Reactive power compensator

Abstract

The invention relates to electrical engineering. A reactive power compensator comprises a voltage and current control unit, and at least one unit of delta-connected capacitors connectable in parallel to an electrical load. The compensator also comprises a three-phase current choke, and at least one unit of delta-connected capacitors connectable to the electrical load via at least one power semiconductor switch. The neutral of the three-phase current choke is connectable to the neutral of a supply transformer via a variable resistance rheostat The invention makes it possible to increase the operating efficiency of a reactive power compensator.

Description

[0001] Reactive power compensator

[0002] AREA OF TECHNOLOGY

[0003] The utility model relates to electrical engineering, in particular to converter technology, and can be used to compensate for reactive power in three-phase 0.4 kV electric power networks.

[0004] PRIOR ART

[0005] The vast majority of consumer electrical installations today are powered by three-phase AC networks. Variable voltage and current are necessary to transform the parameters of transmitted electricity and supply power to geographically remote regions and consumers with relatively low process losses.

[0006] In this case, the entire electrical network is divided into a series of galvanically isolated sections, with only electromagnetic coupling between the windings of the step-up or step-down transformers. Each of these sections is essentially a separate RLC oscillatory circuit.

[0007] The capacitive component of such an RLC circuit is primarily contributed by the power lines, the inductive component by the windings of transformers and electric motors, and the active component by the ohmic resistance of network elements and the purely active load of consumers. These capacitive and inductive elements are considered reactive and can be saturated with energy and then released back into the grid.

[0008] This portion of the energy does not go toward the useful operation of consumer devices and mechanisms and, therefore, is not consumed. Therefore, the portion of the energy exchanged between the capacitive and inductive elements of a network section to saturate is called reactive.

[0009] The share of reactive energy per unit of time is controlled by the parameter tangent of angle phi (tg φ), equal to the ratio of reactive power to active power, where φ is the angle between the vectors of apparent and active power.

[0010] The methods currently used to regulate the ratio of active and reactive power consumption have a number of drawbacks. The most common method is the use of static capacitor banks. This method lacks flexibility under variable load conditions and can lead to deterioration in the operating conditions of electrical consumers.

[0011] Another widely accepted method for precisely regulating the ratio of active and reactive power consumption is the use of synchronous compensators. Their widespread use is limited by the relatively high cost and complexity of operating rotating equipment, especially in extended power systems with numerous power supply centers.

[0012] Also known from the prior art, in particular from patent RU 197031 Ш, IPC class H02M 7 / 155, published March 26, 2020, is a half-wave generator comprising a three-phase steel-coiled inductor, a load, thyristors, and capacitors. In this half-wave generator, delta-connected capacitors are connected in parallel to a three-phase AC source, to which a three-phase steel-coiled inductor, other delta-connected capacitors, star-connected capacitors, and a load are also connected in parallel via thyristors.

[0013] A drawback of the known solution is the flow of direct current from the neutral of the three-phase inductor to the neutral of the supply power transformer, which causes magnetization of the low-voltage windings of the supply power transformer. Another drawback of the known technical solution is the lack of matching of the reactive power in the load circuit with the capacitance of the connected capacitors, which reduces its efficiency.

[0014] Thus, the technical problem is to create an effective reactive power compensator designed to supply the active load with converted reactive power depending on the value of the consumed apparent power.

[0015] DISCLOSURE OF THE TECHNICAL SOLUTION

[0016] The proposed technical solution is based on the objective of increasing the efficiency of a reactive power compensator. This efficiency is expressed by improving the ratio of active to reactive power at the terminals of the consumer's electrical receivers, as well as reducing the amount of active electricity consumed from the grid without changing the operating mode of the consumer's electrical receivers.

[0017] The proposed solution to the stated problem is that a reactive power compensator is declared, which comprises a housing in which a voltage and current control unit is placed, as well as at least one block of capacitors connected in a triangle, made with the possibility of parallel connection to an electrical load, a three-phase current choke with a star connection of windings and at least one block of capacitors connected in a triangle, made with the possibility of connection to an electrical load through at least one power semiconductor switch in parallel to each other, wherein the neutral of the three-phase current choke is made with the possibility of connection to the neutral of the supply transformer through a rheostat with variable resistance.

[0018] The device enclosure can be designed as a wall-mounted or base-mounted drawer, or at least one floor-standing cabinet with a front door. Equipping the device with a voltage and current monitoring unit is necessary for measuring the phase currents and voltages in the load circuit, as well as the angles between the phase current and voltage vectors, and generating a control signal to connect the capacitor banks, which store the reactive component of the electrical energy and discharge it into the consumer load.

[0019] Any device known from the prior art can be used as a voltage and current control unit, in particular, a converter for measuring voltage, current and power of three-phase electrical networks FE1892-A

[0020]

[0021] rt.ru / images / manuals / FE1892-AD.pdf), control and management unit 2014. pdf APrQmglteh.ru .

[0022] A three-phase current choke with windings connected in a star and at least one block of capacitors connected in a triangle constitute an oscillatory circuit, where the three-phase current choke is an inductance, and at least one block of power capacitors is a capacitance.

[0023] The presence of power semiconductor switches, through which a three-phase current choke with star-connected windings and at least one delta-connected capacitor bank are connected in parallel, is necessary to ensure current flow to the oscillatory circuit in the open semiconductor switch mode and current flow in the reverse direction—in the closed semiconductor switch mode. Diodes or thyristors can be used as power semiconductor switches in this case.

[0024] This allows us to conclude that the claimed technical solution meets the “novelty” criterion.

[0025] The technical solution formula is drafted without dividing it into restrictive and distinctive parts to better understand the essence of the claimed technical solution and to more accurately present the essence of the claimed technical solution. BEST OPTIONS FOR IMPLEMENTING THE TECHNICAL SOLUTION

[0026] The claimed technical solution is illustrated by the following examples of specific implementation, but is not limited to them.

[0027] The claimed technical solution is illustrated by the following figures.

[0028] Fig. 1 shows a diagram of the device.

[0029] Fig. 2 shows a graph of the consumer load for active and reactive power (power profile).

[0030] The reactive power compensator comprises a housing in which a voltage and current control unit 1 is located, as well as at least one block of capacitors 2 connected in a triangle, configured to be connected in parallel to an electrical load 6.

[0031] The resonant oscillatory circuit is equipped with a set of relays 8-10, with the help of which the voltage and current control unit 1 controls the amount of reactive component of power in the load circuit and elements, connecting and disconnecting the required number of capacitor blocks 3-5, respectively.

[0032] A three-phase current choke 11 with a star connection of windings and at least one block of capacitors 3-5 connected in a triangle are designed with the possibility of being connected to an electrical load 6 through at least one power semiconductor switch 12 in parallel to each other.

[0033] The three-phase current choke 11 with a star connection of windings consists of three windings located on a magnetic circuit.

[0034] In this case, the neutral of the three-phase current choke 11 is designed with the possibility of connecting to the neutral of the supply transformer 13 through a rheostat 14 with variable resistance.

[0035] The device's housing is grounded (the grounding point is shown in the drawing at position 15). The device is designed for operation in three-phase 0.4 kV networks.

[0036] The device's operating principle is based on accumulating energy in capacitors and releasing it to the load with a delay by locking a power semiconductor switch 12, which is implemented as a diode or thyristor. The delay is achieved by connecting at least one capacitor bank 3-5, connected in a delta configuration, to load 6 using a star-connected phase connection. The power supply to the grid is also delivered by the presence of a three-phase choke 11 in the circuit.

[0037] The equivalent reactive power of three-phase current choke 11 is calculated as the maximum reactive power in the network. The total equivalent reactive power of capacitor blocks 3-5 is less than or equal to the equivalent reactive power of three-phase current choke 11.

[0038] If tg(|) exceeds unity, then the excess reactive power is compensated by capacitor blocks 2 (capacitive elements) at the input of the connected oscillatory circuit.

[0039] The electrical power supplied to the load should be between 10% and 60% of the actual load power consumption. The equivalent reactive power of the choke should not exceed 40% of the supply transformer's full power.

[0040] Voltage and current monitoring unit 1 contains a microcontroller that controls the measurement process and all functional units. It also implements measurement and control algorithms in accordance with a specialized program stored in its internal program memory. Control of the units is performed via hardware and software interfaces implemented on the microcontroller's input / output ports. Measurements are performed using a multichannel analog-to-digital converter (ADC) integrated into the microcontroller.

[0041] The ADC samples instantaneous voltage and current values ​​in parallel across six analog channels. The microcontroller uses these instantaneous voltage and current samples to calculate average values ​​for frequency, voltage, current, active, apparent, and reactive power in each phase of the network over the entire period.

[0042] When voltage and current monitoring unit 1 registers an increase in the active and reactive power values ​​over a network period, the microcontroller of voltage and current monitoring unit 1 generates a control pulse and, using relays 8-10, connects or disconnects capacitor blocks 3-5, located after power semiconductor switches 12, simultaneously proportionally increasing or decreasing the resistance of rheostat 14 in the neutral, respectively. When voltage and current monitoring unit 1 registers a constant active load and an increase in the amount of reactive power, voltage and current monitoring unit 1 connects, using relay 7, capacitor blocks 2, located before power semiconductor switches 12, without changing the resistance of rheostat 14 in the neutral.

[0043] An example of a reactive power compensator operating in operation is shown below. The consumer's hourly load graph is recorded for active and reactive power, with active power measured in kilowatts (kW) and reactive power measured in kilovolt-amperes reactive (kV Amp), Fig. 2.

[0044] The median load A+ is determined to be 58 kW and R+ to be 37 kVAr. The peak active and reactive power values ​​are recorded at 72.8 kW and 44.8 kVAr, respectively.

[0045] The parameters of inductance and capacitors are selected based on reactive power. Manufacturers of chokes and capacitors typically specify the reactive power they correspond to, so it is sufficient to select a power equal to or slightly greater than the median reactive power recorded by the power profile (Fig. 2).

[0046] In this case, the reactive power in the load circuit is related to the values ​​of inductance and capacitance by the following relationships:

[0047] Q = 1 2 X

[0048]

[0049] Where

[0050] I - load current, A;

[0051] — reactance of the choke or capacitor, Ohm

[0052] / - current frequency equal to 50 Hz

[0053] L - choke inductance, H

[0054] C is the total capacitance of capacitors, F.

[0055] The parameters of the power semiconductor switches 12 are selected based on the nominal current, equal to three times the current 7 flowing in the load.

[0056] The number of capacitor blocks 2-5 (regulation stages) depends on the set of capacitors and can vary from 2 to 10.

[0057] Capacitor banks are connected so that the power of the connected capacitors corresponds as closely as possible to the current reactive power of the load. The greater the number of stages, the more accurate the regulation.

[0058] If the reactive power in the load (kVAr) numerically exceeds the value of the active power (kW), then the difference between the active and reactive powers must be compensated by capacitor blocks 2 connected to the power semiconductor switches 12.

[0059] An example of the operation of a reactive power compensator with a three-phase current choke of 100 kV Ar and a capacity of 20 kV Ar capacitors.

[0060]

[0061]

[0062] The resistance of the rheostat in the neutral changes proportionally to the current flowing in the neutral, based on the ratio of 10 ohms for every 1 ampere of current.

[0063] The efficiency of using a reactive power compensator is estimated by reducing the consumption of active electric energy from the network while maintaining the standard value of tg f < 0.4.

[0064] INDUSTRIAL APPLICABILITY

[0065] The claimed technical solution can be manufactured from elements and materials known in the art using known methods of their assembly.

[0066] The use of the claimed technical solution, as demonstrated by the examples provided (Figures 1-2), as well as by specific implementation examples, demonstrates that the claimed technical solution achieves the stated technical result, namely, increasing the efficiency of the reactive power compensator. The efficiency of the reactive power compensator is reflected in an improved ratio of active and reactive power at the terminals of the consumer's electrical receivers, as well as a reduction in the amount of active electricity consumed from the grid, without changing the operating mode of the consumer's electrical receivers.

[0067] This technical solution can be successfully used to compensate for reactive power in three-phase electric power networks of 0.4 kV consumers.

Claims

1. Formula of technical solution 1. A reactive power compensator comprising a housing in which a voltage and current monitoring unit is placed, as well as at least one block of capacitors connected in a triangle, configured to be connected in parallel to an electrical load, a three-phase current choke with a star connection of the windings and at least one block of capacitors connected in a triangle, configured to be connected to an electrical load through at least one power semiconductor switch in parallel to each other, wherein the neutral of the three-phase current choke is configured to be connected to the neutral of the supply transformer through a rheostat with variable resistance.

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