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# Biased relay force

polarized relay force

A biased relay operation.

Problem type:
Axisymmetric multiphysics problem of Magnetostatics coupled to Transient magnetic analysis.

Geometry

Given
Permanent magnet coercive force Hc = 500 kA/m;
Winding material is copper;
Winding number of turns: 312;
Nominal voltage: 3.5 V.
The core and plunger are made of steel with a nonlinear dependence B(H):

Determine the pulling force vs. time dependency after switching the relay on.

Solution
Biased relay operates on the compensation of the magnetic pull of the permanent magnet by the opposing magnetic field of the current in the coil.
Initially the current is zero. The plunger is pulled in by the permanent magnet attraction. The initial state is simulated in DC magnetics problem.
Then the voltage is switched on, and the current in the coil changes the magnetic field distribution and force acting on a plunger, The transient electromagnetic process which leads to stabilization of the field distribution and current in the circuit is simulated in the transient magnetic problem. DC magnetic problem coupled to this Transient Magnetic problem provides the initial distribution of the magnetic field caused by DC Magnet.

Results
The voltage is switched on at 4.5ms. At the moment of 6.3ms the plunger pulling force value changes direction • Video: Biased relay force
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