JPS63924B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves sequentially selecting the taps of a transformer in a currentless state by a tap selector to limit the load current of the transformer from the first tap to the second tap of the transformer. This invention relates to an on-load tap switching device that commutates current with a switching switch via a current resistor.

In conventional power transformers, mineral oil is sealed in the tank to provide both insulation and cooling of the windings and core. In recent years, there has been a strong demand for transformers for power receiving equipment in densely populated buildings and power distribution equipment installed in urban areas to be non-combustible, non-explosive, smaller and lighter, especially from a safety perspective. . Various types of transformers have been proposed to meet these demands, and one method that is especially suitable for high-voltage, large-capacity transformers is one that uses sulfur hexafluoride (SF6) for electrical insulation.
A gas-insulated evaporative cooling transformer that uses carbon fluoride (fluorocarbons) for cooling has been proposed (for example, Denki Shoin, "Denki Kakaku", July 1960 issue, pp. 60-64).
page). This type of evaporative cooling transformer is also useful if it is equipped with a load tap changer in the same way as conventional oil-immersed transformers, and the transformer is provided with a voltage adjustment function. In the on-load tap changer for this purpose,
As in the case of conventional oil-immersed transformers, in order to reduce the size of the tap changer, it is expedient to use a so-called resistive on-load tap changer. In addition, this on-load tap changer consists of a changeover switch and a tap selector, and the changeover switch must be placed in a separate room from the transformer body for ease of inspection.
The tap selector and tap selector are located in the same room as the transformer body and are immersed in the same insulating medium, similar to conventional on-load tap changers for oil-immersed transformers.

One of the problems in this case is that SF ₆ gas has inferior cooling properties compared to oil, so the current limiting resistor of the switching switch and the contact for continuous energization, in particular, have to be larger. Also, SF ₆ gas causes thermal decomposition at relatively low temperatures (150°C to 200°C) using the steel used in structures as a catalyst and generates corrosive gas, so it has the disadvantage that it cannot be heated to very high temperatures. be. In order to solve this difficulty, it is effective to directly cool mainly the heat generating part of the switching switch section using a refrigerant (fluorocarbon) for cooling the windings and core of the transformer. However, inside the changeover switch, there is a problem in dealing with it in the same circulation system as the refrigerant of the transformer, because powder from the contacts due to the arc that occurs during tap switching or powder from mechanical wear from the mechanical parts is generated. There is. Therefore, it is desirable that the switching switch be cooled indirectly from the outside.

FIG. 1 shows a method for indirectly cooling the switch section of an on-load tap changer for a gas-insulated evaporatively cooled transformer, which has the same structure as the conventional on-load tap changer for an oil-immersed transformer as described above. In Figure 1, 1 is the head case of the on-load tap changer, 2 is the transformer tank filled with SF ₆ gas as an insulating medium,
3 is a switching switch, 4 is a tap selector, 5 is a drive mechanism case for the tap selector, 6 is an insulating container for storing the switching switch filled with SF ₆ gas as an insulating medium, 7
is a current limiting resistor of the switching switch; 8 is a flange connecting the insulating container 6 and the top cover of the tap selector drive mechanism 5; and 9 is for relaxing the electric field between the ground potential part and the live part of the switching switch 3. 10 is a live part shield that has the same function as the earth shield 9; 11 is a connection contact for electrically connecting the switching switch 3 and the tap selector 4;
Reference numeral 12 denotes a neutral point connection contact for connecting a neutral point potential section, which is a neutral point of the transformer, configured in the switching switch 3 and a neutral point bushing of the transformer;
3 is a connection lead for keeping the flange 8 at neutral point potential, 14 is a nozzle for spraying refrigerant (fluorocarbon) for the transformer, 15 is a head cover, and 16 is a water droplet of fluorocarbon sprayed from the nozzle 14. It is. The switching switch 3 includes a load tap switching device head case 1, an insulating container 6, a flange 8, and a tap selector drive mechanism 5.
It is sealed by the top lid and the head case cover 15 and filled with SF ₆ gas. The switching switch storage case 6 is made of an insulating material to maintain ground insulation. In addition, the shield rings 9 and 10 of the ground insulation part are necessary in the case of high voltage even in the oil-immersed type, but in the case of the gas-insulated type, the dielectric strength is almost uniquely determined by the highest potential gradient, so it is partially necessary. This is an essential element to alleviate electric field concentration.

The above configuration has the following drawbacks.

(a) Since the switching switch storage case 6 is made of an insulating material, its cooling characteristics are poor.

(b) With one nozzle 14, it is difficult to uniformly cool the entire surface of the insulating container 6, and with multiple nozzles 14, piping becomes complicated and uneconomical.

(c) Although the live part shield ring 10 is fixed to the flange 8, it is unstable because its attachment leg becomes long.

This invention was made in order to eliminate the above-mentioned drawbacks, and by arranging at least the current limiting resistor to face the wall surface of the metal container, and cooling the outer periphery of the metal container by spraying a cooling medium with the cooling means, Provided is a load tap switching device that improves cooling performance.

The figures will be explained below. In Figure 2,
1 to 7, 10, 11, 15, and 16 are the same as the conventional one. A metal container 17 connects the drive mechanism 5 and the insulating container 6, and has an inner wall facing the current limiting resistor 7. Reference numeral 18 denotes an annular body having a plurality of nozzle holes 18a that is at the same potential as the transformer tank 2 and faces the metal container 17, and is supplied with a cooling medium such as fluorocarbon by a pressure feeding means (not shown) such as a pump. be done. Note that the annular body 18 also serves as a ground shield for mitigating the electric field. In addition, the toric body 1
8 and a pressure feeding means (not shown) constitute a cooling means 19. Reference numeral 20 denotes a neutral point connection contact on the switching switch side, which is in slidable contact with the metal container 17.

In the above configuration, the refrigerant is pumped into the annular body 18 from the refrigerant (fluorocarbon) pool of the transformer (not shown) by a pumping means (not shown), and is fed from the nozzle hole 18a along the circumferential direction of the metal container 17. Sprayed. Therefore, the metal container 17, which is heated by the current limiting resistor 7, which is arranged so as to surround the connection contact 11 and the current limiting resistor 7 arranged below it, and whose temperature increases due to Joule heat every time the tap is switched, is cooled down. be done. The refrigerant (fluorocarbon), which has become a vapor due to heating, is cooled by a radiator of a transformer (not shown) according to a phenomenon known in the above-mentioned literature, returns to a liquid, and returns to the original refrigerant reservoir. The refrigerant, which has not evaporated and whose temperature has only increased slightly, falls directly into the refrigerant reservoir, where it is cooled by being mixed with the low-temperature refrigerant that has been cooled by the radiator and turned into a liquid. The refrigerant in the refrigerant reservoir is again pumped to the annular body 18 by the pumping means, and the circulation is repeated.

In the above embodiment, the metal container 17 is a simple cylindrical container with a flange, but it is also effective to have a protrusion on the cylindrical portion to serve as a known cooling fin.

Furthermore, if the metal container 17 is filled with fluorocarbon liquid at least to the extent that the current limiting resistor 7 is immersed, the current limiting resistor 7 is directly cooled by the fluorocarbon, and the heat transferred to the fluorocarbon liquid is transferred by convection or the like. metal container 17
The cooling characteristics are better than in the case of only SF ₆ gas.

Those skilled in the art can easily infer improvements by combining the known techniques as described above, and it goes without saying that the efficiency can be improved without changing the spirit of the present invention.

By adopting the above configuration, the following effects occur.

(b) By using a metal container containing the refrigerant, the heat generated from the current limiting resistor, which generates the largest amount of heat, can be effectively transferred to the refrigerant (fluorocarbon), so the temperature rise of the current limiting resistor can be kept low. I can do it.

(b) Since the refrigerant is evenly sprayed around the circumference of the switching switch, the cooling effect is increased and there is no need to install a large number of nozzles, making it economical.

(c) It also makes it easier to cool the connection contacts.
A cooling effect can also be expected for the continuously energized contacts inside the switching switch connected to this connection contact.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional on-load tap switching device, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 2 is a transformer tank, 3 is a switching switch, 4 is a tap selector, 6 is an insulating container, 7 is a current limiting resistor, 17 is a metal container, and 19 is a cooling means. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Claims] 1 Taps of the transformer are sequentially selected in a no-current state by a selector, and the load current of the transformer is transferred from the first tap to the second tap of the transformer through a current limiting resistor. A cylindrical insulating container suspended in a transformer tank housing the transformer, a metal container connected to the lower part of the insulating container, and the insulating container and the switching switch housed inside the metal container and the current limiting resistor placed close to the wall surface of the metal container, and the current limiting resistor being housed in the metal container to such an extent that it is immersed. an annular body having a plurality of nozzle holes that is held at the same potential as the transformer tank and facing the metal container; and a pressure-feeding means for force-feeding the liquid refrigerant to the annular body; An on-load tap switching device comprising: cooling means for cooling the outer periphery of the metal container by spraying a liquid refrigerant.