Advancing Workplace Safety Through Vintage Equipment Upgrades

Abstract

Many process industry facilities have performed or hired consultants to complete arc flash studies. The analysis typically uses software to calculate the heat energy from an arc flash event which is displayed along with the shock hazard on labels affixed to each electrical panel in the facility. Although the affixed labels are useful, knowing just the heat energy and working distance boundaries for a potential arc flash event is only part of the answer. The actual task(s) or activity involved needs to be considered: both the likelihood and severity of the risk needs to be understood. This paper presents a case study of upgrades to an existing cement plant built in the 1970's. Vintage power distribution equipment include two existing 4160-volt metal-enclosed medium-voltage motor control centers (MCCs) with main vacuum circuit breakers that each fed 4160-volt motor loads. The main vacuum circuit breaker is used as a lockout point in the system. This means that prior to any work being performed on the motor control, the main vacuum breaker needs to be de-energized and then manually racked from the energized bus to establish a zero-energy state. Many documented arc flash events have occurred while electricians have performed the task of manual breaker racking. To address the significant risk, a project was funded to retrofit the existing main breaker section with new cell parts including an integral motor operator that allowed the vacuum breaker to be racked from the energized bus via a remote pendant station. This paper will review details of the retrofit/upgrade and describe site workplace operational changes and safety practices associated with the installation.