Opening a transformer: A job for specialists

A fault in a large transformer at a substation is a headache for the supplier and a challenge for those responsible for the maintenance of the facility. The most common solution is to haul the mechanism to a point where it can be loaded onto a lorry and taken to the factory for review and repair. A complex and costly endeavour.  

The Omexom Specialists Business Unit has another answer: the fault permitting, the team is able to open and repair transformers of all types and sizes onsite. On this occasion, the challenge was of singular proportions: a 100,000 kVA transformer at an ENDESA substation in Santa Coloma de Gramanet, Barcelona, a huge machine weighing 133,500 kg, made in 1968, had failed. As Omexom Specialists Business Manager, Didac Roses, explains, “It suffered a discharge in its uppermost protection.” The evidence pointed to an insulation failure. “When feeding voltage to the transformer, there was a discharge of Buchholz, which means that gas had been produced inside the transformer. We had to figure out what caused the production of gas, which typically occurs when the mechanism’s insulation fails,” added Agustín Redondo, technician in charge of singular field projects for Omexom Specialists.

To confirm the extent of the failure, the transformer had to be opened, that is, the huge, heavy lid that hermetically seals the casing needed to be lifted. First the giant machine was hauled on rails to a point in the substation where it was possible to work in strict compliance with all safety protocols. After roughly 48,000 litres of cooling oil had been drained from the unit and the screws securing the lid were removed, the most delicate part of the job began: a powerful crane hoisted the 18 tonne lid while the team from Omexom Specialists guided the manoeuvre with ropes to prevent the lid from turning and hitting the apparatus it is designed to protect.


Didac Roses recalls, “This was not a very typical job, but Omexom Specialists had done it a few times. Each transformer has its tricks and peculiarities.”  For that reason, a prior study is always performed and an experienced technical team capable of adapting to any machine is employed.

A visual inspection confirmed their suspicions: the insulation had failed. As Agustín Redondo explains, “An insulation failure occurs because the insulating material degenerates. Over time, the cardboard and wood lose their insulating qualities. That’s primarily why transformers fail.”

The fault was so significant that it could not be repaired onsite, as Omexom Specialists have been able to do on other occasions. So the huge lid was replaced, a manoeuvre even more delicate than lifting it. Ultimately, ENDESA decided to scrap the machine.

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