The basic design of low-voltage “air” power circuit breakers was developed in the late 1930’s. For the past seventy five years, and even today, breakers of this design have been used in virtually every industrial application. Between the 1930’s and late 1960’s the breakers utilized series overload devices to sense current and provide time delays. However, while the series overload is a robust and reliable design, it has several limitations. Specifically, overloads do not offer the precision and selectivity available in modern electronic designs and certain protective functions. For instance, ground fault protection is simply not available with overloads.
Despite concerns, however, some new breakers utilized series overload devices up until the 1980’s. Around this time, numerous failures began to manifest due to the fact that many electromechanical overloads were simply reaching the end of their useful lifespan. One of the biggest problems involved oil leaking from dashpots, or oil changing viscosity which affects the time-delay feature of the dashpots. Furthermore, since the old power circuit breakers were well made, they were expected to have long life spans, and were typically employed in applications that were expected to be energized 24/7. This is a problem since replacing the older breakers also required the replacement of switchgear and long periods of downtime.
To address this issue Satin American introduced its product line of etc-11 retrofits in 1988. Today, these kits are available for any United States manufactured power circuit breaker and can be installed by individuals skilled in basic circuit breaker maintenance. In a just a few hours a breaker can be removed from service, retrofit, upgraded, tested and returned to service.
The main components of a solid-state retrofit, which were first introduced during the 1960’s and initially used by major manufacturers on their new breakers, include:
* An Electronic Trip Unit which can be considered the “brains” of the system. The trip unit receives an input from the current sensors and decides if it should start timing for a trip based on this information. Electronic Trip units are generally self-powered meaning that they obtain the power required to run themselves from the circuit being monitored. Basic electronic trip units have up to four protection bands and include long-time protection and at least one of the following bands; short-time, instantaneous and ground fault. Original electronic trip units usually had a system of flags, targets or flip-dots that indicated which band a breaker tripped out on. These units did not provide detailed information such as the current at the time of the trip or indication of which phase the event occurred.
* Current Transformers (CT’s) which are doughnut-shaped devices encircle the current path. These CT’s provide a current output that is proportional to the current flowing through the bus. Current Transformers are rated with a primary and secondary current value. For example a common ratio of a CT is 1600 / 0.2 A, which means that when the primary (bus) current is 1600A, the secondary current is 0.2A.
* Bus Details are often required to re-direct current flow in 1600A frame and below breakers. This is because the original current path was through the series overload device that is removed as part of the retrofit.
* Flux-Trip Actuator is a electromechanical device that converts an electronic trip impulse from the Electronic Trip Unit to mechanical energy which ultimately opens the breaker.
Although a vast majority of breakers have been retrofit in the late 1980’s and 1990’s, Satin American’s ETC-12 proves that the solid state retrofit is even more relevant today. It improves upon the features of the original solid state trip units and provides new features that help maintain an electrically safe workplace and greatly reduces the dangers associated with an arc-flash event. The ETC-12 also address end-of-life issues by providing an easier solution for upgrading breakers that are still equipped with overloads or first generation electronic trip units that are approaching the end of their useful life.