JPS5816610B2 - High voltage bushings of distribution transformers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead wire connection device for a high voltage side bushing in a power distribution transformer.

Conventionally, a distribution transformer that is used by being mounted on a utility pole and connected to a distribution line has a case 1 with a pocket part 2 protruding from the upper side surface and a high-voltage bushing 3 as shown in FIG. The bushing 3 is installed diagonally downward, and the pocket part 2 protects the bushing 3 from damage during transportation, and an appropriate flash gap l is provided between the terminal 4 passing through the bushing 3 and the tip of the pocket part 2. In the event of a lightning strike, a flash circuit is caused during this period to coordinate the insulation between the inside and outside of the transformer.

On the other hand, in a transformer in which the pocket portion 2 is provided in an overhanging manner as described above, the shape of the case 1 becomes complicated and the production cost becomes high.

For this reason, as shown in FIGS. 2 and 3, the case 1 is not specially provided with a pocket portion 2, and the high-pressure bushing 3 is mounted horizontally on the side surface of the case 1 so as to be exposed horizontally. In addition, a U metal fitting 5 is provided protruding from the side of the case 1 to protect the bushing 3, and a suitable flash gap GL is formed to achieve coordination between the inside and outside insulation.

However, in recent years, there has been a trend to raise the insulation level of power distribution lines in order to avoid as much as possible power outages on power distribution lines due to lightning strikes and improve the reliability of power supply.

In this case, even with the bushing of the example type, case 1
The outer part protruding outward from the case 1 is provided with pleats or the like to provide a sufficient insulation distance, but the inner protrusion 6 protruding inward from the case 1 has a flat cylindrical shape for reasons such as mounting. Therefore, the insulating tube 8 is inserted into the lead wire T that penetrates inside the inner protrusion 6 and is connected to the coil, but there is an air space around the lead wire 7. The dielectric constant is as small as 1, and if the flash gap l is extended to increase the flash flash value, the mounting collar 9 of the terminal 4 passing through the bushing 3 will become the discharge electrode, as shown in Figure 2. This causes a flashover A along the inner wall of the inner protrusion 6 of the bushing 3 and the mounting bracket 10 that fixes the bushing 3 to the case 1.
The coordination between the inside and outside insulation is broken, weakening the inside of the device and causing dielectric breakdown.

For this reason, it is possible to extend the insulation distance by increasing the dimension of the inner protrusion 6 of the bushing 3, but the lead wire 7 led out from the inner end of the bushing 3 can be connected to the opposite pole of the bushing 3'. Close to lead wire 7' or iron core 13, etc.
During this period, a flashover occurs, and the diameter of the case 1 must be increased, which not only makes the transformer itself large and uneconomical, but also increases its weight, making it difficult to attach the poles to the electric fence 1. Capacity is also reduced.

Even when the insulation level of the distribution line is increased, the present invention prevents internal flash shorting without increasing the size of the transformer by adjusting the dimensions of the inner protrusion of the bushing to achieve coordination between the inside and outside insulation of the transformer. The present invention provides a lead wire connection device for a bushing in a distribution transformer, and an embodiment thereof is described in the fourth embodiment.
10, the same reference numerals are used to refer to the same items. FIG. 4 shows an example in which the high-pressure bushing 3 is mounted on the upper side surface of the case 1 with a mounting bracket 10 so as to project horizontally. Inside the bushing 3, a terminal fitting 4 shown in FIG. A lead wire 7 made of a bare conductor is connected to the flange 9 and is connected to the coil through the inside of the cylinder of the inner protrusion 6 of the bushing 3.
The outer surface of the bushing 3 is made of a resin material such as vinyl chloride, which has a relatively high dielectric constant and is highly flexible, and covers the mounting flange 9 of the terminal fitting 4 and protrudes outward from the inner protrusion 6 of the bushing 3. A resin insulating layer 12 which is molded in close contact with each other is integrally applied, and an oil-immersed insulating tube 8, which is made by winding insulating paper into a tubular shape and soaking it in oil, is fitted onto the outside of the resin insulating layer 12.

Note that the resin insulating layer 12 attached to the lead wire 7 is not specially molded with resin, but is made of a heat-shrinkable resin tube that has a relatively high dielectric constant and is highly flexible, covering the mounting collar 9 and tightly bonding it as described above. It may be coated at least.

The bushing lead wire connection device according to the present invention is constructed as described above, and the electric field distribution is shown in FIGS. When shown hypothetically with the cylindrical porcelain insulating part of part 6 removed, rl is the lead wire I as an internal electrode.
, r2 is the radius from the center of the internal electrode to the external electrode by the mounting bracket 10, r is the radius from the center of the internal electrode to the outer surface of the resin insulation layer 12, ε is the relative dielectric constant of the air layer,
εX is the relative dielectric constant of the resin insulating layer 12, ε0 is the dielectric constant in vacuum, C is the capacitance per IWL of the conventional product in which the resin insulating layer 12 is not provided on the outer surface of the lead wire T, and E is the same (conventional) C' is the capacitance per 1 m of the present invention in which the resin insulating layer 12 is provided on the outer surface of the lead wire 7, and E' is the electric field strength. .5-
A round steel wire is used, and the outer surface is coated with a resin insulation layer 12t-1,
Describing a case where the wire is coated with a thickness of 2 mm and inserted into the inner protrusion 6 of the bushing 3 having an outer electrode with a diameter of 40 mm, the radius of the lead wire 7 serving as the inner electrode is about 1.3 mm. If rl is 1.3, then rx is 2.51Lm, the radius r2 from the center of the inner electrode to the outer electrode is 20 mm, and the dielectric constant ε of air is almost 1, which is taken as 1, and the resin insulating layer If soft vinyl chloride is used as the resin material in step 12, the dielectric constant is 103H.
2 is 4.0 to 8.0, and now the relative permittivity εx' is 4.0 to 8.0.
When calculated as, the capacitance per 1 m of the conventional one is C
is expressed as , and by substituting the above values, it becomes.

Here, the maximum value E6-max and the minimum value EEIIuIt of the electric field strength E between the internal electrode by the lead wire 7 and the external electrode by the mounting bracket 10 are "'--V-11"---shi++IS! The electric field strength is calculated by substituting the above value as Vi00%.

On the other hand, the capacitance C per 1 m of the resin insulating layer 12 provided on the outer surface of the lead wire T with a thickness of L2mrn is expressed by substituting the above numerical value.

Here, as described above, the maximum value Eεxmax and the minimum value Eezmiyt of the electrolytic strength EεX of the resin insulating layer εX, and the maximum value E'ε of the electric field strength E'ε between the resin insulating layer 12 and the external electrode.
The max and the minimum value E'ε- are expressed as follows, and when the electric field strength is calculated by substituting the above values as Vt-100φ, it becomes as follows.The electric field strength is relaxed by about a factor of 36, and the As shown in Fig. 8, by integrally providing an insulating cylinder made of a resin insulating layer 12 with a large dielectric constant on the lead wire 7 with a small radius, the electric field in that part is weakened and the distance between the inner and outer cylindrical electrodes is relatively reduced. Even when a large potential difference is applied, the electric field distribution becomes discontinuous at the boundary surface and the maximum value of the electric field can be reduced, and the experimental results also show that as shown in Figures 9 and 10, The flash value is the conventional 8
It can be seen that the voltage of 0 to 85 kV increases to 105 to 110 kV, which is very close to the above theoretical value.

In addition, if the thickness of the resin insulating layer 12 is 1 mm, the theoretical formula will be relaxed by about 33 inches, and the thickness of the resin insulating layer 1
It is desirable that the thickness of 2 is greater than or equal to 1.

As described above, in the present invention, it is possible to increase the flash fault value without increasing the insulation distance by increasing the length of the inner protrusion 6 of the bushing 3, and as a result, the bushing 3 can be made smaller and Since it is possible to inevitably reduce the diameter of the transformer case 1, the transformer itself can be manufactured economically without increasing its size, and its weight does not increase.
Therefore, the pole mounting capacity of the transformer does not decrease.

Further, the resin insulating layer 12 is attached to the lead wire 7 connected to the terminal fitting 4 of the bushing 3, covering a part of the terminal fitting 4, using a highly flexible resin material.
Since the bushing 3 is formed by closely covering the terminal fitting 4, there is no need for a gasket between the terminal fitting 4 and the bushing 3, and the structural members can be simplified.

Further, since the resin insulating layer 12 is flexible, the lead wire 7 can be easily bent and the connection to the coil can be made well. Lead wire 7 because it blends well with wire T.
There is no peeling or cracking at all.

Furthermore, the lead wire 1 can be manufactured easily and inexpensively by using a bare conductor and only the resin insulation layer needs to be formed in the necessary parts. Since there is no need to use covered wires, the cost of the transformer can be reduced, and this has advantages that are advantageous in practical terms.

[Brief explanation of drawings]

; Fig. 1 is a partially vertical side view of a high-pressure bushing equipped with a conventional lead wire connection device; Figure 3 shows the transformer with the high-voltage bushing installed in the installation state shown in Figure 2; a top view, and Figure 4 shows the main components of the high-voltage bushing in the installation state shown in Figure 2, which is equipped with the lead wire attachment device of the present invention. FIG. 5 is a vertical side view showing the through conductor of the high-voltage bushing, and FIG. 6 is a diagram illustrating a conventional inner and outer electrode without a resin insulation layer on the lead wire; hypothetically shown as a coaxial cylindrical electrode. Figure 7 is an explanatory diagram hypothetically showing the inner and outer electrodes of the present invention in which lead wires are coated with resin insulating layers as coaxial cylindrical electrodes, and Figure 8 is an illustration of the electric field of the conventional one and the one of the present invention. Figure 9 (a) 20 shows the impact test voltage waveform of the conventional one, and Figure 10 (a) 20 shows the impact test voltage waveform of the present invention. FIG. 3 is a waveform diagram showing a short circuit voltage waveform. 3: High voltage bushing, 4 two terminal fittings, 7: Lead wire, 9
: Mounting flange, 1o: Mounting bracket, 12: Resin insulation layer.

Claims (1)

[Claims] 1. A lead wire to be connected to the coil is inserted into the cylindrical porcelain of the inner protrusion of the bushing and connected to the mounting flange of the terminal fitting, which is fixed integrally with the inside of the bushing by the mounting flange. The outer surface of the lead wire connected to the mounting flange of the terminal fitting has a relatively thick dielectric constant and is flexible from the mounting flange of the terminal fitting to the part that protrudes outward from the inner protrusion of the bushing. A resin material such as rich vinyl chloride is applied in close contact with the lead wire, and a resin insulating layer is integrally formed on the outer surface of the lead wire, covering the mounting collar of the terminal fitting. A bushing lead wire connection device characterized by: