RU1803889C - Ground fault detection method for several phases of buried cable line - Google Patents

Abstract

Usage: refers to the field of electrical measurements and can be used to find places to reduce the insulation resistance of the outer shells of several phases of one circuit of a power cable laid in the ground. SUMMARY OF THE INVENTION: a method for detecting damage to the outer shells of several phases of a cable chain laid in the ground, characterized in that, at each damaged phase, the first and second measurements of voltage drops in the sections of the screen before and after the damage are made, respectively. Grounding at the far end of the screen and the core of the undamaged phase, measuring drops at this phase; splices along the entire length of the core and along the entire length of the screen, the connection at the far end of the screen of each damaged phase with the core of the same phase, the measurement during the second measurement of each damaged phase of the sum of the voltage drop in the section of the screen behind the place of damage and voltage drop along the entire length of the core and the determination of each of the required distances to the MT according to the calculation formula of a new type allows us to limit ourselves to a single trip to the far end of the cable line (CL) for any number of damaged phases of the CR circuit. 2 ill.

Description

The invention relates to the field of electrical measurements and can be used to find places to reduce the insulation resistance of the outer polyethylene shells of several phases of a single circuit of a power cable laid in the ground.

The purpose of the invention is to reduce the time required to detect MP shells by reducing the number of trips to the far end of the CR.

In FIG. 1 and 2 are diagrams illustrating the proposed method.

The circuit contains three damaged phases 1, 2, 3 of one CR circuit and undamaged phase 4 of the same design. Each of phases 1,

2,3,4 has an outer polyethylene sheath 5, a copper shield b, a plastic insulation 7 and an aluminum core 8.

Prior to measurements using a voltmeter 9, a power supply 10 and a switch 11 in phases 1, 2, 3, work is carried out in phase 4. The screen 6 and the core 8 of phase 4 at the far end are grounded. At the near end of phase 4 between the core 8 and the shield b, a voltmeter 9 is turned on and two measurements are made (see positions Ie and NEK of switch 11). During the first measurement in phase 4, the current (U) flows from the source 10 through the conductor 8 of length LA and closes through the ground, during the second measurement the same current flows through the screen 6 of the same length L4 and closes through

00

about

GJ 00 00 O

the ground. Therefore, we can write that the voltmeter 9 readings are equal to:

at the first measurement 11Zh TsNZHY

and at the second measurement of iEk TsVek1-4 (1.1)

where RX and Kack are the linear resistance of core 8 and screen 6, respectively.

Before taking measurements in phases 1, 2, 3, the screen 6 of each of these phases is connected at the far end to a core 8 of the same phase. Further, all work is performed from the side of the near end of the CR, beginning, for example, from phase I. At this phase, the source 10 (using the switch 11) and the voltmeter 9 are connected, as shown in FIG. 2 and make two measurements:

Ui lilxiR3K {U2 liLR) K + li (L-lxi) R9K J

From (1.2), taking into account (1.1), we have

, Х1.Ц1 + JJ3L)

IE

Ui + U2

Then, the similar connections of the voltmeter 9 with the source 10 and the corresponding two measurements are performed, work at the near end with phase 2. After that, the same operations at the near end are repeated with reference to phase 3. As a result, two more peers of the values Ui, Da and, substituting each of them in turn into an expression of the form (1.3), the sought distances X2 and x3 are found for phases 2 and 3, respectively.

Thus, the proposed method does not require additional switching at the far end of the CR during the transition from measurements on one damaged phase to measurements on another damaged phase of the circuit. This reduces lead time.

5

1O 15

twenty

25

thirty

35

40

exploratory work, especially on extended CRs.

Claims (1)

SUMMARY OF THE INVENTION A method for detecting damage to the outer shells of several phases of a cable circuit i laid in the ground, which method measures, at each damaged phase of the circuit, the voltage drop Un at the screen portion of the corresponding i-th damaged phase from the beginning of the cable line to the point of damage shells at the flow of a current of a given value from the power source, a second voltage measurement Uai is made at each damaged phase, including a voltage drop Uoi in the screen section of the corresponding 1st damaged The basics from the end of the cable line to the point of damage to the sheath when a current of the same predetermined value flows from the power supply, characterized in that, in order to reduce the time for performing search operations, before screening on the damaged phases of the cable line, ground the screen and the core of the undamaged phase of the cable line, then on this undamaged phase the voltage drop 1) g is measured over the entire length of the core and the voltage drop is 11Ec over the entire length of the screen when the current flows of the same magnitude before measurements on the damaged phases of the cable line circuit, at the far end of this cable line, the screen of each damaged phase is connected to the core of the same phase, during the second voltage measurement 1) 21, the sum of the voltage drop Uoi and voltage drop is measured on each damaged phase the entire length of the i-th phase and each of the sought distances lxi to the places of damage is determined by the formula and Izh L -) Un U ek Uii + U2i fyr. I G-P --I -