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  • Revision:89th Edition, June 5, 1989
  • Published Date:January 2006
  • Status:Active, Most Current
  • Document Language:English
  • Published By:Institute of Electrical and Electronics Engineers (IEEE)
  • Page Count:34
  • ANSI Approved:Yes
  • DoD Adopted:No

  • Foreword

    (This Foreword is not part of American National Standard C37.121-1989.)

    This new standard has been developed to outline the requirements for unit substations, utilizing other documents such as NEMA 201 covering primary substations, NEMA 210 covering secondary unit substations, and a draft document on articulated unit substations compiled by a working group of the disbanded High Voltage Apparatus Coordinating Committee (HVACC).

    This standard was developed by a working group sponsored by the Power Switchgear Assemblies Technical Committee of the Switchgear Section (8SG) of the National Electrical Manufacturers Association (NEMA/SG/5). During the course of the preparation of this standard, coordination was maintained with the Transformer Section (8TR) of the National Electrical Manufacturers Association.

    Suggestions for improvements gained in the use of this standard will be welcome. They should be sent to National Electrical Manufacturers Association, 2101 L Street, NW, Washington, DC 20037.

    This standard covers the requirements for three-phase unit substations for step-down operation in the range of 112.5 kVA through 10 000 kVA at primary voltages of 601 volts through 38 kilovolts.

    The standard is intended for use as the basis for the coordination of equipment by assisting in the selection of components. A variety of designs for unit substations are possible using various combinations of incoming sections, transformer sections, outgoing sections, and transition (throat) sections. Since the transformer section determines the kVA and voltage capabilities of a unit substation, the ratings of the various types of unit substations are described in terms of transformer capability.