Motor fault analysis and protection in the product

Motor fault analysis and protection in the process of tire production

PLC has been basically popularized and applied in the tire industry, but from the depth and breadth of application development, it generally replaces relay logic control and switching value problems. For control systems above medium complex systems, a PLC always has 20% - 30% surplus software. Therefore, the development and application of the redundant software of the programmable controller must also be discussed and studied by the designers, which has a certain practical significance for further giving full play to the role of PLC in the automation of tire production

1 analysis of common faults of AC asynchronous motor

in the process of tire production, motor damage often occurs. Dozens or hundreds of motors in the tire factory are damaged in a year, which affects the quality and output of tires and brings certain economic losses to the enterprise. According to the use of several years, the reasons are analyzed. Most of them are improper protective measures. It is mainly caused by environmental conditions, line faults, load conditions, voltage level, operation and use, maintenance level and motor quality. Now a brief analysis of the above reasons is made

(1) environmental conditions

the environment plays a very important role in the normal operation of the motor to ensure the safety of experimental operators; The main function is that when the motor fails to reach the thermal balance at the limit temperature, it will be burned due to serious heating. Steam and superheated water are commonly used in the inner tube vulcanization workshop and outer tube vulcanization workshop of tire factories, and the temperature is relatively high in summer. The motor is installed between the steam and superheated water pipelines. The temperature of these pipelines is above 100 ° C. not only the temperature is high, but also the leakage of these pipeline interfaces is easy to spray onto the motor. If it is not handled in time, the insulation of the motor will be damaged to varying degrees. Every year, about 5 motors used in the double-mode vulcanizer in our factory are damaged due to reduced insulation. For another example, in the tread extrusion production line, due to the leakage of the steam stop valve on the head, the leaked steam is sucked into the main motor by the heat dissipation fan on the main motor, which shortens the commutator (commutator) of the 55kW DC motor, so the tire factory should solve the leakage problem of each pipeline in time

(2) high and low voltage

in some cases, the electric voltage will be too high and too low. In a short time, the high and low voltage will not affect the motor. However, if the motor works under low voltage for a long time, the motor will burn out due to overload due to the increase of copper consumption and the decrease of torque; When the voltage is too high, the stator magnetic circuit is saturated, causing a sharp increase in current, causing the motor to burn out

(3) line fault

when the three-phase AC asynchronous motor lacks two or three phases, there is no closed loop in the stator winding, that is, there is no current, and the motor does not rotate at this time. The damage of the motor is mainly caused by the lack of a phase, so regular maintenance of the main circuit contactor and line nodes of the motor is very necessary. Pay special attention to the phase failure of the motor in operation after starting. Once this happens, the power supply should be cut off immediately to protect the motor

(4) load condition

is a complex problem for the causes of motor overload, including heavy load starting, and motor overload caused by oil loss of gear or copper sleeve during mechanical rotation; There are also operators who fail to operate according to the process requirements, which overload the motor and eventually damage the motor equipment

(5) motor quality

for faults caused by the quality of the motor itself, it mainly depends on the motor manufacturer and motor repair department to control the manufacturing quality and repair quality, so that each performance of the motor can meet the technical requirements, so as to reduce the resulting faults

2 analysis of the protection performance of thermal relay

thermal relay is a traditional motor protector that is most widely used. It uses the thermal effect of current to bend the bimetallic sheet and push the node, cut off the control circuit and stop the motor. However, some electric cabinet motors equipped with thermal relays will still be damaged. In my opinion, thermal relays cannot be used as motor protectors in all occasions. Different protection methods should be selected for motor protection according to different occasions of use. Only in this way can the protection of motors be fundamentally solved. For example, the fabric supply motor in the tire cord cutting machine and the tread cutting motor of the tread extrusion line are all motors that start and brake frequently, which are easy to burn out in summer. For this kind of motor, the temperature rise protection of thermistor should be selected, and the effect is ideal. If the thermal relay is still used for protection, due to its frequent starting, the large starting current repeatedly impacts the thermal element, making its performance worse and the action deviates from the setting value. For another example, the hot water circulating pump used in the tread vulcanization, the motor used in the cooling water pump, the induced draft fan motor of the boiler, and the steel wire traction motor in the steel wire extrusion production line are all long-term running motors. Because the heating element is in the hot state for a long time, the performance of the heating element will also change, making the action value deviate from the set value. If the thermal relay wants to act in time and accurately, it needs to be set regularly, which is also a cumbersome thing for the tire factory. Therefore, it is ideal to use electronic protector for long-term motor. Judging from the motor damage in our factory, more than 80% of it is caused by the failure of the thermal relay. According to the analysis of the above situation, thermal relay is no longer an ideal motor protector

3 motor protector of redundant software

3.1 working principle of motor protector collection

the signal is taken from the secondary circuit of motor transformer. After bridge rectification and capacitor filtering, the voltage is obtained on R2, and the base and emitter of transistor T1 are applied with forward voltage. When the motor is working normally or 1.1 times the rated current, adjust the network resistance to make the crystal triode IB, Ube, IC are very small, the crystal triode is cut off, and the electricity on R4 is very low, The thyristor is cut off, and the output voltage on R7 is about zero. In case of motor overcurrent or short circuit, turn on the transistor, trigger the thyristor to turn on, and output a high level on R7 to the PLC input point to control the running state of the motor

3.2 application ladder diagram of motor protector

the program of motor protector adopts the C200H programmable controller address assignment number of Japan 0mron. Press the start button 00300 and pass through the normally closed nodes tim509 and 00301 to make 1000 on self-protection, and the motor starts. At the same time, 3205 internal relay and timer tim509 0n self-protection. When the timer tim509 normally closed delay node is off, the motor starting time is completed, and the motor enters the automatic protection working state. When the motor has overcurrent or short circuit, the input point x00400 0n → 3206 0n, the 3206 normally closed node in the 1000 circuit is off → 1000 output relay is off, and the motor stops working. If there is a short-circuit fault during starting, and the current is greater than the starting current of the motor, at this time 00401 0n → 3207 0n → 1000 output relay 0ff, the motor stops working. Using PLC to protect the motor from phase loss, overcurrent and short circuit, canceling the current relay, simplifying the main circuit of the motor and improving the reliability of motor protection

4 main faults of DC motor and their causes and solutions

(1) DC motor cannot be started

Table 1 causes and solutions of DC motor cannot be started reasons and solutions

after shutdown, replace bearings, Remove sundries

(2) excessive brush spark

Table 2 causes and solutions of excessive brush spark cause solutions

uneven spring pressure on the brush

properly adjust the spring pressure of spring Cui Lixin slightly 1 to keep the pressure of each brush at 1.47 × 104～2.45 × 104pa, or tighten the brush grip bolt according to the feeling on your hand, so that the brush grip is parallel to the surface of the commutator

the distance between the brush grip and the commutator surface is too large

adjust the distance from the brush grip to the commutator, generally 2 ~ 3mm

the brand of the brush does not meet the requirements

replace the original brand

the brush and the brush grip are improperly matched

cannot be too tight or too loose, so as to ensure that the brush can slide freely in the brush grip in the hot state, Sand the brush properly with sandpaper if it is too tight, and replace it if it is too loose.

the mica between the commutators is not pulled clean.

carve the remaining mica with a hand broach.

the mica between the commutators protrudes.

fine turning the commutator.

the center position of the brush holder is wrong.

move the brush holder seat, select the best position for sparks.

the motor is overloaded for a long time.

adjust the load, Within the rated load,

the commutation pole coil is short circuited

rewind the coil

the armature winding is open circuited

disassemble the motor, check the armature winding, and use a millivoltmeter to find out the open circuit. If it cannot be welded, rewind the

the armature winding is short circuited or the commutator is open circuited

when the motor is running, the commutator brush holder is on fire, and the armature is hot. Check whether there are copper chips in the mica slot, or use a millivoltmeter to measure the voltage drop between the commutators, Check the winding short circuit

adjust the applied voltage to the rated value

the commutation pole outgoing line is connected reversely

the curtain motor rotates slightly slowly and fires when loaded, and the two wire ends connected with the brush rod should be replaced

(3. How about the basic configuration 3) the motor speed is abnormal

the excitation winding circuit is open circuit, and the excitation drop transaction cost magnetic voltage is too low

check whether the magnetic field coil is well connected, Connect the wrong field coil or whether there is an open circuit inside the governor, whether the excitation undervoltage relay acts, whether the excitation voltage is normal

the brush is not in the normal position

adjust the position of the brush rod base according to the engraved mark

the armature and field coil are short circuited

check whether there is a short circuit on the surface of the commutator and the connector piece, measure whether the DC resistance of each pole of the field coil is the same

the applied voltage is too high or too low

measure with a multimeter, Adjust the voltage to the allowable range