As the saying goes, "Mechanical equipment is afraid of stopping, electrical equipment is afraid of opening," and this is true in actual production. Generally speaking, the winding machine does not start, and it can be found from several aspects such as wiring error, voltage not meeting the motor nameplate requirement, protection device trip, startup equipment problem, stator and rotor winding failure, and starting load.
The product is restarted after the normal shutdown in the production process. Generally, the motor cannot be started normally due to the wiring error, and the wire-wound motor that is rewired after the new installation or overhaul is often prone to wiring errors. The wiring error referred to here mainly refers to the wiring error between the motor side current transformer and the power distribution cabinet with differential protection function. If this happens during the actual wiring process, it will trip when the motor starts up due to a differential fault reported by the protection device. Therefore, when the motor side transformer and the power distribution cabinet side transformer are connected, special attention should be paid to the fact that the current detected by the two transformers installed at different positions is the same phase winding of the motor, and the same phase can be connected to the motor as differential protection. protective device.
Winding machines are medium and high voltage electrical equipment. In practice, the equipment cannot be turned on because of voltage problems. Unless multiple devices are turned on at the same time, the power supply voltage is greatly reduced and cannot be turned on normally.
Tripping of the protection device is the most common and most important reason why the winding machine cannot be opened normally. The trip of the protection device during start-up is generally due to overcurrent protection and differential protection. There are three reasons for the overcurrent protection: (1) The protection device overcurrent protection value setting is unreasonable. (2) The load is too large or there is a mechanical connection failure. (3) The wound motor itself or the starting device is faulty.
When the winding machine causes a trip signal from the protection device due to overcurrent during the starting process, it should first check whether the overcurrent protection value setting is reasonable. Generally speaking, the winding machine starting current is 3 to 5 times of the rated current, and the protection device sets the motor current protection setting into current quick-break protection and over-current protection. During the start-up of the motor, the current high-speed high value plays a major role in protection. Therefore, it is only necessary to check whether the high-speed value is too low. If it is less than 5 times of the rated current, it can be appropriately amplified according to the requirements of the protection device manual. After amplification, when it is confirmed that the motor and related equipment have no other faults, it can be started again; secondly, it is judged whether it is an overcurrent trip caused by excessive motor load or mechanical failure. This kind of situation generally occurs when the equipment suddenly stops during normal operation and trips when it is turned on again. At this time, the slow-turn motor should be used (mainly for vertical grinding maintenance and online surfacing, located on the non-load side of the winding motor, through the opposite wheel and motor Connected to the motor to determine if the motor failed to start because of a mechanical device that was dragged by the winder. If the mechanical fault is eliminated, the slow-rotating motor can be used to drive the wound-wound motor for about half an hour, and then the re-starting of the wound-wound motor can be performed; finally, the motor itself or the motor starting device is faulty to cause over-current protection of the protection device. Under normal circumstances, if it is the overcurrent protection caused by the winding machine itself or the startup equipment failure, it is often accompanied by differential protection.
At this point, you need to find out in detail which part of the problem has occurred. For the wound motor itself, the stator winding and the rotor winding of the wound motor can be insulated and tested by means of a shaking table (2500V shaker should be used). If there is a low insulation or a large difference, it needs to be tested by special experiments. determination. The winding machine is usually started by a liquid varistor. Our company has experienced a situation in which the motor cannot be started due to the falling off of the static plate of the liquid varistor. Therefore, when the winding machine cannot be started normally, the liquid varistor as the starting device is also an important inspection item.
Among the reasons why the protection device cannot be normally started due to the differential protection, except for the failure of the motor itself, most of the cases are caused by the differential protection circuit. In the actual production process, due to the large vibration of the vertical mill, etc., the differential protection tripping caused by the looseness of the terminal of the current transformer of the motor side is easy to occur. Therefore, when the equipment is inspected and repaired, the terminal of the motor side transformer should be fastened. As an important overhaul.
Analysis and treatment of overheating of winding machine motor
In normal operation, the motor is overheated for the following reasons: voltage is too high or too low, overload, insufficient cooling air volume, motor failure.
The overheating of the wound motor caused by the high or low power supply voltage rarely occurs, and the motor overheating caused by the fault of the motor itself can be checked by the change of the running current and the motor protection device. Motor overheating due to insufficient cooling air volume is the most common cause. The winding motor cooling air is generated by the fan mounted on the motor shaft as the motor rotates, and is blown to the motor winding through the air passage at the top of the motor housing, thereby achieving the purpose of cooling the motor. Due to the relatively large dust on the slag powder production site, after years of operation, it is easy to cause air duct blockage. Therefore, the air duct of the winding machine should be flushed and cleaned regularly.
Collector ring burnout and brush jump spark
The main difference between the winding machine and the squirrel-cage motor is that the three end wires of the winding of the winding machine are connected to three copper or steel slip rings mounted on the rotating shaft, and are connected to the external circuit through a brush. This unique structure of the winding machine leads to the occurrence of the occurrence of the collector ring burnout and the brush jump spark. Generally speaking, the reason for this situation is that the brush and the collector ring are not well meshed, the brush cannot fully contact the surface of the collector ring, the brush and the brush box are not well matched (too loose or too tight), and the brush The pressure is not suitable, the number of brushes is unreasonable, and the collector ring is elliptical.
If the contact area between the brush and the surface of the collector ring is less than 70%, the brush having a good contact surface has a large amount of current flowing, and the amount of heat is large, which is prone to burnt and burned. Further increase the load of other brushes, in severe cases, it will burn out the phase brush and damage the slip ring. Therefore, when routine maintenance of the winding machine, special attention should be paid to whether the contact area between the brush and the collector ring is intact. When the brush production batch used is different, the brush and the collector ring may be damaged due to the difference in the composition ratio of the brush. Therefore, the same production batch should be used when replacing the brush.