JPS5939892B2 - Tap switching device under load - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an on-load tap switching device for a transformer, and relates to protection against short circuits between taps, which is suitable, for example, when a vacuum switch is used as a current switching element.

It is well known that when a vacuum switch is used as a switching switch in a load tap switching device, there are advantages in many aspects such as reducing dirt inside the switching switch and reducing the number of switching operations. Also, if the vacuum switch fails to cut off the current for some reason (e.g. vacuum leak) during switching operation, a short circuit between the taps may occur, causing excessive damage not only to the on-load tap switching device but also to the transformer itself. Therefore, a method of inserting a fuse into the circuit has been considered. FIG. 1 or 2 shows an embodiment of such a conventional system. The on-load tap switching devices shown in Figs. 1 and 2 both reduce the short-circuit current borne by each vacuum switch by pre- or post-operation of the switch SW forming the power supply circuit during tap switching. However, if the first vacuum switch V1 fails to cut off the current during a switching operation from an odd tap to an even tap, for example, after the first vacuum switch V is opened, The arc current continues to flow. Then, when the second vacuum switch V2 is closed, a short circuit is formed between the odd-numbered taps and the even-numbered taps. When such a short circuit between the taps is formed, the first and second fuses F1 and F
2 is fused by the short-circuit current, thereby preventing the short-circuit accident from spreading further. By the way, in the above conventional method, fuse F,
Due to the difference in the insertion points of F2 and F2, there were the following drawbacks. First, in the on-load tap switching device shown in Fig. 1, if only the second fuse F2 blows due to the above short circuit current, the first vacuum switch V1, which has failed to blow, will be energized, which will prevent the accident from spreading. There is a fear. Further, when both the first and second fuses F1 and F2 are blown, the current-carrying circuit becomes open, and there is a risk that dielectric breakdown may occur at the location where the withstand voltage is lowest due to the applied voltage of the transformer. Next, in the on-load tap changer shown in Fig. 2, if only the second fuse blows, the first vacuum switch V1, which failed to break, will become energized, and the first and second fuses will become energized. fuse F1
If F2 and F2 are fused, the current will flow through the circuit passing through the third vacuum switch V3, so it is necessary to make the heat capacity of the current limiting resistor R extremely large, and the third vacuum switch V3 also Long-term current carrying capacity is required, and switch S
Since W was switched while an arc current was flowing, there was a risk of a short circuit between the taps again, and if the transformer was not stopped immediately, there was a risk that the accident would spread to the transformer itself.

Next, during operation, if the vacuum switch on the open side causes dielectric breakdown and a short circuit occurs between the taps, and the fuse on the live side melts, the accident may spread and spread to the transformer. This invention was made to eliminate the above-mentioned drawbacks of the conventional technology, and when switching taps, it prevents the fuse on the side receiving power from blowing out by switching.
In addition, by preventing fuses from blowing on the energized side during operation, even if a short circuit occurs during operation or tap switching, the fault current can be quickly removed without interrupting the power supply circuit. The object of the present invention is to provide a tap switching device.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3 illustrating an embodiment of the invention, T is a transformer winding provided with a plurality of taps. S1 is an odd-numbered tap selector that contacts the odd-numbered taps of the transformer winding T in sequence; S2 is an even-numbered tap selector that faces the odd-numbered tap selector S1 and contacts the even-numbered taps in sequence; V1 is the first
It is closed with a vacuum switch. V2 is a second vacuum switch, V3 is a third vacuum switch, and the second and third vacuum switches V2 and V3 are opened, respectively. One side of each of the vacuum switches Vl, V2, and V3 is configured to converge and supply power to the load L. F1 is a first fuse inserted and connected between the odd-numbered side tap selector S1 and the first vacuum switch V1. F2 is a second fuse connected between the even-numbered tap selector S2 and the second vacuum switch V2. SW is the first and second fuse F1 and F mentioned above.
2 and R is a current limiting resistor connected to the switch S.
It is connected between W and the third vacuum switch V3. The current limiting resistor R can be energized from the odd-numbered tap or the even-numbered tap by operating the switch SW. SWl
is a first short-circuit switch, which is provided so as to short-circuit the first fuse F1 by closing the pole. SW2 is the second
A short-circuit switch is provided so that the second fuse F2 can be short-circuited by closing the switch. As mentioned above, the on-load tap switching device shown in FIG. Power is being supplied to load L.

The tap switching operation for switching the power supply from the odd-numbered taps to the even-numbered taps can be accomplished by proceeding from the left to the right in FIG.

During the operation of the switch SW shown in FIG. 4, solid line arrows indicate the sequence of switching from odd number side taps to even number side taps, and broken line arrows indicate a sequence of switching from even number side taps to odd number side taps. First, the switch SW is switched to close the circuit on the second vacuum switch V2 side. Next, the third vacuum switch V3 is closed and the first vacuum switch V is opened. As a result, a power supply circuit from the even-numbered winding to the load L is formed by the even-numbered tap selector S2, the second fuse F2, the switch SWl, the current limiting resistor R, and the third vacuum switch V3. Next, the first short-circuit switch SWl is opened and the second short-circuit switch SW2 is closed to form a short circuit of the second fuse F2, and then the second vacuum switch V2 is closed. Third
By opening the vacuum switch V3 of switch SW
l Through the current limiting resistor R and the third vacuum switch 3, the load L
The power from the even-numbered taps that was being supplied to the vacuum switch V2 is switched to the supply circuit via the second vacuum switch V2, and the switching is completed. If the first vacuum switch 1 fails to cut off the current during the above-mentioned switching operation from odd-numbered taps to even-numbered taps,
Arc current continues to flow through the first vacuum switch V1 even after opening.

As the switching operation progresses, the second vacuum switch V2 is closed, and an inter-tap short circuit accident between the odd-numbered tap and the even-numbered tap occurs. This short circuit fault current causes the first fuse F1 to
is fused, and the first vacuum switch V1, which was continuing to flow arc current, is opened, so the short circuit is quickly broken and the electrical path for supplying power to the load is secured, making it possible to keep the accident to a minimum. can. In addition, since fuse F2 on the current-carrying side is short-circuited during operation after switching, the odd-numbered vacuum switch V, which is open during operation, may suffer dielectric breakdown due to the intrusion of external lightning, resulting in a short circuit between the taps. If this occurs, the odd-numbered fuse F1 will blow out, disconnecting the short circuit and minimizing the damage, and the transformer can continue operating as long as the tap switch is locked. is obtained. Furthermore, it is no longer necessary for the fuse to have the ability to be constantly energized. Also, as shown in Figure 5, during tap switching operation,
A similar effect can be obtained by using a short-circuit switch SW3 having a movable part that is switched and connected so as to short-circuit the views on the side to which power is supplied by switching. In the above embodiment, the switch SW
Although we have explained the case where the switching operation is performed before the opening/closing operation of each vacuum switch, it can be easily inferred that the same effect as in the above embodiment can be obtained even if this switching operation is performed after the opening/closing operation of the vacuum switch. .

In addition, especially when the switching switch SW performs switching operation after the opening/closing operation of each vacuum switch, if the fuse insertion point is as shown in Figure 1 and a shorting switch is inserted to short-circuit each fuse, the first and second Accident current can be reliably removed not only when the second vacuum switch V1 and V2 fail to disconnect, but also when the third vacuum switch V3 fails to disconnect. Furthermore, it goes without saying that the present invention is applicable not only to vacuum switches but also to those using other switches. As described above, according to the present invention, during a tap switching operation, before the switch that forms the power supply circuit from the switched winding tap to the load is closed, the fuse connected in series to the switch is Since a short-circuit switch is installed, even if the other switch fails to cut the current, the short-circuit accident between the taps can be immediately eliminated, and if the fuse on the live side is short-circuited during operation, Since short-circuit accidents between taps during operation can be eliminated immediately, damage to the tap switching device under load can be kept to a minor level, and the transformer can continue to operate by locking subsequent tap switching. .

The current carrying capacity of 2 fuses can be reduced.

This effect can be expected, and a highly reliable tap switching device under load can be obtained.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams of a conventional on-load tap switching device, Figures 3 and 4 are an embodiment of the present invention, Figure 3 is a circuit diagram, and Figure 4 is an operation sequence diagram. be.

Claims (1)

[Claims] 1 A first switch and a second switch inserted in series between odd-numbered taps and output terminals and between even-numbered taps and output terminals of a transformer winding, respectively, and a first switch and a second switch inserted in series between each of the above-mentioned both switches. a switching circuit that temporarily forms a power supply circuit to the load during tap switching by opening and closing the first and second switches; An on-load tap switching device comprising a short circuit switch that shorts a fuse inserted in series with the switch before closing the switch forming a power supply circuit to the load.