Cable Fault Locator |Low Voltage Hidden Acoustic Magnetic Synchronization

The XHHD530M Low Voltage Hidden Cable Fault Locator is a dedicated instrument for finding faults on underground and concealed low-voltage lines. It is used by the power, broadcast and postal sectors as well as by industrial and mining enterprises and rural users to locate underground cables — including direct-buried shielded cable lines and buried lines — and to identify their faults.

It can detect the route of a buried line, its approximate underground position and basic burial depth, and can locate various earth-leakage faults and broken-core faults. It also works on lines under paddy fields, under concrete, brick, stone or asphalt pavement, on lines inside building walls, and on waterproof cable and cable laid on the ground, all of which can be detected with the appropriate method.

The fault locator consists of a signal transmitter, a signal receiver, a probe and probe rod, and insertion rods. Both the transmitter and the receiver are small, well-built and neatly styled. The instrument offers high sensitivity, strong acoustic-meter synchronization and anti-interference capability, and is easy to carry and quick and accurate in locating fault points. The receiver uses acoustic-meter synchronization with high and low sensitivity gears; the transmitter provides output indication and a KΩ measurement function that can replace a multimeter or a megger to check line continuity, open and mixed faults, and measure earth leakage resistance to determine the nature of the fault. The transmitter adds an "Output 2" terminal that widens the detection methods and functions.

The instrument is composed of a transmitter, a receiver, a probe rod and a probe, a set of insertion rods and plugs, and connecting lines.

The transmitter mainly outputs an intermittent pulse signal as the signal source for fault location, and its KΩ function checks line continuity, open and mixed faults, and measures leakage resistance to determine the nature of the fault. Its "Output 2" terminal outputs a large current.

The receiver uses the probe and the insertion rods to pick up, by the induction method and the insertion method, the space magnetic-field signal and the ground electric-field signal produced by the transmitter signal along the line. After amplification and processing by the receiver, these are turned into sound and meter-pointer deflection.

When a pulse signal is fed into the line, a magnetic field exists in the space around the line. The induction method uses the probe to sense and receive the space magnetic-field signal, which is amplified by the receiver into sound and meter-pointer deflection. By listening to the loudness of the speaker and observing the amplitude of the pointer swing, the operator determines the route of the buried line, the general area of the fault point, the accurate position of the buried line and its basic burial depth.

After the pulse signal is fed into the buried line, a regular distributed electric field related to the nature of the fault forms on the ground surface above the line and the fault point. The insertion method uses two insertion rods to pick up the potential difference between two points in the distributed electric field; after amplification by the receiver this becomes pointer swing and sound. By observing the size and direction of the pointer swing and the loudness of the sound, the operator accurately determines the underground position of the buried line and the exact position of the fault point.

First separate the faulty line at both the leading-in and leading-out ends, including branch loads and meters connected to the faulty line, and then cut off the power before making KΩ measurements. When measuring, both exposed ends of the buried line must be left dangling separately, and must not touch each other or the ground. Measure KΩ for each line from one leading-out end and record the earth resistance of each line to find the fault-line earth resistance and judge the nature and type of the fault. If necessary, do the same test at the other end. Feed the test signal into the line with the smaller earth resistance. This process also verifies whether the transmitter is working normally.

Make the transmitter and receiver work normally. Connect the black output terminal to earth (with a good earth connection, not shared with other earth lines) and the red terminal to the buried line or faulty line. Select the output gear according to the fault type — for measuring the route only, medium or high gear can be used. Set the receiver function switch to the high gear and bring the probe near the transmitter or the buried line; the receiver speaker gives an intermittent "du-du-du" sound. Changing the position of the probe relative to the buried line changes the loudness, and the position with the loudest sound is directly above the buried line's route. Walking along the direction of loudest sound gives the line's laying direction; the accurate underground position and basic burial depth are found by experience.

Make the transmitter and receiver work normally. Connect the black output terminal to earth with a good earth connection placed in the direction opposite to the buried line and in line with it; if the fault point is close to the signal-feeding end, the earthing point should be 5–10 m away from the feeding point. Connect the red terminal to the buried or faulty line and set the output selection to low gear. Set the receiver function switch to high gear and insert the two insertion-rod plugs into the receiver input socket (the probe and the rods share one socket). Hold the receiver in one hand and the red and black rod handles in the other, bring the two tips near the transmitter, then draw the tips about 0.5 m apart and insert them into the ground near the buried line; an intermittent "du-du" sound is heard and the pointer swings with the pulses — otherwise check the rod connections and plugs for broken or mixed lines.

Then separate the two rod tips by a distance chosen between 0.1 and 0.5 m, so that after insertion the pointer swing is about 1–5 divisions. Insert vertically to the line's direction, keeping the red rod in front and the black rod behind, and observe the pointer direction: if it swings to "+", move the two rods toward the red rod; if it swings to "−", move them toward the black rod, until the sound is minimal and the pointer is basically still — then the midpoint between the two rod insertion points is directly above the accurate underground position of the buried line. This is the "lateral symmetric method". It can be verified by the "lateral verification method": keep one rod fixed at the midpoint and insert the other rod at two points on either side; the pointer direction and magnitude, and the sound, should be the same, confirming the accurate midpoint. Inserting every 3–10 m along the general direction finds several midpoints whose line is the accurate route, position and direction of the buried line.

The "longitudinal symmetric method" can also be used: insert the two rods directly above the buried line along its direction, red rod first and black rod behind, with the same rod spacing. When the sound increases but the pointer swing decreases, reduce the rod spacing or switch to the low-sensitivity gear. If the pointer changes from "+" to "−", the fault point has been passed; move the rods back carefully in small steps (or fix one rod and move the other) until the sound is minimal and the pointer is basically still — the midpoint below the two rod insertion points is the fault point. This can be verified by the "longitudinal symmetric verification method", the "cross intersection method" (combining lateral and longitudinal midpoints), the "equipotential circle verification method", the "X-type verification method", and the "long-distance insertion method" with its lateral-side and equal-distance comparison, side-angle, short-distance and two-time comparison variants. Under difficult ground (concrete, brick, or frozen in winter) the rods may be wrapped with water-soaked cloth ("moistening method") to improve contact. Because the electromagnetic field above a buried line is complex, false points may appear near leading-out sections, joints, coils, T-branches, corners, crossings with other buried lines and metal pipes, and changes in burial depth; the nature of the fault must be confirmed and the appropriate verification method used to eliminate false points. All earth-leakage faults are verified by the "equipotential circle verification method".