SU1483407A1 - Method of determining leak current - Google Patents

Abstract

This invention relates to electrical measuring technology. The purpose of the invention is to increase the sensitivity of the determination of leakage current. Periodically, an additional resistance 7 is introduced and outputted into the circuit of the auxiliary current source 5, previously connected between the midpoint of the operating current source 1 and the ground. The leakage current is determined by the formula: I _ut E = (Y _E - Y _E ) (E - U _NEZ ) (U _{NE ut} - U _NE ) (U _NEZ - U _NE ) where U _NE and U _NEZ are the voltage between the average the point of the operating current source and the ground before the leakage occurs, respectively, with the additional resistance introduced and outputted in the auxiliary current source circuit

U _{NE ut} is the voltage between the midpoint of the operating current source and the ground after a leak occurs with additional resistance in the auxiliary current source circuit

E - electromotive force of auxiliary current source

Y _E and Y _E - conductivity of the auxiliary circuit. The method provides a determination of the leakage current increment in case of sudden network closures. 1 il.

Description

The invention relates to electrical engineering, in particular, to the technique of controlling electrical installation insulation.

The purpose of the invention is to increase the sensitivity of determining the leakage current by periodically changing the conductivity of the auxiliary current source circuit.

The drawing is a diagram illustrating this method.

The operating current source 1 is connected to the electricity consumer 2 via a line 3 having conduction for isolating the phases relative to earth 4. Auxiliary current source 5 is connected to earth and through switch 6, additional resistance 7, the main resistance 8 of the auxiliary circuit is connected to the midpoint (neutral ) operating current source 1. The phase-sensitive voltmeter 9 is connected between the ground and the midpoint of the operating current source 1. Voltmeter 10 is connected between the midpoint of the operating current source 1 and its phase output.

The essence of the method is. that an additional resistance 7 is periodically introduced and outputted to the auxiliary current source circuit 5 of the same frequency as the operating current previously connected between the midpoint of the operating current source 1 and the ground, and the neutral bias voltage is measured using an IDI meter P both with the introduced and with the derived additional resistance, and about the current of estrus judged by the results of measurements

The displacement voltage of a neutral of an electrical installation as an alternating, hook and constant gok with the middle (on the left) point of the operating current source and the ground of the auxiliary current source switched on is determined by the formula

- YOU + ZUJ,

(one)

J

00 WITH

ABOUT

J

where Ј is the electromotive force of the auxiliary current source;

YE is the conductivity of the auxiliary circuit, i.e., the circuit containing the auxiliary current source and connected between the neutral and the ground;

U, is the voltage of the / - phase with respect to the midpoint of the operating current source, i.e. relative to the neutral, and for the midpoint / is zero (here and in the following and similar contact, speaking of the phase, imply both the pole and the battery terminal torus, and other similar elements); clamps connected by jumpers are considered as one clamp);

U - the conductivity of the i-phase relative to the earth;

n is the number of phases of the system;

Y - the total conductivity of current-carrying parts relative to the earth, is equal to

and

 Y. i-h)

In this case, the voltage, currents and conductivity in the case of alternating current are described by complex numbers, and in the case of direct current, real numbers. Since the real number is private complex everywhere, except in the case of only direct current, and, 1 and Y are used to denote the voltage and conductivity.

If an additional resistance 7 is introduced into the circuit of auxiliary source 5, this will lead to a change in the bias voltage of the neutral from Piv to CMEG,

GT

-uG + y. (2)

where Y & is the auxiliary circuit conductivity with additional resistance introduced.

If a current leakage occurs on the ground with the added resistance of the mth phase, the neutral bias voltage is. is determined by the formula

cZ, V + ЈTЈ + LT, y ,.

. i, y, -, (O)

I corner Y e - + -

where U, „is the voltage of the m-th phase relative to the neutral;

UCH - leakage conductivity. If, however, a leakage of current to earth occurs when additional resistance is introduced, then the mixing voltage of the neutral (Jieirr is defined by the formula C7, Ug +. | 0,

ABOUT,/ .

(four)

UG + Yi + Y

Using Ohm's law and the fact that the phase voltage relative to the earth is equal to the corresponding phase voltage reduced by the neutral displacement voltage,

with a joint solution (1), ((3), a formula is obtained for the leakage current with the additional resistance derived:

 tv v. (U XЈCT-I)

No. (Ge - IE) frt

Unit - UNC.

Similarly, from (1), (2J, and (4), a formula is obtained for a leakage current of 1up / with additional resistance introduced:

h (jf-) (OMEG-Omeg) UNET.-

Iv ,, (Yl-Yef for the implementation of the proposed method between the average (zero) point of the operating current source 1 and the ground previously

5 include auxiliary current source 5 of the same frequency as the operating current. After such preparation, additional resistance 7 is periodically introduced and output with the help of switch 6 into the circuit of auxiliary current source 5. At the same time,

and voltage is drawn between zero point.

and with ground, both with the added and with the derived additional resistance using a voltmeter 9. In the absence of a lead from the midpoint, an artificial

5 zero point obtained by a star of the same conductivities. The measurements themselves are carried out with a high-resistance voltmeter, which includes between the zero point, natural or artificial, and ground. The measured value

0 is the displacement voltage of the neutral. In AC networks, a phase-sensitive instrument is used for these measurements. To improve measurement accuracy, an artificial zero point is created separately for an auxiliary current source.

5 and for a voltmeter.

Instead of the above, an indirect measurement method can be used, which at least in AC networks allows the use of simpler, more convenient and accurate instruments and does not require a zero point for the voltmeter.

For example, in the case of a symmetric three-phase system, a voltmeter with very high resistance (compared to the total resistance of current-carrying parts relative to earth) measures the voltage modules UA, UB, Uc between phases A, B, C and earth and the phase voltage module (Jr One of the possible options for measuring the voltage L f is that the voltage modulus is measured between any two phases, i.e. the linear voltage, and the value obtained is divided by 3. The indicated value allows to find the displacement voltage vector of the neutral :

.i with, // 2 Til r / 2v 4

i b d - U-e, - Uc. . About U-g

R

0

0

1 / „-31 /,

zs

In the case of direct current installation, a high-voltage voltmeter measures the voltage U between the positive pole and ground and U between the negative pole and ground, which allows you to find the ground voltage relative to the midpoint of the operating current source:

(U.-Uj.

The described periodically repeated measurements of the bias voltage of the neutral allow first of all to establish the time of the leakage, for which each time the current value of the neutral bias voltage is compared with that obtained earlier, and if they do not match, the leakage is recorded. Naturally, both of the compared voltages should relate to the same states of the auxiliary current source, i.e., in both cases, the additional resistance must either be entered or output.

Here it is assumed that during the time between two identical states of the auxiliary current source, no more than one leakage occurs, i.e. during the time between two leaks they manage to perform at least two measurements.

If the leakage current found does not reach values that require special measures, such as disconnecting the mains, the measurements continue as described.

Using this method allows to increase the sensitivity of leakage current detection, which leads to an increase in the reliability of power supply to consumers and the safety of operation of electrical installations.

Claims (1)

Invention Formula The method of determining the leakage current, which consists in measuring the parameters of the auxiliary circuit connected to earth, characterized in that, in order to increase the sensitivity, additional resistance is periodically introduced and removed into the circuit 0 five 0 five 0 five an auxiliary current source having the same frequency as the operating current, pre-connected between the midpoint of the operating current source and ground, measure the voltage between the midpoint of the operating current source and ground both with the input and output additional resistance in the auxiliary circuit. current source, and the leakage current is determined by the formula g, (G-ewZLvt-U), 1y (Ye - Y) where ume and tma. - voltage between the midpoint of the operating current source and the ground until a leakage occurs, respectively, with the additional resistance introduced in the auxiliary source and that introduced by the resistance; Ut№rr- voltage between average the point of the operating current source and the ground after the occurrence of a leak with additional resistance in the circuit of the auxiliary current source; - electromotive force auxiliary current source; YE and Ve are the conductance of the auxiliary circuit, i.e., the circuit containing the auxiliary current source and connected between the midpoint of the operating current source and the ground, respectively, with the additional resistance introduced and outputted in the auxiliary current source circuit.