Taking part of an international bid opened by the National Administration of Power Plants and Electrical Transmissions (known as UTE) in Montevideo, Uruguay, WEG won the project for the on-site repair of a package of power transformers. The bid was also attended by several other world-class transformer companies.

The scope of work includes the repair of 6 x 37MVA - 550 kV power transformers originally manufactured in 1980. The project is being carried out on-site at the Hydro Power Plant of Constitución, near the capital Montevideo. Having started its operations in 1982, the plant has an installed capacity of 333MVA, generating energy for the country´s electrical system.

The option for repair and retrofit of the existing transformers installed in the plant was a customer's own choice, based on a specific study, evidencing that this option would better meet UTE's requirements. The entire project is part of the government strategy of renewing the country´s electrical system.

Project steps:

The plant has two shutdowns scheduled to take place during the year and the WEG repair and retrofit of the 6 transformers will fit into these two windows. Actually there will be 3 transformers to be repaired in each 3-month interval shutdown. This way, WEG will have to repair and retrofit one 550kV transformer per month. This service will be performed in record time, so the precise planning of each step is one of the project team´s greatest challenge.

- 1st Step: Took place in June 2018, when 3 transformers were taken apart on the field and WEG service and engineering teams were sent to the plant site to analyse the equipment. Back to the factory in Brazil, engineering teams started to provide the electrical and mechanical design, which was then presented to the customer for approval. Upon approval, the coils were manufactured, packed in special tanks and shipped with other materials such as 550KV bushings to UTE in Uruguay.

- 2nd Step: The first 3 transformers were repaired and all retrofit services were concluded according to the project schedule. In this stage the active parts were assembled and the cabling connections were provided. Other repair services for this step included the painting and assembly of tanks, accessories and bushings, VPI process, new oil filling, active parts drying process and final tests with the support of WEG Mobile Laboratory, which is fully equipped with test capacity for 400MVA and 550KV transformers.

- 3rd Step: It is in progress and will be identical to the 2nd step where the remaining 3 transformers will be repaired and retrofitted.

The key point for this project was the extremely short delivery time period. Due to the shutdown of the plant system, WEG only had 3 months to repaid and retrofit each three machines, that is, the engineering and service teams repaired a 550KV transformer per month divided into two gaps with a 180-day interval, where the most complex works were carried out by WEG on site.

From the technical point of view, the transformers have been fully redesigned including complete replacement of windings, insulation materials, 550kV low and high voltage bushings and all protection accessories, as well as the installation of a new cooling system. Existing heat exchangers were replaced by radiators / motor fans (ONAN / ONAF). Calculations for the new radiators maintain the transformers operating within temperature parameters standardized UTE, besides reducing the preventive maintenance services on the cooling system.

Due to the critical scope and impact requirements, this repair and retrofit project became for WEG a key reference for new business opportunities on similar projects worldwide. For this specific customer, the six transformers that were already considered obsolete, will gain new life time with renewed production capacity.

Photo: Transformer before repair

Photo: WEG technical team performing on-site service

Photo: Transformer after repair