RU1935U1 - ELECTROMAGNETIC DEVICE FOR LIMITING SHORT CURRENT CURRENTS - Google Patents

Abstract

ELECTROMAGNETIC DEVICE FOR RESTRICTING SHORT CIRCUIT CURRENTS, designed to be connected between two energy carriers, containing a magnetic circuit with primary and secondary windings and a switch, a primary winding is designed to be connected between the buses of the combined power systems, and the switch is connected parallel to the secondary winding, characterized in that the primary and secondary windings placed on one core of the magnetic circuit, which is made with non-magnetic gaps, the secondary winding is short-circuited by a switch.

Description

M.C. H02H 9/02

ELECTROMAGNETIC DEVICE TO LIMIT SHORT CURRENT CURRENTS

The invention relates to electrical engineering, electrical AC networks of all voltage levels and can be used in powerful nodes of power systems with large short-circuit currents (SC),

The main requirements for short-circuit current limiters (RT) are to provide them with minimum resistance in normal operating modes of the network and significantly increase it at K3 I. This ensures high indicators of technical efficiency of RT applications: minimum voltage and power losses in them in normal mode and the desired limitation current p | ei short circuit in the network. These requirements are realized in RT in various ways: in dual current-limiting reactors due to mutual inductive coupling between its windings; in resonant circuits due to the use of resonance between capacitance and inductance; in a controlled reactor with a rotating magnetic field due to direct current magnetization of the main magnetic circuits with working windings 2. The listed known RTs have specific disadvantages: a double reactor provides a twofold increase in inductance during short-circuit due to magnetic coupling between its windings, has significant dimensions and magnetic field; resonant circuits have high technical efficiency (CVC is close to relay), however, they have a high cost and reduced reliability due to a longitudinal compensation capacitor bank; a reactor with a rotating magnetic field increases resistance by 4-5 times during short-circuit, but requires a constant source of magnetization, which means it has increased energy losses and operating costs.

The closest to the proposed invention in terms of technical nature and the achieved result is a current-limiting device for switching between two power systems, containing an intersection switch, additionally equipped with a transformer and resistors, the primary winding of the specified transformer is connected between the buses of the combined power systems.

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counter-parallel to the primary winding, a secondary winding is included, in the circuit of which the indicated intersection switch is connected, and a resistor 3 is connected in parallel to the primary winding.

However, the known device does not have high technical efficiency. This is due to the fact that the windings are placed on different rods, and therefore the inductive resistance of the device in normal psxmte is of increased value, reaching 60-80 / S, as in welding transformer 4. And despite the fact that the windings are connected in parallel and their resulting resistance reduced by about 4 times, it has an increased value () compared to a conventional transformer. Therefore, in the normal mode in the known device, increased losses of voltage and power are created (including due to the resistor). With a short circuit in the network, the resistance of the device will increase by 4 times and a sufficiently high current limitation will be ensured, however, the short circuit current and leakage currents through the primary winding of the known device will not have a sinusoidal shape.

We must bear in mind another drawback of the known device. It follows from the need to connect a secondary winding to the primary circuit. The insulation of the secondary winding should be the same as that of the primary winding.

Therefore, the issue of creating current-limiting devices of high technical efficiency continues to remain relevant. The studies conducted by the author made it possible to find a technical solution that is capable of combining the relay characteristic of the resistance of resonant-type devices with the simplicity of design and the reliability of concrete current-limiting reactors. The following is a description of the claimed technical solution.

The proposed electromagnetic device for limiting short-circuit currents is intended to give, disconnect and & kr, two power systems, comprising a mains with two windings and a switch, the primary winding of which is connected between the buses of the combined power systems, and the switch is connected parallel to the secondary winding; primary and secondary windings are placed on one core of the magnetic circuit; the sterock, on which the windings are placed, is made with non-magnetic gaps; the secondary winding is short-circuited by a switch. nye author conclusion

Comparison of the claimed electromagnetic device with other technical solutions shows that it is structurally reminiscent of a two-winding single-phase transformer. But it differs from the latter in that the magnetic circuit has non-magnetic gaps and the secondary winding is shorted. The presence of nonmagnetic gaps in the rod (s) of the magnetic circuit makes the claimed device similar to an arc suppression reactor of the RZDSOM type. However, the latter has one power winding. The inventive device due to non-magnetic gaps and a short-circuited secondary winding, these two features distinguishing from a double-winding transformer, significantly changes the functional purpose compared with the latter. If the double-winding transformer is designed to convert the electrical energy of one voltage into the energy of another voltage, the claimed device is not intended to convert energy, since it is connected in series with the load. Through the inventive device, energy is transferred in transit from one power system to another. In the case of short circuit in the network, it effectively limits the short circuit current. This is achieved by the fact that the design of the claimed device provides close to the relay characteristic of the resistance: low value in normal operating mode, when the circuit breaker bypasses the secondary winding with its closed contacts; a large value in the short circuit mode in the network when the circuit breaker breaks the secondary circuit. There are also quite distinctive features of the claimed device from the known devices of the GDR type and chokes. Based on the foregoing, it is convenient to conclude that the claimed technical solution meets the criterion of inventive step.

In FIG. I is a circuit diagram of an electromagnetic device for limiting a short circuit current. The device includes a two-core magnetic circuit I with non-magnetic gaps on one of them 2, primary 3 and secondary 4 windings, switching device 5 (circuit breaker, current limiter, fuse, thyristor switch, etc.). In Fig 2 and 3 show variants of schemes of the claimed device. The principle of their work is the same. from the existing level of technology, therefore, it is possible to comply with the proposed solution to the criterion of a Novomagnetic device to limit short-circuit currents: a - general view; b - in the normal mode of the power system network (short-circuit mode of the device - the contacts of the switch 5 are normally closed); c - in the current-limiting mode during short circuit in the power system (idle mode (XX) of the device - the switch contacts are open). In FIG. B shows the dependence of the inductive resistance on the current in the first winding of the device (kz - normal mode, CCx in current-limiting mode).

In the normal mode of operation of the power system network, the b switch closes the secondary winding with its normally closed contacts, creating a short-circuit mode of the electromagnetic device. It is known 4 that in this mode when placing the windings 3 and 4 one above the other, the electromagnetic device has the smallest inductance, the value of which can be approximately determined by the formula

and m /, zgas, (S)

Primary and windings flow around the operating current of the power system load, causing small losses of voltage and power. The latter does not have much effect on the normal operation of the power system.

An electromagnetic device operates as follows. In case of a short circuit in the protected network, the primary current significantly increases its amplitude already during the first half of the industrial frequency period. The current automatically increases in the secondary circuit 4 and when it reaches a certain value, the covadutation apparatus 5 will break the secondary circuit with its contacts.The electromagnetic device will go into the idle mode of the primary circuit with a high inductance, comparable with the inductance of the magnetization circuit of the transformer equivalent circuit at no load. This follows from the equivalent circuit (Fig. 4) and resistance curves (Fig. 5). Inductance of an electromagnetic device in idle mode is calculated based on the total current law. If we take the EMF in the winding of the device approximately equal to the applied voltage, neglecting the voltage losses in the scattering inductance due to their small value, then the magnetization inductance will be equal to

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In this case, the shock current of the short circuit can be significantly limited if a high-speed thyristor switch is used. The sinusoidality of the short-circuit current is provided by a linear current-voltage characteristic, the angle of inclination of which depends on the magnitude of the non-magnetic gaps. The characteristic of the claimed resistance device is close to the relay.

The simplicity of the design of the claimed device is obvious when compared with other specifications that implement the relay characteristic of the resistance.

The technical efficiency of the claimed electromagnetic device is governed by the number of turns of the primary winding and the magnitude of non-magnetic gaps.

The inventive electromagnetic device has not only high technical efficiency, but also a proven manufacturing technology. The manufacturing technology can be based on the manufacturing technology of the magnetic system of the DGR type RZDSOM and power windings of serial transformers of the type TM and TS. An equally important advantage of the claimed electromagnetic devices is their small size in comparison with other types of technical specifications, which will lead to a reduction in capital investments in the construction part of the switchgear. Due to the high technical efficiency of the claimed device, there will be an adequate reduction in the requirements for the breaking capacity of the switchgear, thermal and electrodynamic resistance of devices and live parts of the switchgear, which will also lead to a decrease in the size of the switchgear and its cost. Together, all this will increase the reliability of the power system.

YAL

Author / ZLOBIN Yu.I.

Claims (1)

ELECTROMAGNETIC DEVICE FOR RESTRICTING SHORT CIRCUIT CURRENTS, designed to be connected between two energy carriers, containing a magnetic circuit with primary and secondary windings and a switch, a primary winding is designed to be connected between the buses of the combined power systems, and the switch is connected parallel to the secondary winding, characterized in that the primary and secondary windings placed on one core of the magnetic circuit, which is made with non-magnetic gaps, the secondary winding is short-circuited by a switch.