SU1668957A1 - Method of determining single-phase grounding current in isolated neutral systems - Google Patents

Abstract

This invention relates to electronics and can be applied in networks with isolated neutral. The aim of the invention is to simplify the determination of the current in the network with the capacity of the three phases of each line, which is incommensurably smaller than the total capacity of one phase of all the other lines leaving the busbars. When measuring, line 3 is disconnected from busbars 1, disconnected from switching device 2 (for example, an oil switch) or other equipment, all of its cores are short-circuited between themselves by jumper 5 and connected to the same phase of switching device through a current measuring device 6 2, which is then included. The current from the mains phase under the action of the mains voltage relative to the earth passes through the capacitance of the line relative to the earth and is fixed by an ammeter of the measuring device, after which the line is disconnected from the mains, restore its previous connection and put it into normal operation. 1 il.

Description

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equipment, all its conductors are short-circuited between each other by a jumper 5 and connected through a current measuring device 6 to one phase of the switching device 2, which is then switched on. The current from the network phase under the action of the voltage of the network relative to the earth

The invention relates to power engineering and can be applied in networks of 6-35 kV with insulated neutral, as well as in similar networks of low voltage.

The aim of the invention is to simplify the determination of the current in the network with a capacitance relative to the earth of the three phases of each outgoing lines, incommensurably smaller total capacitance relative to the earth of one phase of all the other lines departing from the busbars.

The drawing shows a distribution network with an insulated neutral and a measurement circuit on one of the outgoing lines.

The three-phase (multi-phase) network 1 with an insulated neutral through switching devices 2, such as oil switches, connects the outgoing lines, represented as tanks 3 of each phase relative to ground 4. One outgoing line, single-phase ground current (033) which is going to be measured, is disconnected from the network 1, its phases are disconnected from the switching device 2 and short-circuited among themselves by means of conductors 5. Through the current measuring device 6, which may include a current transformer and an ammeter, this ini is connected to one phase of the device 2. The load on the line can not otklyuchats.

To measure current 033, the prepared line (in the drawing on the far right of line 3) is connected to one phase of network 1 by switching on the switching device 2. Under the action of the phase voltage of the network, a current flows through all phase capacitances 3 of this line relative to the ground 4 After the end of the measurement, which takes 5-6 seconds, the device 2 is disconnected, then the conductors 5 are removed, the device 6 is disconnected, the line is connected to the terminals of the switching device 2 and switched on This means that the voltage is applied to the load of this line.

through the capacitance of the line relative to the earth and fixed by an ammeter of the measuring device, after which the line is disconnected from the network, restored its previous connection and put it into normal operation. 1 silt

All the measurement of current 033 of one line, taking into account the preparatory work, disassembling the measurement circuit and putting it back into operation, takes 10-20 minutes. As a measuring device 6 in high-voltage networks, a current transformer with an ammeter in its

secondary winding. In low-voltage networks with a current of 033 to 10 A, a direct-current ammeter can be used. You can do the same in the high-voltage network, isolating the ammeter from the ground, if the current 033 is not

exceeds 10 A.

After measuring the current 033 of all the outgoing lines 3 of this network 1, the obtained values of the currents of 033 lines summarize and receive the total current 033 of the network 1.

The technical and economic effect of the application of the proposed method in comparison with the known method consists in simplicity. This knowledge of the current 033 line allows you to accurately calculate the setpoint of its protection against 033 and prevent possible damage from electrical outages from overvoltages when 033 is disconnected, as well as prevent damage from false outages

outgoing lines are protected from 033 and consumers are cut off from power supply.

Claims (1)

The invention The method for determining the current single-phase ground fault in a network with an isolated neutral, which consists in measuring the network parameters and then determining the current of a single-phase ground fault by calculation based on measured parameters, characterized in that, in order to simplify the determination of the current in the network with a capacitance relative to the earth of the three phases of each outgoing the lines, incommensurably smaller total capacitance, relative to the earth of one phase of all other lines leaving the busbars, measure the capacitive current of each line, for which it is disconnected from the busbars, short-circuited just all the phases of the line and connect them to one phase of busbars, after which they change The capacitive current of this line is drawn, and the current is defined as the sum of the measured capacitance-single-phase earth fault in the network currents of all lines.