220kV phase-shifting transformer combined with voltage source converter and method

Abstract

The invention relates to a 220kV phase-shifting transformer combined with a voltage source converter and a method, and belongs to the technical field of phase-shifting transformers. According to the technical scheme, a phase-shifting transformer is formed by connecting a series transformer body and an excitation transformer body through a lead, and an external voltage source converter is connected in series between a phase modulation winding of the excitation transformer and a neutral point through an external lead; an on-load phase modulation switch is connected to an excitation variable phase modulation winding and is connected to a neutral point, on the basis of step-by-step discrete adjustment of gears of the on-load phase modulation switch, a voltage vector within a circular domain range is injected into each gear adjustment point through a serially-connected voltage source converter, and the voltage source converter is used for achieving more accurate control over a phase shift angle. The method is applied to steady-state control and transient regulation of the power flow, more accurate control of the phase shift angle is realized by using the voltage source converter, the dynamic performance is faster and better, the response speed is millisecond level, the cost of the method is much lower than that of a UPFC under the same capacity of phase shift and transformation, and the method has the advantage of engineering application.

Description

Technical Field

[0001] The invention relates to a 220kV phase-shifting transformer combined with a voltage source converter and a method thereof, belonging to the technical field of phase-shifting transformers. Background Art

[0002] Phase-shifting transformer (PST) is an electrical device that realizes phase angle and voltage amplitude adjustment based on the principle of electromagnetic induction. Its basic principle is to superimpose a part of the voltage of one phase in the three-phase transformer with the voltage of another phase or two phases to obtain a change in phase angle, and then change the equivalent impedance of the phase-shifting transformer in series in the line, so as to adjust the line flow. The load side of the transformer is called the L side or L end, and the power side of the transformer is called the S side or L end. Phase-shifting transformers with voltages of 220kV and above are usually double-core structures, that is, they are composed of a series transformer connected in series to the transmission line and an excitation transformer that adjusts the phase shift position. The phase-adjusting on-load tap changer is connected to the phase-adjusting winding of the excitation transformer and to the neutral point. The output voltage of the excitation transformer is adjusted by controlling the gear position of the on-load tap changer. This voltage is connected to the low-voltage winding of the series transformer, which is induced to the high-voltage winding of the series transformer and generates an orthogonal leading or lagging voltage difference. This voltage difference causes a phase angle change between the voltages on both sides of the line connected in series by the phase-shifting transformer. The phase-shifting transformer is adjusted by a mechanical tap changer, with a response speed of seconds and a discrete working point. As a fixed electrical equipment, the phase-shifting transformer adjusts the line flow according to the gear by controlling the on-load voltage-changing tap. The control principle of the mechanical adjustment tap is relatively simple and easy to implement. However, since the on-load tap changer and the phase-changing winding are connected in multiple gears and levels, the corresponding number of turns are connected in series for each gear adjustment, so this adjustment is discrete, and the phase angle change of the phase-shifting transformer is also discrete. Therefore, it is impossible to continuously and smoothly adjust it by controlling the on-load tap changer voltage-changing tap. In addition, the phase-shifting transformer has a changing impedance when adjusting the gear, which will affect the system voltage and power flow. The voltage source converter usually adopts a decoupled dual closed-loop control strategy or a feedforward plus feedback voltage regulation to achieve line power flow control and regulation. Summary of the invention

[0003] The purpose of the present invention is to provide a 220kV phase-shifting transformer and method combined with a voltage source converter, which is applied to steady-state control and transient regulation of power flow, and can adjust voltage amplitude and phase angle in a larger range. The voltage source converter is used to achieve more precise control of the phase shift angle, and the dynamic performance is faster and better, with a response speed of milliseconds, thereby solving the above-mentioned technical problems existing in the existing technology.

[0004] The technical solution of the present invention is: A 220kV phase-shifting transformer combined with a voltage source converter is used for steady-state control of power flow and transient regulation. It is composed of a phase-shifting transformer and an external voltage source converter. The phase-shifting transformer is composed of a series transformer and an excitation transformer connected by leads. The series transformer body of the phase-shifting transformer is composed of a three-phase iron core with a series transformer low-voltage winding and a series transformer series winding in each phase, and the excitation transformer body is composed of a three-phase iron core with an excitation transformer excitation winding and an excitation transformer phase-modulation winding in each phase. The windings in the series transformer body and the excitation transformer body are connected separately according to the connection group, and the two bodies are interconnected by high and low voltage leads or larynx; the external voltage source converter is connected in series with the external lead wires. Between the excitation transformer phase-modulating winding and the neutral point; the on-load phase-modulating switch is connected to the excitation transformer phase-modulating winding and to the neutral point, and the output voltage of the excitation transformer is adjusted by controlling the gear position of the on-load phase-modulating switch. The voltage is connected to the low-voltage winding of the series transformer, and is induced on the series transformer series winding of the series transformer to generate an orthogonal leading or orthogonal lagging voltage difference, which causes a phase angle change between the voltages on both sides of the line connected in series by the phase-shifting transformer; on the basis of the step-by-step discrete adjustment of the gear position of the on-load phase-modulating switch, a voltage vector within a circular domain is injected into each gear adjustment point by using the series-connected voltage source converter, and a more precise control of the phase shift angle is achieved by using the voltage source converter.

[0005] The excitation transformer body comprises an excitation transformer core, an excitation transformer excitation winding and an excitation transformer phase-modulation winding. The excitation transformer core adopts a three-phase three-column or three-phase five-column core, and the core sheets are clamped by clamps. The body adopts an integral set structure, and the upper end is pressed by a pressing plate, and the lower end is supported by a supporting plate. A thin partition is provided to separate the large volume oil gap between the windings and the winding to the ground, thereby reducing the main insulation distance, and making the excitation transformer body structure more compact; the excitation transformer winding is arranged in the order of excitation, The field transformer excitation winding and the field transformer phase modulation winding, the high-voltage lead from the middle of the series transformer series winding is connected to one end of the excitation transformer excitation winding, and the other end of the excitation transformer excitation winding is connected to the neutral point of the excitation transformer excitation winding; the excitation transformer phase modulation winding is star-connected, one end is connected to the delta-connected series transformer low-voltage winding, and the other end is connected to the voltage source converter through three bushings or the terminals of the external voltage source converter and then to the neutral point of the phase modulation system. The on-load phase modulation switch is arranged near the excitation transformer body for easy wiring.

[0006] The excitation variable phase-modulation winding is divided into an inner phase-modulation winding and an outer phase-modulation winding; the inner phase-modulation winding is odd-numbered tapped, and the outer phase-modulation winding is even-numbered tapped. The inner phase-modulation winding and the outer phase-modulation winding are connected in sequence according to the tapping order, and the winding directions of the inner phase-modulation winding and the outer phase-modulation winding are opposite. When current passes through, the current directions between the inner phase-modulation winding and the outer phase-modulation winding and between the odd and even tapped leads are opposite, which effectively avoids the superposition of currents of multiple tapped leads, eliminates the leakage magnetic field generated by the synthesized large current tapped leads, and avoids local overheating.

[0007] The series transformer body comprises a series transformer core, a series transformer low-voltage winding and a series transformer series winding. The series transformer core adopts a three-phase three-column or three-phase five-column core, and the core sheets are clamped by clamps. The body adopts an integral set structure, the upper end is pressed by a pressing plate, and the lower end is supported by a supporting plate. A thin partition is provided to separate the large volume oil gap between the windings and the winding to the ground, thereby reducing the main insulation distance and making the series transformer body structure more compact; the series transformer windings are arranged in the order of series transformer low-voltage winding and series transformer series winding from the core to the outside, the series transformer low-voltage winding is corner-connected, and the vertex is led out to the on-load phase-changing switch of the excitation transformer; the series transformer series winding is III-connected in series with the line, and the head and end of the series transformer series winding are respectively connected to the S end and the L end of the phase-shifting transformer, and the middle lead is connected to the excitation transformer excitation winding through a high-voltage lead or a larynx.

[0008] When the heights of the series transformer body and the excitation transformer body are inconsistent, a double-layer support plate structure is adopted for one of the lower bodies. The support plates of the two bodies are fixed to the oil tank according to the height adjustment of the support plates to prevent the bodies from shifting during transportation and ensure that the transformer is reliably fixed.

[0009] The core clamp limb shield of the series transformer body and the excitation transformer body adopts a horizontal and vertical bidirectional hybrid arrangement to increase the magnetic resistance of the leakage magnetic flux entering the structural component at the end of the body and reduce the stray loss of the clamp. The bidirectional hybrid of the core clamp limb shield effectively shields and guides the magnetic flux, achieving the purpose of controlling the leakage magnetic flux.

[0010] The series transformer body and the excitation transformer body include at least two arrangement methods: 1. When the transformer structure capacity is small, or there is no restriction on transportation, the series transformer body and the excitation transformer body are placed in the same integrated oil tank; 2. A double oil tank structure is adopted, in which one series transformer oil tank contains the series transformer body, and the other excitation transformer oil tank contains the excitation transformer body, which are connected in the middle by a Adam's apple. The phase-adjusting switch of the phase-shifting transformer is usually arranged at the end of the excitation transformer oil tank. The S end and L end of the phase-shifting transformer are each led out by three high-voltage bushings, and there is also a set of neutral point bushings of the excitation transformer; the excitation transformer phase-adjusting winding of each phase of the excitation transformer needs to be led out and connected to the voltage source converter, and the bushing or cable connector of the box cover can be used. The neutral point of the voltage source converter can be grounded nearby, or it can be led back to the series transformer oil tank through a cable and then connected to the grounding wire near the phase-shifting transformer.

[0011] The series transformer body and the excitation transformer body are placed in an integrated oil tank in parallel or T-shaped arrangement. The series transformer body and the excitation transformer body are placed in separate boxes, which is simple to operate and convenient for wiring. At the same time, placing each body in a separate box can reduce the problem of unstable center of gravity of the body.

[0012] The present invention adopts a double-core (two bodies of series transformer and excitation transformer) phase-shift transformer structure, connects the on-load phase-modulating switch and the voltage source converter in series to the side near the neutral point, thereby reducing the insulation level of the on-load phase-modulating switch and the voltage source converter, which not only reduces the comprehensive cost of the phase-shift transformer, but also makes it easier to implement in engineering through low-voltage lead interconnection. When the phase-shift transformer is at zero phase shift angle, there is still enough impedance to meet the product's short-circuit resistance requirements, and no series reactor is required.

[0013] A phase modulation method for a 220kV phase-shifting transformer combined with a voltage source converter. The phase-shifting transformer is composed of a phase-shifting transformer and an external voltage source converter. The phase-shifting transformer is composed of a series transformer and an excitation transformer connected by leads. The external voltage source converter is connected in series between the excitation transformer phase modulation winding and a neutral point through an external lead. An on-load phase-modulating switch is connected to the excitation transformer phase modulation winding and to the neutral point. The output voltage of the excitation transformer is adjusted by controlling the gear position of the on-load phase-modulating switch. The voltage is connected to the low-voltage winding of the series transformer, and is induced on the series transformer series winding of the series transformer to generate an orthogonal leading or lagging voltage difference. The voltage difference causes a phase angle change between the voltages on both sides of the line connected in series by the phase-shifting transformer. On the basis of the step-by-step discrete adjustment of the gear position of the on-load phase-modulating switch, a voltage vector within a circular domain is injected at each gear adjustment point by using the series-connected voltage source converter, and a more precise control of the phase shift angle is achieved by using the voltage source converter.

[0014] The specific steps are as follows: first, the on-load phase-modulation switch of the phase-shifting transformer is used to adjust the output of n operating points, and then the circular domain adjustment of the voltage source converter is used to make these n discrete points continuously adjustable; during discrete adjustment, the size of each phase-modulation angle range is determined by the number of turns of each stage of the excitation phase-modulation winding, and the voltage source converter is used to achieve a smaller angle of phase modulation.

[0015] The on-load phase-modulating switch is in positive and negative modulation on the neutral point side, and discrete phase angle adjustment is performed by serially inserting different numbers of phase-modulating winding turns through different switch gears. When the on-load phase-modulating switch is in extreme tapping, the number of phase-modulating winding turns serially inserted is the largest, and at this time, the discretely adjusted voltage phase angle is the largest.

[0016] When the on-load phase-modulating switch is in the positive tap, the phase angle on the L side is ahead of the S side. By gradually increasing the number of turns of the excitation phase-modulating winding, the phase angle can be gradually increased; by gradually reducing the number of turns of the excitation phase-modulating winding, the phase angle can be gradually reduced. When the on-load phase-modulating switch is in the negative tap, the phase angle on the L side lags behind the S side. By gradually increasing the number of turns of the excitation phase-modulating winding, the phase angle can be gradually increased; by gradually reducing the number of turns of the excitation phase-modulating winding, the phase angle can be gradually reduced. All phase angles adjusted by the on-load phase-modulating switch gear are discrete.

[0017] The present invention combines a large-capacity phase-shifting transformer and a small-capacity voltage source converter. The excitation of the phase-shifting transformer generates a lateral voltage with a large amplitude and discrete changes, and the voltage source converter injects a compensation voltage with a small amplitude and a phase that can be continuously changed within a 360° range. The two injected voltage vectors are synthesized to adjust the high-voltage winding voltage vector of the series unit through electromagnetic induction, thereby regulating the line flow. In this way, not only can the voltage amplitude and phase angle be adjusted in a larger range, but also only the voltage source converter can be used for adjustment within a small range.

[0018] The positive effects of the present invention are: it is applied to steady-state control and transient regulation of power flow, can adjust voltage amplitude and phase angle in a wider range, uses voltage source converter to achieve more precise control of phase shift angle, and has faster and better dynamic performance, with a response speed of milliseconds. The cost of the phase shift converter of the present invention is much lower than that of UPFC at the same capacity, and has more advantages in engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a principle diagram of an embodiment of the present invention; Figure 2 A voltage vector diagram of an embodiment of the present invention; Figure 3 This is a schematic diagram of the winding connection principle of an embodiment of the present invention; Figure 4 This is a schematic diagram of the arrangement of a single fuel tank according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the dual fuel tank arrangement according to an embodiment of the present invention; Figure 6 The series transformer of the embodiment of the present invention is connected to the excitation transformer body (integrated oil tank); Figure 7 The series transformer of the embodiment of the present invention is connected to the excitation transformer body (double oil tank); Figure 8 The series transformer of the embodiment of the present invention is fixed to the upper part of the excitation transformer; Fig. 9 Connecting the excitation variable phase winding of the embodiment of the present invention; Fig.10 It is the magnetic shielding of the limb plates at the end of the series transformer and the excitation transformer core in the embodiment of the present invention; In the figure: S end of phase shifting transformer 1, L end of phase shifting transformer 2, series transformer low voltage winding 3, series transformer series winding 4, excitation transformer excitation winding 5, excitation transformer phase modulation winding 6, on-load phase modulation switch 7, voltage source converter 8, S end voltage vector 9, L end maximum leading voltage vector 10 of switch regulation, L end maximum leading voltage vector 11 of voltage source converter compensation, L end maximum leading voltage vector 12, L end maximum lagging voltage vector 1 of switch regulation 3. Maximum lagging voltage vector 14 of the L-end of voltage source converter compensation, maximum lagging voltage vector 15 of the L-end, neutral point bushing 16 of the excitation transformer excitation winding, terminal 17 of the external voltage source converter, neutral point bushing 18 of the phase modulation system, test terminal 19, oil storage cabinet 21, cooling device 22, integrated oil tank 23, series transformer oil tank 24, excitation transformer oil tank 25, Adam's apple 26, body positioning support plate 27, core clamp limb plate shield 28. DETAILED DESCRIPTION

[0020] The present invention will be further described below through embodiments in conjunction with the accompanying drawings.

[0021] A 220kV phase-shifting transformer combined with a voltage source converter is used for steady-state control of power flow and transient regulation. It is composed of a phase-shifting transformer and an external voltage source converter. The phase-shifting transformer is composed of a series transformer and an excitation transformer connected by leads. The series transformer body of the phase-shifting transformer is composed of a three-phase iron core with a series transformer low-voltage winding 3 and a series transformer series winding 4 in each phase, and the excitation transformer body is composed of a three-phase iron core with an excitation transformer excitation winding 5 and an excitation transformer phase-modulation winding 6 in each phase. The windings in the series transformer body and the excitation transformer body are connected separately according to the connection group, and the two bodies are interconnected by high and low voltage leads or larynx; the external voltage source converter is connected in series with the excitation transformer through external leads. Between the magnetic transformer phase-modulating winding 6 and the neutral point; the on-load phase-modulating switch 7 is connected to the excitation transformer phase-modulating winding 6 and to the neutral point. The output voltage of the excitation transformer is adjusted by controlling the gear position of the on-load phase-modulating switch 7. The voltage is connected to the series transformer low-voltage winding 3, and is induced on the series transformer series winding 4 of the series transformer to generate an orthogonal leading or orthogonal lagging voltage difference. The voltage difference causes a phase angle change between the voltages on both sides of the line connected in series with the phase-shifting transformer; on the basis of the step-by-step discrete adjustment of the gear position of the on-load phase-modulating switch 7, a voltage vector within a circular domain is injected into each gear adjustment point by using the series-connected voltage source converter, and a more precise control of the phase shift angle is achieved by using the voltage source converter.

[0022] The excitation transformer body comprises an excitation transformer core, an excitation transformer excitation winding 5 and an excitation transformer phase-modulating winding 6. The excitation transformer core adopts a three-phase three-column or three-phase five-column core, and the core sheets are clamped by clamps. The body adopts an integral set structure, and the upper end is pressed by a pressing plate, and the lower end is supported by a supporting plate. A thin partition is provided to separate the large volume oil gap between the windings and the winding to the ground, thereby reducing the main insulation distance and making the excitation transformer body structure more compact. The order of arrangement of the excitation transformer windings from the core to the outside is the excitation transformer excitation winding 5 and the excitation transformer phase-modulation winding 6. The high-voltage lead wire led from the middle of the series transformer series winding is connected to one end of the excitation transformer excitation winding 5, and the other end of the excitation transformer excitation winding 5 is connected to the neutral point of the excitation transformer excitation winding; the excitation transformer phase-modulation winding 6 is star-connected, with one end connected to the delta-connected series transformer low-voltage winding, and the other end connected to the voltage source converter 8 through three bushings or the terminal 17 of the external voltage source converter and then connected to the neutral point of the phase-modulation system. The on-load phase-modulation switch 7 is arranged near the excitation transformer body for easy wiring.

[0023] The excitation variable phase-modulation winding 6 is divided into an inner phase-modulation winding and an outer phase-modulation winding; the inner phase-modulation winding is odd-numbered tapped, and the outer phase-modulation winding is even-numbered tapped. The inner phase-modulation winding and the outer phase-modulation winding are connected in sequence according to the tapping order, and the winding directions of the inner phase-modulation winding and the outer phase-modulation winding are opposite. When current passes through, the current directions between the inner phase-modulation winding and the outer phase-modulation winding and between the odd and even tapped leads are opposite, which effectively avoids the superposition of the currents of multiple tapped leads, eliminates the leakage magnetic field generated by the synthetic large current tapped leads, and avoids local overheating.

[0024] The series transformer body comprises a series transformer core, a series transformer low voltage winding 3 and a series transformer series winding 4. The series transformer core adopts a three-phase three-column or three-phase five-column core, and the core sheets are clamped by a clamp. The body adopts an integral set structure, the upper end is pressed by a pressing plate, and the lower end is supported by a supporting plate. The large volume oil gap between the windings and the winding to the ground is separated by a thin partition, thereby reducing the main insulation distance and making the series transformer body structure more compact. The series transformer windings are arranged in the order of series transformer low voltage winding 3 and series transformer series winding 4 from the core to the outside. The series transformer low voltage winding 3 is a corner connection, and the vertex leads to the on-load phase-changing switch 7 of the excitation transformer; the series transformer series winding 4 is a III connection in series with the line, and the head and end of the series transformer series winding 4 are respectively connected to the S end 1 of the phase shift transformer and the L end 2 of the phase shift transformer, and the middle leads are connected to the excitation transformer excitation winding 5 through a high-voltage lead or a throat 26.

[0025] The present invention adopts a double-core (two bodies of series transformer and excitation transformer) phase-shift transformer structure, connects the on-load phase-modulating switch 7 and the voltage source converter in series to the side near the neutral point, thereby reducing the insulation level of the on-load phase-modulating switch 7 and the voltage source converter, which not only reduces the comprehensive cost of the phase-shift transformer, but also makes it easier to implement in engineering through low-voltage lead interconnection. When the phase-shift transformer is at zero phase shift angle, there is still enough impedance to meet the product's short-circuit resistance requirements, and no series reactor is required.

[0026] The phase shifter uses a voltage source converter 8 connected in series to continuously adjust the phase shift angle at a small angle and a small amplitude. Figure 2 , the S-terminal voltage vector 9 is regulated by the on-load phase-adjusting switch 7 to the L-terminal maximum leading voltage vector 10 regulated by the switch, and a compensated voltage is obtained by adjusting the voltage source converter at the vertex of the vector, and the voltage is continuously adjustable within the circular domain. The figure shows the L-terminal maximum leading voltage vector 11 that can be compensated by the voltage source converter, and the L-terminal maximum leading voltage vector 12 is obtained by superposition; similarly, the L-terminal is regulated by the on-load phase-adjusting switch 7 to the L-terminal maximum lagging voltage vector 13 that is regulated by the switch, and a compensated voltage is obtained by adjusting the voltage source converter at the vertex of the vector, and the voltage is continuously adjustable within the circular domain. The figure shows the L-terminal maximum lagging voltage vector 14 that can be compensated by the voltage source converter, and the L-terminal maximum lagging voltage vector 15 is obtained by superposition.

[0027] When the heights of the series transformer body and the excitation transformer body are inconsistent, a double-layer support plate structure is adopted for one of the lower bodies. The support plates of the two bodies are fixed to the oil tank according to the height adjustment of the support plates to prevent the bodies from shifting during transportation and ensure that the transformer is reliably fixed.

[0028] The core clamp limb shield 28 of the series transformer body and the excitation transformer body adopts a horizontal and vertical bidirectional mixed arrangement to increase the magnetic resistance of the leakage magnetic flux entering the structural component at the end of the body and reduce the stray loss of the clamp. The bidirectional mixing of the core clamp limb shield 28 effectively plays the role of shielding and guiding the magnetic flux, achieving the purpose of controlling the leakage magnetic flux.

[0029] The series transformer body and the excitation transformer body include at least two layout methods: 1. When the transformer structure capacity is small or there is no restriction on transportation, it can be placed in the same integrated oil tank 23; 2. A double oil tank structure is adopted, in which one series transformer oil tank 24 contains the series transformer body, and the other excitation transformer oil tank 25 contains the excitation transformer body, and the middle is connected by a larynx; the phase-adjusting switch of the phase-shifting transformer is usually arranged at the end of the excitation transformer oil tank 25, and the S end and the L end of the phase-shifting transformer are each led out by three high-voltage bushings, and there is also a set of neutral point bushings of the excitation transformer; the excitation transformer phase-adjusting winding of each phase excitation transformer needs to be led out and connected to the voltage source converter, and the bushing or cable connector of the box cover can be used. The neutral point of the voltage source converter can be grounded nearby, or it can be uniformly connected to the grounding wire near the phase-shifting transformer after being led back to the series transformer oil tank 24 through a cable.

[0030] The series transformer body and the excitation transformer body are placed in the integrated oil tank 23 in parallel or T-shaped arrangement. The series transformer body and the excitation transformer body are placed in the box separately, which is simple to operate and convenient for wiring. At the same time, placing each body in the box separately can reduce the problem of unstable center of gravity of the body.

[0031] Embodiment 1: When the transformer structure capacity is small, or there is no restriction on transportation, it can be Figure 4 The series transformer body and the excitation transformer body are placed in the same oil tank, which is called an integrated oil tank 23, to save transformer space. In this case, the cooling device 22 can be arranged on both sides of the integrated oil tank 23, and only one oil storage cabinet 21 is used to adjust the volume change of the transformer oil in the integrated oil tank 23 due to temperature.

[0032] In addition, there are six high-voltage 220kV outgoing bushings including three-phase S terminals and three-phase L terminals on the top of the phase-shifting transformer tank, a neutral point bushing 16 of the excitation transformer excitation winding, three terminals 17 of external voltage source converters (using cable plug-in terminals), a neutral point bushing 18 of the phase modulation system (one or a group of neutral point bushings can be grounded nearby, or connected to the grounding wire near the phase-shifting transformer after being led back to the phase-shifting transformer tank through a cable) and four test terminals 19.

[0033] The series transformer body and the excitation transformer body can be placed in the integrated oil tank 23 in parallel or T-shaped arrangement. The series transformer body and the excitation transformer body are placed in separate boxes. The series transformer series winding 4 and the excitation transformer excitation winding 5 need to be connected. The winding method of the two windings is set as the middle outlet. When the two windings are connected, they can be connected in the middle. This connection of the two windings makes the potential of the two windings the same. Under the requirement of ensuring the installation distance of the two bodies, the distance between the bodies can be minimized, and the insulation level of the two windings can be effectively guaranteed. At the same time, the series transformer and the excitation transformer are placed in the box and then connected. This operation is simple and convenient for wiring. At the same time, each body is placed in a separate box to reduce the problem of unstable center of gravity of the body.

[0034] Embodiment 2: When the transformer structure capacity is large or there are restrictions on transportation, Figure 5 The series transformer body and the excitation transformer body are placed in separate oil tanks, namely the series transformer oil tank 24 and the excitation transformer oil tank 25, respectively, and the leads between the series transformer body and the excitation transformer body are connected through the Adam's apple 26. At this time, the cooling device 22 can be arranged on both sides of the series transformer oil tank 24 and the excitation transformer oil tank 25, and two independent oil storage cabinets 21 are used to adjust the volume change of the transformer oil in the series transformer oil tank 24 and the excitation transformer oil tank 25 caused by the temperature.

[0035] When the series transformer and the excitation transformer are in two independent oil tanks, the series transformer oil tank 24 and the excitation transformer oil tank 25 need to be connected by leads. The connecting leads outside the series transformer oil tank 24 and the excitation transformer oil tank 25 are assembled in an independent bus box, and the bus box is installed between the series transformer and the excitation transformer and connected as a whole. This connection device is a larynx 26. The larynx 26 realizes the lead connection between the series transformer and the excitation transformer in a small space, simplifying the overall structure of the double-body phase-shifting transformer. At the same time, the larynx 26 is sealed with the series transformer oil tank 24 and the excitation transformer oil tank 25, which is convenient for actual operation.

[0036] Due to the limitation of transportation height and the requirement of reducing leakage flux density, it is impossible to ensure the same height of the series transformer body and the excitation transformer body. A double-layer support plate structure is used for one of the lower height transformer bodies. The lower support plate fixes the core sheet clamp of the transformer body, and the upper support plate height matches the other transformer body. According to the height adjustment of the support plate, the support plates of the two transformer bodies are fixed to the oil tank to prevent the transformer body from shifting during transportation, ensure the reliable fixation of the transformer, and make the transformer reliable.

[0037] A zinc oxide lightning arrester is used between each tap lead of the inner phase-adjusting winding and the outer phase-adjusting winding to suppress the oscillating potential between taps under impulse voltage, thereby protecting the inner phase-adjusting winding, the outer phase-adjusting winding and the tap leads. The zinc oxide lightning arrester is fixed near the corresponding tap wire, so that the connection structure between the tap wire and the zinc oxide lightning arrester lead is simple, and the insulation distance is easy to ensure. The number of tap leads of the inner phase-adjusting winding and the outer phase-adjusting winding is large, and the leads adopt a rectangular frame clamping structure. This structure can arrange the three-phase tap leads in layers and staggered inside and outside. This arrangement can effectively avoid crossing between tap leads of different phases, and effectively ensure the insulation distance of the leads between phases.

[0038] A current transformer for protection is arranged on the excitation transformer excitation winding 5, and is installed between the vertical bars using a horizontal conductor clamp. If space permits, it has the advantages of easy operation, stable installation, and is not affected by manufacturing tolerances and installation tolerances. The space between the upper clamp and the oil tank is used for horizontal stacking installation, and is fastened with steel screws and laminated cardboard fixing plates and fixed on the web of the clamp. This method is conducive to lead routing and reasonable use of limited space.

[0039] The cores of the series transformer and the excitation transformer are both three-column structures. For the three-column core, the winding ends of the two side columns have very little area covered by the core, and most of the leakage magnetic flux at the ends will enter the oil tank, the core, the clamps and other structural parts, resulting in large losses and the risk of local overheating. As a result, a large amount of leakage magnetic flux in the parts of the two side columns where the body is located without an iron yoke is difficult to control. The cores of the series transformer and the excitation transformer both use the core clamp limb plate shield 28, which is a horizontal and vertical bidirectional mixed arrangement, reducing the magnetic flux saturation on a single set of limb plate shields, increasing the magnetic resistance on the path of the leakage magnetic flux at the end of the body entering the structural parts, and reducing the stray loss of the clamp. The core clamp limb plate shield 28 is bidirectionally mixed, effectively shielding and guiding the magnetic flux, and achieving the purpose of controlling leakage magnetic flux. The core clamp limb plate shield 28 has the characteristics of simple manufacturing and convenient installation, and the material can be selected from the scraps of electrical steel strips, saving costs.

[0040] A phase-modulating method for a 220kV phase-shifting transformer combined with a voltage source converter, wherein the phase-shifting transformer is composed of a phase-shifting transformer and an external voltage source converter, wherein the phase-shifting transformer is composed of a series transformer and an excitation transformer connected by leads, wherein the external voltage source converter is connected in series between an excitation transformer phase-modulating winding 6 and a neutral point through an external lead; an on-load phase-modulating switch 7 is connected to the excitation transformer phase-modulating winding 6 and to the neutral point, and the output voltage of the excitation transformer is adjusted by controlling the gear position of the on-load phase-modulating switch 7. The voltage is connected to the low-voltage winding 3 of the series transformer, and is induced on the series transformer winding 4 of the series transformer to generate an orthogonal leading or lagging voltage difference, which causes a phase angle change between the voltages on both sides of the line connected in series with the phase-shifting transformer; on the basis of the step-by-step discrete adjustment of the gear position of the on-load phase-modulating switch 7, a voltage vector within a circular domain is injected into each gear adjustment point by using the series-connected voltage source converter, and more precise control of the phase shift angle is achieved by using only the voltage source converter.

[0041] Specific steps: first use the on-load phase-modulation switch of the phase-shifting transformer to adjust the output n operating points, and then use the circular domain adjustment of the voltage source converter to make these n discrete points become continuously adjustable; during discrete adjustment, the size of each gear phase-modulation angle range is determined by the number of turns per stage of the excitation phase-modulation winding 6, and the voltage source converter is used to achieve a smaller angle of phase modulation.

[0042] The present invention combines a large-capacity phase-shifting transformer and a small-capacity voltage source converter. The excitation of the phase-shifting transformer generates a lateral voltage with a large amplitude and discrete changes, and the voltage source converter injects a compensation voltage with a small amplitude and a phase that can be continuously changed within a 360° range. The two injected voltage vectors are synthesized to adjust the high-voltage winding voltage vector of the series unit through electromagnetic induction, thereby regulating the line flow. In this way, not only can the voltage amplitude and phase angle be adjusted in a larger range, but also only the voltage source converter can be used for adjustment within a small range.

[0043] The on-load phase-modulating switch 7 is in positive and negative modulation on the side close to the neutral point, and discrete phase angle adjustment is performed by serially inserting different numbers of phase-modulating winding turns through different switch gears. When the on-load phase-modulating switch 7 is in extreme tapping, the number of phase-modulating winding turns serially inserted is the largest, and at this time, the discretely adjusted voltage phase angle is the largest.

[0044] When the on-load phase-modulating switch 7 is in the positive tap, the phase angle on the L side is ahead of the S side. By gradually increasing the number of turns of the excitation phase-modulating winding 6, the phase angle can be gradually increased; by gradually reducing the number of turns of the excitation phase-modulating winding 6, the phase angle can be gradually reduced. When the on-load phase-modulating switch 7 is in the negative tap, the phase angle on the L side lags behind the S side. By gradually increasing the number of turns of the excitation phase-modulating winding 6, the phase angle can be gradually increased; by gradually reducing the number of turns of the excitation phase-modulating winding 6, the phase angle can be gradually reduced. All phase angles adjusted by the gear position of the on-load phase-modulating switch 7 are discrete.

Claims

1. A 220kV phase-shifting transformer combined with a voltage source converter, applied to steady-state power flow control and transient regulation, characterized in that: The phase-shifting transformer is composed of a phase-shifting transformer and an external voltage source converter. The phase-shifting transformer is composed of two bodies, a series transformer and an excitation transformer, connected by leads. The series transformer body of the phase-shifting transformer is composed of a three-phase iron core with a series transformer low-voltage winding (3) and a series transformer series winding (4) in each phase. The excitation transformer body is composed of a three-phase iron core with an excitation transformer excitation winding (5) and an excitation transformer phase modulation winding (6) in each phase. The windings in the series transformer body and the excitation transformer body are connected separately according to the connection group. The two bodies are interconnected by high and low voltage leads or larynx. The external voltage source converter is connected in series between the excitation transformer phase modulation winding (6) and the neutral point through external leads. The on-load phase modulation switch (7) is connected to the excitation transformer phase-modulating winding (6) and to the neutral point, and the output voltage of the excitation transformer is adjusted by controlling the gear position of the on-load phase-modulating switch (7). The voltage is connected to the low-voltage winding (3) of the series transformer, and is induced on the series transformer series winding (4) of the series transformer to generate an orthogonal leading or lagging voltage difference, which causes a phase angle change between the voltages on both sides of the line connected in series with the phase-shifting transformer; on the basis of the step-by-step discrete adjustment of the gear position of the on-load phase-modulating switch (7), a voltage vector within a circular domain is injected into each gear adjustment point by using the series-connected voltage source converter, and a more precise control of the phase shift angle is achieved by using the voltage source converter.

2. A 220kV phase-shifting transformer combined with a voltage source converter according to claim 1, characterized in that: The excitation transformer body comprises an excitation transformer core, an excitation transformer excitation winding (5) and an excitation transformer phase modulation winding (6); the excitation transformer core adopts a three-phase three-column type or a three-phase five-column type core, the core sheets are clamped by clamps, the body adopts an integral set structure, the upper end is pressed by a pressing plate, the lower end is supported by a supporting plate, and a thin partition is provided to separate the large volume oil gap between the windings and the winding to the ground; the excitation transformer windings are arranged in the order of the excitation transformer excitation winding (5) and the excitation transformer phase modulation winding (6) from the core outward. ), a high voltage lead from the middle of the series transformer series winding is connected to one end of the excitation transformer excitation winding (5), and the other end of the excitation transformer excitation winding (5) is connected to the neutral point of the excitation transformer excitation winding; the excitation transformer phase modulation winding (6) is star-connected, one end is connected to the delta-connected series transformer low voltage winding, and the other end is connected to the voltage source converter (8) through three bushings or the terminal (17) of the external voltage source converter and then connected to the neutral point of the phase modulation system. The on-load phase modulation switch (7) is arranged near the excitation transformer body.

3. A 220kV phase-shifting transformer combined with a voltage source converter according to claim 1 or 2, characterized in that: The excitation variable phase-modulation winding (6) is divided into an inner phase-modulation winding and an outer phase-modulation winding; the inner phase-modulation winding is odd-numbered tapped, and the outer phase-modulation winding is even-numbered tapped; the inner phase-modulation winding and the outer phase-modulation winding are connected in sequence according to the tapping order, and the inner phase-modulation winding and the outer phase-modulation winding are wound in opposite directions.

4. A 220kV phase-shifting transformer combined with a voltage source converter according to claim 1 or 2, characterized in that: The series transformer body comprises a series transformer core, a series transformer low-voltage winding (3) and a series transformer series winding (4). The series transformer core adopts a three-phase three-column or three-phase five-column core, the core sheets are clamped by a clamp, the body adopts an integral set structure, the upper end is pressed by a pressing plate, the lower end is supported by a supporting plate, and a thin partition is provided to separate the large volume oil gap between the windings and the winding to the ground; the series transformer windings are arranged in the order of the series transformer low-voltage winding (3) and the series transformer series winding (4) from the core outward, the series transformer low-voltage winding (3) is a corner connection, and the vertex is connected to the on-load phase-changing switch (7) of the excitation transformer; the series transformer series winding (4) is a III connection in series with the line, the head and end of the series transformer series winding (4) are respectively connected to the S end (1) and the L end (2) of the phase shift transformer, and the middle part is connected to the excitation transformer excitation winding (5) through a high-voltage lead or a throat (26).

5. A 220kV phase-shifting transformer combined with a voltage source converter according to claim 1 or 2, characterized in that: the transformer When the structural capacity is small, or when there is no restriction on transportation, the series transformer body and the excitation transformer body are placed in the same integrated oil tank (23).

6. A 220kV phase-shifting transformer combined with a voltage source converter according to claim 1 or 2, characterized in that: A double oil tank structure is adopted, wherein one series oil tank (24) contains the series transformer body, and the other excitation oil tank (25) contains the excitation transformer body, and the two are connected in the middle by a Adam's apple.

7. A phase adjustment method for a 220kV phase-shifting transformer combined with a voltage source converter, characterized in that: The phase-shifting transformer is composed of a phase-shifting transformer and an external voltage source converter. The phase-shifting transformer is composed of a series transformer and an excitation transformer connected by leads. The external voltage source converter is connected in series between an excitation transformer phase-modulation winding (6) and a neutral point through external leads. An on-load phase-modulation switch (7) is connected to the excitation transformer phase-modulation winding (6) and to the neutral point. The output voltage of the excitation transformer is adjusted by controlling the gear position of the on-load phase-modulation switch (7). The voltage is connected to the series transformer low-voltage winding (3), and is induced on the series transformer series winding (4) of the series transformer to generate an orthogonal leading or lagging voltage difference. The voltage difference causes a phase angle change between the voltages on both sides of the line connected in series by the phase-shifting transformer. On the basis of the step-by-step discrete adjustment of the gear position of the on-load phase-modulation switch (7), a voltage vector within a circular domain is injected into each gear adjustment point by using the series-connected voltage source converter, and more accurate control of the phase shift angle is achieved by using the voltage source converter.

8. A phase adjustment method for a 220kV phase-shifting transformer combined with a voltage source converter according to claim 7, characterized in that The specific steps are as follows: first, the on-load phase-modulation switch of the phase-shifting transformer is used to adjust the output n operating points, and then the circular domain adjustment of the voltage source converter is used to make these n discrete points continuously adjustable; during discrete adjustment, the size of each phase-modulation angle range is determined by the number of turns of each stage of the excitation phase-modulation winding (6), and the voltage source converter is used to achieve a smaller angle of phase modulation.

9. A phase modulation method of a 220 kV phase-shifting transformer combined with a voltage source converter according to claim 7, characterized in that: The on-load phase-modulating switch (7) is in positive and negative modulation on the side close to the neutral point, and discrete phase angle adjustment is performed by serially inserting different numbers of phase-modulating winding turns through different switch gears. When the on-load phase-modulating switch (7) is in extreme tapping, the number of phase-modulating winding turns serially inserted is the largest, and at this time, the discretely adjusted voltage phase angle is the largest.

10. A phase modulation method of a 220 kV phase-shifting transformer combined with a voltage source converter according to claim 7, characterized in that: When the on-load phase-modulating switch (7) is in a positive tapping state, the phase angle on the L side is ahead of the S side. By gradually increasing the number of turns of the excitation phase-modulating winding (6), the phase angle can be gradually increased; by gradually reducing the number of turns of the excitation phase-modulating winding (6), the phase angle can be gradually reduced; when the on-load phase-modulating switch (7) is in a negative tapping state, the phase angle on the L side lags behind the S side. By gradually increasing the number of turns of the excitation phase-modulating winding (6), the phase angle can be gradually increased; by gradually reducing the number of turns of the excitation phase-modulating winding (6), the phase angle can be gradually reduced.

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