JPH0224008B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an on-load tap switching device equipped with a detection means for detecting the pressure inside a container in the event of an accident.

In line with rapid economic growth in recent years, especially as cities have become more densely populated, electrical equipment has become smaller, more inflammable, and more compact.
There has been a growing demand for non-explosive materials. In response to this situation, electrical equipment with SF ₆ gas insulation has rapidly become popular, and transformers are also gradually becoming gas insulated. It is desirable that such a gas insulated transformer also have a tap switching function when loaded, similar to the conventional oil-immersed transformer. In this case, a vacuum switch is used as the load switching device to eliminate the risk of generating arced SF ₆ gas and reduce the withstand voltage due to contact consumable powder, and a vacuum switch is used as the current switching element. To ensure electrical insulation, it is useful to apply an SF ₆ gas insulated vacuum switch type on-load tap changer filled with SF ₆ gas.

However, in an on-load tap changer, especially in a so-called resistive on-load tap changer, if a current switching element fails to break and the arc is extinguished before the current switching element connected to the other tap closes. If this is not done, a short circuit will occur between the taps, causing a large current much larger than the rated current to flow, potentially damaging the transformer windings. In particular, in the case of vacuum switch load tap switching devices, the arc caused by the short-circuit current is trapped inside the vacuum switch container until it destroys the vacuum switch, so there is a tendency to be delayed when detecting an accident using pressure or temperature. Become.

A method of electrically detecting short-circuit current using a separate current transformer has also been proposed, but this method requires ground insulation between the transformer's secondary conductor and primary conductor, making it bulky. Moreover, there is a problem that it becomes extremely uneconomical.

As a solution to the above-mentioned problems, in an oil-immersed resistance type on-load tap switch switch having a current-carrying contact, a main arc contact, and a resistance contact, the main arc contact is connected in parallel to the current-carrying contact. A fusible conductor consisting of a thin conductor is connected to a part of the electrical circuit, which is made up of a thin conductor that will melt instantly if a normal tap switching current flows, but a short-circuit current flows between the taps, and when this fusible conductor melts, the surrounding area It is already known to detect the pressure increase in the switching switch caused by the decomposition of the oil by operating a hydraulic relay or an oil flow relay. However, in the case of the SF ₆ insulated load tap changer, the same method as the oil-filled load tap changer is used because the pressure increase in the storage container due to the melting of the fusible conductor as described above is caused by the temperature of the gas body. Since it is only due to the rise, the value is relatively low, and the detection accuracy is extremely poor compared to oil-immersed methods, which poses a problem that it cannot be used in practice.

This invention solves the above-mentioned drawbacks by configuring the fusible conductor that cuts off the fault current from a member whose main component is aluminum, thereby increasing the pressure rise in the contained melter when an arc occurs. Provided is a tap switching device under load that can improve detection accuracy.

It is known that when an arc is generated between metals in a gas-filled sealed container, the pressure rise inside the sealed container will be different even if the same arc energy is applied between the electrodes depending on the metal that forms the foot of the arc. It is well known that when aluminum in particular reacts with SF ₆ , an exothermic reaction occurs, the apparent arc energy increases, and the pressure within the sealed container increases. (for example,
Proceedings of the National Conference of the Institute of Electrical Engineers of Japan (1971), page 1297, paper number 1015) Figure 1 shows an example of this publicly known data. As can be seen from the figure, compared to the materials used in conventional electrical equipment such as iron, copper, and brass tungsten, the pressure inside the container due to arcing between aluminum electrodes is higher than that in aluminum. about 2 to 4 times higher than metals. Therefore, if a material containing aluminum as the main component is used in the area where an arc occurs during an accident, the accuracy of accident detection will be increased by 2 to 4 times compared to the conventional method for the same arc energy during an accident. become.

The figure will be explained below. In Figure 2, 1 is
SF ₆ gas, 2 is the storage container of the switching switch, 3 is the transformer tank that suspends the storage container 2, 4 is the impact pressure relay, 5 is the first input terminal of the switching switch of the on-load tap changer, 6 is the second input terminal of the switching switch, 7 is the first main arc vacuum switch, 8 is the second main arc vacuum switch, 9 is the auxiliary arc vacuum switch, 10 is the current limiting resistor, and 11 is the 1 is a first continuous current-carrying contact that only conducts current; 12 is a second continuous current-carrying contact; 13 is an output terminal of a switching switch;
4 is a fusible conductor made of a fine conductor wire mainly made of aluminum and designed to be immediately fused when a large current flows. An electric circuit in which a first main arc vacuum switch 7 and a fusible conductor 14 are connected in series;
An electric circuit in which a current limiting resistor 10 is connected in series to an auxiliary arc vacuum switch 9, and a first continuously energized contact 11
are connected in parallel, and one end of the parallel connection is connected to the first input terminal 5 and the other end is connected to the output terminal 13. Further, an electric circuit formed by connecting a fusible conductor 14 in series to the second main arc vacuum switch 8 and a continuous current-carrying contact 12 are connected in parallel, and one terminal of each is connected to the second input terminal 6 and the other is connected in parallel. Output terminal 13
It is connected to. The first and second input terminals 5 and 6 are respectively connected to movable contacts of a tap selector (not shown). In the case of a star-connected transformer, the output terminal 13 is a terminal that constitutes the neutral point.

Next, the operation will be explained. When switching the tap from the state in which the continuously energized contact 11 and the main arc vacuum switch 7 are closed to the continuously energized contact 12 side, each vacuum switch and the continuously energized contact operate using a known method. At this time, if the main arc vacuum switch 7 fails to cut off for some reason and the arc is not cut off at least until the main arc vacuum switch 12 is closed, a short circuit will occur between the input terminals 5 and 6. In this state, the fusible conductor 14 melts and the pressure inside the container 2 increases, and the impact pressure relay 4 operates to lock the operation of the on-load tap changer and issue an alarm or trip the transformer. You can send a signal to do so. Since the fusible conductor 14 in the above description is made of a material mainly consisting of aluminum, when it is fused, aluminum trifluoride is generated and at the same time a large amount of reaction heat is generated. Therefore, the pressure in the storage container increases due to the arc energy when the fusible conductor melts and the heat of reaction described above, making it extremely easy to detect the occurrence of an accident using the pressure relay.

In the above embodiment, the energizing contact, the vacuum switch, and the soluble conductor are housed in a container filled with SF ₆ gas, but it is sufficient that at least the soluble conductor is in an atmosphere of SF ₆ gas.

The effects of this invention are listed as follows.

(b) Accurately detect faults in SF ₆ gas insulated tap changeover devices under load by simply changing the materials of the conventional components without forcing the addition of new components to the conventional devices. Can be done.

(b) Since the material to be changed is a material whose main component is aluminum, which is easy to obtain and relatively inexpensive, the economic effect is great.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing experimental data forming the basis of this invention, and FIG. 2 is a configuration diagram showing one embodiment of this invention. In the figure, 1 is SF ₆ gas, 2 is a container, 4 is a pressure relay, and 14 is a soluble conductor.

Claims (1)

[Claims] 1 first and second current-carrying contacts are selectively connected to first and second terminals of the transformer, respectively, and first and second series circuits consisting of a series connection of a fusible conductor and a vacuum switch are formed, respectively; In a device connected in parallel with each of the above-mentioned current-carrying contacts, the above-mentioned fusible conductor is made of a material mainly composed of aluminum and placed in a container filled with sulfur hexafluoride gas, and the pressure inside the above-mentioned container is controlled. An on-load tap switching device equipped with a detection means for detection.