SU801182A1 - Three-phase electric network with device for compensating for earthing current - Google Patents

Description

one

I The invention relates to three-phase AC networks with varying mode of operation of the system neutral and can be used in electrical installations with an isolated neutral of any industry and transport using these networks, for example, on ships of the sea and river transport and fishing fleet.

Three-phase networks with variable operation mode of their neutrals are known. For one of the network, three modes of network neutral operation have been proposed, depending on the mode of operation of the network itself: the network isolated neutral mode in the normal mode of operation of the electrical installation; an earthed mode, grounded through active resistance, in the case of a single-phase short circuit (res.) on the ground (housing) in an electrical installation; dead-earthed neutral mode when punching pre-saver is triggered

However, it has a large number of neutral modes of the system (three) and a significant number of different functions of the network elements (artificial and natural neutral, two relays, zero sequence current transformer - TTPD, magnetic starter, asymmetry, penetrative resistors and others) to provide a single circuit - selective actuation of the protective-disconnecting device (OA). Known device, oto key feeder with about. 3., reduces the reliability of power supply to responsible consumers, while o. h in networks with insulated neutral is not an emergency mode and does not require immediate disconnection. In the ship's conditions, for example, consumers of non-removable load constitute more than half of the installed capacity of the power plant and not. allow even a short break in their power supply. Such a network degrades the electrical safety conditions in the switching modes of its neutral, since for selective shutdown

cheni o. er current increases about. A., and any increase in the leakage current to earth (housing) cannot simultaneously and not worsen the electrical safety conditions in this network; even in normal network operation, i.e., in the absence of it

about. 3., its neutral is not purely insulated, since it is grounded through the capacitance of three asymmetric capacitors and the relay coil, which creates a permanent circuit for earth leakage currents; if a fuse blows in one of the phases of the asymmetry or the breakdown of the capacitor of the asymmetry of the asymmetry relay is triggered, the network will go into neutral mode, grounded through a resistor, even if there is no mains. A., and a network with a grounded neutral is always more dangerous than a network with an isolated neutral of the same voltage.

The network has no insulation control devices and devices that signal the mode of operation of its neutral at the moment. The rules for the installation of electrical installations for coastal enterprises and the USSR Register Rules for ships do not allow the operation of systems with insulated neutral without effectively controlling its isolation. The use of such networks, which provide for an artificial increase in current 6. 3. to the ground (housing), is unacceptable in electrical installations of explosion and fire hazardous premises. In ship conditions, moreover, an increase in the current is about. h unacceptable under the terms of protection from radio reception interference.

A network is known, the reliability of operation of which with the device for switching the operating modes of its neutral depends on the thermal stability of the closing asymmetry contact in the neutral circuit, which, at significant currents, is about. h may be welded and the neutral will be permanently grounded through a resistor in its circuit. The sensitivity of the switching device as a whole depends ultimately on the sensitivity of the applied TTP. However, the sensitivity increases its dimensions and leads to a simultaneous increase in unbalance currents of the TNCN, which lead to false alarms of the device as a whole.

This network is in its normal mode of operation, i.e., in the absence of o in it. z., works with an isolated Neutral, and the appearance in it of Fr. h automatically switched to compensated neutral mode 21.

However, this network does not have a device that shows the operating personnel, in which mode of operation the neutral network is located at this particular time, which is necessary to assess the situation in the system and to take timely measures to prevent and eliminate it. W .; a circuit of three relays FNP and a fourth relay, included in the zero point of this filter, permanently connected to earth (housing) increases current leakage to earth and reduces electrical safety conditions; with a simultaneous increase in voltage relative to ground (housing) in two phases, the formation of a two-phase short circuit is possible through the contacts of these relays connected to phases with low voltage connected to inductance and capacitance; in oh mode h the choke and the capacitance must be tuned, in particular, to compensate for the leakage current of the FERP of the three relays through the fourth; one-time tuning of inductance and capacitance for resonant conditions with the network in o mode. h unreliable since oh. 3. can occur with different network variable parameters, and their automatic tuning would require the installation of additional units reacting to the magnitude and phase of the leakage current, processing units of these signals to drive the inductance and capacitance change mechanism, etc .; The relay-contact system of inductance and capacitance involves a large starting time from the moment of occurrence of. h in the network before the inclusion of compensating elements on the ground, which will be continued by the transition process until reaching the steady-state value. All this worsens the condition of the current compensation accuracy o. 3

The purpose of the invention is to increase the reliability of power supply to consumers, to increase the accuracy of compensation of single-phase circuit current, to reduce electrical safety conditions in the network.

Claims (2)

This goal is achieved by the fact that in a known electrical network with a device for compensating an earth fault current containing an insulation resistance continuous monitoring unit, the first closing contact of the output relay of which is connected in series with the inductor connected to ground, another terminal of the first closing contact of said output The relay is connected to the network zero point, and in parallel. the choke is switched on the maximum voltage relay, the disconnecting contact of which is included in the measuring circuit of the insulation resistance control unit, the first closing contact of the maximum voltage relay is connected to the signal circuit of the insulation resistance control unit, parallel to the first closing contact of the output relay of the unit, continuous monitoring The second make contact of the maximum voltage relay is turned on. The drawing shows a schematic diagram of a three-phase network with a device for compensating a single-phase ground fault current. The device and the network work as follows. Three-phase network with source 1 in the normal mode, in the absence of o. It has an isolated neutral 2, which provides continuous control of the insulation of the phases with respect to the ground (case) by the block 3. The latter has a measuring circuit to the ground (case), which includes the output relay 4 of the insulation control unit or contact a megohmmeter, the closing contacts 5 of the cat-oh are in the signal circuit of unit 3. When about. a., in case of single-phase isolation reduction to a value below the setpoint of the response of the isolation control unit or when single-phase contact of a person to the network, output relay 4 closes its contacts 5 in the audible or light signal circuit of unit 3, and closes its contacts 6 in the compensating throttle circuit 7. The fact of the occurrence of. h detected, technical measures taken to reduce the current magnitude o. er choke 7, which is configured to fully compensate for capacitive current o. h However, the accuracy of current compensation is about. h until the measuring circuit of the unit 3 is switched off, remains low. Therefore, parallel to the inductor (reactor) 7, a coil 8 of a maximum voltage relay is connected, having disconnecting contacts 9 in the measuring circuit of unit 3, closing contacts 10 to maintain the o signal. 3. in the signal circuit of this device and make contacts 11 in series with the choke. Such a combination of contacts and circuits for their inclusion allows contact 9 to eject from operation the block 3 for continuous monitoring of the resistance of the ISOL 5S, which is in o mode. h network is not needed, contact 10 to keep the signal of untapped about. h., and by contact 11, stop choke 7 being turned on to earth, after contacts 6 of relay 4 are disconnected. Next, the operational duty personnel take measures to find and eliminate o. 3. in the network already in conditions of lesser danger, since the negative effect of current is about. 3. The choke is kept to a minimum. It is known that in the mode of unresolved, but compensated o. h the probability of its transition to interfacial short circuit across the earth (housing) is halved. This circumstance is especially important for ship conditions, where effective means of finding a place are. h in an extensive ship se-TVI does not yet exist. After elimination o. h the voltage on the choke, therefore, on the coil of the relay 8 connected in parallel to it, disappears, and the system automatically switches to the isolated neutral mode. In this case, the contacts 11 in the circuit of the droplets 7 are opened, the contacts 10 in the signal circuit and the contacts 9 in the measuring circuit of the device are closed. The xsrol insulation block is activated. The proposed device is advisable to use in networks with voltages up to 1000 V with an insulated neutral when they are transferred to the current compensation mode o. 3. with a large weight of the responsible consumers of the disconnected load in the installed capacity of the electrical installation as a whole. Such networks are, for example, the electrical power installations of the sea and river transport and fishing fleet, the electrical installation of the mining, gvoovozrezochnoy, cotton and textile industry, power plants of ferrous and nonferrous metallurgy, etc. The formula of the invention Electric three-phase network for current compensation single-phase circuit for grounding, containing a block of continuous control of insulation resistance, the first closing contact of the output circuit which is connected via the investigator with the choke connected to the ground. 780 characterized in that, in order to increase the reliability of the power supply to the responsible consumers, increase the accuracy of single-phase current compensation and improve the electrical safety conditions in the network, another output of the first closing contact of the aforementioned output relay is connected to the zero point of the network and parallel to the choke is the maximum winding of the relay - tO on voltage, the break contact of which is included in the measuring circuit of the insulation resistance control unit, the first closing contact of the relay is max installations. Industrial Energy, 1952, № 2. 2. USSR author's certificate N9 576637, cl. H 02 H 1/02, 1975. the maximum voltage is supplied to the signal circuit of the insulation resistance control unit, and parallel to the first closing contact of the output relay of the continuous control unit, the second closing contact of the maximum voltage relay is connected. Sources of information taken into account during the examination 1. Tsapenko EF. Protection against earth faults in the set to 220-380 in mobile -R V about 4J