LINE SECURITY SYSTEM

• US 3,641,547 A
• Filed: 05/25/1970
• Issued: 02/08/1972
• Est. Priority Date: 05/25/1970
• Status: Expired due to Term

• Current Assignee: Elektrowatt AG Bellerivestrasse
• Original Assignee: Martin H. Reiss, William L. Cotter
• Inventors: Reiss, Martin H., Cotter, William L.
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/040,285
• Time in Patent Office: 624 Days
• Field of Search: 340/409,416,276,227.1,253,253B,253Q,253S,256,253R,253A
• US Class Current: 340/511
• CPC Class Codes: G08B 29/06 Monitoring of the line circuits, e.g. signalling of line faults
• CPC Class Codes: G08B 29/123 of line circuits

Abstract

A system for insuring the security of electrical transmission lines extending between a monitor station and a remote station utilizes a voltage source at the monitor station which impresses an AC voltage signal on the transmission lines. At the remote station, the AC voltage signal is rectified and the rectified signal is applied to a current regulator which provides a quiescent pulsed direct current of constant level to the transmission lines. The current regulator is arranged to provide a higher alarm current when an intruder is detected at the remote station. At the monitoring station, a shorted line fault detector provides a signal when a reversal in the direction of normal current flow occurs in the transmission lines, an open line fault detector provides a signal when a drop in current below the quiescent current level is detected, and an alarm current fault detector provides a signal when a rise in current above the quiescent current level is detected. The impressed voltage is periodically reduced in amplitude to a level which barely sustains the minimum quiescent current level to test line impedance.

Claims

1. A system for insuring the security of electrical transmission lines extending between a monitor station and a remote station, the system comprising a current regulator at the remote station, the current regulator being connected to the transmission lines and providing a quiescent pulsed direct current of constant level in response to an impressed periodic AC voltage, the current regulator having actuable means for causing the pulsed direct current to increase to a higher alarm current level upon the occurrence of an event at the remote station, monitoring apparatus at the monitor station, the monitor apparatus being connected to the transmission lines and comprising means for applying a periodic AC voltage to the transmission lines, an open line detector having its input signal obtained from the current flowing in the transmission lines, the open line detector providing an output signal in response to a drop in current below the quiescent current level, means for intermittently reducing the AC voltage applied to the transmission lines to a level barely sufficient to maintain the current at the quiescent current level when the impedance of the transmission lines is within the impedance range that is normal for such lines, a shorted line detector having its input obtained from the current flowing in the transmission lines, the shorted line detector providing an output signal in response to a reversal in the direction of normal current flow in the transmission lines, and an alarm current detector having its input obtained from the current flowing in the transmission lines, the alarm current detector providing an output signal in response to a rise in current to the alarm current level.

2. The system according to claim 1, further including rectifier means at the remote station, the rectifier means causing the current regulator to provide direct current in the transmission lines in response to the impressed AC voltage.

3. The system according to claim 2, wherein the monitoring apparatus further includes latch means connected to the output of each of the detectors, the latch means responding to an output signal from a detector by storing the output signal, and latch reset means for removing the stored signal.