SU154330A1 - - Google Patents

Description

There is a known method for determining the distance to a cable insulation damage, based on the use of a two-dimensional method of a DC bridge with a variable shoulder ratio, with closed and open insulated and non-insulated conductors.

In such cables, in order to monitor their serviceability and determine the distance to the insulation damage, there are two signal cores located under the internal polyethylene hose, one of which (in plastic insulation) is used as a working conductor during measurements, and the other (non-insulated) serves to monitor the state of insulation of the cable as a whole.

If the sheath of the cable is damaged and moisture gets inside the polyethylene hose, the insulation resistance of the uninsulated core decreases first of all, and the insulation resistance of the insulated signal core and all working cores remains within the normal range.

The proposed method makes it possible to increase the accuracy of determining the distance to the point of damage to the insulation of the cable. To do this, using a DC bridge with a variable ratio of the shoulders, four measurements are made — two before the damage, two after the damage. In this case, the first two measurements are made with the insulated and uninsulated conductors closed and open, the second and the third with the permanent resistance between the uninsulated core and the ground connected.

No. 154330-2 -

FIG. 1-4 shows the scheme of four dimensions produced by the proposed method.

All four measurements are made in the area between the amplifying points / 1 and using a direct current fed from the battery E through a direct current resistance, one arm of which is formed by constant resistance R, the other by variable resistance Ri, Rz, RA or R and two - isolated L c: uninsulated L, cable conductors connected to the terminals ./7i and L-2 of the bridge. The equilibrium of the bridge is determined using a galvanometer G.

In all four figures, RU denotes the variable resistance of the isolation of an isolated vessel to earth and the resistance of an uninsulated core.

To make a first measurement (Fig. 1), an insulated core is connected to the J / i terminal. a non-insulated Lf to La clamp; The measurement is made before damage with closed insulated and non-insulated conductors in the serviced amplifier point B. The magnitude of the variable resistance Ri is measured after obtaining complete equilibrium of the bridge circuit. The ratio of the constant resistance R to the temporary resistance determines the coefficient:

P, .

The first measurement must be made necessarily after commissioning the cable in a plastic sheath, and then at least once a month.

The voltage of the measuring battery E at the first measurement is preferably in the order of 500 volts.

For the second measurement (Fig. 2), which, like the first, is produced before the damage, the insulated core is connected to the terminal L ,.

The measurement is made with open insulated and non-insulated conductors and with the connection between clamp L (between non-insulated core) and ground constant resistance RM with a value of 100 com.

The magnitude of the variable resistance R-2 is counted after the equilibrium of the bridge circuit is obtained. The coefficient is then determined.

"about -. As a resistance, it is advisable to apply a resistance magazine, the accuracy class of which is not lower than 0.5.

The resistance value RM can be chosen 200 or 300 com, but for this it is necessary to have two or three resistance magazines. The voltage of the measuring battery E is desirable to choose ior for 300 volts.

For the third measurement (made during the damage immediately after receiving a signal that the insulation resistance decreases in relation to the "earth of an uninsulated core to a value equal to the alarm limit of the alarm device), as in the second measurement, the insulated core is connected to terminal L (Fig. 3 ). It is desirable that the alarm limit is not lower than

-. This means that the third dimension is made during the transition.

resistance (non-insulated dwelling and ground) equal to (or mest) in magnitude normal insulation resistance,

i.e., with the third dimension, nothing is different from the second. In the third dimension, the coefficient is determined.

The fourth measurement is made at the time of the damage immediately after the third measurement and is no different from the first, i.e., the insulated core is connected to the clamp L.

In the fourth dimension, the coefficient is determined:

The distance 1 from point A to the point of damage to the insulation during measurements by the proposed method is determined by the formula:

  To (Zd) - 1) - lz (2n + / - 1) 2 (Zl1 - 1) (n, - n,) (n - g 1)

where / is the dissipation between points A and B. It is possible to accurately determine the distance to the place where the insulation resistance of an uninsulated core decreases, with the values of transient resistance K „as large as normal insulation resistance RH. as well as smaller ones, while the well-known bridge methods make it possible to determine the distance to the fault site with a high accuracy only at –100 on a similar circuit.

Subject invention

The method of determining the distance to the point of damage to the insulation of the cable, based on the use of the method of two measurements with a DC bridge with a variable shoulder ratio, with closed and open insulated and non-insulated conductors. characterized in that, in order to increase the accuracy of determining the distance to the insulation damage, said measurements are made twice, the second and third measurements are made with a permanently connected resistance between the non-insulated core and ground.

 154330