A gas-insulated discharge gap for overvoltage protection of the neutral point of a transformer

Abstract

This application provides a gas-insulated discharge gap for overvoltage protection of the neutral point of a transformer. In this application, a metal housing is connected to form a sealed cavity to accommodate the conductive rod, the moving-side ball head and the static-side ball head for receiving discharges, and gas insulation is provided for them. Thus, when the moving-side ball head approaches the static-side ball head connected to the neutral point of the transformer and discharges in the insulating gas, the induction coil arranged on the outer periphery of the conductive rod can synchronously sense the discharge current conducted from the moving-side ball head into the conductive rod, so as to integrate the overvoltage protection discharge gap of the transformer neutral point and the current transformer into one body through a single-gap discharge structure, reduce the component size, reduce the insulation distance, thereby reducing the space occupied by the components and providing higher safety performance at the same time.

Description

Technical Field

[0001] This application relates to the field of transformer protection equipment, and more particularly to a gas-insulated discharge gap for overvoltage protection of transformer neutral points. Background Art

[0002] After the neutral point of the transformer is led out by the combined electrical apparatus for overvoltage protection of the transformer neutral point, the neutral point is electrically connected to equipment such as a discharge gap, a current transformer, an earthing disconnector, and a lightning arrester respectively, serving as an overvoltage comprehensive protection device for the neutral point of an unearthed transformer in an effectively grounded power grid. Its electrical principle can be referred to Figure 3 as shown. Electrical isolation is achieved between each electrical component through open air insulation technology. As a part of the combined electrical apparatus, the main function of the discharge gap is to release the electrical energy of the overvoltage at the transformer neutral point.

[0003] The existing combined electrical apparatus using air insulation technology often uses a solid-insulated current transformer, which is connected in series in the circuit to measure the current passing through the circuit. For the existing combined electrical apparatus for overvoltage protection of transformer neutral points, due to the use of open air insulation technology, it is vulnerable to external environmental factors such as humidity and altitude, and a safe distance needs to be maintained according to the regulations of the corresponding voltage level during operation. The discharge gap using air insulation technology occupies a large space, which is not conducive to the requirements of building an intensive substation; the current transformer often uses a solid insulation medium for integral casting, and it cannot be integrated with the discharge gap, and it is difficult to compress the installation space of the two. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, this application provides a gas-insulated discharge gap for overvoltage protection of transformer neutral points. As a part of the overvoltage comprehensive protection device for transformer neutral points, it uses SF6 gas insulation technology as a whole, and can release the electrical energy of the overvoltage at the transformer neutral point through internal spherical head gap discharge and at the same time integrate the current transformer to detect the internal discharge current value of the conductive rod connected to the spherical head. This application can simplify the structure of the overvoltage protection device for the transformer neutral point and integrate the function of measuring the discharge current. The specific technical solutions adopted in this application are as follows.

[0005] First, to achieve the above object, a gas-insulated discharge gap for overvoltage protection of a transformer neutral point is proposed, which includes: a metal shell, which is hermetically connected to the common terminal shell of the transformer neutral point and grounded together; a conductive rod, the upper part of which is slidably electrically connected to the top of the metal shell, and the bottom of which is fixedly electrically connected with a moving-side ball head; an induction coil, which is arranged on the outer periphery of the conductive rod to detect the current in the conductive rod; a static-side ball head, which is fixedly arranged in the common terminal shell of the transformer neutral point and electrically connected to the transformer neutral point; the moving-side ball head is located above the static-side ball head, and both the moving-side ball head and the static-side ball head are arranged in an insulating gas; when the conductive rod slides upward along the metal shell, the gap distance between the moving-side ball head and the static-side ball head increases, and the discharge voltage threshold between the ball heads increases; when the conductive rod slides downward along the metal shell, the gap distance between the moving-side ball head and the static-side ball head decreases, and the discharge voltage threshold between the ball heads decreases. When the voltage between the ball heads exceeds the discharge voltage threshold, the insulating gas is broken down, and the discharge current is conducted through the moving-side ball head to the conductive rod and discharged to the grounding circuit.

[0006] Optionally, for the gas-insulated discharge gap for overvoltage protection of a transformer neutral point as described in any one of the above, wherein the grounding circuit includes: an upper flange, which is hermetically connected to the outer periphery of the conductive rod and is arranged above the induction coil; a lower flange, which is hermetically connected to the common terminal shell of the transformer neutral point and is arranged below the induction coil; a metal connector, which is hermetically arranged between the upper flange and the lower flange and is stably electrically connected to both the upper flange and the lower flange; the upper flange, the metal connector and the lower flange are connected on the outer side of the induction coil to form a grounding current path, guiding the discharge current to be grounded unidirectionally from the top end of the conductive rod through the grounding current path.

[0007] Optionally, for the gas-insulated discharge gap for overvoltage protection of a transformer neutral point as described in any one of the above, wherein the metal shell forms a grounding circuit only on the outer side of the induction coil.

[0008] Optionally, for the gas-insulated discharge gap for overvoltage protection of a transformer neutral point as described in any one of the above, wherein the inner side of the upper flange extends downward to the lower flange and forms a shielding cylinder surrounding the outer periphery of the conductive rod, and the bottom of the shielding cylinder is insulated from the lower flange.

[0009] Optionally, for the gas-insulated discharge gap for overvoltage protection of a transformer neutral point as described in any one of the above, wherein the metal connector is a cross-connected metal strip; the bottom of the shielding cylinder is isolated from the lower flange by an insulating connector; the top of the insulating connector abuts against the bottom end of the shielding cylinder, and the bottom of the insulating connector abuts against the upper surface of the lower flange.

[0010] Optionally, for the gas-insulated discharge gap for overvoltage protection of the transformer neutral point described in any of the above, an outer cover is further provided outside the induction coil, and the outer cover of the coil is optionally arranged inside or outside the jumper metal busbar.

[0011] Optionally, for the gas-insulated discharge gap for overvoltage protection of the transformer neutral point described in any of the above, the metal connector is a sealed metal cylinder, the top of the sealed metal cylinder is hermetically connected to the upper flange, and the bottom of the sealed metal cylinder is hermetically connected to the lower flange or is set as a whole; an insulating gas is filled between the bottom of the shielding cylinder and the lower flange.

[0012] Optionally, for the gas-insulated discharge gap for overvoltage protection of the transformer neutral point described in any of the above, the top of the upper flange is sealed by a grounding end cover; a contact seat extending downward into the upper flange and surrounding the outer circumference of the conductive rod is further provided on the upper end surface or the lower end surface of the grounding end cover; a moving-side ball head guide seat is provided at the bottom end of the shielding cylinder; the conductive rod passes through the contact seat and the moving-side ball head guide seat, and is restricted by the contact seat and the moving-side ball head guide seat to drive the moving-side ball head to slide up and down above the static-side ball head.

[0013] Optionally, for the gas-insulated discharge gap for overvoltage protection of the transformer neutral point described in any of the above, the moving-side ball head guide seat and / or the shielding cylinder are made of insulating materials to block electrical contact between the lower flange and the conductive rod; the grounding end cover and the contact seat are both made of conductive materials, and the grounding end cover, the contact seat, the upper flange and the conductive rod are electrically connected.

[0014] Optionally, for the gas-insulated discharge gap for overvoltage protection of the transformer neutral point described in any of the above, a gap distance adjusting mechanism is further provided on the top of the grounding end cover; the static-side ball head is arranged on the common terminal conductor electrically connected to the transformer neutral point; the gap distance adjusting mechanism drives the conductive rod to slide downward or upward along the central axis direction of the induction coil so as to correspondingly increase or decrease the discharge voltage threshold between the moving-side ball head and the static-side ball head.

[0015] Optionally, for the gas-insulated discharge gap for overvoltage protection of the transformer neutral point described in any of the above, a manhole is further provided at the bottom of the common terminal housing of the transformer neutral point, the opening direction of the manhole is directly opposite to the common terminal conductor, and is located below the static-side ball head.

[0016] Beneficial effects

[0017] 1. A sealed cavity is formed by connecting to a metal shell to accommodate a conductive rod and the moving and static spherical heads for gap discharge, and gas insulation is provided for them. In this application, by controlling the up-and-down sliding of the conductive rod in the cavity of the metal shell, the gap distance between the spherical heads is adjusted, thereby controlling the limiting voltage of the gap discharge and achieving neutral point overvoltage protection. Thus, when the moving spherical head approaches the static spherical head connected to the transformer neutral point and discharges in the insulating gas, the induction coil arranged on the outer periphery of the conductive rod can synchronously sense the discharge current conducted from the moving spherical head into the conductive rod, so as to integrate the transformer neutral point overvoltage protection discharge gap and the current transformer into one body through a single gap discharge structure, reducing the component size, reducing the insulation distance, thereby reducing the space occupied by the components and simultaneously providing higher safety performance.

[0018] 2. In this application, isolation and protection of the transformer neutral point discharge gap are achieved through gas insulation technology in the sealed cavity formed by the metal shell. Using SF6 as the insulating medium can effectively reduce the insulation distance of the transformer and ensure that the gap distance value is not restricted by the surrounding atmospheric conditions, so as to reduce the floor area of the transformer equipment and the requirements for the installation space, saving equipment land and installation and commissioning costs.

[0019] 3. In particular, it is worth noting that through the optimization of the grounding circuit of the connected metal shell in this patent, the downward electrical path of the inner shielding cylinder of the induction coil can be isolated and blocked by using the insulating gas medium or the insulating connection piece, so as to ensure that the induction coil only senses the discharge current passing through the conductive rod during the grounding of the transformer neutral point discharge and will not be interfered by the return electrical path signal. Thus, while integrating the discharge spherical head and the gas-insulated current transformer into one body to improve the space utilization rate, this application can also ensure that the induction coil can effectively sense the current signal, compress the equipment installation space, and meet the installation requirements of intensive substations.

[0020] Other features and advantages of this application will be described in the subsequent specification, and some of them will become obvious from the specification or be understood by implementing this application. Brief Description of the Drawings

[0021] The drawings are used to provide a further understanding of this application, and constitute a part of the specification. Together with the embodiments of this application, they are used to explain this application and do not constitute a limitation to this application. In the drawings:

[0022] Figure 1 is a cross-sectional view of the gas-insulated discharge gap for transformer neutral point overvoltage protection in the off state of this application;

[0023] Figure 2 is a cross-sectional view of another gas-insulated discharge gap for transformer neutral point overvoltage protection in the discharge state of this application;

[0024] Figure 3 It is a schematic diagram of the principle of the combined circuit for overvoltage protection of the neutral point of the transformer to which this application is applied;

[0025] In the figure, 1 represents the gap distance adjusting mechanism; 2 represents the contact seat; 3 represents the grounding end cover; 4 represents the conductive rod; 5 represents the upper flange; 6 represents the induction coil; 7 represents the cross-connected metal row; 8 represents the coil outer cover; 9 represents the insulating part; 10 represents the moving-side ball head guide seat; 11 represents the lower flange; 12 represents the moving-side ball head; 13 represents the static-side ball head; 14 represents the common terminal conductor; 15 represents the lower tank body; 16 represents the manhole; 21 represents the moving-side part; 22 represents the current mutual induction part; 23 represents the static-side part; 31 represents the transformer; 32 represents the lightning arrester; 33 represents the grounding disconnector; 34 represents the switch current transformer; 35 represents the discharge gap; 36 represents the discharge current transformer. Specific implementation manners

[0026] To make the objectives and technical solutions of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions of the embodiments of this application with reference to the drawings of the embodiments of this application. Obviously, the described embodiments are some but not all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of this application without creative efforts fall within the scope of protection of this application.

[0027] Those skilled in the art of this technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used here have the same meaning as the general understanding of those of ordinary skill in the art in the field to which this application belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless defined as here.

[0028] The meaning of "and / or" described in this application means that both the case of separate existence and the case of simultaneous existence of both are included.

[0029] The meaning of "inside and outside" described in this application refers to the direction from the outside of the cross-connected metal row to the inner center of the conductive rod relative to the gas-insulated discharge gap for overvoltage protection of the neutral point of the transformer of this application itself; rather than a specific limitation on the device mechanism of this application.

[0030] The meaning of "connection" described in this application can be a direct connection between components or an indirect connection between components through other components.

[0031] In this application, the meanings of "upper" and "lower" refer to the direction from the static side ball head to the gap distance adjustment mechanism when the user is facing the gas-insulated discharge gap for overvoltage protection of the transformer neutral point. This is the upper direction, and vice versa is the lower direction. This is not a specific limitation on the device mechanism of this application.

[0032] Figure 1 A gas-insulated discharge gap structure for overvoltage protection of a transformer neutral point according to this application is installed outside the transformer box body and is provided at the lead-out end of the conductive line led out from the neutral point of the internal circuit structure of the transformer box. The lead-out end of the neutral point includes a conductive inner core electrically connected to the transformer neutral point and a common terminal housing hermetically connected to the outside of the conductive inner core. The inside of the common terminal housing is filled with insulating gases such as SF6 to achieve gas insulation. The common terminal housing itself is grounded to provide ground protection. The discharge gap of this application can collect the discharge current during the discharge process of the transformer neutral point while providing overvoltage protection to the transformer neutral point through the following structure:

[0033] A metal shell, which can be integrally formed or connected through several connecting parts such as flanges. The metal shell is hermetically connected to the common terminal housing of the transformer neutral point and is grounded together with the common terminal housing through the metal material at the connection part. Moreover, the cavity formed inside the metal shell is also interconnected with the common terminal housing, so that the cavity is filled with the same insulating gases such as SF6 as the lead-out end, so that the discharge gap of this application and the lead-out end of the transformer neutral point are in a closed gas-insulated environment together, which can effectively shorten the insulation distance, avoid the influence of the external atmospheric environment on the insulation distance, and ensure the safety of devices and personnel;

[0034] A common terminal conductor 14 is arranged inside the common terminal housing of the transformer neutral point and is electrically connected to the transformer neutral point through the conductive inner core. A static side ball head 13 is also fixedly arranged on the common terminal conductor 14. The static side ball head 13 is installed below the connection part of the metal shell, is located inside the common terminal housing and is electrically connected to the transformer neutral point;

[0035] A conductive rod 4 is slidably and electrically connected between the top of the metal shell, that is, the electrical connection with the metal shell is realized through sliding contact. The bottom of the conductive rod 4 is electrically connected with a moving side ball head 12, and the conductive rod 4 and the moving side ball head 12 are connected as a whole. The moving side ball head 12 can be driven to move down to the bottom position of the metal shell by sliding the conductive rod 4 downward. At this time, the gap discharge is realized by breaking down the insulating gas between the moving side ball head 12 and the static side ball head 13; when the conductive rod 4 slides upward to the top position of the metal shell, the moving side ball head 12 is out of the discharge gap range of the static side ball head 13, blocking the gap discharge, and no current passes through the conductive rod 4 at this time;

[0036] The induction coil 6 is arranged on the outer periphery of the conductive rod 4 and is located inside the metal shell. It is sealed in a gas-insulated environment by the metal shell. The conductive rod penetrates through the induction coil 6 to induce a discharge current formed in the conductive rod 4 through the moving-side ball head 12 during the discharge process between the gaps of the moving-side and static-side ball heads, so as to achieve Figure 3 the function of the discharge current transformer 36 connected in series in the circuits of the transformer 31 and the grounding discharge gap 35, and realizes the measurement of the discharge current passing through this circuit.

[0037] The above-mentioned moving-side and static-side ball heads can be realized by metal spheres, or can be set as hemispherical conductive structures or only have an arc-shaped surface.

[0038] Thus, the discharge structure of the present application can integrate the ball head structure of the discharge gap for protecting the neutral point overvoltage of the transformer and the current transformer into one through the gas-insulated environment formed by the metal shell, and provide gas insulation through the SF6 gas filled inside the metal shell and the common-end shell of the transformer neutral point. This integration method not only saves the space occupied by the device itself, but also can reduce the insulation distance required by the device by using SF6 as the insulating medium, and further reduce the space occupied by the overall transformer system.

[0039] Take Figure 1 the implementation method shown as an example. The above-mentioned discharge gap for protecting the neutral point overvoltage of the transformer can be specifically divided into an upper moving-side part 21, a lower static-side part 23, and an intermediate current transformer part 22:

[0040] The upper moving-side part includes: a gap distance adjusting mechanism 1, a conductive rod 4, a contact seat 2, and a grounding end cover 3. Among them, the conductive rod passes downward through the inside of the induction coil 6 of the intermediate current transformer from the moving contact seat 2 installed inside the grounding end cover 3 at the top of the metal shell; the gap distance adjusting mechanism can usually be fixed on the top of the grounding end cover 3, and by selecting a motor and transmission components such as gears and racks driven by the motor shaft, it drives the corresponding up and down linear movement of the conductive rod meshed with the transmission components at the top; the contact seat surrounds the upper outer periphery of the conductive rod, is arranged in the middle of the grounding end cover 3 and is slidably connected to the conductive rod through a connection structure such as a ball bearing. The contact seat is set as a metal material at least at the position where it is in direct contact with the conductive rod on its inner periphery to achieve electrical connection through sliding contact. The contact seat 2 generally can also extend downward from the upper end face or the lower end face of the grounding end cover 3 to the inner periphery of the upper flange 5 in the current mutual induction part 22. The top of the contact seat 2 forms a metal connection disc structure, which is fixed to the top surface of the grounding end cover 3 through the bottom surface of the metal connection disc structure and maintains the same potential, and thereby keeps the conductive rod at the grounding potential to provide grounding protection for the transformer center point;

[0041] The intermediate current transformer part includes: an induction coil 6, a metal shell body formed by an upper flange 5, a lower flange 11, and a bridging metal row 9, and parts such as an insulating part 9, a coil cover 8, a moving-side ball head guide seat 10, and a shielding cylinder arranged inside it. Its function is to sense the discharge current of the static-side ball head passing through the conductive rod through the induction coil and measure the current of the internal conductor. Electrical connection is achieved through fixed contact among the contact seat 2, the grounding end cover 3, and the upper flange 5 of the current transformer. The top of the upper flange 5 is sealed by the grounding end cover 3. The current transformer is arranged on the lower side of the upper flange. The inside of the upper flange can extend downward to form a shielding cylinder surrounding the outer circumference of the conductive rod 4. The coil is wound around the outside of the shielding cylinder and is supported by the shielding cylinder. The top of the shielding cylinder is provided with the above-mentioned contact seat 2 to provide a limit to the sliding direction of the conductive rod, guiding it to approach or move away from the static-side ball head at the bottom in a vertical up-and-down sliding manner; to prevent the shielding cylinder and the lower flange or the metal shell from forming a grounding return path inside the induction coil and affecting the induction of the discharge current in the conductive rod by the induction coil, generally an insulating part can also be arranged between the shielding cylinder and the lower flange, so that the top of the insulating part 9 abuts against the bottom end of the shielding cylinder, and the bottom of the insulating part 9 abuts against the upper surface of the lower flange 11, ensuring that the shielding cylinder cannot form a shell return through the barrier of the insulating part, so as to ensure that only the current passing through the disconnector conductive rod exists inside the coil. In addition, the insulating connecting part 8 can also form an insulating gas chamber between the lower flange and the shielding cylinder through abutting against the shielding cylinder and the lower flange to achieve insulation protection for the moving and static contacts; the coil surrounds the outside of the insulating gas chamber. Since only the induced current passes through the inside of the coil, it can contact the air under the protection of the coil cover arranged between the upper flange and the lower flange without further adding gas insulation outside the coil; outside the coil, a coil cover can be further arranged between the upper flange and the lower flange or the whole can be sealed by a metal cylinder, so that the coil is not directly exposed to the atmosphere. In other implementation modes, the above-mentioned coil can also be integrally sealed by a grounded shell arranged in a sealed manner, so that the coil is not exposed to the atmosphere and gas insulation is achieved through the sealing provided by the grounded shell outside the coil.

[0042] In this embodiment, in the way of forming an insulating gas chamber by sealing inside the coil, generally it is also necessary to cooperate with a bridging metal row 7 outside the coil cover 9 to achieve grounding of the flange structure. The bridging metal row 7 can be optionally arranged inside or outside the coil cover; while in the way of achieving gas insulation outside the coil through a grounded shell with integral sealing, the way of directly welding the upper and lower ends of the sealed metal cylinder to the flange structure can be adopted to form a larger insulating gas chamber that completely encloses the coil, the ball head, and the conductive rod outside the induction coil, and grounding is achieved through the integral setting of the sealed metal cylinder and the flange structure in the metal shell of the larger insulating gas chamber.

[0043] The lower flange of the current mutual inductance part is electrically connected to the lower tank body 15 formed by the common end shell of the lower side transformer neutral point through a fixed contact structure such as welding or sealing bolts; between the upper flange and the lower flange, in addition to electrical connection through the sealing metal cylinder itself, a jumper metal strip 7 can also be used for electrical connection; the moving side ball head guide seat 10 can be directly fixedly installed at the lower end of the lower side of the current transformer shielding cylinder. An insulating guide ring can be installed inside the moving side ball head guide seat to guide the up and down movement of the conductive rod, or it can be directly set as a metal conductive material; however, considering that there may be burrs on the surface of the moving side ball head guide seat 10 itself, which are likely to break down the insulating gas when the voltage of the static side ball head is relatively high, therefore, in general, a moving contact shielding cover with a smooth metal surface is also installed on the moving side ball head guide seat 10 to cooperate with the electric field strengths on both the moving side of the upper part of the switch and the static side of the neutral point lead-out end, and to shield the electric field between the moving side ball head and the shielding cylinder. If the surface of the moving side ball head guide seat 10 is smooth enough, the above-mentioned moving contact shielding cover can also be omitted without affecting the performance of the device of the present application. The conductive rod shielding cylinder is installed above the moving side ball head guide seat, and the moving side ball head guide seat 10 is fixed to the inner circumference of the lower flange 11 to cooperate with the electric field strengths on both the moving side of the upper part of the switch and the static side of the neutral point lead-out end, and to prevent the conductive rod from making electrical contact with the shielding cylinder.

[0044] In other implementation manners, refer to Figure 2 As shown, to ensure that the grounding end cover 3 and the upper flange only form a grounding loop outside the induction coil 6, and no grounding loop can be formed between the induction coil and the conductive rod to affect the induction of the discharge current by the induction coil, the above-mentioned grounding loop can also be set to be formed by connecting the following conductive components:

[0045] The upper flange 5, which is hermetically connected to the outer circumference of the conductive rod 4 and is arranged above the induction coil 6;

[0046] The lower flange 11, which is hermetically connected to the common end shell of the transformer neutral point and is arranged below the induction coil 6;

[0047] The metal connecting piece, which is hermetically arranged between the upper flange 5 and the lower flange 11 through a metal cylindrical structure and is stably electrically connected to both the upper flange 5 and the lower flange 11 at the same time to provide grounding protection;

[0048] The upper flange 5, the metal connecting piece and the lower flange 11 are connected outside the induction coil 6 to form a grounding current return path, guiding the discharge current to be grounded unidirectionally from the top of the conductive rod 4 through the grounding current return path.

[0049] Among them, an inner side of the upper flange 5 extends downward to the lower flange 11 to form a shielding cylinder surrounding the outer periphery of the conductive rod 4. An insulating gas sealed in a common terminal housing of the metal housing and the neutral point electrically isolates between the bottom of the shielding cylinder and the lower flange 11, thereby omitting the insulating member 9 structure in the previous implementation manner and effectively ensuring that there is no ground return path between the induction coil 7 and the conductive rod 4.

[0050] Thus, when the transformer neutral point needs to be grounded and discharged, the gap distance adjustment mechanism can be set to drive an internal transmission member through a motor to move the conductive rod at the top of the moving spherical head downward, passing through the contact seat 2 and the moving spherical head guide seat 10. During this sliding process, the conductive rod 4 is guided by the moving spherical head guide seat 10 so that the moving spherical head 12 at its bottom end faces directly above the common terminal conductor 14. When the neutral point voltage exceeds the discharge voltage range corresponding to the gap between the moving and static spherical heads, a discharge occurs between the moving and static spherical heads, realizing the electrical connection between the static spherical head, the moving spherical head, the conductive rod, the grounding end cover, and the upper flange of the current transformer. Thus, the discharge current can enter the conductive rod through the discharge method, pass through the grounding end cover 3 and the upper flange from the top of the conductive rod, and be connected to the grounding grid through the jumper metal strip or the sealed metal cylinder and the lower flange and the lower tank body of the current transformer, thereby realizing the overvoltage discharge of the transformer neutral point gas-insulated composite electrical apparatus. Moreover, since there is only the discharge current passing through the conductive rod inside the induction coil, it can detect the value of the discharge current passing through the conductive rod through the induced current triggered by the discharge current during the discharge process.

[0051] Cooperating with the above-mentioned moving side part and the current transformer part, the static side part of the lower connection of the discharge gap to the transformer neutral point lead-out terminal can be electrically connected to the common terminal conductor 14 through the static spherical head 13 to realize the electrical connection between the transformer neutral point and the moving spherical head. The static spherical head is installed at the top end of the common terminal conductor led out from the transformer neutral point oil-gas bushing and is located inside the lower tank body formed by the common terminal housing of the transformer neutral point. The tank body can further be provided with a manhole 16 at the lower part of the tank body near the static side, that is, at the bottom of the common terminal housing of the transformer neutral point. The opening direction of the manhole can face directly the common terminal conductor 14 and is located below the conductive rod 4 and the static spherical head for facilitating the observation and maintenance of the spherical head structure.

[0052] In some implementations, to prevent the moving-side ball head, conductive rod, conductive rod seat, clearance-side end cap, and upper flange from forming a discharge current path downward through the shielding cylinder inside the coil, which may affect the conduction of the discharge current by the grounding path formed outside the current transformer coil by the upper flange, metal connector, and lower flange, and further affect the detection of the discharge current by the induction coil, either any one or both of the above-mentioned moving-side ball head guide seat 10 and shielding cylinder can be selected as insulating materials to block the electrical contact between the lower flange 11 and the conductive rod 4 and form a grounding path connected to the grounding grid through the gas-insulated tank outside the induction coil. To ensure the discharge current path outside the induction coil, the grounding end cap 3 and contact head seat 2 in the above structure can be correspondingly selected as conductive materials to drain the discharge current by connecting the top end of the conductive rod to the grounding electrical path through the electrical connection between the grounding end cap 3, contact head seat 2, upper flange 5, and conductive rod 4.

[0053] Thus, when overvoltage protection is performed according to the voltage value specified by the transformer line, the above structure can drive the conductive rod 4 to slide along the central axis direction of the induction coil 6 to a suitable position through the gap distance adjustment mechanism 1, so that the moving and static side ball heads maintain a suitable gap distance, and this gap distance corresponds to an interval of discharge voltage values. When the neutral point voltage exceeds this voltage value interval, gap discharge occurs, thereby forming a grounding path between the two ball heads, and guiding the current unidirectionally through the conductive rod to connect the upper flange to the grounding end cap for grounding, and forming a unidirectional discharge current that can be detected by the induction coil inside the conductive rod; when the neutral point voltage does not exceed the voltage value interval corresponding to the gap distance, the gap does not discharge, and the electrical contact between the ball heads is disconnected to ensure the independent operation of the transformer neutral point.

[0054] In summary, the above switch structure of the present application has the following advantages:

[0055] 1. The discharge gap provided by the present application integrates the moving side, static side, and current transformer into an integrated structure, places them in the SF6 insulating gas at the same time, realizes the functions of grounding and measuring current simultaneously, occupies less space, and the insulation performance is not affected by the external climate, being safer and more stable;

[0056] 2. For the gas-insulated discharge gap required by this patent, the moving-side ball head, conductive rod, conductive rod seat, gap-side end cover, and upper flange form a discharge current path inside the current transformer coil. Then, the upper flange, metal connector, and lower flange form a grounding path outside the current transformer coil. Finally, the gas-insulated tank is connected to the grounding grid to ensure that the metal shell of this application can be stably grounded, thereby improving the safety of the overall discharge gap structure. By adjusting the gas gap distance between the moving side and the static side ball heads, overvoltage protection of the gas-insulated combined electrical apparatus at the transformer neutral point under the specified voltage value can be achieved. After the conductive rod moves downward and approaches the static side ball head, discharge grounding of the gas-insulated combined electrical apparatus at the transformer neutral point can be realized. The shell and the bridging metal row are connected to the grounding grid, which can protect the outside of the device from being charged and has a higher safety performance.

[0057] 3. In the discharge gap provided by this application, the moving-side ball head guide seat is installed at the bottom end of the shielding cylinder inside the current transformer, which can guide the relatively long conductive rod to move linearly into the lower tank body and approach the static side ball head to form a discharge grounding path for the transformer neutral point. The conductive rod passes through the inside of the current transformer and is connected to the grounding circuit by the grounding end cover, which is convenient for measuring the current passing through the conductive rod.

[0058] 4. The static side of the discharge gap provided by this application is installed on the common terminal conductor led out from the oil-gas bushing at the transformer neutral point, and a maintenance manhole is also provided at the lower part of the tank body at the installation position. The grounding discharge gap provided by this application arranges the moving side and the static side separately, which can facilitate the observation and maintenance of the upper switch structure by using the maintenance manhole at the lower part of the static side.

[0059] The above is only the implementation mode of this application, and its description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of this application. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several deformations and improvements can still be made, and these all belong to the protection scope of this application.

Claims

1. A gas-insulated discharge gap for overvoltage protection of the neutral point of a transformer, characterized in that Comprising: A metal casing, which is hermetically connected to the common terminal casing of the transformer neutral point and grounded together; A conductive rod (4), the upper part of which is slidably electrically connected to the top of the metal casing, and the bottom of which is fixedly electrically connected with a moving-side ball head (12); An induction coil (6), which is arranged on the outer periphery of the conductive rod (4) to detect the current in the conductive rod (4); A static-side ball head (13), which is fixedly arranged in the common terminal casing of the transformer neutral point and electrically connected to the transformer neutral point; the moving-side ball head (12) is located above the static-side ball head (13), and both the moving-side ball head (12) and the static-side ball head (13) are arranged in an insulating gas; When the conductive rod (4) slides upward along the metal casing, the gap distance between the moving-side ball head (12) and the static-side ball head (13) increases, and the discharge voltage threshold between the ball heads increases; When the conductive rod slides downward along the metal casing, the gap distance between the moving-side ball head (12) and the static-side ball head (13) decreases, and the discharge voltage threshold between the ball heads decreases; When the voltage between the ball heads exceeds the discharge voltage threshold, the insulating gas is broken down, and the discharge current is conducted through the moving-side ball head (12) to the conductive rod (4) and discharged to the grounding circuit.

2. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 1, characterized in that The grounding circuit includes: An upper flange (5), which is hermetically connected to the outer periphery of the conductive rod (4) and is arranged above the induction coil (6); A lower flange (11), which is hermetically connected to the common terminal casing of the transformer neutral point and is arranged below the induction coil (6); A metal connecting piece, which is hermetically arranged between the upper flange (5) and the lower flange (11) and is stably electrically connected to both the upper flange (5) and the lower flange (11) at the same time; The upper flange (5), the metal connecting piece and the lower flange (11) are connected on the outside of the induction coil (6) to form a grounding current path, guiding the discharge current to be grounded unidirectionally from the top end of the conductive rod (4) through the grounding current path.

3. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 2, characterized in that, The metal casing forms a grounding circuit only on the outside of the induction coil (6).

4. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 2, wherein The inner side of the upper flange (5) extends downward to the lower flange (11) and forms a shielding cylinder surrounding the outer periphery of the conductive rod (4), and there is an insulating isolation between the bottom of the shielding cylinder and the lower flange (11).

5. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 4, characterized in that, The metal connecting piece is a cross-connected metal row (7); There is an isolation between the bottom of the shielding cylinder and the lower flange (11) by an insulating connecting piece (9); The top of the insulating connecting piece (9) abuts against the bottom end of the shielding cylinder, and the bottom of the insulating connecting piece (9) abuts against the upper surface of the lower flange (11).

6. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 5, characterized in that, A coil outer cover (8) is also arranged on the outside of the induction coil (6), and the coil outer cover (8) is optionally arranged inside or outside the cross-connected metal row (7).

7. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 4, characterized in that The metal connecting piece is a sealed metal cylinder, the top of the sealed metal cylinder is hermetically connected to the upper flange (5), and the bottom of the sealed metal cylinder is hermetically connected to the lower flange (11) or is set as a whole; An insulating gas is filled between the bottom of the shielding cylinder and the lower flange (11).

8. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 4, characterized in that, The top of the upper flange (5) is sealed by a grounding end cover (3); A contact seat (2) extending downward to the inside of the upper flange (5) and surrounding the outer periphery of the conductive rod (4) is also arranged on the end face of the grounding end cover (3); A moving-side ball head guide seat (10) is provided at the bottom end of the shielding cylinder; The conductive rod (4) passes through the contact seat (2) and the moving-side ball head guide seat (10), and is restricted by the contact seat (2) and the moving-side ball head guide seat (10) to drive the moving-side ball head (12) to slide up and down above the static-side ball head (13).

9. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 8, characterized in that, The moving-side ball head guide seat (10) and / or the shielding cylinder are made of insulating material to block the electrical contact between the lower flange (11) and the conductive rod (4); The grounding end cover (3) and the contact seat (2) are both made of conductive material, and moreover, the grounding end cover (3), the contact seat (2), the upper flange (5) and the conductive rod (4) are electrically connected.

10. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 8, characterized in that, A gap distance adjusting mechanism (1) is further provided at the top of the grounding end cover (3); The static-side ball head (13) is arranged on the common terminal conductor (14) electrically connected to the neutral point of the transformer; The gap distance adjusting mechanism (1) drives the conductive rod (4) to slide down or up along the central axis direction of the induction coil (6).

11. The gas-insulated discharge gap for overvoltage protection of the transformer neutral point according to claim 10, characterized in that, A manhole (16) is further provided at the bottom of the common terminal housing of the transformer neutral point, and the opening direction of the manhole is facing the common terminal conductor (14) and is located below the static-side ball head (13).

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