Abstract

The life of the power capacitors and other components in APFC panels depend very much on the operating temperature. In panels with detuned harmonic filter reactors and thyristor switches, the chances of elevated temperature are high, as these components generate relatively more heat. Hence it necessary that the design should be such that the temperature should not increase beyond certain limit. This paper briefs some guidelines about the thermal design of APFC panels and thereby dissipating the generated heat effectively.

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For any panel, the temperature rise can be reduced by the following three ways:

• Operating at lower ambient temperature

• Using devices with lower power loss

• Dissipating the excess heat, so that temperature rise is controlled

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There is minimal control over the first two conditions. But the third condition completely depends upon the design of the panel. By offering effective cooling methods, the excess heat generated by the equipments can be dissipated.

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Below are the methods by which the thermal impedance can be minimised.

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Capacitors should be kept below the reactors, which are the major heat sources. This is because the reactors would increase the ambient temperature around the capacitors and the elevated temperature would reduce the life of the capacitors.

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The reactors should be mounted in the zigzag position (as shown in the below figure), in order to ensure better heat flow. If the reactors are kept one above other, the bottom most reactors would heat up the other reactors that are mounted above them.

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Thyristor switching modules should be mounted vertically (position of heat sink should be parallel to the air flow direction) and in zigzag positions.

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The base, on which the reactors and capacitors are mounted should have cut-outs or perforations for better air flow. The best practice is to use rails / channels for mounting.

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The door edges shall be sealed properly with gaskets, so as to avoid leakage and short cycling of the cooling air.

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Hence, proper thermal design would pave way for maximising the life of important equipments like capacitors, thyristor switches and reactors.