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Forward

(This Foreword is not a part of IEEE C57.116-1989, IEEE Guide for Transformers Directly Connected to Generators.)

ANSI/IEEE C57.12.00-1987, IEEE Standard General Requirements for Liquid Immersed Distribution, Power, and Regulating Transformers, and other related C57 series standards provide guidance to users regarding transformer application, design, connections, performance characteristics, testing etc. However, transformers, directly connected to generators experience excitation and short-circuit duties beyond those covered in the C57 series. Therefore, in 1979, the IEEE Transformers Committee decided that an application guide for such transformers was needed by the industry. Accordingly, a working group was formed and a guide prepared. This guide describes the selection, application, and specification considerations for the unit and unit auxiliaries transformers, taking into account their connections, voltage and kilovoltampere ratings, and excitation and through-fault capabilities during possible operating conditions, both normal and abnormal. Also included are load-tap changing and isolated phase bus-duct heating considering This guide does not address phasing procedures, basic impulse level selection, or loading practices.

This guide is based on the latest knowledge, design, and application experience of the industry. It is intended to provide guidance to application and specification engineers and therefore its use is strictly voluntary. Its use may become mandatory only when required by a duly constituted legal authority or when specified in a contractual relationship.

Scope

This guide describes selection and application considerations for the unit transformer and unit auxiliaries transformer. Consideration is given to connections that include direct connection and connections through generator breakers and load break switches. The considerations referred to in this guide apply to hydroelectric and thermal electric generating stations. Various transformer connections and possible operating problems under normal and abnormal conditions are treated.

Phasing procedures, basic impulse insulation level selection, and loading practices are not covered.