Abstract: Described here in the paper is the low-voltage reactive power compensator as used to the large-sized straight welded pipe production line located at Julong Steel Tube Co.,Ltd.,focusing on the design and type selection.The successful operation of the said compensator leads to the conclusion that reactive power compensation to the low-voltage electric network can not only reduce the cost for power consumption,but also considerably improve the power supply quality of the network and the consistency of tube production as well.