Understanding Circuit Breaker Design and Operation to Improve Safety and Reliability in Underground Mining

Traditional “above-ground” applications of circuit breakers for overcurrent protection in industry are generally well understood. Defined design and test standards, which vary somewhat across the globe, provide a framework for users of these devices to assure that they are not misapplied. Attention to detail in circuit breaker maintenance generally assures that these devices will operate reliability and safety across the industry. However, when circuit breakers are applied in underground mining applications, traditional design and test standards give way to in-country mining safety authorities who typically dictate requirements in these special applications. Because of this, ratings and test requirements for low-voltage molded-case circuit breakers, low-voltage power circuit breakers, medium-voltage vacuum and medium-voltage sulphur hexafluoride (SF₆) circuit breakers in underground mining are typically different. In this environment, the user must be aware of issues specific to the application to assure that these devices operate such that they assure miner safety and operation reliability. This paper will discuss specific circuit breaker applications in underground mining and recommend methods to maximize the effectiveness of these protective devices in this environment.