The thermal relay is attached to the tank with a hot liquid. Relay winding conductivity depends on temperature. With temperature raise the conductivity, current and electromagnetic force fall down.

The tank is cooling down. Calculate the relay switching temperature and time.

**Problem Type:**

An axisymmetric problem of nonlinear transient magnetics.

**Geometry:**

**Given:**

Magnetic permeability of core *μ* = 400;

Conductivity of copper *σ* - *depends on temperature*;

Voltage *U* = *12* V;

Spring force *F* = 0.8 H

Initial temperature *T _{1}* = 200 °C;

Ambient temperature

Time constant

**Solution:**

The temperature falls down as
*T*(t) = *T _{0}* + (

The integration time was chosen to be 3

To calculate the electromagnetic force as a function of time transient magnetic problem is simulated. The temperature function

**Results:**

After **16** hours the temperature falls down to **56°C** and relay switches off.

See the *TEMagn3.pbm* problem in the Examples folder.