JPS6040690B2 - Tap switching device under load - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an on-load tap switching device using a vacuum switch as a current switching element.

If a vacuum switch is used as a current switching element of a load tap changer, it is possible to realize a load tap changer (hereinafter referred to as LTC) having 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 economical point of view of the device. As one method for this purpose, a number of methods have been proposed in which the negative portions of current switching elements in a known one-resistance type or two-resistance type circuit are used for the same purpose. FIG. 1a shows an example of such a conventional circuit. In the circuit diagram of FIG. 1a,
1 is a transformer adjustment winding; 2 is a tap selector option that selects an even numbered tap on the adjustment winding 1; 3 is a tap selector option that selects an odd numbered tap on the adjustment winding I; 4 is the switching switch even number side input terminal connected to the above option 2, 5 is the switching switch odd number side input terminal connected to the above option 3, 6 is the energization fixed support point connected to the above input terminal 4, R,,R2 are current limiting resistors, VS1 and VS2 are vacuum switches, 7 is a resistor fixed contact connected to the input terminal 4 through the limiting resistor R, and 8 is a current-carrying contact connected to the input terminal 5. After fixing, point 9 is the current limiting resistor R connected to the input terminal 5.
2, a movable reinforcement selectively connected to the resistor fixed contact 9 or the energized fixed contact 6; 11, the energized fixed contact 8 or the resistor fixed contact 7; The movable contact 12 that selectively connects is an output terminal of a switching switch, and when LTC is applied to the neutral point of a star-connected transformer, the terminal constitutes the neutral point of the transformer.

FIG. 1b shows the operating sequence of this circuit. As the sequence progresses from left to right on the page, it indicates a switch from an odd number tap to an even number tap, and as the sequence progresses from right to left, it indicates a switch from an even number tap to an odd number tap. Second
The figure shows an example of switching from odd-numbered taps to even-numbered taps.
The operating status of each switch is broken down and shown. The operating order of the conventional circuit will be explained below with reference to FIG.

In the state shown in Figure 2a, the LTC is operating with an odd number of taps, and the load current supplied from the transformer regulating winding 1 is 3-
It is output via the route 5-8-11-VS2-12.
Next, when switching to an even tap, the vacuum switch VS2 is opened as shown in FIG. 2b, and the load current is commutated to the circuit consisting of 3-5-R2-9-10-VSI-12. Next, as shown in FIG. 2c, move the movable contact 11 to 8
Switch from to 7. This switching takes place in a currentless state since the load current has already been transferred to another circuit by the vacuum switch VS2. Next, the vacuum switch VS2 is closed as shown in FIG. 2d. Vacuum switch VS2
By closing, 3-5-R. -9-10-VS
The inter-tap bridging current flows through the I-VS2-11-7-R, 14-2 circuits, and half of the load current is supplied from adjustment winding 1 via tap options 2 and 3. Become. Next, as shown in Fig. 2e, when the vector sum of the inter-tap bridging current and the load current component is interrupted by the vacuum switch VSI, the load current becomes 2-4-R, 17-VS2.
-12. As shown in FIG.
Then the vacuum switch VSI is closed as shown in Figure 2g, and the load current becomes 2-4-6-VSI-1.
2, and the tap switching is completed. In the above conventional circuit, in the state shown in FIG. 2b,
If the vacuum switch VS2 fails to cut off the load current for some reason, the load current will be reduced to 3-5- even in the state shown in Figure 2c.
By continuing to be supplied from the circuit of 8-space arc-7-11-VS2-12, the bridging current between taps flows through the circuit of 3-5-8-space arc-71R, 1-4-2. It turns out.

Furthermore, if this condition continues to the stage shown in Fig. 2g, a short circuit will occur between the taps, which, as is well known, has the disadvantage of developing into a serious accident. The present invention has been made in order to eliminate the above-mentioned drawbacks, by providing a fusing element that melts at a predetermined current exceeding the rated current in a circuit where a short circuit occurs between taps when a vacuum switch fails to break. To provide an on-load tap switching system that eliminates the need to immediately disconnect a transformer from a system even if an accident occurs.

FIG. 3 shows an embodiment according to the present invention and its operating principle.

In Figure 3a, 1 to 12 are the same as subordinates, and 13
is a fusing element made of a fuse or conductor that can normally carry the transformer's rated load current or its overload current, but quickly blows when a specified current exceeds the rated current, such as a short-circuit current between taps. . In general, the rated current or overload current (of the winding to which the LTC is attached) of a transformer is about 1000 A at most even for large capacity transformers, whereas the short-circuit current between taps ranges from tens of thousands of A to hundreds of thousands of A. can be reached, so the above configuration is easy. Figure 3a
, the fusing element 13 is connected to the input terminal 4 and the fixed contact point 6 of the passing fin.
It will be explained that short-circuit protection between taps can be achieved by connecting or inserting between taps. If the vacuum switch VS2 fails for some reason at the stage shown in Fig. 3b, an arc occurs between the energized fixed contact 8 and the resistive fixed contact 7, as shown by the wavy arrow in Fig. 3c. occurs, and if this arc continues through the stages d to f in Figure 3 to the stage g in Figure 3, a short circuit occurs between the taps as shown by the broken line in the figure, and the large current iSHORT becomes 3-5-8. -7-1 1-V
S2-VSI-1 Flows through the circuit of 0-6-13-4-2. Therefore, the fusing element 13 quickly cuts and removes the fault current as shown in FIG. 3M. Transformer load current il
continues to be supplied via 2-4-R, 7-11 and VS2-12. Therefore, if the heat capacity of the resistor R is set sufficiently large, there is no need to immediately stop the faulty transformer, but rather to switch the load to another system and then shut it down to avoid the LTC disaster. Therefore, the accident can be handled without causing a power outage accident or the like. Further, since the inter-tap short circuit current is immediately removed, the influence on the LTC and the transformer body can be kept to a minor level, thereby increasing the reliability of the transformer as a whole. It goes without saying that the operation of the fusing element can be extracted as an alarm signal or the like by various conventionally known methods. Note that ic is a circulating current. 3rd above
In the circuit shown in the figure, if it takes a considerable amount of time to disconnect the faulty transformer from the system, it is necessary to increase the heat capacity of the resistor considerably, which may not be practical in some cases.

Another method according to the present invention for dealing with such a case is shown in FIG. In the circuit diagram of FIG. 4a, 1
4 is a fixed contact exclusively for energizing connected to the even number side input terminal 4 of the switching switch, 15 is a fixed contact exclusively for energizing connected to the odd number side input terminal 5 of the switching switch, and 16 is a fixed contact only for energizing connected to the output terminal 12 with one end connected to the output terminal 12; This is a movable contact configured to be selectively connected to each energizing fixed contact 14, 15. The other configurations are exactly the same as those shown in Figure 1. The operating sequence of this circuit is shown in Fig. 4b, but since the movement of the movable saddle point 16 is only added to the sequence of Fig. 1b, and the rest is the same, the normal tap switching operation will not be explained. Omitted. The situation when the vacuum switch VS2 cannot be shut off is as follows.
The steps up to the stage shown in FIG. 3h are the same in the circuit shown in FIG. 4a. In the circuit of Fig. 4a, as shown in Fig. 3h, the inter-tap short circuit current is removed and the load current of the transformer is passed through 2-4-R, 17-11-VS2-12. After the current is supplied, the current-only contacts 16 and 14 are closed, and in order to commutate the load current to the path consisting of 2-4-14-16-12, the current-limiting resistors R, There is no need to use one with a large heat capacity. Therefore, the blowout of the blowout element 13 is detected by a known method, and the LTC is locked to prevent it from being activated any further.Even after a short-circuit between the taps, there is no particular need to stop the transformer in a hurry. Since it is sufficient to perform LTC maintenance after making sufficient preparations for transformer shutdown, this has the effect of significantly increasing the reliability of the power system in which the LTC-equipped transformer is incorporated.
In addition, by adding energizing contacts 14, 15, 16, vacuum switches VS1, VS2, auxiliary contacts 11, 8,
10, 6 and the fusing element 13 do not need to have continuous current-carrying ability, so there is an effect that the LTC can be constructed economically. 5 and 6 are other embodiments. In FIG. 5, 1 to 13, R, and R2 are the same as in FIG.
In the figure, 1 to 16, R, and R2 are the same as in FIG. 4. In the figure, VS2 is a vacuum switch, 21 and 22 are fixed contacts connected to both ends of the vacuum switch VS2, and 23 is a bridge configured to bridge the fixed contacts 21 and 22 and then close only with one of them. It is a folding type movable contact, and the other end is connected to the output terminal 12. The operating principle of this circuit can be traced sequentially from Figure 5a to Figure 5i.
Since it is thought to be easy to understand, detailed explanation will be omitted. In this circuit, the vacuum switch VS2 is
3-5-8-space arc-7-111-VS2-10-6-4-2 in the state of FIG. 5i, similar to the explanation in FIG. A short circuit occurs between the taps through the circuit. This inter-tap short-circuit removal operation and subsequent operating conditions are the same as those shown in FIG. 3, and therefore their explanation will be omitted. Incidentally, in this circuit, as in the case of FIG. 4, this purpose can be achieved by the circuit shown in FIG. 6 without increasing the heat capacity of the current limiting resistor. FIG. 6c shows an operation sequence in the circuit of FIG. 6a, and since the principle of operation can be easily inferred from the explanation of FIG. 4, the explanation thereof will be omitted. FIGS. 7, 9, 11, and 13 are circuits showing other embodiments. Furthermore, Figures 8, 10, 12 and 14
The figure is a circuit diagram and an operation sequence in which energizing contacts are added to those in FIGS. 7, 9, 11, and 18. 7th
The normal operation, short-circuit occurrence situation between taps, and accident removal method in the embodiments shown in Figures to Figure 12 can be easily understood by referring to the respective operation sequences and Figures 3 to 6, so detailed explanations are omitted. do. Since FIG. 14 is different from the other embodiments described above, an explanation will be added.

FIG. 13 shows another embodiment according to the invention, FIG. 14a shows another embodiment according to another method of the invention, and FIG. 14b shows the operation sequence of FIG. 14a. In Figure 13,
24 and 25 are fixed contacts connected to the input terminals 4 and 5 of the changeover switch, respectively, and 2-6 are the taps of the input terminals 4 and 5 of the changeover switch before operation of any contacts or switches of the changeover switch. These are advance closing movable contacts that are previously closed to the fixed contacts 24 and 25 connected to the input terminals 4 and 5 of the destination (preselection tap) to be switched. 27
is a contact that is conditioned to open when the advance closing movable contact 26 operates and to engage before the vacuum switch VS2 opens.

Short circuit between taps is 3-5-8-11-6-1 as mentioned above.
Since the fault current is generated through the path 3-4-2, the fusing element 13 immediately blows out the fault current after an accident occurs, and removes the fault current, and also reduces the load current by 2 when switching from an odd tap to an even tap. -4-24-R-27-12 route. Even if the current-carrying movable contact 11 is connected to the current-carrying fixed contact 6, the fusing element 13 is fused, so no load current is commutated to the vacuum switch VS2. Therefore, although it is necessary to make the heat capacity of the current limiting resistor R sufficiently large, as long as this point is sufficient, it is possible to eliminate the fault without stopping the supply of load current. In FIG. 14a, the circuit state in which the tap-to-tap short circuit occurs is the same as in FIG. 13. That is, the short circuit between taps is 2-4-13-6-11-8-5
-3. Therefore, the fusing element 13 is fused immediately after a short circuit occurs, and the fault current is removed. The load current is commutated to the path 2-4-24-26-R-28-12.
Subsequently, when the movable remaining point 11 is applied to the energizing fixed contact 6 and the vacuum switch VS is closed, and the energizing-only movable contact 16 is applied to the energizing-only fixed contact 14, the load current becomes 2-4-14.
It is diverted to Kameji, which consists of -16-12. Further, the contact 28 is opened and the tap switching is completed. In addition, Fig. 14b
The broken line indicates the sequence when switching from the right side to the left side in the figure. According to the circuit described in this explanation, not only can a tap dark short circuit be automatically removed, but even after an accident, as long as the tap switching is locked, regardless of the heat capacity of the current limiting resistor R, it can be used for a long time. It is possible to continue supplying the load current over the period of time. As described above, the operation of the fusing element can be used as the tap switching locking signal. In addition, the contact point 27 in FIG.
The contact 28 shown in FIG. 14 is provided for the following reason.

Therefore, it is not necessary if the advance closing contact 26 is driven by an energy storage mechanism as the other contacts and switches of the changeover switch are normally operated. The reason is as follows. The advance closing contact 26 can be used for any tap switching direction.
The preselection tap must be filled prior to operation of any contact on the sliding door switch. This action is controlled by an energy storage mechanism (energy is stored in springs, etc., and by releasing the stored energy at once by removing a latch, etc., it performs a quick cutting action on each contact of the switching switch, preventing flea flushing and disconnection. In addition to making the current limiting resistor more compact and capable of short-time rated heat capacity, it would be mechanically complex to do so with the output of the current limiting resistor. Driven by input theory. in this case,
Immediately after the advance closing contact 26 closes the preselection tap, if the switching switch does not operate due to a loss of operating power or the like, the current limiting resistor may be damaged. To prevent such a situation, it is usual to insert a contact 27 or 28 which is driven by the output shaft of the energy storage mechanism together with other contacts and switches. According to this invention, a fusing element that melts at a predetermined current exceeding the rated current is provided between a pair of current-carrying fixed contacts to which the current-carrying movable contacts are selectively joined and the odd-numbered and even-numbered taps of the transformer. As a result, the following effects are expected.

m Even if there is some kind of abnormality in the vacuum switch and it fails to shut off, resulting in a short circuit between taps, the fault can be removed immediately, so there is little damage to the on-load tap switching device, and the damage does not extend to the transformer. can be prevented.

[2] You can simply insert a fusing element into a part of the conductor that makes up the conventional circuit, without adding any special circuit.
In addition, the current at which the fusing element should cut off the port, that is, the fault current, is two orders of magnitude different even if the overload capacity of the tap changer is taken into account, so use a commercially available fusing element. Even if this is not done, it is extremely economical because it can be modified by simply providing a notch in a part of the conductor used for connection in a conventional circuit.

A simple illustration of the drawings. Figure 1 is a connection diagram and operation sequence of a conventional load tap cutting device, and Figure 2 is an explanatory diagram showing the operation sequence of Figure 1.
FIG. 3 is a subsequent diagram of the present invention and an explanatory diagram of the operation order;
4 to 14 are connection diagrams and operation sequences showing other embodiments, respectively.

In the figure, 1 is a transformer adjustment winding, 2 and 3 are options for even and odd taps, 6 and 8 are current-carrying fixed contacts, 11 is a current-carrying movable contact, 13 is a fusing element, and VS2 is a vacuum switch. Note that the same reference numerals in each figure indicate the same or equivalent parts.
Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14

Claims (1)

[Claims] 1 A pair of current-carrying fixed contacts are selectively connected to the odd-numbered and even-numbered taps of the transformer, and a current-carrying movable contact that is selectively joined to each of the above-mentioned current-carrying fixed contacts is connected to the output terminal via a vacuum switch. A tap switching device under load, characterized in that a fusing element that melts at a predetermined current exceeding the rated current is provided between each of the current-carrying fixed contacts and each of the taps.