CBB capacitors are also called polypropylene capacitors with a capacitance of 10p--10μ. Capacitor derating refers to selecting a product that has a larger rated current than the capacitor when selecting and controlling electrical components. For example, a simple motor control capacitor, the power of the motor is 55KW, and the rated current is about 110A. But when choosing a contactor, we will choose 160A. One of the reasons is that the current will be greater than 110A when the motor starts. The second purpose is to improve the life of the contactor. This is derating, to be precise the derating of electrical components (contactors in the example). However, for protection components, such as circuit breakers (air switches), thermal relays, etc., derating is generally not allowed, because this will reduce the protection sensitivity.

CBB capacitor derating calculation formula:

Three capacitors of equal capacity, C1 = C2 = C3 = C, are connected in a triangle, and any measurement of AB / BC / CA will have a total capacity of 3C / 2. (In the measurement, the internal equivalent capacitors are C2 and C3 connected in series, and then connected in parallel with C1.) So, through measurement, we know any capacity Cx between AB / BC / CA, and can calculate the capacity of each capacitor: C = 2Cx / 3.

The method of judging whether the capacitor is damaged or derated can calculate the capacitance by measuring the compensation current on the capacitor, and then compare it with the actual.

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