Uprating

 

Most power transformers can have their rating improved on-site by Rosh Engineering with minimal disruption to the network. Uprating transformers has three key advantages:

  1. A higher MVA rating saves the costs associated with buying new transformers.
  2. It also saves the disruption to the network & the site associated with replacing plant.
  3. With a lower operating temperature the expected life of the transformer is increased.

The ability of a transformer to dissipate its losses without exceeding the specified temperature rises, as laid down in standards BS171 and IEC76, determines its rating. An increase in the MVA rating by improving the cooling through a re-design of the existing arrangement or by the addition of ancillary equipment is often possible. Improving the rating in this manner can be a cost effective method of realising the full asset value of transformers.

Before recommendations are made a thermal appraisal of the existing cooling arrangement is carried out. New designs are prepared and the necessary equipment specified and procured. Site installation and commissioning complete the service.

A re-design of the cooling can require, new cooling radiators, heat exchangers, oil circulating pump or just cooling fans as necessary.

All designs are supported by detailed thermal calculations giving top oil rise, average winding rise and hottest spot temperature at the enhanced rating. If desired the emergency rating in a 5°C ambient is also given.

Rosh have now up-rated more than 225 transformers throughout the UK and mainland Europe ranging in size from 800kVA to 90MVA. The average rating improvement being 38%.

The average age of a transformer when uprated is 39 years old, with 52 years old being the oldest at the time of the enhancement work. Typical uprating projects are:

·         800kVA uprated to 1250kVA

·         1000kVA uprated to 1800kVA

·         7.5 MVA uprated to 11.25MVA

·         10MVA uprated to 13MVA, emergency rating 17MVA

·         12.5MVA uprated to 18MVA, emergency rating 27 MVA

·         12/24MVA emergency rated transformer uprated to the BS171 rating

·         15MVA uprated to 23MVA, emergency rating 27MVA

·         17.7MVA uprated to 25MVA

·         60MVA uprated to an emergency rating of 80MVA by free standing heat exchangers

·         60MVA uprated to an emergency rating of 90MVA by free standing heat exchangers

 


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