Supervisory system for impedance-earthed power systems

• US 4,729,052 A
• Filed: 07/14/1986
• Issued: 03/01/1988
• Est. Priority Date: 11/19/1984
• Status: Expired due to Term

• Current Assignee: Klaus Winter
• Original Assignee: Klaus Winter
• Inventors: Winter, Klaus
• Primary Examiner(s): Scott, J. R.
• Assistant Examiner(s): DeBoer, Todd E.
• Application Number:
  US06/887,110
• Time in Patent Office: 596 Days
• Field of Search: 361/42-50, 361/65, 361/78, 361/58, 361/76, 361/86, 361/87, 323/209-211, 364/480, 364/482, 364/483, 364/492, 364/571, 364/481, 307/86, 307/87, 340/660-664
• US Class Current: 361/42
• CPC Class Codes: H02H 9/08 Limitation or suppression of earth fault currents, e.g. Petersen coil

Abstract

A device for continuous supervision of the attenuation (d), dissymmetry (k) and mismatch (v) system parameters in impedance earthed power systems. The parameters are calculated from the circle diagram uEN=f(v), i.e., the relative neutral point voltage as a function of the mismatch. The circle diagram is in turn defined by two measuring points for uEN which are derived by connection or disconnection of a reactance complement between system neutral and earth. The invention improves known devices for control of the condition of impedance-earthed power systems. Then the continuous supervision of the mentioned power parameters enables a better detecting of high-resistive earth connections.

The invention can be implemented in any computer system capable of providing the necessary measurement, control and calculating functions.

Claims

1. A device for supervision of attenuation (d), dissymmetry (k) and mismatch (v) parameters in a non-directly earthed power system, comprising:

(a) means for continuously measuring a neutral voltage and a reference voltage in order to define the relative neutral displacement (uEN) with respect to amplitude and phase;

(b) means for switching in regular intervals or because of a change in the value of the relative neutral displacement a reactance complement between system neutral and earth; and

(c) means for calculating a circle diagram uEN=f(v) representing the relative neutral voltage as a function of the degree of mismatch using the values for uEN before and after switching of the reactance complement and for calculating the associated values for the d, k and v parameters from the circle diagram.

2. A device according to claim 1, wherein the calculated values for d, k and v are temporarily stored in a data store and said calculating means continuously calculates the relative changes Δ

d, Δ

k and Δ

v of the d, k and v parameters, respectively, using the last stored and the next to last stored values from said data store for the respective parameters d, k and v.

3. A device according to claim 1 or 2, wherein a change of dissymmetry Δ

k is compared with a change of mismatch Δ

v so as to detect a high impedance earth fault, a minor change in network symmetry of the power system representing a spontaneous earth fault if corresponding network tuning remains unchanged.