Abstract: In operation of a 600MW supercritical unit of a power plant, the two air preheaters were tripped simultaneously, and this caused the boiler MFT (main fuel tripping) tripped. The main reason is that the motor of belt conveyor of slag bin, which was connected into boiler MCC #2 section, was earthed; and the converter, which controls the motor, had not switched off the fault devices, and this had caused the voltage of boiler MCC #2 section was abnormal; the gear oil pumps of air preheater were tripped, then the main motors of air preheater were tripped though interlock circuit. The power source connection mode and power operation mode were corrected; a spare gear oil pump was added; and the gear oil pump and air preheater intertrip logic and settings were modified. Then the accident of main machine tripping, which should be caused by improper connection and operation of auxiliary equipments, can be avoided.
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Key words: air preheater, trip, gear oil pump, treatment