The function of adding capacitance and inductance to low-voltage compensation power capacitors

Low-voltage compensation power capacitors can effectively help enterprise users improve the power factor of the power system and enhance the quality of electrical energy during operation. In power factor compensation schemes, the scheme of adding reactors to low-voltage compensation power capacitors is often used. What is the purpose of this?

Ⅰ. Harmonic Suppression and Protection Function

In the circuit of low-voltage compensation power capacitors, the inductor is connected in series. Its primary function is to suppress grid harmonics. When the power system has harmonics with characteristics such as 5th and 7th orders:

1. Filtering principle: By selecting reactors with an impedance of 7% or 14%, specific harmonic currents of corresponding frequencies can be filtered out.
2. Capacitor protection: Effectively reduces the harmonic current flowing through the capacitor (THD can be reduced from 15% to below 5%)
3. Loss Control: Reduce the additional losses caused by harmonics, thereby lowering the temperature rise of the capacitor by 20-30 degrees Celsius.

II. Limiting Switching Overcurrent

When the low-voltage compensation power capacitor is put into operation, a closing surge current as high as 20 to 50 times the rated current will be generated:

1. Reactor impedance: Increase the circuit reactance value to limit the inrush current within the range of 5 to 8 times the rated current.
2. Equipment protection: Prevent faults such as melting and welding of switch contacts, damage to the gold coating at the ends of capacitors, etc.
3. System Impact: Minimize instantaneous disturbances to the grid voltage (voltage fluctuation of 2%)

III. Prevention of Parallel Resonance

The low-voltage compensation power capacitor and the grid inductance may form a resonant circuit:

1. Resonance prevention: The reactor alters the system's resonance point, avoiding the 4.7 - 6.3 harmonic range.
2. Parameter Design: Precisely calculate the reactance rate based on the system's short-circuit capacity (error ≤ ±2%)
3. Safety Enhancement: Avoid resonance overvoltage (which can be limited to within 1.2Un)

IV. Optimizing Compensation Effect

Installing reactors can significantly improve the operational performance of low-voltage compensation power capacitors.

1. Voltage regulation: Enhance voltage stability (the fluctuation rate is reduced from 5% to 2%)
2. Extended lifespan: Reduces harmonic stress, and the lifespan of capacitors is increased by 2-3 times.
3. Intelligent Control: Combined with dynamic compensation devices, it enables millisecond-level response.