The commonly used tools before motor maintenance mainly include: electric pen, vice, screwdriver, movable hand board, soldering iron, winding machine, scribing board, wheel shifter, chisel, groove cleaner, wire stripper, etc. Commonly used instruments for detecting motors are: digital multimeter, pointer multimeter, megohmmeter, clamp meter, etc. Commonly used materials for motor maintenance are: enameled wire, cable, insulation, wax pipe, insulating paper, grease, etc.
The motor model is three-phase asynchronous motor JO2-52-4, with power: 10KW, wiring: △, voltage: 380V, current: 20A, speed: 1450 r/min, frequency: 50HZ, weight: 107kg, etc. First, remove the motor housing with a screwdriver, and then test whether it is charged with an electric probe. Touch the metal part at the plastic end of the electric pen by hand, and touch the measured part with the metal part at the other end of the screwdriver. There are only a few common problems with the motor, and this big problem will not appear. There are several reasons why the motor can't start and hum. First, the resistance between the rotor and stator is too large. Generally speaking, the insulating paint on the stator core is not cleaned, or the insulating paint in the stator cavity is cleaned again, or the high-speed butter is added to the bearing by mistake when cleaning the bearing. Second, the winding wiring is wrong or the motor load is abnormal.
Megger is used to measure leakage. He said megohmmeter is also called shaking table. It is mainly used to measure the insulation resistance of motor winding to ground and whether the insulation material is aging. It can also be used to measure the insulation of other electrical appliances and equipment. According to the use voltage of electrical appliances, megohmmeters have different specifications, such as 500V, 1000V, 2500V and so on. When the voltage of electrical appliances is low, 500 can be selected.
00V megohmmeter, when the voltage of electrical appliances is high, megohmmeter above 2500V can be selected. Megohmmeter mainly includes: handle, counting plate, terminal, handle and other parts. The megohmmeter consists of a manual DC generator and a double-coil magnetoelectric current comparator.
Check the megohmmeter with a megohmmeter, close the test line, manually press the dial indicator pointer to infinity, and then instantly short-circuit the two test lines. At this point, the pointer should be 0, then disconnect the two test lines, and the pointer should return to the infinite end. When shaking the handle, don't short-circuit the measuring wire for too long, otherwise it will damage the megohmmeter. When measuring the insulation resistance of the motor to the ground, connect the connecting wire at the L end of the megger with the outgoing wire of the motor winding group, and connect the E end with the motor casing, and then turn the megger handle at the speed of 120 r/min. When measuring the interphase insulation resistance of the motor, connect the connecting wire of the L terminal and the connecting wire of the E terminal with the outgoing wire of the two-phase winding to be measured, then turn the handle of the megger, observe the pointer scale on the dial and judge the interphase insulation.
When measuring the insulation resistance of electrical appliances, connect all the wiring contacts of electrical appliances together, then connect the test wire at the L end of megger with the wiring contacts of electrical appliances, and connect the test wire at the E end with the housing of electrical appliances. Just turn the handle of the megger.
When measuring whether the motor winding or cable is short-circuited, connect any test wire of megger to the component lead-out wire on the side, and slowly turn the handle. If the instrument pointer quickly points to the 0 scale, it indicates that the measured element is normal, and if the instrument pointer does not move, it indicates that the measured element is short-circuited. When using a megohmmeter, you should pay attention to the following items:
1; The test line of megohmmeter needs a single multi-core wire, avoiding using more than two parallel wires, 2; When measuring the insulation resistance of electrical appliances, the selected model voltage of megohmmeter should be greater than the rated voltage of the measured voltage, 3; When measuring the insulation resistance of electrical appliances, the power supply must be cut off first, otherwise the human body will get an electric shock or the megger will be damaged. When measuring insulation resistance, the rotating speed of the handle should be 120 r/min. 1 min later, the reading when the hands are at rest is the measured insulation resistance. 5 Before measuring the capacitance, the capacitor should be discharged. Then, connect the test wires on both sides to the two pins of the capacitor, turn the handle for about 65438 0 minutes, and then remove the test wires. If the capacitor is discharged, it shows that the capacitor is good. When turning the handle of the megger, the human body can't touch the metal part of the test line, because the output end of the megger has high voltage output to avoid electric shock. After the test, the tested component must be discharged, otherwise it will lead to an electric shock accident.
Dismantle the motor, check whether the bearing, bearing seat and journal are noisy or worn, and replace or dispose of them. Write down the wire gauge, coil type, number of parallel circuits and winding spacing.
Remove the old winding and record the number of wires in each slot.
After slag removal, stator slot insulation is provided.
Select the appropriate thread form for winding and winding, seal the notch with grooves, and insulate the two ends from each other.
Welding wire, lead wire, end shaping and binding to check insulation resistance.
The winding is prebaked and dipped in insulating paint or paint.
After the winding is dried, it is assembled, tested and put into trial operation.
Generally speaking, the common faults of motors are as follows, and the solutions are as follows.
The motor heats up beyond the standard temperature or smokes. Reason; 1 The voltage is too low or overloaded, and the traction machine is stuck or poorly lubricated. Solutions; a； Test whether the voltage is too low. If the power supply used is too thin and the voltage drop is too large, replace the qualified power cord. b； Measure the motor current with an ammeter. If the voltage is normal and the current is too large, the motor load can be appropriately reduced. c； Troubleshoot the motor, add lubricating oil to the motor, and check whether the motor is stuck. If so, check the bearing or other parts. 2 Poor ventilation or heat dissipation of the motor. solve
Decision-making methods; A, check whether the electric fan is damaged or not firmly fixed with the bearing; B, check whether the cooling fin groove of the motor housing is blocked by foreign objects and whether the motor cover is damaged. 3 The voltage is too high or the wiring is wrong. Solutions; Check whether the voltage used meets the standard value and whether the wiring is wrong. For example, triangles are connected in a star row, and the motor current will increase when it is heavy. 4 or cage rotor disconnected or loose connection of slip ring rotor winding. 5 or too many positive and negative frequent starts. 6 or stator, rotor rub, solve; The bearing is loose or damaged, and there is something wrong with the rotor core. Correct the center line of the rotating shaft. 7 or stator winding short circuit in a small range, or stator winding local grounding. The solution is to check with a megger and open the motor shell for inspection.
The motor can't start with hum, the reason; 1 Open winding or out-of-phase power supply, solutions; There is something wrong with the link between the control switch and the motor junction box, the working voltage is out of phase, the control circuit is abnormal, and the three-phase winding is open. The working voltage is too low, so the inspection may be because the power cord is too low or the triangle is connected in a star shape. 3 Motor load is abnormal. Check whether the motor load is stuck or the resistance is too large, and whether both ends of the motor are damaged or stuck. 4 The resistance between rotor and stator is too large. 5 winding wiring error
The fuse blew after the knife switch was closed, the reason; 1 no phase start, high current. 2 Short circuit between control switch and junction box. 3 Motor load is too large. The fuse is too thin.
It is difficult to start the motor, and the speed drops immediately after the load. The reasons are: 1 The power supply voltage is low or the power supply is too thin, two of them should be staggered to form a star row, three rotor squirrel cage bars are loose or disconnected, and four stator windings are partially staggered. At this time, the current is unbalanced, so you can repair the motor and check whether there is any wiring error between windings. For motors with more than two connections, check whether one connection is broken.
When the motor is unloaded, there is a great imbalance in the three-phase alternating current. 1 The power supply voltage is unbalanced, the three-phase turns of the stator winding are not equal after rewinding, and the internal wiring of the stator winding is wrong.
The motor no-load current is too large, the reason; 1 The power supply voltage is too high, the air gap of the motor itself is large, the number of turns of the motor stator winding is not enough, the motor is improperly assembled, and the rotor is inflexible. It may be that the axial displacement of the rotor is too large, or the end cover screws are not tightened in balance. Adjust the end cover and re-experiment. 5 Motor stator winding should be star-shaped and connected into triangle by mistake.
The casing is charged, the reason; 1 insulation of lead wire or junction box joint is damaged, two winding ends are too long and collide with the end cover, three slots have iron filings and other sundries that have not been removed, and wires are embedded and collide with silicon steel sheets, which should be cleaned up; When four notches are sealed, some wires are put into insulating paper; 5 The shell is not reliably grounded.
Reasons for the decrease of insulation resistance; 1 Moisture intrusion or rain dripping into the motor; 2 dust queen winds up; The insulation of 3-person socket and junction box connector is about to be damaged; 4 insulation aging after motor overheating
The bearing cover is hot, the reason; 1 is a newly installed bearing. Not good; 2. The bearing is dry with little lubricating oil; 3 there is oil leakage and too much lubricating oil; 4 belt tension is too tight or coupling assembly steps are on the same line; 5 There are dust impurities and iron filings in the bearing oil; ⑥ Bearing is damaged; 7. The end cover and the base are not concentric and rotate tightly.
Generally speaking, there are many motor faults at these nine fault points with different reasons, which can be roughly divided into two aspects: electrical faults and mechanical faults. In addition, the motor absorbs electric energy from the power supply and outputs mechanical energy on the shaft, so the power supply and load should be carefully checked before the motor fails. Because the motor itself has many weak links, any accidental factors from the outside may lead to motor failure, so when analyzing the failure, we must carefully understand the phenomenon, from simple to difficult to find out the failure.
In order to improve the practical operation skills on site, according to the unified arrangement of the company, I attended a one-week motor maintenance training from July 13 to July 19. The training is summarized as follows:
First of all, we have an overall understanding of the power plant electrical system. The power plant electrical system consists of generator excitation system, generator, main transformer, GIS, high-voltage auxiliary transformer, start-up standby transformer, 6KV power distribution device, low-voltage auxiliary transformer and low-voltage power distribution device. Power plant substation equipment includes circuit breakers, disconnectors, buses, transformers, lightning arresters, capacitors and grounding devices; The main wiring mode of a power plant is related to the unit capacity, the selection of electrical equipment, the layout of power distribution devices, relay protection and control mode. Commonly used wiring methods include 3/2 circuit breaker wiring, unit wiring, and double-bus sectional bypass.
Second, the generator stator and rotor structure, cooling and ventilation system, sealing oil system, hydrogen system, stator cooling water system and matters needing attention during maintenance, as well as the tests to be done (recording the field temperature and humidity), including AC and DC withstand voltage tests, absorption ratio, polarization index, interlayer insulation and air tightness tests, etc. In addition, the teacher introduced the structure of the transformer, and explained the main structural components of the transformer-iron core, winding, transformer oil, gas relay, insulating sleeve, cooling mode, action principle of tap changer and why it is connected to the high-voltage side of the transformer (the current on the high-voltage side is small, and the capacity requirement of the connected tap changer is not high). Thirdly, four basic wiring forms of motor-motor inching forward and backward control circuit, double interlocking forward and backward control circuit and Y-△ step-down starter are emphatically introduced.
Dynamic control loop (suitable for small power supply capacity and large motor capacity to prevent large starting current from impacting the power grid) to Delta -YY two-speed control loop. And comprehensively study the motor inching forward and backward control circuit, from the low-voltage electrical components, including knife switch (fuse, air switch), AC contactor, thermal relay (protection device) model, internal structure understanding, component function, main parameters and the selection of connecting wire thickness, to how to draw component layout, wiring diagram and common fault finding according to the circuit schematic diagram. And through the way of troubleshooting each other, according to different phenomena to find faults and summarize. /kloc-there was a fault-finding test in the morning of July 9. Test scores include not only effective fault detection and elimination, but also safe and civilized operation, power-on times, correct use of tools and multimeters, and classification of tools after troubleshooting.
Through this training and study of motor maintenance skills, I realize that my hands-on ability and learning ability are insufficient, and I am not strict with myself in my daily work. I will actively adjust my mentality in my future work and study hard in the following aspects:
First, in the field work, the defects encountered and the treatment methods are classified and recorded, and the study is summarized every month.
Second, the working ticket and operation ticket safety measures and dangerous points and control measures must be clear and confirmed before work.
Third, in addition to daily work, we should strengthen theoretical knowledge and study in all aspects of electrical specialty to improve our professional level.
Fourth, adjust the mentality, take the initiative to undertake work tasks, and actively respond to difficulties in work.