From the Editor:
In our May issue of Transformer Technology, we published Part 1 of Transformer Procurement in High Demand Conditions.
INTRODUCTION
Easy and smooth purchase of a good quality power transformer from reputable supplier, who is already entrusted by the customer, with short delivery time, equipped with preferred accessories, can nowadays be deemed to be at least difficult. To say the same in short, easy purchase of power transformer is difficult. As this sounds contradictory, it can be shortened even more to statement: purchase of power transformer is difficult, or complicated shall we say.
This is not only because the power transformer itself is a complicated structure in which supplier needs to find compromise between customer’s requirements, stresses of different types but also cost and remain competitive compared to other bidders.
This is also because of enormous demand for new transformers in a market that has been now observed for recent years. This is largely driven by new applications for which transformers are needed, eg. green energy transformation or data centres which popped out on a large scale. This has made the worldwide available transformer manufacturing base not sufficient to meet all the requirements in a short time, leading to extended delivery times. While many manufacturers now invest in expansion of their production capacity, the process takes time.
There is a number of occasions at which, active participation of the customer in the process can lead to betterments of the final product or to avoidance of problems that can otherwise come out at some larger stage.
That said, customers are forced to search for new suppliers that can deliver faster than their entrusted partners. Many suppliers, who produce mainly to domestic customers, receive more and more requests to expand their markets. This raises some new challenges to them as they need to learn requirements typical for different regions or climates and adapt to new standards with which they might not necessarily be familiar before.
This expands role of the customer as quality guard, to make sure that at the end of the day, they receive exactly that product they specified, on a date that suits them and that the transformer will remain in service for long, trouble-free period as required and expected. And this is what makes the procurement even more complicated. The customer will first need to correctly specify what they want. Then select supplier, who will be capable to deliver what they want and deliver it on time. When the supplier is selected, the rest should not be just left to trust, especially when the relationship between the customer and manufacturer only begins. There is a number of occasions at which, active participation of the customer in the process can lead to betterments of the final product or to avoidance of problems that can otherwise come out at some later stage.
Building a competent multifunctional team on a customer side able to identify their needs is normally the first thing that should be addressed in order to gain correct view from different perspectives.
This paper describes typically performed steps in the procurement process that help reduce and control risk at this stage. Number of example errors, taken directly from experience of the author and his team colleagues are presented to support statements presented in this elaboration.
TYPICAL SCOPE OF THE PROCESS
A transformer purchaser can carry out a certain number of activities in order to purchase good quality transformer from correct provider. While this does not guarantee 100% reliability of the new unit, it can certainly allow reduction of risk related with purchase of wrong product.
Building a competent multifunctional team on a customer side, capable of identifying their needs, is normally the first thing that should be addressed in order to gain correct view from different perspectives. There will be a number of different stakeholders involved with the life of a transformer who might need to contribute in specification writing. It is therefore recommended to form a multifunctional project team familiar with at least operation and maintenance, engineering or protection and control. Likely, this would also include specialists from purchasing, legal/regulatory compliance, health and safety, environment and project management.
Identification of needs and preparation of detailed specification will be a first task to perform. Here, certain standards will provide a basis to follow. Once a standard is quoted, a number of details is already declared. The multifunctional team will need to adapt the specification to their own expectations so that all important details are described. The specification needs to be clear enough to the manufacturer so that they provide final product that conforms with the expectations. The specification also needs to be detailed enough to allow tender review of all invited manufacturers on the same basis.
The specification needs to be clear enough to the manufacturer so that they provide final product that conforms with the expectations.
The team will then need to decide who they will award with the order. For that to happen, they will need to prepare a list of potential manufacturers that would be invited to the tender. The list will certainly need to include correct manufacturers, capable to produce exactly what the customer wants. Thus, at least a thorough market review will need to be performed. Many purchasers will then follow with audits of selected factories to assess their suitability for the job, to assess risks associated and to identify mitigation needs. Final decision will be performed on this basis.
Placement of the order is not the end of the story and not even close to the end. Manufacturers are expected to fully understand customer expectations when they provide their quote. This is not always successful, and it is vital for the customer to check if all requirements are fully understood and met. This can be done at tender stage and then through a design review. For this task, manufacturers are asked to provide detailed description of the transformer construction for review on a customer side. The requirement for the design review should be agreed upon signing the contract.
Should the design be confirmed correct, another vital interest of the customer is to check quality of manufacturing. It is becoming increasingly common practice to inspect the production process at least once before the core and winding assembly (“active part”) is placed in the tank. This is often done before final dryout or else after final dryout on a day of tanking. The in-process inspections complement the checks started at design review stage, but this time from perspective of manufacturing quality.
Once the transformer is built, the manufacturer plans for its final testing. Again, this is a point to be checked by the customer. It became a standard practice these days to witness the final testing to make sure all parameters are at guaranteed levels and all withstand tests are successfully passed.
Successfully tested transformer is then transported to the customer site as per agreement between the customer and the manufacturer. Duty of installation and commissioning is normally agreed at the contract stage and is carried out by appointed party. It is again important that the buyer monitors activities that are going on during this process and that all problems are correctly addressed.
Preparation of a specification
As it was mentioned in passing above, functional requirements need to be first identified. For a completely new transformer, the method described in IEC 60076-8 [1] can be used to identify rated quantities. In case of a replacement transformer, the basic parameters are normally known. They should be however reviewed as they might need to be updated.
After all, no matter how good the specification is, it is of little value if not analysed and understood by the manufacturer. It happened for example recently to the author that seismic requirements of the customer were completely ignored. Unfortunately, this was only noticed when pointed out during design review and would not be followed if not raised by the customer and their consultant. Apparently, the factory did not have capability of seismic assessment on board and needed to appoint external expert for this part of the design. This took them several months to perform. The manufacturer was selected among others on basis of ability to deliver product faster than their competitors. So where is this benefit now with few months of delay?
Also, it can be challenging to write some parts of the specification. One of Doble’s customers experienced problems related to dimensional incompatibility of replacement transformer which was meant to be connected to GIS and cables. This was caused by errors in drawings used as attachments for the specification. Result? Connections on site had to be reworked.
The multifunctional team can benefit from Cigre publications to aid this process. CIGRE brochure 528, was published in 2013 as a sort of application guide for IEC 60076-1 and IEC 60076-8. It includes a lot of useful information on identification and specification of functional requirements. It is an updated follow up document of CIGRE brochure 156 [4], first published in 2000. It will likely be updated again soon, as IEC 60076-1 standard is currently revised.
Progress Inspections
Once the manufacturer is properly selected, order is placed and design review satisfied the customer, production period starts. This is also a point at which mistakes can happen.
Even with correct design, the manufacturing process can introduce problems that were not foreseen before. This is a complex process that involves many people and uses many methods. Lack of correct training of single member of the team or deficiency of technology can introduce a problem that will limit lifetime of the product.
Such a case was identified recently on a Doble customer’s transformer. Again, the transformer operated only for a few years. From the beginning, it exhibited gassing problems.
The gassing pattern developed over years from low to high temperature overheating and the owner finally decided to withdraw the transformer from service for investigation. The internal inspection revealed that CTC cables were not correctly cleaned from enamel insulation before connections were crimped. This led to overheating of the connections due to elevated resistance of the connections. Clearly, the operator took the correct action to withdraw this transformer from service and they did it at the last moment as the CTC copper was already found partly melted in one of the crimps.
In fact, this kind of problem wouldn’t be easy to identify during progress inspection but still possible. Common moments to perform such inspection are either before final dry out or after it and before tanking. By then the crimps were surely covered with crepe paper and therefore not visible. The problem could potentially be detectable through winding resistance measurement, which is often performed at the final stage before dry out, but the differences could be minor and not easy to identify, especially that all crimps were affected. Some customers however appoint their inspectors for regular inspections along the production process. This approach could be more effective in this case.
Checking of the active part before dry out allows final view of the transformer, still at the moment when corrections can be introduced if necessary.
It is advised that customers play an active role in the procurement process rather than order/pay/wait and belive all will be good.
Inspections at the final stage of manufacturing can be effective anyway in case of other problems. Checking of the active part before dry out allows final view of the transformer, still at the moment when corrections can be introduced if necessary. The inspection normally focuses on correctness of the active part build. It includes among others: Check of alignment of blocking system, cleanliness of the insulation surfaces, robustness of leads supports, looseness of certain items etc. Above all, “if something doesn’t look right, it is probably not right”. In the above transformer, where active part inspection was not correctly performed, it was found gassing due to circulating currents between core frame and the core. This started straight after the first energization and manufacturer decided to carry out internal inspection as part of warranty investigation. It was found that earthing lead of core frame was loosely positioned near sharp edges of the core. Operation of the transformer caused moving the lead towards the sharp edges, deterioration of its insulation and intermittent circulating currents leading to gas formation in the oil. This is a good example of a potential problem that could have been identified and corrected during progress inspection.
Factory Acceptance Tests (FAT)
This is a common practice today to witness factory acceptance tests. Cost of a transformer and consequence of a failure in serivce are high enough motivators to make sure that all tests were performed correctly and were satisfactorily passed.
Consultants normally witness all the tests carried out, or else those that were agreed to witness in advance.Consultants do not only check results, they need to make sure all the tests are performed according to applicable standards.
They also need to make sure the equipment is in calibration so that the test results can be trusted. Finally, they need to carry out all the calculations on their own, on the basis of raw results independently from the manufacturer to make sure there is no mistake in the manufacturer’s calculations.
FAT failures happen to every manufacturer, no matter how renowned. All failures should be reported to the customer, and an investigation should be transparent and successful. Customers therefore often support this process by sending their own witness who is familiar with the task. The author has had an opportunity to act as such a witness on a regular basis. Only during recent years has the author witnessed a number of failures to meet guarantee levels of different types.
Installation and commissioning
One might consider FAT as a final stage of the procurement process. In fact, the transformer still needs to be transported, erected and successfully put to service.
One of Doble’s customers found a problem with their transformer during commissioning checks after installation. It was found that the deenergised tap changer had broken, owing to incorrect connection of the leads from the transformer. Interestingly, this problem was not found either during progress inspections or factory acceptance tests, but only when the de-energised tap changer was operated during commissioning checks.
The manufacturer sourced a replacement de-energised tap changer which was installed at site under the supervision of an expert consultant. Commissioning checks and tests were then successfully completed and the transformer put into service, and it has operated successfully with no reported problems since.
Conclusions
Increased demand for transformers complicates their procurement. Customers are forced to search for new suppliers in the market. This raises new challenges and risks. The correct approach from the customer side can reduce the risks and allow introduction of corrective measures where necessary.
Transformer procurement is a complicated process. It consists of many stages at which the customer needs to pay attention to multiple factors. For this reason, a competent team must be formed to address all the necessary subjects.
As it was presented in the text above, failure to perform the task correctly can result in problems in service or even in a factory delaying dispatch of the unit. It is therefore advised that customers play an active role in the procurement process rather than order/pay/wait and believe all will be good… somehow!
Rafał Zaleski graduated from the Silesian University of Technology in 2002 with a Master of Science degree. Following education, he started gaining his first practical experience in Poland with Energo-Complex company. There, he was responsible for transformer condition assessment through electrical testing and analysis of on-line condition tests results. He joined the Doble Engineering Company in 2009 as Senior Test Engineer where he initially continued with transformer condition assessment expanding his skills across other substation apparatus. Nowadays he holds Principal Engineer position within Doble and he is responsible for consultancy services related to purchase of new-built transformers. He was an active member for two CIGRE working groups dedicated to SFRA measurement and interpretations.
This article was originally published in the September 2026 issue of the Innovations In Insulation Systems magazine.
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