Static and rotary electric power converters have different structures but there are common failure factors in both of them. In this chapter, causes of failure in electric power converters is described. All of the failure factors which are described in this chapter are catastrophic factors and lead to destructive damage in the systems. Other types of failure without destructive effect on converter like electromagnetic interference will be presented in the next chapters. All descriptions are based on details of operation of the converters which were presented in the previous chapter. Over temperature, over voltage, mechanical forces and environmental effects like humidity are the main factors of failure in systems. Origins of these factors are described in this chapter. Over temperature is a special factor among them because other failure factors finally act as over temperature in failure process of the converters. Since over temperature is the main failure factor in electric power converters, loss model of components in electric power converters are presented in details. In addition, practical technique for measuring power loss is described. Sample industrial examples of damaged equipments due to these failure factors are shown to give a real sense to reader about failure results.
TopIntroduction: Failure Of Electric Power Converters
In this chapter, we present the failure mechanism in electric power converter based on the background of Chapter 1. Figure 1 shows the state of Chapter 2 in the flowchart of the book.
Figure 1. State of chapter 2 in the flowchart of the book
TopFailure Factors
Meaning of failure in this chapter is the type of failure that leads to damage in a converter. Based on this view, four main reasons of failure are:
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Thermal shock
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Over voltage
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Mechanical forces
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Environmental effects.
TopThermal Shock
Over temperature is the most important factor of failure in all of systems. Thermal damage is a very important factor in the fault of electric power converters. Figures 2 and 3 show sample damaged converters due to over temperature. There are two scenarios for thermal damage: over temperature and thermal shock. Thermal shock occurs when a thermal gradient causes different parts of an object to expand by different amounts. At some point, this stress can exceed the strength of the material, causing a crack to form. To investigate the failure due to thermal damage, first we studied the origins of heat generation.
Figure 2. A thermal damage in an electronic board
Figure 3. Thermal damage in an integrated circuit
Electric Power Losses in Power Electronics
A power electronic converter consists of solid state active devices and some passive devices. Therefore, the power loss of a power electronic converter can be listed as follows (Yuancheng, Ming, Zhou, & Lee, 2006).