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Electric Fuse

In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby interrupting the current. It is a sacrificial device; once a fuse has been burnt it is an open circuit, and it must be replaced or rewired. Figure 1 shows a fuse used for automotive application and Figure 2 shows a fuse for high power application.

Figure 1 - Example of vehicle fuse  




Figure 2 - A 115 kV high-voltage fuse in a substation near a hydroelectric power plant [1]
 

Thermal-electrical modeling of an automotive fuse 

Joule heating arises when the energy dissipated by electrical current flowing through a conductor is converted into thermal energy. EMS for Solidworks provides a fully coupled thermal-electrical analysis for this kind of problem. This example illustrates the use of the capability to model the heating of an automotive electrical fuse due to a steady electrical current. Fuses are the primary circuit protection devices in automobiles. They are available in a range of different current ratings and are designed so that when the operating current exceeds the design current for a period, heating due to electrical conduction causes the metal conductor to melt and—hence—the circuit to disconnect.

An automotive electrical fuse consists of a metal conductor, such as zinc, embedded within a transparent plastic housing. The plastic housing, which only protects and supports the thin conductor, is not represented in the finite element model as shown in Figure 3.

Figure 3 - 3D model of simulated fuse

 
In this example the Electric Conduction solver is coupled to thermal analysis. This simulation generates Electric field, current density, potential, safety factor and Temperature and Heat flux plots. 

Simulation setup

After creating a coupled Electric Conduction and thermal study in EMS, four important steps are to be followed:

1. Apply the proper material for all solid bodies.
2. Apply the necessary electromagnetic inputs.
3. Apply the necessary thermal inputs.
4. Mesh the entire model and run the solver.

Materials

The fuse is made of zinc which has an isotropic temperature depended electric and thermal conductivity as shown in Figure 5.

Table1 -  Material properties

 
Figure 4 - Electric and thermal conductivity curves

Electromagnetic inputs

In this study, fixed voltages as shown in Table 2 are the only electromagnetic inputs.

 

Thermal inputs

In this example, natural convection is applied on the top and bottom faces of fuse. 

Meshing

Meshing is a very crucial step in the design analysis. EMS estimates a global element size for the model taking into consideration its volume, surface area, and other geometric details. The size of the generated mesh (number of nodes and elements) depends on the geometry and dimensions of the model, element size, mesh tolerance, and mesh control. In the early stages of design analysis where approximate results may suffice, you can specify a larger element size for a faster solution. For a more accurate solution, a smaller element size may be required.

Figure 7 - Meshed Model 
 

Electrothermal results

The transient electric results are due to the temperature dependant electrical conductivity and the coupling to transient thermal analysis. The total solution time is set to 150 second with 15 second as the time increment.  

Figure 8 shows the electric field in the fuse after 75 second.  In the figure 9, a 3D vector plot of current density in the fuse is shown. We notice that the maximum current is in the fuse element. 

 

 
 

Figure 8 - 3D plot of Electric field in the fuse at 75 second 




Figure 9 - Current density distribution in the fuse (vector plot)






Figure 10 - Electric potential

 
In figure 11, temperature distribution in the fused is plotted. The high temperature is generated in the fuse element because of the high current density in the same location. Figure 12 plots the temperature as a function of distance along the fuse in the middle portion.

 

Conclusion

EMS for SolidWorks can be used to design and simulate fuses for various applications. Coupled electric and thermal simulation enables engineers to study the thermal effects of the current distribution. Further by employing real life material properties like temperature dependent electrical and thermal conductivities, one can get an accurate representation of what happens to the fuse material under various operating conditions.