Week 7 - Mid-term Project - Natural Convection

Low voltage control panel

It is a component of an electrical distribution system that divides an electrical power feed into branch circuits while providing a protective fuse or circuit breaker for each circuit in a common enclosure. Low voltage (LV) panels are most common across all the industries and one of the more common special requirement which need to be designed in accordance with safety standards prevailing. An electrical panel is that the combination of protection and switch devices assembled in one or a lot of adjacent compartments.

Components of Low voltage panel.

Enclosures: An electrical enclosure is a cabinet for electronic or electricalequipment. To mount switches, knobs and displays and also to prevent electrical shock to equipment users. To safeguard the contents from the environment.

Bus bars: In electric power distribution, a bus bar could be a metallic bar or a strip (copper, or aluminum) that conducts electricity within an electrical equipment for relatively short distances. Bus bars are used to carry substantial electrical currents. When compared to the wires of the same size it helps to reduces losses.

Circuit breaker: An electrical fuse is control designed. To protect a circuit from damage caused by overcurrent or overload or tangency. Its basic operate is to interrupt current flow after protecting relays detect a fault.

AIM

The objective of the project is to design a low voltage control panel as per given specifications and setup the physics & solve the thermal model.

TASK

• The Control panel to be create for the incoming current of 1200A.
• Circuit breaker losses are given as per the following table. The current distribution and bus bar dimensions / Cable dimensions and lengths are given as per the following table
• Assume the circuit breaker dimensions, panel inside dimensions and also assume the placements of the circuit breakers.
• The ambient temperature is 25 C.
• The Non conformal mesh in computational domain & joule heating for the current carrying bus bar & cables.
• Post process the results using the Plane cut, Vector plot, Temperature contour and object face.

Model

The following objects are created in Icepak using the design specification.

Cabinet : It creates a fluid region around the model for which the governing equations are solved.

i) Geometry 

Shape - Prism.

Specified By - Start/end.

Start Xs - -500 mm. 

Start Ys - 100 mm.

Start Zs - -1000 mm.

End Xe - 1500 mm.

End Ye - 4100 mm.

End Ze - 3200 mm.

ii) Properties - The wall type for the cabinet is defined.

Min X - Wall.

Max X - Wall.

Min Y - Wall.

Max Y - Wall.

Min Z - Wall.

Max Z - Wall.

The dimension for the circuit breaker is obtained ABB website from the type provided.

IG block

i) Geometry

Shape - Prism.

Specified By - Start/length.

Start Xs - 400 mm.

Start Ys - 2000 mm.

Start Zs - 240 mm.

Length Xl - 154 mm.

Length Yl - 268 mm.

Length Zl - 210 mm.

ii) Properties

Block type - Solid.

Surface Material - Paint non metallic.

Solid Material - Fe-pure.

Total power - 168.92 W.

I1 block

i) Geometry

Shape - Prism.

Specified By - Start/length.

Start Xs - 425 mm.

Start Ys - 695 mm.

Start Zs - 275 mm.

Length Xl - 103.5 mm.

Length Yl - 205 mm.

Length Zl - 140 mm.

ii) Properties

Block type - Solid.

Surface Material - Paint non metallic.

Solid Material - Fe-pure.

Total power - 56.16 W.

The material for all the circuit breaker are same & the power for the component are provided.

Bus bar A

i) Geometry

Shape - Prism.

Specified By - Start/length.

Start Xs - 472 mm.

Start Ys - 1350 mm.

Start Zs - 100 mm.

Length Xl - 10 mm.

Length Yl - 200 mm.

Length Zl - 800 mm.

ii) Properties

Block type - Solid.

Surface Material - Cu polished surface.

Solid Material - Cu-pure.

Total power - Joule heating.

iii) Joule heating power

Type - Constant.

Current - 800 A.

L - Z length.

Resistivity - 1.72e-8 ohm.

C - 0.0039.

Tref - 25 degC.

Low temperature - 25 degC.

High Temperature - 200 degC.

Similarly for the busbar B,C,D & E are created.

IG Cable

The cable is created using 3 blocks and the total power is divided between the 3 blocks depending on the length of cable.

a i) Geometry

Shape - Prism.

Specified By - Start/length.

Start Xs - 400 mm.

Start Ys - 2238 mm.

Start Zs - 337.5 mm.

Length Xl - 154 mm.

Length Yl - 317 mm.

Length Zl - 15 mm.

ii) Properties

Block type - Solid.

Surface Material - Cu polished surface.

Solid Material - Cu-pure.

Total power - Joule heating.

iii) Joule heating power

Type - Constant.

Current - 200 A.

L - Y length.

Resistivity - 1.72e-8 ohm.

C - 0.0039.

Tref - 25 degC.

Low temperature - 25 degC.

High Temperature - 200 degC.

b i) Geometry

Shape - Prism.

Specified By - Start/length.

Start Xs - 400 mm.

Start Ys - 2585 mm.

Start Zs - 0 mm.

Length Xl - 154 mm.

Length Yl - 15 mm.

Length Zl - 352.5 mm.

ii) Properties

Block type - Solid.

Surface Material - Cu polished surface.

Solid Material - Cu-pure.

Total power - Joule heating.

iii) Joule heating power

Type - Constant.

Current - 200 A.

L - Z length.

Resistivity - 1.72e-8 ohm.

C - 0.0039.

Tref - 25 degC.

Low temperature - 25 degC.

High Temperature - 200 degC.

c i) Geometry

Shape - Prism.

Specified By - Start/length.

Start Xs - 400 mm.

Start Ys - 200 mm.

Start Zs - 0 mm.

Length Xl - 154 mm.

Length Yl - 2385 mm.

Length Zl - 15 mm.

ii) Properties

Block type - Solid.

Surface Material - Cu polished surface.

Solid Material - Cu-pure.

Total power - Joule heating.

iii) Joule heating power

Type - Constant.

Current - 800 A.

L - Y length.

Resistivity - 1.72e-8 ohm.

C - 0.0039.

Tref - 25 degC.

Low temperature - 25 degC.

High Temperature - 200 degC.

The cable for the other circuit breaker are created & required power is provided.

Enclosure

i) Geometry

Shape - Prism.

Specified By - Start/length.

Start Xs - 127 mm.

Start Ys - 100 mm.

Start Zs - -100 mm.

Length Xl - 700 mm.

Length Yl - 2600 mm.

Length Zl - 2300 mm.

ii) Properties

Block type - Solid.

Surface Material - Paint white acrylic.

Solid Material - Steel carbon 1020.

Thermal Specification - Thin is set at all the boundary type & the thickness is 3 mm. The radiation at all the boundary walls are activated.

Grille 1

i) Geometry

Shape - Rectangular.

Plane - X-Y.

Specified By - Start/length.

Start Xs - 127 mm.

Start Ys - 200 mm.

Start Zs - -100 mm.

Length Xl - 700 mm.

Length Yl - 200 mm.

Grille 2

i) Geometry

Shape - Rectangular.

Plane - X-Y.

Specified By - Start/length.

Start Xs - 127 mm.

Start Ys - 2300 mm.

Start Zs - 2200 mm.

Length Xl - 700 mm.

Length Yl - 200 mm.

Assemble - 1

Select all the blocks and click on create --> assembly.

Under the meshing tab choose Mesh separately,

i) Slack setting

Min X - 5 mm.

Max X - 5 mm.

Min Y - 5 mm.

Max Y - 5 mm.

Min Z -  5 mm.

Max Z - 5 mm.

ii) Mesh type

Max element size X  - 15 mm.

Max element size Y - 200 mm.

Max element size Z - 30 mm.

Min Gap X - 1 mm.

Min Gap Y - 1 mm.

Min Gap Z - 1 mm.

Assemble - 2

Select all the blocks and click on create --> assembly.

Under the meshing tab choose Mesh separately,

i) Slack setting

Min X - 10 mm.

Max X - 10 mm.

Min Y - 10 mm.

Max Y - 10 mm.

Min Z -  10 mm.

Max Z - 10 mm.

ii) Mesh type

Max element size X  - 50 mm.

Max element size Y - 100 mm.

Max element size Z - 100 mm.

Min Gap X - 1 mm.

Min Gap Y - 1 mm.

Min Gap Z - 1 mm.

• Macros --> Productivity --> Validation --> Automatic case check tool - It checks the assembly interface between the varies objects and assembly.    

     

Mesh Control

The mesh refinement of the bus bar are done by increasing the element count along the cross section. Select bus bar --> Set --> object mesh parameter & increase the count value.

The Mesh for the three plane passing along the center of the control panel.

X Plane

Y Plane

Z Plane

Surface mesh

Mesh Verification

Face alignment

• It is the measure of mesh quality defined by face alignment index = C0C1.f
• C0 & C1 are the centroids of two adjacent elements are normal vector to the face between the two elements.
• Range of face alignment 0 (bad) to 1 (good) & value greater than 0.1 (preferred) & value greater than 0.15 provide better results.

The min value of the model is 1 which is ideal for the results.

Volume

• Preferable volume of mesh to be greater than 1e-13 for single precision solver & greater than 1e-15 for double precision.
• Max / Min cell volume should be less than 10^7 for single precision & must be less than 10^12 for double precicion since very small volume create divergence of the solution.

The volume of the mesh greater than 10^-13 & Max / Min cell ratio is around 1e6 which is in required range & the single precision is used for this model. 

Skewness

It determines how close to the ideal & based on the equilateral volume. The value greater than 0.5 provide good cell quality.

The min value of the skewness is 1 so only ideal element are formed.

Solver

The three dimensional steady state Navier stokes equations for the model are solved within the computational domain.

General Setup

• Variables solved - flow and temperature.
• Radiation - On.
• Flow regime - Turbulent - The zero equation are solved for the turbulent model.

      Natural convection are consider for this model.

      Gravity vector for the y axis is set to -9.81 m/s2.                    

The defaults value of the parameters are set to default.

Transient Setup

• Time variation - Steady

Solution Initialization

X velocity - 0.

Y velocity - 0.005 m/s.

Z velocity -0.

Temperature - ambient.

Basic settings

No of iterations - 500.

Convergence criteria

Flow - 0.001.

Energy - 1e-7.

Joule heating - 1e-7.

Parallel Settings

Configuration - parallel.

Parallel options - 4 processors.

Advance Solver Setup

Results

The residuals for the following equations are plotted against the number of iterations:

• Continuity equation.
• X-momentum equation.
• Y-momentum equation.
• Z-momentum equation.
• Energy equation.

The solution converged around 400 iterations and the solution has reached a steady state.

Monitor points

These are probes set at the various location in the computational domain to determine the temperature variable. Temperature for the each circuit breaker are created.

Temperature contour

The maximum temp is 67.92 degC for the IG circuit breaker where the total power generated is highest. The joule heating for the bus bar has a very less effect since the temperature are around bus bar are near to the minimum temperature.

Temperature Object face contour

The object face contour provides clarify in the temp distribution of the components in computational domain.

Velocity vector

The max velocity is 11.92 m/s and air flow is dense around the bottom of the control panel.

Velocity particle tracer

The 100 particles tracer originate from the lower grille and exit at the top grille in the computational domain.

Conclusion

In this project the given model of the Low voltage control panel was designed using the Ansys Icepak as per the given specifications and meshed using the non-conformal, per object meshing techniques. The three dimensional steady-state governing equations for the model were solved for flow and temperature within the computational domain in the Icepak. 

• The maximum temperature within the computational domain is 67.5 deg.C.
• The maximum air velocity within the computational domain is 11.92 m/s.

The steady state temperature of circuit breaker are: 

Block 1 (IG) - 67.5 degC.

Block 2 (I1) - 38 degC.

Block 3 (I2) - 58.54 degC.

Block 4 (I3) - 55.68 degC.

Block 5 (I4) - 57 degC.

Block 6 (I5) - 45.18 degC.

Block 7 (I6) - 37.57 degC.

Block 8 (I7) - 39 degC.