Date of Award

Summer 1993

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

First Advisor

Nigro, N. J.

Second Advisor

Elkouh, A. F.

Third Advisor

Heinrich, S. M.

Abstract

Power electronic assemblies are used in solid state motor controllers to start electric motors smoothly by gradually increasing the motor speed to its steady state speed, thus avoiding excessive mechanical loads on the driven system. These electronic assemblies conduct relatively high current and dissipate large amounts of heat during motor starting conditions. The heat produces transient temperatures that affect the electrical performance and mechanical integrity of the assemblies. In this study, a 3-dl solid finite element thermal model of a power electronic assembly is developed with the ANSYS analysis software program. Results predicted by the finite element model for a typical motor starting load are compared to experimental data for verification. The verified finite element model is employed to study the transient temperatures in a power electronic assembly caused by four different motor starting loads. The resulting transient temperature profiles at different locations in the assembly are analyzed. The results of this study indicate that the power electronic assembly experiences high transient temperatures in the thyristor when a 600% full load current stepped motor starting load is simulated. The results also show ramped motor starting reduces the temperatures and significantly decreases the transient temperature gradients observed during the applied motor starting load.

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