Reasons for burning of air compressor starting resistor and improvement measures
From June 2009 to September 2011, there were 29 faults in the air compressors of 29 DF4 locomotives in our workshop. These faults can be roughly divided into the following categories: 1 Air compressor Control circuit failure; 2 air compressor mechanical failure; 3 sewage valve long exhaust; 4 other. It can be seen from the fault statistics that the main fault is the control circuit fault, and the frequent occurrence is that the starting resistor ST is long, and the result is that it is easy to cause burns and even cause a fire. Therefore, it is necessary to analyze the control circuit to take effective measures to prevent the burning of the starting resistor. 2.1 The main components of the compressor control circuit The DF4 locomotive adopts the NFT5 air compressor, and its model is Z-2.4/9, which can supply the compression required by the locomotive air brake system, the control air device and the auxiliary air device. air. The NPT5 air compressor is driven by a DC motor. The rated power of the motor is 22kW and the rated speed is 1000r/min. In order to reduce the inrush current when the air compressor starts, the starting resistor RST-stage step-down starting is used and the air pressure is applied. The exhaust line of the machine is equipped with a no-load solenoid valve 11YV to reduce the starting resistance. In order to make the auxiliary power generation automatically inject after the diesel engine is started, the auxiliary power generation switch 4S is closed, such as an auxiliary power generation control circuit. After the diesel engine starts, the auxiliary generator coil KMG is powered, and the two pairs of main contacts KMG are electrically closed, and the connection between the positive and negative wires of the voltage regulator AVR and the locomotive circuit is turned on, and the starter generator MG is automatically converted into a generator. Run as shown. After the diesel engine of the auxiliary power generation control circuit is operated, the key switch 7S on the main console is closed (the 8S of the auxiliary console is disconnected) to put the air compressor into operation, as shown. The operation and stop of the air compressor is automatically controlled by the air pressure switch 4SPA according to the air pressure in the total air cylinder. When the air pressure in the total air cylinder is lower than 750kP, the air pressure switch 4SPA contacts are closed, and the loop direction is : No load starting, while the main contact 1KMC is closed as shown. It is known that after 3s delay, the contact of the time relay 3KT acts, and the circuit goes: the 2KMC coil of the secondary operation contactor of the wind pump is energized, so that the main contact 2KMC in the loop is closed. The circuit trend is: shorted, the air compressor starts at full voltage, the speed rises to the rated value, and the auxiliary contact 2KMC in the circuit is disconnected, so that the 11YV coil is de-energized, so that the air compressor exhaust pipe and the atmosphere passage are closed. And wind the total air cylinder. When the air pressure in the total air cylinder reaches 900 kPa, the air pressure switch 4SPA contacts are disconnected, the contactor 1KMC and 2KMC coils are powered off, and the air compressor is powered off to stop working. Analysis of the control loop and fault condition of the air compressor, we found that the cause of the air compressor's step-down starting resistor RST is mainly due to the following aspects: (1) Buck resistor contactor 2KMC circuit fault 144 contactor has frequent KMC is a DC electromagnetic contactor with a model number of CZO-250/10, rated voltage of 440V and rated current of 250A. It consists of the main contact of the electromagnetic mechanism, arc extinguishing device and auxiliary contact. And other components. The cause of the 2KMC circuit failure should be caused by itself. The faults caused by its components are generally: 12KMC contactor coil burned or the negative end line is off; 2 contact burned, the contact armature has a slightly larger opening distance; 4 main The contact has foreign matter padding and does not pick up. Due to the failure of the 2KMC circuit of the contactor, it can be seen from the middle that when the contactor 2KMC is not energized, its main contact cannot be closed (or the main contact cannot be closed due to the main contact problem, the air compressor can only step down. Start. The current passes through the starting resistor RST. At this time, the wind pump pump is slow, and it takes a long time to operate to make the total cylinder pressure reach 900 kPa. Therefore, the power-on time of the step-down starting resistor (resistance value of 22) is too long. Directly caused the resistance to heat and burn red. The cause of the malfunction of the relay 3KT is: 3 improper adjustment between relays or excessive delay. When the time relay fault occurs, the 3KT in the loop can't be closed, and it can't play the delay action. That is, after 2s, the 2KMC contactor can't get electricity, the middle 2KMC main contact can't be closed, the wind pump secondary start can't be executed, keep the drop The voltage of the starting resistor RST circuit is energized, causing the RST heat to burn red. Cause of failure of IKMC main contact adhesion: It can be known from the circuit that when the air pressure in the total air cylinder reaches 900 kPa, the air pressure switch 4SPA is automatically disconnected, the contactor 1KMC is powered off, and the auxiliary contact 1KMC is disconnected to make the contactor 2KMC When the power is off, the 2KMC main contact is disconnected, but the 1KMC main contact fault cannot be disconnected, causing the buck start resistor loop to remain energized. BST's working hours are too long, and it is inevitable that it will be hot and red. Fault Hazard As described above, the cause of the start-up resistance RST caused by the control circuit is long or even burned. Usually, when the start-resistance heats up and the red-burning fault occurs, it can only be solved by manually disconnecting the auxiliary power generation switch 4S. Once this failure occurs and is not discovered by people, it will cause the air compressor to start the resistance RST to burn, and even cause the electrical cabinet to catch fire, which directly affects the safety of transportation production, especially in the fire-proof area - refinery, ethylene, etc. If the fault occurs in a burning and explosive place, the damage caused will be incalculable. Through the analysis of the cause of the failure, I believe that the following measures can effectively prevent such failures. Reconstructing the air compressor control circuit The air compressor control circuit is the foundation for protecting the step-down starting resistor circuit. Only when the fault is completely removed can the real protection be achieved. In the middle of the protection circuit (see), the intermediate relay 12K normally closed contact starts to control the power generation of the auxiliary generator. When a fault occurs, it can automatically prevent the air compressor from starting to reduce the heating resistance and protect it. After the diesel engine starts normally, after the auxiliary generator generates electricity, the switch 7S or 8S is closed, the contactor 1KMC circuit is turned on, and the 1KMC is interlocking. Because the 2KMC circuit or 3KT fault, the 2KMC circuit is not turned on, and the protection circuit 5s After the delay, the time relay 4KT is turned on, and the intermediate relay 12K circuit is turned on. Due to the action of the 12K circuit, the newly added alarm bell sounds, notifying the driver that the circuit has failed, and then controlling the 12K reverse interlocking of the auxiliary power generation. When the auxiliary power generation circuit is turned off, the air compressor stops working due to the failure, and the heat generation burn caused by the continuous conduction of the starting resistor RST circuit is prevented. (2) After the pump is finished, the 2KMC main contact is disconnected. When the 1KMC main contact is stuck, the 2KMC main contact is disconnected, and the 1KMC main contact is stuck. Therefore, the 2KMC reverse interlock is connected, after 5s. The relay 4KT is turned on, the intermediate relay 12K circuit is turned on, the 12K reverse interlock is disconnected, the auxiliary power generation circuit is cut, and the air compressor stops working, preventing the RST heat loss from burning. 3.2 Selection and maintenance of contactors and relays The quality of contactors and relays directly affects the quality of the circuit conduction. Therefore, when purchasing, try to select the device that meets the specifications to avoid malfunction due to material quality. Strengthen daily maintenance: 1 frequently clean the contacts, keep the contact surface clean to reduce the contact resistance; 2 check the state of the static and dynamic contacts irregularly, if there is slight burning, it should be polished, and the burning will be replaced immediately. To ensure the reliability of the contact closure and disconnection; 3 check the arc extinguishing device of the contactor to ensure the reliability when the arc is extinguished; 4 periodically disassemble the relay to detect whether the capacitance inside the circuit and the diode are broken down; The time setting of the time relay should be adjusted improperly; 6 the coils in the contactor and relay should be kept intact and there is no off-line phenomenon. After three months of investigation, no damage to the starting resistor was found, and the circuit transformation was improved to achieve the expected results.
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