JPS6011533B2 - DC power transmission protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for a bipolar operated DC transmission system.

As configurations of DC transmission lines capable of bipolar operation, there are two types: a return-to-ground method in which converter stations at both ends of the transmission line are grounded and a neutral wire is omitted, and a return-to-ground method in which only one end of the neutral wire is grounded.

However, if direct current is passed through the ground, problems such as induction disturbance and corrosion occur, so a single point grounding of the neutral wire is used. An example of this is shown in FIG. Converter transformer T1 as shown in Figure 1
, converter B1, DC IJ vector DCLI, and the other three converter circuit groups G2, G3, and G4 are connected to each other by DC transmission lines L1, L2, and L3 in order to perform bipolar operation. There is a DC power transmission system in which one end of the neutral line L2 of the line is grounded.

Note that CB, CB2, C&, and CB4 are AC line breakers connected to the AC sides of the converter transformers T, , T2, T3, and T4, respectively. When this DC transmission system is in bipolar operation, if an accident occurs in the converter circuit group GI, the converter BI gate blocks, and then the converter transformer T
It is protected by disconnecting B to the AC side of I and the disconnector. Conversion circuit group G2 also stops in coordination with this, and unipolar (monopolar) operation continues with conversion circuit groups G3 and G4 of healthy poles.
When a ground fault occurs at fault point A shown in Figure 1, even if the conversion circuit groups GI and G2 of the fault pole are stopped, the healthy pole continues to operate, so the non-grounded end of the neutral wire is A ground potential corresponding to the voltage drop of the conductive wire occurs, and direct current continues to be shunted to the fault point A through the converter BI. In order to stop this divided flow, it is necessary to also stop the healthy pole. As described above, shutting down the entire DC power transmission system despite an accident in the converter circuit group GI is extremely inconvenient as it greatly reduces the power transmission capacity. Therefore, an object of the present invention is to provide a protection device that can stop only the faulty pole and allow the healthy pole to continue operating in this situation.

Now, if we consider the cause of the above-mentioned inconvenience, when only the healthy pole is in continuous rotation, a ground potential equivalent to the neutral wire voltage drop occurs at the ungrounded end of the neutral wire, and a shunt occurs in the converter BI. There is a particular thing.

Therefore, it would be better to eliminate this shunt current by some method, but in order to stop the converter circuit group G1, G2 of the fault pole in the event of an accident, the AC side disconnector CB,
Even after C & has been disconnected, it is detected that a shunt has occurred in the converter BI, and B is applied to the AC side disconnector again to maintain a floating state (the AC side disconnector is closed). After the converter valve is in a standby state (not ignited), the other valves in the phase where the shunt occurs will dissipate the current in the valve where the shunt is occurring. It is possible to continue the operation of the healthy electrode by igniting the ground-side valve of the phase whose potential has become negative with respect to the potential of the ground-side valve to eliminate the shunt. An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2a shows the conversion circuit group GI of FIG. In the figure, the same parts as in FIG. 1 are indicated by the same symbols. Here, among the six valves VI to V6 that constitute the converter BI, the ground side valve V4.
As an example, DC transformers DC-CTI to DC-CT3 are provided to detect the arm currents of V6 and V2. FIG. 2c shows the AC voltage VR. detected by the meter relay transformer (not shown) in FIG. 2a. Vs, V, and valves V4, V6 detected by DC transformer DC-CT1, 2, 3
, V2 arm currents 1, 12, etc. are introduced to determine a predetermined valve that can extinguish the energized valve. Circuits 1, 2, and 33 introduce AC voltage, and circuit 1 outputs an output when AC voltage VT-VR is positive, circuit 2 outputs when AC voltage VR-Vs is positive, and circuit 3 outputs AC voltage. This is a phase detection circuit that outputs an output when the voltage Vs - V is positive. The operation delay circuit TDE operates after a predetermined time T has elapsed after the phase detection regeneration circuit operates.
Circuit 4 is a level detection circuit that outputs an output when arm current is flowing through valves V4, V6, and V2. logical AND
I is a circuit that outputs an output after a predetermined time T from the AC voltage V'-VR>0 on the condition that an arm current is flowing through the valve V2, and this output fires the valve V4 at a predetermined phase. Similarly, the logical product AND2, AND3 is valve V6
, V2. Next, Figure 2a,
The operation of this embodiment will be explained using b and c.

First, we will show a flowchart when an accident occurs. In this embodiment, the 1st line ground termination will be explained.

When a ground fault occurs at the fault point A, the ground fault detection Ry is activated, and the conversion circuit groups G1 and G2 at the fault pole are stopped by alternating the converter gate operation and by opening the circuit breaker B. Even after a predetermined period of time has passed after the faulty pole is stopped, if the arm current of the one-wire ground fault continues in the T-phase grounding side valve V2 due to the shunt from the healthy pole, turn on the AC shutoff circuit breaker CB again and convert. The container 81 is placed in a floating state. Next, the T-phase ground side valve V2
Since an arm current flows through the arm, it is necessary to cancel this current. To do this, when the phase voltage VT is higher than the phase voltages VR and Vs of the other phases among the AC voltages shown in Fig. 2b, the grounding side valves V4 and V6 of these other phases should be ignited. good. If valves V4 and V6 are ignited, valve V2-
Converter transformer T, - valve V4 (or valve V6
) is formed, a phase-to-phase short circuit occurs, and the current flowing through valve V2 disappears by flowing through valve V4 or V6. In FIG. 2c, the arm current detection circuit of the circuit 4 operates due to the arm current flowing through the valve V2, and the AC voltage V. -When VR is positive, the AND circuit ANDI outputs an output after a predetermined time T, and the valve V
4 is ignited, a phase-to-phase short circuit occurs between VT and VR, and valve V
The current of 2 disappears. Incidentally, even if the fault point A is in the R phase or the S phase other than the T phase, the valve in a predetermined phase can be ignited in the same way using the circuit shown in FIG. 2c. logical AND
The blocking conditions shown in I to AND3 are such that the valve to which the arm current is energized is 1 because this embodiment targets a 1-line ground fault.
Although it is designed to operate when only one person is present, there is no necessity to limit it to this. In short, as is clear from the waveform diagram in FIG. 2b, the voltage VR or Vs is higher than the voltage VT.
When the voltage is low, the ground side valve V4 or V6 may be ignited. In addition, if a shunt occurs due to a ground fault such as at accident point B, two valves will be energized, but if the ground side valves V2, V4, and V6 are extinguished, the shunt will inevitably disappear. I can handle it. Next, other embodiments of the present invention will be described.

In the above-mentioned embodiment, it was detected by the arm current that the valve was energized due to the occurrence of a shunt current, but in this embodiment, the presence or absence of forward and reverse voltages applied to the valve is detected, and the current is energized by the shunt current. This is to determine which valve is in use. First, the configuration of this embodiment will be explained below with reference to the drawings.

FIG. 3a shows the conversion circuit group GI in FIG. 1st in the diagram
Parts that are the same as those in the figure are indicated by the same symbols. Here, limiting resistors RI to R3 and light emitting diodes PhDI to PND are connected between the anodes and cathodes of the ground side bulbs V4, V6, and V2.
6 is one method for detecting forward and reverse voltages.

The limiting resistors RI~R3 pass a current proportional to the voltage applied between the anode and cathode of the bulb to the light emitting diodes FNDI~P.
This is a resistance for flowing to M06. The light emitting diodes 1, 3 and 5 are used to detect the forward voltage of the bulb, and the light emitting diodes 2, 4 and 6 are used to detect the reverse voltage of the bulb. FIG. 3b is used for the same purpose as FIG. 2c, and the same functions are designated by the same symbols. circuit 5
is a forward/reverse voltage detection circuit that operates when no voltage is applied to any of the valves V4, V6, and V2 in the nearly reverse direction. It should be noted that the forward voltage drop of the valve that appears during valve communication is assumed to be a bell that can be determined as having no voltage in the normal direction. Logical thin AND4~AND5 is the second
It has the same function as the logical products ANDI to AND3 in FIG. Next, the operation of this embodiment will be explained with reference to FIGS. 3a and 3b.

First, we will show a flowchart when an accident occurs. In this embodiment, a 1-line area will be explained. When a pond fault occurs at the fault point A, the ground fault detection Ry is activated, and the converter circuit groups G1 and G2 at the fault pole are stopped by alternating converter gate operation and disconnector opening. Even after a predetermined period of time has elapsed since the faulty pole was stopped, if a shunt from the healthy pole still occurs, this is detected and B is re-injected into the alternator and disconnector to bring the converter BI into a floating state. When this floating occurs, only a voltage drop in the forward direction of the valve occurs in the energized valve V2 due to the shunt, so the forward/reverse voltage detection circuit determines that the valve is energized.

Since a forward or reverse voltage is applied to the other valves V4 and V6, the forward and reverse voltage detection circuit is determined to be inoperable.
In FIG. 3b, when no forward or reverse voltage is applied to the valve V2, and when the AC voltages V and VR are positive, the logical AND4 outputs after a predetermined time T, and the valve V4 is ignited.
As a result, an interphase short circuit occurs between VT and VR, and the current in valve V2 disappears. As described above, according to the present invention, in the event of a secondary accident involving a converter transformer, the converter is brought into a floating state again after the AC disconnector is opened, and the voltage is lower than that of the energized valve. By igniting the valve to which is applied and commutating current to this valve, it is possible to obtain a DC power transmission protection device that can stop only one pole and continue operation of the healthy pole without stopping both poles of the DC power transmission system. can.

[Brief explanation of the drawing]

Fig. 1 is a general DC power transmission system configuration diagram for bipolar operation with a single point grounding of the neutral wire, Fig. 2 is a diagram showing an embodiment of the present invention, and a corresponds to the conversion circuit group GI in Fig. 1. b is a waveform diagram, c is a circuit diagram of a part that selects an ignition valve, FIG. 3 is a diagram showing another embodiment of the present invention, and a is a circuit diagram corresponding to FIG. 2 a. ,b are circuit diagrams corresponding to FIG. 2c. Figure 1 Figure 2 Figure 2 Figure 3 Figure 3

Claims (1)

[Scope of Claims] 1. In a DC power transmission system operated in bipolar operation in which a converter and a converter circuit group having a converter transformer are connected at both ends and one point of a neutral wire is grounded, the conversion within the converter circuit group is means for detecting that an accident has occurred in the secondary circuit of the converter; and after an output signal from the detecting means opens an AC side breaker provided on the AC side of the converter transformer; means for detecting that there is a grounding valve that is energized in the converter circuit group connected to the breaker circuit even after a certain period of time has elapsed; and an output signal of the detecting means to cause the converter to be in a floating state. and then igniting a ground-side valve to which a lower voltage is applied than the ground-side valve of the energized phase in the converter. 2. The DC power transmission protection device according to claim 1, wherein the arm current of the ground-side valve of the converter is used to detect the energized valve. 3. The DC power transmission protection device according to claim 1, wherein the voltage between the anode and cathode of the ground-side valve of the converter is used to detect the energized valve.