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Transformer Protection Application Guide

Transformer Protection Application Guide About the Author George Rockefeller is President of Rockefeller Associates, Inc. He has a BS in EE from Lehigh University, a MS from New Jersey Institute of Technology, and a MBA from Fairleigh Dickinson University. Mr. Rockefeller is a Fellow of IEEE and Past Chairman of IEEE Power Systems Relaying Committee. He holds nine Patents and is co-author of Applied Protective Relaying (1st Edition). Mr. Rockefeller worked for Westinghouse Electric Corporation for twenty-one years in Application and system design of protective relaying systems.

Table II lists some common ANSI device num-bers associated with transformer protection. A numeric relay generally contains many imple-mentations of these devices within its program-ming, and each instance of a device is referred to, herein, as an “element” in the relay. For example, while the Basler BE1-CDS220 is

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  Devices, Protection, Ansi, Transformers, Transformer protection, Ansi device num bers, Bers

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Transcription of Transformer Protection Application Guide

1 Transformer Protection Application Guide About the Author George Rockefeller is President of Rockefeller Associates, Inc. He has a BS in EE from Lehigh University, a MS from New Jersey Institute of Technology, and a MBA from Fairleigh Dickinson University. Mr. Rockefeller is a Fellow of IEEE and Past Chairman of IEEE Power Systems Relaying Committee. He holds nine Patents and is co-author of Applied Protective Relaying (1st Edition). Mr. Rockefeller worked for Westinghouse Electric Corporation for twenty-one years in Application and system design of protective relaying systems.

2 He worked for Consolidated Edison Company for ten years as a System Engineer. He has also served as a private consultant since 1982. About the Guide This Guide contains a summary of information for the Protection of various types of electrical equipment. Neither Basler Electric Company nor anyone acting on its behalf makes any warranty or representation, express or implied, as to the accuracy or completeness of the information contained herein, nor assumes any responsibility or liability for the use or consequences of use of any of this information.

3 Original issue date 05/96. Revised 05/99, John Boyle; small updates Revised 08/03, Larry Lawhead; small updates Revised 04/07, John Horak; extensive rewrite Revised 06/07, John Horak; minor typographical and editorial corrections Transformer Protection Application Guide This Guide focuses primarily on Application of An overall view of the economic impact of a protective relays for the Protection of power Transformer failure and what can be done to transformers , with an emphasis on the most reduce the risk, including: prevalent Protection schemes and transformers .

4 The direct economic impact of repairing Principles are emphasized. Setting procedures or replacing the Transformer . are only discussed in a general nature in the The indirect economic impact due to material to follow. Refer to specific instruction production loss. manuals for your relay. The references provide a Repair time vs. complete replacement source for additional theory and Application time. guidance. The availability of backup power feed or emergency replacement transformers , and The engineer must balance the expense of the cost of each option.

5 Applying a particular Protection scheme against The possibility that a given Protection the consequences of relying on other Protection scheme can reduce the damage and or sacrificing the Transformer . Allowing a pro- resultant repair time, or that it can change tracted fault would increase the damage to the a replacement into a repair. Transformer and the possibility of tank rupture with a consequent oil fire and consequent Some specific applications that affect Protection personnel safety risks. There is no rule that says are: A tap changer flashover can ordinarily be what specific Protection scheme is appropriate repaired in the field, but if this fault is allowed to for a given Transformer Application .

6 There is evolve into a winding fault, the Transformer will some tendency to tie Protection schemes to the need to be shipped to a repair facility; hence, MVA and primary kV of a Transformer . While Protection that can rapidly sense a tap change there is some validity to this approach, there are fault is desirable. A high magnitude through fault many other issues to be considered. Issues to (external fault fed by the Transformer ) shakes and be considered include: heats a Transformer winding, and the longer the through fault lasts, the greater the risk of it The severity of personnel safety concerns evolving into an internal Transformer fault; hence, and the possibility that a given Protection fast clearing for close-in external faults is part of scheme can reduce these risks.

7 The Transformer Protection scheme. Some The danger to nearby structures and pro- transformers are considered disposable and cesses if a Transformer fails catastrophically readily replaced, reducing the need for ad- and the possibility that a given Protection vanced Protection schemes. Transformer protec- scheme can reduce the possibility of such a tion commonly includes some coverage of failure. 1. external bus and cable, and faults in these zones 2. Protection Example and General Concepts may expose personnel to arc flash hazards.

8 Slow The reader interested in additional information, clearing Protection schemes may be unaccept- advanced or unusual Application advice, and able from an arc flash exposure perspective. detailed settings guidance should refer to Ref. 1. Fires in an indoor Transformer may have high risk This document includes extensive references and of catastrophic facility damage and even higher bibliographies. Also, Ref. 2 and 3, textbooks on personnel safety risks, increasing the need for protective relaying, contain chapters on trans- advanced high speed Protection .

9 The proximity former Protection , and Ref. 4, another IEEE. of flammable process chemicals increases a standard, includes good overall Protection need for Protection schemes that reduce the risk schemes where a Transformer is the interface of a tank fire. The failure of a Transformer used in point between a utility and an industrial customer. a large base load unit-connected generator may cause extended generation-replacement costs; There are three general categories of protective even the loss of a small station service trans- relay technology that arise in the discussions to former can cause a notable disruption of genera- follow: tion and high economic consequences.

10 Similar Electromechanical: uses magnetic flux economic impacts may also exist at industrial created from current and voltage to create sites. Some transformers are custom designs torques on movable disks and relays, which that may have long lead times, increasing the is the source of the term relay. Usually need for advanced Protection schemes. single device number functionality. Solid State: uses low voltage analog signals 1. Failure Statistics created from sensed currents and voltages;. uses discrete electronics and basic logic Table I lists failures for six categories of faults circuits; may contain a basic microprocessor (IEEE , Guide for Protective Relay for logic and some math.)


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