Thyristor triggering system and method for hybrid on-load tap-changer

Abstract

A trigger loop comprises a first branch and a second branch, a first thyristor is connected in the first branch, a second thyristor is connected in the second branch, and the connection directions of the first thyristor and the second thyristor are opposite; the first branch and the second branch are connected in parallel; the trigger loop comprises gate pole contacts, anode contacts and cathode contacts of the first thyristor and the second thyristor; an anode contact of a second thyristor of the trigger loop is connected to the main loop through an auxiliary contact 20 on the main loop, an anode contact of a first thyristor of the trigger loop is connected to the main loop through an upper end point 23 of the main loop, and the trigger loop is connected with the main loop in parallel; the gate pole of the first thyristor is connected to the main loop through an auxiliary contact 22 on the main loop, and the gate pole of the second thyristor is connected to the main loop through an auxiliary contact 21 on the main loop; the main loop comprises a main contact 25, and the trigger loop is used for short-circuiting the main loop in the opening or closing process of the main contact 25.

Description

Technical Field

[0001] The present invention relates to the technical field of on-load tap changers, and more specifically, to a thyristor triggering system and method for a hybrid on-load tap changer. Background Art

[0002] On-load tap changers are important components of power voltage regulating transformers and industrial voltage regulating transformers. They are used to adjust the tap contacts without interrupting the load current of the transformer to change the output voltage or output capacity of the transformer. However, the arcs generated by the transition branches of traditional mechanical on-load tap changers and vacuum on-load tap changers during switching will not only burn the contacts, but also cause energy loss and pollution of transformer oil.

[0003] The application of thyristors can assist in extinguishing each transition branch during the switching process of the on-load tap changer. However, as a power electronic device, the triggering and shutdown of the thyristor needs to be controlled in conjunction with the switching process of the on-load tap changer and cannot affect the action timing of each transition branch.

[0004] Therefore, it is necessary to propose a suitable triggering system and triggering method for the application scenarios of thyristors in hybrid on-load tap changers, so as to redesign the transition branches of the on-load tap changer and realize arc-free switching. Summary of the invention

[0005] The present invention provides a thyristor triggering system and method for a hybrid on-load tap changer, so as to meet the triggering requirements of thyristors in the hybrid on-load tap changer and realize auxiliary arc extinguishing of each transition branch in the switching process.

[0006] In order to solve the above problems, the present invention provides a thyristor triggering system for a hybrid on-load tap changer, the system comprising: a triggering circuit, a main circuit;

[0007] The trigger circuit comprises a first branch and a second branch, the first branch is connected to a first thyristor, the second branch is connected to a second thyristor, and the first thyristor is connected in opposite directions to the second thyristor; the first branch and the second branch are connected in parallel; the trigger circuit comprises gate contacts and anode and cathode contacts of the first thyristor and the second thyristor;

[0008] The cathode contact of the first thyristor and the anode contact of the second thyristor of the trigger circuit are connected to the main circuit through the auxiliary contact 20 on the main circuit, and the anode contact of the first thyristor and the cathode contact of the second thyristor of the trigger circuit are connected to the main circuit through the terminal 23 on the main circuit, and the trigger circuit is connected in parallel with the main circuit; the gate contact of the first thyristor is connected to the main circuit through the auxiliary contact 22 on the main circuit, and the gate contact of the second thyristor is connected to the main circuit through the auxiliary contact 21 on the main circuit; the main circuit includes a main contact 25, and the main contact 25 is arranged between the auxiliary contact 21 and the auxiliary contact 22;

[0009] The trigger circuit is used to short-circuit the main circuit during the opening or closing process of the main contact 25 to prevent the main circuit from generating arcs.

[0010] Preferably, the main contact 25 is a mechanical switch.

[0011] Preferably, the current direction in the main circuit includes from A to B, or from B to A.

[0012] Preferably, after the main contact 25 of the system is opened, and the auxiliary contacts 21 and 22 are opened for at least 10 milliseconds, the first thyristor or the second thyristor is opened, and the auxiliary contact 20 is disconnected.

[0013] Preferably, the continuous current time of the first thyristor or the second thyristor is less than 12 milliseconds.

[0014] According to another aspect of the present invention, the present invention provides a thyristor triggering method for a hybrid on-load tap changer, the method comprising:

[0015] Establishing a trigger circuit, the trigger circuit comprising a first branch and a second branch, the first branch being connected to a first thyristor, the second branch being connected to a second thyristor, the first thyristor being connected in opposite directions to the second thyristor; the first branch and the second branch being connected in parallel; the trigger circuit comprising gate contacts and anode and cathode contacts of the first thyristor and the second thyristor;

[0016] A main circuit is established, wherein the anode contact of the second thyristor of the trigger circuit is connected to the main circuit through the auxiliary contact 20 on the main circuit, and the anode contact of the first thyristor of the trigger circuit is connected to the main circuit through the terminal 23 on the main circuit, and the trigger circuit is connected in parallel with the main circuit; the gate of the first thyristor is connected to the main circuit through the auxiliary contact 22 on the main circuit, and the gate of the second thyristor is connected to the main circuit through the auxiliary contact 21 on the main circuit; the main circuit includes a main contact 25, and the main contact 25 is arranged between the auxiliary contact 22 and the auxiliary contact 21;

[0017] The trigger circuit is used to short-circuit the main circuit during the opening or closing process of the switch to prevent the main circuit from generating arcs.

[0018] Preferably, the main contact is a mechanical switch.

[0019] Preferably, the current direction in the main circuit includes from A to B, or from B to A.

[0020] Preferably, at least 10 milliseconds after the main contact is opened, and the auxiliary contacts 21 and 22 are opened, the first thyristor or the second thyristor is opened, and the auxiliary contact 20 is opened.

[0021] Preferably, the continuous current time of the first thyristor or the second thyristor is less than 12 milliseconds.

[0022] By adopting the above technical solution, a trigger circuit for a thyristor on-load tap changer is established, the trigger circuit includes two reverse-connected thyristors, the trigger circuit forms a parallel circuit including two reverse-connected thyristors, and the trigger circuit is connected to the main circuit to form a parallel connection with the main circuit. The technical solution of the present invention is that the thyristor circuit is triggered by a mechanical contact, does not require an additional trigger control circuit, and the thyristor has a low rated capacity, and will not damage the on-load tap changer and transformer when the thyristor is out of control. The present invention provides a trigger principle for a thyristor on-load tap changer, and realizes the trigger condition of the thyristor through the coordination of the contact timing. The present invention provides a trigger principle for a thyristor on-load tap changer, and establishes the trigger condition of the thyristor through the potential difference in the contact opening process, without the need for an external trigger power supply. The technical solution of the present invention realizes that the main contact does not generate an arc during the closing and closing process, so that the on-load tap changer transitions smoothly without arc shock and heat generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0024] Figure 1A structural diagram of a thyristor triggering system for a hybrid on-load tap changer of the present invention;

[0025] Figure 2 This is the transition branch structure diagram of the existing on-load tap changer;

[0026] Figure 3 A structural diagram of a triggering system of a thyristor triggering system for a hybrid on-load tap changer of the present invention when the switch is disconnected;

[0027] Figure 4 A circuit schematic diagram of a thyristor triggering system for a hybrid on-load tap changer according to the present invention;

[0028] Figure 5 A schematic diagram of a one-phase switch of a hybrid on-load tap changer in a thyristor triggering system for a hybrid on-load tap changer according to the present invention;

[0029] Figure 6 The present invention is a flow chart of a thyristor triggering method for a hybrid on-load tap changer. DETAILED DESCRIPTION

[0030] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0031] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0032] Figure 1 The figure is a structural diagram of a trigger system based on a thyristor on-load tap changer according to an embodiment of the present invention.

[0033] like Figure 1As shown, in an embodiment of the present invention, a trigger system based on a thyristor on-load tap changer includes a trigger circuit and a main circuit. An embodiment of the present invention establishes a trigger circuit for a thyristor on-load tap changer, the trigger circuit includes two reverse-connected first thyristors 1 and second thyristors 2, the trigger circuit forms a parallel circuit including two reverse-connected thyristors, the anode contact of the second thyristor 2 of the trigger circuit is connected to the main circuit formed by AB through an auxiliary contact 20 on the main circuit, the anode contact of the first thyristor 1 of the trigger circuit is connected to the main circuit formed by AB through an upper terminal 23 of the main circuit, and the trigger circuit is connected in parallel with the main circuit. In an embodiment of the present invention, the thyristor circuit is triggered by a mechanical contact, and the thyristor has a low rated capacity, and the on-load tap changer and the transformer will not be damaged when the thyristor loses control. An embodiment of the present invention provides a trigger principle for a thyristor on-load tap changer, and the trigger condition of the thyristor is achieved through the coordination of the contact timing.

[0034] The trigger circuit includes a first branch and a second branch, the first branch is connected to a first thyristor, the second branch is connected to a second thyristor, and the connection directions of the first thyristor and the second thyristor are opposite; the first branch and the second branch are connected in parallel; the trigger circuit includes gate contacts and anode and cathode contacts of the first thyristor and the second thyristor.

[0035] The anode contact of the second thyristor of the trigger circuit is connected to the main circuit through the auxiliary contact 20 on the main circuit, the anode contact of the first thyristor of the trigger circuit is connected to the main circuit through the terminal 23 on the main circuit, and the trigger circuit is connected in parallel with the main circuit; the gate of the first thyristor is connected to the main circuit through the auxiliary contact 22 on the main circuit, and the gate of the second thyristor is connected to the main circuit through the auxiliary contact 21 on the main circuit; the main circuit includes a main contact 25, and the main contact 25 is arranged between the auxiliary contact 22 and the auxiliary contact 21.

[0036] Under normal power-on conditions, current passes through the A-main contact 25-B main circuit, and the thyristor module does not work, that is, the thyristor circuit does not pass current under normal conditions.

[0037] Figure 2 This is a normal current loop structure diagram. Figure 2 As shown, at a certain moment of the alternating current, the current passes through A-main contact 25-B. During the switching process, the main contact 25 in the AB circuit is opened, and the current is maintained through the arc A-arc-25-arc-B. After the alternating current passes through zero, the AB circuit is disconnected. If the arc does not reignite, the arc in this process generates a very high temperature, reaching tens of thousands of degrees Celsius, causing the oil tap to generate gas, the oil temperature rises, and the main contact 25 is burned, affecting the life of the product. In addition, the main contact 25 will also generate an arc during the process from opening to closing.

[0038] To avoid Figure 2In order to overcome the defects of the current loop shown in the figure, the embodiment of the present invention adopts a trigger circuit for a thyristor on-load tap changer, the trigger circuit includes two reverse-connected first thyristors 1 and second thyristors 2, the trigger circuit forms a parallel circuit including two reverse-connected thyristors, the anode contact of the second thyristor of the trigger circuit is connected to the main circuit formed by AB through the auxiliary contact 20 on the main circuit, the anode contact of the first thyristor of the trigger circuit is connected to the main circuit formed by AB through the upper terminal 23 of the main circuit, and the trigger circuit is connected in parallel with the main circuit. In normal state, the current path is the same as Figure 1 As shown in A-main contact 25-B, when the main contact 25 is opened, the contact resistance between the main contact 25 and A and B gradually increases, causing A and B to no longer be at the same potential. At a certain moment, the potential relationship of the alternating current in the direction of AB is VA>V25>VB. Since 20 is closed to A, 21 is closed to A, 22 is closed to B, and 23 is closed to B, then VA=V20=V21, VB=V22=V23, then V20>V23, and a forward voltage from the auxiliary contact 20 to the end point 23 is established at both ends of the thyristor, that is, a voltage drop circuit from the auxiliary contact 20 to the end point 23 is formed, V21>V23 forms a trigger voltage from the gate to the cathode and forms a trigger current, that is, a voltage drop circuit from the auxiliary contact 20 to the end point 23 is formed, which meets the conditions for the thyristor to be triggered and turned on.

[0039] Figure 3 Schematic diagram of the trigger circuit after the main contact 25 is disconnected.

[0040] During the switching process, for the transition branch AB, the load current flowing through the branch is equal to the sum of the currents flowing through the main contacts and the thyristor module. L =I M +I T

[0041] The current loop equation for the trigger system can be expressed as

[0042]

[0043] Among them, I L Indicates the load current flowing through the branch, I M is the current flowing through the main contacts, I T is the current flowing through the thyristor module, U M The voltage across the main contacts when the main contacts are open or closed, U T is the voltage across the thyristor module, L is the parasitic inductance of the entire loop, Z is the overall impedance of the thyristor module, I T (0) represents the current flowing through the thyristor module at the initial moment.

[0044] When the main contacts are opened or closed, the speed at which the current in the main circuit is transferred to the trigger circuit can be expressed as:

[0045]

[0046] To ensure that the current in the main circuit is successfully transferred to the trigger circuit, it is necessary to ensure Need to guarantee (U M -U T )-ZI T >0, so the design of the trigger system needs to ensure that the opening distance of the main contact 25 is large enough to ensure that a large U M At the same time, the parasitic inductance of the entire circuit should be controlled as much as possible, and thyristors with smaller on-resistance should be selected.

[0047] like Figure 3 As shown, after the main contact 25 is disconnected, the thyristor is turned on, and the current flows from A-second thyristor-B. At this time, the A-main contact 25-B loop is short-circuited, and no current passes through, so no arcing occurs. Subsequently, 21 and A, 22 and B are opened, and after the current passes through zero, since 21 and A, 22 and B are opened, no trigger current is generated, so the second thyristor is turned off. In the embodiment of the present invention, the continuous current time of the second thyristor is less than 12 milliseconds.

[0048] When the current is reversed, that is, B-main contact 25-A, the first thyristor can be triggered by the same logic. In addition, the triggering mode of the switch contact 25 from opening to closing is the same.

[0049] Among them, auxiliary contacts 20 and 21, 25, and 21 can be opened after the thyristor is naturally turned off to prevent the thyristor from being affected by the circuit. There must be a disconnection timing requirement with the main circuit, that is, the separation process is 25 separation, then 21 and 22 separation, then the first thyristor or the second thyristor is turned off, and then 20 separation. To ensure that 20 does not produce arcing, 20 can only be opened more than 10 milliseconds after 21 and 22 are separated.

[0050] In the embodiment of the present invention, the trigger circuit is used to short-circuit the main circuit during the opening or closing process of the main contact to prevent the main circuit from generating arcing.

[0051] The embodiments of the present invention are mainly applied to the switching switch of the hybrid on-load tap changer to avoid the generation of arcing, prevent the arcing from decomposing transformer oil and ablation of contacts, thereby reducing the maintenance frequency of the on-load tap changer and improving the reliability of the on-load tap changer.

[0052] Preferably, the main contact 25 is a mechanical switch.

[0053] Preferably, the direction of the current in the main circuit includes from A to B, or from B to A.

[0054] Preferably, the continuous current time of the first thyristor or the second thyristor is less than 12 milliseconds.

[0055] Figure 4 The schematic diagram of the thyristor trigger system circuit is shown in Figure 1, where r and D1 are connected in series to the gate level and the main circuit. r is a resistor used to limit the gate trigger current, and D1 is a diode or silicon stack with single-phase conduction, used to limit the gate reverse current. U is a varistor connected in parallel to both ends of the thyristor to protect the forward and reverse withstand voltage of the thyristor. Connect the thyristor trigger system circuit to the on-load tap changer switch. Figure 5 This is the principle diagram of a single-phase transfer switch of a hybrid on-load tap changer. The thyristor trigger system circuit is connected in parallel on the transition branches of the four transfer switches AB, CD, EF, and A'-B', among which CD and EF share a set of thyristor trigger system circuits. The action sequence from n to n+1 is: the basic circuit of the CD thyristor auxiliary contact is turned on, then the basic circuit of the AB thyristor auxiliary contact is closed, then the basic circuit of the CD thyristor auxiliary contact is opened, then the basic circuit of the A'B' thyristor auxiliary contact is closed, then the basic circuit of the AB thyristor auxiliary contact is opened, then the basic circuit of the EF thyristor auxiliary contact is closed, and then the basic circuit of the A'B' thyristor auxiliary contact is opened.

[0056] According to the above circuit analysis, the present invention connects the thyristor trigger system circuit in parallel to each transition branch of the on-load tap changer, so that no arc is generated during the opening or closing of the mechanical contacts during the switching process of the tap changer, solves the problem of arc in the oil of conventional mechanical switches, avoids the ablation of the contacts and the carbonization of the oil, thereby reducing the maintenance frequency of the on-load tap changer and improving the reliability of the on-load tap changer.

[0057] In the implementation mode of the present invention, the thyristor circuit is triggered by a mechanical switch, and no additional trigger control circuit is required; the thyristor has a low rated capacity, and will not damage the on-load tap changer and the transformer when the thyristor is out of control; the implementation mode of the present invention uses a triggering principle for a thyristor on-load tap changer and cooperates with the timing of the contacts to achieve the triggering condition of the thyristor. The implementation mode of the present invention uses a triggering principle for a thyristor on-load tap changer and establishes the triggering condition of the thyristor through the potential difference during the contact opening process, without the need for an external triggering power supply.

[0058] In the implementation manner of the present invention, the continuous current of the thyristor in the thyristor circuit is less than 12 milliseconds, and no arcing will be generated; since the thyristor circuit of the present invention is triggered by a mechanical switch, no additional trigger control circuit is required; the thyristor is energized for a short time, the rated capacity requirement is low, and the on-load tap changer and the transformer will not be damaged when the thyristor is out of control; the present invention provides a triggering principle for a thyristor on-load tap changer, and the triggering condition of the thyristor is achieved through the coordination of the contact timing. Through a triggering principle for a thyristor on-load tap changer, the triggering condition of the thyristor is established through the potential difference in the contact opening process. The implementation manner of the present invention uses a triggering principle for a thyristor on-load tap changer, and the triggering process will not generate arcing, and the on-load tap changer transitions smoothly without arc shock and heat generation.

[0059] like Figure 6 As shown, the auxiliary contact triggering method 800 starts from step 801:

[0060] Preferably, in step 801: a trigger circuit is established, the trigger circuit comprises a first branch and a second branch, the first branch is connected to a first thyristor, the second branch is connected to a second thyristor, and the first thyristor is connected in opposite directions to the second thyristor; the first branch and the second branch are connected in parallel; the trigger circuit comprises gate contacts and anode and cathode contacts of the first thyristor and the second thyristor;

[0061] Preferably, in step 802: a main circuit is established, the anode contact of the second thyristor of the trigger circuit is connected to the main circuit through the auxiliary contact 20 on the main circuit, the anode contact of the first thyristor of the trigger circuit is connected to the main circuit through the terminal 23 on the main circuit, and the trigger circuit is connected in parallel with the main circuit; the gate of the first thyristor is connected to the main circuit through the auxiliary contact 22 on the main circuit, and the gate of the second thyristor is connected to the main circuit through the auxiliary contact 21 on the main circuit; the main circuit includes a main contact 25, and the main contact 25 is arranged between the auxiliary contact 22 and the auxiliary contact 21;

[0062] Preferably, in step 803: the trigger circuit is used to short-circuit the main circuit during the opening or closing process of the main contact 25 to prevent the main circuit from arcing.

[0063] Preferably, the main contact 25 is a mechanical switch.

[0064] Preferably, the direction of the current in the main circuit includes from A to B, or from B to A.

[0065] Preferably, at least 10 milliseconds after the main contact 25 is opened and the auxiliary contacts 21 and 22 are opened, the first thyristor or the second thyristor is opened and the auxiliary contact 20 is opened.

[0066] Preferably, the continuous current time of the first thyristor or the second thyristor is less than 12 milliseconds.

[0067] The present invention is described in detail above in conjunction with the embodiments of the accompanying drawings. A person skilled in the art can make various variations of the present invention according to the above description. Therefore, certain details in the embodiments should not constitute a limitation of the present invention, and the scope of protection of the present invention shall be defined by the scope of the attached claims.

Claims

1. A thyristor triggering system for a hybrid on-load tap changer, characterized in that: The system comprises: a trigger circuit and a main circuit; The trigger circuit comprises a first branch and a second branch, the first branch is connected to a first thyristor, the second branch is connected to a second thyristor, and the first thyristor is connected in opposite directions to the second thyristor; the first branch and the second branch are connected in parallel; the trigger circuit comprises gate contacts and anode and cathode contacts of the first thyristor and the second thyristor; The trigger circuit is used to short-circuit the main circuit during the opening or closing process of the main contact to prevent the main circuit from generating arcing.

2. A thyristor triggering system for a hybrid on-load tap changer according to claim 1, characterized in that: The anode contact of the second thyristor of the trigger circuit is connected to the main circuit via an auxiliary contact (20) on the main circuit, and the anode contact of the first thyristor of the trigger circuit is connected to the main circuit via an end point (23) on the main circuit, and the trigger circuit is connected in parallel with the main circuit; the gate of the first thyristor is connected to the main circuit via an auxiliary contact (22) on the main circuit, and the gate of the second thyristor is connected to the main circuit via an auxiliary contact (21) on the main circuit; the main circuit includes a main contact (25), and the main contact (25) is arranged between the auxiliary contact (22) and the auxiliary contact (21); The main contact is a mechanical switch.

3. A thyristor triggering system for a hybrid on-load tap changer according to claim 2, characterized in that: The current direction in the main circuit includes from A to B, or from B to A.

4. A thyristor triggering system for a hybrid on-load tap changer according to claim 2, characterized in that: After the switch of the system is opened, and the auxiliary contact (21) and the auxiliary contact (22) are opened for at least 10 milliseconds, the first thyristor or the second thyristor is opened, and the auxiliary contact (20) is opened.

5. The thyristor triggering system for a hybrid on-load tap changer according to claim 1, characterized in that: The continuous current time of the first thyristor or the second thyristor is less than 12 milliseconds.

6. A thyristor triggering method of the system according to claim 1, the method comprising: Establishing a trigger circuit, the trigger circuit comprising a first branch and a second branch, the first branch being connected to a first thyristor, the second branch being connected to a second thyristor, the first thyristor being connected in opposite directions to the second thyristor; the first branch and the second branch being connected in parallel; the trigger circuit comprising gate contacts and anode and cathode contacts of the first thyristor and the second thyristor; A main circuit is established, wherein the anode contact of the second thyristor of the trigger circuit is connected to the main circuit via an auxiliary contact (20) on the main circuit, and the anode contact of the first thyristor of the trigger circuit is connected to the main circuit via an end point (23) on the main circuit, and the trigger circuit is connected in parallel with the main circuit; the first gate of the first thyristor is connected to the main circuit via an auxiliary contact (22) on the main circuit, and the second gate of the second thyristor is connected to the main circuit via an auxiliary contact (21) on the main circuit; the main circuit includes a main contact (25), and the main contact (25) is arranged between the auxiliary contact (22) and the auxiliary contact (21); The trigger circuit is used to short-circuit the main circuit during the opening or closing process of the main contact (25) to prevent the main circuit from generating an arc.

7. A thyristor triggering method according to claim 6, wherein: The current loop equation for the trigger system can be expressed as Among them, I L Indicates the load current flowing through the branch, I M is the current flowing through the main contacts, I T is the current flowing through the thyristor module, U M The voltage across the main contacts when the main contacts are open or closed, U T is the voltage across the thyristor module, L is the parasitic inductance of the entire loop, Z is the overall impedance of the thyristor module, I T (0) represents the current flowing through the thyristor module at the initial moment.

8. A thyristor triggering method according to claim 6, wherein: When the main contacts are opened or closed, the speed at which the current in the main circuit is transferred to the trigger circuit can be expressed as: To ensure that the current in the main circuit is successfully transferred to the trigger circuit, it is necessary to ensure Need to guarantee (U M -U T )-ZI T >0, so the design of the trigger system needs to ensure that the opening distance of the main contact 25 is large enough to ensure that a large U M At the same time, the parasitic inductance of the entire circuit should be controlled as much as possible, and thyristors with smaller on-resistance should be selected.

9. A thyristor triggering method according to claim 6, wherein: After the switch is opened, and the auxiliary contact (21) and the auxiliary contact (22) are opened for at least 10 milliseconds, the first thyristor or the second thyristor is opened, and the auxiliary contact (20) is opened.

10. A thyristor triggering method according to claim 6, wherein: The continuous current time of the first thyristor or the second thyristor is less than 12 milliseconds.

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