How to correctly choose the protection fuse of low voltage reactive power compensation - News - Global IC Trade Starts Here Free Join

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Based on the analysis of relevant national standards and the two main low-voltage reactive power compensation methods, it is essential to carefully select the appropriate low-voltage reactive power protection fuses. This selection should be made by considering two key aspects:

1. For pure capacitive compensation applications where the only components are low-voltage capacitors:

According to GB/T 12747.1-2004, the fuse rating can be determined based on the maximum allowable current specified in the standard, which is calculated as 1.10 × overcurrent capability × rated capacitor current.

For example, in a 25KVAR/400V capacitor compensation circuit:

1) The rated current of the capacitor in this circuit is 36A. If the capacitor has an overcurrent capability of 1.3 times, the maximum allowable current would be 1.10 × 1.3 × 36 = 51.5A. Given that standard fuse ratings are 50A and 63A, the correct choice would be 50A.

2) If the capacitor has a higher overcurrent capability, such as 1.5 times, the maximum allowable current would be 1.10 × 1.5 × 36 = 59.4A. In this case, the suitable fuse rating would be 63A.

2. For non-tuned compensation applications where capacitors are used with series reactors:

In these applications, a series reactor is added to the traditional capacitor compensation loop. This setup helps prevent harmonic amplification, avoid resonance, and improve power quality by absorbing harmonics. As a result, it is widely used in industrial and building power systems.

When selecting fuses for such systems, it's important to consider both the capacitor and the series reactor together. The compensation loop must handle not only the fundamental reactive current but also harmonic currents.

Additionally, since the rated voltage of the capacitor in this type of application is much higher than the system voltage (e.g., a 14% reactance application results in a capacitor rated at 525V, compared to a 400V system), the actual current in the system may exceed the capacitor’s rated current. Therefore, the reactor’s overload capability becomes the key factor in determining the fuse rating.

For example, in a 25KVAR/400V compensation loop with a 14% reactance:

The capacitor’s rated current is 36A. If the reactor has a maximum overcurrent capability of 1.8 times its rated current, the maximum allowable current in the loop would be 1.8 × 36 = 64.8A. Thus, the appropriate fuse rating would be 63A.