Electromechanical hybrid on-load tap-changer and sequential control method thereof

Abstract

The invention discloses an electromechanical hybrid on-load tap-changer and a sequential control method thereof, and relates to the technical field of tap-changers. Comprising a first mechanical switch, a second mechanical switch, a first isolation switch and a first thyristor which are connected in series, and a second isolation switch and a second thyristor which are connected in series, two ends of the first thyristor are connected in parallel with a first transition resistor. Two ends of the second thyristor are connected in parallel with a second transition resistor. One end of the first mechanical switch and one end of the first isolation switch are connected with a first tap of the transformer, the other end of the mechanical switch is connected with one end of the second thyristor and one end of the load resistor, and one end of the second mechanical switch and one end of the second isolation switch are connected with a second tap of the transformer. The other end of the second mechanical switch is connected with one end of the first thyristor and one end of the load resistor, and the other end of the load resistor is connected with the neutral point of the transformer. The electromechanical hybrid on-load tap-changer is relatively simple in structure.

Description

Technical Field

[0001] The present invention relates to the technical field of tap changers, and in particular 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 from western my country. It can meet the requirements of new energy power generation and grid connection, and is a key component of the new power system with new energy as the main body. Among them, the converter transformer is the core equipment for realizing AC-DC conversion. The onload tap changer (OLTC) is located inside the converter transformer and plays an important role in DC transmission power regulation and flexible and stable operation of the system. It is a high-precision mechatronics equipment that needs to complete the gear switching in a very short time according to the given switch timing, while meeting the requirements of time accuracy and timing stability, and ensuring the reliability of the switch structure and timing switching.

[0003] Mechanical on-load tap changers are widely used in my country's UHV transmission and transformation projects. Arcs are easily generated during the tap switching and voltage regulation process, and there are electrical losses and mechanical damage, which greatly reduces the reliability of voltage regulation. With the development of power electronics technology, a variety of high-power power electronic devices with high voltage resistance are gradually applied to OLTC. The full power electronic OLTC has a fast voltage regulation speed, low failure rate, and can achieve arc-free voltage regulation. However, the use of devices such as thyristors (Silicon Controlled Rectifier, SCR) and metal-oxide-semiconductor field-effect transistors (Metal-Oxide-Semiconductor Field-EffectTransistor, MOSFET) as main switches will not only increase the equipment cost, but also have problems such as high conduction loss and low withstand voltage level. While retaining the mechanical switch, the power electronic OLTC 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 that the load current is continuous and no arc is generated during the voltage regulation process, multiple power electronic switching elements need to be introduced, which makes the structure of the electromechanical hybrid on-load tap changer more complex, thereby increasing the complexity of the timing design of the gear switching. Summary of the invention

[0005] Based on this, it is necessary to provide an electromechanical hybrid on-load tap changer and a timing control method thereof to address the above technical problems. The electromechanical hybrid on-load tap changer has a relatively simple structure and reduces 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 comprises a first mechanical switch, the second current-carrying branch comprises a second mechanical switch, the first transition branch comprises a first isolating switch and a first thyristor connected in series with each other; a first transition resistor is connected in parallel at both ends of the first thyristor; the second transition branch comprises a second isolating switch and a second thyristor connected in series with each other, and a second transition resistor is connected in parallel at both ends of the second thyristor; one end of the first mechanical switch and one end of the first isolating switch are both connected to the first tap of the transformer, the other ends of the mechanical switch are 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 isolating switch 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, and the other end of the load resistor is connected to the neutral point of the transformer.

[0008] Preferably, an action buffer zone of the first mechanical switch and the second mechanical switch is provided in the action sequence of the electromechanical hybrid on-load tap changer when performing tap switching.

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

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

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

[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 by any embodiment of the first aspect, and the method comprises:

[0013] The switching states of the first mechanical switch, the second mechanical switch, the first isolating switch, the second isolating switch, the first thyristor and the second thyristor are controlled to realize the tapping gear switching of the electromechanical hybrid on-load tap changer.

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

[0015] At the moment when the load current passes through zero, the first isolating switch and the first thyristor are turned on in sequence, 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 zero-crossing moment of the load current, the first thyristor is disconnected;

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

[0018] When the voltage between the tap N and the tap N+1 passes through zero, the first isolating switch is disconnected;

[0019] At the next load current zero-crossing moment, the second mechanical switch is turned on in sequence, and the second thyristor and the second isolating switch are turned off; a mechanical buffer time is reserved when the second mechanical switch is turned on.

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

[0021] When the load current passes through zero, the second isolating switch and the second thyristor are turned on in sequence, and the second mechanical switch is turned off; a mechanical buffer time is reserved when the second mechanical switch is turned off;

[0022] When the voltage between the tap N and the tap N+1 passes through zero, the first isolating switch is turned on;

[0023] When the product of the load current and the first transition resistance is equal to the voltage between the tap N and the tap N+1, the second isolating switch and the second thyristor are disconnected;

[0024] When the load current crosses the zero point, the first thyristor is turned on;

[0025] At the next time when the load current crosses zero, the first mechanical switch is turned on in sequence, and the first isolating switch and the first thyristor are turned off; when the first mechanical switch is turned on, a mechanical buffer time is reserved.

[0026] At least one of the above technical solutions 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 switching the tapping gear, only the switching states of the switches and the thyristors need to be adjusted to achieve the gear switching of the electromechanical hybrid on-load tap changer. Such a design reduces the number of components of the electromechanical hybrid on-load tap changer, simplifies the structure of the electromechanical hybrid on-load tap changer, and thus reduces the complexity of the timing design of the gear 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 exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

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

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

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

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

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

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

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

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

[0037] Fig. 9 The present invention provides an electromechanical hybrid on-load tap changer, wherein the current waveforms of each switch are when the tap N is switched to the tap N+1;

[0038] Fig.10 The voltage waveforms of each switch when a mechatronic hybrid on-load tap changer provided by the present invention switches from tap N to tap N+1;

[0039] Fig.11 A schematic diagram of a curve showing the relationship between the action time and the initial phase of an electromechanical hybrid on-load tap changer provided by the present invention.

[0040] Description of reference numerals:

[0041] 100. Electromechanical hybrid on-load tap-changer; 101. first mechanical switch; 102. second mechanical switch; 103. first disconnector; 104. first thyristor; 105. first transition resistor; 106. second disconnector; 107. second thyristor; 108. second transition resistor; 109. transformer; 110. first tap; 111. load resistor; 112. second tap; 113. neutral point. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution 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 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 making creative work are 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 those commonly understood by technicians in the technical field of the present application; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "including" and any variations thereof in the specification and claims of the present application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions. In the description of the embodiments of the present 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 number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0044] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0045] In the description of the embodiments of the present application, unless otherwise clearly specified 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 elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0047] In recent years, with the continuous deepening of scholars' research, the performance of electromechanical hybrid OLTC has been continuously improved. However, research has found that the existing hybrid OLTC has problems such as the voltage regulation range not meeting the requirements of UHV lines and the lack of effective electromechanical coordinated control strategies and timing optimization solutions; in addition, in order to ensure that the load current is continuous and arc-free during the voltage regulation process, multiple power electronic switching elements need to be introduced and the timing control process is complicated. Therefore, it is urgent to design a new type of electromechanical hybrid OLTC to achieve a simpler switch structure and action timing.

[0048] Based on this, the present invention provides an electromechanical hybrid on-load tap changer, which can ensure that the load current is continuous and arc-free during the voltage regulation process, while the structure of the on-load tap changer is relatively simple.

[0049] The detailed implementation process of the electromechanical hybrid on-load tap changer provided by the present invention is described below through specific embodiments. Figure 1 The figure is a schematic diagram of the structure 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 comprises: two current-carrying branches and two transition branches; the first current-carrying branch comprises a first mechanical switch 101, the second current-carrying branch comprises a second mechanical switch 102, the first transition branch comprises a first isolating switch 103 and a first thyristor 104 connected in series with each other; a first transition resistor 105 is connected in parallel at both ends of the first thyristor 104; the second transition branch comprises a second isolating switch 106 and a second thyristor 107 connected in series with each other, 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 the first isolating switch 103 are connected in parallel with each other. One end of each of the mechanical switches is connected to a first tap 110 of a transformer 109, the other end of each of the mechanical switches is connected to one end of a second thyristor 107 and one end of a load resistor 111, one end of each of the second mechanical switch 102 and one end of each of the second isolating switch 106 are connected to a second tap 112 of the transformer, the other end of each of the second mechanical switch 102 is connected to one end of a first thyristor 104 and one end of a load resistor 111, and the other end of each of the load resistors 111 is connected to a neutral point 113 of the transformer 109; the first current-carrying branch and the second current-carrying branch are used to connect the tap of the transformer 109.

[0050] The first tap 110 is the tap N of the transformer 109, and the second tap 112 is the tap N+1 of the transformer 109; the switching action of the electromechanical hybrid on-load tap changer 100 when switching the tapping gear between the tap N and the tap N+1 is symmetrical. It should be noted that if the transformer 109 has M taps, then N∈[1,M-1].

[0051] The first thyristor 104 and the second thyristor 107 can both be a group of anti-parallel thyristors; in the transition branch, the isolating switch and a group of anti-parallel thyristors are connected in series, which can prevent the overvoltage or overcurrent between the tap levels from damaging the thyristors, and at the same time, the transition resistor is connected in parallel at both ends of the anti-parallel thyristors to limit the size of the circulating current. The electromechanical hybrid on-load tap changer 100 is a symmetrical Z-type; the electromechanical hybrid on-load tap changer 100 only requires two groups of anti-parallel thyristors, two isolating switches and two transition resistors, with a small number of components, a symmetrical structure and high reliability.

[0052] Optionally, the electromechanical hybrid on-load tap changer 100 sets an action buffer zone for the first mechanical switch 101 and the second mechanical switch 102 in the action sequence when the tap is switched. The electromechanical hybrid on-load tap changer 100 has a simple structure and reliable sequence, and can achieve rapid arc-free voltage regulation while effectively suppressing the generation of arcs. The two mechanical action buffer zones also provide sufficient action time for the switch, ensuring reliable action of the switch.

[0053] like Figure 2 As shown, when the tapping position of the electromechanical hybrid on-load tap changer 100 is at the tap N, the first mechanical switch 101 is turned on, the first thyristor 104, the second mechanical switch 102, the first isolating switch 103, the second isolating switch 106 and the second thyristor 107 are turned off, and the load current of the tap N flows to the neutral point 111 of the transformer 109 through the first mechanical switch 101.

[0054] like Figure 3 As shown, when the tapping position of the electromechanical hybrid on-load tap changer 100 is at the tap N+1, the second mechanical switch 102 is turned on, the second thyristor 107, the first mechanical switch 101, the first isolating switch 103, the second isolating switch 106 and the first thyristor 104 are turned off, and the load current of the tap N+1 flows to the neutral point 111 of the transformer 109 through the second mechanical switch 102.

[0055] Based on the above electromechanical hybrid on-load tap changer, the present invention further provides a timing control method for the electromechanical hybrid on-load tap changer, and the implementation of the method is described in detail below.

[0056] In an exemplary embodiment, the method includes: controlling the switching states of a first mechanical switch, a second mechanical switch, a first isolating switch, a second isolating switch, a first thyristor, and a second thyristor to achieve tapping gear switching of the electromechanical hybrid on-load tap changer.

[0057] Specifically, in an exemplary embodiment, when the tap gear switching is switched from tap N to tap N+1, the switching states of the first mechanical switch, the second mechanical switch, the first isolating switch, the second isolating switch, the first thyristor and the second thyristor are controlled, including:

[0058] At the moment when the load current passes through zero, the first isolating switch and the first thyristor are turned on in sequence, and the first mechanical switch is turned off; a mechanical buffer time is reserved when the first mechanical switch is turned off;

[0059] At the next zero-crossing moment of the load current, the first thyristor is disconnected;

[0060] When the product of the load current and the first transition resistance is equal to the voltage between the tap N and the tap N+1, the second isolating switch and the second thyristor are turned on;

[0061] When the voltage between the tap N and the tap N+1 passes through zero, the first isolating switch is disconnected;

[0062] At the next load current zero-crossing moment, the second mechanical switch is turned on in sequence, and the second thyristor and the second isolating switch are turned off; a mechanical buffer time is reserved when the second mechanical switch is turned on.

[0063] Among them, the mechanical buffer time can be set to 10ms.

[0064] The process of switching tap N to tap N+1 includes 6 circuit states and 5 action sequences. The circuit states and action sequences of switching tap N to tap N+1 are specifically described as follows:

[0065] State 1: First mechanical switch K a In the on state, the load current flows through the first mechanical switch K a , the electromechanical hybrid on-load tap-changer works in a stable state before switching. The first isolating switch CR1 and the second isolating switch CR2 isolate the first thyristor Q1 and the second thyristor Q2 from the two taps. See Figure 2 .

[0066] Action 1: When the load current passes through zero, the first isolation switch CR1 and the first thyristor Q1 are turned on in sequence, and the first mechanical switch K is turned off. a ; First mechanical switch K a Mechanical buffer time should be reserved when the electromechanical hybrid on-load tap-changer switches from state 1 to state 2.

[0067] State 2: The load current flows through the first isolation switch CR1 and the first thyristor Q1, the first transition resistor R1 is short-circuited, and the second isolation switch CR2 isolates the second thyristor Q2 from the tap N+1. Figure 4 shown.

[0068] Action 2: After action 1 is completed, at the next load current zero-crossing moment, the first thyristor Q1 is disconnected. When the current flowing through the first thyristor Q1 is less than its holding current, the load current is automatically transferred to the branch where the first transition resistor R1 connected in parallel with the first thyristor Q1 is located, and the electromechanical hybrid on-load tap changer is switched from state 2 to state 3.

[0069] State 3: The load current flows through the first isolation switch CR1 and the first transition resistor R1, and the isolation switch CR2 isolates the second thyristor Q2 from the tap N+1; Figure 5 shown.

[0070] 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 the tap N and the tap N+1, the second isolating switch 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 process.

[0071] State 4: The load current flows through the first isolating switch CR1, the first transition resistor R1, the second isolating switch CR2 and the second thyristor Q2 at the same time, and the taps N and N+1 supply power to the load, resulting in a circulating current. Figure 6 shown.

[0072] Action 4: After action 3 is completed, when the voltage between tap N and tap N+1 passes through zero, the first isolating switch CR1 is disconnected; the electromechanical hybrid on-load tap changer switches from state 4 to state 5.

[0073] State 5: The load current flows through the second isolation switch CR2 and the second thyristor Q2, the second transition resistor R2 is short-circuited, and the first isolation switch CR1 isolates the first thyristor Q1 from the tap N. Figure 7 shown.

[0074] Action 5: After action 4 is completed, first provide the second mechanical switch K b The closing signal of the second thyristor Q2 and the second isolation switch CR2 is provided, and the second mechanical switch K b The second disconnector CR2 leaves a mechanical buffer time. At the moment when the load current passes through zero, the electromechanical hybrid on-load tap changer switches from state 5 to state 6.

[0075] State 6: Second mechanical switch K bIn the on state, the load current flows through the second switch K b The first isolating switch CR1 and the second isolating switch CR2 isolate the first thyristor Q1 and the second thyristor Q2 from the two taps respectively. Figure 3 .

[0076] Based on the above states and action sequences, such as Figure 8 As shown, Figure 8 A timing control strategy diagram of an electromechanical hybrid on-load tap changer switching from tap N to tap N+1 is given.

[0077] The switching actions of the tap gear switching from tap N+1 to tap N and from tap N to tap N+1 are symmetrical. Therefore, if the electromechanical hybrid on-load tap changer is to be switched from transformer tap N+1 to transformer tap N, the action sequence is sequentially from action 5 to action 1. For example, when the tap gear switching is switched from tap N+1 to tap N, the switching states of the first mechanical switch, the second mechanical switch, the first isolating switch, the second isolating switch, the first thyristor and the second thyristor are controlled, including:

[0078] When the load current passes through zero, the second isolating switch and the second thyristor are turned on in sequence, and the second mechanical switch is turned off; a mechanical buffer time is reserved when the second mechanical switch is turned off;

[0079] When the voltage between the tap N and the tap N+1 passes through zero, the first isolating switch is turned on;

[0080] When the product of the load current and the first transition resistance is equal to the voltage between the tap N and the tap N+1, the second isolating switch and the second thyristor are disconnected;

[0081] When the load current crosses the zero point, the first thyristor is turned on;

[0082] At the next time when the load current crosses zero, the first mechanical switch is turned on in sequence, and the first isolating switch and the first thyristor are turned off; when the first mechanical switch is turned on, a mechanical buffer time is reserved.

[0083] Further, the transformer tap N+1 is switched to the transformer tap N, and the working state is switched from state 6 to state 1 in reverse order; this embodiment is not limited here.

[0084] In an exemplary embodiment, the frequency is 50 Hz and the load current i n The effective value of I n =1kA; winding voltage u between two taps n The effective value is 6kV, 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 2.7Ω.

[0085] The specific action sequence in this embodiment is as follows:

[0086] Action 1: When the load current passes through zero point at 10ms, the closing signal of the first isolating switch CR1 is provided first, and then the closing signal of the first mechanical switch K is provided. a Set 10ms to 20ms as the mechanical action buffer 1, until 20ms, the first mechanical switch K a The first isolating switch CR1 is actuated, and the electromechanical hybrid on-load tap changer is switched from state 1 to state 2, achieving zero-current conduction of the first thyristor Q1.

[0087] Action 2: After action 1 is completed, the load current crosses the zero point at 20ms, and the trigger signal of the first thyristor Q1 is stopped. When the current flowing through the first thyristor Q1 is less than its holding current, the load current is automatically transferred to the branch where the first transition resistor R1 connected in parallel with the first thyristor Q1 is located, and the electromechanical hybrid on-load tap changer switches from state 2 to state 3.

[0088] Action 3: After action 2 is completed, at 28.6ms i n R1=u n At this time, the second isolating switch CR2 is closed and the second thyristor Q2 is triggered. The second thyristor Q2 is turned on with zero current, and the electromechanical hybrid on-load tap changer switches from state 3 to state 4, and the system enters the circulating current process.

[0089] Action 4: After action 3 is completed, the voltage crosses zero at 38.3ms, at which time the first isolating switch CR1 is disconnected, and the state of the electromechanical hybrid on-load tapchanger is switched from state 4 to state 5. The load current is switched from tap N to tap N+1, and the load current flows through the second isolating switch CR2 and the second thyristor Q2.

[0090] Action 5: After action 4 is completed, 40ms i n =0, first provide the second mechanical switch K b The closing signal of the second isolating switch CR2 is then provided, and the mechanical action buffer 2 is set to 40ms to 50ms. Until the 50ms moment, the second mechanical switch K b The second isolating switch CR2 is actuated, and the tap changer switches from state 5 to state 6.

[0091] At this point, the state switching of the electromechanical hybrid on-load tap changer from tap N to N+1 is completed, and the entire switching process lasts for 50ms. The action sequence of switching from tap N+1 to tap N is opposite to the above five action states, and this embodiment will not be repeated here.

[0092] Furthermore, the transition loss is calculated based on the above switch action sequence; 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:

[0093] When the electromechanical hybrid on-load tap-changer operates in state 4, the current flowing through the transition resistor R1 is:

[0094]

[0095] The power P2 consumed in the first transition resistor R1 is:

[0096] Therefore, during the process of switching the electromechanical hybrid on-load tap changer from tap N to tap N+1, the total loss W of the first transition resistor R1 is expressed as: W=W1+W2=P1(t3-t2)+P2(t4-t3).

[0098] Among them, t2, t3, and t4 are the triggering moments of action 2, action 3, and action 4 respectively.

[0099] Since action 2 occurs at the load current i n = 0, if the time when action 2 occurs is taken as the timing starting point, when action 3 occurs, the following conditions are met: Then the triggering time t3 of action 3 and the initial phase angle The relationship can be expressed as:

[0100] Since action 4 needs to happen at u n =0, so the triggering time t4 of action 4 satisfies:

[0101]

[0102] From the above action sequence, we can know that the entire switching process of the tap changer lasts for 50ms. For the sake of clarity, the current waveforms and voltage waveforms of the electromechanical hybrid on-load tap changer switching from tap N to tap N+1 are plotted as follows: Fig. 9 and Fig.10 In addition, in order to achieve zero current conduction of the second thyristor Q2 while making the duration of the circulating current process as short as possible to reduce losses, a relationship diagram between the switching time and the initial phase angle of the tap switch action 3 and action 4 is drawn, as shown in Fig.11 As shown. Fig.11 It can be seen that when the initial phase is π, the working time of state 4 is the shortest, the circulation time is the shortest, and the loss is the smallest; when the initial phase is 2π, the circulation time is the longest and the loss is the largest. It can be calculated that the transition resistance loss is about 266kJ.

[0103] 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 tapchanger are respectively connected to tap 3 and tap 4, and the tap gear of the electromechanical hybrid on-load tapchanger is tap 3, if it is necessary to switch the tap gear of the electromechanical hybrid on-load tapchanger to tap 2, the current-carrying branch that does not carry current (the current-carrying branch connected to tap 3) can be slid to tap 2, connected first to tap 2, and then the tap gear from tap 3 to tap 2 is switched.

[0104] The electromechanical hybrid on-load tap changer and the optimization control strategy for the switch action timing provided by the present invention have the characteristics of lightweight, 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, no arc is generated during the switching process, and the additional loss is reduced.

[0105] At the same time, in order to solve the problem of mechanical switch action error, a reasonable mechanical action buffer zone is set to provide sufficient action time for the switching switch, ensuring the reliable action of the switch. Furthermore, in order to solve the problem of difficulty in balancing 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 lower transition loss. The mechanical loss and action error are fully considered, the transition resistance loss is analytically calculated, and the relationship between the initial phase and the tap changer loss is clarified. The overall optimization of the switching timing is completed without generating additional losses, solving the problem of difficult coordinated control of the electromechanical timing.

[0106] The novel tap changer structure and timing optimization control strategy proposed in the present invention effectively improve the reliability of switch action, can provide new ideas for the localization design improvement and optimization of on-load tap changers, is beneficial to the arc extinguishing of the tap changer, and has certain practical value for improving the reliability of switch action and optimizing the timing control strategy.

[0107] When applying the timing control method of the electromechanical hybrid on-load tap changer provided by the present invention, the steps in the above embodiments may not be executed in the order in which they are performed. The specific execution order of the steps may be determined as required, and the present invention does not impose any limitation thereto.

[0108] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present invention.

Claims

1. An electromechanical hybrid on-load tap changer, characterized in that: The electromechanical hybrid on-load tap changer comprises: 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 isolating switch and a first thyristor connected in series, and a first transition resistor is connected in parallel at both ends of the first thyristor; The second transition branch comprises a second isolating switch and a second thyristor connected in series, and two ends of the second thyristor are connected in parallel with a second transition resistor; One end of the first mechanical switch and one end of the first isolating switch are both connected to the first tap of the transformer, and 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 isolating switch 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, and the other end of the load resistor is connected to the neutral point of the transformer.

2. The electromechanical hybrid on-load tap changer according to claim 1, characterized in that: An action buffer zone for the first mechanical switch and the second mechanical switch is provided in the action sequence of the electromechanical hybrid on-load tap changer when performing tap switching.

3. The electromechanical hybrid on-load tap changer according to claim 1, characterized in that: The first tap is tap N, and the second tap is tap N+1.

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

5. The electromechanical hybrid on-load tap changer according to claim 3, characterized in that: When the tapping gear of the electromechanical hybrid on-load tap changer is at tap N+1, the second mechanical switch is turned on, the second thyristor, the first mechanical switch, the first isolating switch, the second isolating switch and the first thyristor are turned off, and the load current of the tap N+1 flows to the neutral point of the transformer through the second mechanical switch.

6. A timing control method for an electromechanical hybrid on-load tap changer, characterized in that: Applied to the electromechanical hybrid on-load tap changer according to any one of claims 1 to 5, the method comprises: The switching states of the first mechanical switch, the second mechanical switch, the first isolating switch, the second isolating switch, the first thyristor and the second thyristor are controlled to achieve the tapping gear switching of the electromechanical hybrid on-load tap changer.

7. The method according to claim 6, characterized in that When the tapping gear is switched from tap N to tap N+1, the switching states of the first mechanical switch, the second mechanical switch, the first isolating switch, the second isolating switch, the first thyristor and the second thyristor are controlled, including: At the moment when the load current passes through zero, the first isolating switch and the first thyristor are turned on in sequence, 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 load current zero-crossing moment, disconnecting the first thyristor; At the moment when the product of the load current and the first transition resistance is equal to the voltage between the tap N and the tap N+1, turning on the second isolating switch and the second thyristor; When the voltage between the tap N and the tap N+1 passes through zero, disconnecting the first isolating switch; At the next load current zero-crossing moment, the second mechanical switch is turned on in sequence, and the second thyristor and the second isolating switch are turned off, and a mechanical buffer time is reserved when the second mechanical switch is turned on.

8. The method according to claim 7, characterized in that When the tap gear is switched from the tap N+1 to the tap N, the switching actions of the tap gear switching from the tap N+1 to the tap N and from the tap N to the tap N+1 are symmetrical; then the switching states of the first mechanical switch, the second mechanical switch, the first isolating switch, the second isolating switch, the first thyristor and the second thyristor are controlled, including: At the moment when the load current passes through zero, the second isolating switch and the second thyristor are turned on in sequence, and the second mechanical switch is turned off; and a mechanical buffer time is reserved when the second mechanical switch is turned off; When the voltage between the tap N and the tap N+1 passes through zero, turning on the first isolating switch; When the product of the load current and the first transition resistance is equal to the voltage between the tap N and the tap N+1, disconnecting the second isolating switch and the second thyristor; When the load current crosses zero, turning on the first thyristor; At the next time when the load current crosses zero, the first mechanical switch is turned on in sequence, and the first isolating switch and the first thyristor are turned off; a mechanical buffer time is reserved when the first mechanical switch is turned on.

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