SU928264A1 - Method of determination of conductor short-circuiting location in cable line - Google Patents

Description

I

The invention relates to electrical measuring equipment and can be used to determine the location of damage to the conductor insulation in power cable lines with single-phase closures.

There is a known method for determining the place of closure of a conductor in a cable line, according to which the conductor closure position in a cable line is determined by applying alternating current to a damaged conductor, separating two signals induced by electromagnetic fields of a single current and a pair current over a cable line, and fixing the difference phases of these signals. The current of the pair is absent behind the fault site and a phase jump of the SR is possible.

The disadvantage of this method is that the signal st is a weak field of a pair of currents is extremely difficult

highlight against a strong, signal from the floor of a single current. Besides,

the phase shift itself is a very uncertain quantity, since it depends on the conductivity of the earth in the zone of the damage site and may be small. As a result, the search for a place of damage - in most cases, does not give a positive result.

The closest to the invention to the technical essence is a method for determining the location of the conductor closure in a cable line, including the impact of alternating currents on two conductors (damaged and intact) at one end of the cable, grounding the intact conductor at the other end of the cable, fixing the phase shift of signals induced electromagnetic fields of alternating currents. At the same time, the frequencies of the alternating currents that are affected, the cores are chosen with constant multiplicity in time, and the signals induced by the electromagnetic fields of alternating currents.

convert to signals with the same frequencies 2.

However, despite the high sensitivity and accuracy of determining the location of damage by this method, it cannot be applied when searching for short circuits in single-core cables, since the method is based on the effect of alternating currents on two cores. In addition, a disadvantage of the method for locating damage in stranded cables is the need to install grounding at the other end of the undamaged core, which requires additional time in connection with exits to the far end of the line to install and remove grounding and to get work permit for both ends of the cable line.

The purpose of the invention is to expand the field of application of the device by searching for a place of damage not only in multicore cables, but also in single-core cables and reducing the time for searching for damage.

The goal is achieved by the fact that in the well-known method of determining the conductor closure in a cable line, including the impact of an alternating current of the main frequency on the edged core at one end of the cable line, the selection of the main frequency signal and the auxiliary frequency signal over the cable line path, the conversion of the selected signals into signals equal frequency and fixation of the phase shift of the converted signals, the impact of alternating current on the damaged core is periodically interrupted through the period of the main frequency and the time equal to the duration of exposure, wherein the auxiliary hour Toth signal is recovered by the route of the cable line is selected equal to / Ora subharmonic of the fundamental frequency.

FIG. 1 shows a block diagram of a device implementing this method; in fig. 2 - the form of the signal sent to the cable; in FIG. 3, the spectral composition of the signal sent to the cable.

FIG. 3 accept the notation. K is the harmonic number, with a value of 1, 2, 3, etc. correspond to frequencies 1/2 f, fo, 3/2 o,

etc. Al is the amplitude of the sinusoid of the corresponding frequency.

The device contains an alternating current source 1 connected to the core 2 of the cable line, a control unit 3 and an receiving unit it consisting of stages 5 and 6 of extracting the signals of the main and auxiliary frequencies, frequency doubler 7 and measuring

body phase shift 3.

The method is implemented as follows.

Let the power electrical cable be damaged (short circuit 2

5 per shell) at point X. The source 1 with the block 3 ensures the flow of the alternating discontinuous current of the chain, the damaged core 2 is the earth, and the duration of each effect on core 2 and the duration of each pause are equal to the period of the main frequency.

The impact on the damaged vein (Fig. 3) is carried out mainly

(more than 63) currents with frequencies p / 2 and p, and these two harmonics have the same amplitude.

The currents of these frequencies create an electromagnetic field above the cable path. The receiving unit t is moved along the cable and, using selective cascades 5 and 6, the signals induced by electromagnetic fields, respectively, with the frequencies fo and f, are separated. Auxiliary frequency signal

o / 2, passed through frequency doubler 7 is converted to a signal with frequency o, and phase meter 8 controls the phase shift between the signal with frequency o coming from the output of stage 5 and the signal with the same frequency o coming from doubler 7.

The current flowing in the damaged core changes its phase shift at the fault site, with the amount of phase shift being a function of the frequency of the current. Capacitive current Jc flows past the damage site due to the capacity of the core-sheath. A current J flows through to the damage site, which is the algebraic sum of capacitive toKa Зр and current

JD flowing through transient damage resistance.

Claims (2)

5 Thus, the current D flowing in front of the fault site has a phase angle ar arctg j ofcigZ H where is the current frequency; R is the transient damage resistance; t is the capacity of the core-sheath of the cable section beyond the fault site. Therefore, in front of the site of the damage, the current angle with the frequency fff is yi afctg a TfotR, and the phase angle of the current with the frequency f 0/2 is equal to, Drctg. The frequency doubling unit 7 doubles the measurement scale of the phase angle Ug. The result of the phase meter 8 shows the phase shift% aarctgJffo CR-arcl $ aJTfijE in front of the damage site Phase i of the current with the frequency fo and phase angle the frequency b / is equal to THD, but the scale of the measurement of the phase angle H after the signal passes through block 7 is doubled, and as a result the phase meter 8 shows the phase shift –y behind the fault location; . Thus, a change in the phase shift angle at the cable damage site is V4a-y / z -Ottstg DxT% The value of the phase i (.JlTOi, l "jump to V may be sufficient to reliably detect the damage. Jffo RC is in the range of 30-0.3, the phase jump lies in the range of 7, 1 If necessary, the foCR value can be changed by switching the capacitor between the core 2 and the cable at the far end of the cable. The proposed method is easy to implement, as it requires : only one current source, essential for this mode The operation of periodically interrupting the effect of the current on the core through each period of the fundamental frequency Q for a time equal to the duration of the action is carried out using block 3, performed, for example, in the form of one trigger and a coincidence circuit. The use of the proposed method is primarily due to the possibility of detecting circuits not only in stranded, but also in single-core cables. In addition, the proposed method in comparison with the known method eliminates the need to install grounding at the far end of an intact conductor and reduces the required number by an alternating current source by half. The invention method for determining the location of the conductor closure in a cable line, including the impact of alternating current of the main frequency on the damaged core at one end of the cable line, the selection of the signal of the main frequency and the auxiliary frequency signal over the cable line path, the conversion of the selected signals into signals with the same frequency and fixation phase shift of the converted signals, characterized in that, in order to broaden the scope of application and shorten the search time for damage, the effects of alternating current After each period of the fundamental frequency, the time to the damaged core is interrupted for a time equal to the duration of the action, and the auxiliary frequency of the signal allocated over the cable line path is chosen equal to the second subharmonic of the main frequency. Sources of information taken into account during the examination 1. USSR author's certificate No. 523368, cl. G 01 R 31/08, 197. 2. USSR author's certificate,. 750398, cl. G 01 R 31/08, 1979 (prototype).