SU1686576A1 - Device for protective switching-off circuit under closing to earth - Google Patents

Abstract

The invention relates to electrical engineering and is intended to protect DC networks. The purpose of the invention is to provide a preliminary diagnosis of the insulation state by analog display of the leakage current. In the proposed device, the frequency at the output of the generator 9 depends on the voltage level at the control input, which in this case is a function of the current through the windings 6 and 7 from a source of alternating voltage of constant magnitude. This current depends on the magnitude of the inductances of the windings 7, which are a parametric value in dependence of the magnitude of the leakage current (through the magnitude of the magnetic permeability of the core). Since the current from the EMF of the leakage current (variable component from the generator 9) in windings 6 and 7 does not leak due to their counter-switching, the amount of current through the windings 6 and 7 is determined only by their inductances (parametric). Thus, the creation in the proposed device, the dependence of the frequency of the generator on the magnitude of that NW e

Description

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This leakage allows you to display the leakage current from the output of the winding 8 at an analog value (in MA) and disconnect the damaged line not by the fact that there is a ground fault, but by the leakage current, the threshold value of which can be set by element 14, to the input of which analog The signal from the output of the converter 13. 1 C p. f-ly, 1 Il.

The invention relates to electric power industry, in particular to protective disconnect devices, and can be used in the operation of direct current networks for protection against earth faults.

The aim of the invention is to provide pre-emergency diagnostics of the insulation condition by analog display of the leakage current value, as well as expanding the monitoring zone by providing signaling and analog display of the leakage current value in case of damage outside the protected area.

The drawing shows a structural block diagram of the proposed device.

The device comprises a switching device 1 for disconnecting the direct current network supplying load 2. The device 1 is equipped with a free trip mechanism 3 activated by key element 4. The wires of the protected network are passed through the window of the core 5 of the leakage current sensor, and on the core 5 along its entire circumference, the first secondary winding b and the second secondary winding 7 are wound with a double wire with an equal number of turns, and a third secondary winding 8 is wound over the windings 6 and 7. Windings b and 7 on cheny counter, to the ends of the windings b and 7 combined among themselves, and their start terminals are the generator field winding 9 AC introduced in this oscillator circuit. In other words, the counter-connected windings 6 and 7 of the leakage current sensor are the excitation winding of the alternator 9. The negative pole of the power supply network is grounded through the separation capacitor 10, the secondary winding of the first transformer 11 and the primary winding of the second transformer 12. The primary winding of the first transformer is connected to the output of the alternator 9. The third secondary winding 8 of the leakage current sensor is connected to the input of the converter 13 a current-voltage, the output of which is connected through the first threshold element 14 to the starting input of the key element 4. The secondary winding of the second transformer 12 with the transformation ratio is one — through the amplifier 15 is connected to one from the inputs of the subtraction unit 16, to the second input of which the output is connected

current-to-current converter 13 is voltage. The output of the subtraction unit 16 is connected via a second threshold element 17 with an actuator 18 by means of a warning device, which may be an incandescent lamp. A galvanometer 19 is connected to the output of amplifier 15. It serves for continuous measurement of the total leakage current, a galvanometer 20 connected to the output of transducers 13 is used to measure the leakage current in the protection zone, and a galvanometer 21 that is used to measure current (differential) is connected to the output of block 16. from the power supply to the sensor.

The alternator 9 is powered by the rectifier 22, whose input through an isolating transformer 23 is connected to the output of the inverter 24. connected by its input to the protected wire

network.

The proposed device works as follows.

When switching on the switching device 1 and in the absence of leakage to the ground

(ideal insulation) direct current does not induce leakage current in the secondary windings 6-8 of the EMF sensor, and separation capacitor 10 separates the wires of the network at a direct current from the ground, while

and for AC, there is no earth circuit due to the lack of connection to the ground of the network wires. Therefore, the included alternator 9 is idling because the secondary

the winding of the transformer 11 is included in the open circuit.

Under actual operating conditions of the DC network, there is always a leak through the insulation to earth, and in this case

a circuit is formed to allow leakage current to flow through the ground, windings of transformers 11 and 12, and capacitor 10 to the protected network. The passage of leakage current through the capacitor 10 is provided to those. that a constant component of the leakage current is superimposed by a variable component

generator 9 current The passage of a leakage current with a variable component through the wires causes the pointing in the secondary windings of 6-8 EMF sensors whose frequency is equal to the generator current frequency rj In the proposed circuit, the current generator frequency is a parametric value depending on the leakage current to earth or ground fault It happens like this. The emf induced by the leakage current (variable component from generator 9) in windings b and 7. interconnected and having an equal number of turns mutually compensate each other and the current through these windings. induced by the flow from the leakage current never flows. In turn, the current in the oppositely connected windings 6 and 7, which are simultaneously the excitation winding of the alternator 9. depends on the values of the inductances of windings 6 and 7, which depend on the magnetic permeability of the core 5 of the leakage current sensor If we consider that the magnetic permeability of the core 5 of the sensor depends on the intensity of the magnetic field induced in it by the leakage current (variable component), and this intensity, in turn, depends on the magnitude of the leakage current, it groans to understand that the magnitude of the inductances 6 and 7 of the secondary windings of the sensor is a function of the magnitude of the leakage current, since from the magnitude of the inductances of windings b and 7, which are the simultaneous excitation winding of the generator 9. The frequency of the current produced by this generator depends on. this frequency is always proportional to the magnitude of the leakage current. Thus, the frequency of the variable component of the leakage current always varies in proportion to the magnitude of this current. It should again be emphasized that the EMF in the windings b and 7 from the leakage current is always mutually compensated and do not affect the operation of the generator 9. And the current in these windings is determined only by the value of their inductance. In other words, the operation of the generator 9 is determined by its feedback with the network wires according to the magnitude of the leakage current.

Ensuring the above dependence of the frequency of the current generator 9 on the magnitude of the leakage current provides the following advantages for the protective disconnection of the direct current network. Emf. induced in the secondary winding 8 will always have a frequency equal to the frequency of the current generator 9, which, in turn, depends on the magnitude of the leakage current. Since the resistance value of the winding 8 depends on the frequency ca

induced in it under the action of EMF, will be proportional to this frequency, and hence to the magnitude of the leakage current. The independence of the magnitude of this current from magnetic

The parameters of the core 5 are provided by using a current-voltage magneto-electronic converter 13.

Under natural conditions of operation of a direct current network, leakage exists at

both sides of the core 5 sensor. The leakage current in the protection zone is released in the winding 8 of the sensor, and the total leakage current flows through the circuit connecting the negative pole of the power supply and ground in

including in the secondary winding of the transformer 12 with a unit transformation ratio. From the secondary winding of the transformer 12, through the amplifier 15, a voltage level proportional to the total leakage current is fed to the first input of the subtraction unit 16, to the second input of which a voltage level from the output of the converter 13 is applied, proportional to the leakage current in the protection zone. At the output of the subtraction unit 16, a signal is generated that is proportional to the difference in the input values and the magnitude of the leakage current outside the protection zone from the power source to the core 5 of the leakage current sensor. When

when this signal exceeds a predetermined value defined by the threshold element 17, the executive body 18, for example, a glow lamp, signals the presence of damage in the network outside the protection zone of the leakage current sensor

For continuous monitoring of the magnitude of the leakage current, galvanometers are used. Galvanometer 19, connected to the output of amplifier 15, serves to control the total

a leakage current, a galvanometer 20. connected to the output of the converter 13 serves to control the leakage current in the protection zone, and a galvanometer 21 connected to the output of the subtracter 16 serves to control

leakage current outside the protection zone.

The use of the proposed device will make it possible to increase the information content of the state of isolation in DC grids, which distinguishes it from the knowledgeable

Claims (2)

Claim 1. Device for the protective disconnection of a direct current network at earth fault, containing a switching device, to the input of which through the disconnection circuit the output of the first threshold organ is connected, a leakage transformer with three secondary windings an alternating current generator hl and h You need it so that, in order to provide a pre-emergency diagnosis of the insulation condition by analog display of the leakage current, the ends of the first and second secondary windings of the leakage current transformer are combined between themselves, and their beginnings are connected to the control input of the alternator, which used a frequency generator controlled by the voltage, the output of which is connected to the primary winding of the newly introduced first transformer, the secondary winding of which is connected in series with the newly introduced capacitor in the circuit for connection between the pole of the monitored network and the ground, and the third winding is connected via a newly introduced current converter - voltage to the input of the first threshold organ, while d of said transducer is connected with the newly introduced value measuring device leakage current. 2. The device according to claim 1, characterized in that, in order to expand the monitoring zone by providing an alarm and analog display of the leakage current in the event of damage outside the protected zone, the primary winding of the newly introduced second transformer is connected in series with the secondary winding of the first transformer, the winding of which is connected through a newly introduced amplifier to one of the inputs of the newly introduced subtraction unit, the second input of which is connected to the output of the current converter - voltage, and the output of the subtraction unit connected to the input audio inputted again measuring device and to the input of the newly introduced second threshold body, which is connected to the output of the newly inputted alarm.