Tank and Covers 3.2.1 The power transformers shall be of the breathing type or hermatically sealed tank type. The tank shall be manufactured using high quality heavy-gauge steel with all joints welded and pressure tested. The tank bottom, sides and covers shall be adequately reinforced with stiffeners to withstand pressure at least 25% greater than the required operating design value without permanent deformation and It shall permit hoisting of the complete power transformer filled with oil or synthetic liquid and also to dampen transformer noise. If specified a Test Certificate conducted internally shall be provided for review. 3.2.2 If breathing-type power transformers are specified, they shall be provided with a suitably located conservator tank, fitted with a breather filled with silica gel or other suitable dehydrating chemical agent, oil/liquid level indicator and a drain valve. 3.2.3 Inspection openings shall be provided to give access to the internal connections of bushings, winding connections, and ground links. The tank covers and manhole covers shall be provided with suitable lifting eye bolts. The overall unit shall be provided with suitable lifting lugs. 3.2.4 The power transformers shall be equipped with a permanent heavy duty rigid steel base skid assembly suitable for skidding or rolling in any direction as well as for bolting or welding to foundations. The base skid assembly shall have provisions for lifting and jacking the transformer unit. 3.2.5 After fabrication, the tank, radiators, and base shall be chemically cleaned inside and outside and painted with rust inhibiting primer and high quality finish coats. 3.2.6 Hermetically sealed transformers shall be fit with a pressure relief device. If the oil in transformer expands in volume excessively due to any reason it shall rupture a diaphragm and find its way out preventing the pressurization of the transformer. Alarm and trip devices shall be provided for the pressurerelief device. The contacts shall be wired into a terminal box for remote annunciation and tripping functions. 3.2.7 Canopies shall be provided for the transformer devices to shelter from rain. 3.3 Cooling System 3.3.1 Power transformers shall be designed suitably for naturally air cooled (ONAN) for operation at the specified rating. 3.3.2 When specified in the Project Specification and/or data sheets, increased capacity shall be obtained by the addition of one-stage or two-stage fan cooling (ONAF). If fan cooling is not initially required, the power transformer shall be furnished with provisions for future fan cooling, and all components shall be so designed that they are able to cope with increased rating without any modifications (except for the fan cooler’s addition). Transformer rated 10MVA and above shall be rated for ONAF. 3.3.3 Where future installed forced cooling is specified, cooling fan control devices shall be provided on the power transformers. The cooling fans shall be controlled by a high (top) oil temperature relay with provision for a manual override switch The fan control