RU144337U1 - DEVICE FOR MEASURING EARTH RESISTANCE WITHOUT DISCONNECTING THE DARK-PROTECTED CABLE - Google Patents

Abstract

A device for measuring the resistance of grounding conductors of overhead power transmission line poles without disconnecting a lightning protection cable, comprising detachable current clamps, a current meter, a current source, a voltmeter, current and potential electrodes, characterized in that the magnetic current clamp meter is made of a nanocrystalline alloy having high magnetic permeability.

Description

Application area

The inventive device relates to the field of electrical engineering and can be used to monitor the condition of grounding conductors of overhead power transmission lines without disconnecting the lightning protection cable.

State of the art

A device for measuring the resistance of grounding conductors of overhead power lines, containing the device F-4103, connected to the measuring current and potential electrodes in a single-beam or two-beam circuit [1, p. 12]. The disadvantage of this device is the impossibility of its use for measuring the resistance of the grounding poles of the supports of overhead power lines with a voltage of ON kV, on which a lightning protection cable is connected to the support.

The reason for this is that part of the measuring current passes through the ground electrode of the test support, while all the generator current flows through the auxiliary current electrode. This is explained by the fact that part of the generator current is sucked off from the ground electrode of the studied support to neighboring supports, passes through their ground electrodes, and returns to the generator through an auxiliary current electrode.

There is a known method and measuring schemes that implement it, which makes it possible to measure the resistance of grounding conductors of overhead power transmission lines with a voltage of 110 kV without disconnecting the lightning protection cable [1, p. 20]. In this case, a resistance meter (for example, the F-4103 device) with additional current and potential electrodes is used. Measurements are carried out in three ways. A significant drawback is the measurement error of up to 25%. In addition, numerous measurements and the subsequent processing of their results significantly increase the time of measuring the resistance of the grounding support.

The closest in technical essence to the claimed solution is a device containing: a current source, clamp meters (detachable current transformers) included in a current meter, voltmeter and potential probe of the cable [1, p. 26]. The disadvantage of this device is the lack of sensitivity when measuring the resistance of grounding conductors of reinforced concrete supports overhead power lines. Clamp meters must have an internal diameter of at least 700 mm in order to be able to measure the current flowing down the reinforced concrete support into the ground. The magnetic core of such pincers should be made of a material with a very high magnetic permeability at low magnetic fields. As such material, for the manufacture of clamp meters with a diameter of 350 mm, in [1, p. 27] it is proposed to use permalloy with a relative magnetic permeability µ _rel = ~ 8000. In the manufacture of magnetic cores from permalloy with a diameter of pincers exceeding 700 mm, the current error of current-measuring pincers (f _in ) increases more than 2 times due to an increase in the average length of the magnetic flux [2, p. 47]:

where I ₂ is the rated secondary current; z ₂ is the resistance of the secondary current branch; l _m - the average length of the magnetic flux in the magnetic circuit; µ _a is the absolute magnetic permeability of the material of the magnetic circuit; S _m - the cross section of the magnetic circuit; f is the frequency of the alternating current; w _2n - the number of turns of the secondary winding, F ₁ - primary ppm; ψ is the loss angle; α is the phase shift between the secondary emf and secondary current.

In addition, deformation of the magnetic core made of permalloy, with possible impacts and bends, leads to a sharp deterioration in its absolute magnetic permeability and a further increase in the measurement error.

Technical result

The technical result consists in increasing the accuracy of measuring resistance by a device for measuring the resistance of grounding conductors of overhead power transmission lines without disconnecting the lightning protection cable and is achieved by replacing a permalloy magnetic circuit in a known device with a magnetic circuit made of 5BDSR nanocrystalline alloy [3], which has a higher relative magnetic permeability (µ _rel = ~ 50,000).

Utility Model Disclosure

In FIG. 1 shows the structure of the proposed device for measuring the resistance of the grounding conductors of overhead power lines without disconnecting the lightning protection cable.

The device contains a detachable clamp meter 1, a current meter 2, a current source 3, a voltmeter 4, a current electrode 5 and a potential electrode 6.

The detachable clamp meter 1 is put on the monitored support of the power line 7, the current meter 2 is connected to the output of the clamp meter, the current generator 3 is connected to the support 7 and the current electrode 5, the voltmeter 4 is connected to the support 7 and the potential electrode 6.

Device Description

Before starting the measurement, two rod electrodes are clogged at a distance of 20-30 meters from the base of the support. Through one of them, the current electrode 5, closes the circuit of the flow of current flowing through the support 7 into the ground. The second, potential electrode 6, is used to measure the voltage drop across the resistance of the grounding device of the test support. The electrodes 5 and 6 can be located both along the same line (single-beam pattern), and at the vertices of an isosceles triangle (double-beam pattern). In both cases, the distance between them should be at least 10 meters to minimize electromagnetic interference in the connecting wires.

The test current is supplied to the body of the support 7 by connecting the generator 3 with one output to the metal element of the support 7, and the second output to the current electrode 5.

The current flowing to the ground through the grounding device of the considered support 7 is measured using current-measuring clamps 1 with a detachable magnetic core of large diameter, covering the reinforced concrete pillar of the support, and a current meter 2.

The voltage drop across the grounding device of the support is measured as the potential difference between the metal elements of the support 7 and the point of zero potential, which is used as a potential electrode 6.

Grounding resistance is determined by Ohm's law

where U is the voltage measured by a voltmeter; I is the current measured by a milliammeter; - transformation coefficients of clamp meters.

Due to the high magnetic permeability of the material of the magnetic circuit µ _a , the nominal current error of the clamp meter, calculated by the formula (1), decreases. This allows to reduce the error in measuring the current I and calculating the ground resistance R.

Information sources

1 Celebrovsky Yu.V., Mikitinsky M.Sh. Measurement of grounding resistance of VL poles. M .: Energoatomizdat, 1988.

2 Current transformers / V.V. Afanasyev, N.M. Adonyev, V.M. Kibel et al. - L.: Energoatomizdat, Leningrad. Department, 1989.

3 feast: //www.amet.ru.

Claims (1)

A device for measuring the resistance of grounding conductors of overhead power transmission line poles without disconnecting a lightning protection cable, comprising detachable clamp meters, a current meter, a current source, a voltmeter, current and potential electrodes, characterized in that the clamp meter magnetic circuit is made of a nanocrystalline alloy having high magnetic permeability.