SU67100A1 - Method for elimination of disturbing action of stray currents when measuring ground resistance using auxiliary earthing switches - Google Patents

Description

In large cities and industrial areas with developed electricity grids and tram traffic, the measurements of the resistance of grounding necessary for monitoring the condition of electrical installations are greatly hampered due to the presence of earth currents in the ground.

A number of methods have been proposed to reduce the harmful effects of these currents, but all of them are palliative and can only reduce, but not eliminate, the distortions introduced by these currents.

In the method proposed according to the invention, the task of eliminating the stirrer; its action on the stray 70KV when measuring grounding resistance is solved by preventing stray current into the electrical circuit. For this purpose, several earthing switches are used around the measured ground, which serve to connect the measuring current to the ground through it, and several earthing switches, which measure the voltage drop across it. Each of two

the groups of these earthing switches are interconnected by resistances and search for the last points, the equipotential ground to be measured with respect to stray currents; these points are then used to connect some of the devices for measuring ground resistance.

In the implementation of the proposed method, it is also possible to limit two earthing switches for supplying current to the measured ground and two meters for measuring the voltage drop, completely free of each pair on either side of the measured ground and connecting them resistances, which together with the resistances, form a gap between the measured and the pair of ground wires, the Wheatstone bridges, which balance the effects of stray currents.

In FIG. 1 illustrates the principle of eliminating interfering influences underlying the invention, FIG. 2 and 3 depict practically the nearly acceptable layout of the Auxiliary Grounds, and FIG. 4, 5 and 6 are examples of the application of the proposed method for measuring with known devices.

As is well known, when measuring grounding resistance, it is usually necessary to use two auxiliary groundings, one of which serves to turn on the measured ground in the circuit, and the second as a probe. In this case, the stray currents enter both the circuit of the measuring current source and the probe circuit, and distort the measurement results, and sometimes even prevent them from being produced. A radical elimination of the influence of stray currents can be achieved by using several additional grounds and an equal number of probes located around the measured ground (in two concentric circles, as shown in Fig. 1). Here R is the measured ground, Rdi is the additional ground, and K:, i. R ,, 2- probes. Assume that stray currents have a direction shown by solid arrows, and the current from an auxiliary source is directions shown by dashed arrows. By interconnecting all additional grounds with the help of resistances ri, r ... and probes through resistances r /, ..., these resistances can be chosen such that for any distribution of stray currents in the ground, the connecting rings of the probes and additional groundings have the same potential as the measured ground. If these rings are used to connect certain devices for measuring the grounding resistance, the influence of stray currents will be eliminated and the stray currents will not go to either the ammeter circuit or the voltmeter circuit because the connection points of the ground wires to the devices will be equipotential in stray currents.

The arrangement of the electrodes of FIG. 1 requires a large amount

additional grounding and probes and can hardly be applied in practice. It is much easier to implement the arrangement of the electrodes of FIG. 2 or 3. Two additional grounds and two probes are required here. As in FIG. 1, in FIG. 2 and 3 through R. denotes the measured ground, through R d n R d., Additional ground, and through R 31 and R,) 2 - probes. The solid arrows indicate the direction of the stray currents, and the dotted arrows indicate the measuring current. To eliminate the disturbing effects of stray currents, it is necessary to arrange the electrodes symmetrically and connect the earthing switches Rd, and R I ,. and also Rig with dragging resistances on which points can always be found that have the same potential as R

FIG. 4, 5 and 6 are given three typical schemes of devices for measuring the resistance of grounding as applied to the principle of eliminating disturbing influences described above and the arrangement of the electrodes of FIG. 2 or 3. FIG. 4 shows a circuit for including an ammeter and a voltmeter for measurements according to the proposed method. FIG. 5 depicts the bridge Shtesel and FIG. 6 is a BerenLegco compensation device that, in devices like in FIG. 4 and in FIG. 5 or 6, the presence of resistances p and ga, g /, and rz does not affect the measurement result. FIG. The 5 and 6 large dotted rectangles are limited to the main devices already known, and the small dotted rectangles the additional device that allows the proposed method to eliminate the effects of stray currents.

The position of the sliders on the resistances TI and g, corresponding to the condition of equivalence of these sliders with resistance / can be found with the help of the zero instrument.

The application of the method described is not limited to the examples given: it is equally suitable.

for all known devices of this kind. The resistances g and g / required for the implementation of the method can be enclosed in a separate box with six output terminals, or they can be structurally combined with the rest of the instruments for measuring the grounding resistance. It is also easy to carry out the proposed method using conventional wire resistors.

Subject invention

Claims (2)

1. A method for eliminating the disturbing effect of stray currents in measuring grounding resistance using auxiliary earthing switches, characterized in that several earthing switches serving to feed the measuring current through the ground to the measured ground connection and several grounding switches serving RdS ff34 0 Кз5 to measure the voltage drop across it, position around the measured ground, interconnect the resistances and find the last points, equipotential ground measured against the circulating currents, and then use these points to connect some of the other devices to measure grounding resistances . 2. P: implementation of the method according to claim I, characterized in that two grounding conductors are used to connect the current to the measured ground and two grounding conductors to measure voltage drops, and by arranging the grounding conductors of each pair on both sides of the measured grounding their resistances, which, together with the resistances of the earth, form the balancing action of the circulating currents between the Wheatstone bridges between the measured and the pair of grounding conductors. FIG. 2 R3i © -®- - About ff32 about - with Rdi G - FIG. 3 - Kdg % . W / f / a ", No. Rdi fij FIG. five ::: g; i -i I -Lalla1 / -ll / ; P t / A 2 ff (i