RU2831140C1 - Hybrid circuit breaker and method of its operation - Google Patents

Abstract

FIELD: electrical communication equipment.

SUBSTANCE: hybrid automatic circuit breaker is intended for switching on and off of electrical equipment using direct current in normal operation mode, as well as for its protection and automatic shutdown in case of unacceptable overload or short circuit. Hybrid switch comprises mechanical switch with parallel connected semiconductor device and dissipative element. To smooth current surges and reduce current rise rate, inductance L and RC-circuit are connected to load circuit, wherein the resistance R is introduced into the circuit when current is detected, and to limit the critical current and short-circuit current, a fast-acting fuse F with the corresponding rating is placed in front of the mechanical switch. For the use of the switch in the area of high currents without significant loss of its operation speed, it can be used as several semiconductor devices connected in parallel, and several parallel connected and synchronously actuated mechanical switches.

EFFECT: limitation of current in circuit breaker to maximum permissible value for used semiconductor device in short circuit mode in load circuit, as well as avoiding additional losses in operating mode under load without said short circuit.

4 cl, 2 dwg

Description

The proposed invention relates to the field of electric power engineering and can be used as a high-speed switch for switching on and off electrical equipment using direct current during normal operation, as well as for its protection and automatic shutdown in the event of an unacceptable overload or short circuit. The device can be used to protect traction substations and contact network feeders in installations of main, urban and industrial electrified transport, to protect semiconductor converters, electrical machines, and direct current lines in industrial installations.

The following high-speed direct current switches are well known and widely used: VA 41-39 (Automatic switch type VA41-39, Moscow, Informelectro, 1989), BVP 105A, VB-11 (DC electric trains ET2, ET2M, ER2T, ED2T, Moscow: Center for Commercial Developments, 2003), BVP-5 (Grishchenko A.V., Strekopytov V.V., Rolle I.A. Design and repair of electric locomotives and electric trains. Moscow: Academy, 2008).

The disadvantages of the above devices are caused by the method used to extinguish the arc that occurs on the circuit breaker power contacts when opening the DC circuit, namely, the use of the principle of magnetic arc extinguishing, by means of various types of arc extinguishing chambers with a deionic grid. The use of such an arc extinguishing principle has a number of disadvantages, such as: strong erosion of the circuit breaker power contacts when the arc ignites, which leads to the need for their frequent replacement, adjustment of the movement path and the pressing force of the movable power contact of the circuit breaker, the need for frequent replacement of burnt-out partitions in the arc extinguishing chamber, the duration of the time of complete opening of the DC circuit, reaching several tens of milliseconds.

For the above reasons, switches of this type are large in size, require frequent inspection and are expensive to maintain. The arcing problem becomes very acute for switch applications that require high switching frequencies, such as conveyor drives, industrial heaters, test benches, etc.

The development of power semiconductor electronics has led to the creation of high-power solid-state semiconductor elements capable of interrupting an electric circuit in a few microseconds without arcing or eroding contacts. However, the disadvantage of a solid-state switch is the high thermal losses created by the high constant current I2R.

Advances in power electronics have made it possible to combine a conventional mechanical switch with a semiconductor switching device into a so-called hybrid circuit breaker for interrupting short-circuit current in an electric circuit. Such a hybrid circuit breaker comprises a mechanical switch for interrupting the circuit upon detection of a short-circuit current, and a solid-state semiconductor device connected in parallel with the mechanical switch for conducting the short-circuit current when the mechanical switch opens. Depending on the characteristics and conditions of use, the semiconductor device may include a set of series- or parallel-connected controllable semiconductor units, such as thyristors, insulated-gate bipolar transistors, and gate-integrated thyristors.

In this regard, the closest to the claimed solution is the solution for US application for invention No. 20130021708 “Hybrid Circuit Breaker” (IPC H02H3/023; H01H2009/543; H01H9/542, ABB RESEARCH LTD., Switzerland, application No. 20130021708 dated 09/26/2012, priority dated 06/26/2010, publication 01/24/2013). According to the description of the technical solution, when the current reaches a critical value, the mechanical switch opens and the parallel branch closes, containing one or a set of series or parallel connected controlled semiconductor elements, generally working as a single element, for example, thyristors, GTO (turn-off thyristor), IGBT (insulated gate bipolar transistor) or IGCT (integrated gate-commutated thyristor), etc. When the contacts of the mechanical switch open to a distance that excludes breakdown of the medium in which the mechanical component of the switch opens, the parallel circuit with the semiconductor element is disconnected (opened). In this case, the opening of the power contacts occurs without the occurrence of an arc. Suppression of the voltage arising in the circuit is performed in a dissipative circuit (FV) connected in parallel to the contacts of the mechanical switch, for example, a suppressor, varistor, arrester, etc.

In order to reduce the reaction time and ensure a shorter switching time of the hybrid circuit breaker to critical currents, an additional electric circuit is provided, connecting the main electric circuit and the ground. In the additional electric circuit, an impedance unit and a control unit are provided, configured to connect the impedance unit to the main circuit at the moment of occurrence of an excess of the critical current. In this case, the impedance unit can be, for example, resistance, inductance, capacitance, or a combination thereof. According to the invention, the main task of introducing an additional electric circuit at the moment, for example, of formation of short-circuit currents in the main electric circuit, consists in reducing the total resistance and instantly increasing the current in the main circuit, which leads to a faster response of the mechanical switch and a faster disconnection of such a hybrid circuit breaker.

The disadvantage of the technical solution is the fact that during the time required to extinguish the arc, an instantaneous increase in current, for example, short-circuit current, can lead to the destruction of the protected equipment and the failure of both the semiconductor component and the entire declared hybrid circuit breaker.

Thus, the devices disclosed in the prior art do not provide a solution to a number of technical problems, in particular, the creation of a high-speed automatic switch capable of breaking direct current without arcing, both in operating mode and in short-circuit mode, operating in a wide range, up to tens of kiloamperes and kilovolts, of currents and voltages, requiring virtually no maintenance.

The technical problem is solved as follows. The present invention proposes a hybrid circuit breaker, which comprises a mechanical switch, designed with the ability to interrupt a circuit upon detection of a short-circuit current, a semiconductor device connected in parallel with the mechanical circuit breaker. An inductance L, placed in series behind the mechanical switch, and an RC circuit, placed in series behind the inductance L, are included in the load circuit, such that a resistance R is introduced into the electric circuit upon detection of a current.

The features common to the analogue are the presence of a mechanical switch, designed with the ability to interrupt the circuit upon detection of a short-circuit current, and a semiconductor device connected in parallel with the mechanical circuit breaker.

The features that distinguish the device from its analogue are the inclusion in the load circuit of an inductance L, placed in series behind the mechanical switch, an RC circuit placed in series behind the inductance L, in such a way that the resistance R is introduced into the electrical circuit when current is detected.

In the first particular case, the device is characterized by the fact that a fuse link F is placed in front of the mechanical switch.

In the second particular case, the device is additionally characterized by the fact that it contains several parallel-connected, synchronously triggered blocks of mechanical switches and semiconductor devices.

In the third particular case, the device differs in that a vacuum switch is used as a mechanical switch.

The technical solution is a combined circuit breaker, in the load circuit of which an inductance L and an RC circuit are included, leading to smoothing of current surges in the main circuit and a significant decrease in the rate of current increase, which does not allow the current in the semiconductor circuit to exceed the maximum permissible current for the semiconductor device used during the full turn-off time t (the time from the moment of sending a signal to open the contacts until the moment of divergence of the contacts to the distance necessary to restore the electrical strength of its interelectrode gap), thereby leaving it in a working condition.

The introduction of the inductance L and RC circuit into the circuit allows to transfer the "short circuit" mode in the circuit with an instantaneous increase in current in the circuit to the controlled "overload" mode, when the smoothly increasing current in the circuit can be correctly switched off without destroying the switch. The characteristics of the inductance L and RC circuit are calculated for each specific load connection circuit and the occurrence of a short circuit current in it. In this case, the resistance R is in the off state in the normal mode and is introduced into the circuit only at the moment when the current in the circuit reaches a critical value, which allows to avoid additional losses during operation under load.

When adding a fuse link F to the circuit, galvanically isolated from the main DC circuit, the hybrid switch control unit BU with the current sensor DT monitors the current increase to a critical level and the current increase rate. At the same time, depending on the current increase rate, the control unit is programmed in such a way that if the current increase rate in the circuit is below the threshold value, according to which, during the time from the moment the contacts begin to open until the moment the contacts diverge by the distance necessary to restore the electrical strength of its interelectrode gap, the current in the semiconductor circuit does not exceed the maximum permissible current for the semiconductor device used and the "overload" mode occurs, then the switch is controlled according to the operating principle described above.

If the rate of increase of the current strength is higher than the threshold value, then the control unit BU does not send a signal to open the contacts of the mechanical switch (SMex) and close the semiconductor device, and the current in the circuit is interrupted by the fast-acting fuse link F.

In order to increase the range of application of the switch, namely, when using the switch according to the invention for high-speed switching off of large currents, not only several semiconductor devices can be used, but also, according to the invention, several parallel-connected and synchronously opening/closing mechanical switches. It is known that the speed of the switch depends to a large extent on the opening speed of the mechanical component of the switch. On the other hand, an increase in the current strength of the circuit leads to the need to increase the area of the contact surface, increase the mass and, accordingly, to a decrease in the opening speed of the mechanical switch. The use of several parallel-connected and synchronously opening/closing mechanical switches makes it possible to significantly increase the possibility of using the switch in a wide range of current strength in the circuit without losing its speed.

As a mechanical switch according to the present invention, a vacuum switch with various types of drive is used. The absence of charge carriers and high electric strength of vacuum, for example, the breakdown voltage of 1 mm in length in vacuum reaches 100 kV, (Chunikhin A.A. Electrical apparatus. Moscow: Energoatomizdat, 1988) allow to significantly increase the speed of the hybrid switch, which will be limited only by the speed of opening of the mechanical component of the switch. Vacuum switches are currently the most efficient and durable. Their service life without revision reaches twenty-five years.

The proposed invention is illustrated by the following figures:

Fig. 1 - part of a functional diagram containing an inductance L and an RC circuit;

Fig. 2 - part of the functional diagram, additionally containing a fast-acting fuse link L.

The following positions are indicated on the figures:

S _mech - mechanical switch;

G1, G2 - one or a set of series or parallel connected controlled semiconductor elements, generally operating as a single element, such as thyristors, GTO (Gate Turn-Off Thyristor), IGBT (Insulated Gate Bipolar Transistor) or IGCT (Integrated Gate Commutated Thyristor);

V - dissipative circuit, for example, suppressor, varistor, spark gap, etc.;

S - power source;

N - load;

L - inductance;

C - capacitor;

R - resistor;

F - fast acting fuse link.

The control unit BU and the current sensor DT, galvanically isolated from the main circuit, are not reflected in the diagram. The power source S and the load N are connected in series with the diagram. The load can include a combination of resistive, inductive loads and motors. The elements of the diagram are switched in the sequence as indicated in the description.

To understand the principles of operation and features of various inventions, a description of the figures of the technical solution is given below. Although the text of the description explains in detail the preferred embodiments of the technical solution, it is necessary to understand that other embodiments of the invention are also possible. Accordingly, there is no need to limit the scope of legal protection of the technical solution exclusively to the presented implementations and lists of subsystems, units and components. The invention can be implemented in other ways. At the same time, when describing the preferred embodiments of the technical solution, for a specialist to clearly understand the basic principles of the invention, it is necessary to clarify the terms used in the description.

It should be noted that the units and parts of the device used in the singular in the description and formula also represent plural forms, unless otherwise stated. For example, an indication of a component element of the device also means an indication of a set (multitude) of such elements.

Also, in describing the preferred embodiments, special terms are used to ensure clarity of understanding. It is assumed that the term is used in the broadest sense in which it can be interpreted by specialists in the given technical field and includes all technical equivalents used in the same way and for the same purpose. Thus, in particular, the term "hybrid" refers to a technical solution combining a mechanical switch and a set of semiconductor elements. The term "load circuit" is understood to be a part of an electric circuit having an active or imaginary impedance. "Inductance" is understood to be, in essence, a concentrated element of an electric circuit in which magnetic energy is accumulated. "RC circuit" is understood to be a section of a complete circuit consisting of a capacitor and a resistor. The terms "capacitance" and "resistance" in the context of the present description are identical to the terms "capacitor" and "resistor", respectively, unless otherwise specified in the description. The term "mechanical switch" is understood to be an electrical switching device intended for direct closing or opening of an electric circuit. In the description, a vacuum switch is also classified as a mechanical switch, in which vacuum acts as a medium for extinguishing an electric arc when opening or closing an electrical circuit.

The words “consisting”, “comprising”, “including” mean that at least the specified component, element, part or method step is present in the device, but do not exclude the presence of other components, materials, parts, even if such component, material, part performs the same function as the specified one.

The materials from which the various elements of the present invention are made, indicated below in the description of examples of a specific implementation of the device, are typical, but not mandatory for use. The materials indicated in the present examples of implementation can be replaced by numerous analogs that perform the same function as the examples of materials given in the description.

Let us turn to the attached figures. Fig. 1 shows a part of the functional diagram of a hybrid circuit breaker, consisting of a set of thyristors (GTO, IGCT) and/or bipolar transistors IGCT G1…G _n and a dissipative circuit V, constituting a solid-state semiconductor device, in parallel to which a mechanical circuit breaker S _mech is connected, connected to a galvanically isolated control unit BU and a current sensor DT (not shown in the diagram). An inductance L and an RC circuit, located in series behind the mechanical circuit breaker, are introduced into the load circuit.

An alternative embodiment of the invention, shown in Fig. 2, provides for the additional installation of a fast-acting fuse link F, placed in front of the mechanical switch behind the current source.

The device operates as follows. In the operating mode, the contacts of the mechanical switch S _mech are closed, those of the solid-state semiconductor device are open, and the resistance R is not introduced into the load circuit. When a critical current occurs in the circuit, the control unit of the hybrid switch BU with the current sensor DT, galvanically isolated from the main DC circuit, sends a signal to open the power contacts of the mechanical switch S _mech , close the contacts of the semiconductor device, and introduce resistance R into the power circuit. When the contacts of the mechanical switch diverge by a distance required to restore the electrical strength of its interelectrode gap, the control unit sends a signal to open the contacts of the semiconductor device and remove resistance R from the load circuit. The energy remaining in the circuit is absorbed by a parallel-connected component V of the solid-state device, for example, a suppressor, varistor, or arrester.

In the presence of a fast-acting fuse link, the device operates as follows. Galvanically isolated from the main DC circuit, the control unit of the hybrid switch BU with the current sensor DT monitors the current increase to a critical level and the rate of current increase. In this case, depending on the rate of current increase, the control unit is programmed in such a way that if: di/dt < di _threshold /dt threshold value, according to which, during the time from the moment of the start of opening of the contacts until the moment of divergence of the contacts by the distance necessary for restoring the electrical strength of its interelectrode gap, the current in the semiconductor circuit will not exceed the maximum permissible current for the semiconductor device used and the "overload" mode occurs, then the switch is controlled according to the operating principle of the switch specified above; if di/dt >= di _threshold /dt threshold value, the control unit BU does not send a signal to open the contacts of the mechanical switch S _mech and close the semiconductor device. A "short circuit" mode occurs and the current is interrupted by the fast-acting fuse link F.

The embodiments of the present invention are not limited to the above examples of specific implementation. Other forms of implementation of the technical solution may be proposed without departing from the meaning of the invention.

The above examples of implementation are given to demonstrate the industrial applicability of the device and to give a general impression of the device. The scope of legal protection of the technical solution is determined by the invention formula, and not by the description provided.

Claims (4)

1. A hybrid circuit breaker comprising a control unit, a mechanical switch S _mech , configured to interrupt an electrical circuit upon detection by the control unit (CU) of a short-circuit current di/dt, a semiconductor device connected in parallel with the mechanical circuit breaker, configured to receive commands from the control unit (CU), characterized in that an inductance L, placed in series behind the mechanical switch, and an RC circuit placed in series behind the inductance L are included in the load circuit in such a way that the resistance R is configured to be introduced into the electrical circuit upon detection of a critical current in the circuit, and a fuse link F is placed in front of the mechanical switch. 2. The switch according to item 1, characterized in that it contains several parallel-connected synchronously operating blocks of mechanical switches and semiconductor devices. 3. The switch according to item 1, characterized in that a vacuum switch is used as a mechanical switch. 4. A method for controlling the operation of a hybrid circuit breaker according to claim 1, wherein the di/dt parameter in the electric circuit is monitored using a control unit (CU), and if said parameter does not exceed the threshold value di _threshold /dt, when a critical current occurs in the circuit, the control unit (CU) sends a signal to open the power contacts of the mechanical switch S _mech , close the contacts of the semiconductor device and introduce resistance R into the power circuit; otherwise, the control unit (CU) does not send a signal to open the contacts of the mechanical switch S _mech and close the semiconductor device, and the fuse link F is activated to interrupt the current in the circuit.

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