On the spot transformer repair in the far corner of Brazil Transformer technology is not standing still. As well as improving the equipment itself ABB is leading the way on maintenance and support, including on-the-spot the repair for transformers operating in distant locations where return to base would be difficult and exceptionally expensive
When ABB was called in to repair a failed transformer in the world’s largest hydro electric power plant close to Brazil’s the border with Paraguay, the conventional policy of transporting it to the nearest factory was out of the question. The transformer concerned weighed over 180 tons, the roads were poor, risk of further damage high and the nearest factory was 800 miles away.
Instead of taking the transformer to the factory ABB engineers put into effect their policy of taking the factory to the transformer. A fully equipped workshop with clean room was constructed on the site of the power station concerned at Itaipu. The transformer was taken inside, dismantled, repaired, reassembled and tested on the spot.
A power transformer failure can, and usually does, have serious consequences for all parties. Power consumers can lose out as their supply is cut or reduced. This is bad enough for domestic consumers but for industry it can be extremely damaging, threatening their businesses’ survival.
At Itaipu the transformer was damaged when an electric failure occurred. The repair called for a complete replacement of the winding blocks.
It is vital that companies like ABB can respond quickly and flexibly to such serious situations, especially in the developing world where local conditions can be very difficult. This is why several large utilities in South America asked ABB for new solutions that would enable large transformer units to be repaired on site. The main factor was the difficulties of transportation but other issues had to be addressed also. These included:
- Reducing the repair lead time
- Avoiding transportation problems and associated costs
- Ensuring that the same high standards of work where achieved on site as were expected when equipment was returned to the factory
A key component of ABB’s on-site repair process is being able to provide a high voltage test capability. This is a vital service and important both for transformer commissioning and for diagnostic assessment before or after a failure. Since 1992 the performance and reliability of more than 520 transformers has been improved following on site work. So far ABB has carried out more than 96 major on site transformer repairs including equipment produced by other manufacturers. The repairs to the Itaipu hydroelectric power station is the latest in a line of on-site repair successes it is also the largest ever attempted.
How it was done
The specially constructed on-site transformer repair facility at Itaipu required a strong solid foundation supporting a special 20 metre high metal fabrication with a floor area of 500m2. It was built to withstand winds of up to 150km/h and had to remain watertight under heavy rainfall. Inside it had to provide an ultra clean environment where the transformer’s active part, weighing some 180 tons, could be assembled. The clean room area was strictly temperature and pressure controlled. A mobile facility with vacuum, drying and oil treatment was brought on site. Mobile cranes and lifting devices were also erected inside the repair shop.
STEP BY STEP
After draining the oil from the transformer’s active part, the upper core frame was opened and the upper core yoke disassembled. Next all internal leads and the HV winding mechanism were disconnected followed by the windings, main insulation and core winding insulation. The windings were then craned out from the core limbs. The repair included replacing the complete pressboard core insulation with fibreglass. And in order to retighten the core it had to be laid horizontally, a really heavy lifting job.
All factory parts, including the windings and main insulation, arrived fully tested. These were then assembled on-site.
A complex drying process is adopted after assembly. This is made up of a series of vacuum and hot oil circulation cycles.
The final steps are on-site testing and commissioning.
At every step careful checks are carried out to ensure that the repair process is as stringent as it would be had the transformer been taken to an ABB plant. Every phase is conducted strictly to ISO 9001 and ISO 14001 procedures.