Schweitzer Engineering Laboratories, Inc.
SEL-487B Data Sheet
Busbar and Breaker Failure Protection,
Automation, and Control System
Major Features and Benefits
The SEL-487B Relay provides bus current differential protection, circuit breaker failure protection, and
backup overcurrent protection. The relay has 21 analog current inputs and three analog voltage inputs. For
buses with no more than seven terminals, use one SEL-487B in a single-relay application. For buses with
eight to ten terminals, use two SEL-487B relays. For buses with as many as 21 terminals, use three SEL-487B
relays; each relay provides as many as six independent and adaptable zones of protection. Contact SEL
Research and Development for methods on protecting larger systems.
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Busbar differential protection operates in less than one cycle to increase system stability margins and
reduce equipment damage.
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Flexible zone selection and six differential zones provide protection for multiple busbar applications.
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Failed CT detection elements reliably indicate open and shorted CTs for alarming and/or blocking.
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Differential protection accommodates as high as 10:1 CT ratio mismatch without auxiliary CTs.
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Differential protection is secure for external faults with minimal CT requirements.
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Breaker failure protection for each terminal integrates bus and breaker failure protection.
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Instantaneous and inverse time-overcurrent elements provide backup protection for each terminal.
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Negative- and zero-sequence over- and undervoltage elements provide for differential element supervi-
sion.
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Three dedicated check zones are available in each relay to supervise complex bus differential schemes.
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Interconnection with automation systems uses IEC 61850 or DNP3 protocols directly or DNP3
through a Communications Processor. Use FTP for high-speed data collection.
SEL-487B Bus Differential Relay
