A mechanical and electrical hybrid on-load tap-changer and its timing control method

Abstract

The present invention discloses an electromechanical hybrid on-load tap-changer and its timing control method, which relates to the technical field of tap-changers. It includes: a first mechanical switch, a second mechanical switch, a first disconnector and a first thyristor connected in series with each other, and a second disconnector and a second thyristor connected in series with each other; a first transition resistor is connected in parallel across the first thyristor, and a second transition resistor is connected in parallel across the second thyristor; one end of the first mechanical switch and one end of the first disconnector are both connected to the first tap of the transformer, and the other end of the mechanical switch is respectively connected to one end of the second thyristor and one end of the load resistor. One end of the second mechanical switch and one end of the second disconnector are both connected to the second tap of the transformer, and the other end of the second mechanical switch is respectively connected to one end of the first thyristor and one end of the load resistor. The other end of the load resistor is connected to the neutral point of the transformer. The structure of this electromechanical hybrid on-load tap-changer is relatively simple.

Description

Technical Field

[0001] The present invention relates to the technical field of tap changers, and particularly to an electromechanical hybrid on-load tap changer and a timing control method thereof. Background Art

[0002] UHV DC transmission is an effective solution to realize the eastward transmission of clean energy in the western regions of China. It can meet the requirements of new energy power generation grid connection and is a key component of a new power system with new energy as the main body. Among them, the converter transformer is the core device for realizing AC-DC conversion. The on-load tap changer (OLTC) is located inside the converter transformer and plays an important role in aspects such as DC transmission power regulation and flexible and stable operation of the system. It belongs to a high-precision mechatronic device and needs to complete the gear switching according to the given switch timing within an extremely short time, while meeting the requirements of time accuracy and timing stability, and ensuring the reliability of the switch structure and timing switching.

[0003] In China's UHV power transmission and transformation projects, mechanical on-load tap changers are generally used. During the tap-changing voltage regulation process, electric arcs are easily generated, and there are also electrical losses and mechanical damages, greatly reducing the voltage regulation reliability. With the development of power electronics technology, a variety of high-voltage-resistant high-power power electronic devices have gradually been applied to OLTCs. The all-electricity-type OLTC has a fast voltage regulation speed and a low failure rate, and can achieve arc-free voltage regulation. However, using devices such as silicon controlled rectifiers (SCRs) and metal-oxide-semiconductor field-effect transistors (MOSFETs) as main switches will not only increase the equipment cost, but also have problems such as high on-state losses and low breakdown voltage ratings. The electromechanical hybrid OLTC retains the mechanical switch and adds power electronic devices to the transition circuit, which has significant advantages in arc-free switching and reliability and has higher application value.

[0004] However, in order to ensure continuous load current and no arc generation during the voltage regulation process, it is necessary to introduce multiple power electronic switch components, resulting in a relatively complex structure of the electromechanical hybrid on-load tap changer, thereby increasing the complexity of the timing design for gear switching. Summary of the Invention

[0005] Based on this, in view of the above technical problems, it is necessary to provide an electromechanical hybrid on-load tap changer and a timing control method thereof. The structure of the electromechanical hybrid on-load tap changer is relatively simple, reducing the complexity of the timing design during gear switching.

[0006] The present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an electromechanical hybrid on-load tap-changer, comprising: two current-carrying branches and two transition branches; the first current-carrying branch includes a first mechanical switch, the second current-carrying branch includes a second mechanical switch, the first transition branch includes a first disconnector and a first thyristor connected in series; a first transition resistor is connected in parallel across the first thyristor; the second transition branch includes a second disconnector and a second thyristor connected in series, and a second transition resistor is connected in parallel across the second thyristor; one end of the first mechanical switch and one end of the first disconnector are both connected to the first tap of the transformer, and the other end of the mechanical switch is respectively connected to one end of the second thyristor and one end of the load resistor; one end of the second mechanical switch and one end of the second disconnector are both connected to the second tap of the transformer, and the other end of the second mechanical switch is respectively connected to one end of the first thyristor and one end of the load resistor; the other end of the load resistor is connected to the neutral point of the transformer.

[0008] Preferably, an action buffer zone for the first mechanical switch and the second mechanical switch is set in the action timing sequence when the electromechanical hybrid on-load tap-changer performs tap-changing.

[0009] Preferably, the first tap is tap N, and the second tap is tap N + 1.

[0010] Preferably, when the tap position of the electromechanical hybrid on-load tap-changer is at tap N, the first mechanical switch is turned on, and the first thyristor, the second mechanical switch, the first disconnector, the second disconnector, and the second thyristor are turned off. The load current of tap N flows through the first mechanical switch to the neutral point of the transformer.

[0011] Preferably, when the tap position of the electromechanical hybrid on-load tap-changer is at tap N + 1, the second mechanical switch is turned on, and the second thyristor, the first mechanical switch, the first disconnector, the second disconnector, and the first thyristor are turned off. The load current of tap N + 1 flows through the second mechanical switch to the neutral point of the transformer.

[0012] In a second aspect, the present invention provides a timing control method for an electromechanical hybrid on-load tap-changer, which is applied to the electromechanical hybrid on-load tap-changer provided in any one of the embodiments in the first aspect. The method includes:

[0013] Controlling the switch states of the first mechanical switch, the second mechanical switch, the first disconnector, the second disconnector, the first thyristor, and the second thyristor to achieve the tap position switching of the electromechanical hybrid on-load tap-changer.

[0014] Preferably, when the tap position switching is from tap N to tap N + 1, controlling the switch states of the first mechanical switch, the second mechanical switch, the first disconnector, the second disconnector, the first thyristor, and the second thyristor includes:

[0015] At the moment when the load current passes through the zero point, the first disconnector and the first thyristor are sequentially turned on, and the first mechanical switch is turned off; a mechanical buffer time is reserved when the first mechanical switch is turned off;

[0016] At the next moment when the load current passes through the zero point, the first thyristor is turned off;

[0017] At the moment when the product of the load current and the first transition resistance is equal to the voltage between tap N and tap N+1, the second disconnector and the second thyristor are turned on;

[0018] At the moment when the voltage between tap N and tap N+1 passes through the zero point, the first disconnector is turned off;

[0019] At the next moment when the load current passes through the zero point, the second mechanical switch is sequentially turned on, and the second thyristor and the second disconnector are turned off; a mechanical buffer time is reserved when the second mechanical switch is turned on.

[0020] Preferably, when the tap position is switched from tap N+1 to tap N, the switching actions of the tap position from tap N+1 to tap N and from tap N to tap N+1 are symmetric; then controlling the switching states of the first mechanical switch, the second mechanical switch, the first disconnector, the second disconnector, the first thyristor and the second thyristor includes:

[0021] At the moment when the load current passes through the zero point, the second disconnector and the second thyristor are sequentially turned on, and the second mechanical switch is turned off; a mechanical buffer time is reserved when the second mechanical switch is turned off;

[0022] At the moment when the voltage between tap N and tap N+1 passes through the zero point, the first disconnector is turned on;

[0023] At the moment when the product of the load current and the first transition resistance is equal to the voltage between tap N and tap N+1, the second disconnector and the second thyristor are turned off;

[0024] At the moment when the load current passes through the zero point, the first thyristor is turned on;

[0025] At the next moment when the load current passes through the zero point, the first mechanical switch is sequentially turned on, and the first disconnector and the first thyristor are turned off; a mechanical buffer time is reserved when the first mechanical switch is turned on.

[0026] The above at least one technical solution adopted by the present invention can achieve the following beneficial effects:

[0027] The electromechanical hybrid on-load tap-changer provided by the present invention only includes four switches, two thyristors and two transition resistors. When performing tap position switching, only the switching states of the switches and thyristors need to be adjusted to achieve the tap position switching of the electromechanical hybrid on-load tap-changer. Such a design makes the number of components of the electromechanical hybrid on-load tap-changer small, simplifies the structure of the electromechanical hybrid on-load tap-changer, and thus can reduce the complexity of the timing design for the tap position switching of the electromechanical hybrid on-load tap-changer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0029] Figure 1 is a schematic structural diagram of an electromechanical hybrid on-load tap-changer provided by the present invention;

[0030] Figure 2 is a schematic state diagram of an electromechanical hybrid on-load tap-changer provided by the present invention;

[0031] Figure 3 is a schematic transition state diagram of an electromechanical hybrid on-load tap-changer provided by the present invention;

[0032] Figure 4 is another schematic transition state diagram of an electromechanical hybrid on-load tap-changer provided by the present invention;

[0033] Figure 5 is another schematic transition state diagram of an electromechanical hybrid on-load tap-changer provided by the present invention;

[0034] Figure 6 is another schematic transition state diagram of an electromechanical hybrid on-load tap-changer provided by the present invention;

[0035] Figure 7 is another schematic transition state diagram of an electromechanical hybrid on-load tap-changer provided by the present invention;

[0036] Figure 8 is a schematic diagram of the timing control strategy for an electromechanical hybrid on-load tap-changer provided by the present invention to switch from tap N to N + 1;

[0037] Figure 9 is the current waveforms of each switch when an electromechanical hybrid on-load tap-changer provided by the present invention switches from tap N to N + 1;

[0038] Figure 10 is the voltage waveforms of each switch when an electromechanical hybrid on-load tap-changer provided by the present invention switches from tap N to N + 1;

[0039] Figure 11 Schematic diagram of the relationship curve between the operating time and the initial phase of an electro-mechanical hybrid on-load tap-changer provided by the present invention.

[0040] Description of the reference numerals in the drawings:

[0041] 100, electro-mechanical hybrid on-load tap-changer; 101, first mechanical switch; 102, second mechanical switch; 103, first disconnecting switch; 104, first thyristor; 105, first transition resistor; 106, second disconnecting switch; 107, second thyristor; 108, second transition resistor; 109, transformer; 110, first tap; 111, load resistor; 112, second tap; 113, neutral point. Detailed implementation manners

[0042] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion. In the description of the embodiments of this application, the technical terms "first", "second", "third", "fourth", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means two or more unless otherwise specifically defined.

[0044] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0045] In the description of the embodiments of the present application, unless otherwise clearly defined and limited, technical terms such as "connection" should be understood in a broad sense. For example, it can be directly connected, or indirectly connected through an intermediate medium. It can be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0046] In recent years, with the continuous in-depth research of scholars, the performance of the electromechanical hybrid OLTC has been continuously improved. However, it is found that the existing hybrid OLTC has problems such as the voltage regulation range not meeting the requirements of UHV lines, lack of effective electromechanical collaborative control strategies and timing optimization schemes. In addition, in order to ensure continuous load current and no arc generation during the voltage regulation process, multiple power electronic switch components need to be introduced and the timing control process is complex. Therefore, it is urgent to design a new type of electromechanical hybrid OLTC to achieve a simpler switch structure and action timing.

[0047] Based on this, the present invention provides an electromechanical hybrid on-load tap-changer, which can ensure continuous load current and no arc generation during the voltage regulation process, and at the same time, the structure of the on-load tap-changer is relatively simple.

[0048] The following will illustrate the detailed implementation process of the electromechanical hybrid on-load tap-changer provided by the present invention through specific embodiments. As Figure 1 shown, it is a schematic structural diagram of an electromechanical hybrid on-load tap-changer 100 provided by an embodiment of the present invention. The electromechanical hybrid on-load tap-changer 100 includes: two current-carrying branches and two transition branches; the first current-carrying branch includes a first mechanical switch 101, the second current-carrying branch includes a second mechanical switch 102, the first transition branch includes a first disconnector 103 and a first thyristor 104 connected in series; a first transition resistor 105 is connected in parallel at both ends of the first thyristor 104; the second transition branch includes a second disconnector 106 and a second thyristor 107 connected in series, and a second transition resistor 108 is connected in parallel at both ends of the second thyristor 107; one end of the first mechanical switch 101 and one end of the first disconnector 103 are both connected to the first tap 110 of the transformer 109, and the other end of the mechanical switch is respectively connected to one end of the second thyristor 107 and one end of the load resistor 111. One end of the second mechanical switch 102 and one end of the second disconnector 106 are both connected to the second tap 112 of the transformer, and the other end of the second mechanical switch 102 is respectively connected to one end of the first thyristor 104 and one end of the load resistor 111. The other end of the load resistor 111 is connected to the neutral point 113 of the transformer 109; the first current-carrying branch and the second current-carrying branch are used to connect the taps of the transformer 109.

[0049] The first tap 110 is tap N of the transformer 109, and the second tap 112 is tap N+1 of the transformer 109; the switching actions of the electromechanical hybrid on-load tap-changer 100 are symmetric when switching the tap position between tap N and tap N+1. It should be noted that if the number of taps of the transformer 109 is M, then N∈[1,M-1].

[0050] Among them, the first thyristor 104 and the second thyristor 107 can both be a set of antiparallel thyristors; in the transition branch, the disconnector is connected in series with a set of antiparallel thyristors, which can prevent overvoltage or overcurrent between taps from damaging the thyristors. At the same time, the transition resistor is connected in parallel across the antiparallel thyristors, which can limit the magnitude of the circulating current. The electromechanical hybrid on-load tap-changer 100 is of symmetric Z type; the electromechanical hybrid on-load tap-changer 100 only requires two sets of antiparallel thyristors, two disconnectors and two transition resistors, with few components, symmetric structure and high reliability.

[0051] Optionally, an action buffer area for the first mechanical switch 101 and the second mechanical switch 102 is set in the action timing when the electromechanical hybrid on-load tap-changer 100 switches taps. The electromechanical hybrid on-load tap-changer 100 has a simple structure and reliable timing. While realizing fast arc-free voltage regulation, it effectively suppresses the generation of arcs. The two set mechanical action buffer areas also provide sufficient action time for the switching switch, ensuring the reliable action of the switch.

[0052] As Figure 2 shown, when the tap position of the electromechanical hybrid on-load tap-changer 100 is at tap N, the first mechanical switch 101 is turned on, and the first thyristor 104, the second mechanical switch 102, the first disconnector 103, the second disconnector 106 and the second thyristor 107 are turned off. The load current of tap N flows through the first mechanical switch 101 to the neutral point 111 of the transformer 109.

[0053] As Figure 3 shown, when the tap position of the electromechanical hybrid on-load tap-changer 100 is at tap N+1, the second mechanical switch 102 is turned on, and the second thyristor 107, the first mechanical switch 101, the first disconnector 103, the second disconnector 106 and the first thyristor 104 are turned off. The load current of tap N+1 flows through the second mechanical switch 102 to the neutral point 111 of the transformer 109.

[0054] Based on the above electromechanical hybrid on-load tap-changer, the present invention also provides a timing control method for the electromechanical hybrid on-load tap-changer. The implementation manner of this method will be described in detail below.

[0055] In an exemplary embodiment, the method includes: controlling the switching states of a first mechanical switch, a second mechanical switch, a first disconnector, a second disconnector, a first thyristor, and a second thyristor to achieve tap position switching of an electromechanical hybrid on-load tap-changer.

[0056] Specifically, in an exemplary embodiment, when the tap position is switched from tap N to tap N + 1, controlling the switching states of the first mechanical switch, the second mechanical switch, the first disconnector, the second disconnector, the first thyristor, and the second thyristor includes:

[0057] At the moment when the load current passes through zero, the first disconnector and the first thyristor are sequentially turned on, and the first mechanical switch is turned off; a mechanical buffer time is reserved when the first mechanical switch is turned off;

[0058] At the next moment when the load current passes through zero, the first thyristor is turned off;

[0059] At the moment when the product of the load current and the first transition resistance is equal to the voltage between tap N and tap N + 1, the second disconnector and the second thyristor are turned on;

[0060] At the moment when the voltage between tap N and tap N + 1 passes through zero, the first disconnector is turned off;

[0061] At the next moment when the load current passes through zero, the second mechanical switch is sequentially turned on, and the second thyristor and the second disconnector are turned off; a mechanical buffer time is reserved when the second mechanical switch is turned on.

[0062] Wherein, the mechanical buffer time can be set to 10 ms.

[0063] During the process of switching from tap N to tap N + 1, it includes 6 circuit states and 5 action timings. The circuit states and action timings of switching from tap N to tap N + 1 are specifically described as follows:

[0064] State 1: The first mechanical switch K a is in the conducting state, and the load current flows through the first mechanical switch K a , and the electromechanical hybrid on-load tap-changer works in the stable state before switching. The first disconnector CR1 and the second disconnector CR2 isolate the first thyristor Q1 and the second thyristor Q2 from the two taps. Please refer to Figure 2 .

[0065] Action 1: At the moment when the load current passes through zero, the first disconnector CR1 and the first thyristor Q1 are sequentially turned on, and the first mechanical switch K is turned off a ; a mechanical buffer time should be reserved when the first mechanical switch K a is turned off, and the electromechanical hybrid on-load tap-changer switches from state 1 to state 2.

[0066] State 2: The load current flows through the first disconnector CR1 and the first thyristor Q1. The first transition resistor R1 is short-circuited, and the second disconnector CR2 isolates the second thyristor Q2 from the tap N+1. As Figure 4 shown.

[0067] Action 2: After Action 1 is completed, at the next zero-crossing moment of the load current, the first thyristor Q1 is turned off. When the current flowing through the first thyristor Q1 is less than its holding current, the load current automatically transfers to the branch where the first transition resistor R1 in parallel with the first thyristor Q1 is located, and the electromechanical hybrid on-load tap-changer switches from State 2 to State 3.

[0068] State 3: The load current flows through the first disconnector CR1 and the first transition resistor R1, and the disconnector CR2 isolates the second thyristor Q2 from the tap N+1; As Figure 5 shown.

[0069] Action 3: After Action 2 is completed, when the product of the load current and the first transition resistor R1 is equal to the voltage between tap N and tap N+1, the second disconnector CR2 and the second thyristor Q2 are turned on; The electromechanical hybrid on-load tap-changer switches from State 3 to State 4, and the system enters the circulating current process.

[0070] State 4: The load current flows through the first disconnector CR1, the first transition resistor R1, the second disconnector CR2 and the second thyristor Q2 at the same time. Taps N and N+1 supply power to the load, and a circulating current appears. As Figure 6 shown.

[0071] Action 4: After Action 3 is completed, at the moment when the voltage between tap N and tap N+1 passes through zero, the first disconnector CR1 is turned off; The electromechanical hybrid on-load tap-changer switches from State 4 to State 5.

[0072] State 5: The load current flows through the second disconnector CR2 and the second thyristor Q2. The second transition resistor R2 is short-circuited, and the first disconnector CR1 isolates the first thyristor Q1 from the tap N. As Figure 7 shown.

[0073] Action 5: After Action 4 is completed, first provide the closing signal of the second mechanical switch K b , then provide the turn-off signals of the second thyristor Q2 and the second disconnector CR2, and leave the mechanical buffer time for the second mechanical switch K b and the second disconnector CR2. At the zero-crossing moment of the load current, the electromechanical hybrid on-load tap-changer switches from State 5 to State 6.

[0074] State 6: The second mechanical switch K bIn the conducting state, the load current flows through the second switch K b , the first disconnector CR1 and the second disconnector CR2 isolate the first thyristor Q1 and the second thyristor Q2 from the two tap points respectively. Please refer to Figure 3 .

[0075] Based on the above state and action timing, as Figure 8 shown Figure 8 a timing control strategy diagram for the electromechanical hybrid on-load tap-changer to switch from tap N to N+1 is given.

[0076] The switching actions of the tap position from tap N+1 to tap N and from tap N to tap N+1 are symmetric. Therefore, if the electromechanical hybrid on-load tap-changer is to be switched from transformer tap N+1 to transformer tap N, the action timing is sequentially from action 5 to action 1. For example, when the tap position is switched from tap N+1 to tap N, the switch states of the first mechanical switch, the second mechanical switch, the first disconnector, the second disconnector, the first thyristor and the second thyristor are controlled, including:[[]]

[0077] At the moment when the load current passes through the zero point, the second disconnector and the second thyristor are sequentially turned on, and the second mechanical switch is turned off; a mechanical buffer time is reserved when the second mechanical switch is turned off;

[0078] At the moment when the voltage between tap N and tap N+1 passes through the zero point, the first disconnector is turned on;

[0079] At the moment when the product of the load current and the first transition resistor is equal to the voltage between tap N and tap N+1, the second disconnector and the second thyristor are turned off;

[0080] At the moment when the load current passes through the zero point, the first thyristor is turned on;

[0081] At the next moment when the load current passes through the zero point, the first mechanical switch is sequentially turned on, and the first disconnector and the first thyristor are turned off; a mechanical buffer time is reserved when the first mechanical switch is turned on.

[0082] Furthermore, when switching from transformer tap N+1 to transformer tap N, the working state can be sequentially switched from state 6 to state 1 in reverse order; this embodiment is not limited here.

[0083] In an exemplary embodiment, the frequency is 50 Hz, and the effective value I n of the load current i n = 1 kA; the effective value of the winding voltage u n between the two tap points is 6 kV, the phase difference between the winding voltage and the load current is 30°, and the resistance values of the first transition resistor R1 and the second transition resistor R2 are both 2.7 Ω.

[0084] In this embodiment, the specific action timing is as follows:

[0085] Action 1: At 10 ms, the load current passes through zero. First, a closing signal for the first disconnector CR1 is provided, and then a turning-off signal for the first mechanical switch K a is provided. Set 10 ms to 20 ms as the mechanical action buffer 1. Until the 20 ms moment, the first mechanical switch K a and the first disconnector CR1 complete their actions, and the electromechanical hybrid on-load tap-changer switches from state 1 to state 2, realizing zero-current conduction of the first thyristor Q1.

[0086] Action 2: After Action 1 is completed, at 20 ms, the load current passes through zero. The trigger signal for the first thyristor Q1 is stopped. When the current flowing through the first thyristor Q1 is less than its holding current, the load current automatically transfers to the branch where the first transition resistor R1 in parallel with the first thyristor Q1 is located, and the electromechanical hybrid on-load tap-changer switches from state 2 to state 3.

[0087] Action 3: After Action 2 is completed, at 28.6 ms, i n R1 = u n , at this time, the second disconnector CR2 is closed and the second thyristor Q2 is triggered, and the second thyristor Q2 conducts with zero current. The electromechanical hybrid on-load tap-changer switches from state 3 to state 4, and the system enters the circulating current process.

[0088] Action 4: After Action 3 is completed, at 38.3 ms, the voltage passes through zero. At this time, the first disconnector CR1 is disconnected, and the state of the electromechanical hybrid on-load tap-changer switches from state 4 to state 5. It switches from tap N to tap N + 1, and the load current flows through the second disconnector CR2 and the second thyristor Q2.

[0089] Action 5: After Action 4 is completed, at 40 ms, i n = 0. First, a closing signal for the second mechanical switch K b is provided, and then a turning-off signal for the second disconnector CR2 is provided. Set 40 ms to 50 ms as the mechanical action buffer 2. Until the 50 ms moment, the second mechanical switch K b and the second disconnector CR2 complete their actions, and the tap-changer switches from state 5 to state 6.

[0090] So far, the state switching of the electromechanical hybrid on-load tap-changer from tap N to N + 1 has been completed, and the entire switching process lasts for 50 ms. The action timing for switching from tap N + 1 to tap N is opposite to the above 5 action states, and this embodiment will not elaborate on it here.

[0091] Furthermore, the transition loss is calculated based on the above switch operation timing; when the electromechanical hybrid on-load tap-changer operates in state 3, the load current flows through the first transition resistor R1, and a circulating current is generated in state 4. The loss generated on the first transition resistor R1 during state 3 is:

[0092] When the electromechanical hybrid on-load tap-changer operates in state 4, the current flowing through the transition resistor R1 is:

[0093]

[0094] The power P2 consumed on the first transition resistor R1 is:

[0095] Therefore, during the process of the electromechanical hybrid on-load tap-changer switching from tap N to N + 1, the total loss W of the first transition resistor R1 is expressed as: W = W1 + W2 = P1(t3 - t2) + P2(t4 - t3)

[0096] where t2, t3, and t4 are the trigger times of action 2, action 3, and action 4, respectively.

[0097] Since action 2 occurs at the moment when the load current i n = 0, if the moment when action 2 occurs is taken as the starting point of timing, when action 3 occurs, it satisfies: Then the relationship between the trigger time t3 of action 3 and the initial phase angle can be expressed as:

[0098] Since action 4 needs to occur at the moment when u n = 0, the trigger time t4 of action 4 satisfies:

[0099]

[0100] From the above operation timing, it can be seen that the entire switching process of the tap-changer lasts for 50 ms. For a clear illustration, the current waveforms and voltage waveforms of each switch when the electromechanical hybrid on-load tap-changer switches from tap N to N + 1 are drawn, as shown in Figure 9 and Figure 10 respectively. And, in order to achieve zero-current turn-on of the second thyristor Q2 while minimizing the duration of the circulating current process to reduce losses, the relationship diagram between the switching times of action 3 and action 4 of the tap-changer and the initial phase angle is drawn, as shown in Figure 11 shown. From Figure 11 it can be seen that when the initial phase is π, the working time of state 4 is the shortest, the circulating current time is the shortest, and the loss is the smallest; when the initial phase is 2π, the circulating current time is the longest and the loss is the largest. It is calculated that the transition resistor loss is about 266 kJ.

[0101] It should be noted that, taking N as 3 and N + 1 as 4 as an example, if the two current-carrying branches of the electromechanical hybrid on-load tap-changer are respectively connected to tap 3 and tap 4, and when the tap position of the electromechanical hybrid on-load tap-changer is tap 3, if it is necessary to switch the tap position of the electromechanical hybrid on-load tap-changer to tap 2, the non-current-carrying current-carrying branch (the current-carrying branch connected to tap 3) can be slid to tap 2, connected to tap 2 first, and then the tap position is switched from tap 3 to tap 2.

[0102] The electromechanical hybrid on-load tap-changer and the optimized control strategy for the switch operation timing sequence provided by the present invention have the characteristics of light weight, simple control, and high reliability compared with other typical tap-changer structures of the same type. Each switch can achieve zero-voltage or zero-current breaking, and no arc is generated during the switching process, reducing the additional loss.

[0103] At the same time, aiming at the problem of mechanical switch action error, a mechanical action buffer zone is reasonably set, providing sufficient action time for the switching switch to ensure the reliable action of the switch. Further, aiming at the problem that it is difficult to balance the mechanical load and electrical load of the on-load tap-changer, a timing control strategy for fast arc-free switching is proposed, which has low transition loss, comprehensively considers mechanical loss and action error, analyzes and calculates the transition resistance loss, clarifies the relationship between the initial phase and the tap-changer loss, and completes the overall optimization of the switch timing sequence without additional loss generation, solving the problem that it is difficult to coordinate and control the electromechanical timing.

[0104] The novel tap-changer structure and the timing optimization control strategy proposed by the present invention effectively improve the reliability of the switch operation, can provide new ideas for the domestic design improvement and optimization of the on-load tap-changer, are beneficial to the arc extinction of the tap-changer, and have certain practical value for improving the reliability of the switch operation and optimizing the timing control strategy.

[0105] When applying the timing control method of the electromechanical hybrid on-load tap-changer provided by the present invention, it is not necessary to execute according to the order of each step in the above embodiments. The execution order of each specific step can be determined as needed, and the present invention does not limit this.

[0106] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not conflict, it should be considered as the scope recorded by the present invention.

Claims

1. A mechanical and electrical hybrid on-load tap-changer, characterized in that, The electromechanical hybrid on-load tap-changer is of a symmetric Z type. The electromechanical hybrid on-load tap-changer includes: two current-carrying branches and two transition branches; The first current-carrying branch includes a first mechanical switch; The second current-carrying branch includes a second mechanical switch; The first transition branch includes a first disconnector and a first thyristor connected in series, and a first transition resistor is connected in parallel across the first thyristor; The second transition branch includes a second disconnector and a second thyristor connected in series, and a second transition resistor is connected in parallel across the second thyristor; One end of the first mechanical switch and one end of the first disconnector are both connected to the first tap of the transformer. The other end of the first mechanical switch is respectively connected to one end of the second thyristor and one end of the load resistor; One end of the second mechanical switch and one end of the second disconnector are both connected to the second tap of the transformer. The other end of the second mechanical switch is respectively connected to one end of the first thyristor and one end of the load resistor. The other end of the load resistor is connected to the neutral point of the transformer; the first tap is tap N, and the second tap is tap N+1; the switching actions of the tap position from tap N+1 to tap N and from tap N to tap N+1 are symmetric; When the tap position of the electromechanical hybrid on-load tap-changer is switched from tap N to tap N+1, the timing control mode of the electromechanical hybrid on-load tap-changer is as follows: At the moment when the load current passes through zero, the first disconnector and the first thyristor are sequentially turned on, and the first mechanical switch is turned off; a mechanical buffer time is reserved when the first mechanical switch is turned off; At the next moment when the load current passes through zero, the first thyristor is turned off; At the moment when the product of the load current and the first transition resistor is equal to the voltage between tap N and tap N+1, the second disconnector and the second thyristor are turned on; At the moment when the voltage between tap N and tap N+1 passes through zero, the first disconnector is turned off; At the next moment when the load current passes through zero, the second mechanical switch is sequentially turned on, and the second thyristor and the second disconnector are turned off. A mechanical buffer time is reserved when the second mechanical switch is turned on.

2. The on-load tap-changer of the electro-mechanical hybrid type according to claim 1, wherein, Action buffer areas of the first mechanical switch and the second mechanical switch are set in the action timing sequence when the electromechanical hybrid on-load tap-changer performs tap switching.

3. The on-load tap-changer of the electro-mechanical hybrid type according to claim 1, characterized in that, When the tap position of the electromechanical hybrid on-load tap-changer is at tap N, the first mechanical switch is turned on, and the first thyristor, the second mechanical switch, the first disconnector, the second disconnector, and the second thyristor are turned off. The load current at tap N flows through the first mechanical switch to the neutral point of the transformer.

4. The on-load tap-changer of the electro-mechanical hybrid type according to claim 1, characterized in that, When the tap position of the electro-mechanical hybrid on-load tap-changer is at tap N+1, the second mechanical switch is turned on, and the second thyristor, the first mechanical switch, the first disconnector, the second disconnector, and the first thyristor are turned off. The load current of tap N+1 flows through the second mechanical switch to the neutral point of the transformer.

5. A timing control method for an electro-mechanical hybrid on-load tap-changer, characterized in that, Applied to the electro-mechanical hybrid on-load tap-changer according to any one of claims 1-4, the method includes: Controlling the switch states of the first mechanical switch, the second mechanical switch, the first disconnector, the second disconnector, the first thyristor, and the second thyristor to achieve the tap position switching of the electro-mechanical hybrid on-load tap-changer.

6. The method according to claim 5, characterized in that When the tap position is switched from tap N+1 to tap N, the controlling the switch states of the first mechanical switch, the second mechanical switch, the first disconnector, the second disconnector, the first thyristor, and the second thyristor includes: At the moment when the load current passes through zero, turn on the second disconnector and the second thyristor in sequence, and turn off the second mechanical switch; reserve a mechanical buffer time when turning off the second mechanical switch; At the moment when the voltage between tap N and tap N+1 passes through zero, turn on the first disconnector; At the moment when the product of the load current and the first transition resistance is equal to the voltage between tap N and tap N+1, turn off the second disconnector and the second thyristor; At the moment when the load current passes through zero, turn on the first thyristor; At the next moment when the load current passes through zero, turn on the first mechanical switch in sequence, and turn off the first disconnector and the first thyristor; reserve a mechanical buffer time when turning on the first mechanical switch.

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