Non-destructive status determination for electric power cables
First Claim
1. The method of identifying and determining the energization status of a cable operable at a given frequency and having a conductive neutral member and an internal resistive screen layer which comprises the steps of:
- contacting said neutral member with at least a first probe;
advancing a second probe in increments into said cable;
injecting a test signal differing in frequency from said given frequency across said probes after each incremental advance;
measuring the circuit resistance between said probes with a monitor after each incremental advance;
discontinuing the advance of said second probe upon contact thereof with said screen layer evidenced by said circuit resistance falling within a predetermined range of values;
inserting in parallel with said circuit resistance a shunt resistance of value similar to that of said circuit resistance;
measuring the flow of current through said probes with said shunt resistance in place;
discontinuing the injection of said test signal and disconnecting said shunt resistance upon observation of a predetermined flow of said current;
injecting a signal of said given frequency across said probes; and
confirming the presence of said signal of said given frequency at said monitor during the injection thereof.
1 Assignment
0 Petitions
Accused Products
Abstract
Method and apparatus for identifying and determining the energization status of a cable having a conductive neutral member and an internal resistive screen layer involving probes radially movable relative to the cable to contact the neutral member and the internal resistive screen. Narrow-band AC signals and resistance measurements are utilized for self-testing and for cable testing. A microprocessor controls probe-heating in the advancing of probes through plastic sheath to reach the neutral wire and resistive screen layer. Resistance measurements made under control of the microprocessor are monitored with probe advance. Oscillators provide two signals of different frequencies, one of which is that of the power being transmitted through the cable, to provide distinctive signals indicative of cable energization status.
36 Citations
12 Claims
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1. The method of identifying and determining the energization status of a cable operable at a given frequency and having a conductive neutral member and an internal resistive screen layer which comprises the steps of:
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contacting said neutral member with at least a first probe; advancing a second probe in increments into said cable; injecting a test signal differing in frequency from said given frequency across said probes after each incremental advance; measuring the circuit resistance between said probes with a monitor after each incremental advance; discontinuing the advance of said second probe upon contact thereof with said screen layer evidenced by said circuit resistance falling within a predetermined range of values; inserting in parallel with said circuit resistance a shunt resistance of value similar to that of said circuit resistance; measuring the flow of current through said probes with said shunt resistance in place; discontinuing the injection of said test signal and disconnecting said shunt resistance upon observation of a predetermined flow of said current; injecting a signal of said given frequency across said probes; and confirming the presence of said signal of said given frequency at said monitor during the injection thereof. - View Dependent Claims (2, 3, 4, 5)
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6. The method of identifying and determining the energization status of a cable operable at a given frequency and having a conductive neutral shield member and a resistive screen layer disposed internally of said shield member which comprises the steps of:
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contacting said neutral shield member with a first probe; advancing a second probe through said shield member in increments toward said screen layer; measuring the alternating current resistance between said probes at a frequency higher than said given frequency after each incremental advance of said second probe; discontinuing the advance of said second probe upon measurement of a predetermined resistance between said probes; and removing said probes from said cable.
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7. An instrument for identifying and determining the energization status of a power distribution cable operable at a given frequency having a conductive neutral shield member and an internal resistive screen layer comprising:
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a first probe means for contacting said neutral shield member; a second probe disposed radially external of said cable; means for advancing said second probe toward said screen layer in increments; means for checking the alternating current resistance at a second frequency differing from said given frequency between said first probe and said second probe after each incremental advance of said second probe means; means for discontinuing the advancing of said second probe upon contact thereof with said screen layer as indicated by detection of said alternating current resistance at a predetermined value; and a microprocessor for controlling all said previously mentioned means. - View Dependent Claims (8, 9, 10, 11, 12)
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Specification