IEEE C37.91-2021

$92.63

IEEE Guide for Protecting Power Transformers

Published By	Publication Date	Number of Pages
IEEE	2021

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Category: IEEE

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Description

Revision Standard – Active. Guidelines for protecting three-phase power transformers of more than 5 MVA rated capacity and operating at voltages exceeding 10 kV is provided to protection engineers and other readers in this guide. In some cases, a user may apply the techniques described in this guide for protecting transformers of less than 5 MVA ratings or operating at voltages less than 10 kV. Information to assist protection engineers in properly applying relays and other devices to protect transformers used in transmission and distribution systems is also provided. General philosophy, practical applications, and economic considerations involved in power transformer protection are discussed, with an emphasis on practical applications. Types of faults in transformers are described. Technical problems with the protection systems, including the behavior of current transformers during system faults, are discussed, as well as associated problems, such as fault clearing and post trip reenergization.

PDF Catalog

PDF Pages	PDF Title
1	IEEE Std C37.91 Front cover
2	Title page
4	Important Notices and Disclaimers Concerning IEEE Standards Documents
8	Participants
10	Introduction
11	Contents
13	1. Overview 1.1 General 1.2 Scope 1.3 Word usage
14	1.4 Purpose 1.5 Device numbers 2. Normative references
15	3. Definitions, acronyms, and abbreviations 3.1 Definitions
16	3.2 Acronyms and abbreviations 4. Philosophy and economic considerations
17	5. Types of failures in transformers
18	6. Relay currents 6.1 General
19	6.2 Minimum internal faults 6.3 Maximum internal faults 6.4 Performance of CTs
21	6.5 Reasons for mismatch
23	7. Electrical detection of faults 7.1 General
24	7.2 Fuse protection and self-powered resettable fault interrupters
26	7.3 Differential protection
47	7.4 Overcurrent relay protection
49	7.5 Ground-fault protection
55	7.6 Fault detection for special-purpose transformers
65	7.7 Backup and external fault protection
68	7.8 Temperature relays 7.9 Miscellaneous relays 8. Mechanical detection of faults 8.1 General 8.2 Gas accumulator relay 8.3 Gas detector relay
69	8.4 Pressure relays
72	9. Thermal detection of abnormalities 9.1 General 9.2 Winding hot-spot measurement thermal relays
73	9.3 Calculated thermal model relays 9.4 Top-insulating liquid temperature protection
74	9.5 Fuses or overcurrent relays 9.6 Thermal relays for tank temperature 9.7 Overexcitation protection
76	10. Fault clearing 10.1 General
77	10.2 Relay tripping circuits 10.3 Circuit breakers 10.4 Tripping of remote circuit breakers
79	10.5 Circuit switcher
80	10.6 Fuses 10.7 Self-powered resettable fault interrupters 11. Post-trip analysis prior to re-energizing
81	12. Gas analysis 13. Special protective schemes 13.1 General
82	13.2 Grounding transformer inside the main transformer differential zone
85	13.3 Unbalanced voltage protection for wye-connected, three-legged core-type transformers
86	13.4 Differential protection of single-phase transformers connected in three-phase banks
90	14. Other considerations
91	Annex A (informative) Application of the transformer through-fault-current duration guide to the protection of power transformers
112	Annex B (normative) Examples of setting transformer protection relays B.1 General B.2 Relays for protecting a step-up transformer
119	B.3 Setting relays for a network autotransformer
125	B.4 Relay settings for a transformer supplying energy to distribution systems
129	B.5 Calculating slope for use in a transformer differential relay
132	Annex C (informative) Thermal overload protection C.1 General theory
133	C.2 Winding temperature monitoring on transformer with on-load-tap changer C.3 Limitations of traditional winding temperature indicator
137	C.4 Protection
138	C.5 Microprocessor-based relays for transformer thermal winding protection
139	C.6 Methods for calculating winding temperature
141	Annex D (informative) Phase shift and zero-sequence compensation in differential relays D.1 General D.2 Example
142	D.3 Reasons for using internal compensation
143	D.4 Differential current compensation connections
147	D.5 Examples
151	Annex E (informative) Bibliography
160	Back cover