Series reactor, which was adopted by the AC, its role is with the power factor compensation capacitors in series, on the steady-state nature of harmonic (5,7,11,13 times) constitute a series resonance. Reactance are usually 4.5 to 6 percent rate in the reactor, the five sub-harmonic reactance is usually the rate of 6% is a high sense of the value of the reactor, the three times the rate of harmonic reactance is usually 12 13%, and two sub-harmonic reactance is usually rate of 26 27% of them are very high sense of the value of reactor. First, access series reactor, capacitor voltage is higher coefficient-K = 1 d 1, such as the K = 6% 1.06 10.06 1 ≈-d = the operating voltage increased 6%, operating current also will be about 6%. Operating experience that is equipped with a capacitor in series reactor capacity accounts for 2 / 3 and above, it will not generate harmonic resonance, and can effectively absorb the power harmonics and improve the system voltage waveform, improve system power factor, and can effectively curb the closing surge and operating over-voltage, the effective protection of the capacitor.