How to choose the right electromagnet

As executive mechanisms, electromagnetic drives are widely used, which convert energy electric current into the translational movement of the working body. They are called a solenoid.

Depending on the design, type and conditions of use of the output coordinate of the solenoid operator, the mechanisms can be: for executive power, mechanisms with rectilinear movement of the working body — movement, speed and effort; for executive power mechanisms with rotary movement of the working body — angle of rotation, frequency of rotation or developed torque. Per the control action, an electrical control signal magnetizing coil is obtained.

Traveling electromagnets can be alternating (single-phase and three-phase) and direct current.Their main characteristics are — stroke of the armature, the relationship between the movement of the armature and the traction effort, the relationship between the position of the armature (its movement) and the energy consumption and reaction time... These characteristics depend on the shape of the magnetic circuit, consisting of a yoke and armature, the location of the magnetizing coils and the type of supply current (AC or DC). Depending on the stroke of the armature (its maximum displacement), short-stroke and long-stroke electromagnets are distinguished.

Electromagnets must meet the following requirements:

1. The selected design must match the stroke length, thrust force and specified thrust characteristic. For large pulling forces and a short length of the armature stroke, short stroke is used, and for small pulling forces and significant armature strokes, long stroke electromagnets; for large movements of the armature — electromagnets with a closed cylindrical magnetic circuit and quasi-constant traction force.

2. For high-speed systems, it is necessary to use electromagnets with a laminated magnetic circuit, and for delayed systems - with an uncharged magnetic circuit and a rotary armature with a massive copper sleeve.

3. Number of work cycles should be less than the permissible one.

4. Be comfortable to operate and easy to maintain.

The selection of an electromagnet is made according to voltage, current and energy consumption. After choosing an electromagnet, calculate its heating coils, assuming that the average permissible heating temperature 85 ... 90 ° C.

AC electromagnets with the same perfect mechanical work, they consume more electricity than DC electromagnets.Because they consume reactive power and also they have additional losses in the magnetic circuit and short circuit.

In addition, there are differences in the nature of the traction force of alternating current electromagnets, as the current flows through the coil, it changes according to a sinusoidal law, then the magnetic flux sinusoidal. Therefore, the electromagnetic force also changes harmonically the Law. And hence — the vibrations of the armature and the noise during operation of the electromagnet. I have electromagnetic mechanisms with direct current, an electromagnetic flux is created in the DC coil and its action does not depend on the direction of the current. At the same costs, the direct current electromagnet develops efforts twice as high as the alternating current electromagnet.

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