Dramatic increases in the cost of raw materials have sent the price of new power transformers soaring, yet global demand is such deliveries are often quoted in months or even years. As a result, there is a growing interest in services that will extend the life and increase reliability of existing transformers. And those services are exactly what Alstom Grid’s, Service Business has been set up to provide.
In 2005, the price of copper on world markets was less than $4,000 per tonne. At the end of 2010, that price had risen to $9,000 per tonne. There is a lot of copper in a power transformer – not to mention transformer steel, which has also seen large price increases – so it is inevitable that the price of transformers has also risen steeply. The result is that budgets for replacing ageing transformers, which looked perfectly reasonable and adequate just a few years ago, now fall woefully short of the mark.
For this reason, utilities and other users of power transformers are being forced into a position where their only option is to delay replacement as long as possible, even though this means, in many cases, keeping transformers in service that have long passed the end of their design life. This course of action is not without its problems. In particular, it leads to an increased risk of in-service transformer failures.
Such failures are potentially disruptive and costly, not only for utility companies that face revenue penalties if they fail to meet Ofgem targets for consumer minutes lost, but also for industrial organisations where an out-of-service plant can easily result in production losses running to thousands of pounds an hour. And, when a power transformer fails, difficulties in finding the money for a replacement are only part of the problem.
Because of the strong and growing demand for power transformers from the emerging economies, there is a world shortage of manufacturing capacity, which means that delivery times of many months are typical and, particularly for the largest types, delivery times well in excess of a year are by no mean unusual. In other words, if a transformer fails, its owner not only faces a huge chunk of unplanned expenditure, they may well also have to wait a very long time before a replacement arrives and their operations can be returned to normal.
What’s to be done? The answer is to look after in-service transformers very carefully so as to extend their lives and minimise the risk of failure and, if the worst happens and a transformer does fail, to investigate fully the possibility of repairing rather than replacing it.
All of this falls within the scope of the new Alstom Grid’s Service Business, which has recently started operations from fully refurbished and comprehensively equipped premises in Stafford. These new premises are adjacent to Alstom Grid’s main power transformer factory, which is now the UK’s largest manufacturing plants for power transformers.
Alstom Grid’s Service Business is North Europe’s largest transformer service provider and has a dedicated site team of 29 skilled employees with a wealth of transformer and tap changer experience. The business’s new premises in Stafford include a 2000 m2 workshop, adding up to the 3,000 m2 service workshop, with 120 tonne, 30 tonne and 20 tonne cranes, vertical and horizontal winding machines, a vacuum process oven, silicone process plant, HV test module and oil laboratory. Transformers in the voltage range 3.3 – 132 kV with ratings up to 100 MVA can be handled. Larger units can be considered on a bespoke project basis.
Services available include condition assessment, fault investigation, manufacture of replacement windings, core refurbishment, oven processing, re-design and re-manufacture, general refurbishment, modernisation and extension with comprehensive HV testing.
While these facilities and services repair damaged transformers, much of the Service Business’s work ensures that transformers deliver the highest possible level of in-service reliability, with the minimum risk of failure. The key to achieve these objectives is regular condition assessment, together with carefully planned and properly implemented routine maintenance.
“We can, of course, provide all of these services for our clients,” said Philip Inskip, Business Manager for Alstom Grid’s - Transformer Services Business, “but there is one small snag – power transformers are not exactly portable. It’s one thing to bring a transformer to our premises for major refurbishment or repair – and, indeed we have special transport systems in place for doing just that – but it’s hardly convenient to bring a transformer in for routine assessment and maintenance. For this type of work, we take our services to the transformer.”
This is made possible by the mobile nature of the new equipment the Service Business has at its disposal. Firstly they have a mobile test facility that has been designed to fit into a 13-meter container. Based on the latest static frequency technology, this module can be transported to site anywhere in the UK or Europe and has the capability of performing a wide range of HV tests including partial discharge measurements. This system is supported by a wide range of portable diagnostic equipment enabling Alstom Grid’s Transformer Service to comprehensively assess the condition of a transformer or to identify a suspected fault.
Secondly the oil process plant is equipped for vacuum processing of transformer oil and in addition to moisture removal, degassing and filtering. It incorporates oil regeneration columns, acid and sludge removal facilities, and can treat oil to minimise the effects of corrosive sulphur. It even has its own generator set to allow completely standalone operation when no external power source is available. As would be expected, testing is an important part of the vehicle’s operations and, because of this, it has a well-equipped on-board oil testing laboratory.
“Testing an oil sample from a power transformer is rather like analysing a blood sample from a human patient,” said Jon Sherwood, an expert transformer design engineer who works in the Service Business. “With a little care and by using the right equipment to evaluate it, the oil sample will tell you a lot about the health of the transformer as well as giving a valuable indication of what steps, if any, need to be taken to keep it in good working order.”
Because oil testing is so central to the work carried out in the mobile Oil Process Plant, the Alstom Grid engineers decided that it should be fitted with the latest in portable oil test sets – the new OTS80PB from Megger. Among the features that particularly appealed to the engineers about this instrument, which is capable of testing at up to 80 kV, were its robust test vessel that has been specifically designed to help users deal with the practical aspects of oil sampling, and the unique test chamber drain for spilt oil, which makes it easy to maintain the necessary high standards of cleanliness in the testing laboratory.
Also of importance in this application are the automatic oil temperature measurements, support for both output voltage and output current breakdown detection, and the facilities for storing results internally and on standard USB memory sticks. The OTS80PB is complemented in the vehicle’s oil test laboratory by a Karl Fischer test set, which was also supplied by Megger.
“With our portable laboratory and the other facilities of our mobile test module we can help our customers to greatly extend the life of their transformers, while also improving reliability,” said Philip Inskip, “and, with the even wider range of options we’ve got at our new workshop in Stafford, we can repair failed transformers and, in many cases, re-design existing units for new applications and refurbish them to extend the life of a customer’s asset.”
“We believe the services we provide offer a genuine solution to the present-day problems of high transformer prices and long deliveries. Treat your old transformers well, keep them fit and healthy and, just like you and me, they’ll have long useful lives!”
