ANSI C57.12.50 : 1981

REQUIREMENTS FOR VENTILATED DRY-TYPE DISTRIBUTION TRANSFORMERS, 1 TO 500 KVA, SINGLE-PHASE, AND 15 TO 500 KVA, THREE-PHASE, WITH HIGH-VOLTAGE 601 TO 34500 VOLTS, LOW-VOLTAGE 120 TO 600 VOLTS

Institute of Electrical & Electronics Engineers

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1. Scope
    1.1
    1.2
    1.3
    1.4
    1.5
2. Related Standards and Guides
    2.1 General
    2.2 Terminology
    2.3 Revision of American National Standards Referred
         to in This Document
Part I: Basic Electrical and Mechanical Requirements
3. Usual Service Conditions
4. Ratings and Characteristics
    4.1 Kilovolt-Ampere Ratings
    4.2 Kilovolt-Ampere and Voltage Ratings
    4.3 Taps
    4.4 Insulation Levels
    4.5 Polarity, Angular Displacement, and Terminal
         Markings
    4.6 Impedance Voltage
5. Construction
    5.1 Insulation System
    5.2 Accessory Location
    5.3 Nameplate
    5.4 Transformer Connections
    5.5 Tap Changing
    5.6 Lifting Facilities and Stability
    5.7 Grounding Facilities
    5.8 Transformer Enclosure
6. Routine Tests
7. Tolerances
Part II: Other Requirements or Alternatives That May Be
         Specified for Some Applications
8. Other Ratings and Characteristics
    8.1 Other Kilovolt-Ampere Ratings
    8.2 40 degree C Average Ambient Temperature
         Conditions
    8.3 Other Winding Temperature Rises
    8.4 Other Insulation Systems
    8.5 Other High-Voltage Ratings and Connections
    8.6 Y-Y Connected Transformers
    8.7 Increased Neutral Insulation
    8.8 Other Basic Lightning impulse Insulation Levels
         (BILs)
9. Other Construction
    9.1 High-Voltage Connection Arrangements
    9.2 Low-Voltage Connection Arrangements
    9.3 Surge Arresters
    9.4 Unit Substation
    9.5 Temperature Devices
    9.6 Forced-Air Cooling
    9.7 Provision for Future Forced-Air Cooling
    9.8 Space Heaters
    9.9 Current Transformers (or Provision for Their
         Addition in the Future)
    9.10 Terminal Blocks
    9.11 Contacts
    9.12 Jacking and Moving Facilities
10. Other Tests

Abstract

Defines characteristics relating to performance, limited mechanical and electrical interchangeability, and safety of the equipment described, and to assist in the proper selection of such equipment.