RU2642488C1 - Excitation system of asynchronized electric machine - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: longitudinal excitation winding (1) and transverse excitation winding (2), located on the rotor of the asynchronized machine, are connected in series and fed by a three-phase transformer (3) through two back-to-back three-phase controlled rectifier. The first rectifier is formed by thyristor groups (4) and (5), the second one - by thyristor groups (6) and (7). The rectifiers are controlled by an automatic excitation controller (8), influencing their thyristor groups (4-7). The common point (9) of the windings (1) and (2) is galvanically connected to the neutral (10) of the secondary windings of the transformer (3) by the circuit (11). A rejection filter from parallel inductance (12) and capacitor (13) is introduced in the circuit (11) and is tuned to the third harmonic of the mains frequency. The secondary windings of the transformer (3) are made of semi-windings and are connected in a zigzag.

EFFECT: simplification of the excitation system and reduction of energy losses in its elements.

3 cl, 2 dwg

Description

Technical field

The invention relates to electrical devices designed to control the longitudinal-transverse excitation of asynchronized generators and compensators, which are used in the electric power industry to generate active and reactive power.

State of the art

Along with traditional synchronous generators and compensators having one excitation winding on the rotor, machines with longitudinally-transverse excitation (asynchronized machines) are used in the electric power industry, having two (longitudinal and transverse) excitation windings on the rotor located at a certain angle to each other (for example , 90 electric degrees) around the circumference of the rotor.

Asynchronized machines have the preferred technical characteristics in comparison with synchronous machines for stability under disturbances in the power system [Labunets I.A., Lokhmatov A.P., Shakaryan Yu.G. "Modes of operation, static and dynamic characteristics of asynchronized turbogenerators." Ed. AN USSR, Kiev, 1987].

In the absence of disturbances, the currents in the excitation windings of the asynchronized machine are maintained equal. With significant short-term disturbances in the power system (load shedding, short circuits), the currents in the rotor windings are separately regulated in magnitude and direction for rotation and even rotation of the magnetic field of the excitation relative to the rotor.

A prototype diagram of the inventive asynchronous machine excitation system is shown in FIG. 1 [Chernyshev E.V., Kuzin G.A., Voronov V.K., Kartoshkin A.V. “The experience of industrial operation of a static reversible thyristor self-excitation system on a turbogenerator TZFA-110-2UZ”, railway station “Electric Stations” No. 11, 2005, p. 6-8].

The prototype contains longitudinal and transverse field windings located on the rotor of the machine, each of which is connected to the secondary windings of the supplying three-phase transformer through two counter-parallel connected rectifiers controlled by an automatic field regulator (ARV). Each of the field windings is powered separately from the corresponding pair of controlled rectifiers. Each of the four controlled rectifiers is made according to the scheme of a three-phase Larionov bridge and contains at least six thyristors.

To supply the field winding with rectified current of one direction, the ARV turns on the corresponding rectifier in the mode of controlled six-phase rectification and turns off the thyristors of the on-parallel connected bridge.

As follows from the diagram of FIG. 1 for supplying current from a cabinet with controlled rectifiers to field windings located on a rotating rotor of an electric machine, the prototype requires four busbars (usually tens of meters long) and four brush-ring contacts on the rotor, designed for a long flow of field current.

The disadvantage of the prototype is the complexity and multielement of the power circuit (at least 24 thyristors), increased electrical energy losses in thyristors, busbars and brush-ring contacts of the rotor.

Modern powerful asynchronized turbogenerators and compensators have a small number of turns of field windings, which determines the operation of field systems with low values of field voltage and high currents (up to several thousand amperes). This exacerbates the noted drawbacks, since thyristors for current limiting or parallel connection of thyristors are required, which leads to further complication of the excitation system, an increase in losses in thyristors, busbars and transformers.

Utility Model Essence

The technical result of the invention is to simplify the excitation system and reduce energy losses in its elements. The result is achieved by changing the configuration of the power circuit, providing a reduction in the number of power thyristors required to provide all power supply modes for two field windings, reducing the required number of power busbars (and their total length) and brush-ring contacts on the rotor of an asynchronized electric machine.

The subject of the invention is the excitation system of an asynchronized electric machine, comprising longitudinal and transverse excitation windings located on its rotor, connected to the secondary windings of the supplying three-phase transformer via two counter-parallel connected rectifiers controlled by an automatic excitation regulator, characterized in that the said excitation windings are connected in series, and their common point through the galvanic coupling circuit is connected to the zero point of the secondary windings of the pit present a three-phase transformer.

This allows you to get the above technical result.

The first development of the invention consists in the fact that a third-harmonic filter of the frequency of the supply network, made in the form of a parallel LC circuit, is introduced into the circuit of the galvanic coupling indicated.

This improves the harmonic composition of the excitation currents.

The second development of the invention is that the secondary windings of the supplying three-phase transformer are made of semi-windings and connected in a zigzag.

This allows you to expand the range of regulation of the excitation currents.

A brief description of the drawings.

In FIG. 1 shows a functional diagram of a prototype.

In FIG. 2 presents a functional diagram of the inventive excitation system.

The implementation of the invention in view of its developments

The inventive excitation system (Fig. 2) contains a longitudinal excitation winding 1 and a transverse excitation winding 2 located on the rotor of an asynchronized machine having brush-ring contacts for supplying the excitation currents to the windings 1 and 2.

The excitation system is powered by a three-phase transformer 3. Windings 1 and 2 are connected to the supply transformer 3 through two on-parallel connected three-phase controlled rectifiers, each of which is made according to a three-phase bridge circuit (Larionov circuit). The first bridge rectifier is formed by thyristor groups 4 and 5, the second bridge rectifier is formed by thyristor groups 6 and 7. Each thyristor group consists of three thyristors. Thyristors inside groups 4 and 7 are connected by cathodes, thyristors inside groups 5 and 6 by anodes.

Rectifiers are controlled by an automatic excitation regulator 8, acting on their thyristor groups 4-7.

Windings 1 and 2 are connected in series. Their common point 9 is galvanically connected to the zero point 10 of the secondary windings of the supply transformer 3 by a circuit 11. Galvanic coupling can be carried out, as shown in FIG. 2, through an inductance 12 introduced into the circuit 11, which together with the capacitor 13 forms a parallel LC circuit. With appropriate settings, this circuit forms a protective filter of the third harmonic of the frequency of the supply network 14 in circuit 11.

In order to avoid saturation of the core of the transformer 3, its secondary windings supplying the excitation system can be made of semi-windings and connected in a zigzag.

The excitation system operates as follows.

Automatic controller 8 generates control actions on the thyristors of groups 4-7 in the form of a sequence of phase control pulses. Depending on the desired direction of the current through the windings 1 and 2, thyristor groups 4, 5 or 6, 7 work simultaneously.

In the steady state, the controller 8 generates control actions in which the constant components of the rectified excitation currents in the windings 1 and 2 are equal to each other and equal to the total current sequentially flowing through them. In the circuit 11 connected to the common point of the windings 1 and 2, the difference of their currents flows. Therefore, the constant component of the current flowing in circuit 11 is close to zero. But in the circuit 11 flows an alternating component equal to the difference between the alternating components of the rectified excitation current flowing in the windings 1 and 2. The main harmonic of this component is equal to the triple frequency of the supply network.

The introduction of a barrage filter (from inductance 12 and capacitor 13) into circuit 11, tuned to the third harmonic of the supply frequency, significantly (6-7 times) reduces the current load of circuit 11 and improves the harmonic composition of the excitation current in both windings 1 and 2.

In identical operating modes of the inventive excitation system and prototype (identical winding parameters, the same excitation power and excitation currents), the current consumed by the inventive excitation system from the secondary windings of transformer 3 is two times lower compared to the prototype, in which the excitation current is the sum of the excitation currents of two windings.

With dynamic disturbances in the power system (short circuit, load shedding, power surges), the automatic controller 8, in accordance with the control program incorporated in it (aimed at maintaining stability and stabilizing the operation of the excited machine), can simultaneously boost the excitation currents in windings 1 and 2 or change them independently in magnitude and sign. With simultaneous forcing, the currents in the windings change almost the same and the claimed excitation system works similarly to the above.

With significant dynamic disturbances in the power system, accompanied by an angular shift of the rotor of the asynchronized machine, the effects of the regulator 8 on the thyristors of groups 4-7 are directed to the corresponding rotation of the vector of the resulting magnetic field of windings 1 and 2 to maintain the stability of the generator (compensator) and the power system. In this case, the excitation currents in the windings 1 and 2, set by the regulator 8, can significantly differ from each other, which will lead to the appearance of a significant differential current in the circuit 11.

However, this mode occurs extremely rarely (only in case of accidents in the power system) and exists for a short time, since it helps to return the rotor to its original position and, as a result, equalizes the currents set by regulator 8 in the field windings 1 and 2. Therefore, the current-carrying capacity of the circuit elements 11 (barrier filter from the elements 12 and 13, the cable and the brush-ring contact) can only be selected based on the conditions of their thermal and mechanical resistance to rarely occurring short-term overloads.

The prototype requires four brush-ring contacts on the rotor of an asynchronized machine, each of which is designed for a long flow of the full excitation current, and for the operation of the inventive system requires only two brush-ring contacts for such a load and a third lightweight contact design for short-term currents flowing through common point 9 of windings 1, 2 and circuit 11.

It follows from the foregoing that the set of features of the claimed excitation system provides a two-fold decrease in the number of controlled valves, a two-fold decrease in the load current of the secondary windings of the supply transformer, a decrease in the number of working brush-ring contacts on the rotor of the machine, and the number of bus leads to them (three instead of four in prototype), and in the stationary mode of operation of the machine, only two of the three contacts are loaded with current. A decrease in the number of stationary-loaded brush-ring contacts and busbar drives, in turn, reduces energy losses, reduces the power of cooling systems, simplifies the design of the brush-contact assembly of the machine rotor, reduces the material consumption and cost of the excitation system, and increases its reliability.

The implementation of the secondary windings of the transformer 3 from the semi-windings and connecting them according to the zigzag circuit provides a magnetically balanced mode of the transformer 3, which eliminates its saturation and, thus, extends the range of regulation of the excitation currents in dynamic modes.

Claims (3)

1. The excitation system of an asynchronized electric machine, containing longitudinal and transverse excitation windings located on its rotor, connected to the secondary windings of the supplying three-phase transformer through two counter-parallel connected rectifiers controlled by an automatic excitation regulator, characterized in that the said excitation windings are connected in series, and their common point through the galvanic coupling circuit is connected to the zero point of the secondary windings of the supplying three-phase transformer pa. 2. The system according to claim 1, characterized in that a third-harmonic filter of the frequency of the supply network, made in the form of a parallel LC circuit, is introduced into the circuit of the indicated galvanic connection. 3. The system according to claim 1, characterized in that the secondary windings of the supplying three-phase transformer are made of semi-windings and connected in a zigzag.

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