IEEE C57.12.24-2009 pdf download IEEE Standard for Submersible, Three-Phase Transformers, 3750 kVA and Smaller: High Voltage, 34 500 GrdY/1 9920 Volts and Below; L ow Voltage, 600 Volts and Below
7.5.2 Tank integrity
The transformer shall be of sealed-tank construction as defined in IEEE Std C57.12.80-2002. Thetransformer shall remain effectively sealed for a top oil temperature range of -5 C to +120 °C underoperating conditions as described in IEEE Std C57.91-1995
The completely assembled transformer tank shall be of sufficient strength to withstand a static internalpressure of 50 kPa gauge (7 psig) without permanent distortion and 103 kPa gauge (15 psig) withoutrupturing. The completely assembled transformer shall be tested for leaks at a minimum of 50 kPa gauge(7 psig) measured above the static head of liquid for not less than six hours. Alternative methods for leakdetection such as helium leak detector method may be used.
The completely assembled transformer tank shall be capable of passing the fault current tests as defined inIEEE Std C57.12.20-2005.
7.5.3 Hardware
All external hardware, nuts, bolts, washers, etc, shall be austenitic stainless steel, silicon bronze, or thefunctional equivalent.
7.5.4 Other material
All valves, fittings. pipe plugs or caps and bushing flanges shall also have corrosion resistance propertiesAny thread sealant used shall be non-conducting.
7.5.5 Cover
The cover shall be welded in place
7.5.6 Hand holes
If a hand hole is required, it shall be welded to the cover, be adequately sized, and be suitably located topermit access to internal components.
7.5.7 Base
The transformer base structure shall consist of bars parallel to the long axis of the transformer, The basestructure shall provide a 40 mm (1 % in) minimum clearance from the floor to the tank bottom, with cornersleft clear for jacking.
7.5.8 Lifting provisions
The lifting provisions shall be permanently attached and arranged on the tank to provide a distributedbalanced lift in a vertical direction for the completely assembled transformer; they shall be designed toprovide a minimum safety factor of 5 assuming a two-point lift. This safety factor of 5 is the ratio of theultimate stress of the mmaterial used to the working stress. The working stress is the maximum combinedstress developed in the lifting provisions by the static load of the completely assembled transformer.
Four lifting lugs shall be provided for lifting the transformer with four slings at a maximum angle of30 degrees with respect to the vertical. The bearing surfaces of the lugs shall be free of sharp edges. Eachug shall have a hole for attaching a 40 mm (1 % in) clevis and shall be located to result in a distributedbalanced lift in a vertical direction.
7.5.9 Grounding provisions
A grounding pad or connecting points shall be provided near the primary bushings for grounding eachcable shield.