JPS5854723B2 - On-load tap changer protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for an on-load tap changer.

A conventional on-load tap changer generally consists of a switching switch, a tap selector, and a current limiting impedance.

The tap selector simply selects the tap of the transformer, etc., and all load current switching operations are performed using a switching switch that limits the bridging current between adjacent taps of the transformer, allowing tap switching without interrupting the transformer circuit. have it carried out.

Therefore, whether the current limiting impedance is a resistance type or a reactor type, the design is such that this switching and cutting-off operation can be carried out quickly.

However, if any of the contacts of this switching switch become unable to shut off for some reason, there is a risk that not only will the tap changer be damaged, but that it will also spread to the transformer and cause it to burn out.

Although various protective devices have been proposed in this case,
Since the system simply detects an abnormality and immediately disconnects the transformer from the grid, it has the disadvantage of significantly reducing the reliability of the system's operation.

FIG. 1 shows an example in which a one-resistance on-load tab switch is connected to the neutral point side of the main winding of a transformer.

1 is a transformer main winding, 2 is a tap selector, 3 is a switching switch, 4 to 6 are current switching contacts of the switching switch, and 7 is a resistor as a current limiting impedance.

If the current switching contacts of the switching switch 3 are opened and closed in the order shown in FIG. 2 from the state shown in the figure, switching from the predetermined tap to the next stage tap has been performed.

In FIG. 2, the shaded area indicates the closed state of each current switching contact, and therefore the resistor 7 connected to the contact 5.
A large current will flow for the time T1.

In general, the heat capacity of the resistor 7 is small, so it is not allowed to conduct electricity for a long time, so the resistive load tap changer is used for purposes other than to extend the distance after the contacts open as much as possible in a short time. A quick cutting operation is absolutely necessary for the purpose of shortening the flow time as much as possible.

Next, if the switching switch 3 does not operate as expected for some reason, or if the resistor is disconnected, the contact 4 of the switching switch 3 should be connected at point a in Figure 2. If the current cannot be cut off and continues to arc, a short circuit will occur between the taps at the same time as contact 6 is closed, and the shorted circuit will be
A short-circuit current ranging from 10 to several tens of times the rated current of the transformer will flow.

If left as is, the tap changer will of course be severely damaged, and the transformer windings will also be damaged.

In addition, if contact 5 is unable to cut off the current and the bridge circuit continues due to the arc even if the switching is completed, current limiting resistor 7 connected to contact 5 will immediately melt due to its small heat capacity and the 5th In this case, the contact 6 becomes unable to shut off, resulting in the dangerous situation described above.

Of course, various protections against such accidents have been developed in the past, but these systems generally only detect abnormally large arc energy caused by failure to shut off or melting of a resistor from changes in oil flow or oil pressure. Since the protection device cannot release the fault condition of the on-load tap changer, the transformer must be immediately disconnected from the system by the operation of the protection device, and the operation of the fluid must be used for indirect detection. Therefore, responsiveness and stability are lacking.

This significantly reduces the operational reliability of the system.

This invention was made to eliminate the above-mentioned drawbacks, and will be explained in detail below using the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the protection circuit according to the present invention, and the same parts as in FIG. 1 are designated by the same symbols.

Reference numeral 8 indicates contact 5, 9 indicates contact 4, and 10 indicates contact 5, contact 6 in order to monitor whether the cutoff state is normal or not.
4. Contacts that open and open in the order shown in FIG. 2 in accordance with the opening and closing of 6, 11 a vacuum switch for interrupting short-circuit current caused by the inability of contacts 4 and 5, and 12 12 of contact 6, respectively, 13.14 is an electromagnetic solenoid that, once activated by the current to operate the vacuum switches 11.12, maintains its operating state until it is manually opened even if the current disappears; 15 is an electromagnetic solenoid that maintains the operating state until it is manually opened; It can be said that there is no possibility that all phases cannot be shut off at the same time, so a zero-sequence current is always generated.This zero-sequence current is passed through the electromagnetic solenoid 13.
．． Current transformers 16 and 17 are opened and closed by electromagnetic solenoids, and vacuum switches 11 and 12 of each branch are operated, that is, tap changers on load. A contact point for notifying a failure of the
Reference numerals 18 and 19 are relay coils for supplying the signals received from the contacts 16 and 17 with contacts for operation locking and failure indication of the load tap changer drive device, and 20 is a part of the drive device control panel.

In the circuit configured in this way, if the contacts 4 of each phase are closed and the operation is normal, the secondary side of the current transformer 15 will have:
Since no current flows and its terminals are short-circuited by the cut-off state monitoring contact 9, the electromagnetic solenoid 13 does not operate.

However, if, for example, U-phase contact 4 becomes unable to break when switching to the next tap, and the arc generated at point a in Figure 2 continues to be drawn to point b, contact 6 closes, as shown by the broken line in Figure 3. A short circuit current like this will flow.

At the same time, the current transformer 15 converts a zero-sequence current corresponding to the short-circuit current and supplies it to the secondary side.

At this time, the cutoff state monitoring contact 9 is open as shown in FIG. 2, so the electromagnetic solenoid 13 operates.
The vacuum switch 11 opens the shunt on the contact 4 side that has failed to shut off, canceling the short-circuit condition between the taps, and
The relay coil 18 is closed, energizing the relay coil 18, locking the operation of the tap changer drive device under load, and at the same time providing a failure indication.

If the monitoring contact 10 remains open when the contact is turned on, the electromagnetic solenoid 14 will be energized at the same time, and the vacuum switch 12 will also open, disconnecting the switching switch from the neutral point [phase] and disconnecting the transformer. inhibits the stability of

However, as shown in FIG.
Since the terminals are short-circuited, the vacuum switch 12 does not operate, and therefore the load current can continue to flow through the tap on the contact 6 side that is turned on by this switching.

Since FIGS. 2 and 3 are constructed completely symmetrically with respect to the contacts 4 and 6, even if the contact 6 becomes unable to shut off, it operates in the same manner as described above.

Further, contact 5 cuts off the current only when switching from contact 4 to contact 6.

If the contact 5 becomes unable to break, the bridge current is started to be cut off at point C, and if the arc is not extinguished within the normal arc time T2, there is a risk of melting the resistor 7, so cut it off when it reaches point d. Both ends of the resistor 7 are short-circuited by the condition monitoring contact 8, and the resistor 7 is temporarily changed to a short-circuited state between taps to protect the resistor 7, and the vacuum switch 11 is operated as described above to instantly eliminate the short-circuit current. At the same time as the release, the operation of the load tap switching drive device is locked and a fault is displayed, allowing continued operation with the next tap.

Furthermore, in recent years, vacuum switch-type on-load tap changers that use vacuum switches for contacts 4 to 6 are about to enter the practical stage, but this type of on-load tap changer has excellent breaking performance and a long electrical life. It is thought that this will become the mainstream of on-load tap changers in the future.

It can also be applied directly to this vacuum switch type tap changer.

Further, in this invention, (1) a resistor type is taken as an example, but it goes without saying that it is also applicable to a multi-resistance type.

As described above, this invention has high response and high stability because no fluid is involved in the detection medium that cannot be shut off, and also selectively shuts off only the shunt on the side where abnormal shutoff has occurred, thereby canceling or preventing short circuits between taps. Therefore, a fixed tap can be operated for a long period of time, which has the excellent effect of significantly improving the operational reliability of the entire system.

[Brief explanation of drawings]

The contacts in FIGS. 1 and 3 are a circuit diagram showing an example of a conventional on-load tap changer, FIG. 2 is a diagram showing the sequence of FIG. 1, and FIG. 3 is an implementation of the protection circuit according to the present invention. FIG. 2 is a circuit diagram showing an example. 8... Contact, 11, 12... Vacuum switch, 13.14... Electromagnetic solenoid, 15.
...Converter, 16.17...Contact, 18
, 19...Relay coil O

Claims (1)

[Claims] 1. In an on-load tap changer consisting of a tap selector that changes tap connections, a switching switch that switches on and off the load current, and a current-limiting impedance that limits the bridging current between taps, each branch of the switching switch a vacuum switch inserted into the circuit for interrupting short-circuit current between taps, a contact for notifying a failure of each shunt, an electromagnetic solenoid for activating the vacuum switch and the contact for notifying the failure, and an electromagnetic solenoid for operating the vacuum switch and the contact for notifying the failure; A monitoring contact that operates in response to each current switching contact of each shunt of the switch to selectively short-circuit and open both ends of the electromagnetic solenoid, and a short-circuit current between taps that occurs when each shunt of the switching switch cannot be cut off. and a current transformer for converting and supplying the electromagnetic solenoid to the electromagnetic solenoid.