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White Paper WP131003EN Effective September 2015 The importance of trip-free operation and its characteristics Anthony T. Ricciuti Specialist Engineer, Eaton One of the many, often desirable characteristics in the specifications and marketing literature for medium voltage circuit breakers is “Trip-Free.” Unfortunately, there are many misconceptions about this characteristic. Definitions Physical requirements For IEEET rated products, there are several related definitions of “Trip-Free”: For IEEE rated products, if a mechanical opening release operation is maintained on a medium voltage circuit breaker, then any closing release operation signal must not result in contact movement that reduces the open gap between the contacts by more than 10%. This characteristic is often confused with the definition of “Trip-Free.” • In the most general definition of “Trip-Free,” the contacts of the circuit breaker must return to the open position and remain there when an opening operation follows a closing operation, regardless of whether the closing signal, force, or action is maintained. • A common variant is called “Electrically TripFree.” For a medium voltage circuit breaker to be considered “Electrically Trip-Free,” the circuit breaker must be able to receive and respond to an electrical opening signal regardless of whether an electrical closing signal is energized. • “Mechanically Trip-Free” operations refer to a mechanical release mechanism that can open the medium voltage circuit breaker regardless of whether any closing release device operated by any means is activated or maintained. • Medium voltage circuit breakers can also be “Hydraulically Trip-Free” or “Pneumatically Trip-Free” if they contain a hydraulic or pneumatic opening release device (respectively) that are capable of opening the circuit breaker regardless of whether any closing release device operated by any means is activated or maintained. Any of these variants of “Trip-Free” operation may include a “Trip-Free Relay,” in which its operation alters a closing release circuit, permitting an opening release to operate unimpeded by a closing release operation in any state. For IEC rated products, although the standard recommends that the suitability for “Trip-Free” operations should be provided to customers that are specifying medium voltage circuit breakers, no specific definition is provided for this function. However, if any opening release operation is initiated simultaneously with any closing release operation signal, contact movement up to and including a momentary touching of the main circuit breaker contacts is acceptable before the circuit breaker completes the opening operation. Additionally, because electrical opening release operation circuits typically employ auxiliary switch contacts internal to the circuit breaker, and therefore the electrical release operation circuit remains open until the main contacts of the circuit breaker have closed, when an electrical opening release operation circuit is maintained, the momentary touching of the main contacts is acceptable before the circuit breaker completes the opening operation. Summary Eaton VCP-T, VCP-W, VCP-WC, VCP-WG, and VCP-WHD medium voltage circuit breakers meet the IEEE definitions of “Trip-Free,” “Electrically TripFree,” and “Mechanically Trip-Free.” White Paper WP131003EN The importance of trip-free operation and its characteristics Effective September 2015 Eaton medium voltage circuit breaker operation Preforming this action While maintaning Mechanical close action Electrical close signal Mechanical open action Electrical open signal On (close) button mechanically No effect No effect Breaker opens Breaker opens On (close) button electrically No effect No effect Breaker opens Breaker opens Off (open) button mechanically No contact movement. Breaker may discharge stored energy. No contact movement. Breaker may discharge stored energy. No effect No effect Off (open) button electrically Contact touch allowed. Breaker opens and remains open. Contact touch allowed. Breaker opens and remains open. No effect No effect Figure 1. Eaton circuit breaker operation References About Eaton C37.04-1999—IEEE Standard Rating Structure for AC High-Voltage Circuit Breakers, Institute of Electrical and Electronics Engineers, 3 Park Avenue, New York, NY 10016-5997, USA. Eaton is a power management company with 2014 sales of $22.6 billion. Eaton provides energy-efficient solutions that help our customers effectively manage electrical, hydraulic and mechanical power more efficiently, safely and sustainably. Eaton has approximately 100,000 employees and sells products to customers in more than 175 countries. For more information, visit www.eaton.com. C37.100-1992—IEEE Standard Definitions for Power Switchgear, Institute of Electrical and Electronics Engineers, 3 Park Avenue, New York, NY 10016-5997, USA. 62271-100—IEC International Standard for high-voltage switchgear and controlgear—alternating-current circuit breakers. Author Anthony T. Ricciuti is a Specialist Engineer at Eaton in Pittsburgh, PA. Anthony has a Bachelor’s degree in Mechanical Engineering from the University of Pittsburgh, and has more than 20 years of experience in the design, testing, and analysis of circuit breakers. Eaton 1000 Eaton Boulevard Cleveland, OH 44122 United States Eaton.com © 2015 Eaton All Rights Reserved Printed in USA Publication No. WP131003EN / Z17245 September 2015 Eaton is a registered trademark. All other trademarks are property of their respective owners.