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Electrothermal Simulation of Busbars using EMS for Solidworks Application


Electrical Busbars

In electric power distribution, a busbar, shown in Figure 1 is a metallic strip or bar, typically housed inside switchgears, panel boards, and busway enclosures for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low voltage equipment in battery banks as shown in Figure 2. They are generally uninsulated, and have sufficient stiffness to be supported in air by insulated pillars. These features allow sufficient cooling of the conductors, and the ability to tap in at various points without creating a new joint. Thus, the electrical bus bar collects the electrical energy at one location. When the fault occurs in any section of the bus bar, all the circuit equipment connected to that section must be tripped to give complete isolation in the shortest possible time [1].
 

Busbars used to connect electrical feeders 

Figure 1 - Busbars used to connect electrical feeders



High power cables connecting by busbars

Figure 2 - High power cables connecting by busbars

Electrothermal simulation of busbar conducting DC current using EMS for Solidworks

This example simulates a busbar that transports DC current from a transformer to an electrical device as shown in Figure 3. The current conducted in the busbar produces heat due to the resistive losses, a phenomenon referred to as Joule heating. The Joule heating effect is described by conservation laws for electric current and energy. Once solved, the two conservation laws give the temperature and electric field, respectively.

Electric Conduction or the so called current flow analysis belongs to the low-frequency electromagnetic domain or regime. They also do not depend on time. Furthermore, the size of the object is much smaller than the wavelength. Unlike the Electrostatic analysis which deals with insulators and electric conductors, the Electric Conduction deals with only conducting media which can sustain a current flow.

In our case, Electric Conduction solver is coupled to a thermal analysis. This kind of simulation solves for the Electric filed, current density, potential and safety factor. Thermal analysis takes the heat power computed by the Electric conduction solver and in addition to others thermal inputs, it generates thermal results: temperature, heat flux and temperature Gradient. 

Installed busbar

Figure 3 - Installed busbar 


3D simulated model of busbar

Figure 4 - 3D simulated model of busbar
 

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 solve

Materials

The busbar is made of copper while the bolts are made of titanium.  In the table below electric conductivity of each material is listed.

Table1 - Table of materials 
 
Components / Bodies Material Conductivity (S/m)
Bolts Titanium 740700
Busbar Copper 5.998e+7

Electromagnetic inputs

In this study, fixed voltages (Table 2) are the only electromagnetic input.

Table 2 -  Applied Fixed Voltage 
 
Name Fixed Voltage
Bolt 1 0.02 V
Bolt 2/3 0 V



Applied fixed voltages
 
Figure 5 - Applied fixed voltages.
 

Thermal inputs

In this example, natural convection is applied on all surfaces expect bolts contact surfaces and the ambient temperature is 293.15 K.

 
Convection properties
 
Figure 6 - Convection properties

Meshing

Meshing is a very crucial step in any FEA simulation. 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. Mesh quality can be adjusted using Mesh Control, which can be applied on solid bodies and faces. In figure 7, smaller mesh is observed in the bolts and parts in contact with them. 

Meshed Model

Figure 7 - Meshed Model

Electrothermal results

Figure 8 shows the electric field in the busbar which are concentred around the bolts. Thus, the current density will be also concentred around the bolts as shown in Figure 9. 

3D plot of Electric field in the busbar

Figure 8 - 3D plot of Electric field in the busbar 


Current density distribution in the busbar
Figure 9 - Current density distribution in the busbar.
 
 
In figure 10, temperature distribution in the busbar is shown. The maximum temperature is located in the Bolt where 0.02 V is applied as DC voltage. The difference between maximum and minimum temperature in the busbar is about 8 K. Figure 11 shows the power dissipated in the busbar element.
Temperature distribution in the busbar
Figure 10 - Temperature distribution in the busbar

 
 
 Dissipated power by Joule effect in the busbar
Figure 11 - Dissipated power by Joule effect in the busbar

Conclusion

EMS can calculate the electric field and the temperatures in busbars that are used for power applications. Further one can see the temperature gradient throughout the busbar to ensure that overheating does not happen.

Reference

[1]: https://wikivisually.com/wiki/Busbar