JPS6040691B2 - Tap switching device under load - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an on-load tap changer (hereinafter referred to as LTC) using a vacuum switch as a current switching element.

If a vacuum switch is used as a current switching element of an LTC, it is possible to realize an LTC with well-known features and innovative performance.

However, since vacuum switches are relatively expensive, it is necessary to reduce the number of vacuum switches used, that is, the number of contacts that control current switching, as much as possible from the standpoint of equipment economy. As one method for this purpose, various methods have been proposed in which some of the current switching elements in a known one-resistance type or two-resistance type circuit are used in common. FIG. 1 shows an example of such a conventionally known circuit and its operation sequence.
In the circuit diagram of Fig. 1, 1 is the regulating winding of the transformer, 2,
3 is a tap option of a tap selector that selects an even numbered tap and an odd numbered tap on the adjustment winding 1; 4 is an input terminal on the even numbered side of the switching switch connected to the tap option 2;
5 is an input terminal on the odd number side of the sliding door switch connected to option 3, 6 and 7 are energized fixed contacts connected to each of the input terminals 4 and 5, and 8 is the energized fixed contact 6 and 7. A movable current-carrying contact that selectively engages, 9 an output terminal of the switching door switch, and 10 a make-after-break vacuum switch constituted by the fixed current-carrying contacts 6 and 7 and the movable current-carrying contact 8. The fusuma contacts, VS, and VS2 are vacuum switches, and R is a current limiting resistor. The illustrated vacuum switch VS is in a closed state, and the vacuum switch VS shown in FIG. 2b, which will be described later, is in an open state. FIG. 2 shows the tap switching operation process of the circuit of FIG. 1. The operating principle of the conventional circuit will be explained below with reference to FIG. In the state shown in FIG. 2a, the LTC is operated with an odd number of taps, and the load current of the transformer, etc. flows through the connections 3-6-7-8-VS and -9. In order to switch from odd-numbered taps to even-numbered taps, first turn on the vacuum switch VS as shown in Figure 2b.
, are opened and the load current fl is commutated to the electric circuit consisting of 3-5-R-VS2-9. Next, as shown in FIG. 2c, the vacuum switch cutoff point 10 is activated, and the energized movable contact 8 is engaged with the energized fixed contact 6. Subsequently, the vacuum switch VS is opened as shown in FIG. 2d. At the stage d in Figure 2, the load current is from even taps to 2-4-6-81 VS, -9
As well as being supplied through strategies consisting of
The circulating current IC determined by the voltage difference between the taps and the current limiting resistor R is 2
It flows into a turtle path consisting of 14-6-81 VS and 1 VS2-R-5-3. If the vacuum switch VS2 is turned on as shown in FIG. 2e, the circulating current IC is immediately cut off and the tap switching is completed. A substantially similar process is followed for reverse switching. In the operating sequence of FIG. 1b, the transition from odd-numbered taps to even-numbered taps proceeds from left to right as shown, and vice versa from right to left. The conventional circuit described above has the following drawbacks. That is, if the vacuum switch VS fails to cut off the load current il for some reason at the stage shown in Fig. 2b, then the vacuum switch VS fails to cut off the load current il at the stage shown in Fig.
In order to proceed to the switching process, the energized movable contact 8 switches to the energized fixed contact 7.
When the wire is separated from the wire, the load current il is still flowing through this military path, so an arc is generated. For this reason, 3-5-7
There was a risk that the path of the one-space arc 6-4-2 would lead to a short circuit between taps. Such dangers in conventional circuits are not limited to the circuit shown in Figure 1a,
The same thing can be said if everything follows the following principle. In other words, the circuit shown in FIG. 1a is configured as shown in FIG. This circuit doubles as switch A and switch C of the well-known one-resistance type circuit shown in FIG.
In other words, a so-called arc switch (SchaltKontakt) is a switch inserted in series between the input terminals 4 and 5 of the sliding door switch and the output terminal 9 without passing through a current-limiting impedance, such as switches A and C in Fig. 3a. In a circuit with
If these are to be used for both the odd-numbered tap side and the even-numbered tap side, the switching contact 10 shown in FIG. 1a is definitely required. If this switching contact 10 is provided, the process of switching to the preselected tap by activating the switching contact 10 after cutting off the load current flowing to the tap in operation is necessarily included. Therefore, if the main arc switch suddenly fails during this tap switching process, a space arc will occur during the operation of the functional contact 10, and if the preselected tap is turned on, a short circuit will occur between the taps. Occur. As is well known, when a short circuit occurs between taps, the current reaches from several 1 to 10 pings or more of the rated current, so the damage is not limited to the LTC, but can also cause fatal damage to the transformer itself. become.

Furthermore, if a transformer suddenly trips due to such an accident, in the complex interconnected power systems that have been developed in recent years, part of the system will become overloaded and the transformer will drop out of the system. Furthermore, as a result of this, other power systems are repeatedly overloaded and shut down, and power outages can spread over a wide area and become a major social problem. LTC is a device for switching taps, but even if it loses its function, as long as the energizing function remains, there is no need to suddenly disconnect the transformer from the grid as described above. However, conventional LTQ does not have a function to eliminate the fault when a short circuit occurs between taps, so it is necessary to immediately disconnect the transformer from the grid when a short circuit occurs between taps, or else However, the disadvantage was that there was a risk of fire. This invention was made in order to eliminate the above-mentioned drawbacks, and by providing a fusing element that melts with a predetermined current exceeding the rated current in a part of the circuit, even if a short circuit occurs between taps, the LTC and transformer can be To provide an on-load tap switching device capable of continuing operation of a transformer with the tap switching sliding door locked even after an accident occurs without causing fatal damage to the transformer. An embodiment according to the present invention and its operating principle will be described below with reference to FIG.

In Figure 4a, 1 to 9 are the same as the conventional one, and 11 is able to normally carry the transformer's rated load current or its overload current continuously, but it can be used normally due to large currents such as short-circuit current between taps. On the other hand, a fusing element made of a fast-acting fuse or a pongee conductor is connected between the input terminal 5 and the current-carrying fixed contact 7. Next, referring to FIG. 4, it will be explained that short-circuit accidents between taps can be eliminated.

When the vacuum switch VS, opens as shown in Figure 4b, if for some reason the vacuum switch VS fails to cut off the load fin flow, a space arc is generated at the stage shown in Figure 4c. An inter-tap short circuit (path indicated by a broken line in the figure) occurs, an excessive current flows as described above, the fuse is blown, and the inter-tap short circuit fault is eliminated. When the fault current is removed, the load current il of the transformer becomes 3-5-R-V as shown in Figure 4d.
It is supplied via a turtle path consisting of S2-9. Next, the fourth
When the vacuum switch VS, is opened as shown in Figure e, the load current flows through the paths 2-4-6-8-VS, 19, and the inter-tap circulating current il flows through the circuit shown by the broken line in the figure. flows through. Next, when the vacuum switch VS is turned on in the state shown in FIG. 4f, only the load current il is supplied from the even-numbered tap, and the tap switching is completed. FIG. 5 shows the reverse switching to the above, ie, switching from even taps to odd taps. As shown in FIG. 5a, the vacuum switch VS. When switching to odd number taps when supplying load current il through
First, the vacuum switch VS2 is closed as shown in FIG. 5b.
At this time, the load current il is supplied through the hazy path shown by the solid line in the figure, and the inter-tap circulating current ic flows through the electric path shown by the broken line in the figure. Next, as shown in FIG. 5c, the vacuum switch VS becomes polarized and tries to cut off the vector sum of the load current il and the circulating current ic. At this time, if the current fails to cut off for some reason, the next stage, the fifth
At the stage shown in Figure d, a short circuit occurs between the taps via a space arc as shown in the figure, and an excessive current flows through the path shown by the broken line in the figure. Therefore, as shown in FIG. 5e, the fusing element 11 quickly cuts and removes the inter-tap short circuit current. continue,
As shown in FIG. 5f, the vacuum switch VS. closes and completes the tap switching operation. However, at this time, unlike the switching from an odd-numbered tap to an even-numbered tap, since the fusing element 11 is fused, it is not possible to supply the load current ii through the vacuum switch VS, as shown in FIG. 5f. Load current il'
The current is applied via the current limiting resistor R in the formula 3-5-R-VS2-9. Therefore, as long as the heat capacity of the current limiting resistor R is sufficient, there is no need to immediately stop the faulty transformer, and necessary operations such as switching the load to another system can be performed. The following items are expected as effects of the present invention.

{i) Even if there is some kind of abnormality in the vacuum switch that causes the insulation to fail and short-circuit between taps, the failure can be quickly removed, so damage to the LTC can be kept to a minimum and damage to the transformer can be avoided. It can be prevented. 'o} LT even after failure
Locking the tap switching operation of C allows the transformer to continue operating, which has a great effect on system reliability.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a subordinate circuit and its operation sequence; Figure 2 is an explanatory diagram of the operation of a conventional circuit; Figure 3 is a conventional circuit diagram and its operation sequence; Figure 4 is a circuit diagram according to the present invention and its operation sequence. FIG. 5 is an explanatory diagram showing the operation when switching in the reverse direction in the circuit diagram of FIG. 7 is a current-carrying fixed contact, 8 is a current-carrying movable contact, 9
is an output terminal, 11 is a fusing element, VS is a first vacuum switch, VS2 is a second vacuum switch, and R is a resistor. Note that the same reference numerals in each figure indicate the same or corresponding parts. 1st
Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 First and second current-carrying fixed contacts are selectively connected to the first and second taps of the transformer, respectively, and a current-carrying movable contact selectively connected to each of the above-mentioned current-carrying fixed contacts is connected to a first vacuum switch. and a resistor and a second vacuum switch are connected in series between the first tap and the output terminal, the first current-carrying fixed contact and the first A tap switching device under load, characterized in that a fusing element is provided between the tap and the tap at a predetermined current exceeding the rated current.