RU2263991C2 - Controlled reactor-autotransformer - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed device that can be used for reactive power correction in power transmission lines and for regulating total voltage level across this line has core with main leg carrying power winding built of top and bottom parts, compensating winding, and control winding. Control winding is wound on top part of power winding and incorporates sections closed through controllable thyristor unit. Device may also have second control winding similar in circuit arrangement and control process to first one but disposed between main leg and top part of power winding used for extending reactive power adjustment range.

EFFECT: ability of combining reactive power and voltage regulation functions within wide range in single device.

3 cl, 3 dwg

Description

The invention relates to electrical engineering, in particular to controlled autotransformer reactors, and can be used to compensate for excess reactive power of the power line and changes in it the general voltage level.

A controlled reactor is known (USSR Author's Certificate No. 1541681, class H 01 F 29/14 [1]), the reactive power of which is changed by regulating the magnitude of the direct current in the magnetization winding. The reactor has a secondary winding for powering a static reactive power compensator used to control the voltage on the power lines.

Also known is a three-phase combined autotransformer reactor (USSR Author's Certificate No. 1781711, class H 01 F 29/14 [2]), designed to improve long-distance power transmission modes and having the ability to directly connect to a high-voltage line. The change in the reactive power consumed by the autotransformer (RA) reactor is carried out by changing the current of the control winding, covering one of the rods of the phase module. The magnitude of the short circuit current of this winding is regulated by thyristors counter-parallel connected to its circuit. A change in the ignition 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 the RA. To eliminate odd harmonics, the RA is equipped with phase-shifting and compensation windings, which complicates the design of the device.

The main winding of the RA, made by an autotransformer circuit, consists of two parts, between which an additional autotransformer (DAT) of small power is connected, which is combined with the RA. Magnetic circuit DAT is magnetized by direct current. If there is no magnetization, then the voltage across 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 RA connected, for example, to the power line can be regulated. The voltage varies between 8-14%, which is not enough to carry out deep regulation of the voltage on the line.

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

- increased content of higher harmonics caused by saturation of the core and the operation of thyristors at incomplete opening angles;

- large inertia of the reactor associated with the presence of a constant component in the magnetic flux.

The indicated shortcomings of the reactors have been largely eliminated in transformer-type CSRs (GN Alexandrov, On the methodology for calculating transformer-type shunt reactors. - Electricity, 1998, No. 4 [3]). This reactor has a transformer design with a closed magnetic circuit and windings: the main winding, control winding and compensation to suppress odd harmonics. The control winding (UO) covers the main rod, and the main winding (OO) is located on top of the UO and covers it along its entire length.

The change in the current of the UO, carried out by thyristor blocks, leads to the displacement of the magnetic flux from the main rod and, as a result, an increase in the resistance to this flux. In this case, the reactor current increases.

An improved model of this reactor has an acceptable level of higher harmonic, losses in the nominal mode do not exceed 0.5%; but not intended to directly regulate line voltage.

It is known that for the implementation of the long-distance power transmission mode optimal for losses of active power, it is necessary to regulate not only the reactive power at the end nodes of the line, but also the overall voltage level on it (Electrical systems. T.III. Transmission of electrical energy by direct and alternating current of high voltage. Under Edited by V.A. Venikov. - M.: Higher School, 1975 [5]). To ensure minimum losses of active power in power lines, it is necessary to change the voltage on it in proportion to the square root of the transmitted power.

To some extent, such a regime can be provided by reactors [1] and [2]. However, due to technical imperfections (noted above) and insufficient voltage regulation range, their use for optimal control of extended ultra-high voltage power transmission modes is very problematic.

The closest in technical essence to the proposed device is an autotransformer reactor [2], which is capable of regulating reactive power and voltage at one of the terminals of the main winding.

The purpose of the invention is the combination in the proposed device of the functions of regulation of reactive power and voltage regulation of the extended range.

This goal is achieved by the fact that a controlled autotransformer reactor containing a magnetic circuit with yokes and a main rod around which all the windings are located: the main winding, consisting of upper and lower parts with a middle terminal, a compensation winding, a control winding and controlled thyristor blocks with an oncoming parallel connected thyristors, is made so that the control winding covers the upper part of the main winding. In addition, the control winding is divided into sections connected in series, having the same height equal to the height of the upper part of the main winding, and parallel to the sections, controlled thyristor blocks are connected in series with current-limiting chokes. A controlled autotransformer reactor can be made with a second control winding, similar to the device discussed above, which is located between the upper part of the main winding and the main rod. In addition, the beginning of the main winding and its average output are connected to the input node of the controlled autotransformer reactor through switches, for example, load switches.

The controlled autotransformer reactor (URA) consists of a closed magnetic circuit having a main rod 1, side yokes 2, end yokes 3, ring magnetic shunts 4, the upper part of the main winding 5, the lower part of the main winding 6, the compensation winding (in Fig. 1 shown), the control winding 7.

The upper part of the main winding 5 is covered over the entire height of the control winding, divided into sections, of the same height equal to the height of the upper part of the main winding. Parallel to these sections, controlled thyristor blocks (TB) 8 are connected in series with current-limiting chokes (TD) 9 necessary to limit the short circuit current of the sections. Figure 2 also shows the compensation winding 10, the control winding (UO) and the main winding (OO), consisting of the upper 5 and lower 6 parts with the middle terminal 11.

UO closes TB, designed for the full power of the URA. With locked thyristors, the current in the UO is absent and the reactor power is minimal (idle mode). With fully open thyristors, the current in OO and UO is maximum (the highest power of the URA). In this mode, the voltage at OO is equal to the rated voltage, as in idle mode. This is possible, since the short circuit voltage of the URA is 100%. The latter is achieved by arranging OO and UO on the main rod with the corresponding air gap.

A short-circuited UO cannot have flux-targeting with a URA magnetic flux. Therefore, in the nominal operating mode of the URA, the magnetic flux must be closed in such a way that its total flux linkage with the UO is zero while ensuring the necessary number of flux linkage with the main winding. This means that the main part of the magnetic flux passes outside the MA - in the inter-winding space and in the volume occupied by the windings.

In URA, at a rated current, almost the entire magnetic flux is displaced into the air. The flow distribution in nominal mode is shown in figure 1. Powerful magnetic flux in the air can cause additional losses.

To collect it and direct it to the magnetic circuit, the ends of the windings on both sides are covered by ring magnetic shunts 4.

The reactive power of the URA is regulated by closing the individual sections of the UO. Figure 2 UO is divided into 4 sections. Separate sections of the MA have different spatial positions with respect to OO. In this case, at a short circuit voltage OO relative to UO as a whole equal to U _k = 100% short-circuit voltage OO relative to individual sections of the MA will differ from 100% (different sizes of gaps) and the current sections may exceed the nominal value. Chokes are introduced to limit it. When you turn on one section of UO, the URA current increases by about 25%. When thyristors TB-5 are closed, all inductors of individual sections are bypassed and the OO current increases to the nominal value.

Continuous regulation of the reactive power of the URA is carried out by changing the unlocking angle of the thyristors. With incomplete unlocking of the thyristors, higher harmonics appear in the current curve. However, the higher harmonics arising in the current curve of the thyristor-switched circuit excite the higher harmonics in the magnetic flux, and they, in turn, induce counter-EMF in the short-circuited circuit. As a result, higher harmonics in the OO URA current curve are effectively suppressed. When the UO is divided into sections, the suppression efficiency increases in proportion to the division ratio.

The main purpose of the URA is the optimal control of long-distance power modes by voltage on the line and the consumption of excess reactive power generated by this line. An optimal control process is that in which, when the active power transmitted through the line increases, the line voltage and the reactive power consumption at the end nodes increase simultaneously [5].

With an increase in the reactive power consumed by the URA, the voltage at the average OO terminal simultaneously increases. Consider this process in detail.

Suppose that the UO is divided into four sections and the first section is switched using TB-1. As the section current increases, the displacement of the magnetic flux from the main rod in the space between the windings increases, which leads to an increase in the OO current. At the same time, there is a decrease in the flux linkage of the upper part of the main winding with the magnetic flux of the URA and a decrease in its counter-EMF. The consequence of this is the redistribution of the voltage applied to the OO between its parts in the direction of increasing voltage at the middle OO terminal. As the sections of the UO are closed, the voltage on the line connected to the middle terminal of the OO increases and reaches the nominal value when all UO sections are shorted. The voltage drop on the upper part of the OO in this mode is practically zero, since there is no counter-EMF due to the displacement of the magnetic flux from the zone of placement of the upper part of the OO.

With a smooth change in the current of the UO section, when the thyristor turn-on angle is controlled, the reactive power of the URA gradually increases (decreases) simultaneously with an increase (decrease) in the voltage at the middle OO terminal.

The introduction of the second control winding, located between the upper part of the OO and the main rod, opens the possibility of changing the reactive power of the URA without changing the voltage at the middle output of the OO. To regulate the current in the sections of the additional MA, a system similar to that described above and relating to the MA located between the upper and lower parts of the OO can be used.

To implement the optimal loss mode of the long-distance power line, it is necessary to change the voltage at its end nodes in accordance with the expression

where U _m is the voltage at the beginning (end) of the line; P is the active power at the beginning (end) of the line; g _m is a parameter determined by the generalized line constants.

In this case, the reactive power of reactors (URA) at the ends of the line should change in the expression

where Q _m is the reactor power at the beginning (end) of the line; U _m is the optimal voltage value at the beginning (end) of the line, determined by (1); b _m is a parameter depending on the generalized line constants.

The parameters g _m and b _{m are} determined by the formulas

where A , B , C and D are generalized constant lines [5].

The voltage on the line U _m , determined by (1), is proportional to the square root of the active power of the corresponding end of the line. In this case, the reactive power consumed by the URA is determined by (2). Current control in the sections of the UO, carried out by thyristors TB, causes a simultaneous change in voltage on the line and consumption from the line of reactive power. These changes should be as close as possible to the values of U _m , Q _m , determined by (1) and (2), respectively.

Figure 3 shows a diagram of the inclusion of URA at the ends of the power line. The upper part of the main winding (BOO) is connected to the buses of the terminal substations, and the line is connected to the middle terminals (CB) of the main winding of the URA.

When the line load is 10-20% of its natural power, the URAs operate in an autotransformer mode, which reduces the voltage on the line by 30-40% of the nominal level. The magnitude of the decrease in the overall level of voltage on the line is consistent with the requirements of maintaining the necessary margin of stability of power transmission.

It should be noted that the URA at the starting end of the line works to lower the voltage, and at the receiving end - to increase the voltage to the voltage level of the buses of the receiving node.

In the range of line load variation up to 20-25% of its natural power P _{c, the} reduced voltage remains unchanged (for example, U _{power lines} = 0.7 U _nom . Maintaining a constant voltage at the end nodes of the line can be carried out by regulating the reactive power of the URA installed in these nodes. For this, it is necessary to use the RO URA, located on the main rod close to it with a gap with respect to the upper part of the OO. To simplify the drawing in figure 1, this winding is not shown. If such a RO is not provided for in the URA, then regulation is carried out by other means provided for in this case at the end nodes of the line.

With a further increase in load (over 20-25%), the current of the UO sections located between the upper and lower parts of the OO is regulated (increased), due to which the voltage at the middle OO output of the URA (on the power line) increases and the excess reactive power consumed by it increases line. This process of simultaneously increasing voltage and reactive power consumption ends when the voltage on the line is equal to the nominal. For lines of 500 kV with a wire grade 3 × ASO-500 with a length of 500, 1000, 1500 km, the indicated voltage is achieved at a load of 0.35 R _c , respectively; 0.6 R _s ; 1,0 R _c (where R _c is the natural power for a 500 kV transmission line, R _c = 900 MW) [5]. As the line length increases, the range of optimal regulation of voltage and reactive power as a function of line load expands. At loads exceeding the indicated values (for example, for a 500 kV transmission line 500 km long P> 0.35 P _s ), the voltage on it is maintained at a constant level equal to the nominal one. Voltage regulation is performed by the URA during its operation in the reactor mode. The translation of URA into this mode can be carried out in various ways. The most acceptable is a method that is based on switching the initial and average conclusions of the main winding. In the nominal load mode of the URA (by reactive power), the voltages at the initial and average terminals OO are equal and can be closed through a switching device 12, for example, a load switch. Then the beginning of OO can be disconnected from the input terminal of the URA, for example, by a separator (see figure 2).

Thus, switching is reduced to shunting the findings of the beginning and middle of the main winding and the subsequent disconnection of the beginning of this winding from the input terminal of the URA.

With a further increase in line load, the URA works in the mode of maintaining voltage (at the point of its connection) at a given level. To do this, a gradual decrease in the UO current is achieved, reaching zero at a load equal to the natural power of the line.

The proposed device - URA allows for optimal control of ultra-long power lines of ultra-high voltage, which is based on the simultaneous regulation of the total voltage level and reactive power consumption at the end nodes.

The use of URA in ultra-long power lines allows you to:

- transmission of energy through the line without intermediate reactive power compensation devices;

- successful implementation of power lines with increased natural power due to a more efficient way to compensate for excess line capacitive power;

- lower costs for the construction of power lines;

- More reliable operation of ultra-long power lines.

Claims (3)

1. A controlled autotransformer reactor containing a magnetic circuit with yokes and a main rod, around which the main winding is located, consisting of two parts with an average terminal, the initial terminal of the first part of which is connected to the busbars of the terminal substations of the power line, and the middle terminal is to the power line, compensation and control windings, controlled thyristor blocks with on-parallel connected thyristors, characterized in that the control winding covers the first part of the main winding, located on the first and second portions thereof and consists of series-connected and are equal in height of the first portion of the main winding sections, which are connected in parallel driven thyristor units, the initial and average output of the main winding are connected to the input terminal managed reactor autotransformer via switching devices. 2. The controlled autotransformer reactor according to claim 1, characterized in that it is provided with a second control winding located between the first part of the main winding and the main core of the magnetic circuit, consisting of sections connected in series and equal in height to the first part of the main winding, parallel to which controlled thyristor blocks. 3. The controlled autotransformer reactor according to claim 1 or 2, characterized in that a current-limiting reactor is connected in series with the controlled thyristor unit.

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