Systems for transmitting information in an alternating current electricity supply system

• US 4,254,403 A
• Filed: 08/06/1979
• Issued: 03/03/1981
• Est. Priority Date: 07/18/1974
• Status: Expired due to Term

• Current Assignee: ABB Metering Systems Limited
• Original Assignee: General Electric (Shanghai) Co., Ltd. (General Electric Company)
• Inventors: Gray, Frederick M., Fielding, Geoffrey, Perez-Cavero, Leonardo, Cross, Michael W. A.
• Primary Examiner(s): Groody, James J.
• Application Number:
  US06/063,965
• Time in Patent Office: 575 Days
• Field of Search: 455/352, 340/310 R, 340/310 A, 340/310 CP, 340/538, 307/3, 328/115, 328/151, 328/128, 328/127, 375/68
• US Class Current: 375/259
• CPC Class Codes: H02J 13/00009 using pulsed signals
• CPC Class Codes: H02J 13/0001 using modification of a parameter of the network power signal
• CPC Class Codes: H04B 2203/542 using zero crossing information
• CPC Class Codes: H04B 2203/5495 having measurements and testing channel
• CPC Class Codes: H04B 3/542 the information being in digital form
• CPC Class Codes: H05B 47/185 via power line carrier transmission
• CPC Class Codes: Y04S 10/52 Outage or fault management, e.g. fault detection or location

Abstract

A system for transmitting information in an alternating current supply system wherein information is transmitted by reducing the instantaneous value of the supply voltage during a corresponding period in each of a selection of cycles of the supply voltage, the selection of cycles determining the information transmitted. To minimize disturbance of the system voltage the period of alteration includes a voltage zero. The alteration is effected by closing a switch connected across the system for the period the voltage reduction is required.

Claims

1. In a system for transmitting information in an A.C. electricity supply system by reducing the instantaneous value of the A.C. supply voltage during the same small fractional part of each of a selection of cycles of the supply voltage waveform, said part including a time of voltage zero, a transmitter comprising:

controllable switch means connected across said supply system in an effective zero impedance path so as to effectively shortcircuit said supply system throughout the whole of any period that the switch means is closed and thereby draw from said system throughout the whole of any period that said switch means is closed a current of sufficient magnitude to reduce the instantaneous value of the A.C. supply voltage during the time that said switch means is closed and conducting; and

switch control means for closing said switch means for a said small fractional part of any selected single cycle of the supply voltage waveform.

2. A transmitter according to claim 1 wherein said switch means comprises an electronic switch of the kind which, once closed, remains closed until the current through the switch means returns to zero so that in each selected cycle the switch means is closed and conducting for a period determined by the system impedance.

3. A transmitter according to claim 2 wherein said switch control means comprises:

peak detection means which produces an output indicative of the occurrence of a peak value of the voltage of the supply system;

timing means which initiates a timing period in response to the output of said peak detection means; and

a pulse generator which generates an operating pulse for the switch in response to the end of the timing period defined by said timing means.

4. A transmitter according to claim 3 including an AND gate having a first input to which the output of the pulse generator is applied;

and a code generator for supplying pulses to a second input of the AND gate in accordance with the desired selection of cycles, the output of the AND gate being utilized to control the operation of said electronic switch.

5. A transmitter according to claim 4 including means for applying a signal to a further input of the gate so as to allow the gate to open only when the supply voltage waveform has a predetermined slope, and means for applying a signal to a further input of the gate so as to allow the gate to open only when the instantaneous value of the supply voltage is less than a predetermined value.

6. A transmitter according to claim 2 in combination with an alternating current electricity supply system distribution transformer having primary and secondary windings, said switch being connected across a secondary winding of said distribution transformer.

7. In a system for transmitting information in an A.C. electricity supply system by reducing the instantaneous value of the A.C. supply voltage during the same small fractional part of each of a selection of cycles of the supply voltage waveform, said part including a time of voltage zero, a receiver comprising:

an integrator which integrates the instantaneous value of the supply voltage system for short periods each less than the supply voltage cycle period and each starting at a zero crossing of the waveform of said voltage, the integrator being reset between successive integration periods; and

means for detecting when the output of said integrator for an integration period differs from the output of the integrator for the preceding integration period.

8. A receiver according to claim 7 wherein said detecting means comprises a capacitance arranged to charge to the peak value of the output of said integrator;

means for partly discharging said capacitance between integration periods; and

means for monitoring the supply of charging current to said capacitance.

9. A receiver according to claim 8 wherein said integrator comprises:

a capacitance connected in series with a resistance across said voltage;

an electronic switch connected across said integrator capacitance; and

means for opening said switch during each said integration period.

10. A receiver according to claim 9 wherein said means for opening said switch comprises:

reference means arranged to produce an output indicative of the occurrence of zero-crossings in said voltage at the receiver;

timing means responsive to the output of the reference means to produce an output signal for a predetermined period following said each zero-crossing; and

driver means for utilizing the timing means output to open said switch.