Circuit breaker and switchgear repair fundamentals 

Can a circuit breaker be repaired?

Circuit breakers are mechanical devices with moving parts and therefore they are the most likely switchgear component to wear out and cause unintended outages. While not all circuit breakers can be repaired, there are options. Switchgear modernization is the process of repairing, reconditioning or replacing power circuit breakers used in switchgear, typically with little to no changes to the enclosure and busbar. Modernizing switchgear also includes the option to upgrade protective relaying, control components and wiring.

Retrofit is a very commonly heard term in the industry, but the term is often used incorrectly.  Many use the term retrofit when referencing replacement circuit breakers or the alteration of a piece of existing equipment in some way.  When thinking about “retroactively” changing something from the original, retrofit is the first word that comes to mind.  Eaton does not recommend “retrofitting” switchgear because it can impact safety and reliability when altering components that perform a critical function (interrupting mechanism, interlocks) or reusing components with questionable integrity (primary bushings and disconnects).  

The prevalence of the so-called retrofit was one of the main drivers of the development of IEEE Std. C37.59, a standard which provides directions and requirements for the conversion of qualified power switchgear equipment.  There were incidents of accidents, injuries, equipment damage and even death being reported from retrofitted circuit breakers in the field.  Upon further investigation of these retrofitted circuit breakers, it was discovered that these devices didn’t undergo design verification testing such as high-power lab tests, BIL tests, mechanical interlock tests and di-electric tests.  As a result, IEEE created guidelines and processes to ensure the safety of users with converted circuit breakers and published IEEE Std C37.59-1991.  There are very few providers of "retrofit" circuit breakers within the market.

There are two key differences between the types of replacement circuit breakers:

1)  The interchangeable replacement circuit breaker doesn’t require any modifications or changes to the existing switchgear to install and operate that replacement circuit breaker.  This sometimes is referred to as a direct replacement.

2) The non-interchangeable replacement requires some type of change to operate properly. Some replacement circuit breakers are classified as non-interchangeable because there may also be control wiring changes required to defeat external “52X” and “52Y” control relays as new and current circuit breakers have these features built into them and don’t need the old external relays.  These older control relays also may affect the timing of the control scheme and introduce timing delays to the overall protection scheme as these relays are just as old as the circuit breaker being replaced.  When it’s necessary to defeat these control relays, it is also necessary to prevent the old air circuit breaker from being applied in that switchgear cubicle. 

Eaton does this by placing a rejection bar in the switchgear cubicle which physically prevents the air breaker from entering but allows the MVVR to enter and operate normally.  When this change is required, it would then define the MVVR as a non-interchangeable replacement circuit breaker.

A retrofill is a custom engineered solution used when a replacement is not available or is not practical.  The retrofill process is typically non-reversible and permanently modifies the switchgear cubicle.  The modifications may involve cutting or drilling, new primary circuit conductors, new doors or panels and new secondary control wiring. 

Retrofills are performed on medium-voltage and low-voltage switchgear and require the switchgear to be completely de-energized during installation and commissioning.  Eaton has performed many retrofill conversions that consist of the VCP-W or VCP-T circuit breaker for medium-voltage applications and the Magnum DS circuit breaker for low-voltage applications.  Each type includes its related components such as a cassette or compartment adaptor and qualifies these by the requirements set forth in IEEE Std C37.59-2018 and relevant IEEE standards.  Once the retrofill is completed, the switchgear circuit breaker compartment resembles equipment currently in production and has all the advantages of today’s technology and safety improvements.

This level of reconditioning cannot be performed effectively on-site because it requires specific machinery as well as dedicated personnel and processes at a facility equipped for this high quality, procedure-based servicing. 

IEEE Std C37.59-2018 doesn’t include a definite clause for reconditioning but there are some strict requirements concerning reconditioning that should be followed. One of the most important requirements concerns changing a part during reconditioning from the qualified design. If a part is no longer available and is replaced with a reverse engineered part or some other design, then the converted circuit breaker must undergo design verification as stated in IEEE Std C37.59-2018. Depending on the part and complexity, this may involve re-testing the circuit breaker at the high-power test lab. 

A common trend during reconditioning of low-voltage power circuit breakers is converting the trip unit to a newer, solid-state type device. The new trip unit must be qualified on the circuit breaker to determine if it can still satisfy the short-circuit interruption rating(s). The new trip unit may alter the current carrying structure, the sensor mounting, and possibly the operating mechanism to integrate the new trip actuator, along with the new trip unit itself. IEEE Std C37.59-2018 clause 6.2.5.4 addresses trip unit conversion and the required design tests to validate the conversion.