Motor-CAD is a unique software package for the thermal analysis of electric motors and generators, used by many leading motor manufacturers and universities world wide. The software is used to provide rapid analysis of design and manufacturing changes. Its analytical based algorithms give instantaneous calculation speeds and allow 'what-if' analysis in real time.
The software has a highly developed user interface that makes for easy data input and interpretation of results.
The cross section of the motor to be analysed is input using the graphical editors shown below:
Both radial and axial cross-section editors are required such that the 3-dimensional aspects of heat transfer can be modeled. The visual feedback provided is useful for eliminating errors in data input and gives the user an indication of the main heat transfer paths. Many geometric configurations are available, i.e. motor types, housing types, mounting types, winding types, etc.
Below we see the visual feedback provided when inputting the motor winding details. The diagram gives an indication of the layered winding model used to calculate the temperature build up in the winding. The winding is automatically divided into several layers of different thermal conductivity. The slot fill is visually indicated by the amount of yellow copper to green insulation shown in the diagram.
Thermal Calculation
The thermal model in Motor-CAD is based upon analytical lumped-circuit analysis making it extremely fast to calculate. This allows the user to perform 'what-if' calculations in real time. Alternative numerical methods, such as finite-element analysis [FEA] and computational fluid dynamics [CFD], typically require several days/weeks to put a representative 3-dimensional model together. The numerical model may then take several hours (days for a complex transient problem) to calculate a solution.
All the thermal resistances and capacitances in the Motor-CAD model are calculated automatically from geometric dimensions and material properties. The user need not be familiar with complex heat transfer phenomena such as dimensionless analysis of convection. Motor-CAD automatically selects and solves the most appropriate formulation for a given surface and the cooling type selected. Motor-CAD features efficient, accurate and robust mathematical algorithms for forced and natural convection, liquid cooling, radiation and conduction. An extensive library of proven laminar and turbulent convection correlations are used to give accurate models for all internal and external surfaces. The airgap model includes laminar, vortex and turbulent convection.
Steady-State Calculation
Below we see a screen-capture of the schematic diagram solved. This diagram is used extensively for post processing of steady-state calculations. The resistances and power sources shown in the schematic are colour coded to the components shown in cross-section editors. Resistances with a vertical orientation represent radial heat transfer and those with a horizontal orientation represent axial heat transfer. Those with a 'C' in them are convection resistances and those with an 'R' are radiation resistances. Resistances plotted in two colours represent interface resistances between two components.
The diagram shows labels next to the component resistances and nodes. With the click of a button the user can alter the schematic to display nodal temperatures and thermal resistance or power values. The schematic diagram is very useful for visualising where there may be restrictions to heat transfer and what can be done to improve the cooling.
Transient Calculation
Thermal transients can also be modeled, in which case thermal capacitances are automatically added to the circuit. It is essential to carry out detailed thermal transient analysis when using complex duty-cycle loads if the motor is to be driven to its full potential. The graph below shows a typical thermal transient. In this case we have a repetitive duty cycle (3 times overload followed by half full load). It is seen that the winding has a much shorter thermal time constant than the bulk of the machine and would burn out in a relatively short time under an overload condition. In this case measured temperature data is also plotted on the same graph and excellent correspondence between calculation and test is shown.
Flow Network Analysis
For cooling types such as through ventilation the fluid flow must be predicted before the heat transfer circuit can be calculated. Flow network analysis is used in Motor-CAD to calculate the flow of fluid through the machine. Often in a through ventilated machine this involves flow in three parallel paths, i.e. stator ducting, rotor ducting and airgap. A typical flow circuit calculated in Motor-CAD is shown below:
This user can input the characteristic for the fan. The intersection with the calculated system resistance characteristic is used to determine the total flow through the machine - see below:
All the thermal components in the heat transfer and flow circuit solved are calculated automatically from the geometry, materials and cooling types selected. In this way the user need not be an expert in heat transfer or fluid dynamics.
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发表于 2010-9-10 10:01
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