RU2727923C1 - Electrical complex for balancing single-phase load - Google Patents

Abstract

FIELD: electrical equipment.SUBSTANCE: invention relates to the electrical equipment. Technical result is achieved by the fact that electrical complex for balancing of single-phase load consists of three-phase transformer T1, three-phase transformer T1 consists of primary windings A, B, C, connected by "star without neutral wire" and secondary windings consisting of semi-windings a-1, b-1, c-1 and a-2, b-2, c-2, connected according to special scheme: beginning of semi-winding a-1 is connected to load and end of semi-winding a-2, end of semi-winding a-1 is connected to beginning of semi-winding b-2, beginning of semi-winding a-2 is connected to end of semi-winding s-1, beginning of semi-windings b-1 and c-1 are connected to different inputs of balancing device C1, beginning of semi-winding b-1 is also connected to load, end of semi-winding b-1 is connected to beginning of semi-winding c-2, end of semi-winding b-2 is connected to end of semi-winding c-2. Primary windings A, B, C of transformer T1 have terminals for connection to three-phase power supply system, for example to power transmission line, which in its turn is connected to power supply of three-phase alternating voltage, thus supplying electric power to transformer T1.EFFECT: technical result consists in reduction of unbalance of currents of power supply system of single-phase load at incomplete matching of load power and balancing device of balancing complex.9 cl, 4 dwg

Description

, в том числе системы электрообогрева, например, индукционные системы нагрева при помощи теплоспутников: к таким системам обогрева относится «скин-система» и индукционная система (система обогрева вихревыми токами). Изобретение направлено на повышение электромагнитной совместимости трехфазной системы электроснабжения с однофазной нагрузкой и на повышение энергетической эффективности систем электроснабжения путем снижения несимметрии токов нагрузки в трехфазной системе электроснабжения.The invention relates to the field of electrical engineering and can be used in three-phase power supply systems for supplying single-phase loads in order to reduce the asymmetry of currents and voltages. Any single-phase load can be connected to the complex as a balanced load; the currents of a single-phase load are distributed most symmetrically along the phases of a three-phase network, having an active-inductive character with a power factor cosφ =

, including electrical heating systems, for example, induction heating systems using heat traces: such heating systems include a "skin system" and an induction system (eddy current heating system). The invention is aimed at increasing the electromagnetic compatibility of a three-phase power supply system with a single-phase load and at increasing the energy efficiency of power supply systems by reducing the asymmetry of load currents in a three-phase power supply system.

As you know, the most efficient power transmission system currently used, including in Russia, is a three-phase symmetric power supply system. At the same time, a single-phase load is often used, among which household appliances, lighting and some types of industrial loads can be distinguished. A significant disadvantage of a single-phase load is that when it is connected in a three-phase power supply system, current unbalance occurs and, accordingly, voltage unbalance. Due to the asymmetry of currents, the equipment of the power supply system is unevenly loaded: cable and overhead lines, transformers, which leads to an overestimation of the installed capacity of this equipment, a decrease in the capacity of power transmission lines, an increase in electricity losses and, consequently, to a decrease in energy efficiency and economic efficiency of transmission and use of electricity generally. Voltage unbalance negatively affects the operation of symmetrical three-phase equipment, for example, synchronous and asynchronous AC motors, in which energy losses, winding temperatures increase, rotor vibration increases and equipment service life decreases. Also, unbalanced current and voltage can lead to false triggering of relay protection.

It should be noted that the household and general economic single-phase load is characterized by low power, uneven use during the day and is connected to phase voltage in such a way that the whole power supply system is loaded symmetrically. A single-phase industrial load of high power, in turn, can rarely be balanced in the same way and requires the use of special technical means. In order to reduce the asymmetry of the consumed current of a single-phase load of high power, special balancing electrical systems are often used in transformer substations of industrial enterprises, including those based on special transformers.

The Russian industry has experience of using balun transformers with different winding connection schemes. In particular, balancing transformers are widely used in traction power supply systems, where well-proven transformers that convert three phases into two, shifted by 90 °, assembled according to the following schemes: Scott's scheme, DST scheme, Kubler's scheme and others have found the greatest application [1]. The disadvantage of using these circuits to power a single-phase load is that, at best, the load is only partially symmetrical, at worst, the load current unbalance becomes even greater.

There are also balancing electrical complexes for converting three phases into one; all such complexes based on special transformers are built using balancing devices, for example, according to the Steinmetz scheme [1] or according to another special scheme, in particular, those given in the sources [2, 3]. Complete balancing of a single-phase load without balancing devices is impossible. The balancing device itself is a reactive element, for example, a choke if the resistance of the balancing device should be inductive, as well as a capacitor or synchronous compensator if the resistance of the balancing device should be capacitive.

The disadvantages of the Steinmetz circuit are: the need to use simultaneously two balancing devices - capacitive and inductive, - the dependence of the balancing quality on the matching of the load power and the power of the balancing devices, as well as the need to compensate for the reactive power of the load before balancing, since the circuit effectively works only with a purely active load [ 1]. At the same time, in industry, most of the loads are of an active-inductive nature. These disadvantages are partially eliminated in the invention [4], which is based on the use of a complex voltage regulation circuit by switching the taps of the transformer windings, as well as regulation of the inductance and capacitance of balancing devices (balancing unit).

. Недостатком устройства является то, что качество симметрирования нагрузки зависит от согласования мощности нагрузки и емкостного балансирующего устройства. Под согласованием понимается то, что их сопротивления и мощности должны быть пропорциональны друг другу со специально рассчитанным коэффициентом μ. Рассогласование этих мощностей приводит к несимметрии фазных токов симметрирующего комплекса, а в некоторых случаях и к появлению значительной емкостной или индуктивной составляющей в данных токах. При этом идеальное согласование мощности балансирующего устройства и симметрируемой однофазной нагрузки достижимо редко. Так, например, в области электрообогрева фактическая протяженность внеплощадочных трубопроводов может отличаться от проектной более чем на 5%, электромагнитные параметры теплоспутников не нормированы соответствующими стандартами и также имеют отклонения от параметров, учтенных в проектах, в связи с чем фактическое значение мощности нагрузки обогрева не соответствует проектным значениям, следовательно, не согласовано с мощностью балансирующего устройства.There is also a diagram of a transformer balancing device with a special connection of the secondary windings [5] when connecting the primary windings according to the "star without neutral wire" or "zigzag without neutral wire" scheme: the windings of phases a and b are connected in series and opposite, and the winding of phase c is connected in series with a capacitor C _1, and connected in series and in accordance with a phase winding. Thus, all three secondary windings of the transformer are connected in series; a single-phase load Z _{n is} connected to the output terminals of the secondary windings a and b. This circuit is built using only one capacitive balancing device and balances an active-inductive single-phase load with a power factor cosφ =

... The disadvantage of the device is that the quality of the load balancing depends on the matching of the load power and the capacitive balancing device. Matching means that their resistances and powers must be proportional to each other with a specially calculated coefficient μ. The mismatch of these powers leads to asymmetry of the phase currents of the balancing complex, and in some cases to the appearance of a significant capacitive or inductive component in these currents. At the same time, ideal matching between the balancing device power and the balanced single-phase load is rarely achievable. So, for example, in the field of electrical heating, the actual length of off-site pipelines may differ from the design one by more than 5%, the electromagnetic parameters of heat tracers are not standardized by the relevant standards and also have deviations from the parameters taken into account in the projects, and therefore the actual value of the heating load power does not correspond the design values are therefore not consistent with the capacity of the balancing device.

The aim of this invention is to create an electrical complex for balancing a single-phase load, which is characterized by less asymmetry of currents with inconsistent initial parameters of the load power and the balancing device.

Also, the aim of this invention is to reduce the loss of electrical energy in the equipment of the balancing electrical complex and the power supply system.

Another object of the invention is the possibility of connecting to an electrical complex for balancing a single-phase load of induction heating systems using heat traces without the use of power factor correcting devices, since their power factor cosφ corresponds to the coefficient μ of matching the power of the load and the balancing device.

These goals are achieved due to the fact that the secondary windings of the three-phase transformer are made in the form of six half-windings located on three rods of the magnetic circuit of the transformer, on which the primary windings are also located. The semi-windings of the secondary windings are connected to each other, to the load and the balancing device in such a way that the load currents are distributed over all phases of the primary winding, which, in the case of matched power of the load and the balancing device, leads to complete balancing of the single-phase active-inductive load to the three-phase power supply network, and in the case of an inconsistent one - to a lower current asymmetry of the electrical complex than when using a transformer balancing device from a source [5]. In this case, the primary winding of the transformer is connected according to the "star without neutral wire" scheme.

It is possible to connect the primary winding of the transformer according to the delta, star with a neutral wire, or zigzag with a neutral wire, but with this connection, zero sequence currents also flow in the primary windings, which reduces the efficiency of the balancing complex, as well as the quality of balancing the load. It is possible to connect the primary winding of the transformer according to the zigzag scheme without a neutral wire, but this option is more difficult to manufacture and requires more materials for manufacturing. The phase order of the primary windings does not matter; the phase order of the secondary windings also does not matter if they are connected according to a special scheme of the present invention, taking into account the direction of winding on the rods.

, для согласования мощности нагрузки и балансирующего устройства параллельно нагрузке может подключаться компенсирующее устройство, изменяющее характер нагрузки до соответствующего коэффициенту мощности cosφ =

при активно-индуктивном характере, что способствует лучшему симметрированию нагрузки. Свойства компенсирующего устройства зависят от начального характера нагрузки:In another embodiment of the electrical complex for balancing a single-phase load for the case when the load has a character different from active-inductive with a power factor cosφ =

, to match the power of the load and the balancing device, a compensating device can be connected in parallel with the load, changing the nature of the load to the corresponding power factor cosφ =

with an active-inductive nature, which contributes to a better balancing of the load. The properties of the compensating device depend on the initial nature of the load:

, то компенсирующее устройство представляет собой техническое средство, обладающее индуктивностью, например, дроссель, в том числе регулируемый посредством ответвлений, вручную или автоматически для чего может использоваться программируемый логический контроллер и различные коммутационные аппараты, например, вакуумные контакторы;- if the load is purely active, active-capacitive or active-inductive with cosφ>

, then the compensating device is a technical means with inductance, for example, a choke, including adjustable by means of taps, manually or automatically, for which a programmable logic controller and various switching devices, for example, vacuum contactors, can be used;

, то компенсирующее устройство представляет собой техническое средство, обладающее емкостью, например, синхронный компенсатор, конденсатор или батарею конденсаторов, в том числе регулируемую посредством параллельного подключения отдельных модулей конденсаторов с меньшей емкостью, вручную или автоматически для чего может использоваться программируемый логический контроллер и различные коммутационные аппараты, например, вакуумные контакторы.- if the load is active-inductive with cosφ <

, then the compensating device is a technical means with a capacity, for example, a synchronous compensator, a capacitor or a capacitor bank, including one that is regulated by parallel connection of individual capacitor modules with a smaller capacity, manually or automatically for which a programmable logic controller and various switching devices can be used eg vacuum contactors.

In another embodiment of an electrical complex for balancing a single-phase load in order to reduce the consumed reactive power, therefore, reduce electricity losses in the power supply system, a reactive power compensator can be connected to the input of a three-phase transformer, which is a technical means with a capacity, for example, a battery of three-phase capacitors , a synchronous compensator or an adjustable compensating device (active filter, STATCOM or others).

In another embodiment of an electrical complex for balancing a single-phase load in order to more accurately match the load power and the balancing device, the winding of a three-phase transformer can be performed with a tapping system that, by means of switching, manual or automatic, allows you to regulate the voltage on the load and the balancing device, and, accordingly, their power in such a way that the power of the load and the balancing device are matched. For the purpose of automatic control, a programmable logic controller and on-load control devices (OLTC) can be used. The number of taps depends on the required range of voltage regulation and the accuracy of voltage regulation, for example, with the number of taps 10 pcs., Located uniformly throughout the transformer winding, voltage regulation from 0% to 100% with an accuracy of 10% is possible.

The invention is illustrated by the embodiments and explanations shown in the drawings, which show the following:

Figure 1 shows a linear electrical diagram of an electrical complex for balancing a single-phase load.

Figure 2 shows a linear electrical diagram of another embodiment of an electrical complex for balancing a single-phase load.

Figure 3 shows a vector diagram of currents and voltages of an electrical complex for balancing a single-phase load.

Figure 4 shows an example of a primary tapping system of a transformer for voltage regulation of a load and a balancing device.

Figure 1 shows a linear electrical diagram of an electrical complex for balancing a single-phase load, which includes a three-phase transformer T1. Three-phase transformer T1 consists of primary windings A, B, C, connected in a "star without a neutral wire" and secondary windings, consisting of half-windings a-1, b-1, c-1 and a-2, b-2, c -2, connected according to a special scheme: the beginning of the half-winding a-1 is connected to the load Z _H and the end of the half-winding a-2, the end of the half-winding a-1 is connected to the beginning of the half-winding b-2, the beginning of the half-winding a-2 is connected to the end of the half-winding c-1 , the beginning of the half-windings b-1 and c-1 are connected to different inputs of the balancing device C1, the beginning of the half-winding b-1 is also connected to the load Z _H , the end of the half-winding b-1 is connected to the beginning of the half-winding c-2, the end of the half-winding b-2 is connected to end of half-winding c-2. The semi-windings of the secondary windings a-1 and a-2, b-1 and b-2, c-1 and c-2, located on the legs A, B and C, respectively, are wound in the same direction. The primary windings A, B, C of transformer T1 have terminals for connection to a three-phase power supply system, for example, to a power line, which in turn is connected to a three-phase alternating voltage power supply, thus supplying electrical power to transformer T1. Secondary half-windings a-1 and b-1 have terminals for connecting the load. Secondary half-windings b-1 and c-1 have terminals for connecting a balancing device.

,

. Данные коэффициенты рассчитываются по формулам (1, 2):The electrical complex for balancing a single-phase load works as follows. When voltage is applied from a three-phase alternating voltage power source, for example, through a power line to the primary windings A, B, C of the transformer T1, the primary windings A, B, C induce a voltage in the secondary half-windings a-1, b-1, c-1 and a -2, b-2, c-2 of the transformer T1, which is k times greater or less than the input voltage, where k is the transformation ratio of the transformer T1. Since the transformer T1 has the primary windings A, B, C connected according to the "star without a neutral wire" scheme, and the secondary semi-windings a-1, b-1, c-1 and a-2, b-2, c-2 are connected in series with each other, the balancing device C1 and the load Z _H according to a special scheme, then the line voltage U _{H of the} secondary windings of the three-phase transformer T1 is induced on the load Z _H , and on the balancing device C1, the voltage U ₁ , equal to twice the phase voltage of the secondary windings of the transformer T1, data the voltages are shifted in phase with respect to each other by 150 °, and the phase of the load current I _H differs from the current phase of the balancing device I ₁ by 30 °. With the power of the balancing device C1 matched to the load power Z _H , in the semi-windings a-1, b-1, c-1 and a-2, b-2, c-2 of the secondary windings of the transformer T1, a three-phase asymmetric current system is formed, while the current there is no negative sequence in this system of currents, and the zero sequence current flows only in the secondary windings, in the primary windings A, B, C only the symmetrical system of currents I _A , I _B , I _{C of} positive sequence flows, since the zero sequence current in the connection scheme windings "star without neutral wire" do not leak. In this case, the unbalance coefficients for the positive and negative sequence currents in the primary windings are equal to zero:

,

... These coefficients are calculated by the formulas (1, 2):

(1)

(2)

- действующее значение тока нулевой последовательности, А;where -

- effective value of zero sequence current, A;

- действующее значение тока обратной последовательности, А;-

- effective value of the negative sequence current, A;

- номинальный ток, А.-

- rated current, A.

,

, а для изобретения

,

.If the powers of the balancing device C1 and the load Z _{H are} not matched, then the three-phase asymmetrical system of currents formed in the secondary windings includes the negative sequence current, which is distributed over the primary windings A, B, C of the transformer T1 more evenly than in the prototype. The conducted research: mathematical, including the finite element method, and physical modeling showed that in the complete absence of a balancing device, for example, in the event of its failure, the asymmetry coefficients for the prototype are:

,

, and for invention

,

...

Figure 2 shows a linear electrical diagram of another embodiment of an electrical complex for balancing a single-phase load, characterized in that the winding of secondary semi-windings with different digital indices a-1, b-1, c-1 and a-2, b-2, c -2 is made opposite to each other. Accordingly, the end and the beginning of the semi-windings with a changed winding direction are reversed.

FIG. 3 shows a vector diagram of currents and voltages of an electrical complex for balancing a single-phase load, which illustrates and explains the principle of operation of a balancing complex.

FIG. 4 shows an example of a tapping system of the primary windings A, B, C of the transformer T1 to regulate the voltage across the load Z _H and the balancing device C1. Such taps, if necessary, can be removed from the transformer windings in different quantities.

List of used literature

1. Zakaryukin V. P. Modeling of traction power supply systems equipped with balancing transformers: monograph / V. P. Zakaryukin, A. V. Kryukov, I. M. Avdienko. - M .: Berlin: Direct-Media, 2017 .-- 166 p.

2. Strupinsky ML Design and operation of electrical heating systems in the oil and gas industry / ML Strupinsky, NN Khrenkov, AB Kuvaldin. - M .: Infra-Engineering, 2015 .-- 272 p.

3. RU 2290739 C1 Patent for invention of the Russian Federation. Power supply device for single-phase inductive-resistive loads, ensuring the symmetry of the primary three-phase network: IPC H02M 5/14, H01F 30/12 / M.L. Strupinsky, V.M. Esekhin; patentee Strupinsky M.L., Esekhin V.M. - No. 2005137391/09; declared 02.12.2005; publ. 27.12.2006, Bul. No. 36.

4. RU 2477555 C2 Patent for invention of the Russian Federation. Power supply device for direct electric heating of the pipeline system: IPC H02J 3/26 / D. RADAN (NO); Patent holder SIEMENS AKTSIENGESELLSHAFT (DE). - No. 2011115102/07; declared 07.24.2009; publ. 03/10/2013, Bul. No. 30.

5. Fillipov AO Reduction of electrical energy losses in rural networks of 0.38 kV using a transformer balancing device dis. Cand. tech. Sciences in the specialty 05.20.02 / Anton Olegovich Fillipov. - St. Petersburg - Pushkin: FGOU VPO "St. Petersburg State Agrarian University", 2010. - 141 p.

Claims (9)

1. An electrical complex for balancing a single-phase load, consisting of a balancing technical means with an electric capacity, and a three-phase transformer with primary windings A, B, C connected according to the "star without a neutral wire" scheme, characterized in that the secondary windings consist of half windings a-1, b-1, c-1 and a-2, b-2, c-2, while the beginning of the half-winding a-1 is connected to the load and to the end of the half-winding a-2, the end of the half-winding a-1 is connected to the beginning half-windings b-2, the beginning of half-winding a-2 is connected to the end of half-winding c-1, the beginning of half-windings b-1 and c-1 are connected to different inputs of a balancing technical device with electric capacity, the beginning of half-winding b-1 is also connected to the load, end half-winding b-1 is connected to the beginning of half-winding c-2, the end of half-winding b-2 is connected to the end of half-winding c-2. 2. An electrical complex for balancing a single-phase load according to claim 1, characterized in that the primary windings of the three-phase transformer A, B, C consist of half-windings, which are connected according to the "zigzag" scheme. 3. An electrical complex for balancing a single-phase load according to claim 1, characterized in that at least one of the semi-windings of the secondary windings of a three-phase transformer is wound in the opposite direction, while the end and the beginning of this semi-winding are interchanged when connected. 4. An electrical complex for balancing a single-phase load according to claim 1, characterized in that a compensating device is connected to the load, which is a technical means with inductance. 5. An electrical complex for balancing a single-phase load according to claim 1, characterized in that a compensating device is connected to the load, which is a technical means with a capacity. 6. An electrical complex for balancing a single-phase load according to claim 1, characterized in that a reactive power compensator is connected to the primary windings of a three-phase transformer. 7. An electrical complex for balancing a single-phase load according to claim 1, characterized in that at least one winding of a three-phase transformer has at least one branch for voltage regulation. 8. An electrical complex for balancing a single-phase load according to claim 7, characterized in that the transformer is adapted to change the voltage under load using a tap changer. 9. Electrotechnical complex for balancing a single-phase load according to claim 1, characterized in that the balancing technical means with electrical capacity consists of several capacitors connected in parallel by means of switching devices controlled by a programmable logic controller.

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