SU1208519A1 - Apparatus for measuring value of earth shorting current - Google Patents

Abstract

This invention relates to electrical measuring technology and may be electrical. It is used to measure the earth fault current and the chassis in three-phase AC installations with an insulated neutral power system. The purpose of the invention is to increase the safety and convenience of measurement. The device contains a capacitor 1, a transformer 2, to the outputs of which measuring voltmeters 3 are connected according to the number of phases. To achieve this goal, a thyristor switch 4, a high-frequency isolation transformer 5 and a control unit 6 are additionally introduced into the device. The entire device can be placed on a mobile platform along with a control panel. Block 6 contains a multivibrator on semiconductor devices. 1 il. i a c

Description

one

The invention relates to electrical measuring equipment and can be used to measure earth fault current (on the housing) in three-phase AC installations with an insulated neutral power system.

The purpose of the invention is to enhance safety and ease of measurement.

The drawing shows a diagram of the device.

The device contains a capacitor 1, a voltage transformer 2, the outputs of which are connected to measuring voltmeters 3 of an electromagnetic system of accuracy class 1.5 by the number of phases, a thyristor switch 4, a high-frequency isolating transformer 5, a control unit 6, the first output of which is connected through a high-frequency isolating transformer 5 with the control input of the thyristor switch 4, the second output of the control unit 6 is connected to the first terminal of the capacitor 1 and the grounded neutrals of the voltage transformer 2, he first output thyristor switch 4 is connected to the second terminal of the capacitor, and a second output connected to a first input of the voltage transformer and with a first adhesive for connecting my control object, second and third inputs connected with the corresponding terminals for connection to a control object ..

The entire device is placed on a mobile platform with a front control panel.

The thyristor switch 4 is made in the form of a series of symmetric thyristors, the number of which is chosen depending on the nominal voltage of the installation in which the measurements are made. ,, for example, for installation of 6 kV - 15 thyristors TC-160 12 class.

The control unit 6 is a multivibrator made on semiconductor devices with a switching frequency of 10 kHz,

Turning on the thyristor switch 4 is performed by launching the multivibrator of the control unit 6 from the control key (not shown) „

The mobile platform is equipped with a three-phase contact system, pos08519, 2

to automatically switch the voltage transformer installed on it with busbars of the switchgear when driving the platform, for example, into a voltage transformer cell.

In order to make measurements, a mobile platform is inserted into a special chamber — a cell with high voltage conductors — an armature. When inserted, the voltage transformer 2 is connected to the busbar of the cell. Thus, after installing the platform, network voltages can be measured 5. Then by switching the key of the control unit 6, the thyristor switch 4 is activated, by means of which the capacitor 1 is connected to one of the high-voltage terminals of the voltage transformer 2 to one of the mains phases) and the voltage is measured relative to earth at the phase to which the terminal is connected

densator,

It is necessary that the thyristors be switched each half-period by pulses synchronized with the transition of the capacitor current through zero.

When a capacitor is connected to one of the phases of the network, an artificial asymmetry is created and the voltage is measured relative to earth at the phase to which the capacitor is connected. In this case, the capacitive current I ground fault is determined by the formula

W-k-U |, .U, Ca

c - id, i

}

. J A 5

where Uj, is the effective value of the voltage relative to earth on the phase to which the capacitor is connected; and, is the linear voltage; WITH,. additional capacity; k is the transformation ratio of the voltage transformer;

K circular network frequency.

50 In real networks, asymmetry capacitance of the 1st phase is possible, which can occur through unequal phase voltages relative to the earth. In this case, in order to obtain a calculation of the 55 magnitude of the capacitive earth fault current, it is necessary to measure the voltage V on each of the three phases and determine the source voltage

my current value is the arithmetic average of three values 3,.

Thus, this device allows you to automate the process of measuring capacitive current to earth, thus ensuring the safety and convenience of measurement, and reduces the likelihood of emergency situations in electrical networks.

Claims (1)

Invention Formula A device for measuring the magnitude of the earth fault current, containing a capacitor, a voltage transformer, to the outputs of which measuring voltmeters are connected, characterized in that, for the sake of safety and convenience of measurement, a thyristor is inserted into it nineteen" switch, high frequency isolating transformer, control unit, the first output of which is connected to the control input of the thyristor switch, the second output of the control unit is connected to the first capacitor output and grounded neutrals of the voltage transformer, the first output of the thyristor switch is connected to the second the output of the condenser, and the second output of the thyristor switch and the first input of the voltage transformer are combined and connected to one terminal for connections to the control object, the second and third inputs of the voltage transformer are connected to the corresponding other terminals for connection to the control object.