The feature of harmonic in time domain and the harmonic impedance coefficient ZFn of network

When the harmonic current of nonlinear electric equipment is injected into a network, a disturbance is formed. According to the IEC/TC-77(EMC) and other standards for power systems and plants, the disturbance´s degree can be expressed by the network harmonic voltage, resulting from the harmonic current injected into the network from electric equipment. It can also be expressed by U_n/ U₁, the ratio of the Nth harmonic voltage (RMS). This is also called the sine wave distortion factor of the N th harmonic voltage, designated DF_n%. A different coefficient ZF_n is proposed that is the ratio of the harmonic voltage of the network bus (RMS) to the harmonic current injected into the network system. An example of its application is presented. It is claimed that compared to the general voltage distortion factor DF_n%, ZF_n can show electromagnetic compatibility more clearly