If there is a temporary overload, forced ventilation can be installed to avoid overheating of the windings on a TRIHAL cast resin dry type transformer. For ratings above 630 kVA, TRIHAL transformers used in the UK have provision for the future fitting of cooling fans as standard, as such forced ventilation can be fitted on to an existing installed transformer to obtain a temporary 40% increase in power. TRIHAL transformers for use in the UK can also be supplied with the fans fitted at the time of manufacture to provide the 40% increase in power. For ratings below 630kVA it is required that the need for forced cooling in the future is advised at the time of order so that the transformer can be designed to accommodate the fans. If cooling fans are to be fitted to a TRIHAL transformer, the following points must be taken into account due to the increase in power rating. a) The cross-sections of the cables or busbar trunking. b) The rating of the transformer protection circuit breaker. c) The sizing of the air intake and outlet apertures in the transformer room for ventilation purposes. d) The service life of the fans, which is much shorter than that of the transformer (3.5 years as against 30 years).
