JP2635964B2 - Tap switching device under load - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an on-load tap switching device provided in a distribution transformer.

[Prior Art] In a gas-insulated transformer with a tap changer under load, a vacuum valve is mainly used as a contact for a switching switch of the tap changer under load in order to make the whole transformer oil-less.

In the case of this type of tap switching device, if the vacuum valve loses the shut-off capability due to breakage of the vacuum of the vacuum valve or the like, a short circuit occurs between taps, and an accident occurs in the tap switching device under load and the entire transformer. It may spread.

Therefore, in this type of tap switching device, when a short circuit occurs between taps, it is necessary to detect the short circuit current and immediately stop the operation of the transformer. Therefore, a tap selector and a contact for selecting an odd-numbered tap are required. A current transformer for detecting a short-circuit current is mounted on either a conductor connecting to the (vacuum valve) or a conductor connecting between the tap and a tap selector for selecting an even-numbered tap.

FIG. 3 shows a configuration of a main part of a conventional tap change device under load. In FIG. 3, W is a tap winding of a transformer, and ta and tb are odd numbers provided on the tap winding W, respectively. Taps and even-numbered taps. Generally, a plurality of these taps are provided.

Sa and Sb are an odd-numbered tap selector and an even-numbered tap selector for selecting an odd-numbered tap ta and an even-numbered tap tb, respectively. These tap selectors are driven by a mechanism (not shown) to select taps.

1 'is the tap selector between Sa and Sb and the tap selector
A switching switch that opens and closes between Sa and Sb and an output terminal. The switching switch 1 ′ includes a main contact Va and a vacuum valve.
Vb, an auxiliary contact Vr also formed of a vacuum valve, a current limiting resistor R and a current transformer CT.

Ca and Cb are first and second input terminals of a switching switch connected to tap selectors Sa and Sb, respectively, and N is an output terminal (neutral terminal if a neutral point is provided in the transformer).
The main contacts Va and Vb are connected between the input terminal Ca and the output terminal N and between the input terminal Cb and the output terminal N, respectively. The auxiliary contact Vr and the current limiting resistor R are connected in series, and a series circuit of the auxiliary contact and the current limiting resistor is connected between the first input terminal Ca and the output terminal N. The current transformer CT is attached to a conductor connecting between the tap selector Sb and the main contact Vb, and detects a current flowing through the main contact Vb.

In this example, the odd-numbered tap selector Sa is set by the main contact Va.
And a first switching circuit 1A 'for opening and closing between the output terminal and the main terminal Vb and the current transformer CT for switching between the even-numbered tap selector Sb and the output terminal. A circuit 1B 'is configured.

In the tap switching device shown in FIG. 3, it is assumed that the even-numbered tap tb is selected and the load is energized. If normal at this time, the main contact Vb closes and the main contact
Va and auxiliary contact Vr are both open. In this state, if the vacuum valve constituting the main contact Va breaks down and loses its shutoff ability and becomes closed, taps ta and tb
The short circuit is made without passing through the current limiting resistor R, and a large inter-tap short circuit current flows. This short-circuit current is detected by the current transformer CT, the power is immediately cut off, and the operation of the transformer is stopped.

[Problems to be Solved by the Invention] As described above, if the operation of the transformer is stopped when the current transformer CT detects the short-circuit current between taps, serious problems such as burnout of the tap winding W may occur. Although an accident can be avoided, the power is cut off at the same time as the current transformer CT detects a short-circuit current, so that the power supply to the load is stopped and the load is cut off.

As described above, in the conventional on-load tap switching device, there is a case where the power supply has to be shut down immediately to protect the transformer, so that the uninterruptible power supply is ensured and the reliability of the power supply is ensured. There was a problem in doing so. Further, in the conventional tap switching device, even when the power supply is immediately shut off when the tap is short-circuited, the tap winding and the like may be damaged due to the electromagnetic mechanical force due to the short-circuit current between the taps.

An object of the present invention is to make it possible to continue the operation of the transformer even when the breaking capability of the contactor is lost, and to prevent the tap winding from being damaged by a short-circuit current between taps. A switching device is provided.

[Means for Solving the Problem] As shown in FIG. 1 showing an embodiment of the present invention, an odd-numbered tap selector Sa for selecting an odd-numbered tap ta is provided.
And an even-numbered tap selector Sb for selecting the even-numbered tap tb
A first switching circuit 1A having a main contact Va for opening and closing between the odd-numbered tap selector Sa and the output terminal, and a main contact for opening and closing between the even-numbered tap selector Sb and the output terminal In the on-load tap switching device provided with the second switching circuit 1B having Vb, the operation of the transformer can be continued even if the breaking ability of any of the contacts is lost, and the short-circuit current between taps can be maintained. Thus, it is possible to prevent the tap winding from being damaged.

Therefore, in the present invention, at least one of the first switching circuit 1A and the second switching circuit 1B is connected to the current limiting reactor L connected in series to the main contact, and the auxiliary contact closed during the tap switching process. And a series circuit of the auxiliary contact and the current limiting resistor. The series circuit of the auxiliary contact and the current limiting resistor is connected in parallel to the series circuit of the current limiting reactor and the main contact.

[Effects of the Invention] When a vacuum valve is used as a contact for a switching switch, for example, since there is considerable reliability, it is unlikely that two or more contacts will lose their interrupting ability at the same time. Further, even when the breaking ability of the contact has been lost, it is possible to conduct electricity through the contact. Therefore, in the following description,
It is assumed that only one contact loses the breaking capability at a time, and that the contact having lost the breaking capability also has a normal energizing capability.

In the above configuration, the tap on the other side in a state where power is supplied from the tap selector that selects the tap on either side of the odd-numbered tap or the even-numbered tap through the main contact connected to the tap selector. If the interruption capability of the main contact leading to the selector is lost, the gap between the taps is bridged through the current limiting reactor L. At this time, the bridging current between the taps flowing through the taps is limited by the current-limiting rear chlorine, so that operation can be continued for a short time (for example, about 30 minutes) without damaging the tap windings. It is possible to take urgent measures such as switching the load during this time.

Further, when the auxiliary contact loses the interrupting ability and the current is continued through the auxiliary contact, the current limiting resistor is melted and the current is interrupted. Since power can be supplied through the main contact, power supply to the load can be continued.

In this specification, a state in which the taps are electrically connected without the interposition of an impedance element is referred to as an inter-tap short circuit, and a state in which the taps are connected through a current-limiting impedance element is referred to as an inter-tap bridge.

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

[I] Embodiment of FIG. 1 (a) Configuration of Embodiment FIG. 1 shows an embodiment according to the present invention, in which W is a tap winding of a transformer having a plurality of taps, Sa , Sb are tap selectors for selecting the odd-numbered tap ta and the even-numbered tap tb of the tap winding W, respectively. Ca
Is a first input terminal of the switching switch 1 connected to the tap selector Sa, Cb is a second input terminal of the switching switch connected to the tap selector Sb, and N is an output terminal of the switching switch. .

Va, Vr, and Vb are odd-numbered tap-side main contacts, odd-numbered tap-side auxiliary contacts, and even-numbered tap-side main contacts, all of which are vacuum valves. L
R and R are current-limiting reactors and current-limiting resistors, respectively, and CT is a current transformer that detects a current flowing through the main contact Vb.

One end of each of the main contacts Va and Vb and the auxiliary contact Vr is connected to the output terminal N of the switching switch 1, and the other end of the main contact Va is connected to one end of the current limiting reactor L and the other end of the auxiliary contact Vr. The ends are connected to one end of the current limiting resistor R, respectively. The other end of each of the current limiting reactor L and the current limiting resistor R is connected to a first input terminal Ca of the switching switch, and the other end of the main contact Vb is connected to a second input terminal Cb of the switching switch. ing. A current transformer CT is mounted on a conductor connecting between the main contact Vb and the second input terminal Cb of the switching switch.

The current limiting reactor L has a continuous rating with respect to the load current, and can conduct electricity for a short time (for example, 30 minutes) with respect to the current at the time of bridging between the taps ta and tb. The current limiting reactor L is provided to limit the bridging current between taps when one of the main contacts Va and Vb loses the breaking ability and both the main contacts Va and Vb are closed. When the bridge current between the taps and the load current overlap and flow between the taps ta and tb, the current can be supplied for a short time (for example, 30 minutes), and an odd number connected to the current limiting reactor L The impedance of the current limiting reactor L is selected so that the voltage effect at the tap ta is not excessive.

The current limiting resistor R is for limiting the bridging current between taps at the time of tap switching.
It is designed to withstand a very short load current and a bridging current between taps flowing through it.

The current transformer CT introduces a secondary current proportional to the current flowing through the main contact Vb to a control circuit (not shown), and when the bridging current between taps exceeds a normal duration, the control circuit has a contact disconnection fault. An alarm (hereinafter referred to as V alarm) is generated and the tap switching operation is locked. In the vicinity of the current limiting resistor R, there is a current limiting resistance abnormality detecting device (not shown) separated by a space, and the abnormality detecting device detects a current limiting resistance abnormality when detecting a current limiting resistance abnormality (hereinafter referred to as an R alarm). Is issued to lock the tap switching mechanism. The detection of the abnormality of the current limiting resistance is performed by heat ray radiation, pressure wave, or sudden pressure increase applied to the surrounding space caused by overheating or fusing of the current limiting resistance. Among them, a device (for example, an SP relay) for detecting an abnormality by a sudden increase in pressure is widely used as a conventional technology.

(B) Operation of the embodiment FIGS. 4 to 10 show the contacts Va and V in various cases.
The behavior of r and Vb is represented by a symbol. In these figures, a circle indicates a closed state of each contact in a normal state, and a square indicates a closed state due to the loss of the breaking ability of the contact (hereinafter, this state). Is referred to as a state of interruption failure.). Further, the mark “x” indicates that the current limiting resistor R connected in series with the contact is melted off and the current supply is interrupted as a result of a certain contact being in a breaking failure state.

(B-1) Normal Operation (FIG. 4) The normal operation sequence is shown in FIG. Ta and Tb in the leftmost column (step column) in FIG. 4 indicate that the tap positions are located on the odd-numbered tap ta and the even-numbered tap tb, respectively. Tab-1 to Tab-3 indicate steps when the tap is switched from ta to tb, and Tba-1 to Tba-3 indicate steps when the tap is switched from tb to ta. Here, the numbers assigned to Tab and Tba respectively represent the order in time series in each process.

An example in which the tap position is switched from tap ta to tb will be described. When the tap is switched to the tap ta, only the main contact Va is closed, and the load current flows through the tap selector Sa, the current limiting resistor L, and the main contact Va. In the first step Tab-1 in which the tap is switched from ta to tb, the main contact Va and the auxiliary contact Vr are closed, and the load current is shunted to the current limiting reactor L and the current limiting resistor R with different phase differences. The shunt state when the main contact Va and the auxiliary contact Vr are closed depends on the ratio of the impedance of the current limiting reactor L and the current limiting resistor R, but the absolute value of the impedance of the current limiting reactor L and the current limiting resistor R is assumed. If the values are equal and the impedance angle difference is 90 °, the load current Flows through the current limiting reactor L and the current limiting resistor R.

In the second step Tab-2, only the auxiliary contact Vr is closed. At this time, the load current flows only through the current limiting resistor R.

In the third step Tab-3, both the auxiliary contact Vr and the main contact Vb are closed. At this time, the load current flows through the main contact Vb, and the bridging current between taps returns through the current limiting resistor R. Therefore, the sum of the load current and the bridging current between the taps flows between the taps ta and tb of the tap winding W and on the side of the main contact Vb, and the bridging current between the taps flows through the auxiliary contact Vr and the current limiting resistor R. Flows.

In the state switched to the tap tb, only the main contact Vb is closed, and the load current flows only through the main contact Vb. When the tap position is switched from tap tb to ta, Tb → Tba
The order is −1 → Tba−2 → Tba−3 → Ta.
The current distribution in steps Tba-1, Tba-2 and Tba-3 is equal to the current distribution in steps Tab-3, Tab-2 and Tab-1, respectively. motion.

The operation when one of the contacts is in the interruption failure state will be described separately for each case.

(A) When the main contact Vb is in the disconnection failure state while the tap ta is selected (FIG. 5).

The situation in this case is shown in FIG. In step C1-1, when the main contact Vb is in the disconnection failure state, the main contact V
Since both a and Vb are closed, the load current flows on the main contact Vb side, and the bridging current between taps is the main contact Vb → the main contact Va → the current limiting reactor L → the tack winding W → the main contact Vb Reflux. The control circuit (not shown) to which the secondary current of the current transformer CT is led estimates that the main contact has a faulty disconnection state based on the magnitude and duration of the current detected by the current transformer CT.
An alarm is issued to lock the tap switching operation. Step C1
Since power can be supplied for a short time (for example, 30 minutes) in the state of −1, switching of the system load or the like is performed during this time, and the load of the faulty transformer is transferred to another power source, and then a fault occurs. Stop the transformer.

 The following processing may be performed in addition to the above.

That is, when the V alarm (contact disconnection failure alarm) is issued, the lock of the tap switching operation is continued for a predetermined time. Here, the predetermined time means that if the V alarm is issued by closing the main contact (Va or Vb) and the auxiliary contact Vr, the bridge current flowing through the grain limiting resistor R causes the current limiting resistor R This is the time (several seconds to several minutes) at which an overcurrent causes overheating and the R alarm is issued by a current-flow resistance abnormality detecting device (not shown).
After a predetermined time, the tap switching operation is unlocked, and the tap is switched to the side opposite to the current tap. In this case, the tap position is switched from the odd-numbered tap ta to the even-numbered tap tb. Steps C1-2 to C1-4 show this tap switching process.
In step C1-2, all of the main contact Va, the auxiliary contact Vr, and the main contact Vb are closed. Originally, in this step, only the main contact Va and the auxiliary contact Vr are closed,
In this case, since the interruption failure state of the main contact Vb occurs and the main contact is in the closed state, 3
All three vacuum valves close. In step C1-2, the load current flows on the main contact Vb side, and the bridging current between taps is shunted to the current limiting reactor L and the current limiting resistor R with different phases. The current distribution in Step C1-3 is represented by Step Tab.
Same as -3, normal. The current distribution in step C1-4 is the same as step Tb and is normal, but the main contact Vb is in the disconnection failure state, so that the normal distribution state is limited only when the tap position is at the tap tb. Therefore, step C1−
When it becomes 4, the tap switching operation is locked again. In this state, since the transformer has a continuous rating in terms of the temperature rise, measures such as load transfer can be performed with more time margin than the measures of system switching in step C1-1.

(B) A case where a disconnection failure state occurs in the main contact Va while the tap tb is selected (FIG. 6).

The situation in this case is shown in FIG. The current distribution in step C2-1 where the disconnection failure state occurred in the main contact Va
This is the same as the current distribution of C1-1.

Since the current transformer CT is provided on the tap tb side, as described above, when the tap ta is selected (Ta), V
If an alarm is issued, it can be estimated that the main contact Vb is in a cut-off condition.
In a state where the tap tb is selected as in this case (T
When the V alarm is issued in b), the occurrence of the disconnection failure state is not limited to the main contact Va, but may be the main contact Vr. In the example shown in FIG. 6, it is assumed that an interruption failure state has occurred in the main contact Va.

The treatment in step C2-1 is the same as in step C1-1. To move the tap position to the opposite side of the current tap, the tap position is switched from tap tb to ta. Steps C2-2 to C2-4 show the progress. The processing in step C2-4 is the same as the processing in step C1-4.

(C) When the main contact Va has a disconnection failure while the tap ta is selected (FIG. 7).

As shown in FIG. 7, the current distribution at step C3-1 where the main contactor Va has a breaking failure state is the same as the normal state when the tap position is stationary at ta, and the abnormality is displayed outside. Therefore, other parts (tap winding W, current-limiting reactor L, current-limiting resistor R, etc.) are not damaged due to the main contact Va having the breaking failure. In other words, in the stationary state where the tap ta is selected, a blocking failure is latent. However, after the tap has been switched, ie tap t
After switching from “a” to tap “tb”, an interruption failure state becomes apparent, a bridging current flows between taps, and a V alarm is issued. Steps C3-2 to C3-4 show the progress at the time of tap switching. The state of step C3-4 is the same as the state of step C2-1.
After step C3-4, the process of switching the tap position to the opposite tap (returning to the original tap ta side in this case) is the same as steps C2-2 to C2-4 in FIG.

(D) With the tap tb selected, the main contact Vb
In the event of a shut-down failure (FIG. 8).

As shown in FIG. 8, the same can be said of step C4-1 in the case of FIG. 7 described above with respect to step C4-1 in which the main contact Vb has an interruption failure state, and the tap tb is selected. In the stationary state, the interruption failure state is latent. After the taps are switched, that is, after the taps are switched from tb to ta, an interruption failure state becomes apparent, a bridging current flows between the taps, and a V alarm is issued. Steps C4-2 to C4-4 show the progress at the time of tap switching. Step C4-4 is the same as step C1-1. Step C4
After -4, the process of switching the tap position to the opposite tap (returning to the original tap tb in this case) is the same as steps C1-2 to C1-4 in the case of FIG.

(E) When the tap ta is selected and the main contact Vr has an interruption failure state.

The situation in this case is as shown in FIG. 9, and the current distribution in step C5-1 where the interruption failure state has occurred is the same as step Tab-1 in FIG. Step Tab-1 at the time of tap switching shown in FIG. 4 is a very short time, but step C5-1 is continuous. This step C5−
In the case of 1, the bridging current between taps does not flow, but the load current is continuously shunted to the current limiting resistor R, and the current limiting resistor R eventually overheats and melts, leading to step C5-2. However, in this case, no V alarm is issued, and in the process from step C5-1 to step C5-2, an R alarm is issued and the tap switching operation is locked. In step C5-2, energization is continued, and the current distribution in this state is the same as the steady-state current distribution in the stationary state in which the tap ta is selected. Therefore, even if continuous energization is performed, it is considered unlikely that the tap winding W and the current limiting reactor L will be overheated and damaged. However, in this state, the current limiting resistor R is melted and the tap cannot be switched. Immediately switch the system load to another current and stop the operation of the transformer. If the load is very light, the process may not reach step C5-2 and may remain at step C5-1. Even in this case, since the temperature of the current limiting resistor rises considerably, the abnormality can be detected by installing a current limiting resistor abnormality detecting device that operates with a hot wire.

(F) When a failure state of the auxiliary contact Vr occurs at the time of switching from the tap ta to tb (FIG. 9).

Let us consider a case where the auxiliary contact Vr should be closed for a very short time transiently when the tap is switched from the tap ta to tb, but the closing continues as it is. In this case, the progress of steps C5-2 'to C5-4' from step C5-1 in FIG. 9 is followed, and a V alarm is issued in step C5-3 '. As a result, the tap switching operation is locked for a predetermined time. During this time, the current limiting resistor R is overheated and blown by the bridging current between taps, leading to step C5-4 '. An R alarm is issued in the process from step C5-3 'to step C5-4'. Step C5
The process at -4 'is the same as the process at step C5-2.

(G) The auxiliary contact Vr with the tap tb selected
When a disconnection failure occurs (Fig. 10).

The situation in this case is as shown in FIG. 10, and the auxiliary contact Vr
The current distribution in step C6-1 where an abnormality occurred
It is the same as step ba-1 in the figure, except that step Tba-1
Is a very short time at the time of tap change, and step C6-1 is continuous. In step C6-1, a V alarm is issued,
The tap switching operation is locked. The lock of the tap switching operation continues for a predetermined time, during which time the current limiting resistor R is overheated and melted, and an R alarm is issued. The treatment in Step C6-2 is the same as the treatment in Step C5-2.

(H) When a failure state of the auxiliary contact Vr occurs when switching from the tap tb to the tap t (FIG. 10).

This corresponds to, for example, a case where the auxiliary contact Vr transiently closes for a very short period of time when the tap is switched from tb to ta, and the closing continues as it is.

In this case, as shown in FIG.
Following the course of C6-2 'to C6-4', no V alarm is issued. An R alarm is issued in the process from step C6-3 'to C6-4'. The situation and treatment from step C6-3 'to step C6-4' are the same as those in steps C5-1 to C5-2.

(I) Classification of interruption failure status (Fig. 11).

In the above, the situation and the treatment when the tap is stationary and when the contact breaks down during the tap switching operation have been described with reference to FIGS. 5 to 10. If the tap position after the tap change is regarded as the tap position at the time of the occurrence of the interruption failure, the interruption failure state can be included in the interruption failure state when the tap is stopped. FIG. 11 shows a contact failure state of the contact in such a case. In FIG. 11, the meanings of the symbols in the column indicating the content of the interruption trouble state are as follows.

The symbol “△” means that the contact during energization has caused a disconnection failure. In this state, the tap winding W, the reactor L, and the current-limiting resistance are obtained even if continuous energization is performed unless tap switching occurs. R does not overheat.

The mark “x” means that the main contact on the side opposite to the main contact being energized has a problem with the means, and energization within a short time is possible in this state.

XXA indicates the auxiliary contact Vr when the current main contact is Va.
Means that a shut-down failure has occurred. In this case, the current limiting resistor R is overheated by the load current, leading to fusing.

The XXB mark means that the auxiliary contact Vr has caused a disconnection failure when the main contact Vb is energized, and indicates a case where the current limiting resistor R is overheated and blows due to the bridging current. I have.

As long as there is one contact failure per contact, the first
With the configuration of the present invention shown in the figure, in all cases shown in FIG. 11, the power supply is not interrupted, and at least the time required for emergency operation such as system switching after the V alarm or the R alarm is generated. Can be operated as it is.

Immediately after the V alarm is issued, the contact failure state is
It may not be known which of Va, Vr or Vb has occurred. However, it is possible to specify which of the contacts has caused the blocking failure by the locked tap position and the presence or absence of the R alarm within a predetermined time during which the switching operation is locked. That is, when the V alarm is issued and the tap switching is locked, if the locked tap position is ta, the contact in which the interruption failure state has occurred is the auxiliary contact Vb. When the locked tap position is tb, if the R alarm is issued within a predetermined time, the contact in which a trouble state has occurred can be estimated to be the auxiliary contact Vr, and if the R alarm is not issued within the predetermined time, a malfunction occurs. The contact in which the state has occurred can be estimated to be the main contact Va. If only the R alarm is issued, it can be estimated that a breaking failure state has occurred in the auxiliary contact Vr.

In the embodiment shown in FIG. 1, the first and second input terminals Ca and Cb of the switching switch are an odd-numbered tap side input terminal and an even-numbered tap side input terminal, respectively.
This may be reversed.

[II] Embodiment of FIG. 2 FIG. 2 shows another embodiment of the present invention. In this embodiment, both the first switching circuit 1A and the second switching circuit 1B have the same configuration. doing. That is, the first switching circuit 1A
Comprises a series circuit of a current limiting reactor L 'and a main contact Va and a series circuit of a current limiting resistor R' and an auxiliary contact Vr connected in parallel, and the second switching circuit 1B comprises a current limiting reactor L And the main circuit of the main contact Vb and the series circuit of the current limiting resistor R 'and the auxiliary contact Vr' are connected in parallel.

FIG. 12 shows a normal tap switching operation sequence in the case of the configuration shown in FIG. The representation in FIG. 12 is in accordance with FIG.

In this embodiment, when the tap is switched from ta to tb, the main contact Va is opened after the auxiliary contact Vr is closed, and then the auxiliary contact Vr 'is closed while the auxiliary contact Vr is closed. After the auxiliary contact Vr 'closes, the auxiliary contact Vr opens,
Next, the main contact Vb closes and the auxiliary contact Vr 'opens.

The situation and measures to be taken in the event of a contact failure are the same as in the embodiment shown in FIG.

FIG. 13 shows the classification of the contact failure state in the embodiment of FIG. The representation in FIG. 13 is the same as that in FIG. 11, except for those marked with () in the column of “Tap position” and in the column of “Generated product” indicating the contact with which the breaking fault condition has occurred. , () Are viewed as a combination of comrades. The measures to be taken when a contact failure condition occurs in the contact are the same as those in the configuration of FIG. In the embodiment shown in FIG. 2, since the load current flows through the current limiting reactor in both the odd-numbered tap and the even-numbered tap, there is no unbalanced voltage drop between the odd-numbered tap and the even-numbered tap. The voltage drop occurring in the reactor is smaller than in the configuration of FIG. In other words, when the configuration is as shown in FIG. 2, when the current limiting reactor on the odd-numbered tap side and the current-limiting reactor on the even-numbered tap side are separately configured, the above-described voltage drop is caused by the configuration shown in FIG. 1 /
In the current limiting reactor coil, when the odd-numbered tap coil conductor and the even-numbered tap coil conductor are wound in parallel to form a single coil and a magnetic circuit structure, the above-mentioned voltage drop becomes the first. It becomes 1/4 of the case of the figure.

In the two embodiments described above, the current transformer CT is mounted on the even-numbered tap side, but may be mounted on the odd-numbered tap side.

In the above example, a vacuum valve is used as the contact. However, another energizing switching element, for example, a thyristor may be used.

In the above embodiment, the current transformer CT is used as the current detector, but a current detector other than the current transformer, such as a current detector using a Hall element, may be used.

[Effects of the Invention] According to the present invention, the following effects can be obtained.

(A) Even in the case where a contact breaking failure state occurs, the transformer can be operated at least for the time required for emergency measures such as switching of loads, so that a power failure can be avoided.

(B) Since the bridging current between taps when a contact failure state occurs in the contacts, damage to the tap windings and the tap switching device under load can be prevented.

(C) Since there is no need to supply power immediately when a contact failure state occurs in the contact, it is possible to identify the contact that has caused the disconnection failure after a lapse of a short period of time after continuing the energization. As a result, if the contact in which the disconnection failure occurs is identified as the main contact of the tap on the side opposite to the current-carrying tap, the tap is switched to the opposite side so that the bridging current between the taps due to the contact disconnection failure is determined. Can be eliminated, and overheating and damage of the tap winding can be prevented.

[Brief description of the drawings]

1 and 2 are circuit diagrams showing the electrical configuration of a different embodiment of the present invention, FIG. 3 is a circuit diagram showing the electrical configuration of a conventional example, and FIG. 4 is a circuit diagram of the embodiment of FIG. FIG. 5 to FIG. 11 are explanatory diagrams for explaining the steps of the tap switching operation, and FIG. 5 to FIG. 11 show the state of each contact in each case in various cases when the contact failure state occurs in the embodiment of FIG. , FIG. 12 is an explanatory diagram for explaining the steps of the tap switching operation of the embodiment of FIG. 2, and FIG. 13 is a diagram of the embodiment of FIG. It is explanatory drawing which showed the state of each contact for every step. 1 ... Switching switch, 1A ... First switching circuit, 1B ...
Second switching circuit, W: tap winding, ta: odd-numbered tap, tb: even-numbered tap, L, L '... current-limiting reactor, R, R' ... current-limiting resistance, Va, Vb …… Main contact, Vr, Vr ′
…… Auxiliary contact.

Claims (3)

(57) [Claims] An odd-numbered tap selector for selecting an odd-numbered tap, an even-numbered tap selector for selecting an even-numbered tap,
A first switching circuit having a main contact for switching between the odd-numbered tap selector and the output terminal, and a second switching circuit having a main contact for switching between the even-numbered tap selector and the output terminal. A tap switching device under load comprising: a current limiting reactor connected in series to the main contact; and a tap switching device, wherein at least one of the first switching circuit and the second switching circuit includes: A series circuit of an auxiliary contact and a current limiting resistor closed in the process, wherein the series circuit of the auxiliary contact and the current limiting resistor is connected in parallel to the series circuit of the current limiting reactor and the main contact. A tap change device under load, characterized in that: 2. The current limiting reactor is provided in only one of the first switching circuit and the second switching circuit, and the switching circuit in which the current limiting reactor is not provided includes a current flowing through a main contact. 2. The on-load tap switching device according to claim 1, further comprising a current detector for detecting the on-load tap. 3. The current limiting reactor is provided in both the first switching circuit and the second switching circuit, and each of the current limiting reactors is connected to a series circuit of a current limiting reactor and a main contact of each switching circuit. A series circuit of a resistor and an auxiliary contact is connected in parallel, and one of the first main switching circuit and the second main switching circuit detects a sum of a current flowing through the main contact and a current flowing through the auxiliary contact. 2. The on-load tap switching device according to claim 1, further comprising a current detector.