JPH0132733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting a ground fault in a DC transmission line, particularly a ground fault occurring on the neutral line of a DC transmission line operated in bipolar operation.

This type of device forms part of a protection device for DC power transmission lines, and a conventional device is shown in FIG. In the figure, 1P is a power transmission line that transmits positive polarity current, 1G is a neutral line, 1N is a power transmission line that transmits negative polarity current, 2a and 2b are reactors connected to each end of power transmission line 1P, and 2C , 2d is the power transmission line 1N
A reactor connected to each end of the reactor 3a, an AC/DC converter connected between the reactor 2a and the neutral wire 1G,
3b is an AC/DC converter connected between reactor 2c and neutral wire 1G, 3c is an AC/DC converter connected between reactor 2b and neutral wire 1G, and 3d is an AC/DC converter connected between reactor 2d and neutral wire 1G. 4a is a setting device that generates a command current signal for setting the current value in the power transmission lines 1P and 1N, and 4b is a setting device that generates a bias current value to be added to the direct current of the power transmission lines 1P and 1N. A setting device that generates a bias signal for setting; 5a and 5b are adders that add the command current signal and the bias signal with the polarities shown; 6 is a contact that leads the bias signal from the setting device 4b to the adders 5a and 5b. , 6a, 6b generate ignition pulses for constant current control of the AC/DC converters 3a, 3b based on the output signals of the adders 5a, 5b.
Control circuit to supply to 3b, 7a and 7b are neutral wire 1
DC alternators 8a and 8b are provided at each end of G, and 8a and 8b are delay circuits that have a predetermined delay time and use the output of the DC current transformer 7a as an input signal; 9a and 9b are delay circuits 8
The output signals of a and 8b and the transmission device 10 described below
A differential protection relay that protects the power transmission lines 1P and 1N when an abnormality is detected by inputting the output signals of the DC current transformers 7a and 10b. This is a transmission device that transmits the current value for comparison. One end of the neutral wire 1G is grounded.

Next, the operation will be explained. Power transmission line 1P, 1N
The specified current value to be applied to is set in the setting device 4a,
Furthermore, in order to facilitate the detection of a ground fault that occurs on the neutral wire 1G, the contact 6 is closed in a timely manner, and the setting device 4b is
The bias signal is sent to adders 5a and 5 via contact 6.
Input the polarity shown in b. For this reason, adder 5
The outputs of a and 5b have unequal values and are inputted to control circuits 6a and 6b, and the ignition pulses controlled thereby control AC/DC converters 3a and 3b.
AC/DC converters 3a, 3b send DC power to power transmission lines 1P, 1N via reactors 2a, 2c in accordance with the ignition pulse. This DC power is transmitted to the power transmission line 1P, 1
The AC power is converted into AC power by AC/DC converters 3c and 3d at the other end of the N, and is supplied to a load (not shown).
Since the DC currents flowing in the power transmission lines 1P and 1N have opposite polarities, the current flowing in the neutral line 1G is equivalent to the difference between the two, and is transformed by the DC current transformers 7a and 7b, and is transformed by the delay circuits 8a and 8b. is input to the differential protection relays 9a, 9b via the transmission device 10.
differential protection relay 9 on the other side via b, 10a
It is also input to b and 9a. In this way, the differential protection relays 9a and 9b compare the currents detected at both ends of the neutral wire 1G, and the difference between them is determined by the setting device 4.
If the bias is higher than the bias set in b, the protection operation output is activated.

On the other hand, during the period when the contact 6 is not closed, the outputs of the adders 5a and 5b are balanced, so the outputs of the AC/DC converters 3a and 3b are balanced, and the current flowing through the neutral wire 1G is Effectively becomes zero.

Conventional detection devices have the above configuration, and require complex transmission equipment that is easily affected by noise. Also, since the power transmission system cannot be left in an unbalanced state for a long period of time, the neutral line The disadvantage is that the timing control, that is, the synchronization control required to compare the current values detected at both ends of the circuit, is also complicated.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the voltage on the transmission side of the power transmission line is detected by a DC transformer, and this voltage and the voltage flowing through the grounding point of the neutral wire are It is an object of the present invention to provide an accident detection device for a DC power transmission line whose configuration can be simplified by using the current state as a logical condition for accident detection.

Hereinafter, FIG. 2 showing an embodiment of the present invention will be described. In FIG. 2, the same symbols as in FIG. 1 indicate the same parts, and 11a and 11b are power transmission lines 1.
DC transformer installed on the power transmission side of P, 1N, 12
is a DC current transformer for detecting the current flowing through the grounding point of the neutral wire 1G, 13a and 13b are detectors that respond to a predetermined input voltage or lower, and output from the DC transformers 11a and 11b. DC undervoltage relay (hereinafter referred to as
(referred to as a relay), 13c acts as a detector that responds when the input voltage is below a predetermined value, and the DC current transformer 1
A DC current relay (hereinafter referred to as a relay) with the output of 2 as an input signal, 14 is a relay 13a and 1
This is an AND gate that performs an AND operation between the inverted logic of the output of relay 13b and the output of relay 13c to obtain an accident detection signal.

Next, the operation will be explained with reference to the time charts shown in FIGS. 3 and 4. As explained in Fig. 1, when the contact 6 is closed between times _t1 and _t2 , the power transmission lines 1P and 1N become unbalanced, and an unbalanced current equivalent to twice the bias set in the setting device 4b is generated. It flows to the sex line 1G (Fig. 3 a, b). However, when the neutral wire 1G has not experienced a ground fault and is healthy, the current flowing through it (FIG. 3c) exceeds a predetermined value, so the relay 13c does not respond. Therefore, the AND gate 14 is not opened and no accident detection signal is output (FIG. 3d).

On the other hand, when the ground fault shown in Figure 2 occurs, the neutral wire 1G is connected to the neutral wire 1G via this ground fault point.
The current of G (Fig. 4c) is shunted to the DC current transformer 12.
Since a current i ₁ −i ₂ (i ₁ is the current due to the power transmission line 1P (Fig. 4 a), and i ₂ is the current due to the power transmission line 1N (Fig. 4 b)) of a predetermined value or more flows through, the relay 13c responds. do. However, since the voltages of the power transmission lines 1P and 1N do not drop below the predetermined value, the relays 13a and 13b do not respond. Therefore, the AND gate 14 is opened and an accident detection signal is output (FIG. 4d).

When a ground fault occurs on the power transmission line 1P or 1N, the output voltage of the DC transformer 11a or 11b drops below a predetermined level, so the relay 13a or 13b
In response, AND gate 14 is inhibited, and no accident detection signal is output.

In addition, in the above example, AC/DC current was added to the current of the power transmission line with both positive and negative poles in order to detect a ground fault, but the same effect can be obtained even if bias current is added to one or both of them at different times. be effective.

As described above, according to the present invention, a ground fault in the neutral wire is detected from the logical condition based on the voltage state of the power transmission line on the power transmission side and the current state of the grounding point of the neutral wire. This has the effect of simplifying the process and increasing reliability.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional detection device, FIG. 2 is a block diagram of a detection device according to an embodiment of the present invention, and FIGS. 3 and 4 are timing charts of the operation of the detection device shown in FIG. . 1N, 1P...Power line, 1G...Neutral line, 3a
~3d... AC/DC converter, 4a, 4b... Setting device,
5a, 5b...adder, 6a, 6b...control circuit, 11a, 11b...DC transformer, 13a-1
3c...Relay, 14...and gate. In addition, in the figures, the same reference numerals indicate the same parts.

Claims (1)

[Claims] 1. When a bias current is added to the transmission current of the positive and negative power transmission lines, a ground fault in the neutral wire is detected by determining the level of the current flowing in the neutral wire of the power transmission line. A ground fault detection device for a neutral line for DC power transmission includes a first detection circuit that responds when the current through the grounding point of the neutral line exceeds a predetermined value, and a positive polarity and negative polarity transmission circuit. Second and third detection circuits that respond when the voltage detected on the power transmission side of the wire falls below a predetermined value, and predetermined logic conditions based on the outputs of the first to third detection circuits, and the above What is claimed is: 1. A ground fault detection device for a neutral line for DC power transmission, comprising a logic circuit that outputs a signal indicating the occurrence of a ground fault for a neutral line.