Transformers and process safety

Transformer fires can cause a process incident due to interruption of power to the unit. Give importance to the maintenance and fire detection and protection systems of your transformers. A good article by the US dept of interior mentions the following:
“The following devices should deenergize the transformer and trigger the transformer fire suppression system:
• Heat and/or fire sensors appropriately located near or on the transformer
• Manual discharge (control switch, pushbutton)
Depending on the type of sensors used and the details of the design, it may be desirable to require two sensors to operate before activating suppression to reduce false operation.
In addition, remote activation through the use of SCADA might be considered where operating practices permit and sufficient information is available to the remote operator.
Heat sensing fire detectors are the most reliable way of activating fire suppression for transformers. Techniques that should be considered include linear heat detectors (heat sensing cable) and infrared detectors. The appropriate method of detection is chosen when designing or re-designing the system.
Control system considerations include:
· Operation of the fire suppression system should deenergize the transformer to prevent water from discharging onto an energized transformer.
· Loss of power to fire suppression system pump motors, solenoids, and controls should be annunciated so the problem can be detected, diagnosed, and remedied.
· Activation of the suppression system should be annunciated and input to the SCADA system.
· Activation of the suppression system should block drains and pumping of oil-contaminated water from sumps into waterways.
· Activation of the suppression system should stop transformer fans and oil pumps that might feed the fire.
· Power the fire detection system from a reliable source, have continuous internal monitoring, and have sufficient output contacts for necessary alarm and control functions.
· Power the fire suppression system from a reliable source not affected by the loss of the transformer being protected.
· At unattended plants where high-volume deluge systems are retained, detection and control circuits should be designed to suppress the fire while reasonably minimizing the amount of water discharged. The purpose of this is to suppress the fire while limiting the risk of overtopping containment structures and contaminating waterways. It is reasonable to apply water for a limited time, temporarily shut down, and then reactivate water discharge to suppress any remaining fire. This might be accomplished through detectors that continue to sense fire, timers that cycle the system, or other means. In addition, high level detection in the containment structure is recommended to shut off fire suppression to prevent overflow. High level detection might be supplemented by video monitoring and remote deactivation through the use of SCADA.
Read the complete article in this link.