KR840002133Y1 - High current under oil expulsion fuse - Google Patents

Abstract

No content.

Description

High Current Oil Release Fuse

1 is a schematic diagram of an emission fuse within a fuse holder and connected to a current limiting fuse.

2 is a partial cross sectional front view showing a pressure tube in the fuse;

3 shows a portion of the discharge fuse with a nebulizer fuse clamp mounted on an end of the fuse.

* Explanation of symbols for main parts of the drawings

9 fluid 10 release fuse

11 current limiting fuse 12 fuse assembly

13: surrounding structure 14: fuse link

15: fuse holder 16: pressure holding member

17, 21, 30 and 38: passage 18: epoxy sleeve

19: pressure holding room 20 and 22: contactor

23 and 31: inner diameter 24: pressure tube

25: screwed portion 26: fuse clamp

27: slot 28: metering orifice

29 shoulder 32 gas atomizer

34: orifice 36: screw clamp

40: safety ball

The present invention relates to an uner oil expulsion fuse, which is commonly used in high voltage devices to protect against fault currents in electrical devices. The emission fuse is ideally suited to be used in series with the auxiliary current limiting fuse because it can be used to cut off the current under low failure without operating an expensive current limiting fuse. . The low fault current that clears to some extent is limited because there is no regulated pressure in the discharge fuse.

The oil-in-oil fuse of the present invention increases the maximum blocking ability of the emission fuse by 200 to 300% compared to the conventional one. The emission fuse of the present invention is capable of creeping approximately 8,000 amperes (effective value) asymmetrically at 8.3 kv, while the standard fuse has a normal capacity of creeping 3,500 amps. This is accomplished by mounting a pressure tube in the fuse housing that increases the ability of the fuse to withstand the pressure waves caused under high breakdown conditions. By controlling the back pressure in the fuse, the fuse can be cleaned of arc in a low failure state. The thrust generated upon release of gas pressure from the fuse can be reduced by installing a gas atomizer on the fuse housing to disperse the gas upon melting.

Hereinafter, the present invention will be described in more detail according to the accompanying drawings.

As shown in FIG. 1, the emission fuse 10 is mounted on the end of the current limiting fuse 11. The fuses 10 and 11 thus joined are supported in the enclosure 13 by the fuse holder 5. The enclosure is filled with insulating fluid 9 such as oil to insulate the built-in electrical devices. As shown in the figure, the fuse 10 is entirely immersed in the fluid 9.

According to the present invention, the fuse 10 generally includes a fuse assembly 12 having electrically conductive contacts 20 and 22 at both ends and formed of a glass wound epoxy sleeve 18. A fuse link 14 extends through the fuse assembly 12 and is electrically interconnected to the contacts 20, 22. The fuse link 14 is made to melt under selected load current and temperature conditions to open the circuits across the contacts 20, 22. When the fuse link 14 is melted, pressure is generated in the fuse assembly.

An apparatus for accumulating high pressure gas at the time of melting of the fuse link 14 is provided on the fuse assembly. This device is in the form of a pressure bearing member 16 having a pressure chamber 19. The pressure bearing member 16 is mounted on the contactor 20. The gas pressure generated in the fuse assembly at the time of melting of the link 14 generates pressure even in the pressure chamber 19. This high pressure gas is released at a suitable time to be discharged through the fuse assembly 12, to help purge the fuse by cleaning the arc product and the ionized gas of the fuse assembly. The gas generating pressure in the pressure holding chamber 19 is relatively clean, but an oil vappor is added which is an excellent arc extinguishing material.

An apparatus is also provided for maintaining a selected back pressure within the fuse assembly to clean the fuse under low failure conditions. This device is in the form of a fuse clamp 26 mounted on the contact 22. A metering orifice 28 is provided in the clamp 26, selected to maintain sufficient back pressure in the fuse assembly to allow it to withstand voltage stress until deionization is sufficient to prevent re-collision. It is in size. Since the arc distance increases with increasing pressure, it is generally known that the pressure required to withstand the rated voltage stress can be determined for a given fuse.

A device to assist in cleaning the fuse is also provided in the fuse assembly 12. Such a device is in the form of an elastic pressure tube 24 located in the sleeve 18 and extending into the contacts 20 and 22 past the ends of the sleeve 18. The pressure tube is formed of a nontracking non-conducting material such as Teflon to prevent arc-over upon fuse cleaning.

More specifically with reference to the drawings, the sleeve 18 is in the form of a hollow tube made of a long elastic material with some elasticity, such as a glass fiber wound epoxy mixture. The passage 17 is formed through the pressure tube 24. Fuse cleaning requires the sleeve to have a very high hoop strength of up to 2000 psi to withstand the pressure created within the fuse assembly when working with the fuse material.

The contacts 20 and 22 are made of an electrically conductive material, such as copper, and fit into the ends of the sleeve 18. The contactor acts as a device for forming an external contactor to the circuit and is made of a material that absorbs or withstands the heat of arc during fuse cleaning without severe damage. Each contact has a central passage 21 having an enlarged portion 23 that forms a continuous portion of the passage 17 in the pressure tube 24. At the end of each contact 20, 22 a screw 25 is provided. At the end of each contact 20 and 22 is also provided a slot 27 for receiving the end of the fuse link 14.

A seamless connection is made between the contacts 20, 22, the pressure tube 24 and the sleeve 18. This is accomplished by inserting and fitting the pressure tube 24 into the inner diameter 23 of the contacts 20 and 22. The sleeve 18 is then wound directly on the tube 24 and the contacts 20, 22. Essentially, a tight contact must be provided, because the gas or liquid that can be ionized under voltage stress in the gap can become coronal and eventually fail. Bill gaps can also form different dielectric regions that can cause voltage stress concentrations and cause flashovers.

Non-gas and non-carbonized insulator devices in the form of pressure tubes 24 are provided in the sleeve 18 made of a material such as Teflon. The tube 24 must withstand high pressure shock waves generated by the vaporization of the fuse link 14 and oil present in the housing during current interruption. The tube must also be able to withstand the high temperatures of fuse cleaning without melting, cracking or carbonizing. Teflon is a suitable material because of its untracked high temperature properties. However, other materials having the same flexibility can also be used. The tube 24 essentially must not accumulate or retain any contaminants in its inner diameter 31 or in any case. This is because this contaminant may cause flashover between the end contacts 20 and 22.

The end of the fuse link 14 is retained in the contact 22 by a fuse clamp 26 that is screwed into the mating portion 25 of the contact 22. The clamp 26 is used to press secure the end of the fuse link 14 toward the shoulder 29 in the contact 22. The fuse clamp 26 must also be made of a material that withstands the heat and pressure generated during the fuse cleaning operation without corrosion. An apparatus in the form of a metering orifice 28 is provided in the fuse clamp 26 to generate a minimum back pressure of about 150 psi in the pressure tube 24 in the fuse material. The orifice 28 is connected to the inner diameter 31 of the pressure tube 24 via a passage 30 formed in the fuse clamp. Under low current sweep conditions, back pressure is insufficient to satisfactorily clean the arc product from the fuse assembly. By providing the metering orifice 28 in the fuse clamp 26, the back pressure can be formed sufficiently to prevent re-collision after the arc is extinguished when the current is zero.

The pressure bearing member 16 includes a pressure chamber 19 and is mounted on the contactor 20 by a threaded clamp 36 having a passage 38 and a safety hole 40. The passage 38 connects the pressure chamber 19 to the inner diameter 31 of the tube 24. The clamp 36 is screwed into the mating portion 25 of the contact 20 sufficient to press secure the upper end of the fuse link 14 toward the shoulder 29 on the contact 20. The safety hole 40 allows the fuse to be filled with oil through the orifice 28 when the fuse is immersed in oil. Retaining air in the pressure chamber 19 is important for the operation of the gas pressure holding member 16. This is accomplished by always placing the retaining member 16 above the safety hole 40. When gas pressure is formed in the tube 24, the pressure in the pressure chamber 19 increases. When the pressure in the inner diameter 31 drops, the high pressure gas in the pressure chamber 19 is discharged through the inner diameter 31 and the orifice 28 in the clamp 26 to clean the fuse with arc product and ionized gas. Done. The volume ratio between the holding chamber and the fuse will depend on the size of the fuse. In general, the holding room should be larger than the fuse. However, it is known that the volume ratio of 10 to 1 between the holding chamber 19 and the fuse 10 is satisfactory in the case of 15.5kv, 2000 ampere blocking.

Another important thing about fuse clamp 26 is to reduce the overall breakdown of fuse cleaning. When the oil-in-water fuse is opened, a large volume of gas is generated due to vaporization of the fuse link and the surrounding oil. When this gas is discharged out of the fuse holder through the orifice 28 in the clamp 26, a large amount of hot foam is formed. This problem can be solved by providing a spray device in the form of a fuse clamp gas atomizer 32 for the fuse clamp 26 as shown in FIG. The gas atomizer 32 includes a plurality of orifices 34 in communication with the passage 30. Thus, the nebulizer sprays the high pressure gas emitted from the fuse into a large number of fine spray gases, which are sprayed into the oil surrounding the electrical apparatus, cooled there and finally condensed. The size and number of orifices should be calculated to produce a back pressure of about 150 psi to achieve adequate low current cleaning of the fuse.

The gas atomizer 32 may also be used to change the discharge direction of the gas such that, during cleaning operations, the gas discharge output pulls the discharge fuse assembly into the fuse holder. Here, if the fuse is used in a bayonet-type fuse holder, the gas discharge output through the orifice can push the fuse out of the fuse holder. By reorienting the orifice, the gas generates a force against the movement of the fuse assembly from the insert fuse holder. Under these circumstances, the larger the force generated during the cleaning operation, the greater the force holding the fuse in the tank.

During operation, as the fuse link 14 melts and arcs occur, the fuse link and the oil around it evaporate, rapidly increasing the pressure in the fuse. The initial increase in pressure is absorbed by the pressure tube 24 reinforced by the outer sleeve 18. The gas expands in both directions from the arc point, thereby increasing both the pressure in the pressure chamber 19 and the fuse clamp 26. Some of this gas exits through the metering orifice 28 in the fuse clamp 26 and a small amount exits through the safety hole 40 in the clamp 36. Proper selection of the flow rate through orifice 28 is essential to maintain proper back pressure in the fuse to enable low current fuse cleaning. The gas pressurized into the holding chamber 19 stays in the holding chamber until the fuse pipe pressure drops. When the current cycle reaches the zero point where arc disappears, the pressure drops. At zero current, arc disappears and arc pressure drops. When the pressure in the inner diameter 31 drops, gas in the pressure holding chamber 19 begins to be discharged through the inner diameter 31 to purge the arc residue and ionized gas through the fuse clamp 26. When the pressure is lowered in the inner diameter 31 of the tube 24, the oil flows back into the inner diameter 31 through the orifice 28, and extrudes the remaining air through the safety hole 40. Since the safety hole 40 is disposed below the pressure holding chamber 19 in the oil, the oil cannot be introduced into the pressure holding chamber 19.

The fuse 10 can be fabricated by removing the clamps 26 and 36 from the contacts 20 and 22, respectively. A new fuse link 14 is inserted into the inner diameter 31 of the tube 24 and the end of the link 14 is disposed in the slot 27. Next, clamps 26 and 36 are snapped into place to secure the link 14 in position in the contact.

Claims (1)

A tubular assembly having an electrically conductive contact at each end and having a non-tracking non-conductor device for preventing flashover, a fuse link supported therein and connected to each contact, gas pressure supported on one end of the housing By means of an orifice device disposed at the opposite end of the housing from the gas pressure retaining chamber to maintain back pressure in the retaining chamber and the housing, so that gas formed in the retaining chamber at the time of melting of the fuse link when the pressure in the assembly drops Wherein the pressure is blown back through the housing to purge the assembly of arc products.