RU2731209C1 - Device for uniform distribution of single-phase load by phases of three-phase network - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electric engineering, in particular, to circuits of AC distribution networks, and can be used in devices of energy conversion of three-phase network into energy for supply of single-phase load. Device for uniform distribution of single-phase load by phases of three-phase network comprises transformer, which winding is made with tap, wherein the terminal leads of the transformer winding are the first and second inputs of the device, and the tapping of the transformer winding is the output of the device, the other output of which is combined with the third input of the device.

EFFECT: technical result is simplification of device, high manufacturability, reduced material consumption and weight and dimensions, as well as high efficiency.

4 cl, 2 dwg

Description

Technology area

The invention relates to circuits of AC distribution networks, and can be used in devices for converting the energy of a three-phase network into energy to power a single-phase load.

State of the art

Known is a three-phase to single-phase converter containing an autotransformer with an output through the winding of which the load is connected to two phases of the supply network, and a capacitor through which the output of the autotransformer winding is connected to one of these phases, additional capacitors through which the output of the autotransformer is connected to another of the indicated phases and with the third phase of the supply network connected to the point of connection of the load to the winding of the autotransformer (see USSR AS No. 402075).

Known converter of electrical energy of three-phase voltages and currents in single-phase, containing a single-phase transformer or autotransformer, a three-phase transformer, two blocks of ballast reactive elements: capacities and inductances - and a control unit for ballast reactive elements and control of the symmetrical mode of operation of the specified converter (see RU2333563C1).

Known transformer converter of electrical energy of three-phase voltages and currents in single-phase, containing a transformer converter of electrical energy of three-phase voltages and currents in two-phase, reactive ballast elements and a control unit for symmetric operation of the converter and control of reactive ballast elements, one of the phases of the two-phase winding of the transformer converter of three-phase electrical energy voltages and currents in two-phase is connected in series with the first ballast element and in series opposite to the second phase of the two-phase winding and the second ballast element, in parallel to which a single-phase receiver and the third ballast element are connected in series with each other (see RU2292625C1).

The need to use additional components in known solutions: capacitors and ballast reactive elements complicates the design of the device, reduces its reliability, and also complicates the production process, reducing the manufacturability of its manufacture.

Moreover, the need to adjust for a specific load, by changing the capacitance of the capacitors to be switched on, limits the possibility of using the known converter, since it complicates its operation and creates the risk of an undefined distribution of phase currents of the loaded network.

A device for converting a three-phase current into a single-phase one is known, made in the form of an induction machine with a three-phase primary system and a single-phase secondary winding, the primary system is formed of two stators common to the secondary system with windings that create magnetic fields rotating in opposite directions, forming a pulsating magnetic field penetrating secondary winding circuit (see USSR AS No. 72443).

Known power supply device for single-phase inductive-resistive loads, providing the symmetry of the primary three-phase network, containing a magnetic circuit consisting of three cores A, B, C of the same cross-section, a primary three-phase winding, consisting of at least three identical sectioned windings located on the corresponding cores of the magnetic circuit, interconnected in a star, the sectional leads of which are connected through the sectional switch to a three-phase network and the secondary winding, made in such a way that on each core of the magnetic circuit there are two partial windings with an unequal number of turns, and the partial windings of each core of the magnetic circuit with with the same indices have an equal number of turns, and the partial windings of the secondary winding are connected in series (see RU 2290739 C1).

A three-phase-single-phase transformer is known, containing windings connected in a "zigzag", the beginning of the first halves of which are the inputs of phases A1, B1, C1 of the supply network, and the beginning of the second halves of the windings are connected to each other and are the output of a single-phase load, the other output of a single-phase load is connected to the input phases A1 of the supply network, while the windings are made on a three-rod magnetic circuit (see RU 2656612 C1).

The disadvantage of the known solutions is complexity, excessive material consumption and cumbersomeness. The need to wind many transformer windings, up to six or more, complicates the process of their production.

A device for transmitting electricity is known, comprising: a cable, a transformer connected to a cable, a transformer for converting a three-phase alternating current into a single-phase one, while the transformer has a core in a torus configuration with a chord passing through the inner part of the torus, a primary winding wound around the torus, and a secondary winding wound around the chord and connected to the cable (see EP2954544B1).

The disadvantage of the known solution is the need to use a magnetic circuit of a complex shape, as well as the complexity and laboriousness of the process of winding on a magnetic circuit of a complex shape.

A device is known for converting a three-phase current into a single-phase and vice versa, which is a three-phase machine with a locked two-phase rotor, the stator windings of which are included in a three-phase network, and one phase of the rotor into a single-phase network, the second phase of the rotor, which has a partial magnetic connection with the first phase, is included on active resistance connected in series with inductive resistance (see USSR AS No. 89488).

The known device can be used only in low-power installations and is characterized by excessive complexity and weight and dimensions, as well as energy dissipation on the active resistance, which leads to increased heating and a decrease in efficiency.

Known is a three-phase-single-phase transformer containing input and output clamps, to which a transformer is connected, having primary windings in all three phases and two secondary windings in phases A and C, the primary windings are connected in a "zigzag", and the windings of phases A and B are connected, B and C, C and A, the first extreme terminals of the primary windings are connected to the input terminals, two of the second extreme terminals of phases A and C are connected to each other, and the secondary windings are connected oppositely and connected to the output terminals, and the third of the second extreme terminals of phase B connected directly to the zero working output of the supply network (see RU2668086).

The known solution is characterized by complexity, excessive number of windings, high material consumption and weight. The need to connect the neutral wire of a three-phase network limits the scope, since the possibility of using a neutral wire is not always available.

The closest in technical essence - the prototype - is a device for uniform distribution of a single-phase load over the phases of a three-phase network, which contains a single-phase transformer with one primary and one secondary winding, the terminals of the primary winding are two inputs of the device, one of the terminals of the secondary winding is the third input of the device, the other terminal of the secondary winding is one of the outputs of the device, the other output of which is the fourth input of the device, while the four inputs of the device are made with the possibility of connecting to a four-wire three-phase supply network containing three phase and one neutral wire (See RU No. 2679595 C1, Fig. 1).

The known device facilitates the equalization of currents in all three phases and the neutral wire when feeding single-phase loads.

However, the presence of two windings, requiring means of ensuring their mutual isolation, complicates the design of the device, and the need to wind more than one winding requires corresponding additional operations that complicate the production process, which means a decrease in manufacturability.

The use of a transformer with separate, galvanically not interconnected windings contributes to an increase in the overall power of the transformer. The transformer power of the known device is √3 / 2 ≈ 0.866 of the load power. A high value of the overall power of the transformer leads to a high value of losses in the transformer and reduces the efficiency of the device as a whole, and also contributes to an increase in its material consumption.

Another disadvantage of the known solution is the need to use a four-wire power supply network, including a neutral wire, which is not always possible and limits the scope of the known solution.

In addition, the use of a neutral leads to additional wire losses and reduces the overall power factor of the system.

Disclosure of essence

The technical result is to simplify the device, improve manufacturability, reduce material consumption and weight and size parameters, as well as increase efficiency.

The specified technical result is achieved by the fact that in a device for uniform distribution of a single-phase load over the phases of a three-phase network containing a transformer, the transformer winding is made with a tap, while the extreme terminals of the transformer winding are the first and second inputs of the device, and the tap of the transformer winding is the output of the device, the other the output of which is combined with the third input of the device.

In addition: - the transformer is single-phase,

- the tap of the transformer winding is made from its midpoint,

- the first, second and third inputs of the device are made with the ability to connect to the phase wires of a three-wire three-phase supply network, and two outputs of the device are with single-phase load wires.

A device for uniform distribution of a single-phase load over the phases of a three-phase network is illustrated using drawings, where in FIG. 1 shows a diagram of the device, FIG. 2 - a variant of the connection diagram for a device with a reduced output voltage.

In the drawing, the following designations are made.

1, 2, 3 - inputs of the device for connecting the phases of a three-phase supply network A, B and C, respectively, 4 and 5 - outputs of the device for connecting a single-phase load D1 and D2, respectively, 6 - a transformer, 7 - the first half-winding of a transformer, 8 - second half-winding of the transformer, 9 - tap of the transformer winding, 10 - step-down autotransformer, 11 - tap-off of the winding of the step-down autotransformer.

The device for uniform distribution of a single-phase load over the phases of a three-phase network contains a single-phase transformer connected according to the autotransformer circuit, which has one winding, all turns of which are made in the same direction. The winding is equipped with a tap from its midpoint, which divides the winding into two half-windings with an equal number of turns, wound with a wire of the same cross-section.

The extreme terminals of the transformer winding are two inputs of the device, and the tap of the transformer winding is one of the outputs of the device, the other output of which is combined with the third input of the device.

Three inputs of the device are made with the ability to connect to a three-wire three-phase supply network containing three phase wires, and two outputs of the device are a single-phase output, with the ability to connect the load.

An autotransformer can be connected to the output of the device to form a single-phase output voltage of the required value.

Transformer 6 is single-phase and can be performed on a toroidal or rod-shaped magnetic circuit. The transformer has a single winding consisting of the first 7 and the second 8 half-windings, which have the same number of turns, and the whole winding is designed for the line voltage of a three-phase network.

The required overall power of the transformer relative to the power consumption of the load is 1 / (2√3) ≈0.289, which is three times less than the required overall power of the closest analogue.

Implementation of the invention

The device for uniform distribution of a single-phase load works as follows.

A multi-phase supply network is characterized by the values of line and phase voltages. The phase voltage of a three-phase network is 1 / √3 of the line voltage and for standard line voltages of 220 V, 380 V or 10 kV, the phase voltages are 127 V, 220 V or 5.8 kV, respectively. In addition to three-phase networks of standard voltages, the device for uniform distribution of a single-phase load over the phases of a three-phase network can be used in a three-phase network with other values of the line and corresponding phase voltages.

A device for uniform distribution of a single-phase load, with a transformer connected according to the autotransformer scheme, provides the conversion of the energy of a three-phase network into energy for supplying a single-phase load, taking power from all three phases of the supply network.

When the number of turns of the two half-windings is equal, the currents in phases A, B are equal to each other, and the current in phase C is twice as large. In this case, power consumption in phases A, B, C occurs in the proportion of 25% -25% -50%. The device provides the most favorable operating mode of the supply network, since the supply wires are loaded evenly.

In the embodiment, when the first and second half-windings are made with an unequal number of turns, the distribution of currents in phases A and B becomes different, which may be useful in some specific applications of the device, for example, in an asymmetrically loaded network.

When a three-phase supply voltage is applied to inputs 1, 2 and 3 of the device, in which the phase wires are designated as A, B and C, respectively, an output single-phase voltage is generated at the outputs 4 and 5 of the device. When the load is connected to the outputs D1, D2, current flows through the load.

A device for uniform distribution of a single-phase load provides a 2 / √3≈1,155 times lower voltage at its outputs in comparison with the line voltage of the network. So, provided that the device operates from a standard three-phase electrical network with a rated voltage of 380 V, the voltage at the outputs of the device is 330 V.

The device for uniform distribution of a single-phase load has a smaller number of windings: one instead of two windings of the closest analogue, which means it does not require means of interwinding insulation, it is structurally simpler and easier to manufacture. Simplification of the manufacturing process of the device means higher manufacturability of its manufacture.

A device for uniform distribution of a single-phase load is characterized by a lower current flowing through the windings compared to the prototype, this follows, in particular, from a comparison of device circuits. Smaller currents provide a reduction in the required total overall power of the transformer. The lower overall power of the transformer of the device for uniform distribution of the single-phase load means a decrease in the weight and dimensions of the device as a whole, a decrease in its material consumption.

Lower overall power of the transformer also means lower losses when converting the same amount of energy, which in turn means higher efficiency of the device for even distribution of the single-phase load as a whole.

Calculations using vector voltage diagrams show that the output voltage is:

Un = (√3 / 2) * Ul≈0.866Ul

where Uн - load voltage,

Ul is the line voltage of the supply network (that is, the voltage between any two phases).

Despite the simplicity of the device, the prior art does not contain identical solutions.

At the same time, the set of features of the device for the uniform distribution of a single-phase load, namely the use of only one transformer winding, as well as the connection diagram of the device outputs with the phase lines of a three-phase network through a winding that implements the autotransformer connection of the transformer, is not an obvious solution that provides the maximum possible, with the use of a transformer, the simplicity of the design of the device, the maximum simplicity of its manufacture and the minimum weight and dimensions with high efficiency.

A device for uniform distribution of a single-phase load requires only three phase wires of a three-phase supply network for operation and does not require a neutral wire, which provides the ability to connect to any three-phase network and expands the scope of the device.

The ability to operate the device to evenly distribute a single-phase load without the need for a neutral wire also reduces wire losses and increases the overall power factor of the system.

To change the voltage supplying the load, an adjustable autotransformer can be connected to the device output, while the proportionality of power consumption from the phases of the supply network remains unchanged.

Example.

A variant of the device for uniform distribution of a single-phase load (Fig. 2) with the possibility of lowering the output voltage includes a second transformer made in the form of a step-down autotransformer providing a decrease in the output voltage. With the ratio of the number of turns of the first and second half-windings of the step-down autotransformer as 2: 1, the voltage across the load is determined by the expression:

Un = Ul / √3≈0.577Ul,

That is, at a line voltage of 380 V, the output voltage is 220 V.

The transformer of the device can be made on the basis of a conventional single-phase transformer, using a standard magnetic circuit, while only one core can be used to wind the wire.

The device for uniform distribution of a single-phase load does not require the use of additional components and assemblies, such as capacitors, ballast reactive elements, switches, etc., which makes the device simple and reliable.

A device for uniform distribution of a single-phase load can be made using standard-shaped transformer iron and winding wire.

Thus, a device for uniform distribution of a single-phase load over the phases of a three-phase network is structurally simpler and more technologically advanced in manufacturing, has lower material consumption, weight and dimensions, and also provides greater efficiency.

Claims (4)

1. A device for uniform distribution of a single-phase load over the phases of a three-phase network, containing a transformer, characterized in that the transformer winding is made with a tap, while the extreme terminals of the transformer winding are the first and second inputs of the device, and the tap of the transformer winding is the output of the device, the other output of which combined with the third input of the device. 2. The device according to claim 1, characterized in that the transformer is single-phase. 3. The device according to claim 1, characterized in that the tap of the transformer winding is made from its midpoint. 4. The device according to claim 1, characterized in that the first, second and third inputs of the device are made with the possibility of connecting to the phase wires of a three-wire three-phase supply network, and two outputs of the device - with wires of a single-phase load.

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