Earth contact monitoring device for a polyphase three-phase filter circuit

US4429338A · kind A · utility

Assignee

• Siemens Aktiengesellschaft · DE

Inventors

• Michael Becker · Knittlingen, DE
• Alfons Fendt · Erlangen, DE
• Dusan Povh · Nuremberg, DE
• Klaus Renz · Fürth, DE
• Gerhard Schuch · Erlangen, DE
• Hermann Waldmann · Radebeul, DE

Key dates

• Filing date: Jul 6, 1982
• Grant date: Jan 31, 1984
• Expiry date: Jul 6, 2002

Classification

• Technology area (CPC H): Electricity
• CPC primary: H02H7/00
• WIPO field: Electrical machinery, apparatus, energy
• WIPO sector: Electrical engineering

Abstract

A monitoring system for detecting earth contact of at least one phase of a polyphase network. Each of the phases in the network is connected by a capacitive-inductive filter to a neutral node which is connected to earth. In one embodiment of the invention, the current flowing from the neutral node to earth is detected by an induction current transformer which provides a signal responsive to said earth current. The output signal of the induction current transformer is conducted through at least one low pass filter for suppressing harmonics, and rectified to produce a direct current voltage signal, the amplitude of which is proportional to the amplitude of the fundamental frequency component of said signal. A fault indicating signal is produced when the direct voltage signal exceeds a predetermined value.