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

A voltage probe to measure powerline 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 (or even lower) to a very-high upper limit of 1 GHz (or higher). The intrinsic high-frequency limitations of the lowfrequency notch circuit are overcome by means of a coordinated parallel high-frequency path. The combination of the two is capable of the extremely wide frequency response (in excess of 6 decades) with an excellent flatness, within ± fractions of a decibel in the passband. In addition to the basic bandwidth requirement, this voltage probe also satisfies the important requirements of a high-linearity (large transients) and low-phase distortion (high fidelity of reproduction in the time domain). 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 the standards and regulations. The design lends itself to reproducible and reliable realization with ordinary components and with little need to resort to practical tricks or tweaking. Design variations are offered for possible simplified circuits with reduced performance. © 1989 IEEE