26 Thomas Meets
Change is in the wind Thomas Marks, General Manager of the Association of Electrical & Mechanical Trades (AEMT), spoke to James Stevens, Sales and Marketing Director of Preformed Windings, about how motor coil technology has developed over the years and how current technology is supporting the drive for increased efficiency and reliability in rotating machinery. 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 resinrich. 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 Quarter 4 2021
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. 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 lowcost and lowquality 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
James Stevens, Sales and Marketing Director at Preformed Windings.
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
“The technology is now available so that we can have measurable metrics for the quality of a coil."
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 www.theaemt.com
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