Shaded-pole motor

A shaded pole motor is an electric motor and is one of the asynchronous motors. However, in contrast to the three-phase asynchronous motor fed the shaded pole motor runs with single-phase alternating current. The engine is mechanically very simple.

  • 4.1 advantages
  • 4.2 disadvantages
  • 5.1 Application examples for split-pole asynchronous motors
  • 5.2 Application examples for split-pole synchronous motors

Construction

When shaded pole motor, the stator consists of a dynamo sheet package with laminated, salient poles, which are divided into a main pole and a shaded pole. The stator windings are arranged concentrically. Primary and secondary windings, called the main line, is set around the stator yoke and the pole shafts. The shaded-pole consists of a small groove which is cleaved from the main pole. To the shaded pole is a short-circuit winding, which usually has only 1-3 turns. This short-circuit winding, also called short-circuit ring together with the power winding in the operation, forming a shorted transformer. Thus, a favorable field distribution is achieved, you can converge the pole tips or even overlap. To achieve the same effect, the pole shoes are connected to the so-called scattering sheets in some engines.

The shaded pole motor has a rotor that is constructed as a squirrel cage and usually consists of entangled arranged rods. In the rotor, a torque is produced by a rotating field produced by the stator unequal. The properties of the shaded pole motor are heavily influenced by the formation of scattered sheets, spreading ridges and scattered column. Thus, the scattered lands and scattered column are afflicted in series production with little tolerance, they are calculated exactly in advance in the construction planning of the motor.

Synchronous operation

If the rotor of shaded pole motors of a magnetically hard material made ​​, these engines run on an asynchronous motor and after the run they are drawn almost in synchronism. Then they run as a synchronous motor on. These runners are also called Hystereseläufer. A similar performance has also the reluctance motor.

Working low-speed shaded pole motors also as a single-phase synchronous motors. In these the stator rotating field induces eddy currents in the rotor ring which cause the asynchronous start. After start-up formed by the stator rotating field in the magnetic material of the rotor salient poles. Due to the fact the rotor assumes the speed of the stator rotating field.

Low-speed shaded pole motor

Slow speed shaded pole motors are usually built as an external rotor. So they have a correspondingly low speed, they are provided with 10 or 16 poles. The stator consists of these motors from an annular exciting coil and two made ​​of steel sheet stand halves. This stand halves carry on the periphery as claw poles metal-sheet lobes. The polarity of the claw poles is determined by the magnetic field of the excitation coil. For this reason, the polarity of the claw poles of a stator half is the same.

By this construction, every second pole claw acts as shaded pole. To the pole gap of a stator half of a common shorting ring is built. This short circuit ring obtained the phase shift of the magnetic fluxes in the gap Poland against the main poles.

About the claw poles of the rotor is slipped in pot form. On the side there is a runners made ​​of hard magnetic material ring, called the rotor ring. Because of the hard magnetic material of the rotor ring of the low-speed shaded pole shows the typical speed behavior of shaded pole motors with rotors made of hard magnetic material.

With the so-called Kreuzpolschaltung a change in speed is realized in shaded pole motors.

Function

A flow of current in the stator winding in the stator generates a magnetic flux Φ. This is divided into the Hauptpolfeld? H and in the Spaltpolfeld øs, which goes by the applied to the stator winding short circuit.

The Spaltpolfeld induced in the short-circuited winding a voltage, which is the short-circuit current Is is created. This builds by self-induction of the river Φ 'S, which lags behind the main field? H. Together, the two rivers generate an unequaled, so-called elliptical rotating field that will take the rotor in the rotor. This elliptical rotating field is a poor quality rotating field.

The magnetic poles of the induced by the two -phase currents magnetic field wander successively following stator poles: main pole shaded pole 1 to 1, 2 to the main pole shaded pole 2 Thus, the rotational direction is always from the main pole for shaded pole.

To make the spinner round, the gap poles are at times turn again split, with a second shorted an additional phase shift is produced. The phase angle of the magnetic fluxes can be increased by an accurate choice of the spreading ridges.

A signal generated in this way rotating field is sufficient to move the rotor. However, it is also strongly dependent on load and leads to a lower starting torque than AC motors with the same power. The starting torque is dependent on the Spaltpolbreite and the scattering bar width and increases with the width of the two factors. The starting torque is approximately 50% of the nominal torque. The special Statorform occur when large shaded pole stray fields with corresponding stray field losses. The power density is by design very much smaller than in Shaded Pole Motors. Also the efficiency of the shaded pole motor is significantly lower than with an equally powerful three-phase asynchronous motor or capacitor motor. This is due to the ohmic losses in the shorted turns. This disadvantage is avoided in some engines by allowing, for example, the short-circuit winding turns off in refrigerator compressors after startup.

Direction of rotation

The direction of rotation of pole motors can usually be electrically non- modified as it is determined by the pole arrangement, and only the main strand is accessible from the outside. In order for a normal shaded pole gets a different direction of rotation, you would have to dismantle the bearing plates, remove the rotor and reinstall in direction changed. This is very cumbersome and due to the design ( bearing plates with rivet instead of screw ) is not always possible.

However, the direction of rotation can be switched by a special arrangement. For this, the engine is designed, as were two shaded pole motors mirror mounted on a drive shaft. A second short-circuit winding can be grown. There are engines with four gap Poland, the windings may be shorted pairs.

Pros and Cons

Benefits

  • Very simple in construction
  • Inexpensive
  • High smoothness
  • Maintenance-free
  • Long service life
  • Robust
  • An auto- start

Disadvantages

  • Low efficiency
  • Poor power factor
  • Can only be used for low power ( about 2/3 power of a normal three-phase motor )
  • Low power density
  • In the " standard type" no direction reversal

Areas of application

Because of their very simple structure shaded pole motors are manufactured in large series. They are used as economical propulsion engines with low power levels up to about 300 watts always used when no high starting torque is required. Shaded-pole synchronous motors are built up to 3 watts for benefits. The mentioned advantages and disadvantages of the shaded pole motor over other asynchronous determine its Applications: Its low efficiency ( about 30%) prevents the use in large benefits. Its main advantage, the ability to operate it without additional capacitor to an AC supply, has been organized eg in the household sector provided a certain distribution. The motor is especially suitable for drives with short-time operation. Its typical for asynchronous motors smooth running, low maintenance and high durability have made it the default drive for small axial and radial fans and fans.

Application examples for split-pole asynchronous motors

  • Fan motor for electric heaters
  • Drain pump in washing machines
  • Pump in tumble dryers
  • Drive motor for turntables
  • Motor for fans
  • Drive motor for refrigeration units and freezers
  • As a spin dryer - direct drive

Application examples for split-pole synchronous motors

  • Drive motor for Programmed time switches
  • Electric clocks
  • Electrical time relay
  • Writing instruments
Magnetic core Electromagnetic induction Motor capacitor
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