Directing against the problems of miss-operation and mal-function existing in the main protection design of boilers

a new design scheme of hard-wired trip circuit for main fuel trip(MFT) has been put forward

and the manual botton trip and the operation mode 2 out of 3 for MFT relay acted by DCS being redesigned.The above-mentioned design scheme can reduce the posibility of mal-function for MFT under prerequisite of ensuring no miss-operation of MFT.If the lose of power supply in DCS is used as the condition of MFT's operation

the power supply of hard-wired trip circuit for MFT can directly use the power supply of DCS

and being designed according to negative logic;in the case of hard-wired trip circuit for MFT is designed to adopt positivelogic and independent power supply

it is necessary to use the action of manual MFT botton as the trip condition of MFT soft logic;the connection mode of contacts on manual MFT botton has large influence in hard-wired trip circuit for MFT.