Audio bandwidth interface apparatus for pilot wire relays
First Claim
1. An audio bandwidth interface apparatus for use with a protective relay for an electrical power distribution system, said apparatus comprising:
- (a) means for receiving an output signal from said protective relay, which output signal is representative of line current conditions at a predetermined location in said electrical power distribution system;
(b) means for converting said protective relay output signal into a first square wave signal;
(c) means for generating at least a first local signal having at least a first frequency within the audio band;
(d) means for generating a local audio bandwidth output signal for transmission to at least one remote audio bandwidth interface apparatus over an audio band communication channel, said local audio bandwidth output signal comprising said first local signal modulated by said first square wave;
(e) means for receiving, from said audio band communication channel, a remote signal comprising the local audio bandwidth output signal generated by at least one remote audio bandwidth interface apparatus;
(f) means for converting said remote signal into a second square wave signal;
(g) means for imparting a predetermined delay to said first square wave signal; and
(h) means for comparing the phase of said delayed first square wave signal with the phase of said second square wave signal and generating a trip output signal when said phase comparison exceeds predetermined limits.
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Abstract
An apparatus for enabling pilot wire relays to communicate across voice-grade, non-metallic communication channels converts sinusoid signals representative of phase currents at a location in an electric power distribution system to audio band signals representative of the phase of the current signal at that location. These audio band signals are transmitted over a voice-grade non-metallic communication channel to a remote interface module where they are converted to square waves which are compared against square waves representative of the currents in the electrical power distribution system at that location.
78 Citations
19 Claims
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1. An audio bandwidth interface apparatus for use with a protective relay for an electrical power distribution system, said apparatus comprising:
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(a) means for receiving an output signal from said protective relay, which output signal is representative of line current conditions at a predetermined location in said electrical power distribution system; (b) means for converting said protective relay output signal into a first square wave signal; (c) means for generating at least a first local signal having at least a first frequency within the audio band; (d) means for generating a local audio bandwidth output signal for transmission to at least one remote audio bandwidth interface apparatus over an audio band communication channel, said local audio bandwidth output signal comprising said first local signal modulated by said first square wave; (e) means for receiving, from said audio band communication channel, a remote signal comprising the local audio bandwidth output signal generated by at least one remote audio bandwidth interface apparatus; (f) means for converting said remote signal into a second square wave signal; (g) means for imparting a predetermined delay to said first square wave signal; and (h) means for comparing the phase of said delayed first square wave signal with the phase of said second square wave signal and generating a trip output signal when said phase comparison exceeds predetermined limits. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for enabling a protective relay for an electrical power distribution system to communicate with at least one other protective relay comprised in the steps of:
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(a) receiving the output signal from said protective relay, which output signal is representative of line conditions at a predetermined location in said electrical power distribution system; (b) converting said protective relay output signal into a first square wave signal; (c) generating at least a first local signal having at least a first frequency within the audio band; (d) generating a local audio bandwidth output for transmission to said at least one remote audio bandwidth interface apparatus over an audio band communication channel, said audio bandwidth output signal comprising said first local signal modulated by said first square wave; (e) receiving, from said audio band communication channel, a remote signal comprising the local audio bandwidth output signal generated by at least one remote audio bandwidth interface apparatus; (f) converting said remote signal into a second square wave signal; (g) imparting a predetermined delay to said first square wave signal; and (h) comparing the phase of said delayed first square wave signal with the phase of said second square wave signal and generating a trip output signal when said phase comparison exceeds predetermined limits. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A pilot wire relay system for protecting at least a portion of an electrical power distribution system, said pilot wire relay system comprising:
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(a) a first pilot wire relay positioned at one end of a protected zone of said electrical power distribution system for monitoring electrical current flowing in the electrical power distribution system at said one end; (b) a second pilot wire relay positioned at the other end of said protected zone for monitoring current flowing in the electrical power distribution system at said other end; and (c) a first audio bandwidth interface module connected between said first pilot wire relay and one end of an audio bandwidth communication channel and a second audio bandwidth interface module connected between said second pilot wire relay and the other end of said audio bandwidth communication channel, each of said first and second audio bandwidth interface modules comprising; (1) means for receiving an output signal from the pilot wire relay to which said audio bandwidth interface module is connected, which output signal is representative of line current conditions at the end of the protected zone at which said pilot wire relay is positioned; (2) means for converting said pilot wire relay output signal into a first square wave signal; (3) means for generating at least a first local signal having at least a first frequency within the audio band; (4) means for generating a local audio bandwidth output signal for transmission to the second audio bandwidth interface module over the audio bandwidth communication channel, said local audio bandwidth output signal comprising said first local signal modulated by said first square wave; (5) means for receiving, from said audio bandwidth communication channel, a remote signal comprising the local audio bandwidth output signal generated by the second audio bandwidth interface module; (6) means for converting said remote signal into a second square wave signal; (7) means for imparting a predetermined delay to said first square wave signal; and (8) means for comparing the phase of said delayed first square wave signal with the phase of said second square wave signal and generating a trip output signal when said phase comparison exceeds predetermined limits. - View Dependent Claims (18, 19)
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Specification