IEEE C57.12.21-1992 pdf free.American National Standard Requirements for Pad-Mounted,Compartmental-Type Self-Cooled,
Single-Phase Distribution TransformersWith High Voltage Bushings; High-Voltage,34500 GRYD/19920 Volts and Below; Low-Voltage,240/120 Volts; 167 kVA and Smaller.
IEEE C57.12.21 This standard is intended for use as a basis for determining performance, interchangeability, and safety ofthe equipment covered, and to assist in the proper selection of such equipment.
This standard covers certain electrical, dimensional， and mechanical characteristics and takesinto consideration certain safety features of single-phase, 60 Hz, mineral-oil-immersed, self-cooled, pad-mounted, compartmental-type distribution transformers with high-voltage bushings.These transformersare rated 167 kVA and smaller,with high-voltages of 34500 GRD/199o0 volts and below for operationbetween one phase and grounded neutral, and low-voltage of 240/120 volts.These transformers aregenerally used for step-down purposes from an underground primary cable supply.
NOTE—Refer to latest federal regulations concerning polychlorinated biphenyl (PCB) contaminations in transformers.
This standard covers bushing and terminal arrangements for both radial and loop feed systems.1.4 This standard does not cover the electrical and mechanical requirements of any accessorydevices that may be supplied with the transformer.
All characteristics, definitions, terminology, voltage designations, and tests, except as otherwise specifiedherein, shall be in accordance with the following American National Standards (see 2.2):
ANSI C57.12.00-1987，American National Standard Requirements for Overhead-Type DistributionTransformers,500 kVA and Smaller; High-Voltage, 34,500 Volts and Below;Low Voltage,7970/13800 YVolts and Below.
ANSI C57.12.20-1988，American National Standard Requirements for Overhead-Type DistributionTransformers, 500 kVA and Smaller; High-Voltage,34,500 Volts and Below; Low-Voltage, 7970/13800 YVolts and Below.
ANSI C57.12.28-1988，American National Standard for Switchgear and Transformers—Pad-MountedEquipment—Enclosure Integrity.
ANSI C57.12.70-1978(Reaff.1987),American National Standard Terminal Markings and Connections forDistribution and Power Transformers.
No applied voltage test is required on the high voltage winding. Induced voltage tests shall be performedby applying between the terminals of one winding a voltage that will develop from the high-voltage lineterminals to ground a voltage of 1000 volts plus 3.46 times the rated transformer winding voltage, in nocase shall the line to ground voltage developed exceed 40,000 volts for 125 kV BlL and 50,000 volts for150 kV BIL.For this test the neutral terminal shall be grounded.
A pad-mounted, compartmental-type transformer shall conform to ANSI C57.12.28 and consist of a tankwith high voltage and low-voltage cable terminating compartment, as shown in figure 1.The compartmentshall be separated by a barrier of metal or other rigid material.
The high-voltage and low-voltage compartments shall be located side-by-side on one side of thetransformer tank. When viewed from the front, the low-voltage compartment shall be on the right.
Access to the terminal compartments shall be provided by a single door or by individualcompartment doors. If individual compartment doors are provided, they shall be so constructed as toprovide access to high-voltage compartment only after the door to the low-voltage compartment has beenopened.There shall be one or more additional captive fastening devices that must be disengaged beforethe high-voltage door can be opened. Where the low-voltage compartment door is of a flat-panel deign, orwhere only a single door is provided, the door shall have three-point latching with a handle provided for alocking device. lf a lit-up hood or single door provides access to both the high-voltage compartment andthe low-voltage compartment,one-point latching with provision for a locking device shall be provided,along with an additional door or lift-out panel that must be removed before access can be gained to thehigh-voltage compartment.IEEE C57.12.21 pdf download.