Views: 8 Author: Site Editor Publish Time: 2023-02-01 Origin: Site
Capacitive induction motors have two windings, a start winding and a run winding. The two windings are spaced 90 degrees apart. A capacitor with a large capacity is connected in series on the starting winding. When the running winding and the starting winding pass through single-phase alternating current, due to the effect of the capacitor, the current in the starting winding is 90 degrees ahead of the current in the running winding in time, and reaches the maximum value first.Two identical pulsed magnetic fields are formed in time and space, so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, an induced current is generated in the rotor of the motor, and the current interacts with the rotating magnetic field to generate The electromagnetic field torque makes the motor spin up.
Capacitor start motors can be divided into capacitor split phase start motors and permanent split phase capacitor motors. It is characterized by simple structure, quick start and stable speed, and is widely used in electric fans, exhaust fans, range hoods and other household appliances. The stator winding of the capacitor-split motor has a main winding and an auxiliary winding (starting winding), and a large-capacity starting capacitor is connected in series in the starting winding, so that the main and auxiliary windings generate a voltage phase difference close to 90° after power-on. As a result, a large starting torque is generated to make the rotor start and run. When the permanent split-phase capacitor motor is powered on and running normally, the large-capacity capacitor is connected in series with the starting winding. Due to the small starting torque of the permanent split-phase motor, it is suitable for electrical appliances such as exhaust fans and exhaust fans. Capacitor-started motor, the running winding group is set in forward and reverse phase connection method, as long as the serial connection direction of the running winding and starting winding is switched, the reverse and forward direction of the motor can be easily realized.
How to judge whether the capacitor is burnt out
一、External observation and auscultation method
1. If it is found that the shell of the capacitor is deformed and bulging,it means that the insulating medium or electrodes inside the capacitor must be damaged, and it should be withdrawn from operation immediately and replaced with a new one.
2. If it is found that the high-voltage porcelain bottle of the capacitor flashes and bursts, or oil sprays or overflows the internal insulating medium, etc., it should also be judged as damaged capacitors immediately. The damaged products must be properly handled and recycled, and replaced with new ones.
3. When the capacitor is in normal operation, there should be no sound. If you hear abnormal "cracking", "cracking" discharge sounds or "humming" dull sounds, it means that there must be a fault inside the capacitor, and the capacitor should be stopped immediately for further inspection or replacement.
4. When the capacitor is running, if it is found that the group of capacitor switches has an accident trip or a high-voltage drop and the fuse is blown, it should be out of operation, and it can be put into operation again after it is confirmed that the capacitor is not faulty.
二、Insulation shaking meter test method
Discharge and untie the external connection of the capacitor to be tested.
Select a megohmmeter with a voltage level equivalent to the working voltage of the capacitor (general regulations: use a 500-volt or 1000-volt megohmmeter below 1000 volts; use a 1000-volt or 2500-volt megohmmeter for a voltage above 1000 volts) insulation resistance. Wear insulating gloves or stand on the insulator when shaking the test, keep a constant speed at a speed of about 120 rpm, and then reliably touch the test line (pen) to the conductor under test of the capacitor for one-time measurement.After charging the capacitor for 30 to 60 seconds by the shaker generator and reading the data, quickly remove the test line (pen) from the tested product to cut off the circuit, and then lower and terminate the rotation of the shaker handle，in order to prevent the remaining charge of the charged capacitor from being discharged through the internal circuit of the megger and damage the indicator needle, and burn the internal components such as the diode in the megger.
Discharging the capacitor in a short circuit can be judged according to the following three results:
1. If the needle of the megohmmeter starts from zero when shaken, gradually increases to a certain value and tends to be stable, and there is a crisp sound and sparks of discharge when the capacitor is short-circuited after shaking, it means that the capacitor has good charging and discharging performance.As long as the insulation is not lower than the specified value, the capacitor can be judged to be qualified, and it can be put into operation with confidence.
2. If the megohmmeter has some readings, but there is no discharge spark when there is a short circuit, it means that the connecting wire between the electrode plate and the terminal is broken, and it must be out of operation or replaced with a new one.
3. If the megohmmeter stops at zero, it means that the capacitor has been broken down and damaged, and should not be used again.
三、Test with a multimeter
Turn the multimeter to the high stop R×1000. When the black and red hands touch the two poles of the capacitor at the same time, the pointer should swing quickly at a large angle, and then the pointer will slowly return to its original position. Then exchange the black and red hands for testing, and the multimeter repeats the above actions, indicating that the capacitor is intact.During the test, if the hands of the watch do not swing or swing very little, or the hands of the watch do not return when they swing to the maximum position or return to a certain position and stay still, it means that the capacitor is broken. After confirming that the capacitor is damaged, just replace it with a new one according to the capacity and voltage marked on the original capacitor.
What is the reason why the starting capacitor is easy to burn out
1. The product quality problems of the filter capacitor itself, such as unqualified manufacturing process and materials, discrepancy between the marked capacity and the actual capacity, and aging caused by long-term use will cause burnout.
2. External environmental influences, such as installing in a place with poor heat dissipation or close to a heat source, poor wiring of capacitors, poor contact, etc. can also easily cause burnout.
3. Harmonic problem, harmonics cause the filter capacitor to resonate, causing the capacitor to over-current and burn out.
Several reasons for capacitor burnout
1) Burning caused by insufficient withstand voltage and overvoltage;
2) Burning caused by exceeding the maximum operating current;
3) Burning caused by exceeding the maximum working temperature;
4) Burning caused by frequency mismatch and excessive loss;
5) The capacitor is burned due to the dryness of the electrolyte.