IEEE C37.91-2008 pdf download IEEE Guide for Protecting Power Transformers
1.Overview
This guide is intended to provide protection engineers and other readers with guidelines for protectingthree-phase power transformers of more than 5 MVA rated capacity and operating at voltages exceeding10 kV. In some cases, a user may apply the techniques described in this guide for protecting transformersofless than 5 MVA ratings or operating at voltages less than 10 kV.
1.1Scope
The scope of this guide includes general philosophy, practical applications, and economic considerationsinvolved in power transformer protection
Emphasis is placed on practical applications. General philosophy and economic considerations inprotecting transformers are reviewed. Types of faults in transformers are described, Technical problemswith the protection systems, including the behavior of current transformers (CTs) during system faults, arediscussed. Associated problems. such as fault clearing and reenergization, are discussed as wel.
1.2 Purpose
The purpose of this guide is to provide protection engineers with information that helps them to properlyapply relays and other devices to protect transformers used in transmission and distribution systems.
2.Normative references
The following referenced documents are indispensable for the application of this document (i.e., they mustbe understood and used. so cach referenced document is cited in text and its relationshin to this document explained). For dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments or corrigenda) applies.
3.Definitions
For the purposes of this guide, the following terms and definitions apply. The Authoritative Dictionary ofEEE Standards Terms (B11″ should be referenced for terms not defined in this clause. Definitions ofseveral terms used in this guide are provided in IEEE Std C37.100.
3,1 harmonic sharing: The principle of summing the magnitudes of the harmonic contents of the threoperating currents in a differential application and checking if the ratio of the sum of the harmoniccomponents and the fundamental frequency component of the operating curent in each phase exceeds aprespecified threshold.
IEEE C37.91-2008 pdf download
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