A notch-filter network for wide-band measurements of transient voltages on the power line

A voltage probe to measure power-line disturbances in a broad frequency range in the presence of high-amplitude transients is described. Design options and experimentally verified performances are shown. The design is based on the sharp suppression of the fundamental AC power frequency by means of an RC notch filter, whereas all other frequencies are passed from a very low-3-dB limit of 300 Hz to a very high upper limit of 1 GHz. The intrinsic high-frequency limitations of the low-frequency notch circuit are overcome by means of a coordinated parallel high-frequency path. The combination of the two is capable of extremely wide frequency response (in excess of 6 decades) with excellent flatness, within fractions of a decibel in the passband. This voltage probe also satisfies requirements of high linearity and low phase distortion. The other performance parameters (such as in-band attenuation, input impedance, power frequency rejection, power dissipation, and dimensions) are equal to or better than those of the relatively narrow bandwidth voltage probes currently specified in standards and regulations