IEEE C57.12.26-1992 pdf free.IEEE Standard for Pad-Mounted,Compartmental-Type, Self-Cooled,Three-Phase Distribution Transformers for Use With Separable Insulated High-Voltage Connectors (34 500 Grd Y/19 920 V and Below;2500 kVA and Smaller).
IEEE C57.12.26 A pad-mounted,compartmental-type transformer shall consist of a tank with high-voltage and low-voltage cableterminating compartments, as shown in Fig 3 or Fig 7.The compartments shall be separated by a barrier of metal orother rigid material.
Cabinet security shall be evaluated in accordance with the test procedures and requirements of the design test methodfor cabinet security described in ANSI C57.12.28-1988[1].
The high-voltage and low-voltage compartments shall be located side-by-side on one side of the transformer tank.When viewed from the front, the low-voltage compartment shall be on the right.
Each compartment shall have a door that is constructed so as to provide access to the high-voltage compartment onlyafter the door to the low-voltage compartment has been opened. There shall be one or more additional fasteningdevices that must be removed before the high-voltage door can be opened. Where the low-voltage compartment dooris of a fiat panel design, the compartment door shall have three-point latching with a handle provided for a lockingdevice.Hinge pins and associated barrels shall be constructed of corrosion-resistant material, passivated AISIType304 or the equivalent.
The transformer tank and compartments shall be so constructed as to limit disassembly, breakage, and prying open ofany doors, panels, and sills with the doors in the closed and locked position.
The bottom edges of the compartment shall be so constructed as to provide for the use of hold-down devices that areaccessible only from inside the compartments.The transformer shall be provided with lifting provisions that are permanently attached and arranged on the tank insuch a manner as to provide a distributed balanced lift in a vertical direction for the completely assembled transformer.The transformer shall be designed to provide a safety factor of 5.The safety factor of 5 is the ratio of the ultimate stressof the material used to the working stress. The working stress is the maximum combined stress developed in the liftingprovisions by the static load on the completely assembled transformer.
The electrical characteristics of the completely assembled high-voltage connectors shall be as shown in Table 4.Theelectrical characteristics and clearances of the completely assembled low-voltage terminals shall be as shown in Table 3.IEEE C57.12.26 pdf  download.