Circuit breaker current monitoring

Abstract

Abstract A circuit breaker monitoring system for monitoring three-phase circuit breakers includes three channels that convert a respective phase current through a respective set of circuit breaker contacts into a sequence of digital signals each representative of an instantaneous value of current through the contacts. Each channel includes a transformer having a primary winding that receives current corresponding to that through the breaker contacts. A resistor across the secondary winding develops a voltage proportional to the current. An input buffer voltage follower couples this voltage to the input of a high-speed 12-bit bipolar analog-to-digital converter that provides the digital signals. A microprocessor coupled to a 12K RAM working memory, a 4K EPROM that may store breaker monitor software and a 2K E 2 PROM that may store programmable operating parameters and digital signals representative of accumulated fault current, processes the digital signals to provide a digital RMS current signal representative of the RMS value of the current through breaker contacts immediately after opening each time a source of a nonmaskable CPU interrupt signal provides that signal in response to the occurrence of auxiliary breaker contacts changing state. The microprocessor is coupled through a parallel input output interface to a 20-character LCD alphanumeric display and to relays for indicating an alarm condition when breaker contacts need servicing, including extinguishing a green light and illuminating a red light. Another parallel input/output interface intercouples the microprocessor and a keyboard. A serial input output interface may couple a computer or printer with the microprocessor and both are coupled to a counter timer clock. A real time clock with battery backup provides date and time information.

Inventors

• 👤 Stephen G. LaPalme

Bibliographic Details