ARC flash risks in switchgear metering compartments revision 05/12/2016

摘要

Power quality metering is a situation that often does not afford the safety of de-energizing equipment before connecting probes; this is especially true for continuous processes such as those found in refineries. In this situation, a connection to energized equipment may be more common. When potential and current transformers are present in switchgear, it is usually desirable to make the probe connections to the secondary of these transformers. Generally, these connections are made in switchgear metering compartments, which are presumed to have low arc flash risk due to the limited exposure to energized power conductors. Often in these situations, only shock hazard is considered and arc flash hazard is not; but is it safe to assume there is no arc flash hazard? The NFPA 70E-2015 Standard states that opening doors to expose bare energized parts requires arc flash personal protective equipment (PPE). The standard also states that work on control circuits with exposed energized parts greater than 120 V requires arc flash PPE. Therefore, according to NFPA 70E, in a control cabinet containing, for example, voltage transformers with exposed primary terminals above 120 V, an arc flash hazard exists and arc flash PPE is required. However, the question remains, what level is the hazard and how should it be assessed? This paper will evaluate arc flash energy in metering compartments, determine if arc flash hazard should be a legitimate concern when working in energized metering compartments, and improve overall awareness when working in these situations.