RU2352010C2 - Adjustable autotransformation reactor - Google Patents

Abstract

FIELD: electrics.

SUBSTANCE: device includes magnetic conductor with main core carrying network winding with taps, compensation winding and control winding circuited to control unit. Network winding outputs are connected to primary winding of voltage amplification transformer over excitation adjustment unit, while secondary winding of voltage amplification transformer is connected to power transmission line splitting. Control winding covers main core. Voltage amplification transformer features compensation winding. High harmonic filters are connected to compensation windings, and control unit and excitation adjustment unit are made of fully adjustable semiconductor devices.

EFFECT: extended functional capabilities.

4 cl, 4 dwg

Description

The invention relates to electrical engineering, in particular to controlled shunt reactors-autotransformers (USRAT), and can be used to compensate for the excess reactive power of a high-voltage power line and changes in it over a wide range of the general voltage level.

Known controlled reactor transformer (URT) having a three-phase primary and secondary windings, the latter combined with a DC magnetizing winding (USSR Author's Certificate No. 1541681, class H01F 29/14 [1]).

URT is intended for use at lowering substations of distribution networks as a transformer and at the same time adjustable inductance of a reactive power compensator. At full load of the substation, the URT works as a transformer, if the load is small - in the reactor mode. At an intermediate load, the URT performs the function of both a controlled reactor and a power transformer with an appropriate degree of loading of active and reactive powers. By changing the magnitude of the direct bias current, it is possible, due to a change in the magnetic state of the steel of the magnetic circuit, to control the inductive resistance of the primary winding and, as a result, the amount of reactive power consumed and the voltage level on the secondary winding.

Similar functions are performed by a three-phase controlled reactor with additional and secondary windings, the first of which is used to magnetize the cores of the magnetic circuit with direct current, and the second is intended to power the load (USSR Author's Certificate No. 1658224, class H01F 29/14 [2]).

Also known is a three-phase controlled autotransformer reactor (URAT), used to improve long-distance power modes and connected directly to a high-voltage line (USSR Author's Certificate No. 1781711, class H01F 29/14 [3]). The change in reactive power consumed by URAT is carried out by changing the current of the control winding. The magnitude of the current is regulated by in-parallel thyristors connected to its circuit. Changing the opening angle of the thyristors leads to a decrease (increase) in the indicated current, but higher harmonics are generated in the current of the main winding of URAT. To eliminate odd harmonics, URAT is equipped with compensation windings, which complicates its design. The main winding, made by an autotransformer circuit, consists of two parts, between which an additional autotransformer (DAT) of small power is turned on, which has a magnetic circuit separate from URAT, which is magnetized by direct current. If there is no magnetization, then the voltage on the DAT winding, connected in series to the main winding, increases, and at a certain level of magnetization it decreases. Thus, the voltage at the middle terminal of the main winding of the URAT, connected, for example, to a power line (power transmission line) can be regulated. However, the voltage change lies within (8 ÷ 14)%, which is not enough to carry out deep regulation of the voltage on the line required to optimize the power transmission mode with varying transmitted power.

All controlled shunt reactors (CSR) with DC magnetization of the core, including transformer reactors of the type [1], [2], [3], have serious disadvantages:

- increased content of harmonics in the current of the main winding, caused by saturation of the core and the operation of the thyristors at incomplete opening angles;

- large electrical inertia associated with the presence of a constant component in the magnetic flux;

- a complex control circuit, including additional phase shifting and compensation windings;

- insufficient voltage regulation range, which excludes their use for optimization of long-distance power transmission modes.

A number of shortcomings of the reactors were largely eliminated in transformer-type transformer type (CT) CSR (RF Patent No. 2221297, class H01F 38/02 [4]). CShR TT contains a closed magnetic circuit without gaps, on the main core of which windings are placed: network, control and compensation. The network winding is connected directly to the power transmission line, the control winding is closed to an automatically controlled thyristor unit, and higher harmonics filters are connected to the compensation winding.

An increase in the current of the control winding leads to the displacement of the magnetic flux from the main rod, which leads to an increase in resistance to this flux and an increase in the magnetization current.

Managed shunt reactors of all types are designed primarily to maintain voltage in the controlled nodes of high-voltage networks at a given level. At the same time, it is known that in order to optimize the regime of long-distance power lines in terms of active power losses, it is necessary to regulate the overall voltage level on this power line (Venikov V.A., Siuda I.P. Calculations of long-distance AC power transmission modes. Higher School) , 1966 [5]). For optimization, it is necessary to increase the total voltage level on this power line with an increase in the active power transmitted through the power lines according to a certain law. To some extent, such a regime can be provided by the URT and URAT described above. However, due to technical imperfections and an insufficient range of voltage regulation, their use for optimal control of extended power transmission lines is very problematic.

The closest in technical essence to the proposed device is URAT according to [3], designed to regulate reactive power and voltage at one of the terminals of the main (network) winding, to which a power line can be connected.

The purpose of the invention is the expansion of the functionality of the device, which allows you to adjust reactive power and in a wide range of voltage on the power lines.

This goal is achieved by the fact that the controlled shunt reactor-autotransformer contains a magnetic circuit with a main rod, yokes, two side yokes, a network winding located on the main rod, connected by an autotransformer circuit with the terminals for connecting an additional control device, a compensation winding, a control winding that controls the network current winding block. At the same time, the primary winding of the boost booster transformer is connected to the conclusions of the network winding through the excitation control unit, the secondary winding of which is connected in series to the power line to change the overall voltage level produced as a function of the transmitted power. Moreover, the excitation control unit of the boost booster transformer is made on fully controllable power semiconductor devices. The control winding covers the main rod and is closed to the current winding of the network winding unit, and the compensation winding is located in the space between the control winding and the network winding, and suppression filters of higher harmonic components are connected to the compensation winding. The boost booster transformer contains a compensation winding located in the space between the primary and secondary windings, and filters for suppressing higher harmonic components are connected to the compensation winding.

The construction of the USRAT consists of a closed magnetic circuit having a main rod 1, end yokes 2, side yokes 3, upper 4 and lower 5 ring shunts with radial cuts, control windings 6, network winding 7 and compensation winding 8 (Fig. 1).

The design of the boost booster transformer (VDT) is similar to the design of USRAT and has a main rod 9, end yokes 10, side yokes 11, upper 12 and lower 13 shunts with radial cuts, primary winding 14, secondary winding 15 and compensation winding 16 (figure 2).

Figure 3 shows the basic single-line circuit of the USRAT, in which the network winding 7, having terminals 17, is connected to the phase voltage, and the compensation winding 8, connected in a triangle in a three-phase design to suppress the 3rd harmonic, has filters of higher harmonic 18, consisting from a series-connected capacitor and inductor tuned to resonance at the frequency of the suppressed higher harmonics (3rd, 5th, 7th). The control winding 6 is connected to the control current of the network winding unit 19, which is formed on the basis of the use of fully controllable semiconductor power devices. The primary winding 14 of the RCCB is connected to the terminals of the block 20 regulating the excitation of the RCCB, made on a fully controllable semiconductor power devices. The input of unit 20 is connected to the terminals 17 of the network winding 7. The compensation winding 16 of the VDC, connected in a triangle in a three-phase design to suppress the 3rd harmonic, has filters of higher harmonic 21, consisting of a series-connected capacitor and inductor, tuned in resonance at the frequency of the suppressed higher harmonics (3rd, 5th, 7th). The secondary winding 15 of the VDT is connected in series to the power line 22.

Figure 4 shows a diagram of the inclusion of CSR and the UHF included in its composition in long-distance power transmission of extra-high voltage 22, connected to the buses of the transmitting 24 and receiving 25 power systems by means of switches 23. The voltage changes (increases) on the power line 22 and remains unchanged on the tires of power systems. VDT of the transmitting power system operates in the voltage increase mode, the receiving - in the voltage reduction mode. USRAT and VDT at the end nodes are connected directly to the line through disconnectors, because switching of load and emergency currents is carried out by switches 23. The voltage at the USRAT and the switches 23 is equal to the voltage of the power system tires. Change (increase) in voltage - with an increase in the transmitted power, it is made only on the power transmission line section between the points of connection of the RCCB to the line. The process of optimizing the power transmission mode is divided into two stages. When the line loads are 30 ÷ 50% of the transmission capacity, automatic voltage regulation is performed at the points of connecting USRAT to the line. To maintain the voltage at a constant level, the reactive power of the CSR Q _* should change in function of the transmitted active power P according to the law

where Q _*, R _* - USHRAT and power lines, expressed in relative units of natural power line; λ is the wavelength of the line [5].

Voltage regulation can be carried out by a regulator that affects the change in reactive power of the UShRAT, not as a function of the transmitted power P _* , but upon the deviation of the voltage from the set value. With a positive voltage deviation, the power of the USRAT should increase, with a negative - decrease. For the stability of the mode, stabilizing signals can be used according to the parameters of the transient process.

In the range of power transmission line changes within 50-100% of its capacity, the voltage on the line is changed according to the law

where Z _C - wave impedance of the line (Ohm); P is the active power of the line (MW) [5].

If the voltage on the line is regulated according to the law (2), then the transmission mode of natural power will be maintained at any value of power P, which favorably affects the voltage distribution along the line and the level of active power loss.

Changing the reactive power of USRAT at the first stage of the regulatory process is carried out by changing the resistance to the main magnetic flux, which closes within its magnetic circuit. The increase in the current of the control winding 6, produced by adjusting the control angle of the fully controlled semiconductor devices (thyristors) of the block 19, causes the main magnetic flux to be displaced from the rod 1, on which all the windings are placed, into the gap space between the windings 6 and 7. The latter leads to an increase in the magnetizing current (consumed reactive power)

To increase the transmission capacity (with an increase in the transmitted power), the general level of the line voltage is regulated according to the law (2). The controller generates a control action applied to the terminal stage (driver), which generates control signals to turn on (turn off) the fully controlled semiconductor devices of block 20 in the excitation control circuit of the RCCB. The input of block 20 is connected to the terminals 17 of the network winding 7, and the output to the primary winding of the RCCB. At the starting end of the power transmission, the VDT increases the voltage on the power lines from the voltage level of the tires 24 to a value determined by the law (2); at the receiving end of the VDT reduces the voltage to the level of tires 25 (see figure 4).

The rated power of the VDT is determined by the value of its adjustment range and the maximum value of the operating current of the power line. Reactor power in reactor mode is determined by the value of capacitive power that is generated by power lines in idle mode. When operating in the autotransformer mode, USRAT is loaded with power transmitted through the VDT.

The operation of fully controlled power semiconductor devices belonging to block 19 causes higher harmonics in the current of the winding 6. The latter creates the conditions for the appearance of higher harmonics in the magnetic flux of the USRAT, which induce higher harmonics in the current of the main (network) winding 7. Connecting filters of higher harmonic ( 3rd, 5th, 7th) to the compensation winding 8, located in the space between 6 and 7 windings, provides the proper level of harmonic suppression (Alexandrov G.N. Suppression of higher harmonic in ulation shunt reactor type transformer. Izv. RAN Power 1999, №3 [6]). When connecting the compensation windings of three phases of USHRAT into a triangle, the total power of the filters does not exceed 10% of its power [6].

The operation of the excitation control unit 20 of the VDT, containing fully controllable power semiconductor devices, causes the appearance of higher harmonic not only in the magnetic flux of the USRAT, but also in the magnetic flux of the VDT. In order to suppress higher harmonic currents in the main winding of 7 USRAT in this mode, filters 18 are used, connected to winding 8. In the VDT in the space between the primary 14 and secondary 15 windings, a compensation winding 16 connected to a triangle (three phases of the VDT) with filters connected to it 21 higher harmonics (3rd, 5th, 7th). With appropriate settings for these filters, the level of higher harmonics in the current of the secondary winding 15 is reduced to the required level. The total power of the filters does not exceed 10% of the power of the RCCB.

The current winding of the network winding unit 19 and the excitation control unit 20 of the VDT are made on the basis of fully controllable power semiconductor devices (thyristors) with artificial switching. The phase regulation of the current value is used when the power devices are turned on in parallel. The magnitude of the control angle for the opening (closing) of power devices is generated by the controller that implements the control law (1) or (2). With an increase in the control angle, the current value in the control windings 6 or 14 decreases, but at the same time the level of higher harmonic and, accordingly, the load of filters to suppress them increase.

When the control angle of the power semiconductor devices of block 19 is changed, a new mode (increased conductivity of the network winding 7) occurs almost after one period, which allows us to consider USRAT as a high-speed device (Aleksandrov G.N., Shakirov M.A. transformer-type shunt reactors based on magnetoelectric equivalent circuits. Izv. RAS. Energetika, 2005. No. 4 [7]). Such high speed makes it possible to effectively limit the forced component of the overvoltage in power lines. Overvoltage limitation can be ensured in the operation mode of the USRAT to increase the power line voltage. This requires an emergency effect on the control angles of the power semiconductor devices of blocks 19 and 20 to increase the conductivity of the network winding 7 and reduce the overall voltage level on the power lines. The latter can be done by shorting the primary winding of the VDT.

By regulating the excitation of the RCCB, the voltage on the line changes (increases), remaining unchanged on the buses 24 and 25 of the terminal substations. Therefore, they do not require a switchgear and circuit breakers for the rated line voltage. LUGGAGE with its related VDT are connected directly to the line without switches, and the line is connected to the buses of the terminal substations through switches with the rated voltage of the buses (see figure 4). Such a technical solution can significantly reduce the cost of power transmission. The line itself, for example, with a rated voltage of 750 kV, can simply be "built-in" into a network with a voltage of 500 kV through the use of a power supply system with high-voltage transformer, providing an additional voltage ΔU = 250 kV. In addition, a phased change in transmission capacity is possible. At the first stage, the line operates at a voltage of 500 kV, and the USRAT at its ends perform the functions of a controlled reactor (regulation law (1)). If it is necessary to increase the throughput capacity of the USRAT at the ends of the line, the VDT with the control range ΔU = 250 kV is supplemented. The line with such a phased strategy should be performed in dimensions of 750 kV at a voltage of terminal substations of 500 kV.

The proposed device allows optimal control of ultra-long power lines based on new technology, which provides, depending on the load of the transmission, to conduct a mode with maintaining a constant voltage on the line or changing it in the function of the transmitted power. The latter provides transmission over the natural power line at any load.

Such a control technology when turning on the proposed USRAT at the ends of the line allows:

- energy transmission over an ultra-long line without intermediate reactive power compensation devices and with minimal losses;

- "embed" in the existing system-forming network lines of increased voltage (bandwidth) without the construction of switchgears at substations for this voltage;

- to carry out more flexible control of normal and post-emergency power transmission modes due to high speed and extended regulation range.

Claims (4)

1. A controlled shunt reactor-autotransformer containing a magnetic circuit with a main rod, yokes, two side yokes, located on the main rod, a network winding connected in an autotransformer circuit with terminals for connecting an additional control device, a compensation winding, a control winding, a unit controlling the current of the network winding characterized in that the primary winding of the boost transformer, the secondary ohm is connected to the conclusions of the network winding through the excitation control unit the failure of which is connected in series to the power line to change the overall voltage level produced in it as a function of the transmitted power. 2. The controlled shunt reactor-autotransformer according to claim 1, characterized in that the excitation control unit of the boost transformer is made on fully controllable power semiconductor devices. 3. The controlled shunt reactor-autotransformer according to claim 1, characterized in that the control winding covers the main shaft and is closed to the control unit for the current of the network winding, and the compensation winding is located in the space between the control winding and the network winding, and suppression filters are connected to the compensation winding higher harmonic components. 4. The controlled shunt reactor-autotransformer according to claim 1, characterized in that the boost transformer contains a compensation winding located in the space between the primary and secondary windings, and suppression filters of higher harmonic components are connected to the compensation winding.

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