JPS6214086B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a so-called vacuum valve type on-load tap changer that uses a vacuum valve (hereinafter referred to as VCB) as a current interrupting element of an on-load tap changer (hereinafter referred to as LTC). be.

LTC, which uses VCB as the current interrupting element, has superior interrupting ability compared to the conventional oil-submerged interrupting method, has a long life, does not contaminate the insulating oil, and has advantages in terms of maintenance, and has a large capacity VCB. Recently, it has become increasingly used as it has become easier to obtain.

In the case of LTC, even if a malfunction such as inability to shut off or insulation breakdown occurs, it is detected as soon as possible to prevent it from leading to a major accident, and the signal is used to trip the circuit breaker, preventing major damage to the transformer itself. A protective relay is required to prevent this.

Conventional oil-submerged isolation type LTCs are generally equipped with a protective relay that captures and detects gas generated by decomposition of insulating oil due to inability to shut off or dielectric breakdown in the form of pressure rise or oil flow. be. In this case, even during normal switching, some gas is generated due to the arc generated from the arc contact in oil, so there is a problem in the detection sensitivity.

By the way, in VCB type LTC, VCB
The problem of failure to shut off due to a drop in the degree of vacuum must be addressed, but since the contacts are housed inside a vacuum container, even if failure to shut off occurs, there will be no abnormality such as pressure rise or oil flow outside the vacuum container. In many cases, this does not occur, and there is a concern that this could lead to major accidents such as subsequent short circuits between taps.

The present invention has been made in view of the above circumstances, and includes a no-load switching contact that does not interrupt current during normal operation between the vacuum valve and the tap winding.
The circuit is configured to interrupt the arc only when the VCB is unable to interrupt, and by detecting the decomposed gas generated at this time, a tap switching device under load can prevent major accidents such as short circuits between taps. The purpose is to provide.

Below, embodiments of the VCB type LTC according to the present invention in a reactor type and a resistance type will be described. 1st
The figure shows a circuit example of a reactor-type VCB type LTC, which includes movable contacts 1 and 2 of the tap selector that switch and connect each tap T ₁ to _{T 4} of the winding W of the transformer, reactors 3 and 4, and the energizing main. Two circuits connected in series in the order of contacts 5 and 6 are connected in parallel, and the terminal 8
are commonly connected. Further, the reactors 3 and 4 of both circuits and the main contacts 5 and 6 are connected by a circuit having a VCB 7. FIG. 1 shows the state in which tap _T2 is selected.

The operation sequence of the LTC in this circuit is shown in FIG. 2, which is the case when switching from tap _T2 to _T3 . Normally, the current is divided into two circuits: 1→5→8 and 2→6→8. At the beginning of switching, the main contact 5 opens and the current circuit changes from 1 → 7 → 6 → 8.
2→6→8, but at this time, the current flowing through the current-carrying contact 5 flows to the parallel circuit VCB7 side, so the current-carrying contact 5 does not interrupt the current. next
When VCB7 interrupts the current, the current changes from 2→6→8
The current flows through only one circuit, and the movable contact 1 is in a no-load state. In this state, the movable contact 1 is switched from tap _T2 to _T3 .

Next, VCB 7 is turned on with movable contacts 1 and 2 bridging taps T ₂ and T ₃ , and then main contact 5 is turned on. At this time, between T ₂ and T ₃ , 2 → 7 → 1,
Subsequently, a circulating current limited by the current limiting reactors 3 and 4 flows through the circuit 2→6→5→1. Up to this point, half the switching cycle has been completed. Next, the other main contact 6 opens without producing an arc, and the currents are 1→5→8 and 2→7→5.
→It starts to flow in circuit 8. From this point on, the circuit operates in the same sequence as the left circuit in the first half, and movable contacts 1 and 2 of the tap selector are both applied to tap _T3 , and the current is divided into the left and right circuits to complete the switching.

In such a circuit, if VCB7 causes a vacuum breakdown and an arc continues between its contacts, contact 1 of the tap selector, which switches under no-load conditions, will cut off the current, causing an arc in the oil. Generates decomposition gas. The on-load tap switching device according to the present invention is designed to detect this decomposed gas. In other words, Figure 5 shows the reactor type LTC.
This figure shows the configuration when installed on a transformer. LTC tank 21 on the side wall of transformer tank 20
A LTC is installed inside the transformer tank 20 at a partition wall between the transformer tank 20 and the transformer tank 20. In this type of LTC, a tap selector 22 and a switching switch 23 are housed in the same tank 24. Terminals are provided on the transformer tank side of this LTC, and these terminals are connected to a transformer winding 25 and a current limiting reactor 26 in the transformer tank 20. On the other hand, LTC tank 21
A conservator 27 is provided to fill the entire inside of the LTC tank 21 with insulating oil, and a gas detection relay 28 is installed at the top of the tank 21. With this structure, a vacuum failure in the VCB can be detected by detecting gas generated from the contacts of the tap selector 24 using the gas detection relay 20.

Next, the case of resistive LTC will be explained. In the case of a resistance type LTC, as will be described later, the tap selector 22 and the switching switch 23 are generally housed in separate containers, so an arc is generated at the contact of the tap selector 22 like in a reactor type LTC. It is not desirable to detect it. This is the tap selector 22
This is because the contacts are stored in the same tank 20 as the transformer body, so it is not easy to repair the contacts, and when gas is detected, it is not possible to determine whether there is an abnormality in the transformer body or in the LTC. .

FIG. 3 shows an example of a resistance type LTC circuit. Two movable tangents 9 and 10 of the tap selector are connected to adjacent taps T ₁ and T ₂ of the transformer winding W,
Each energizing main contact 11, 12, VCB 13, 1
6 are connected in series and are commonly connected at an unterminated end 19. In addition, the main contacts 11, 1 for energization of each two circuits
2 and the common connection point 19 from the middle of VCB13, 16
Current limiting resistors 17 and 18 are connected in parallel with the circuit between
A series circuit of VCB14 and 15 is inserted.

The operating sequence in this circuit is shown in FIG. 4, which shows the state in which tap _T1 is selected. The current at this time is from tap T ₁ to 9→11→
It flows from 13 to 19. To explain the case of switching from tap _T1 to tap _T2 , first, VCB 14 of the circuit including resistor 17 is turned on, and then VCB 13 is opened. Next, the current-carrying contact 12 on the unloaded tap _T2 side is turned on, followed by the VCB 15 on the same side. As a result,
The load currents are T ₁ →9→11→17→14→19 and T ₂ →10→
A circulating current flows through two circuits, 12→18→15→19, and also between T ₁ and T ₂ (9→11→17→14→15→18→12→10). Next, the VCB 14 is opened to cut off the load current and circulating current of the circuit including the VCB 14, leaving the tap _T1 side in an unloaded state. Subsequently, the energizing contact 11 is opened with no load, and after the VCB 16 is turned on, the VCB 15 of the circuit including the resistor 18 is opened, completing the tap switching.
When switching from T ₂ to T ₁ , the operation is exactly the opposite.

As described above, during normal switching, the current-carrying contacts 11 and 12 open under no load, so they do not arc or generate gas. However, if a vacuum breakdown occurs in any of the VCBs 13, 14, 15, and 16 and an arc continues between the contacts, the current-carrying contacts 11 and 1 open under no load.
2 interrupts the current, causing an arc in the oil and generating decomposition gas. The on-load tap switching device according to the present invention is designed to detect gas generated from this current-carrying contact.

FIG. 6 shows an example of a configuration in which a resistive LTC is attached to a transformer. A low-drag LTC normally consists of an oil tank 30 that houses a tap selector 22 and a switching switch 23, and an LTC head 29 that takes in the driving force for operating the LTC from the outside. The oil tank 30 has a structure that maintains oil-tightness from the outside, and serves as a separate container for the tank. This LTC
is installed so as to be suspended from the top surface of the transformer tank 20. Therefore, the tap selector 22 is placed in the same room as the transformer main body and is directly connected to the transformer winding 25, and the switching switch 23 is placed in a separate room from the transformer main body as described above. On the other hand, the oil tank 30 and the LTC head 29 are in the same room, and the conservator 27 is connected to this room so that the room is filled with insulating oil. Also
A gas detection relay 28 is installed at the top of the LTC head 29. Because of this structure,
A vacuum failure in the VCB can be detected by detecting the gas generated from the current-carrying contacts using the gas detection relay 28.

As explained above, according to the present invention, in a load tap switching device using a vacuum valve as a current interrupting element, a no-load switching contact is connected between the vacuum valve and the tap winding, and the vacuum valve is unable to shut off. We installed a gas detection relay that detects the decomposed gas generated by the arc of the no-load switching contact when a fault occurs, so it detects a failure due to vacuum breakdown of the VCB, and uses the detection signal to shut off the circuit to prevent a major problem. This makes it possible to prevent accidents.

In addition, since the present invention detects generated gas, it not only detects failure to shut off due to vacuum breakdown accompanied by sudden decomposition gas, but also detects gradual shutoff, which was impossible with conventional oil-submerged shutoff contacts. It also has the effect of detecting defects in current-carrying contacts that generate gas.

[Brief explanation of the drawing]

1 and 3 are circuit diagrams showing the reactor type and resistance type LTC of the present invention, FIGS. 2 and 4 are operation sequence diagrams in the circuit examples of FIGS. 1 and 3, respectively, and FIG. FIG. 6 is a configuration diagram showing an embodiment of the present invention for a reactor type and a resistance type. 1... Tap selector movable contact, 2... Tap selector movable contact, 3... Current limiting reactor, 4... Current limiting reactor, 5... Main contact, 6... Main contact, 7
...VCB, 8...Common connection point, 9...Tap selector movable contact, 10...Tap selector movable contact,
11... Current-carrying contact, 12... Current-carrying contact, 13...
VCB, 14...VCB, 15...VCB, 16...
VCB, 17...Current limiting resistor, 18...Current limiting resistor,
19... Common connection point, 28... Gas detection relay,
27...Conservator, 22...Tap selector, 20...Transformer tank, 23...Switching switch, 26...Current limiting reactor, 30...Oil tank, 2
9...LTC head, 25...Transformer winding, 21...
...LTC tank.

Claims (1)

[Scope of Claims] 1. In a load tap switching device using a vacuum valve as a current interrupting element, a no-load switching contact is connected between the vacuum valve and the tap winding, and the vacuum valve is unable to shut off. A tap switching device on load, characterized in that it is provided with a gas detection relay for detecting decomposition gas generated by arcing of the no-load switching contact. 2. The on-load tap switching device according to claim 1, wherein the no-load switching contact is a contact of a tap selector. 3. The on-load tap switching device according to claim 1, wherein the no-load switching contact is an energizing contact connected between the contact of the tap selector and the vacuum valve.