Portable High Voltage Bridge Cable Fault Locator Murray Bridge Tester 15kV |

The high voltage bridge is designed on the MURRAY bridge principle and can be used to locate the breakdown points of various wires and cables after laying as well as defective points that have not broken down but have a low insulation resistance value. It can of course also be used to locate defective points of various wires and cables in a cable factory.

The equipment uses a switching power supply to form a high-voltage constant-current source, with a no-load voltage of 15000V and a short-circuit current of 50mA. 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 cable is reliably grounded through a braided shielding layer, the operating knobs on the panel are at low potential, and the bridge is operated through an insulated rod. The high-voltage constant-current source and the bridge are integrated in one portable aluminum-alloy 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 is especially suitable for judging breakdown points of short cables and breakdown points near the terminals, and it is easy to operate.

The XHHG521C is positioned as the bridge-type rough-ranging tool in cable fault locating work — it quickly finds the approximate breakdown position of most cable breakdown points, and works best when combined with the wave-reflection method and a pinpointing device so that the methods complement each other and locating becomes faster and more reliable. The manual identifies three groups it is especially suited to. The first is cable manufacturers, who can use it inside the factory to locate breakdown points of all kinds of wires and cables; with an optional digital capacitance meter it can also find broken-wire points, and because it is light it can be carried to the site to provide locating service for cable users. The second is professional locating teams, such as the cable repair and test crews of large and medium power supply bureaus and large electricity-consuming enterprises. The third is small-scale users, such as small power supply bureaus and medium electricity-consuming enterprises, whose cable inventory is small, generally clearly routed and not very long and whose faults are few, for whom a full wave-reflection locating set is expensive and requires highly skilled and experienced operators, whereas this device is convenient to operate and can meet daily needs. Unlike the other instruments in the same category, which pinpoint jacket faults or trace cable routes, this device is a MURRAY bridge that measures the fault distance itself, with the whole bridge arranged at high potential and operated safely from the low-potential panel.

The high voltage bridge is especially suitable for:

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 balance adjustment reading. That is, the fault distance is obtained from the proportional relationship and the known cable length. The basis of the bridge 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 reading is a per-mille value; G is the galvanometer, with an adjustable electrical balance zero point; at the far end, short-circuit the two ends B and D with a special C-type clamp short-circuit line.

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: within one year from the date of purchase, free repair is provided for product quality problems, with lifetime maintenance and technical service.

It is a high voltage bridge designed on the MURRAY bridge principle, used to locate the breakdown points of wires and cables after laying as well as defective points with a low insulation resistance but no breakdown, and it can also be used to locate defective points of various wires and cables in a cable factory.

The input voltage is AC 220V (±10%), 50/60Hz (±2Hz); the no-load voltage is ≥15000V; the short-circuit current is ≥50mA; and the locating ratio accuracy is ±(0.2%·L±1) meter. The test voltage must not exceed 15kV.

Based on the MURRAY bridge, the bridge is balanced by adjusting the proportional potentiometer and watching the galvanometer, and the fault distance is obtained from L1 = P‰·L, where P is the per-mille balance reading and L is the known cable length.

It has over-current protection and zero-position protection, with adjustable output voltage, adjustable impulse frequency and signal frequency adjustment; the test range has no blind area, and compared with the wave-reflection method it has no blind area and is especially suitable for short cables and breakdown points near the terminals.

The packing list includes the main unit (1 set), output line (2 pieces), power line (1 piece), ground wire (1 piece) and short-circuit line (1 piece).