6kV Cable Outer Sheath Fault Tester Murray Bridge 100mA Cable Fault Locator |

The cable outer sheath fault tester is designed on the MURRAY bridge principle and can be used to locate the breakdown points of various wires and cables as well as defective points that have not broken down but have a low insulation resistance value.

The equipment uses a motorized voltage regulator and an R-type transformer to form a high-voltage constant-current source, with push-button control for raising and lowering the voltage. The no-load voltage is 5000V with a short-circuit current of 100mA; it adopts a high-sensitivity amplifier and a galvanometer for balance indication, and together with a proportional potentiometer forms a balanced bridge, with the whole arranged at high potential. The measuring cable is a specially designed twin-core high-voltage rubber cable, and a four-terminal resistance measurement method avoids the error introduced by lead resistance. The operating knobs on the panel operate the internal high voltage through an insulated rod, and the panel is at low potential overall. The equipment is also fitted with a 12806 display, with one-key operation: input the cable length and the fault distance is calculated automatically. The high-voltage source and the bridge are integrated in one portable protective case, so the equipment is high in voltage, light in weight, easy to operate and safe to use. Compared with the wave-reflection method, the bridge balance method has no blind area, and it is especially suitable for judging breakdown points of short cables and breakdown points near the terminals.

The XHHG521B is positioned for outer-sheath (jacket) fault distance testing on cables after laying, with the cable length keyed in and the fault distance computed automatically on the 12806 display — so a field crew gets a direct distance reading through one-key operation instead of reading a raw bridge balance. It is engineered for power supply bureau and industrial plant cable test and maintenance crews that must locate jacket breakdown points and low-resistance jacket defects on cables already in service; for cable service teams that inspect the outer sheaths of various wires and cables; and for operators who need a guided, easy-to-use instrument where the cable length is entered and the distance appears on the display, all in one portable case. It is used both for high-resistance linear breakdown points after laying (such as at cable intermediate joints) and for flashing breakdown points, as well as for defect points that have not yet broken down but show a low resistance. Unlike the other instruments in the same category, which pinpoint sheath faults on site or trace cable routes, this device is a MURRAY bridge that measures the jacket fault distance itself, with the whole bridge arranged at high potential and operated safely from the low-potential panel.

For a cable under test, let the distances from the two ends of the cable to the breakdown point be L1 and L2, the total length of the cable be L, and the corresponding conductor resistances be R1 and R2. After the bridge is connected according to the wiring diagram and balanced, L1 = P‰·L, where P (per mille) is the dial reading. That is, the fault distance is obtained from the proportional relationship and the known cable length, and the basis of the method is that the conductor (or shielding-layer) resistance is uniform and proportional to the length.

Wiring notes: HV is the high-voltage constant-current source; the faulty cable is CD and the auxiliary cable is AB, with the same conductor cross-section and the same length L, and the distance from the fault point to the measuring end is X; the measuring clamps are connected to the two ends A and C of the cable conductors, with the two sides of each clamp being the current and potential terminals, both reliably connected to the cable; R is the balance potentiometer, whose dial reading is a per-mille value; G is the galvanometer, with an adjustable electrical balance zero point; at the far end, the two ends B and D must be short-circuited and the short circuit must be reliable.

Reverse-connection calibration: lower the voltage and discharge, swap the measuring clamps, and repeat the steps to obtain another reading P2, which should give P1 + P2 = 1000. The fault point position is X = 2 × L × P1‰, and particular attention should be paid to the “2” in the formula, because the auxiliary cable doubles the cable involved in the calculation.

Other notes: sometimes interference affects the galvanometer zero point, in which case re-zero at the final sensitivity position (with the test voltage reduced to zero and everything else unchanged, zero it, then raise the voltage again and adjust the balance for a more accurate value); when conductors of different cross-sections are used as the auxiliary cable, convert to the length of the faulty cable, so if the faulty cross-section is Sx and the auxiliary cable is S, the formula becomes X = P1‰ × (1 + Sx/S) × L; if all three cores of a three-core cable have broken down or are short-circuited with each other, a core with the best insulation resistance can be selected as the auxiliary cable. Understanding the factors affecting sensitivity helps: the larger the current through the bridge, the higher the sensitivity; the larger the cable conductor resistance, the higher the sensitivity, meaning thin and long cables have higher sensitivity while thick and short cables have lower sensitivity, so for cables of large cross-section and short length the current should be increased as far as possible and a higher amplifier sensitivity used.

Warranty: the product is warranted for one year from the date of sale, with lifetime maintenance.

It is a cable outer sheath fault tester designed on the MURRAY bridge principle, used to locate the breakdown points of various wires and cables as well as defective points with a low insulation resistance but no breakdown.

The no-load voltage is ≤6000V, the short-circuit current is ≤100mA, the locating ratio accuracy is ±(0.1%·L±1) meter, the weight is 25kg, and the working power supply is AC 220V and a 9V battery.

The balanced bridge gives L1 = P‰·L from the proportional relationship and the known cable length. With the 12806 display, the cable length is keyed in (initial value 1000) and a single press on the test page automatically collects the bridge ratio coefficient P and calculates the fault distance X; the result is shown on the result page.

The equipment can generate a maximum of 6000V, so it must be used with at least two people present and with the grounding terminal reliably grounded. Before touching high-voltage parts, always discharge first and hang up the ground wire, and do not press the voltage-reduction button while the zero-position indicator is lit.

The high-voltage source and the bridge are integrated in one portable protective case with a 12806 display and one-key operation, where the cable length is entered and the fault distance is calculated automatically. The product is warranted for one year from the date of sale with lifetime maintenance.