why armature slots are skewed Reduce the magnetic locking - Cogging torque skewed slot Unveiling the Purpose of Skewed Armature Slots in Electric Motors

Skewedrotorslots The design of electric motors involves intricate engineering to ensure efficient and smooth operation. One such design consideration, particularly in squirrel cage induction motors, is the skewing of rotor slots.作者：Y Xiang·2025—This paper investigated theskewfactor ofskewedrotorslotsand proposes an electromagnetic force wave analysis method. While it might seem like a minor detail, why armature slots are skewed is a fundamental question with significant implications for motor performance. This article delves into the engineering rationale behind this practice, exploring how it addresses critical operational challenges like noise, vibration, and torque instability.

The concept of skewing refers to angling the slots in the rotor relative to the motor's axis of rotation, rather than having them perfectly parallel. This slight tilt, often by an angle equivalent to a fraction of a stator tooth pitch, is not arbitrary but a deliberate engineering choice. The primary drivers behind why armature slots are skewed are to minimize vibration, eliminate cogging torque, and reduce harmonics in the air gap fluxThe motor may be noisy, or there may be stray torques that lower the torque during starting or acceleration..

Addressing Cogging and Magnetic Locking

One of the most significant benefits of skewed armature slots is the mitigation of cogging torque and magnetic lockingFundamentals of DC Motors - Monolithic Power Systems. When rotor slots are not skewed (i.eSkew angle in squirrel cage induction motor., they are axial), there's a tendency for the rotor's magnetic poles to align perfectly with the stator's poles.Why is the rotor of an induction motor skewed? This alignment, especially at specific speeds or during startup, can create a strong attractive force known as magnetic locking. This phenomenon, often referred to as cogging, can lead to undesirable jerky movements, increased starting current, and reduced overall torque, particularly during low-speed operation.

By skewing the rotor slots, this direct alignment is broken.作者：S Ji·2023·被引用次数：4—As shown in Figure 2, theskewedstatorslotdesign is a layer of stator punches evenly rotated to place the winding coil teeth so thatslotsare deflected by a ... As the rotor turns, the conductors within the skewed slots gradually enter and leave the magnetic field produced by the stator teethThe motor may be noisy, or there may be stray torques that lower the torque during starting or acceleration.. This gradual interaction prevents the rotor from snapping into a locked position, thereby smoothing out the torque delivery. The reduction of magnetic locking is a paramount reason for employing skewed rotor slots. This also translates to lower cogging torque, a crucial factor for applications requiring precise control and quiet operation.

Minimizing Noise and Vibration

The occurrence of cogging torque and harmonic fluxes directly contributes to motor noise and vibration. When the magnetic fields interact in a pulsating or jerky manner due to poorly aligned slots, the motor casing and internal components can resonate, producing an audible magnetic hum and noticeable vibrationsInduction motor uses special design rotor. Looks like a cage used for squirrels. It's the reason why it's known as a squirrel cage type rotor.. Skewed slot designs are highly effective in making the motor run quiet and reduce magnetic hum and noise in the motor.

Furthermore, the uneven pulling and pushing forces generated by the interaction of stator and rotor poles, especially when slots align perfectly, can induce significant vibrations. Skewing helps to distribute these forces more evenly over the length of the rotor. This smoothing out of forces directly leads to a reduction in noise and vibration and contributes to a smoother running motor with smooth out torque fluctuations.

Reducing Harmonics and Improving Air Gap Flux

The magnetic field in the air gap between the stator and rotor is not a perfect sinusoid; it contains higher-frequency components known as harmonics. These harmonics, introduced by the slotting of both the stator and rotor, can have detrimental effects on motor performance. They can lead to parasitic torques, increased losses, and reduced efficiency.

Skewing the armature slots is a practical method to reduce harmonics in the air gap flux.Analysis of Vibration and Noise for Different Skewed Slot ... By averaging the magnetic flux linkage over the skewed conductor length, the effect of individual slot harmonics is diminished.2025年6月20日—The rotor of an induction motor is skewed (slots are not parallel to shaft but at a slight angle) mainly to:Reduce the magnetic locking( ... This results in a cleaner, more sinusoidal air gap flux distribution, which improves the overall electromagnetic performance of the motor. The angled orientation ensures that the rotor conductors are not simultaneously exposed to the same magnetic pole, thereby attenuating the harmonic content.

Practical Considerations and Variations

While skewing is highly beneficial, it's important to note that it's not always applied universally. In very small DC machines, for instance, armature slots are sometimes not made axial but are skewed.The Rotor Slots Are Slightly Skewed In Squirrel Cage In... This can make the winding process a bit more challenging, but the benefits in terms of performance often outweigh this difficulty. The degree of skew, or the skew angle, is a critical design parameter. Research and analysis, such as the studies investigating the effects of rotor step skewing, demonstrate that an excessively large skewed angle can potentially affect the motor's electromagnetic performance.2023年5月11日—Skewing the rotor slotsensures that the rotor conductors gradually enter and leave the magnetic fieldproduced by the stator teeth. This ... Therefore, an optimal skew is carefully determined based on the specific motor design and application requirementsMethod of winding skewed armature and device therefor.

The NIDEC CORPORATION and other researchers have extensively studied the properties of skewed slots and their impact on motor dynamicsWhy rotor skewing is used in a three phase squirrel cage .... The effectiveness of a normal skewed slot has been proven in reducing vibration and noise. Advanced designs, such as double skewed slot configurations, have also been explored to further enhance performance2026年1月13日—Normalskewed slothas proven to be an effective method to reduce vibration and noise of squirrel-cage induction motor. Doubleskewed slotis .... Ultimately, the decision to skew armature slots and the specific design employed are driven by a desire to optimize motor efficiency, ensure quiet and smooth operation, and prevent undesirable phenomena like magnetic rotor locking.2025年6月20日—The rotor of an induction motor is skewed (slots are not parallel to shaft but at a slight angle) mainly to:Reduce the magnetic locking( ...