Abstract: Power electronic components,frequency converters and nonlinear loads as well as asymmetric transformer structure and technology result in harmonic voltage or harmonic current. In reactive power compensation devices,harmonic affects power capacitors by increasing capacitor loss,harmonic current and leading to capacitor overheat and reducing service life of capacitors. In order to reduce or avoid the harm of high-order harmonics to capacitors,measures should be taken on power quality and harmonic suppression devices. In this paper,series reactors of installation of low-voltage shunt capacitors and compensation capacity were analyzed,and a formula was derived on the basis of rated parameters and field data. The rated reactive output capacity and actual reactive output capacity of the compensation unit were figured out as a reference for compensation device design and engineering application.