Thermal relay - QuickField simulation example
Switching temperature and operating time of a thermal relay attached to a hot-liquid tank, including the temperature dependence of winding resistance. With temperature raise the conductivity, current and electromagnetic force fall down.
How to calculate the switching temperature and time of a thermal relay?
Answer Typical applications Geometry
Given
Solution
Results
The tank is cooling down. Calculate the relay switching temperature and time.
Engineering question
Model the temperature-dependent winding conductivity in transient magnetics and calculate the electromagnetic force during cooling to determine when the relay switches.
thermal protection relays, relay windings, temperature-sensitive relays
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Simulation problem
Problem Type
Axisymmetric problem of transient magnetics.
Magnetic permeability of core μ = 400;
Voltage U = 12 V;
Spring force f = 0.8 H
Initial temperature T1 = 200 °C;
Ambient temperature T0 = 20 °C;
Time constant ts = 10 hrs;
Conductivity of copper σ - depends on temperature:
The temperature falls down as
T(t) = T0 + (T1-T0)·exp( -t / ts).
The integration time was chosen to be 3ts, integration step ts/5.
To calculate the electromagnetic force as a function of time transient magnetic problem is simulated. The temperature function T(t) was added to the material properties of 'winding' block.
After 16 hours the temperature falls down to 56°C and relay switches off.
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