Through this graph, it is clear that the wound rotor motor addresses current, torque, and speed control much better than other designs. By varying the resistance, these motors will need less initial inrush current to compensate, have a stronger starting torque, and can maximize their starting torque by also making it the pullout torque example curve R2 in Figure 2.
Wound rotor motors can handle what other asynchronous motors cannot, namely speed, current, and torque control. The ability to increase rotor resistance when starting the motor allows for heavy loads to be smoothly accelerated to rated speed. There are disadvantages of wound rotor motors, and they are a consequence of their complex designs. The secondary circuit introduces more opportunities for error, and the slip ring brushes can be a safety concern if not regularly checked worn brushes can spark and increase the risk of fire.
These motors are also expensive to maintain, which adds to their already costly price tag. Their complexity also lowers the overall motor efficiency, and a squirrel cage motor should be chosen if efficiency is a primary concern or design constraint. Though expensive and less efficient, the wound rotor motor and its adjustable torque-speed characteristics are great for driving large ball mills, large presses, variable speed pumps, cranes, hoists, and other high inertial loads.
They also are great for any application that desires smooth startup and the ability to change speeds. They cover the bases that other induction motors cannot, and are invaluable to designers who need absolute control over speed and torque output. This article presented an understanding of what wound rotor motors are, how they work, and what their primary characteristics are that establish when they should be specified over standard induction motors.
For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products. Guides Christian Cavallo Share:. Select From Over , Industrial Suppliers. Receive Daily Industry Updates. Search Over 6 Million Products. These holes allow water, dust, and heat to easily dissipate off the surface of the rotor. Drilled rotors are a great choice for drivers that live in wetter climates as they'll help increase stopping power in wet, rainy conditions.
If you're looking at drilled rotors for a performance vehicle, you'll want to stay away. Drilled rotors don't work well under high-heat and can fail pretty quickly in a race-type driving scenario.
As mentioned before, slotted rotors feature slots around the exterior surface of the rotor. They're a great choice for heavy-duty trucks and SUVs, especially those that need improved stopping power when towing or hauling.
The slots are designed to draw more air in between the pad and rotor surface, which improves cooling and heat dispersion. They're also designed to help remove excess brake debris and pad glaze that can occur at higher temperatures. While they are more efficient in a few ways, they come with the downside of not lasting as long, which also affects the life of your pads.
Lastly, drilled and slotted rotors are primarily designed for performance vehicles, like sports cars, that need enhanced cooling and heat dispersion. This type of rotor was designed to improve braking at high speeds during racing or track days. Where there is friction there is heat. Over time, heat in combination with driving style performance vs street driving and climate can affect your rotors integrity.
While your everyday driving usually does not call for specialty rotors, the continual force and heat with off road or track driving does. Similarly, slotted rotors have small trenches that are grooved into the surface, acting as gutters for water and heat. These benefits of performance rotor types have their own setbacks, the largest being durability. As the stators north pole rotates pass a rotor bar, current is induced along the rotor bar. This circular flow of the current along the rotor bars through the shorting rings and around the laminations causes the rotor to become an electro-magnet.
It is at this stationary locked rotor starting point that the electromagnetic strength of the rotor is strongest.
The electromagnetic rotor will begin to accelerate to synchronous speed or the speed at which the stators magnetic field is rotating. This results in a decrease in current flow and torque. As the relative motion rotating force between the rotor bars and stator magnetic field approaches zero, the current flow along the rotor ceases.
The rotors magnetism will cease and the rotor will slow down until the torque generated by the motor equals that of the driven equipment. If the motors load is increased the motors speed will decrease.
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