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 low-voltage reactive power protection fuses. This selection should be made by considering two key aspects:

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

According to the standard GB/T12747.1-2004, the fuse rating can be determined based on the maximum allowable current specified in the standard. The formula used is: 1.10 × overcurrent capability × capacitor rated current.

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

1) The rated current of the capacitor is 36A. If the capacitor meets the 1.3 times overcurrent capability, the maximum allowable current is 1.10 × 1.3 × 36 = 51.5A. Standard fuse ratings are 50A and 63A, so the appropriate choice is 50A.

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

2. For non-tuned compensation applications that include low-voltage capacitors and series reactors:

In these applications, a series reactor with a specific reactance rate is added to the traditional capacitor compensation system. This setup helps prevent harmonic amplification, avoid resonance, and improve overall power quality. It's commonly used in industrial and building power distribution systems due to its reliability and efficiency.

When selecting fuses for such applications, it’s important to analyze the entire circuit, including both the capacitor and the reactor. This is because the loop must handle not only the fundamental reactive current but also harmonic currents.

Additionally, since the capacitor's rated voltage is often higher than the system voltage (e.g., 525V for a 14% reactance application compared to a 400V system), the actual current in the system may exceed the capacitor's rated current. Therefore, the reactor's parameters determine the loop's overload capacity, specifically its maximum overcurrent capability.

For example, in a 25KVAR/400V compensation loop with a 14% reactance, the capacitor's rated current is 36A. If the reactor's maximum overcurrent capability is 1.8 times the rated current, the maximum allowable current is 1.8 × 36 = 64.8A. Thus, the appropriate fuse rating would be 63A.