Seismic Capability of Bushings
Seismic Capability of Bushings
Seismic Capability of Bushings
SEISMIC CAPABILITY OF BUSHINGS MANUFACTURED BY ABB POWER T&D COMPANY INC., ALAMO, TN
BACKGROUND
Historically, several different methods have been used for the justification of the seismic capability of electrical equipment, including transformer bushings. These methods usually involved some form of static calculations to estimate the forces generated during a seismic event of a given ground acceleration, and then comparing this force to the capability of the equipment, which may have been derived from calculations or from actual measurements. The way the calculations were to be done, what factors to include, how the comparisons were to be made, what was an acceptable margin, and what the specified conditions themselves were could be vastly different from application to application, or from customer to customer. Still other customers required actual shaketable testing to various requirements. All of this led to great difficulty for suppliers of electrical equipment in generating seismic qualification documents, and in getting them approved by the end customers. What was then needed was a more standardized way of specifying seismic requirements, and of qualifying equipment, that could be more universally accepted. Two standards groups have attempted to address these concerns.
SEISMIC STANDARDS
IEEE Std 693-1997 IEEE Std 693-1997 IEEE Recommended Practice for Seismic Design of Substations is a newly revised document covering the seismic design and qualification of all types of electrical equipment found in power substations. This document is a revision of the 1984 recommended practice, but it has been greatly expanded and completely reworked, such that it is effectively a new document. It simplifies the process of specifying seismic requirements by providing a single standard set of design recommendations for seismic qualification of each equipment type. This means that the seismic criteria, qualification methods and levels, and performance requirements are standardized for a given equipment type. Three qualification levels are recommended: low, moderate, and high. The user determines which level the equipment is to be qualified to, and includes this as part of their specification. In this way the equipment manufacturer has a very clear understanding of what must be done to obtain the qualification. IEEE 693 does not allow calculations as the only means of qualification of bushings, but requires testing. IEC Technical Report 1463 IEC 1463: 1996-07 Bushings-Seismic qualification is an IEC document covering the seismic qualification of power bushings, and is based on static coefficient calculations to compare the expected forces generated during a seismic event to the cantilever withstand capability of the bushing. While ABB believes this document to be technically sound, it is not widely accepted in the United States, and as such is not the preferred method of seismic qualification of the ABB Power T&D Company, Components Division Inc., Alamo, TN, USA. Also, it should be noted that bushings meeting the requirements of IEEE 693 will, in most cases, meet the requirements of IEC 1463.
TD44-661-2 Technical Data January,2000 Page 3 Because it is not practical to test every individual design, similar equipment may be grouped together for the purpose of qualification, with the most seismically vulnerable piece of equipment being tested. This allows similar equipment to be qualified, based on the testing done on the original equipment, so that the actual test need not be repeated, and is described in 5.7, Qualifying equipment by group. In order to use this grouping, it must be demonstrated that the new equipment to be qualified is less seismically vulnerable than the equipment tested. The exact method for grouping is left to agreement between the supplier and the user, and will vary somewhat depending on the equipment.
ORDERING OF STANDARDS
IEEE Std 693-1997 IEEE Customer Service 445 Hoes Lane P.O.Box 1331 Piscataway, NJ 08855-1331 Tel:- 1-800-678-4333 or 732-981-0060 Website:- http://standards.ieee.org IEC 1463 American National Standards Institute 11 West 42 Street New York, NY 10036 Tel:- 212-642-4900 Website:- http://web.ansi.org
nd
STATUS
Our standard line of bushings was designed before seismic considerations were an issue. Even so, every bushing does have a certain strength inherent in the design, and most are able to withstand significant seismic events. We have been in the process of evaluating our bushings to the requirements of IEEE 693, and have had time history shake-table tests performed on a 196 kV bushing, and on a 550 kV bushing. These tests were performed by the Pacific Earthquake Engineering Research Center at the University of California, Berkeley. The 196 kV bushing tested was our style 196W0800AY. It met all the requirements of the high qualification level, and is used as the basis of comparison for other bushings that are qualified by group. The 550 kV bushing tested was our style 550W2000UW. As this was a standard bushing, designed before seismic considerations were much of an issue, we did not expect that it would pass all the requirements for qualification. What this testing did reveal was the actual performance level of the bushing, which was approximately 0.25g horizontal ground motion. Allowing a margin of approximately 10% yields an acceptable ground motion of 0.22g. Because the desired ground motion must be doubled for the test, this translates into a horizontal motion of 0.45g, as applied to the flange of the bushing. Work is underway to develop a 550 kV bushing with improved strength and seismic withstand capability. The test for bushings below 161 kV is simpler, and is the static pull test described previously.
TD44-661-2 Technical Data January,2000 Page 4 The following table lists commonly used bushings by style number and gives the qualification level per IEEE 693 requirements. IEEE 693 Qualification Levels of Select Type O Plus C Condenser Bushings Style Number Qualification Level High High High High High High High High High High High High High High High Moderate Moderate Moderate --Equivalent Acceleration at the: Ground 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.5 0.5 0.5 0.22 Bushing Flange 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 0.45 Static Pull Test Static Pull Test Static Pull Test Static Pull Test Static Pull Test Static Pull Test Static Pull Test Static Pull Test Static Pull Test Grouping with Tested Equipment Grouping with Tested Equipment Time History Shake-Table Test Grouping with Tested Equipment Grouping with Tested Equipment Grouping with Tested Equipment Grouping with Tested Equipment Grouping with Tested Equipment Grouping with Tested Equipment Time History Shake-Table Test Qualification Method
025W0412AT 025W2000BE 025W3000BF 034W0412AP 046W0412AU 069W0412AN 115W0800AA 115W1216AK 138W1620XC 161W0800AA 161W1216AK 196W0800AY 196W0800XA 196W1216XP 196W2530XD 362W1600UM 362W2000UJ 362W3000CB 550W2000UW
The information given in the above table is meant to give quick answers to questions concerning the seismic capability of ABB Alamo bushings. It is not meant to serve as documentation of qualification. For qualification documents for a specific bushing, contact your ABB customer service representative.
TD44-661-2 Technical Data January,2000 Page 6 Technical Support If a technical question arises regarding the product detailed in this Technical Product Literature contact: ABB Inc. Power Technology Products Division USA 1128 Highway 412 S. Alamo, TN 38001-3813 USA Phone: (800) 955-8399 (731) 696-5561 Fax: (731) 696-5269 Comments ABB Inc. continually strives to make its instruction literature current, accurate, and easy to understand. Suggestions to improve this document may be sent to: Literature Coordinator fax (731) 696-5269 or use the above mailing address. For a reply, please include name, company, phone number, and/or fax number. DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITY THERE ARE NO UNDERSTANDINGS, AGREEMENTS, REPRESENTATIONS, OR WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OTHER THAN THOSE SPECIFICALLY SET OUT BY AN EXISTING CONTRACT BETWEEN THE PARTIES. ANY SUCH CONTRACT STATES THE ENTIRE OBLIGATION OF SELLER. THE CONTENTS OF THIS DOCUMENT SHALL NOT BECOME PART OF OR MODIFY ANY PRIOR OR EXISTING AGREEMENT, COMMITMENT, OR RELATIONSHIP. The information, recommendations, description, and safety notations in this document are based on our experience and judgement. THIS INFORMATION SHOULD NOT BE CONSIDERED TO BE ALL INCLUSIVE OR COVERING ALL CONTINGENCIES. If further information is required, ABB Inc. should be consulted. NO WARRANTIES, EXPRESSED, OR IMPLIED, INCLUDING WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY, OR WARRANTIES ARISING FROM COURSE OF DEALING OR USAGE OF TRADE, ARE MADE REGARDING THE INFORMATION, RECOMMENDATIONS, DESCRIPTIONS AND SAFETY NOTATIONS CONTAINED HEREIN. In no event will ABB Inc. Company Inc. be responsible to the user in contract, in tort (including negligence), strict liability or otherwise for any special, indirect, incidental or consequential damage or loss whatsoever including but not limited to damage to or loss or use of equipment, plant or power system, cost of capital, loss of profits or revenues, cost of replacement power, additional expenses in the use of existing power facilities, or claims against the user by its customers resulting from the use of the information, recommendations, description, and safety notations contained herein.
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