Cable fault location

Claim 5

Apparatus for locating a fault in a cable comprising at least two conductors, which apparatus comprises an impulse generator with connecting means for applying a single voltage impulse between two conductors of the cable, a waveform display or recording device and, coupled between said connecting means and said display or recording device, linear coupler comprising a primary winding and a second winding, the primary winding being connected in the connecting means for connection in series between the impulse generator and one of said two conductors and the secondary winding having a damping resistor connected in shunt therewith, the arrangement being such that said linear coupler will obtain the derivative of the current waveform resulting from the application of a voltage impulse to the cable to give across the secondary winding a signal output which is a pulse of relatively short duration each time a reflection of the voltage impulse returns to the impulse generator.

Claim 6

Apparatus for locating a fault in a cable comprising at least two conductors, which apparatus comprises an impulse generator with connecting means for applying a single voltage impulse between two conductors of the cable, a waveform display or recording device and, coupled between said connecting means and said display or recording device, linear coupler comprising a primary winding and a second winding, the primary winding being connected in the connecting means for connection in series between the impulse generator and one of said two conductors and the secondary winding having a damping resistor connected in shunt therewith, the arrangement being such that said linear coupler will obtain the derivative of the current waveform resulting from the application of a voltage impulse to the cable to give across the secondary winding a signal output which is a pulse of relatively short duration each time a reflection of the voltage impulse returns to the impulse generator.

Claim 7

Apparatus as claimed in claim 3, wherein the linear coupler is connected in series with a line conductor of the cable.

Claim 8

Apparatus as claimed in claim 3, wherein the linear coupler is connected in series with the earth return conductor.

Claim 9

Apparatus as claimed in claim 3, wherein an electrostatic screen is provided between the primary and secondary windings of the linear coupler.

Claim 10

Apparatus for locating a fault in a cable comprising at least two conductors, which apparatus comprises an impulse generator with connecting means for applying a single voltage impulse between two conductors of the cable, a digital transient recorder for recording the waveform of the resultant reflected signal from the cable and, coupled between said connecting means and said digital transient recorder, a linear coupler comprising a primary winding and a secondary winding, the primary winding being connected in the connecting means for connection in series between the impulse generator and one of said two conductors and the secondary winding having a damping resistor connected in shunt therewith, the arrangement being such that said linear coupler will obtain the derivative of the current waveform resulting from the application of a voltage impulse to the cable to give across the secondary winding a signal output which is a pulse of relatively short duration each time a reflection of the voltage impulse returns to the impulse generator, said digital transient recorder including means for regularly repetitively sampling the waveform to be recorded, analogue digital conversion means arranged to convert the sample signal amplitudes into digital form, and a digital signal store for recording the digitised sampled information.

Claim 11

Apparatus for locating a fault in a cable comprising at least two conductors, which apparatus comprises an impulse generator with connecting means for applying a single voltage impulse between two conductors of the cable, a digital transient recorder for recording the waveform of the resultant reflected signal from the cable and, coupled between said connecting means and said digital transient recorder, a linear coupler comprising a primary winding and a secondary winding, the primary winding being connected in the connecting means for connection in series between the impulse generator and one of said two conductors and the secondary winding having a damping resistor connected in shunt therewith, the arrangement being such that said linear coupler will obtain the derivative of the current waveform resulting from the application of a voltage impulse to the cable to give across the secondary winding a signal output which is a pulse of relatively short duration each time a reflection of the voltage impulse returns to the impulse generator, said digital transient recorder including means for regularly repetitively sampling the waveform to be recorded, analogue digital conversion means arranged to convert the sample signal amplitudes into digital form, and a digital signal store for recording the digitised sampled information.

Claim 12

Apparatus as claimed in claim 7, which includes a visual waveform display device for immediate visual display of the waveform.

Claim 13

Apparatus as claimed in claim 8, wherein the visual waveform display device is a cathode ray oscilloscope.

Claim 14

Apparatus as claimed in claim 7, which includes means for transmitting the information in digital form to a remote location.

Claim 15

Apparatus as claimed claim 10 in combination with means at said remote location for comparing the transmitted information representative of the waveform normally to be expected or with pre-computed information representative of possible fault conditions.

Claim 16

Apparatus as claimed in claim 10, which includes means at said remote station for displaying the transmitted information for visual analysis.

Claim 17

Apparatus as claimed in claim 10, which includes a store at said remote location arranged to receive the transmitted information.

Claim 18

Apparatus as claimed in claim 7, which includes means for feeding information read-out from the store, at the location of the generator or at said remote location, to a digital-to-analogue converter to provide an analogue waveform and a display device arranged for displaying the analogue waveform from the converter.

Claim 19

Apparatus as claimed in claim 7, wherein said digital store at the location of the generator is a temporary store and wherein means are provided for reading out the information in that store onto a permanent record.

Claim 20

Apparatus as claimed in claim 3, wherein said display device comprises a cathode ray oscilloscope.

Claim 21

Apparatus as claim in claim 3, wherein the impulse generator comprises a capacitor and a high voltage direct current source connected for charging said capacitor through a resistor, and a switch for connecting the high voltage side of said capacitor to a conductor of the cable under test, the low voltage side of said capacitor being connected via said primary winding to an earthed conductor of the cable.

Claim 22

A method as claimed in claim 1, wherein one of said two conductors comprises an earth or neutral conductor of the cable.

Claim 23

A method as claimed in claim 1, for locating a fault in one core of a multicore cable, wherein one of the said two conductors comprises a further core of the cable.