The role of pressure transmitter in the fault control of booster pump
1. The pressure transmitter is damaged during commissioning
At the time of design, the power plant's request is to control the outlet pressure at 0.85 MPa. The pressure transmitter provided by the manufacturer has a range of 0 to 1 MPa and an output of 4 to 20 mA. During installation and commissioning, the inverter reports a fault, and the booster pump automatically switches to the power frequency operation. The water pressure exceeds 1 MPa, causing the outlet pressure transmitter to be damaged. After the manufacturer replaces the pressure, the inverter has a range of 0 to 1.6 MPa and outputs a pressure transmitter of 4 to 20 mA. Its rated voltage is 24 VDC, the accuracy is 0.5, and the fault is eliminated. It can be seen that when the three-channel pressure transmitter is selected, the pressure range should consider the maximum pressure under the power frequency condition. The parameters of the two digital pressure gauges were changed to 1.600 for the HIS and HIo settings to ensure the same range as the pressure transmitter (see Table 2).
Table 2 is the main parameter setting table of the digital pressure gauge
2, the inverter reported "no load" fault
F0422—No load applied to inverter is often reported during inverter operation. After three instruments analysis, this is a fault caused by lack of water. In the design circuit, the water shortage fault signal is provided by the inlet pressure transmitter. The set value is 0.1 MPa. When there is water shortage, only the alarm signal is issued, and the shutdown is not controlled. The flushing water of the water system is provided by a spray pump of a coal-containing wastewater treatment system, and the water system pressure can reach 0.5 MPa when the spray pump is turned on. When the spray pump is stopped, the water system pressure is about 0.2 MPa. At this time, the inverter is started, the water pressure drops, and the “water shortage alarm” indicator lights up without stopping the inverter operation. The inverter continues to operate in this state, the water outlet pressure can only be 0.4 MPa or less, and the inverter cannot be boosted to the set value, that is, the “inverter no load” fault is reported. At the same time of the fault, the system automatically switches to the power frequency working condition, and the booster pump continues to operate. If it is not processed in time, the booster pump may be overheated and burned in the event of a real water shortage.
Inverter setpoint and PID adjustment amount parameter settings
For the problem of “water shortage failure” without stopping the machine, a water shortage fault relay KB4 (see Fig. 2) has been added, and its coil is connected in parallel with the “water shortage alarm” indicator, and its normally closed contact string is after the stop button. Thus, when the system is short of water, the entire control loop is disconnected and the booster pump stops working. In order to facilitate the judgment of the cause of the shutdown, the normally open contact of KB4 is also added to realize the “water shortage fault” self-holding, and the “water shortage fault” alarm can be reset by the stop button. At the same time, the lower limit set value of the inlet pressure transmitter is changed to 0.3 MPa to avoid the false water inlet signal generated by the return water pressure after the bypass valve is opened to prevent continuous operation in the absence of water.