There are two possible reasons:
1. Because the magnetic core is burned with fire after removing the coil, the magnetic permeability of the core decreases, causing the no-load current to increase.
2. The parts were loosened during disassembly, causing displacement when put back in use, which in turn increased the no-load current.
Single-phase motor:
Single-phase motor generally refers to a small-power single-phase asynchronous motor powered by a single-phase AC power supply (AC220V). This type of motor usually has two-phase windings on the stator and a common squirrel-cage rotor. The distribution of the two-phase windings on the stator and the difference in power supply can produce different starting characteristics and operating characteristics.
When a single-phase sinusoidal current passes through the stator winding, the motor will generate an alternating magnetic field. The strength and direction of this magnetic field change sinusoidally with time, but it is fixed in spatial orientation, so This magnetic field is also called an alternating pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same speed and opposite directions of rotation. When the rotor is stationary, these two rotating magnetic fields produce two torques of equal magnitude and opposite directions in the rotor, so that the combined The torque is zero, so the motor cannot rotate. When we use external force to rotate the motor in a certain direction (such as clockwise rotation), the cutting magnetic force line movement between the rotor and the rotating magnetic field in the clockwise direction becomes smaller; the motion between the rotor and the rotating magnetic field in the counterclockwise direction becomes smaller. The cutting magnetic field line movement becomes larger. In this way, the balance is broken, the total electromagnetic torque generated by the rotor will no longer be zero, and the rotor will rotate in the pushing direction.
To make the single-phase motor rotate automatically, we can add a starting winding to the stator. The starting winding and the main winding are 90 degrees apart in space. The starting winding must be connected in series with a suitable capacitor. This makes the current in the main winding approximately 90 degrees out of phase in phase, which is the so-called phase separation principle. In this way, two currents that are 90 degrees different in time are passed into two windings that are 90 degrees different in space, and a (two-phase) rotating magnetic field will be generated in space.
Under the action of this rotating magnetic field , the rotor can start automatically. After starting, when the speed rises to a certain level, the starting winding is disconnected with the help of a centrifugal switch or other automatic control device installed on the rotor. During normal operation, only the main winding works. Therefore, the starting winding can be made to work in a short time. But many times, the starting winding is not disconnected. We call this kind of motor a single-phase motor. To change the direction of this kind of motor, just change the terminal of the auxiliary winding.
In single-phase motors, another method of generating a rotating magnetic field is called the shaded-pole method, also known as single-phase shaded-pole motors. The stator of this kind of motor is made of salient pole type, and there are two types: two-pole and four-pole. Each magnetic pole has a small slot at 1/3--1/4 of the full pole surface. Divide the magnetic pole into two parts. Put a short-circuiting copper ring on the small part, as if to cover this part of the magnetic pole. So it is called shaded pole motor. The single-phase winding is installed on the entire magnetic pole, and the coils of each pole are connected in series. When connected, the polarities generated must be arranged in order of N, S, N, and S. When the stator winding is energized, a main magnetic flux is generated in the magnetic poles. According to Lenz's law, the main magnetic flux passing through the short-circuited copper ring generates an induced current in the copper ring that lags 90 degrees in phase. The magnetic flux generated by this current The flux also lags behind the main magnetic flux in phase, and its role is equivalent to the starting winding of a capacitor motor, thereby generating a rotating magnetic field to rotate the motor.