A phase shifter

Abstract

The present invention discloses a phase shifter, comprising: a three-winding transformer and a series isolation transformer connected in series; the three-winding transformer comprises a plurality of primary windings, a plurality of secondary windings and a plurality of adjustable secondary windings, wherein the plurality of primary windings and the plurality of secondary windings are respectively connected in star shape and grounded through a neutral point; the primary side of the series isolation transformer is respectively connected in series with the plurality of adjustable secondary windings, and the secondary side of the series isolation transformer is respectively connected in series with the plurality of secondary windings. The present invention integrates voltage transformation, power transmission and power flow control, reduces the installation cost of the phase shifting transformer, and saves the floor space of the substation.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission lines, and in particular to a phase shifter. Background Art

[0002] There are multiple branches operating in parallel in the power system. Under this operating mode, a loop will be formed between these parallel branches. The impedance distribution of these parallel branches is uneven and there are differences, which will lead to unbalanced loads between lines. Some lines are underloaded and some lines are overloaded. In addition, circulating currents will be generated in these loops, reducing the effective utilization rate of transmission lines.

[0003] Phase Shifting Transformer (PST) is a power flow control device that changes the amplitude and phase difference of the voltage on both sides of the line by superimposing a suitable voltage vector on the original voltage of the line, thereby changing the line transmission power and controlling the power flow distribution, avoiding overload and underload of the transmission line or transformer main equipment, and improving power supply reliability. By switching the tap of the transformer secondary winding with the on-load tap changer, the output of the series compensation voltage with adjustable phase and amplitude can be achieved, thereby realizing the control of the system power flow.

[0004] The traditional phase-shifting transformer consists of an excitation transformer and a series transformer, which are installed on two independent cores and in two independent transformer oil tanks. However, the wiring method of the traditional phase-shifting transformer requires an additional excitation transformer on the busbar, which occupies the substation space and even requires the expansion of the substation, increasing the investment cost of the phase-shifting transformer. Especially when the voltage level and capacity are high, the excitation transformer and the series transformer cannot be installed in the same transformer oil tank, and each transformer oil tank needs to be installed independently, which greatly increases the cost and floor space. Summary of the invention

[0005] The object of the present invention is to provide a phase shifter to solve the problem of high installation cost of traditional phase shifting transformers.

[0006] To achieve the above object, the present invention provides a phase shifter, comprising: a three-winding transformer and a series isolation transformer connected in series;

[0007] The three-winding transformer comprises a plurality of primary windings, a plurality of secondary windings and a plurality of adjustable secondary windings, wherein the plurality of primary windings and the plurality of secondary windings are respectively connected in star shape and grounded through a neutral point;

[0008] The primary side of the series isolation transformer is respectively connected in series with the plurality of the adjustable secondary windings, and the secondary side of the series isolation transformer is respectively connected in series with the plurality of the secondary windings.

[0009] Preferably, each phase circuit comprises one primary winding, one secondary winding and three adjustable secondary windings;

[0010] The primary winding and the secondary winding of each phase constitute a transformer unit, and the transformer unit is used for the main transformer of the substation to provide the voltage of the secondary winding before compensation;

[0011] The three adjustable secondary windings per phase are respectively connected in series with the primary side of the series isolation transformer, the secondary side of the series isolation transformer is connected in series in each phase bus of the substation, and the three adjustable secondary windings per phase and the series isolation transformer constitute a phase shifting unit, and the phase shifting unit is used to provide a series compensation voltage in each phase line;

[0012] The transformer unit is connected to the phase shift unit, and adds the voltage of the secondary winding before compensation to the series compensation voltage in each phase line to obtain the head end voltage of each phase transmission line after compensation.

[0013] Preferably, the three adjustable secondary windings in each phase are connected in series in sequence, the winding voltages of the adjustable secondary windings connected in series in sequence are added, and the winding voltage is injected into the corresponding phase line through the series isolation transformer to obtain the corresponding phase series compensation voltage.

[0014] Preferably, the corresponding phase series compensation voltage formula is:

[0015] U Δi =U a +U b +U c ;

[0016] Where U Δi represents the series compensation voltage in the i-th phase line, U a ,U b ,U c Respectively represent the three winding voltages of the adjustable secondary winding.

[0017] Preferably, the voltage formula of the first end of each phase of the transmission line after compensation is:

[0018] U Si =U a0 +U Δi ;

[0019] Where U Si represents the voltage at the head end of the i-th phase transmission line after compensation, U a0 Represents the voltage of the secondary winding before compensation.

[0020] Preferably, it further comprises a circuit breaker, the primary winding is connected to the incoming line of the substation via the circuit breaker, and the secondary winding is connected to the busbar of the substation via the circuit breaker.

[0021] Preferably, the circuit breaker comprises a bypass switch connected to a busbar of the substation, and the bypass switch is used to control the operating states of the transformer unit and the phase shift unit.

[0022] Preferably, when the bypass switch is closed, the phase shift unit does not operate, and the transformer unit is used as a main transformer in a substation;

[0023] When the bypass switch is disconnected, the phase shift unit and the transformer unit operate simultaneously, and the series interval transformer in the phase shift unit provides the series compensation voltage in each phase line and injects it into the line for phase shifting.

[0024] Preferably, the series isolation transformer is connected to the outgoing line of the substation via the bypass switch, and the transformation ratio of the series isolation transformer is 1:1.

[0025] Preferably, it also includes an on-load voltage-regulating switch, which is arranged on the adjustable secondary winding. By controlling the switching position of the on-load voltage-regulating switch, the winding voltage provided by each adjustable secondary winding can be adjusted in three ranges: positive, zero and negative.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The phase shifter includes a three-winding transformer and a series isolation transformer connected in series. The three-winding transformer includes multiple primary windings, multiple secondary windings and multiple adjustable secondary windings, wherein the multiple primary windings and multiple secondary windings are respectively connected in star shape and grounded through a neutral point. The primary side of the series isolation transformer is respectively connected in series with multiple adjustable secondary windings, and the secondary side of the series isolation transformer is respectively connected in series with multiple secondary windings. It can simultaneously realize the functions of voltage transformation, power transmission and flow control. Compared with the prior art, it can replace the main transformer of the substation to realize the functions of voltage transformation and power transmission, and can also realize the function of flow control, eliminating the excitation transformer in the traditional phase shifting transformer, saving costs, reducing floor space, and making the construction of the substation and the layout of equipment more flexible. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the implementation mode will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 is a schematic diagram of the topological structure of a phase shifter provided by an embodiment of the present invention;

[0030] Figure 2 is a schematic diagram of a topological structure of a phase shifter provided by another embodiment of the present invention;

[0031] Figure 3 is a vector diagram of the output voltage on the series side of an improved phase-shifting transformer provided by another embodiment of the present invention;

[0032] Figure 4 A method of connecting an improved phase-shifting transformer to a power grid provided by a certain embodiment of the present invention;

[0033] Figure 5 is a schematic diagram of a phase A topology structure provided by another embodiment of the present invention;

[0034] Figure 6 It is a schematic diagram of the phase shift range of phase A of an improved phase shifting transformer provided in yet another embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0037] It should be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0038] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0039] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0040] See also Figure 1A certain embodiment of the present invention provides a phase shifter, comprising: a three-winding transformer and a series isolation transformer connected in series, the three-winding transformer comprising a plurality of primary windings, a plurality of secondary windings and a plurality of adjustable secondary windings, wherein the plurality of primary windings and the plurality of secondary windings are respectively connected in star shape and grounded through a neutral point, the primary side of the series isolation transformer is respectively connected in series with the plurality of adjustable secondary windings, and the secondary side of the series isolation transformer is respectively connected in series with the plurality of secondary windings.

[0041] The three-winding transformer includes three primary windings and three secondary windings for voltage transformation and power transmission, and nine secondary windings with load voltage regulation function, which includes three primary windings and 12 secondary windings in total. Each phase has one main winding and four secondary windings. The four secondary windings include three adjustable secondary windings and one secondary winding. The primary winding and secondary winding responsible for voltage transformation and power transmission can realize the function of the main transformer of the substation. The adjustable secondary winding and the series isolation transformer can realize the function of power flow control. The three-phase winding transformer is connected to the incoming line of the substation and is responsible for providing voltage transformation and power transmission functions. The series isolation transformer is connected to the outgoing line of the substation that needs phase shifting. The transformation ratio is 1:1 and is responsible for injecting the series compensation voltage into the transmission line.

[0042] The function of the main transformer of the substation can be realized by the primary winding and secondary winding responsible for voltage transformation and power transmission, and the function of power flow control can be realized by the adjustable secondary winding and the series isolation transformer, and the phase shifting unit can be constructed. Specifically, the three adjustable secondary windings of each phase are respectively connected in series with the primary side of the series isolation transformer, and the secondary side of the series isolation transformer is connected in series in each phase bus of the substation. The three adjustable secondary windings of each phase and the series isolation transformer constitute a phase shifting unit. The phase shifting unit is used to provide a series compensation voltage in each phase line. The transformer unit is connected to the phase shifting unit, and the voltage of the secondary winding before compensation is added to the series compensation voltage in each phase line to obtain the head end voltage of each phase transmission line after compensation.

[0043] The corresponding phase series compensation voltage formula is:

[0044] U Δi =U a +U b +U c ;

[0045] Where U Δi represents the series compensation voltage in the i-th phase line, U a ,U b ,U c Respectively represent the three winding voltages of the adjustable secondary winding.

[0046] The voltage formula of the first end of each phase transmission line after compensation is:

[0047] USi =U a0 +U Δi ;

[0048] Where U Si represents the voltage at the head end of the i-th phase transmission line after compensation, U a0 Indicates the voltage of the secondary winding before compensation.

[0049] See also Figure 2 The topological structure of the improved phase-shifting transformer takes a three-phase line as an example, where the primary winding is A, B, C, the secondary winding is a0, b0, c0, and the adjustable secondary winding is a1, a2, a3, b1, b2, b3, c1, c2, c3. The topological structure of the improved phase-shifting transformer consists of a transformer unit and a phase-shifting unit. The transformer unit consists of a primary winding of A, B, C and a secondary winding of a0, b0, c0. The primary windings of A, B, C and the secondary windings of a0, b0, c0 are all star-connected, and the neutral point is directly grounded. The transformer function is realized according to the transformation ratio, and it can be used as the main transformer of the substation.

[0050] The phase shift unit is mainly composed of adjustable secondary windings a1, a2, a3, b1, b2, b3, c1, c2, c3 and a series isolation transformer. Among them, the secondary windings c1, b1, a1 are connected in series in sequence, the voltages on c1, b1, a1 are added, and injected into the A phase line through the series isolation transformer to obtain the series compensation voltage U of the A phase transmission line. ΔA , the secondary windings c2, b2, and a2 are connected in series in sequence, the voltages on c2, b2, and a2 are added, and injected into the B phase line through the series isolation transformer to obtain the series compensation voltage U of the B phase transmission line ΔB , the secondary windings c3, b3, and a3 are connected in series in sequence, the voltages on c3, b3, and a3 are added, and injected into the C phase line through the series isolation transformer to obtain the series compensation voltage U of the C phase transmission line ΔC The transformation ratio of the series isolation transformer is 1:1, its primary side is connected to the adjustable secondary winding, and the secondary side is directly connected in series in each phase line.

[0051] The winding voltages provided by the adjustable secondary windings a1, b1, c1, a2, b2, c2, a3, b3, and c3 are respectively denoted as U a1 , U b1 , U c1 , U a2 , U b2 , U c2 , U a3 , U b3 , U c3 , the series compensation voltage in the three-phase line is:

[0052] U ΔA =Ua1 +U b1 +U c1

[0053] U ΔB =U a2 +U b2 +Uc2;

[0054] U ΔC =U a3 +U b3 +U c3

[0055] The voltage before compensation is the voltage U on the secondary winding a0, b0, c0 a0 , U b0 , U c0 , the line head end voltage after compensation is U Sa , U Sb , U Sc The voltage expression of the first end of the transmission line after compensation is:

[0056] U Sa =U a0 +U ΔA =U a0 +U a1 +U b1 +U c1

[0057] U Sb =U b0 +U ΔB =U b0 +U a2 +U b2 +U c2 ;

[0058] U Sc =U c0 +U ΔC =U c0 +U a3 +U b3 +U c3

[0059] The on-load voltage regulating switch can be switched within the range of (0, ±1, ±2, ..., ±m). The on-load voltage regulating switch is set on the adjustable secondary winding. By controlling the switching position of the on-load voltage regulating switch, the winding voltage provided by each adjustable secondary winding can be adjusted in the positive, zero and negative ranges.

[0060] See also Figure 3According to the vector diagram of the output voltage on the series side of the improved phase-shifting transformer, to maintain the three-phase voltage balance at the head end of the system after compensation, the on-load voltage regulators of the adjustable secondary windings a1, b2, and c3 need to be adjusted to the same position, the on-load voltage regulators of the adjustable windings b1, c2, and a3 need to be adjusted to the same position, and the on-load voltage regulators of the adjustable secondary windings c1, a2, and b3 need to be adjusted to the same position. The positions of the on-load voltage regulators can be different between the three groups a1-b2-c3, b1-c2-a3, and c1-a2-b3, so that the three windings in the same group can provide voltages of different amplitudes, and can be superimposed to obtain series compensation voltages of different amplitudes and phases.

[0061] As the number of adjustment levels increases, the number of series compensation voltage vectors that can be output also increases. When the on-load voltage regulator can be adjusted at the (0, ±1, ±2, …, ±m) level, the number of series compensation voltage vectors that can be output is M:

[0062] M=3m 2 +3m+1;

[0063] The improved phase-shifting transformer is three-phase symmetrical. Taking phase A as an example, the tap switching positions of the secondary windings a1, b1 and c1 are respectively denoted as k a , k b , k c The voltage vectors between adjacent taps of the secondary windings a1, b1 and c1 are respectively denoted as U astep , U bstep and U cstep , the expression of the output voltage on the series side is:

[0064] U ΔA =U a1 +U b1 +U c1 =k a U astep +k b U bstep +k c U cstep

[0065] U ΔB =U a2 +U b2 +U c2 =k a U bstep +k b U cstep +k c U astep ;

[0066] U ΔB =U a3 +U b3 +U c3=k a U cstep +k b U astep +k c U bstep

[0067] See also Figure 4 , it can be seen from the way the improved phase-shifting transformer is connected to the power grid that the three-winding transformer is connected to the incoming line end of the substation. In the transformer unit, the primary windings A, B, C and the secondary windings a0, b0, c0 are installed in the three-winding transformer body to realize the function of the main transformer of the substation. In the phase-shifting unit, the adjustable secondary windings a1, b1, c1, a2, b2, c2, a3, b3, c3 are arranged in the three-winding transformer body to obtain the power required for phase shifting from the primary winding. The series transformer can be installed on any outgoing line as needed to realize the phase shifting function for the line. The series transformer is provided with a bypass switch, which can make the series transformer exit operation when a fault occurs or when phase shifting is not required. At this time, the improved phase-shifting transformer is only used as the main transformer of the substation. When the bypass switch is closed, the phase-shifting transformer does not operate, and the transformer unit is used as the main transformer of the substation. When the bypass switch is disconnected, the phase-shifting unit and the transformer unit operate simultaneously. The series interval transformer in the phase-shifting unit provides the series compensation voltage in each phase line and injects it into the line for phase shifting.

[0068] See also Figure 5 , take phase A as an example to enlarge the structure. The three-winding transformer body is arranged on the incoming line side of the substation, and the transformer unit is installed in the three-winding transformer body. The primary winding A is connected to the incoming line through a circuit breaker, and the secondary winding a0 is connected to the substation bus through a circuit breaker. The adjustable secondary windings c1, b1, and a1 are connected in series in sequence to form an open triangle, and the opening is connected to both ends of the A-phase winding on the primary side of the series isolation transformer. The secondary side of the series isolation transformer is directly connected in series in the A-phase line of the substation outgoing line, and the series compensation voltage U of the A-phase is increased. ΔA When the bypass switch is closed, the phase-shifting unit of the improved phase-shifting transformer loses its function, and only the transformer unit works. At this time, only the main transformer function of the substation is realized. When the bypass switch is disconnected, the phase-shifting unit of the improved phase-shifting transformer works, and the series isolation transformer injects the series compensation voltage into the line to realize the phase-shifting function. At this time, the improved phase-shifting transformer is used as the main transformer of the substation and the line phase-shifting transformer at the same time.

[0069] Taking phase A as an example, some rated parameters of the improved phase-shifting transformer are given as follows:

[0070] Improved phase-shifting transformer primary side rated voltage U T1 Take the substation incoming line rated voltage U N1 :

[0071]

[0072] Improved phase-shifting transformer secondary rated voltage U T2 Take the substation bus rated voltage U N2 :

[0073]

[0074] See also Figure 6 , we can know the phase shift range of phase A of the improved phase shift transformer, where U a0 is the phase voltage of phase A before phase shift, U Sa is the phase voltage in the A phase line after phase shift, α is the phase shift angle, U sN is the rated voltage on the secondary regulating winding.

[0075] Assuming the maximum phase shift angle required by the system is α, the calculation formula is as follows:

[0076]

[0077] Among them, the calculation formula for the rated voltage on the adjustable secondary winding is as follows:

[0078]

[0079] The transformation ratio of the series isolation transformer is 1:1, and the maximum series compensation voltage U injected into the line by the series transformer Δmax Equal to the rated voltage U of the secondary voltage regulating winding sN :

[0080] U Δmax =U sN ;

[0081] The rated current of the secondary side of the series isolation transformer is equal to the rated current I of the line where the series transformer is installed. N :

[0082] I n2 =I N ;

[0083] Rated capacity S of series isolation transformer 2 for:

[0084] S 2 =3U Δmax I N ;

[0085] The rated capacity S of the transformer part of the improved phase-shifting transformer is equal to the rated transmission capacity S of the line where it is located. N :

[0086]

[0087] Therefore, the total capacity of the improved phase-shifting transformer is S T Main transformer capacity S 1 Rated capacity S of the series isolation transformer 2 sum:

[0088] S T =S 1 +S 2 ;

[0089] An improved phase-shifting transformer provided by the present invention can simultaneously realize the functions of voltage transformation, power transmission and flow control. Compared with the prior art, it can replace the main transformer of the substation to realize the functions of voltage transformation and power transmission, and can also realize the function of flow control. It eliminates the excitation transformer in the traditional phase-shifting transformer, saves costs, reduces floor space, and makes the construction of the substation and the layout of equipment more flexible.

[0090] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A phase shifter, characterized in that: include: Three-winding transformers connected in series and series isolation transformers; The three-winding transformer comprises a plurality of primary windings, a plurality of secondary windings and a plurality of adjustable secondary windings, wherein the plurality of primary windings and the plurality of secondary windings are respectively connected in star shape and grounded through a neutral point; The primary side of the series isolation transformer is respectively connected in series with the plurality of the adjustable secondary windings, and the secondary side of the series isolation transformer is respectively connected in series with the plurality of the secondary windings; Each phase circuit comprises one primary winding, one secondary winding and three adjustable secondary windings; The primary winding and the secondary winding of each phase constitute a transformer unit, and the transformer unit is used for the main transformer of the substation to provide the voltage of the secondary winding before compensation; The three adjustable secondary windings per phase are respectively connected in series with the primary side of the series isolation transformer, the secondary side of the series isolation transformer is connected in series in each phase bus of the substation, and the three adjustable secondary windings per phase and the series isolation transformer constitute a phase shifting unit, and the phase shifting unit is used to provide a series compensation voltage in each phase line; The transformer unit is connected to the phase shift unit, and adds the voltage of the secondary winding before compensation to the series compensation voltage in each phase line to obtain the head end voltage of each phase transmission line after compensation.

2. The phase shifter according to claim 1, characterized in that: The three adjustable secondary windings of each phase are connected in series in sequence, the winding voltages of the adjustable secondary windings connected in series in sequence are added, and the winding voltage is injected into the corresponding phase line through the series isolation transformer to obtain the corresponding phase series compensation voltage.

3. The phase shifter according to claim 2, characterized in that: The corresponding phase series compensation voltage formula is: IN Δi =U a +U b +U c ; Where U Δi represents the series compensation voltage in the i-th phase line, U a ,U b ,U c Respectively represent the three winding voltages of the adjustable secondary winding.

4. The phase shifter according to claim 3, characterized in that: The voltage formula of the first end of each phase transmission line after compensation is: IN Si =U a0 +U Δi ; Where U Si represents the voltage at the head end of the i-th phase transmission line after compensation, U a0 Represents the voltage of the secondary winding before compensation.

5. The phase shifter according to claim 1, characterized in that: It also includes a circuit breaker, the primary winding is connected to the transformer substation incoming line via the circuit breaker, and the secondary winding is connected to the transformer substation bus via the circuit breaker.

6. The phase shifter according to claim 5, characterized in that The circuit breaker comprises a bypass switch connected to the busbar of the transformer substation, and the bypass switch is used to control the operating status of the transformer unit and the phase shift unit.

7. The phase shifter according to claim 6, characterized in that: When the bypass switch is closed, the phase shift unit does not operate, and the transformer unit is used for the main transformer of the substation; When the bypass switch is disconnected, the phase shift unit and the transformer unit operate simultaneously, and the series interval transformer in the phase shift unit provides the series compensation voltage in each phase line and injects it into the line for phase shifting.

8. The phase shifter according to claim 7, characterized in that The series isolation transformer is connected to the outgoing line of the substation via the bypass switch, and the transformation ratio of the series isolation transformer is 1:

1.

9. The phase shifter according to claim 1, characterized in that: It also includes an on-load voltage-regulating switch, which is arranged on the adjustable secondary winding. By controlling the switching position of the on-load voltage-regulating switch, the winding voltage provided by each adjustable secondary winding can be adjusted in three ranges: positive, zero and negative.

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