JPS61266013A - Ground fault protector for dc circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a ground fault protection device that detects and protects ground faults in a DC circuit.

[Technical Background of the Invention] With advances in technology for converting alternating current into direct current (forward conversion) or converting direct current into alternating current (inverse conversion), direct current power transmission has been put into practical use.

For example, the neutral line type DC single-circuit power transmission currently in practical use in Japan has a configuration as shown in Figure 10.
8 (hereinafter referred to as literature) as described in pages 29-30. In this method, a neutral wire is provided in addition to the 274 bodies of (÷) and (-) Fi, and the neutral point is grounded at either the forward or reverse conversion station, and therefore (+) and ( -) Even if either of the two conductors of the pole has a ground fault (- line ground fault), there is an advantage that 172 power can be transmitted in a healthy tank.

Therefore, in order to take advantage of the above-mentioned advantages, the protection device is also required to have the ability not only to simply detect a fault when a ground fault occurs, but also to select which pole has a ground fault.

[Problems with Background Art] As shown in the above-mentioned documents P102 to P104, a ground fault overcurrent relay called 7GDG has been used for ground fault detection in a conventional DC circuit. This relay responds to DC overcurrent in the grounding wire, but since the DC-CT described in documents P55 to P57 is generally used to detect this current, it responds only to the magnitude of the current and does not detect the polarity of the current. cannot be determined.

Therefore, although it is possible to detect a ground fault using only the conventional ground fault overcurrent relay, it is not possible to determine which pole is the ground fault.
In order to determine which pole has a ground fault, another relay provided for each other pole is used, but a DC voltage relay is a resistive voltage divider type D
Since it is often combined with C-PT for economical reasons, its operating speed is slow and there are protection limitations. In addition, the line current during operation fluctuates widely within the range of 10% to 100% of the rated value, and large overcurrents do not flow in the event of a ground fault, so when using a DC current relay, sensitivity coordination is required. There are restrictions above.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and is capable of selectively determining in which pole a ground fault has occurred in a bipolar power transmission line in which the neutral point is grounded at one point. The purpose of this invention is to provide a ground fault protection device for DC circuits that detects at high speed.

[Summary of the Invention] The present invention focuses on the fact that the polarity of the neutral point grounding wire current (direction in which DC current flows) is uniquely determined by the voltage polarity of the DC circuit and the ground fault point, and This detects at high speed which of the two poles a ground fault has occurred based on the polarity and magnitude of the current.

[Embodiments of the Invention] Examples will be described below with reference to the drawings. Figure 1 shows an embodiment of the present invention, in which 1 is an AC system, 2-1.2-2
is a converter transformer, 3-1.3-2 is a converter, 4.5 is a DC line, and 6 is a grounding wire, which are the main components of a converter station for DC bipolar single-line power transmission with a so-called neutral point grounding type. It shows. Reference numeral 7 denotes a C-CT capable of detecting the magnitude and polarity of a current in a grounding line; for example, a Hall CT using the Hall effect has been put into practical use.

This is a ground fault overcurrent relay which is one of the main elements of the present invention, and responds by using the output of the DC-CT 7 as an input. 9.10 is a DC-PT that detects the magnitude and polarity of the ground potential of the DC circuit 4.5, and is, for example, a resistive voltage division type DC-PT. Reference numeral 11 denotes an overvoltage relay, which is one of the main elements of the present invention, and responds to the voltage difference between the outputs of the DC-PT 9.10 as input. Also, U
is a selective protection sequence in which the outputs of the ground fault overcurrent relay and overvoltage relay U are input, and a selective protection output is sent out. Note that, for convenience, a portion in which the converter transformer and the converter are combined is referred to as a DC power supply.

FIG. 2 is a functional block diagram of the ground fault overcurrent relay 8,
In the figure, 12.13 are half-wave rectifier circuits with opposite polarities, and 14
-1, 14-2 are level detection circuits that receive the outputs of the half-wave rectifier circuits 12 and 13, respectively, and send out an output when the magnitude difference is greater than a predetermined value.

In other words, once the earth fault overcurrent relay is in operation, if the input (2) is of positive polarity (i.e., the polarity in which DC current flows from the grounding point to the neutral point) and the current is greater than the predetermined value, output A is sent out. Also, conversely, when the input I has negative polarity and the current is greater than a predetermined value, the output B is configured to be sent out.

Note that during normal operation, the grounding wire current is extremely small, so normally the ground fault overcurrent relay does not send out either the A or B output once.

Figure 3 is a functional block diagram of the overvoltage relay U, in which 15.16 is a half-wave rectifier circuit with opposite polarity, and 17-1 is a half-wave rectifier circuit with opposite polarity.
．． 17-2 is a level detection circuit which receives the output of the half-wave rectifier circuits 15 and 16, and sends out an output when the magnitude thereof is greater than a predetermined value; 18-1 and 18-2 are level detection circuits 17-1, respectively. This is a return delay wind circuit (TDD) which takes the outputs of .17-2 as inputs and delays the return of the signals.

That is, in the overvoltage relay U, when the input V is positive (that is, the voltage of the DC circuit 4 is higher than the voltage of the DC circuit 5) and the voltage is higher than the predetermined value, the output C is sent out, and Conversely, if the input V has negative polarity and the voltage is higher than the predetermined value, the output will be sent out, and the return of both outputs C and D is determined by TD018-1.
It is configured so that the return is delayed by TD018-2.

FIG. 4 shows a selective protection sequence circuit of the present invention,
With the output signals A and B of the ground fault overcurrent relay 8 and the output signals C and D of the overvoltage relay 11 as inputs, the AND circuit 19-1. ...19-4 and OR circuit 20-
1.20-2 is used to construct a logic circuit.

According to this sequence circuit, in the case of a ground fault on the DC line 4 side, a signal E is sent out, and in the case of a ground fault on the DC line 5 side, a signal F is sent out, and the following logic is applied between the input and output signals. The relationship in the equation holds true.

E-(A-C)+ (B-D) F-(B-C)+ (A-D) ・・・・・・(
1) Next, the effects of this embodiment will be explained. In FIG. 1, when the converters 3-1, 3-2 operate as forward converters, the potential of the DC line 4 is always higher than the potential of the DC line 5.

Therefore, unless the output of converter 3-1.3-2 is extremely small, a positive voltage is applied to overvoltage relay U, and the voltage is large enough to be expected to operate the relay. Therefore, in this case, the output C of the overvoltage relay 11 is always on the operating side, that is, the logical value is "1".
It has become.

Now, if we consider the case where a ground fault occurs in the DC circuit 4 on the high potential side, the converters 3-1 and 3-2 operate as forward converters, so current flows toward the ground fault point. , Figure 5 (a
) A new current is generated as shown in ().

Therefore, it can be seen that current flows in the ground wire from the ground point to the neutral point.

Therefore, if the ground fault current exceeds the predetermined value, the ground fault overcurrent relay 8 will operate, and its output A will be on the operating side, that is, the logical value "1".
”.

In addition, when a ground fault occurs, if the fault point is close to the installation point of the DC-PT9, a significant voltage drop is predicted, resulting in an input that does not meet the operating conditions of the overvoltage relay 11. As is clear, the relay has a delay low circuit 18-1 when returning.
．． Since the circuit 18-2 is built in, its operating output is preserved during the scheduled time after the occurrence of a fault, so that the output C is on the operating side, that is, at the logical value "1".

Therefore, in the selection protection sequence shown in FIG. 4, the signal E
becomes "1".

Also, considering the case where a ground fault occurs in the DC line 5 on the low potential side, since converters 3-1 and 3-2 operate as forward converters, current flows toward the ground fault point, and the A new current as shown in FIG. 5(b) is generated.

Therefore, it can be seen that current flows through the grounding wire from the neutral point toward the grounding point.

Therefore, if the ground fault current exceeds the expected value, the ground fault overcurrent relay will operate once, and its output B will be on the operating side, that is, the logical value "1".
”.

As mentioned above, at this time, the output C of the overvoltage relay is on the operating side at least for the scheduled time, that is, the logical value is "1", so
In the selection protection sequence shown in FIG. 4, the signal B and the signal C have the logical value "1" and the others have the logical value "0", so the signal F becomes "1".

Next, when the converter 3-1.3-2 operates as an inverse converter, the potential of the DC line 5 is always higher than the potential of the DC line 4. Therefore, unless the output of the forward converter (not shown) is extremely small, overvoltage relay U
A voltage of negative polarity is applied to the voltage, and its magnitude can be sufficiently expected to operate the relay.

Therefore, in this case, the output of the overvoltage relay is always on the operating side, that is, the logic value is "1".

Now, if we consider the case where a ground fault occurs in the DC circuit 5 on the high potential side, since the converters 3-1 and 3-2 operate as reverse converters, the ground fault will be detected by the forward converter (not shown). A current flows toward , and a new current as shown in FIG. 6(a) is generated.

Therefore, it can be seen that current flows in the ground wire from the ground point to the ground fault point.

Therefore, if the ground fault current is above the predetermined value, the ground fault overcurrent relay 8 will operate, and its output A will be on the operating side, that is, the logical value "
1”.

In addition, when a ground fault occurs, if the faulty Sakai point is close to the DC-PTIO installation point, a significant voltage drop is expected, but even in this case, as mentioned above, the output of the overvoltage relay U will be at least as low as expected. Since the time is on the operating side, that is, the logical value is "1", the selection protection sequence in FIG.
becomes.

Also, considering the case where a ground fault occurs in the DC line 4 on the low potential side, a current flows from the forward converter (not shown) toward the ground fault point, as shown in Fig. 6(b). A new current is generated. Therefore, it can be seen that current flows into the ground wire from the neutral point toward the ground point.

Therefore, if the ground fault current exceeds the expected value, the ground fault overcurrent relay will operate once, and its output B will be on the operating side, that is, the logical value "1".
”.

In addition, when a ground fault occurs, if the fault point is close to the installation point of DC-PT9, a significant voltage drop is expected, but even in this case, as mentioned above, the output of overvoltage relay U will remain constant for at least the scheduled time. is on the active side, that is, the logical value is "1", so the selection protection sequence circuit diagram in FIG. 1”.

As explained above, in this embodiment, converter 3-1.
Regardless of whether the operation in 3-2 is a forward conversion operation or an inverse conversion operation, if a ground fault occurs in the DC line 4 due to the selective protection sequence, an operation output is obtained on the signal E, and the DC line 5
When a ground fault occurs in a ground fault, an operating output can be obtained as signal F, and the time to obtain that operating output simply depends on the operating time of the ground fault overcurrent relay, so it is much faster than conventional relays. It is possible to selectively protect fast DC circuits.

The application of the present invention is not limited to the so-called neutral point one-end grounded DC system described in FIG.

That is, it can be similarly applied to a neutral line DC system.

Here, in a neutral line type DC system, the current patterns at the time of failure are as shown in Figures 5 (a), (b), and 6.
Corresponding to Figures (a) and (b), Figures 7 (a) and (b)
, and as shown in Fig. 8(a) and (b), but in both cases, the input current and input voltage polarities of the DC overcurrent relay 8 and the overvoltage relay 11 are the same, and the response tendency is the same. Therefore, the same effect can be obtained.

In the present invention, the configuration is even simpler if the voltage polarity of the protected DC system is fixed.

FIG. 9 shows another embodiment of the present invention, which is a so-called neutral point one-end grounded DC system.

In the figure, 22-1, 22-2 is a battery used as a DC power source, 4.5 is a DC circuit, 6 is a grounding wire, and 8 is a ground fault overcurrent relay. Items with the same symbols as in Figure 1 are It has the same functionality.

Here, assuming that the DC line 4 is always at a higher potential than the DC line 5, in the event of a ground fault in the DC line 4, the fifth
A fault current having a pattern similar to that shown in FIG. 5(a) flows, and when a ground fault occurs in the DC line 5, a fault current having a pattern similar to that shown in FIG. 5(b) flows.

Therefore, as mentioned above, when there is a ground fault in the DC line 4, the output A of the ground fault overcurrent relay becomes "1", and when there is a ground fault on the DC line 5, the output B of the ground fault overcurrent relay 8 becomes "1". By using the outputs A and B of this ground fault overcurrent relay,
It is clear that the selective protection of the single-end grounded type DC system shown in FIG. 9 is possible, and that the high-speed selective protection that is the object of the present invention can be achieved in this case as well.

[Effects of the Invention] As explained above, according to the present invention, it is possible to selectively and quickly detect in which pole of a bipolar transmission line in which a neutral point is grounded, a ground fault has occurred. A DC circuit ground fault protection device comes with a ratio provided.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the main configuration of a DC bipolar single line power transmission converter station with one end grounded at the neutral point and the relay installation points of the earth fault protection device of this embodiment, and Figure 2 is a diagram for explaining the earth fault overcurrent relay. Fig. 3 is a functional block diagram of the overvoltage relay, Fig. 4 is a selection protection sequence diagram, Fig. 5 is a diagram for explaining fault current during forward converter operation, and Fig. 6 is a diagram for inverse conversion. Figure 7 is a diagram to explain the fault current during forward converter operation in the neutral line system, Figure 8 is a diagram to explain the fault current during forward converter operation in the neutral line system, and Figure 8 is the reverse conversion in the neutral line system. Figure 9 is a diagram showing the present invention applied to a DC system using a DC power source (battery) with one end grounded at the neutral point, and Figure 10 is a diagram for explaining the fault current during operation of the equipment. FIG. 2 is a diagram for explaining DC bipolar single-line power transmission. 1... AC system 2-1.2-2... Converter transformer 3-1.3-2... Converter 4.5... DC line 6... Ground wire 7... DC-
CT Dan...Ground fault overcurrent relay 9.10...D
C-PTU... Overvoltage relay 12.13.15.16... Half-wave rectifier circuit 14-1.
14-2.17-L 17-2...Level detection circuit 1
8-1.18-2...-Return delay low circuit (TDD) 19
-1 to 19-4...AND circuit 20-1.20-2...OR circuit 21...Selection protection sequence circuit 22-1.22-2...DC power supply (battery) 23
...Neutral wire (7317) Agent Patent attorney Kensuke Norichika (and 1 other person) Figure 4 Figure 9 Figure 10

Claims (1)

[Claims] Connect multiple DC power supplies in series, and connect one of these intermediate connection points.
In a ground fault protection device for a DC circuit in which a point is grounded by a ground wire, when the magnitude and polarity of the DC current flowing through the ground wire meet predetermined conditions, a ground fault overcurrent relay that derives a protective output corresponding to the polarity. and an overvoltage relay that derives a status output corresponding to the polarity when the magnitude and polarity of the line voltage of the DC circuit connected to the converter group meet predetermined conditions, and the ground fault overcurrent relay and the overvoltage relay. 1. A ground fault protection device for a DC circuit, comprising: a selection output device that determines which DC line has a ground fault based on output from a relay.