ANSI C57.12.20-1997: STANDARD FOR OVERHEAD TYPE DISTRIBUTION TRANSFORMERS, 500KVA AND SMALLER: HIGH VOLTAGE, 34500 VOLTS AND BELOW: LOW VOLTAGE, 7970/13800Y VOLTAS AND BELOW

ANSI C57.12.20-1997: STANDARD FOR OVERHEAD TYPE DISTRIBUTION TRANSFORMERS, 500KVA AND SMALLER: HIGH VOLTAGE, 34500 VOLTS AND BELOW: LOW VOLTAGE, 7970/13800Y VOLTAS AND BELOWANSI standard C57.12.20-1997 on overhead type distribution transformer

Scope: This standard is intended for use as a basis for determining the performance, interchangeability, and safety of the equipment covered, and to assist in the proper selection of such equipment.

This standard covers certain electrical, dimensional, and mechanical characteristics and takes into consideration certain safety features of single- and three-phase, 60-Hz, mineral-oil-immersed, self-cooled, overhead-type distribution transformers 500 kVA and smaller, with high voltages 34500 volts and below and low voltages 7970/13800Y volts and below. Such transformers may include one or more of the following features:

1) High-voltage, overcurrent protection
2) High-voltage, overvoltage protection
3) Low-voltage, overcurrent protection
4) Low-voltage, overvoltage protection

This standard is intended for use in conjunction with the following American National Standards. All characteristics, definitions, terminology, voltage designations, and tests, except as specified herein, shall be in accordance with these referenced American National Standards. When the following referenced standards are superseded by a revision approved by the American National Standards Institute, Inc., the latest revision shall apply.

Ratings: Kilovolt-ampere ratings are continuous and are based on not exceeding either a 65°C average winding temperature rise or an 80°C hot-spot temperature rise. The temperature rise of the insulating oil shall not exceed 65°C when measured near the top of the tank. Kilovolt-ampere ratings for single-phase and three-phase transformers shall be as shown in Table 1. These ratings are based on the usual temperature and altitude service conditions specified in ANSI/IEEE C57.12.00 .

Voltage ratings for single-phase and three-phase transformers shall be in accordance with Tables 2, 3, and 4. No taps are to be provided unless otherwise specified in accordance with 3.2.2

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