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Freeze Protection For Biomass Delivery To Generator Station

Problem:

A customer was using tubular radiant heaters during the winter to thaw open-top rail cars delivering a coal/biomass mixture. Premature failure of three heaters per day was a constant problem because the thermal system was originally designed to switch all heaters ON/OFF using electromechanical relays. Switching the 1.2 megawatt load, coupled with high line voltages led to this failure rate.

Solution:

Since electrical noise was not a problem, Watlow recommended replacing the relays with QPAC SCRs using phase-angle firing. This approach allowed the customer to stage the heater switching, apply a "soft start" and limit high voltage to 80 percent of line voltage. Heater failure is now down to only three per year.