SU1483406A1 - Method of determining leak current - Google Patents

Abstract

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 polarity of the auxiliary current source. The drawing is a diagram illustrating this method. The operating current source 1 is connected to the electricity consumer 2 via line 3 having conductions for isolating the phases relative to earth 4. Auxiliary current source 5 is connected to the midpoint / neutral / operating current source 1 via switch 6, auxiliary circuit 7 and ground. Phase-sensitive voltmeter 8 is connected between the ground and the midpoint of the source 1 of the operating current. A voltmeter 9 is connected between the midpoint of the operating current source 1 and its phase output. 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 polarity of the auxiliary current source.

The drawing is a diagram illustrating this method.

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

The essence of the method is to periodically switch and return to the initial position the terminals of the auxiliary current source having the same frequency as the operating current previously connected between the midpoint of the operating current source and ground, and measure the neutral bias voltage as in the initial and the switched positions of the terminals of the auxiliary current source, and the leakage current is judged by the measurement results.

The bias voltage of the UHE neutral of the electrical installation of both alternating and direct current when the secondary current source is on between the average (zero) point of the operating current source and the ground of the auxiliary current source is determined by the formula (initial polarity):

/ 7m

- e Ј

YЈ

EY + ЈfUlY,

(H

- electromotive force of auxiliary current source;

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

and, is the voltage of the rth phase relative to the midpoint of the operating current source, i.e., relative to the neutral, and for the midpoint i is zero (here and later in a similar context, speaking about the phase implies both the pole and the battery terminal and other similar elements (clamps connected by jumpers are considered as one clamp);

Y, is the conductivity of the fth 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

ten

15

20

25

thirty

35

40

In this case, the voltages, currents, and conductances 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 a special case of the complex, everywhere, except in the case of DC only, U, I and U are used to denote the voltage and conductivity.

If you switch the terminals of the auxiliary current source, i.e., change the phase (polarity) of its electromotive force to the opposite, this will lead to a change in the bias voltage of the neutral from UN / to

and,.

If at the initial position of the auxiliary power supply terminals from the g-th phase to the ground there is a leakage current, then the neutral bias voltage is determined by the formula

P V .Yvr + E Yi + gfrY,

 yy, + y. + y- (3)

where it is the voltage of the mth phase relative to the neutral;

 - leakage conductivity.

If the leakage current to earth occurs when the terminals of the auxiliary current source are switched, then the bias voltage L / V / FM is determined., - y; -D- + p.

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 (I), (2J and (3)), a formula is obtained for the leakage current / ut at the initial position of the auxiliary clamps current source:

- 2 D (Hett - UHB)

45

 - Um

Similarly, from (I), (2) and (4), a formula is obtained for the leakage current / y with the switched terminals of the auxiliary current source:

50

.

- 2Ј (-Ј / „,

Uitf ФUliE.

In order to implement the proposed method, between the middle (zero) point of the operating current source I and the earth, an auxiliary current source 5 is switched on at the same frequency as the operating current. After such preparation, the clamps of the auxiliary current source are periodically switched by means of switch 6, i.e. they are swapped and returned to their original position. In this case, the voltage between the zero point and ground is measured, both at the switched terminals and at their initial position. If there is no output from the midpoint, an artificial zero point is used, which is obtained by means of a star from the same conductivities. The measurements themselves are performed by a high-resistance phase-sensitive voltmeter, which includes between the zero point, natural or artificial, and the ground. The value measured 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 the auxiliary current source and for the 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 symmetrical three-phase system, a voltmeter with a very high resistance (compared to the total resistance of current-carrying parts relative to the ground) measures the voltage modules UA with / in lie. between phases A, B, C and earth and the phase voltage module Ur. One possible way of measuring the voltage Uf is to measure the voltage modulus between any two phases, i.e. the linear voltage, and the value obtained is divided by d / 3. This allows one to find the displacement voltage vector of a neutral:

7G VI- (X..lzD-UZ

 2 zi g 3Uf

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

UH (

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 compared voltages should be related

to the same states of the auxiliary current source, i.e., in both cases, its clamps must either be switched or be in the initial position. Here it is assumed that in the time between two identical states of the auxiliary current source, no more than one leakage occurs, i.e. during the time between the two leaks, they manage to perform at least two measurements.

0 If the detected leakage current does not reach

values that require special measures

for example, network disconnection, then measurements

continue as described above.

The use of this method makes it possible to increase the accuracy of determining the leakage current, which leads to an increase in the reliability of power supply to consumers and the safety of operation of electrical installations.

0

Claims (1)

Invention Formula five five The method of determining the leakage current, which consists in measuring the parameters of the auxiliary circuit connected to earth, characterized in that, to increase sensitivity, the polarity of the auxiliary current source of the same frequency periodically varies as the operating current previously connected between the midpoint of the operating source current and ground, measure the voltage between the midpoint of the source Q of the operating current and ground for each polarity of the auxiliary current source, and the leakage current is determined by the formula -2Ј (, f ,, - 6 / U) CW- where UHC and Unff are the voltage between the midpoint of the operating current source and the ground before a leakage occurs, respectively, with the initial polarity of the auxiliary current source and the opposite; UHEYT voltage between average the point of the source of operating current and ground at the initial polarity of the auxiliary current source after the occurrence of a leak; E-electromotive force auxiliary current source; Yf is the conductivity 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. five 0