Protective relay circuit providing a combined distance and overcurrent function

Claim 2

A protective relay circuit for providing a combination distance and overcurrent relay function for controlling the trip coil of a circuit breaker protecting an alternating current power transmission line, comprising: difference circuit means for producing a difference signal proportional to the difference between a signal proportional to an a-c power line current multiplied by a preselected constant reference impedance and a signal proportional to line voltage; an alternating current level detector responsive to the difference signal from said difference circuit means for producing an output signal when said difference signal exceeds a predetermined threshold value representative of a preselected parameter of said power line; means for generating a voltage polarity signal from a line voltage signal of said alternating current power transmission line; coincidence detector means for producing a coincidence signal output in response to detecting coincidence between the output of said alternating current level detector and the voltage polarity signal; coincidence-responsive means for receiving said coincidence signal output and being operative, when enabled, to effect operation of said trip coil in response to a coincidence signal output of a predetermined minimum duration; and said protective relay circuit permitting production of an effective coincidence signal output only if said difference signal exceeds said predetermined threshold value.

Claim 3

A protective relay circuit in accordance with claim 1 wherein said coincidence-responsive means includes characteristic timer means, said characteristic timer means producing a signal output for use in controlling the trip coil of the circuit breaker only in response to said predetermined minimum time duration coincidence signal output of said coincidence detector means.

Claim 4

A protective relay circuit in accordance with claim 2 wherein said characteristic timer means maintains its signal output for a predetermined period of time once a signal output is generated.

Claim 5

A protective relay circuit in accordance with claim 2 wherein said protected alternating current power transmission line includes series capacitor compensation with a voltage breakdown device connected across the capacitor, said level detector producing an output when the difference signal exceeds a predetermined value which is a function of the capacitor voltage at which said voltage breakdown device breaks down.

Claim 6

A protective relay circuit in accordance with claim 2 wherein said protected alternating current power transmission line includes series capacitor compensation with a voltage breakdown device connected across the capacitor, said level detector producing an output signal when said difference signal exceeds a value corresponding to the breakdown voltage of said breakdown device.

Claim 7

A protective relay circuit in accordance with claim 2 wherein said protected alternating current power transmission line includes series capacitor compensation with a spark gap protective device connected across the capacitor, said alternating current level detector producing an output signal when the difference signal from said difference circuit exceeds a value correponding to the breakdown voltage of the spark gap.

Claim 8

A protective relay circuit in accordance with claim 2 in which said characteristic timer means is set to detect coincidence for less than 90 electrical degrees, and said level detector is adjusted to produce an output signal only for difference signals exceeding a value which corresponds to normal load current multiplied by the reference impedance.

Claim 9

A protective relay circuit in accordance with claim 1 wherein said alternating current level detector includes a plurality of voltage breakdown devices connected in series.

Claim 10

A protective relay circuit in accordance with claim 1 wherein said alternating current level detector includes at least one pair of inverse parallel connected diodes.

Claim 11

A protective relay circuit in accordance with claim 1 wherein said coincidence detector means includes an AND gate.

Claim 12

A protective relay circuit in accordance with claim 1 wherein said difference circuit means includes means for providing amplification.

Claim 13

A protective relay circuit in accordance with claim 11 wherein the gain of said amplification means of said difference circuit means is adjustable.

Claim 14

A protective relay circuit for providing a combination distance and overcurrent relay function for controlling the trip coil of a circuit breaker protecting an alternating current power transmission line, comprising: first means for coupling to the line and responsive to line voltage for developing first and second reference voltages representative of the line voltage and having a certain phase relation thereto; second means for coupling to the line and responsive to line current for developing a representative voltage related to the line current by a predetermined constant impedance and having a certain phase relation thereto; summing means for summing said representative voltage related to the line current by the predetermined constant impedance and said first reference voltage representative of the line voltage to produce a difference signal output; threshold means for receiving the difference signal output of said summing means, said threshold means providing a signal output only when said difference signal output of said summing means exceeds a selected predetermined threshold value representative of a preselected parameter of said power line; means responsive to said second reference voltage represetative of the line voltage for providing a voltage polarizing signal indicative of the direction of the fault location with respect to said relay; coincidence detector means for producing a coincidence signal output in response to detecting coincidence between the output of said threshold means and the voltage polarizing signal; coincidence-responsive means for receiving said coincidence signal output and being operative, when enabled, to effect operation of said trip coil in response to a coincidence signal output of a predetemined minimum duration; and said protective relay circuit permitting production of an effective coincidence signal output only if said difference signal exceeds said predetermined threshold value.

Claim 15

A protective relay circuit for providing a combination distance and overcurrent relay function for controlling the trip coil of a circuit breaker protecting an alternating current power transmission line, comprising: first means for coupling to the line and responsive to line voltage for developing first and second reference voltages representative of the line voltage and having a certain phase relation thereto; second means for coupling to the line and responsive to line current for developing a representative voltage related to the line current by a predetermined constant impedance and having a certain phase relation thereto; summing means for summing said representative voltage related to the line current by the predetermined constant impedance and said first reference voltage representative of the line voltage to produce a difference signal output; threshold means for receiving the difference signal output of said summing means, said threshold means providing a signal output only when said difference signal output of said summing means exceeds a selected predetermined threshold value representative of a preselected parameter of said power line; means responsive to said second reference voltage represetative of the line voltage for providing a voltage polarizing signal indicative of the direction of the fault location with respect to said relay; coincidence detector means for producing a coincidence signal output in response to detecting coincidence between the output of said threshold means and the voltage polarizing signal; coincidence-responsive means for receiving said coincidence signal output and being operative, when enabled, to effect operation of said trip coil in response to a coincidence signal output of a predetemined minimum duration; and said protective relay circuit permitting production of an effective coincidence signal output only if said difference signal exceeds said predetermined threshold value.

Claim 16

A protective relay circuit in accordance with claim 13 wherein said coincidence-responsive means includes characteristic timer means, said characteristic timer means producing a signal output for use in controlling the trip coil of the circuit breaker only in response to said predetermined minimum time duration coincidence signal output of said coincidence detector means.

Claim 17

A protective relay circuit in accordance with claim 14 wherein said characteristic timer means maintains its signal output for a predetermined period of time once a signal output is generated.

Claim 18

A protective relay circuit in accordance with claim 14 wherein said protected alternating current power transmission line includes series capacitor compensation with a voltage breakdown device connected across the capacitor, said threshold means producing an output when said difference signal output exceeds a predetermined value which is a function of the capacitor voltage at which said voltage breakdown device breaks down.

Claim 19

A protective relay circuit in accordance with claim 14 wherein said protected alternating current power transmission line includes series capacitor compensation with a voltage breakdown device connected across the capacitor, said threshold means producing an output when said difference signal output exceeds a value corresponding to the breakdown voltage of said breakdown device.

Claim 20

A protective relay circuit in accordance with claim 14 wherein said protected alternating current power transmission line includes series capacitor compensation with a spark gap protective device connected across the capacitor, said threshold means producing an output when said difference signal output of said summing means exceeds a value corresponding to the breakdown voltage of said spark gap.

Claim 21

A circuit in accordance with claim 14 in which said characteristic timer is set to detect coincidence for less than 90 electrical degrees, and said threshold means is adjusted to produce a signal output only for summing means outputs exceeding a value corresponding to normal load current multiplied by said predetermined constant impedance.

Claim 22

A protective relay circuit in accordance with claim 13 wherein said threshold means includes a plurality of voltage breakdown devices connected in series.

Claim 23

A protective relay circuit in accordance with claim 13 wherein said threshold means includes at least one pair of inverse parallel connected diodes.

Claim 24

A protective relay circuit in accordance with claim 13 wherein said coincidence detector means includes an AND gate.

Claim 25

A protective relay circuit in accordance with claim 13 wherein said summing means includes means for providing amplification.

Claim 26

A protective relay circuit means in accordance with claim 23 wherein the gain of said amplification means of said summing means is adjustable.