SU116051A1 - Device for detecting a fault in an electrical cable - Google Patents

Description

The proposed device for detecting a place of damage in an electrical box is related to known similar devices assembled according to a DC bridge scheme, one pair of arms of which is formed by magazines of calibrated resistances, the other pair by one of the wires of the cable being tested, and the free end of the measuring diagonal is connected cable conductor (or to earth in case of conductor closure to earth). However, these devices make it relatively easy to find a place only if the transitional resistance between the cable cores does not exceed a few kilo, but for large transient resistance, it is very difficult to find a place with a slightly weakened insulation.

In order to increase the sensitivity of the device at large transient resistances at the site of damage, it is proposed to include an electric capacitor in the output diagonal of the bridge, charging the output voltage of the bridge and discharging each time to the galvanometer of the bridge.

FIG. 1 shows a circuit diagram of the device proposed; in fig. 2 is a diagram by which the damage location in the cable is determined.

The MI and M2 stores of calibrated resistances form one pair of bridge shoulders and n connected by a Reochord B. To the ends 1 and 2 of the MI and MZ stores there is a wire G of the cable being tested, forming the other two arms of the bridge (Fig. 2). In the measuring diagonal of the bridge, connected at one end to the BI engine of Reochord B and the other free end 3 to the second cable conductor (Fig. 2) or to the ground, in the event of a conductor closing to ground, an electric capacitor C is connected. Parallel to capacitor C via a key K and the two-pozsionny switch I am switched on a 1010 inch galvanometer G. The switch I is set to the position I pru rough tuning of the bridge (the J4L-116051-2 is turned on

The storage resistance is /) and in the fine tuning position. The bridge is powered by a battery E.

Capacitor C is charged by the output voltage of the bridge and its charge is recorded by closing the key / C with a galvanometer G.

By changing the resistance of sections 1-2 and / -4 (where 4 is the position of the slider B of the reichord), a potential difference equal to zero is set on the capacitor C. Under this condition, the following relationship holds true:

X R, -, I,

where: / is the cable length, K is the length of the cable section, and the known resistance of the device in sections 1-4 and / -2.

Therefore, the distance from the end of the cable core to the point of damage is determined by the formula:

-R ::

The measurement accuracy depends on the accuracy of the cable length measurement and on the accuracy of the calibrated resistances of the device, as well as on the insulation quality of the device circuits.

Subject invention

A device for detecting a fault in an electrical cable, assembled according to the scheme of a direct current bridge, one pair of arms of which is formed by calibrated resistors, the other pair is one of the wires of the cable being tested, and the free end of the measuring diagonal is connected to another cable core (or to ground in case of conductor closure to ground), characterized in that, in order to increase the sensitivity of the device with large transient resistances in the place of damage, measure the diagonal of the bridge This capacitor is charged by the output voltage of the bridge and discharged with each measurement to the galvanometer of the bridge.