JPH06303725A - Dc transmission system - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a DC power transmission system having a bipolar structure, even if a ground fault occurs in a DC power transmission line with one pole.
It is to provide what prevents accidents due to protection interlocking operation on the accident pole side and prevents bipolar stop. [Configuration] A first AC-DC converter for converting AC into DC, a DC transmission line for transmitting the output of the first AC-DC converter, and a second for inversely converting DC transmitted from the DC transmission line into AC.
A DC power transmission system comprising a DC circuit consisting of an AC / DC converter, wherein a ground point of the DC circuit is connected to a reverse conversion operation side according to an operating state of the AC / DC converter at both ends of the DC power transmission line. DC power transmission system to switch to.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct current power transmission system in which two alternating current systems are interconnected by a direct current power transmission line.

[0002]

2. Description of the Related Art FIG. 4 shows an example of the configuration of a DC power transmission system that interconnects two AC systems. As shown in FIG. 4, one alternating current system 1 is connected to an alternating current bus 2, and the alternating current bus 2 is connected to a conversion transformer 3. The conversion transformer 3 is an AC / DC converter 4 (hereinafter, simply referred to as a converter). , And the converter 4 is connected to the DC transmission line 6 via the smoothing reactor 5. The DC transmission line 6 is connected to the converter 8 via the smoothing reactor 5.
Connected from the converter 8 to the conversion transformer 9
The conversion transformer 9 is connected to the AC bus bar 10, and the AC bus bar 10 is connected.
Is connected to the other AC system 11. The conversion transformer converts the AC bus voltage into a voltage most suitable for the converter, and the converter converts AC into DC or DC into AC power. The AC / DC converter end of any one of the DC circuits including the DC power transmission line 6 and the converters 4 and 8 is grounded.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention A grounding point 12 of a DC circuit in a DC power transmission system interconnecting two AC systems is
Conventionally, it was fixed to either one of both ends. Therefore, for example, in a DC power transmission system having a bipolar configuration as shown in FIG. 2, when a ground fault accident f1 occurs in a DC power transmission line with one pole when the converter at the ground end is in the forward converter (REC) operation, Current if flows from the ground fault point to the accident pole side via the grounding point 12, and at that time, commutation failure occurs on the inverse converter (INV) side or a bypass pair (corresponding to DC short circuit) due to protection operation. Then, the current is continuously supplied from the sound pole side to the accident point, and the accident will continue unless the sound pole is stopped, that is, the bipolar is not stopped.

Here, the above-mentioned commutation failure on the inverse converter side and the protection operation of the converter will be supplemented. The commutation of the converter can only be carried out while the voltage across the valve, which then carries the current, is positive. As for the forward converter, there is a sufficient period during which the voltage across the commutated valve is positive, so it is unlikely that commutation will fail. On the other hand, in the inverse converter, since the voltage applied to both ends of the commutating valve has a short positive period, there is a high possibility of commutation failure due to the influence of voltage fluctuation or failure of the AC system.

That is, in the inverse converter, a DC short circuit may occur depending on the timing of ignition of the valve and occurrence of commutation failure. In addition, in the explanation of the protection of the converter, the following operations are usually combined depending on the mode of failure.

The GS (gate shift) operation shifts the control angle of the converter from the forward converter region to the inverse converter region, releasing DC circuit energy to the AC side. The BPP (bypass pair) operation is an operation in which a pair of upper and lower converters of an AC input arbitrary phase are made to flow simultaneously. This state is a short-circuit state when viewed from the DC side, and an open state when viewed from the AC side. Generally, there are many protection operations by BPP on the inverse converter side.

The GB (gate block) operation is an operation of stopping the gate pulse applied to the converter. An object of the present invention is to provide a bipolar DC transmission system that prevents a bipolar stop even if a ground fault occurs in a DC transmission line of one pole by protection interlocking operation on the accident pole side. There is a place to do it.

[0008]

In order to achieve the above object, in the present invention, an operation (accommodation) command for determining the operation state of the AC / DC converter is used, and it is always grounded in the operation of the inverse converter (INV). It is intended to provide a method of switching the ground point of the DC circuit in advance so as to be the end.

[0009]

By means of the winding means, as shown in FIG. 3, a ground fault accident f1 of a one-pole DC transmission line occurs in the bipolar configuration, and the current if of the sound pole is transmitted from the ground fault point to the fault pole side via the ground point. If a commutation failure occurs on the reverse converter (INV) side at that time or if a bypass pair (corresponding to a DC short circuit) occurs due to the protection operation, the accident is surely caused by the protection interlocking operation on the accident pole side. It can be removed and bipolar stop can be prevented.

[0010]

Embodiments will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a DC power transmission system according to an embodiment of the present invention. First, the operation (accommodation) command 13 for determining the operation state of the AC / DC converter is power transmission from the A end to the B end, that is, the AC / DC converters 4A and 4B are the forward converter (REC) operation AC / DC converter 8
When A and 8B are operated by inverse converter (INV), grounding breaker 15 at B end is issued by grounding breaker closing command 14 at B end.
Throw in. On the contrary, the operation (accommodation) command 16 transmits power from the B end to the A end, that is, the AC / DC converters 4A and 4B are the inverse converters (I
NV) operation, AC / AC converters 8A and 8B are forward converters (RE
C) When operating, the grounding breaker 18 at the A end is closed by the grounding breaker closing command 17 at the A end.

That is, the present invention focuses on the following two points. (1) Commutation failure tends to occur on the reverse converter operating side. (2) There is BPP as a protection operation, and this is generally found on the inverse converter side.

As shown in FIG. 2, it is assumed that a one-pole ground fault occurs while the ground end is operating the forward converter. In this case, generally, a GS (gate shift) operation is first performed at both ends of the forward / back converter of the fault pole, and at this time, the supply current to the ground fault may be cut off. However, if the BPP operation is started before the reason (1) or the current is not cut off, the sneak current from the sound pole flows through the DC short-circuit circuit from the ground point to the ground fault point, causing the ground fault point. The current continues to be supplied to the fault and the fault cannot be eliminated.

Therefore, as shown in FIG. 3, it is switched from the pre-operating state so that the inverse converter operating side always becomes the grounding point, and from the reason of the above (1) and (2), the wraparound including the forward converter side of the fault pole is performed. By configuring the current route, the fault is eliminated by normal fault operation.

[0014]

As described above, according to the present invention,
By switching the ground point of the DC circuit in advance according to the operating status of the AC / DC converter, a ground fault of a DC pole with one pole occurs in the bipolar configuration, and the current of the healthy pole is grounded via the ground point. Even if it goes around from the point to the accident pole side, and if commutation failure occurs at the reverse converter (INV) side at that time or it becomes a bypass pair (corresponding to DC short circuit) due to protection operation, protection linkage on the accident pole side Accidents can be reliably removed by operation, and bipolar stop can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a DC power transmission system according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a dipole showing a sneak current when a ground fault occurs when a forward converter (REC) end is a ground end.

FIG. 3 is a configuration diagram of a dipole showing a sneak current when a ground fault occurs when the inverse converter (INV) end is a ground point.

FIG. 4 is a block diagram of a DC power transmission system

[Explanation of symbols]

1, 11 ... AC system, 2, 10 ... AC busbar, 3, 9 ... Conversion transformer, 4, 4A, 4B, 8, 8A, 8B ... AC / DC converter, 5, 7 ... Smoothing reactor, 6, 6A, 6B ... DC power transmission line, 12 ... DC circuit grounding point, f1 ... Ground fault accident point, if
… Current flowing from the sound pole, 15, 18… Circuit breaker for grounding,
13, 16 ... Operation (accommodation) command, 14, 17 ... Grounding circuit breaker closing command.

Claims (1)

[Claims] 1. A first AC / DC converter for converting AC to DC, a DC transmission line for transmitting the output of the first AC / DC converter, and a DC / DC converter for converting DC transmitted from the DC transmission line to AC. A DC power transmission system comprising a DC circuit including two AC / DC converters, wherein a ground point of the DC circuit is connected to a reverse conversion operation side according to an operating state of the AC / DC converters at both ends of the DC power transmission line. A DC transmission system characterized by switching to the end.