US 4,472,676 A · Leakage impedance measuring system including a superimposed measuring voltage having a frequency differing slightly from system frequency

Abstract

A process and an apparatus for the determination of the total leakage impedance and the maximum conductor contact current of an ungrounded AC power supply system resulting from the total leakage impedance. An AC measurement current having a frequency that differs slightly from power frequency by a ratio other than a whole number is fed into the AC power supply system, which measurement current flows through the system leakage impedances to produce between supply system and ground, an interference pattern having the AC measurement voltage superimposed on the system voltage component at an interference pattern frequency (difference or beat frequency) of the pattern envelopes which is small with respect to the system frequency. By extracting and processing of the components of the interference pattern, it is possible to determine the AC measurement voltage component contained in the interference pattern. This allows a very precise determination of the total leakage impedance corresponding to the system frequency, and also of the maximum conductor contact current corresponding the total leakage impedance.

Claims22

Dependent claims

Apparatus for measuring the magnitude of the leakage impedance (Z.sub.E tot) of an ungrounded alternating-current power supply system having a given system frequency (f.sub.N), comprising

(a) means (18) for applying between the conductors of the system and ground a measurement voltage (V.sub.M) having a measurement frequency (f.sub.M) which differs slightly from system frequency by a ratio that is other than a whole number, thereby to inject a measurement current (i.sub.M) in the system which produces across the total leakage impedance a voltage drop (V.sub.EM) that is superimposed on the system component voltage (V.sub.EN) to produce an interference pattern having an envelope (FIG. 3);
(b) detector means (A1, A2, A3) for detecting from the envelope of the interference pattern the total leakage voltage drop (V.sub.EM);
and
(c) display means (38, 46, 66) connected with said detector means for displaying total impedance (Z.sub.E tot) as a function of the total leakage voltage drop.

1 more element

The method for measuring the magnitude of the leakage impedance (Z.sub.E tot) of an ungrounded alternating-current power supply system having a given system frequency (f.sub.N), comprising the steps of

(a) applying between the conductors of the system and ground a measurement voltage (V.sub.M) having a measurement frequency (f.sub.M) which differs slightly from system frequency by a ratio that is other than a whole number, thereby to inject a measurement current (i.sub.M) in the system which produces across the total leakage impedance a voltage drop (V.sub.EM) that is superimposed on the system component voltage (V.sub.EN) to produce an interference pattern having an envelope (FIG. 3);
(b) detecting from the interference pattern envelope the total leakage voltage drop (V.sub.EM);
and
(c) displaying the total leakage voltage drop (Z.sub.E tot) as a function of the total leakage voltage drop (V.sub.EM).

1 more element

Dependencies are inferred from the claim text.

Leakage impedance measuring system including a superimposed measuring voltage having a frequency differing slightly from system frequency

Life of this patent

Leakage impedance measuring system including a superimposed measuring voltage having a frequency differing slightly from system frequency

Life of this patent

Abstract

Claims22