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A cogeneration power plant experienced a power failure following an inadvertent trip of the gas turbine generator set. The planned automatic reconnection of the plant to the utility power grid was not available due to ongoing maintenance operations. The plant therefore "went dark," which should have caused a standby diesel generator to start and automatically power the 4160V emergency power bus.
The downsized emergency bus provided adequate power for the essential plant systems required to get the plant back online. The plant could then be powered through the cogeneration turbine generator, or via connection to the utility grid.
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As expected, the standby generator started automatically but was unable to connect onto the emergency power bus. This left the plant in a total power blackout for a prolonged period of time. The lack of essential power led to a fatality when an elevator became stuck between floors.
The forensic investigation included analyzing the complex combination of gas turbine cogeneration equipment, utility connection systems, and standby power systems. The systems were manufactured by different companies over several decades of operation. These diverse systems were managed by an overall plant DCS as well as individual DCS, PLC, and switchgear controllers for the various electrical and mechanical subsystems.
Forensic testing determined that a failed switch in one of the 4160 volt transformer breakers provide an incorrect control signal to the master power control system. The invalid signal prevented automatic connection of the emergency generator onto the essential system bus. The breaker's switch had failed due to "deferred maintenance" after the breaker had been submerged in a flooding incident.
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