Analysis of the Causes of an Accident in an Air Compressor and Countermeasures

* Analysis and countermeasures for the accidents of the air compressors Li Zongbai, Liang Youqian (Northwest Institute of Mining and Metallurgy, Gansu Baiyin 730900) [] Analyzed and solved the failure failure of the air compressor caused by the time delay of the direct-drive drag synchronous motor. As well as the operational safety hazards caused by equipment manufacturing and installation quality, the air compressor electrical design, installation and operation safety countermeasures are proposed.

[] air compressor; synchronous motor; excitation; solenoid valve; fault; economic operation 0 Overview Air compressor (hereinafter referred to as air compressor) is a kind of air pressure generating device that converts the mechanical energy of the prime mover into gas pressure energy, widely used Industrial and mining enterprises in the industrial field. In order to meet the mining needs, a mining enterprise in Gansu Province purchased and installed a L8-60/8 air compressor. During the start-up process, the high-voltage power distribution cabinet of the synchronous motor was unable to start the operation due to the quick-break and overload protection actions. After the fault was started, due to other installation quality, the air compressor could not be unloaded after reaching the set pressure, and was forced to stop by manual emergency. Fortunately, the equipment and personal accidents were not caused. The author was invited to assist in the analysis of the causes and troubleshooting, and finally through the fault disposal, successfully solved the air compressor startup problems and operational safety hazards. The equipment has been in good condition for many years.

1 Basic information of the equipment The L8-60/8 air compressor adopts high-voltage synchronous motor rigid straight-line drag, rated working pressure 8kg/cm2, and adopts the pressure-opening intake valve adjustment method to realize the three-stage adjustment of the exhaust volume (ie 100 %, 50%, 0%1, the relevant performance parameters are as follows: piston stroke 220mm; number of revolutions 428r / min; displacement 60m3 / min; secondary exhaust gauge pressure 0.8MPa; shaft power 320kW; synchronous motor rated power 350kW Synchronous motor rated voltage 6000V; high voltage power distribution cabinet GG-1; thyristor excitation finishing cabinet KGLF-300/75; gas storage tank volume 6m3; cooling method is water.

The synchronous motor adopts GL type induction overcurrent relay for quick disconnection and overload protection. The electrical control safety settings are as follows: 1) The safety protection settings of synchronous motor are mainly short circuit protection, overload protection, de-energizing protection, low voltage; 2) The safety protection settings of the air compressor are mainly water shut-off, oil cut, over-temperature of the 丨-class and 丨丨-class exhaust, and over-pressure of the 丨-class and 丨丨-grade exhaust.

2 Fault appearance) During the start of the air compressor, the high-voltage power distribution cabinet of the synchronous motor is fast-acting and overload-protected, and cannot be started normally.

Do not press the air compressor to start the operation state. After the system pressure reaches the set pressure, the air compressor can not be unloaded (both manual and automatic load reduction are invalid), and forced to take emergency emergency stop. Fortunately, equipment and personal accidents have not been caused.

Non-ferrous metallurgy design and research 3 fault analysis According to the fault representation analysis, the fault causes may have the following points: 1) The difference between the air compressor and the synchronous motor (coaxiality). The L8-60/8 air compressor adopts the high-voltage synchronous motor rigid straight-through drag. During the installation process, the hollow press and the motor are installed separately. If the air compressor and the motor are installed with different axes, the motor rotor will be unbalanced and the motor will be unbalanced. The starting current is too large, causing the motor overcurrent action to trip.

2) Synchronous motor excitation time lag. The synchronous motor is usually started by the asynchronous start method. When the rotor speed reaches the quasi-synchronous speed (that is, close to 95% of the synchronous speed), the DC excitation is sent to the rotor, the rotor is pulled into synchronous operation, and the synchronous motor completes the starting process. However, in fact, the synchronization of the synchronous motor from start to pull is a relatively complicated process, and if the conditions are not suitable, it will cause a startup failure. Normally, when the rotor speed reaches the quasi-synchronous speed, the polarity of the rotor and the polarity of the rotating magnetic field of the stator match, that is, the power angle 0 is in the range of 0.~180. The synchronous torque causes the rotor to accelerate, and the rotor is pulled. Synchronous operation; if the power angle 0 is between 180.~360., the synchronous torque acts as a brake, and the rotor cannot be pulled into synchronous operation. Another case is if the rotor is engaged with the excitation time lag, causing the synchronous motor When the starting time is longer at the quasi-synchronous speed, the stator current is too large, the motor overcurrent protection action trips, and the motor fails to start. This is especially true in heavy-duty and high-inertia drag systems.

3) The solenoid valve is faulty. The solenoid valve is an important control device for the air compressor to realize the load adjustment from full load to half load or no load state. It can be manually or automatically controlled. The failure of the solenoid valve will cause the air compressor to continue to run at full load.

4 Troubleshooting 4.1 Check the centering of the air compressor and the synchronous motor (coaxiality) Open the connecting bolt of the coupling between the air compressor and the synchronous motor, first use the feeler gauge to detect the coupling at multiple points around the coupling. Gap, the test results show that the gap is uniform; then use the steel ruler to detect, fix the steel ruler on the air compressor side coupling, and manually crank the car to detect the gap change between the motor end coupling and the air compressor end coupling. In the case, the test results also show that the gap is uniform, indicating that the centering (coaxiality) of the air compressor and the synchronous motor is good to eliminate the failure factors of the different axes of the air compressor and the synchronous motor.

4.2 Check the rotor DC excitation system The synchronous motor rotor excitation circuit uses the bridge three-phase full-controlled rectifier circuit to fix the excitation winding power supply. When the rotor speed reaches the quasi-synchronous speed, its “time base circuit” integrated block acts as the detection frequency switch. The component automatically energizes the thyristor excitation device in accordance with the polarity, so that the synchronous motor is brought into synchronous operation. Turn on the excitation device power, put the control handle in the manual position, press the start button, the excitation device works, manually adjust the excitation voltage, the voltage can be linearly adjusted from 10% of the rated value to 125%, the excitation system works normally, the failure factor exclude.

4.3 Synchronous motor no-load start In order to eliminate the load (air compressor 丨 on the synchronous motor start failure, under the connection condition between disconnecting the synchronous motor and the air compressor, the synchronous motor is started at no load. Turn on the thyristor excitation device power supply. Put the control handle in the automatic position, press the start button, the excitation device works, manually adjust the excitation voltage to the rated value, press the host start button, the synchronous motor is energized to start, but when the start is about 8s, its overcurrent protection action, high voltage The switch trips and the start fails.

4.4 Adjusting the excitation time According to the overcurrent protection action of the synchronous motor when it is idling, it may be that the rotor excitation excitation input lags, causing the synchronous motor rotor to run asynchronously for too long, and the rotor does not get DC excitation in time. When the inverter is running synchronously, the stator current is too large, causing the overcurrent protection action to trip. According to this, adjust the thyristor "time base circuit" excitation time (from LI2s), start the synchronous motor again, the synchronous motor is smoothly driven into the synchronous operation after the asynchronous start, complete the start.

4.5 Start the air compressor After the coupling between the air compressor and the synchronous motor is reliably connected, the air compressor is started according to the normal driving procedure, and the air compressor is smoothly started and put into operation.

4.6 Air compressor overall operating condition assessment In order to assess the various operating conditions of the air compressor, ensure that the air compressor is safely operated, and monitor its operating conditions. 0) Adjust the excitation current so that the synchronous motor is normally excited. In the under-excited and over-excited state, observe the DC excitation system and various monitoring instruments, everything is normal.

2) Observe the air compressor cooling system, lubrication system, 丨 grade and 丨丨 grade exhaust temperature and pressure, everything is normal.

3) Close the shut-off valve on the wind load side, and the wind pressure will rise quickly. Manually control the solenoid valve when the exhaust pressure is 1, 2, 3, 4, 5kg/cm2, so that the air compressor is in no-load. Alternate operation under load condition, good operation, but when the exhaust pressure reaches 6kg/cm2 or more, the manual unloading fails, the air compressor carries the load continuously, and the wind pack pressure exceeds the system set pressure in a short time, but the manual unloading It does not work, and the automatic load shedding has not started. At this time, it is forced to take emergency emergency stop to prevent serious accidents caused by overpressure of the wind bag.

Analysis and countermeasures for the cause of the accident of the air compressor. 59. Judging from the above situation, the possible causes of this attempted accident are: (1) There is a problem of small suction force in the solenoid valve body, and the first-stage suction valve cannot be opened when the system pressure is increased; (2) The equipment is shipped and installed. The solenoid valve load adjustment setting value is too high or other quality problems of the solenoid valve cause the solenoid valve to refuse when the system pressure exceeds the set pressure.

For the above two problems, first consider replacing the solenoid valve, and secondly, please have the qualified installation unit re-set the solenoid valve's set value according to the system pressure requirements. After being processed, the cause of the malfunction is eliminated, and the air compressor is continuously operated normally.

5Electrical design, installation and operation safety measures 5.1 Solenoid valve manufacturing design quality In the equipment manufacturing design, the solenoid valve power should ensure that it can overcome the action resistance of the high pressure gas to the spool, and ensure that the air compressor system pressure reaches or exceeds the rated pressure. The solenoid valve can still operate reliably.

The solenoid valve is switched between the frequent start-and-stop state during the operation of the air compressor. In order to ensure the reliability of its operation, the breaking capacity of each relay contact of the control circuit should have sufficient margin to ensure safety. Separate the coils to avoid contact sticking in frequent splits.

5.2 Air compressor engineering design selection Air compressor engineering design selection should adhere to the principle of production application, advanced technology and economic rationality, should not over-emphasize the advanced nature of equipment, but should also consider the economics of equipment investment and operation. And use the unit to maintain technical strength and level. At present, the mainstream air compressors on the market are piston type, single screw type, twin screw type, centrifugal type, etc. The piston type is commonly used in mines in China, followed by screw type. The piston air compressor consumes a small amount of electricity and is easy to adjust the air supply volume, but it has been gradually eliminated due to noise, maintenance, and gas pressure pulsation; the screw air compressor consumes a large amount of electricity, but Stable operation, low noise, small maintenance, and a tendency to gradually replace it.

5.3 Installation of air compressor According to the Regulations on Safety Supervision of Pressure Vessels, the installation of air compressors should be commissioned by regular installation units with corresponding qualifications and installation experience to ensure compliance with the relevant requirements of construction specifications and after passing the test operation and acceptance. Delivery. Before the installation unit delivers the air compressor to the use unit, it shall perform necessary verification according to various indication instruments designed and manufactured by the equipment to ensure the accuracy of the instrument indication. The scope of the test shall include the cooling system, the lubrication system, the exhaust gas temperature of the 丨 and 丨丨 grades, and the class of 丨 and control instruments. The air compressor load adjustment and operation schedule shall be determined according to the quantity of production input load, air volume, working pressure, and pipe network pressure loss.

6 Conclusion After the analysis and countermeasure analysis of the accidents of this air compressor, the following conclusions can be drawn: different types of air compressors have different performances, and practicality is fundamental. The selection of engineering design should be determined according to the user's requirements and the use and maintenance capabilities. The equipment installation should strictly follow the construction specifications to ensure the installation quality. During the use process, the appropriate operating conditions should be determined according to the load changes to ensure the air compressor. In economic operation, it is imperative to seek "foreign" and advanced, otherwise it will pose hidden dangers to the safety and economic operation of equipment.

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