Analysis and Solution of Large Axial Fan Pump Switching Low Oil Pressure

The first phase of a power plant in Zhuhai is a 2 × 700 MW coal-fired unit. The boiler is a sub-critical pressure produced by Japan's Mitsubishi Heavy Industries Co., Ltd., with an intermediate reheat, quadratic tangential, balanced ventilation, and solid slag discharge control cycle drum boiler. Each boiler is equipped with two MLHIR140-type 50% capacity adjustable-blade axial fans and two ML-HI-R175 50% capacity adjustable-blade axial-flow fans. Each fan oil system is equipped with two vane pumps mounted in parallel above the tank, one for operation and one for backup, providing control oil and lubricants to the system. In normal operation, the hydraulic pressure at the outlet of the pump is 6.86 MPa; when the system control hydraulic pressure is lower than 4.9 MPa, the hydraulic pressure "low" alarm signal is generated and connected with the standby oil pump; when the system control hydraulic pressure is lower than 2.45 MPa, Low "alarm signal, delay 3 s fan tripping. The system lubricating oil pressure is normal 0.125 MPa; when the system lubricating oil pressure is lower than 0.098 MPa, the standby oil pump is self-starting; when the lubricating oil pressure is lower than 0.049 MPa, it sends a "low" alarm signal and the delay time of 20 s fan trips. When the main pump is out of power, the standby pump electrical interlock automatically start. Therefore, the normal operation of the pump is an important guarantee for the safe operation of the fan. 1. Accident Example At 17:08 on June 11, 2003, the pressure loss of the busbar caused by the action of the busbar switch relay during the switch-over of 400 V PC2A12 section (boiler section) of Unit 2 in the power plant led to the operation of the 2B draft fan operating oil pump Power loss, standby pump start but the establishment of hydraulic pressure is too long, the system lubricating oil pressure is "low" state, B-side fan full trip. In addition, due to A air preheater zero speed power taken from the plant power 400V PC2A12 segment, air preheater zero speed relay power failure contact closure start, A side fan tripping, resulting in boiler MFT action, the unit solution. After this accident, the air preheater zero speed power supply is changed by the unit uninterruptible power supply UPS. 2. Analysis of the causes Unit 1 and unit 2 of Zhuhai Power Station have been operating for 4 years since they were put into operation in 2000 respectively. The phenomenon of low oil pressure switched by the multi-fan pump in the first two years was not obvious, but the phenomenon of low oil pressure was switched by the fan Often appear. The reason, in the following two aspects: a) French-made vane pump blades after running for a period of time after the blade wear, virtually make the pump large circular gap, the pump output decreased; b) as every 15 d Or two weeks) to switch the oil pump, the exhaust pipe outlet pump connected to the upper part of the tank, through the atmosphere (the exhaust pipe has a spring valve, when the oil pressure spring valve will automatically shut down), under the action of atmospheric pressure, ten The day will save almost all the oil accumulated on the outlet of the backup pump (flowing back to the tank), so the pump will make a loud noise when the standby pump is switched on and sometimes the starting is unsuccessful. Sometimes the oil pressure is slow to establish, When a few days when the pump switch, the hydraulic pressure to establish faster. To track the actual start-up time for the fan oil system pump to switch the backup pump, technicians track the time it takes for the 2A and 2B blower pumps to switch the backup pump to establish hydraulic pressure during September and October 2003. Press the time record in Table 1. Table 1 shows that the technical staff shortens the pump switching cycle, but the pump is still unable to establish a normal hydraulic pressure, we can see standby pump starting time is not reliable, standby pump in this state can not be a reliable backup, the system must be transformed .