JPH065443A - On-load tap changer - Google Patents

Abstract

PURPOSE:To realize an on-load tap chamber having a current limiting resistor disposed in a limited space in a transformer tank by burying a heat generating part of the resistor in low melting point metal to prevent a local. temperature rise, thereby remarkably increasing a conducting capacity. CONSTITUTION:A resistance wire 13 is electrically insulated with an insulator 18, and a resistance layer protected by a sheath 17 is buried in metal 14 having a low melting point. The entirety is contained in a sealed vessel 15 having heat dissipating fins 16. Thus, since heat of the wire generated during switching operation of a tape changer is once used as melting heat of the metal, a temperature of the wire can be suppressed to a predetermined value or less. Further, since melting heat of the metal is large, a thermal capacity of the wire 13 may be small, and hence a current limiter can be formed in size corresponding to the case of a device using insulation oil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load tap changer for a power transformer, and more particularly to a current limiting resistor for suppressing a cross current at the time of tap change.

[0002]

2. Description of the Related Art In recent years, as a result of an extreme increase in power demand,
The tendency toward non-combustion is increasing due to the large capacity of the entire electric power equipment and the congestion of cities. Therefore, in power equipment, SF ₆ is used as an insulating medium instead of conventional insulating oil.
There is an increasing demand for gas-insulated equipment that uses insulating gas such as gas.

By the way, in the resistance type tap changer at the time of load, in order to cope with such a demand for non-combustibility,
The problem is low cooling efficiency of the insulating gas. That is, since the cooling efficiency of insulating gas is low, which is almost one-tenth of the cooling efficiency of insulating oil, a simple calculation shows that the device using insulating gas has the same level as the conventional device using insulating oil. In order to cool the resistance and maintain nonflammability, a large resistance having a capacity ten times that of the conventional one must be used.

On the other hand, as a method of cooling the resistance in the insulating gas, there are already many known techniques. For example, a method for circulating and cooling a gas by providing a gas sending fan (Japanese Utility Model Laid-Open No. 57-50834) and a method for injecting a liquefied refrigerant into a resistance (Japanese Patent Publication Nos. 63-923 and 63).
No. 924) and the like are known.

However, the former is as low as about one-fifth of the cooling efficiency of insulating oil, requires a large resistance having a capacity about five times that of insulating oil, and requires an auxiliary device such as a fan. . In the latter case, the refrigerant must have uniform resistance and resistance, which is problematic in terms of uniformity and reliability. Further, it is wasteful to operate both of them at all times, and a detector, a sensor and the like are newly required to operate only when the taps are switched. In any case, the conventional method has a drawback that the structure of the tap changer under load becomes complicated.

In the load tap changer,
Since all of its constituents and resistors are connected to the windings of the transformer, they have a potential, and the conventional method of cooling from the outside requires electrical insulation between the potentials. Providing such an insulating structure complicates the structure of the tap changer during load and greatly restricts the layout structure.
The load tap changer becomes large in size. In order to prevent the above problems from occurring, it is required to effectively utilize the internal natural cooling to improve the cooling efficiency.

FIG. 6 is a diagram showing a current limiting resistor used in a conventional insulating oil type load tap changer. Figure 6
As shown in (B), the current limiting resistor has a structure in which a plurality of resistors 30 are stacked, an insulating plate 31 is arranged on the upper and lower end surfaces thereof, and fixed by a tightening stud 32 and a tightening nut 33. . In addition, the strip-shaped resistor 3 of the adjacent resistor 30
The four are connected by a connection plate 35. Since such a current limiting resistor requires a large cooling area for cooling, each resistor 30 has a strip-shaped resistor 34 formed in a meandering shape and housed in a resistor case, as shown in FIG. 6 (A). It has been configured.

When the current limiting resistor having the above-described structure is used in the insulating gas type load tap changer, the heated insulating gas moves upward, so that the upper resistor is excessively heated. The drawback is that the temperature rises locally. Further, if the resistance temperature rises to a high level, SF ₆ gas is thermally decomposed, which causes problems such as a decrease in dielectric strength and oxidation of iron-based parts used inside.

Further, in the conventional insulating gas type load tap changer, the cooling performance of the current limiting resistor is very poor, and the capacity is required to be 10 times that of the insulating oil type current limiting resistor. .

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art. The purpose of the present invention is to prevent a local temperature rise and to greatly increase the current-carrying capacity. Moreover, it is an object of the present invention to provide a load tap changer equipped with a current limiting resistor that can be arranged in a limited space in a transformer tank.

[0011]

In order to achieve the above object, the first aspect of the present invention uses a current limiting resistor and a switching switch which suppress a cross current at the time of short-circuiting between taps when switching taps under load. In a load tap changer for a gas insulated transformer housed in an insulated transformer tank, the heat generating portion of the current limiting resistor is embedded in a low melting point metal. According to a second aspect of the present invention, in a load tap changer equipped with a current limiting resistor that suppresses a cross current when a tap short circuit occurs during load tap change, in a container made of a metal or an insulating member having a high heat transfer coefficient. A plurality of current limiting resistors made of metal or ceramics are housed in the container, and a paraffin filler having a low melting point is filled in the container.

[0012]

According to the present invention, the temperature of the closed container containing the resistance portion and the low melting point metal can be suppressed to the melting point of the low melting point metal or lower. In addition, since the current limiting resistor covers the resistance part with a filling material so that it does not come into direct contact with SF ₆ gas, the heat generated inside the resistor at the time of tap switching is immediately taken away and stored, and then gradually the SF ₆ gas is gradually stored. Dissipate heat inside.
Furthermore, when the load changes significantly, tap switching is continuously performed, so the temperature of the resistor naturally rises rapidly in proportion to the number of switches, but in such a case, the filler melts and the resistor is melted. Since the temperature of the resistor is taken away, the local temperature rise of the resistor can be suppressed.

[0013]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an embodiment of the present invention. FIG. 1A is a sectional view taken along line II-II in FIG. 1B, and FIG.
2 is a cross-sectional view taken along line I-I of FIG. In FIG. 1, 1 is a plate-shaped resistance band, and terminals 5 and 5 for electrically connecting to both ends.
have. Reference numeral 2 is a container made of a metal or an insulator with good heat dissipation. Reference numeral 3 is an insulating bush for electrically and thermally insulating the resistance band 1 and the container 2. A hole 6 is provided above the container 2 so that the filling material can be injected. Four
Is a low melting point paraffinic filler (eg candle wax). The filler 4 is an electrical insulator, and melts at 200 ° C. and becomes solid at 100 ° C. or lower. Therefore, when injecting into the container 2, it is heated to 200 ° C. or higher and then injected. When the temperature returns to room temperature, it becomes solid and supports the resistance band as shown in the figure and also serves as electrical insulation.

FIG. 2 is a sectional view of a load tap changer using the current limiting resistor configured as described above together with a load tap changer. In FIG. 2, reference numeral 200 denotes a load tap changer, which includes a gear device 11 for transmitting power from an electric operating mechanism (not shown) to the upper part, a power storage device 10 for receiving a power and performing a momentary operation, and a current interruption operation by the momentary operation. It is composed of a cut-off section 8 for cutting.

The current limiting resistor 100 is arranged on the outer peripheral portion of the cutoff portion 8. Reference numeral 7 is a transformer tank, and the tap changer 200 under load is airtightly attached by a cover 9. The inside of the transformer tank is filled with SF ₆ gas 12 at a predetermined pressure.

The use of the current limiting resistor of this embodiment has the following advantages. (1). Since SF ₆ gas, which is the insulating medium inside the transformer, and the resistance band are not in contact with each other, the gas is not decomposed.
For example, when performing continuous tap switching換等, SF ₆ gas for the filling material is interposed between the resistance band itself with SF ₆ gas is reached the decomposition temperature does not reach the decomposition temperature, decompose There is no such thing. (2). Under normal operating conditions, the number of times of switching is about 20 times a day, which is also at intervals of 30 minutes or more. Therefore, the amount of heat generated in the resistance band is small and the filling material is always 10
The temperature is 0 ° C. or lower and is in a solid state. Therefore, the filler not only electrically insulates the resistance bands but also acts as a structure for suppressing vibration during the switching operation, so that a compact and inexpensive current limiting resistor can be provided.

FIG. 3 is a sectional view of another embodiment of the present invention. As shown in the figure, in the current limiting resistor of the present embodiment, the resistance wire 13 is electrically insulated by the insulating material 18, and then the jacket 17 is formed.
The sealed container 1 in which the resistance layer protected by is embedded in the metal 14 having a low melting point, and which has the radiation fins 16 as a whole.
It is stored in 5.

The resistance wire 13 is an iron-chromium alloy or nickel-chromium alloy heating wire having a required resistance, and the insulating material 18 is magnesia containing magnesium oxide as a main component or alumina containing aluminum oxide as a main component. Etc., and an iron pipe, a stainless steel pipe, or the like is used for the jacket 17. Further, as the low melting point metal 14, a metal having a melting point of about 100 ° C., which is not a thermal problem with the insulating gas and surrounding insulating components, is used. As such a low melting point metal 14, bismuth,
Alloys such as lead, tin, or cadmium are used.
A metal having a desired melting point can be easily obtained by adjusting the component ratio such as one having a temperature of 00 ° C. or less or one having a temperature of 130 ° C. or less. The material of the radiation fin 16 and the closed container 15 is preferably aluminum and copper, which have good thermal conductivity.

In the current limiting resistor constructed as described above, the heat generated in the resistance wire 13 is conducted through the surrounding insulating material 18 and reaches the outer jacket 17 and the heat is generated by the low melting point metal 1
Used as heat to melt 4. Since the amount of heat generated in the resistance wire 13 is known, the required amount of the low melting point metal can be calculated back from the heat of fusion of the low melting point metal 14. Therefore, the temperature of the closed container 15 and the heat radiation fins 16 can be suppressed to a temperature equal to or lower than the melting point of the low melting point metal 14 by using the amount of the low melting point metal 14 that becomes the amount of heat of fusion equal to the total amount of heat generated by the resistance wire 13.

Therefore, in the current limiting resistor of the tap changer under load, the heat of the resistance wire generated during the switching opening / closing operation of the tap changer once the heat generating portion is embedded in the low melting point metal is temporarily changed to the low melting point metal. Since it is used as the heat of fusion of, the temperature of the current limiting resistor can be suppressed below a predetermined value. Also, since the heat of fusion of the low melting point metal is large, the heat capacity of the resistance wire can be small, so that the current limiting device can have a size comparable to that of a device using insulating oil.

FIG. 4 is a sectional view of still another embodiment of the present invention. The same parts as those in the embodiment of FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the closed container 1
Inert gas 19 such as nitrogen gas and helium gas in part 5
Is contained. The gas layer 19 can suppress an increase in pressure acting on the closed container 15 due to volume expansion when the temperature of the low melting point metal 14 rises and melts.

FIG. 5 is a sectional view of another embodiment of the present invention. The same parts as those in the embodiment of FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, a part of the closed capacity 15 is a bellows 20. The bellows 20 can absorb an increase in temperature of the low melting point metal 14 and an increase in internal pressure caused by volume expansion due to melting.

[0023]

As described above, according to the present invention, the heat generated in the resistance portion is prevented by embedding the resistance portion, which is the heating element of the current limiting resistor, in the low melting point metal or the low melting point filler. Since it is consumed as the heat of fusion of the low melting point metal or low melting point filler, the temperature of the resistance part or the closed container containing the low melting point metal or low melting point filler should be below the melting point of the low melting point metal or low melting point filler. It is possible to suppress, and it is not necessary to increase the heat capacity of the resistance part, and the size of the current limiting resistor of the load tap changer used for gas-insulated equipment can be made about the same as the case of oil insulation. Become. Therefore, according to the present invention, it is possible to provide a small-sized tap switching device at load including a current limiting resistor which is highly reliable in terms of temperature.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, in which FIG. 1A is a sectional view taken along line II-II in FIG. 1B, and FIG.
A sectional view taken along line I-I of FIG.

FIG. 2 is a state diagram in which the current limiting resistor is attached to a transformer.

FIG. 3 is a sectional view of another embodiment of the present invention.

FIG. 4 is a cross-sectional view of yet another embodiment of the present invention.

FIG. 5 is a sectional view of another embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional current limiting resistor, FIG.
Is a top view of the resistor, and FIG. 6B is a side view of the current limiting resistor in which a plurality of resistors are stacked.

[Explanation of symbols]

1 ... Resistance band, 2 ... Container, 3 ... Insulation bush, 4 ... Filler material, 5 ... Resistance band terminal, 6 ... Hole, 7 ... Transformer tank, 8 ...
Cutoff part, 9 ... Cover, 10 ... Energy storage device, 11 ... Gear device, 12 ... SF ₆ gas, 13 ... Resistance wire, 14 ... Low melting point metal, 15 ... Closed container, 16 ... Radiating fin, 17 ... Outer cover,
18 ... Insulation material, 19 ... Gas, 20 ... Bellow, 100 ... Current limiting resistor, 200 ... Load tap changer.

Claims (2)

[Claims] 1. A gas-insulated transformer load tap changer in which a current limiting resistor and a switching switch for suppressing cross current when a tap short circuit occurs during load tap changeover are housed in a gas-insulated transformer tank. 2. The tap changer under load, wherein the heat generating portion of the current limiting resistor is embedded in a low melting point metal. 2. A load tap changer equipped with a current limiting resistor that suppresses a cross current at the time of tap short circuit during load tap change, in a container made of a metal or an insulating member having a high heat transfer coefficient. A tap changer under load, characterized in that a current limiting resistor made of a plurality of metals or ceramics is housed and a paraffin filler having a low melting point is filled in the container.