With two employees dead and three injured (two very seriously), Gulf States Electric Utilities (Beaumont, Texas, U.S.), now part of Entergy (New Orleans, Louisiana, U.S.), had to find a solution.

The accident occurred on Jan. 5, 1993, at the Sabine Power Station near Bridge City, Texas. Sabine personnel had racked-in a retrofitted Toshiba breaker and sent the close command, but the breaker did not close.

With the breaker indicator showing that it was still open, the operator (in a full flash suit) began racking-out the breaker to troubleshoot the problem with his supervisor standing nearby. Neither knew that the breaker received the closed command, which unlatched and began its closing operation but could not complete the close due to mechanical problems.

The breaker was still receiving the close command while it was being racked-out. As it moved, the mechanical bind was relieved, the trip-free protection failed and the breaker closed while partially racked-out. The resulting electrical arc-flash and explosion critically burned them and slammed them back against the wall; both died. The arc-flash traveled around a corner and burned three other individuals.

By wearing a full-body flash suit during racking procedures on an energized bus, the primary operator at the Sabine Station was doing everything required by “A”-NFPA A70E and OSHA 29CRF-1910-S-App. While the suit provided him with some protection, it did not save his life.

Entergy began looking for more effective ways to protect its workers. First, it quickly corrected the problems with retrofitted Toshiba breakers. Second, after considering various solutions, Entergy began to retrofit all rackable breakers (2300-V and above) with remote racking systems.

GE breakers were the first to be remotely racked, and Entergy is working on Allis Chalmers and Westinghouse units. For these breakers, Entergy uses a PLC-controlled SARRACS^™ unit, manufactured by Siemens (Alpharetta, Georgia, U.S.). It comes with a 40-ft (12-m) cable and allows operators to stand well away from the breaker during racking.

Remote racking devices provide other safety features. At the time of the accident, the operator at Sabine Station racked the breaker with a drill motor. While this method works and saves wear and tear on the operators arms, the more sophisticated SARRACS^™ unit:

• Measures the racking motor amperage and automatically compares it to the expected amperage draw; significant differences can indicate a problem.

• Has limit switches that indicate when the switchgear is fully in racked-in and racked-out positions.

• Has a motor current limiter to prevent the switchgear from racking-in too far and damaging the electrical bus (if the PLC should fail).

The SARRACS^™ unit captures torque data by monitoring the amount of current needed to rack the breaker. Plotted on a screen and recorded, the torque (current) profile can be compared to profiles from previous operations and/or device-specific profiles. A profile change can indicate a problem.
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