Views: 5 Author: Site Editor Publish Time: 2022-12-14 Origin: Site
Starting capacitors are ac electrolytic capacitors or pp and polyester capacitors used to start single-phase asynchronous motors. So what happens when the starting capacitor fails? Will the motor run if the capacitor is broken? How to replace and repair, what should we pay attention to?
The method of how to judge the start capacitor is broken
1. look: see whether the capacitor bulge, swelling;
2. listen: connected to the motor to listen to the motor buzzing sound, with the hand to move the rotor speed is slow and weak;
3. smell: some capacitors have burnt smell because the current is too large to burn the surface (plastic shell capacitor);
4. Use multimeter capacitor stop to measure
Single-phase electric current flows through the motor does not produce a rotating magnetic field, need to use the capacitor to split phase, the purpose is to make the current in the two winding to produce nearly 90 ゜ phase difference, in order to produce the rotating magnetic field.
Capacitive induction motor has two windings, namely the starting winding and the running winding. The two windings differ in space by 90 degrees. A capacitor with large capacity is connected on the starting winding. When the running winding and the starting winding pass through single-phase ac, the current in the starting winding is 90 degrees ahead of the current in the running winding in time due to the action of the capacitor, and reaches the max value first.Two identical pulse 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, the rotor of the motor generates an induced current, and the current interacts with the rotating magnetic field to generate electromagnetic field torque, which makes the motor rotate.
To make the single-phase electric machine rotate automatically, we can add a starting winding in the stator. The starting winding and the main winding are 90 degrees apart in space, and the starting winding should be connected with a suitable capacitor in series, so that the current and the main winding are approximately 90 degrees apart in phase, namely the so-called phase separation principle.So two currents 90 degrees apart in time flow into two 90 degrees apart in space windings, which will create a rotating magnetic field in space. Under the action of the rotating magnetic field, the rotor can start automatically. After starting, when the speed rises to a certain value, the starting winding will be disconnected by means of a centrifugal switch or other automatic control device installed on the rotor, and only the main winding will work in normal operation.Therefore, the starting windings can be made into short-time operation mode. But in many cases, the starting windings are not disconnected. We call this kind of motor as capacitive single-phase motor. To change the steering of this kind of motor, it can be realized by changing the position of the capacitor series connection.
Common causes of starting capacitor damage are:
1. the voltage is too low;
2. Excessive load; Low speed and repeated start or long start time;
3. Influence of peripheral environment; For example, it is installed near the heat source in a place with poor heat dissipation or in a humid working environment;
4. Bad contact, capacitor wiring is also easy to cause burning capacitor;
5. Centrifugal switch adhesion (single motor with centrifugal switch).
Note for starting capacitor maintenance:
1. Find out the cause of the failure;
2. Can buy the same capacity, the same type of capacitor replacement;
3. If a capacitor of the same model cannot be found, search for its parameters and replace it with a new one.
Will the motor run if the capacitor is broken
The damage of the starting capacitor can cause the motor can’t start. If the power is on for a short time, it will only buzz, resulting in the current surge. If the winding is energized for a long time, it will overheat seriously and burn the motor. So it should be replaced immediately.
Precautions for starting capacitor replacement:
1. When dealing with the fault capacitor or replacing it, disconnect the switch or unplug the capacitor after disconnecting the power supply, and discharge the capacitor.
2. After the discharge of the capacitor, there will be a part of the residual charge temporarily discharged, should be again a manual discharge.
3. When discharging, first connect the grounding end of the grounding wire, and then use the grounding rod to discharge the capacitor several times until there is no discharge spark and discharge sound, and then fix the grounding end.
4. Due to the faulty capacitor may have bad lead contact, internal broken line or fuse broken, so some charge may not be released, so the maintenance personnel in contact with the faulty capacitor before, should also wear insulation gloves, first with a short route to the fault capacitor poles short, and then can begin to remove and replace.
5. If multiple capacitors are used in series, they should also be discharged separately.