Introduction

False False Breaker Trip Reporting

A Supervisory Control (early 1970's predecessor of SCADA) system at a major Electric Utility reported circuit breaker operations at several substations occurring at random, over the span of several weeks.

Subsequent inspection of the breaker control equipment at those substations revealed that no breaker operations took place and a Supervisory Control equipment was providing false information.

Several dozens of these systems were purchased and installed by that Utility. Naturally, the reliability of the equipment and the qualifications of the personnel involved in its design and manufacturing were seriously challenged by the Utility management.

It has been mildly suggested during the meeting preceding field investigations that the equipment be put in perfect operating condition by the "end of the week" or replaced with similar product made by those "who know what they are doing".

The diagram in Figure 5 depicts a typical system configuration.

The rest of the day was spent at the Master Station ( a 90" tall cabinet full of PC cards with mostly discrete transistors and indicating lights). The oscilloscope measurements indicated proper signal levels suggesting that the problem was on the RTU level. It is worth mentioning here that the understanding of the substation noise was rather sketchy in those days and the equipment tended to be overdesigned.

Similar investigations were performed at the Remote Terminal Units in question. Oscilloscope measurements provided no clues.

An MG-6 relay connected in "buzzer" mode was used to generate a substantial amount of noise; again no false operations were observed.

As the week came to a close, the 52a wiring (see above) check was done in desperation. The RTU terminals looked fine; however, a walk to the breaker control box in the yard was very fruitful; the corresponding terminals had loose screw connections! It was discovered later that the same problem existed at all suspected RTU locations. End result: happy Customer!