ã€Abstract】 Imported 310DA3 Centrifugal Air Compressor frequent downtime problems and countermeasures Luoyang Petrochemical Plant polypropylene company in 1995 from the United States ELLIOTT company introduced 310DA3 Centrifugal Air Compressor (hereinafter referred to as air compressor), since Since commissioning, the failure rate is high. Up to now, the crew of unplanned downtime has reached hundreds of times, the most serious one, once due to lubricating oil failure caused by centrifugal compressor parts seriously damaged, and cause major equipment accidents. Although I plant several times to invite foreign businessmen to the scene to solve the problem, but with little success. In response to this issue, we have made long-term efforts on the meter side, have taken many measures to receive the expected results. 1 Control System Introduction The centrifugal air compressor unit uses a separate ESD (emergency stop system) for control. The control system regulates inlet, outlet and temperature control methods at all levels, monitors operating system parameters, provides alarm and trip displays, organizes drive and stop sequences, translates operating modes, stores relevant data and provides hard-copy output via printer interface. Solidification software is used in the ESD system, and the user can not call the internal program. Control panel using a microcomputer. 2 air compressor operation since the main reasons for downtime This centrifuge early on caused frequent unplanned downtime, from the display of information, the main reasons for the shutdown are as follows: 1) the conditions of the interlock; 2) mechanical reasons; 3 ) Controller or drive failure; 4) vibration sensor failure; 5) unit vibration value is high; 6) main motor current ripple interlock. It seems that the cause of shutdown of the unit is many. Of course, can not rule out the crew design or manufacturing problems. However, as a professional instrument maintenance staff, we need to analyze from the perspective of instrumentation, and try to rule out the control problems. 3 Analysis of downtime Unit put into operation early, we and foreign businessmen have suspected DMD controller problems, replace the backup controller, the unit's health has not improved, so that we basically ruled out the controller has a problem, and that the problem out In the periphery. The reasons for the analysis are as follows: 3.1 Mechanical and technical reasons for the unit interlock down There are several reasons for downtime in this regard: 1) some mechanical components of the new unit damaged by long-distance transport; 2) whether the installation method and accuracy meet the standards; 3) Some designs do not meet the specific conditions of our factory; 4) Lack of experience of process and maintenance personnel. 3.2 On the drive or controller failure caused by downtime Initially, many times due to drive failure caused by downtime, we promptly replaced the new drive, but the problem remains, prove that the fault is caused by external causes, the analysis that the failure may be The following two reasons. 1) Power System As in this system design, all instrumentation equipment does not UPS system. The required 110V AC power supply for the control system (220V AC transformers) requires very tight (+ 5%) fluctuation. Therefore, the controller will automatically diagnose "controller failure" when the meter is powered off instantly or the voltage fluctuates too much. 2) anti-interference ability a) poor quality controller, especially anti-interference ability. b) many sources of interference. In the early stage of operation, due to more faults, to facilitate the handling of problems, the on-site control box door often does not close. The mobile phones and walkie-talkies that are used in the field not only have a large transmitting power, but also large numbers, and the impact is also small. We have conducted experiments to confirm that the mobile radiotelephone is a common source of interference in vibration monitoring systems. c) Ground does not meet the requirements. In 1996, there were many occasions because of the interlocking parking caused by thunder and lightning. This fully proves that the unit control system grounding does not meet the requirements. 3.3 Shaft vibration on the unit This centrifugal air compressor has two vibration probes on the gearbox to monitor the vibration of the gear shaft on the high and low speed sides respectively. Probe shaft vibration detection using eddy current principle, the probe consists of high-frequency signal through the coil composition, when the distance changes, the resulting physical physics of the probe high-frequency signal energy loss, so that the remaining energy and distance corresponding This voltage signal is sent to the controller for display and alarm. The vibration transducer (preamplifier) ​​in the factory is calibrated according to a certain metallic material, the coaxial cable is also caused by a certain percentage of electrical length fault or vibration value exceeded the maximum number of parking. We think there may be the following reasons. 1) vibration detection system failure. Probes have to undergo a rigorous anti-magnetization process at the factory, requiring no end-shields to scratch or peel off when used. And we in the installation, in accordance with the manufacturer's installation method, due to the actual distance between the probe and the shaft can not be seen, the probe is often to touch the shaft and then returned, and then measure the gap voltage, the distance between the two adjustments (If not, although the gap voltage can be measured, the probe can not sense the rotor vibration.) If the force is too high, the probe may be damaged. 2) The gap voltage is not suitable. Based on the reference provided by ELLOTT, the gap voltage during installation is 4-6V. Based on our experience with Bentley vibration probes (either 3300V or 7200 Series), the gap voltage is at (9-10) V + 0.5V, so this reference may be too small. 3) The shield of the extension cable and signal cable may be damaged or the grounding is not good, and strong interference from the outside influences the signal. 4) The connection between the extension cable and the signal is poor, causing the transmitter to output a 4-20 mA signal below 3 mA while "Vibration Transmitter Failure" appears. 5) If the vibration transmitter installation insulation is poor, the shell or cable connector hit the wall of the junction box, the vibration circuit will be grounded, the same will be "vibration transmitter failure." 6) Due to the presence of instrument cables and electrical cables in the wiring closet, "electrical noise" interference can occur with each other if improperly installed. 7) Improper grounding. 8) There is dust or oil on the impeller. If the inlet air filter is not good, dust on the impeller will directly affect the detection of vibration values. For example, in August 1996, dust was found on the impeller during the dismantling of the unit, reaching a maximum thickness of 1.5 mm. 9) Internal mechanical problems. 3.4 About Motor Current During the past few years, the motor current fluctuates. Since the signal detection and display belongs to the electrical and instrumentation, the problem is not good to judge. According to the analysis, there may be the following reasons. 1) The load fluctuates when the unit is running. 2) Detection and transmission unit failure. 3) Power cables are subject to external influences causing voltage fluctuations. For example, in March 1996 and October 1997, all the other plants were started by the plant to cause the current to fluctuate between 50-100mA. 4) some of the components to adapt to poor environmental ability. According to our observation, current fluctuations often occur after a period of time, which may be related to the heat generated by the test element and thus affecting normal operation. 4 measures to improve After long-term observation of maintenance analysis, basically clear down the cause of the failure caused by the instrument and one by one has been improved. 1) It is recommended to minimize the downtime caused by the import of machinery and process. For example, once the level 1 outlet pressure transmitter in the open, stop showing fault, because the inlet valve is fully closed at this time, making a vacuum outlet level, the transmitter detects the vacuum pressure, the output signal is lower than 3.0 mA and the alarm, we modified the software by ELLOTT, making the loop in the inlet valve is fully closed invalid. 2) Conduct a thorough inspection of the wiring of the existing instrument, and rectify the possible place of poor contact. 3) In August 1996, an online UPS system was added to completely eliminate the shutdown of generating units caused by power outages. 4) The grounding system shall be rebuilt according to the requirements of foreign investors. The grounding bus shall be connected to the pipe network buried underground, and the instrumentation and the protection ground shall be completely isolated. 5) Carefully check the shield of each signal line, and replace the signal cable shield is not good; increase the insulation of the vibration transmitter. 6) Check the probe, draw its operating characteristic curve, select the mid-point of its working linear segment, and with foreign recognition, adjust the gap voltage to 8V by the foreign supervisor. 7) Strict probe installation, confirm each part before installation, the cable is intact, check whether there is any bad connection or oxidation phenomenon, and check the installation at any time, and take care to avoid damaging the components, the screw thread and the probe. 8) The establishment of special maintenance team to strengthen the standardization of on-site management, control the door must be closed before booting. 9) Strengthen the inspection of instruments and found that abnormalities were checked and dealt with promptly, annihilating the accident in the bud. V. CONCLUSION After long-term research and development, no small gain has been achieved in this respect. The failure rate has dropped markedly, and the unplanned stoppage of the unit has been basically eliminated. The results obtained from the statistics in Table 1 can be seen. The table in 1999 unplanned parking once. October 1999 controller crashes, all the keys can not be operated, the unit still running can not stop, after forced parking, check the controller board is faulty, after troubleshooting to normal, and from the United States to buy a new control Spare. Table 1 Unplanned parking statistics Time Non-scheduled parking frequency 1996 71 1997 36 1998 1 1999 1 Currently the unit is in good working condition and we will make persistent efforts in the future to ensure the long-term stable operation of the equipment.
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