Safety-level high-voltage current-limiting fuse for nuclear power plant

Abstract

The utility model relates to the field of circuit protection, in particular to a safety-level high-voltage current-limiting fuse for a nuclear power plant, which comprises a fusion tube, an inner cap and a contact are respectively arranged at two ends of the fusion tube, a melt made of high-purity silver is arranged in the fusion tube in a penetrating manner, and two ends of the melt are respectively fixed on the inner cap; an impactor is fixed at the contact and the inner cap at one end of the fusion tube in a penetrating manner, and a conductive metal wire of the impactor is fixedly connected to the inner cap at the other end of the fusion tube; a metallurgical effect point is arranged at the middle position in the length direction of the melt; narrow necks are uniformly arranged on the two sides of the metallurgical effect point at intervals in the length direction of the melt; the fusion tube is filled with an arc extinguishing medium. The fuse provided by the utility model can break smaller current and has strong shock resistance.

Description

Technical Field

[0001] The invention belongs to the field of circuit protection, and in particular relates to a fuse for circuit protection in a nuclear power plant. Background Art

[0002] The safety-grade medium-voltage switchboard of a nuclear power plant supplies power to the equipment that must be operated to maintain the safety state of the reactor under accident conditions, including two types of motors and step-down transformers that supply power to the 380V low-voltage distribution system. In order to ensure the interchangeability of fuses and avoid incorrect replacement, the safety-grade medium-voltage switchboards of nuclear power plants all use a fuse with a rated current of 250A, which is combined with a contactor to provide short-circuit and overload protection for the powered equipment. Currently, high-voltage current-limiting fuses are divided into two types: suitable for motor protection and transformer protection. In view of the requirements of nuclear power plants, there are relatively high requirements for the seismic performance of high-voltage current-limiting fuses. However, the basic structure of the current high-voltage current-limiting fuses is a fuse tube, a melt and an arc-extinguishing medium are inserted into the fuse tube, contacts are arranged at both ends of the fuse tube, and an inner cap is arranged in the fuse tube to fix the two ends of the fuse. Due to the limitations of the fuse specifications, the fuse cannot break a smaller current, and the seismic performance of the fuse is relatively poor. Summary of the invention

[0003] The purpose of the patent of this invention is to provide a high-voltage current-limiting fuse suitable for the safety-grade medium-voltage distribution board of a nuclear power plant, which can break smaller currents and has strong seismic resistance; it can meet the power supply requirements of two types of loads, namely, motors and step-down transformers supplying power to 380V low-voltage distribution systems, and provide short-circuit and overload protection for two types of loads, namely, the powered motors and step-down transformers supplying power to 380V low-voltage distribution systems, and at the same time meet the seismic requirements of nuclear power plants.

[0004] To achieve the above-mentioned purpose, the technical solution provided by the present invention is a safety-grade high-voltage current-limiting fuse for a nuclear power plant, comprising a melting tube made of high-strength porcelain, inner caps are arranged at both ends of the melting tube, contacts are respectively connected to the outer peripheries of the two ends of the melting tube, and the inner caps are conductively connected to the contacts; a melt made of high-purity silver is passed through the melting tube, and the two ends of the melt are respectively fixed on the inner caps; a striker is passed through and fixed at the contact and the inner cap at one end of the melting tube, and the conductive metal wire of the striker is fixedly connected to the inner cap at the other end of the melting tube; a metallurgical effect point is arranged at the middle position in the length direction of the melting tube; narrow necks are evenly spaced on both sides of the metallurgical effect point along the length direction of the melting tube; and an arc-extinguishing medium is filled in the melting tube.

[0005] Preferably, the melt is in a curved wave structure in its length direction.

[0006] Preferably, both ends of the melt are fixedly connected to the inner cap via two welding points respectively.

[0007] Preferably, a sink is provided at the inner cap.

[0008] Preferably, a circle of sealant is provided at the contact surface between the contact and the outer peripheral side of the melting tube.

[0009] Preferably, the striker includes a guide member, and a striker disposed in the guide member, a spring is disposed between the striker and the guide member, the metal wire binds the striker in the guide member, and in the initial position, the spring is in a compressed state.

[0010] Preferably, a spring card is welded and fixed on the inner side of the inner cap connected to the metal wire, and the metal wire is conductively connected to the spring card.

[0011] The high-voltage current-limiting fuse of the present invention can reduce the minimum breaking current of the fuse to 2.1 kA by arranging a metallurgical effect point at the center of the fuse and combining the narrow neck of the fuse.

[0012] High-strength porcelain is used as the fuse, and a bent structure of the melt is used to buffer the impact energy. Through two welding connection points at both ends of the melt, the bonding strength between the melt and the inner cap and the strength of the melt tube are improved, so as to improve the impact resistance and seismic performance of the fuse.

[0013] By setting a striker in the fuse, the fuse can be alarmed immediately after it works, reminding the operator to deal with the fault in time. It can also be used in load switch-fuse combination appliances, and the striker pushes the release of the matching load switch to open the switch.

[0014] The fuse and contactor of the present invention form a combined electrical appliance, which meets the power supply requirements for motors and step-down transformers supplying power to 380V low-voltage power distribution systems, and provides short-circuit and overload protection for two types of loads, namely, the powered motors and step-down transformers supplying power to 380V low-voltage power distribution systems, and at the same time meets the earthquake resistance requirements of nuclear power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the fuse structure.

[0016] Figure 2 It is a structural schematic diagram of the connection between the spring card and the inner cap.

[0017] Reference numerals:

[0018] Contact 1, inner cap 2, welding point 21, melting tube 3, arc extinguishing medium 4, melt 5, metallurgical effect point 6, inner cap 7, contact 8, striker 9, spring card 10, constantan wire 11, welding point 101. DETAILED DESCRIPTION

[0019] The safety-grade high-voltage current-limiting fuse for nuclear power plants of the present invention is shown in FIG. Figure 1 to Figure 2 , mainly including contacts (1, 8), inner caps (2, 7), melting tubes 3, arc extinguishing medium 4, melt 5, melt metallurgical effect point 6, impactor 9, spring card 10, and metal wire 11, among which.

[0020] The melting tube 3 is a tubular structure with openings at both ends. It is made of high-strength ceramic tubes, such as alumina ceramic tubes, which can withstand the high temperature and high pressure generated by breaking short-circuit currents, avoiding the risk of yellowing, blackening, or even arc leakage caused by the epoxy resin impregnated fiberglass tube being unable to withstand high temperatures.

[0021] Inner caps (2, 7) are connected to the two ends of the fuse tube 3 respectively, and contacts (1, 8) are connected to the two ends of the fuse tube 3 outside the inner caps (2, 7) respectively. A circle of sealant is provided at the peripheral contact surface between the contacts (1, 8) and the fuse tube 3, which is used to seal the contact surface between the contacts and the fuse tube. The inner caps (2, 7) are cap-shaped structures made of conductive materials, and a sink is provided on the end surface of the inner caps to increase the filling amount of the arc extinguishing medium. The contacts (1, 8) are also cap-shaped structures made of conductive materials and are in conductive contact with the inner caps. The contacts (1, 8) are terminal blocks for connecting the fuse to other circuits. A cavity is reserved between the contacts (1, 8) and the inner caps (2, 7).

[0022] The melt 5 is made of high-purity silver. The melt 5 is a long sheet structure with a bent wave structure. The bending process can withstand the impact of the starting current of the motor. A plurality of melts 5 are arranged in a straight-pull parallel structure in the melting tube 3. The two ends of the melt 5 pass through the inner cap (2, 7) and are welded to the inner cap (2, 7). When the end of each melt 5 is welded to the inner cap, two welding points 21 are used to ensure that when one of the welding points 21 fails, the other welding point 21 can ensure the conductive connection between the melt 5 and the inner cap. When the fuse is subjected to vibration impact, the bent wave structure of the melt 5 can buffer part of the vibration impact energy and improve the shock resistance of the fuse. The melt adopts a straight-pull parallel structure to avoid crossing, confusion, entanglement, and inconsistent shapes between the melts.

[0023] A metallurgical effect point 6 is arranged at the center of the melt 5 along the length direction, and a plurality of narrow necks are arranged at intervals and evenly on both sides of the metallurgical effect point 6 along the length direction of the melt 5. The metallurgical effect point 6 is located on one or both sides of the melt 5. The melting point of the material of the metallurgical effect point 6 is lower than that of the melt 5. By combining the narrow neck metallurgical effect point, the minimum breaking current of the fuse is reduced to 2.1kA, and the small current breaking capacity of the fuse is improved; by combining the narrow neck metallurgical effect point, the dual protection of the fuse against overload and short circuit is realized.

[0024] The melting tube 3 is filled with arc extinguishing medium 4, which is made of high-purity quartz sand. The high-purity quartz sand absorbs arc energy when breaking short-circuit current and has a strong arc extinguishing ability, so that the maximum breaking current of the fuse reaches 50kA.

[0025] A spring card 10 is welded on the surface of the inner cap 7 at one end of the melting tube 3 facing the center direction of the melting tube 3, and both ends of the spring card 10 are conductively connected to the inner cap 7 through welding points 101. A striker 9 is fixedly arranged in the contact 1 at the other end of the melting tube 3, and a constantan wire 11 on the striker 9 passes through the melting tube 3 and is welded to the spring card 10.

[0026] The striker 9 includes a guide member and a striker inserted in the guide member, a spring is arranged between the striker and the guide member, a metal wire binds the striker in the guide member and compresses the spring, the metal wire is conductively connected to the conductive member, and the metal wire is a high-strength, high-resistance conductive metal wire. The metal wire is in a tensioned state, and the metal wire bears the tensioning force that binds the striker and compresses the spring. One end of the metal wire located outside the conductive member is connected in series with the constantan wire 11, and is conductively connected to the spring card 10 at the inner cap at the other end of the fusion tube through the constantan wire 11. Since the metal wire bears the tensioning force, the constantan wire 11 can be inserted in the fusion tube 3 in a relaxed state without being subjected to force, thereby avoiding the risk of the constantan wire being pulled off or worn off.

[0027] The fuse with the above structure can withstand the transformer load impulse current and has passed 100 times of 1800A, 0.1s transformer impulse current test verification; it can also withstand earthquakes and provide power to the powered equipment in both operating basis earthquakes (OBE) and safe shutdown earthquakes (SSE), and has passed actual earthquake resistance tests, namely 5 operating basis tests and 1 safe shutdown test verification.

[0028] When in use, a micro switch can be set on one side of the fuse. When the fuse striker pops out, the switch state of the micro switch can be changed, so that the alarm circuit connected in series with the micro switch is turned on and an alarm is sounded.

[0029] Or a striker is used in the fuse of the load switch-fuse combination appliance, and the striker pin is ejected to change the release state of the load switch, so that the load switch is opened.

[0030] Working principle of fuse:

[0031] The fuse is connected in series in the main circuit. Since the resistance value of the metal wire of the striker is much higher than the resistance value of the fuse, the current flows through the fuse during normal flow. When the main circuit is overloaded or short-circuited, the fuse of the fuse accelerates to melt due to the existence of the metallurgical effect point. After the fuse melts, the current flows through the metal wire of the striker. The metal wire melts under the thermal effect, and the striker pops out of the fuse housing under the elastic force of the spring, triggering the alarm circuit to alarm. The striker can also push the release of the matching load switch to open the switch.

Claims

1. A safety-grade high-voltage current-limiting fuse for a nuclear power plant, characterized in that: It comprises a melting tube made of high-strength porcelain, inner caps are arranged at both ends of the melting tube, contacts are respectively connected to the outer peripheries of the two ends of the melting tube, and the inner caps are conductively connected to the contacts; a melt made of high-purity silver is passed through the melting tube, and the two ends of the melt are respectively fixed on the inner caps; a striker is passed through and fixed at the contact and the inner cap at one end of the melting tube, and the conductive metal wire of the striker is fixedly connected to the inner cap at the other end of the melting tube; a metallurgical effect point is arranged at the middle position in the length direction of the melt; narrow necks are evenly spaced on both sides of the metallurgical effect point along the length direction of the melt; and an arc extinguishing medium is filled in the melting tube.

2. The safety-grade high-voltage current-limiting fuse for nuclear power plants according to claim 1, characterized in that: The melt presents a curved wave structure in the length direction thereof.

3. The safety-grade high-voltage current-limiting fuse for nuclear power plants according to claim 1, characterized in that: The two ends of the melt are fixedly connected to the inner cap via two welding points respectively.

4. The safety-grade high-voltage current-limiting fuse for nuclear power plants according to claim 1, characterized in that: The inner cap is provided with a sinking platform.

5. The safety-grade high-voltage current-limiting fuse for nuclear power plants according to claim 1, characterized in that: A circle of sealant is provided at the contact surface between the contact and the outer peripheral side of the melting tube.

6. The safety-grade high-voltage current-limiting fuse for a nuclear power plant according to any one of claims 1 to 4, characterized in that: The striker includes a guide member and a striker arranged in the guide member, a spring is arranged between the striker and the guide member, the metal wire binds the striker in the guide member, and the spring is in a compressed state in an initial position.

7. The safety-grade high-voltage current-limiting fuse for nuclear power plants according to claim 6, characterized in that: A spring card is welded and fixed to the inner cap connected to the metal wire, and the metal wire is conductively connected to the spring card.

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