Motor-CAD is a unique software package for the thermal analysis of electric motors and generators, ud by many leading motor manufacturers and universities world wide. The software is ud to provide rapid analysis of design and manufacturing changes. Its analytical bad algorithms give instantaneous calculation speeds and allow 'what-if' analysis in real time. The software has a highly developed ur interface that makes for easy data input and interpretation of results. The cross ction of the motor to be analyd is input using the graphical editors shown below: Both radial and axial cross-ction editors are required such that the 3-dimensional aspects of heat transfer can be modeled. The visual feedback provided is uful for eliminating errors in data input and gives the ur 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 e the visual feedback provided when inputting the motor winding details. The diagram gives an indication of the layered winding model ud to calculate the temperature build up in the winding. The winding is automatically divided into veral 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 bad upon analytical lumped-circuit analysis making it extremely fast to calculate. This allows the ur to perform 'what-if' calculations in real time. Alternative numerical methods, such as finite-element analysis [FEA] and computational fluid dynamics [CFD], typically require veral days/weeks to put a reprentative 3-dimensional model together. The numerical model may then take veral 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 ur need not be familiar with complex heat transfer phenomena such as dimensionless analysis of convection. Motor-CAD automatically lects and solves the most appropriate formulation for a given surface and the cooling type lected. 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 ud to give accurate models for all internal and external surfaces. The airgap model includes laminar, vortex and turbulent convection. Steady-State Calculation Below we e a screen-capture of the schematic diagram solved. This diagram is ud 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-ction editors. Resistances with a vertical orientation reprent radial heat transfer and tho with a horizontal orientation reprent axial heat transfer. Tho with a 'C' in them are convection resistances and tho with an 'R' are radiation resistances. Resistances plotted in two colours reprent interface resistances between two components. The diagram shows labels next to the component resistances and nodes. With the click of a button the ur can alter the schematic to display nodal temperatures and thermal resistance or power values. The schematic diagram is very uful for visualising where there may be restrictions to heat transfer and what can be done to improve the cooling. TraTRAnsient Calculation Thermal transients can also be modeled, in which ca thermal capacitances are automatically added to the circuit. It is esntial 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 ca we have a repetitive duty cycle (3 times overload followed by half full load). It is en 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 ca 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 ud 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 ur can input the characteristic for the fan. The interction with the calculated system resistance characteristic is ud to determine the total flow through the machine - e below: All the thermal components in the heat transfer and flow circuit solved are calculated automatically from the geometry, materials and cooling types lected. In this way the ur need not be an expert in heat transfer or fluid dynamics. |
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