Use of a single-phase active power filter for generator negative sequence current reduction

The negative sequence current appearing on generator terminals may downgrade performance and even damage the generator. Therefore, most generators use negative sequence current relays to detect the negative sequence current and, if necessary, alarm or trip the generators before damage can occur. However, tripping major generation facilities may create social, security, and economic problems. In addition, sometimes, negative sequence current may cause supersynchronous resonance in the rotor shaft. If this problem is not corrected in time, the shaft may be damaged. This paper presents a feasible method for negative sequence current reduction at the generator terminal through a special function single-phase active power filter (APF), which can be connected to system either at Y₀ or Δ side of the transformer between the generator and the transmission lines. The control algorithm and digital simulation results of this method are also presented in this paper.