size stator in them. Repair companies can't physically VPI a stator bigger than their tanks can accommodate, so they must turn to resin rich instead.

The biggest change comes with supporting customers in creating a specification that is applicable to the repair market.

Moving away from subjective requirements is also a new development. 'No voids to the naked eye' is quite often found in specifications for coils. Subjectively, somebody with better eyesight or better lighting could spot a void that, perhaps, others couldn't. The technology is now available so that we can have measurable metrics for the quality of a coil.

“The technology is now available so that we can have measurable metrics for the quality of a coil."

We can put in measurable requirements, such as testing for a low PD number and good tan delta results. This is fundamentally what you're trying to achieve when we say, 'no voids.' Ultimately, you want a very homogenous insulation mass, with as much mica in there as possible, suspended in resin and without any voids.

TM: In your view, what are the biggest challenges the repair industry is currently facing?

JS: COVID-19 has made planned maintenance difficult. Where groups of people need to converge in one place, it is challenging. So unplanned maintenance has increased.

Aside from the pandemic, the other challenge we're facing is an influx of low cost and low quality products.

The supply base into the repair market hasn't necessarily always communicated what quality is and what quality means to the end-user.

This is a problem because an end-user may receive tenders for repairing their equipment, and on paper, they look similar; only one is cheap, and one is more expensive.

Historically, the warranty period offered for the cheap and more expensive options has been very much the same. So, unfortunately, if you're an end-user looking at a solution that costs less with the same warranty period and you're not clear on what the benefits of either are, it is difficult to justify not picking the cheaper option. The solution here is to improve our communications on the benefits of quality. These are a much longer asset life, a potentially more efficient machine when in operation, and once repaired, a better machine than it was originally out of the box.

So it's nice to see magazines like Renew talk about the circular economy, the repair industry, and what these benefits are to the end-user.

TM: Are there some opportunities that you're grasping for the future?

JS: A large generator or motor has a considerable amount of material in it.

If you can repair that asset and put it back into service at improved efficiency and quality levels, you have the best of both worlds: a long-lasting frame and asset life and modern-day efficiency.

“We expect one of our sets of coils to last decades, and not only that but perform far more efficiently in service."
We often see brand-new motors and generators coming up for repair, particularly motors, with six to 18 months of service – it is hugely inefficient. If you expect a service life of more than two years, the repair market can improve assets that originally weren't fit for purpose.

We expect one of our sets of coils to last decades, and not only that but perform far more efficiently in service.

TM: What about the Internet of Things or Industry 4.0?

JS: Rather than having a machine fail in service, and all the stress, downtime, and unplanned maintenance that comes with that, we can instead predict when assets will need repairing. This allows end-users to plan and schedule maintenance for quiet periods in production, for example.

The growth in data available also allows us to learn. Partial discharge monitoring has come a considerable way in the last five to ten years. We can learn about PD, how it develops, and its effect on machine efficiency and operating conditions to develop our products.

We're now working closely with organisations that carry out condition monitoring from the design stage.

We're able to embed monitoring within the coils or the rewind. We're collaborating with these organisations so that we can start to predict asset life from the design stage.

Right now, we have conditioning companies, coil makers, repair companies, and end-users, all working together to collaborate, learn, and improve the product to reduce downtime and improve efficiency.

TM: What is the one thing you'll be telling your customers about the repair industry?

The older frames tend to have more space in them, which allows you to put more insulation – and sometimes even more copper – into the coil so that you end up with a much better asset.

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