Failure analysis of sudden pressure drop in compressed air system
Failure Analysis of Sudden Pressure Drop in the Instrument Compressed Air System of the Whole Plant
The instrument compressed air system of the power plant serves as the instrument control air source and is the operating power for the pneumatic devices of the generator set (switching and regulating pneumatic valves, etc.). When the equipment and system are operating normally, the working pressure of a single air compressor is 0.6~0.8 MPa, and the system steam supply main pipe pressure is not less than 0.7 MPa.
1. Fault process
Instrument air compressors A and B of the power plant are in operation, and instrument air compressor C is in hot standby status. At 11:38, the operation personnel’s monitoring found that the pneumatic valves of Units 1 and 2 were operating abnormally, and the valves could not be opened, closed, and adjusted normally. Check the local equipment and find that the three instrument air compressors are working normally, but the drying towers of the three instrument air compressors have all lost power and are out of service. The solenoid valves at the inlet of the drying towers have all been powered off and closed automatically. Pipe pressure decreases rapidly.
Further inspection on site found that the upper-level power supply “air compressor room thermal control distribution box” of three instrument air compressor drying towers was out of power, and the bus bar of the upper-level power supply “380 V instrument air compressor MCC section” lost voltage. Troubleshoot the faults of the thermal control distribution box in the air compressor room and its loads (air compressor drying tower, etc.) and confirm that the fault is caused by other load abnormalities in the MCC section of the instrument air compressor. After isolating the fault point, power on the “380 V instrument air compressor MCC section” and the “air compressor room thermal control distribution box”. The power supply of the three instrument air compressor drying towers was restored and put back into operation. Their inlet electromagnetic After the valve is powered on, it will also open automatically, and the pressure of the instrument’s compressed air supply main pipe will gradually increase to normal pressure.
2. Failure analysis
1. The power supply design of the drying tower is unreasonable
The power supply for the three instrument air compressor drying towers and the inlet solenoid valve control box is taken from the thermal control distribution box in the instrument air compressor room. The power supply of this distribution box is a single circuit and only draws from the 380 V instrument air pressure. The MCC section of the machine has no backup power supply. When the busbar voltage failure occurs in the MCC section of the instrument air compressor, the thermal control distribution box of the instrument air compressor room and the drying towers of the instrument air compressors A, B, and C are all powered off and out of service. The inlet solenoid valve also automatically closes when there is a power outage, causing the pressure of the instrument’s compressed air supply main pipe to drop rapidly. At this time, the pneumatic valves of the two units could not be switched and adjusted normally due to the low pressure of the power air source. The safe operation of the No. 1 and No. 2 generator units was seriously threatened.
2. The design of the drying tower power supply working status signal loop is imperfect. The drying tower power supply equipment is on-site. The drying tower power supply working status remote monitoring component is not installed, and the power supply signal remote monitoring loop is not designed. The operating personnel cannot monitor the working status of the drying tower power supply from the centralized control room. When the drying tower power supply is abnormal, they cannot detect and take corresponding measures in time.
3. The pressure signal circuit design of the instrument compressed air system is imperfect. The instrument compressed air main pipe is in place, the system pressure measurement and data remote transmission components are not installed, and the system pressure signal remote monitoring circuit is not designed. The centralized control duty officer cannot monitor the main pipe pressure of the instrument compressed air system from a distance. When the system and main pipe pressure change, the duty officer cannot immediately detect and take countermeasures quickly, resulting in extended equipment and system failure time.
3. Corrective measures
1. Improve the power supply of drying tower
The power supply mode of the drying tower of three instrument air compressors has been changed from a single power supply to a dual power supply. The two power supplies are mutually locked and automatically switched to improve the power supply reliability of the drying tower. The specific improvement methods are as follows.
(1) Install one set of dual-circuit power automatic switching device (CXMQ2-63/4P type, distribution box) in the 380 V public PC power distribution room, with its power sources drawn from the backup switching intervals of the 380 V public PCA section and PCB section respectively. , and its outlet is connected to the power incoming end of the thermal control distribution box in the air compressor room for instruments. Under this wiring method, the power supply of the thermal control distribution box in the instrument air compressor room is changed from the 380 V instrument air compressor MCC section to the outlet end of the dual-circuit power switching device, and the power supply is changed from a single circuit to It is a dual circuit capable of automatic switching.
(2) The power supply of the three instrument air compressor drying towers is still derived from the thermal control distribution box in the instrument air compressor room. Under the above wiring method, each instrument air compressor drying tower also realizes dual power supply Power supply (indirect way). The main technical parameters of the dual-circuit power automatic switching device: AC input and output voltage 380/220 V, rated current 63 A, power-off switching time not greater than 30 s. During the dual-circuit power switching process, the thermal control distribution box of the instrument air compressor room and its load (drying tower and inlet solenoid valve control box, etc.) will be powered off for a short time. After the power switching is completed, the drying tower control circuit will restart. After receiving power, the drying tower is automatically put into operation, and its inlet solenoid valve is automatically opened, eliminating the need for personnel to restart the equipment and perform other operations on the spot (a function of the original electronic control design of the drying tower). The power outage time of dual-circuit power supply switching is within 30 s. The operating conditions of the unit allow 3 instrument air compressor drying towers to be powered off and outage for 5 to 7 minutes at the same time. The dual-circuit power supply switching time can meet the normal requirements of the instrument compressed air system. job requirements.
(3) At the 380 V public PCA section and PCB section power distribution cabinets, the rated current of the power switch corresponding to the dual-channel power switching device is 80A, and the incoming and outgoing cables of the dual-channel power switching device are newly laid (ZR-VV22- 4×6 mm2).
2. Improve the drying tower power supply working status signal monitoring loop
Install an intermediate relay (MY4 type, coil voltage AC 220 V) inside the dual-power automatic switching device box, and the relay coil power is taken from the outlet of the dual-power switching device. The normally open and normally closed signal contacts of the relay are used to make the closing signal (drying tower powered working state) and opening signal (drying tower power outage state) of the dual power switching device enter the unit DCS control system and displayed on on the DCS monitoring screen. Lay the operating status signal DCS monitoring cable (DJVPVP-3×2×1.0 mm2) of the dual power supply switching device.
3. Improve the pressure signal monitoring circuit of the instrument compressed air system
Install a signal remote transmission pressure transmitter (intelligent, digital display type, power supply 24 V DC, output 4 ~ 20 mA DC, measuring range 0 ~ 1.6 MPa) on the main pipe of the compressed air for the instrument, and use the compressed air for the instrument The system pressure signal enters the unit DCS and is displayed on its monitoring screen. Lay the compressed air main pipe pressure signal DCS monitoring cable for the instrument (DJVPVP-2×2×1.0 mm2).
4. Comprehensive maintenance of equipment
The three instrument air compressor drying towers were stopped one by one, and their bodies and electronic and thermal control components were comprehensively inspected and maintained to eliminate equipment defects.
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