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What performance of the motor is affected by winding slot ma

source：未知 time：2024-08-15 09:06nbsp; click：

A motor factory has manufactured nearly 100 YKK high-voltage motors for customers, with frame sizes ranging from H450 to 710. The heat load was designed to be very low, and the design temperature rise was lower than 68K. However, within less than half a year of operation, more than 40 motors had high temperature problems. From the test data, the temperature rise of motors with fewer slots is acceptable, while motors with too high temperature rise all use more slots. Today, Ms. Can will talk to you about the relationship between slot matching and motor performance.

Stator and rotor slot fit and motor additional losses

The additional losses of asynchronous motors are mainly caused by air gap harmonic flux. These harmonic magnetic fluxes produce high-frequency iron losses in the stator and rotor cores, and high-frequency current losses in the squirrel-cage rotor. Among them, the stator and rotor tooth harmonic flux plays the most significant role.

When the number of stator and rotor slots is very close, the width of the rotor tooth top will be very close to the wavelength of the stator tooth harmonics. Therefore, the pulse vibration in the rotor teeth caused by the stator tooth harmonic flux is small, and the pulse vibration loss is also very small. Similarly, the pulsation loss in the stator teeth caused by the harmonic flux of the rotor teeth is also small.

Therefore, when selecting slot matching for asynchronous motors, the number of slots in the stator and rotor should be as close as possible to reduce additional losses, but not equal, because this will generate synchronous additional torque and make the motor unable to start.

Although the harmonic loss in the rotor increases compared with the rotor with fewer slots, the pulsation loss generated in the stator teeth also decreases due to the decrease in the harmonic amplitude of the rotor teeth, so the total additional loss is similar to that of the rotor with fewer slots.

However, for the cast aluminum rotor with skew slots, the additional loss on the rotor side is much larger than that on the stator side because the loss caused by the transverse current between the bars is large and increases rapidly with the increase in the number of slots.

Therefore, in the cast aluminum rotor motor with inclined slots, the combination of few slots and near slots is generally adopted, that is, the number of slots in the stator and rotor is close, and the number of slots in the rotor is slightly less than the number of slots in the stator.

When the stator is an open slot or a semi-open slot and the rotor is a straight slot cast aluminum rotor, if the number of slots in the rotor is more than the number of slots in the stator, the no-load additional loss will increase, so it is best to use the combination of few slots and near slots.

Stator and rotor multi-slot combination and rotor air path

The motor with multi-slot combination may also have a serious defect, that is, the rotor tooth spacing. The area occupied by the ventilation slot tube is large, and the distance between the tubes is too small, which affects the ventilation and heat dissipation. Especially for multi-pole motors with radial ventilation, the impact is more serious.

Therefore, when using multi-slot combination, be sure to carefully check the rotor tooth spacing. A more direct and clear method is: remove the air-to-air cooler on the top of the motor, run the motor at no load, and use an anemometer to test the wind speed at the stator ventilation duct from the top of the motor. If the wind speed is found to be almost zero, it is possible that the rotor slot tooth spacing is too small, and the number of rotor slots must be appropriately reduced.

Methods to reduce motor temperature rise

● Using magnetic slot wedges can reduce motor temperature rise by about 10K.

● Using closed slots on the rotor can also reduce surface additional loss.

● Properly increasing the air gap is also a very convenient and effective way for manufacturers to reduce temperature rise. This method can not only reduce motor surface additional loss, improve motor efficiency, but also improve motor ventilation. Its disadvantage is that it will increase no-load current and reduce the power factor of the motor.

● For YKK series motors, the air-to-air cooler can be replaced.

● For cast aluminum rotor motors, while keeping the number of stator slots unchanged, selecting an appropriate number of slots to match the number of rotor slots will have a significant effect.

● When the number of stator and rotor slots remains unchanged, replacing the cast aluminum rotor with a copper bar welded rotor can achieve better cooling effect, but the cost will increase a lot.

Choosing a less-slot-near-slot fit will not only help reduce the hysteresis loss and eddy current loss on the surface of the motor, but also help improve the ventilation and heat dissipation conditions of the rotor, thereby improving the motor efficiency and reducing the temperature rise of the motor.

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