JPH0224092B2 - - 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 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 are reactors connected to each end of the power transmission line 1N, 3a is an AC/DC converter connected between the reactor 2a and the neutral wire 1G, and 3b is connected between the reactor 2c and the neutral wire 1G. An AC/DC converter 3c is an AC/DC converter connected between the reactor 2b and the neutral wire 1G, 3d
is an AC/DC converter connected between the reactor 2d and the 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, 1N, and 4b is the power transmission line 1P, 1N. 5a and 5b are adders that add the command current signal and the bias signal with the polarities shown;
6 inputs the bias signal of the setting device 4b to adders 5a and 5.
Contacts 6a and 6b leading to the AC/DC converters 3a and 6b generate firing pulses for constant current control of the AC/DC converters 3a, 3b by the output signals of the adders 5a, 5b.
a, 3b, a control circuit 7a, 7b is a DC current transformer provided at each end of the neutral wire 1G, 8a, 8
b has a predetermined delay time, and the DC current transformers 7a, 7
Delay circuits using the output of b as an input signal, 9a, 9b
inputs the output signals of the delay circuits 8a, 8b and the output signals of the transmission devices 10a, 10b described below, and when an abnormality is detected by comparison, the transmission lines 1P, 1N
Differential protection relay with protective operation, 10a, 10
b is a transmission device that transmits the outputs of the DC transformers 7a and 7b for comparison with the current value at the other end. 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
b, 9a. In this way, the differential protection relays 9a and 9b compare the currents detected at both ends of the neutral wire 1G at the same time, and determine if the difference between them is greater than the bias set by the setting device 4b. When this occurs, the protective operation output is activated.

On the other hand, during the period when there is no ground fault and 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 neutral The current flowing through line 1G will be essentially zero.

Conventional detection devices have the above-mentioned configuration, and require complex transmission equipment that is easily affected by noise.Also, the power transmission system cannot be left in an unbalanced state for a long time, so 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, is also complicated.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and it adds three current values detected from the power transmission side of a power transmission line and a neutral line, and compares this addition result with a reference level. By comparing the
It is an object of the present invention to provide a power transmission line ground fault detection device that can be easily configured and has improved operational reliability.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 2, the same symbols as in FIG. 1 indicate the same parts, and 11a, 11b, and 11c are DC transformers that transform the current flowing through the power transmission end and the ground end of the power transmission lines 1P, 1N and the neutral wire 1G. Current transformer 12 is an adder 13 that adds the outputs of DC current transformers 11a, 11b, and 11c in positive polarity, negative polarity, and positive polarity.
is a signal 13a indicating that a ground fault has occurred in the neutral wire 1G when the output of the adder 12 is greater than a predetermined value.
This is a detector that outputs .

Next, the operation will be explained with reference to the timing diagrams shown in FIGS. 3 and 4. In FIGS. 3 and 4, a, b, and c are DC current transformers 11a, 11b, 1
1c is the detection signal, and d is the output signal of the adder 12. As explained in _{FIG .}
When closed, the power transmission lines 1P and 1N become unbalanced, and an unbalanced current equivalent to twice the bias set in the setting device 4b flows through the neutral wire 1G. but,
When the neutral wire 1G is healthy and has not experienced a ground fault, the output of the adder 12 becomes substantially zero as shown in FIG.
Do not output a.

On the other hand, when a ground fault occurs in the neutral wire 1G, the current in the neutral wire 1G is shunted through this ground fault point, so the output of the DC current transformer 11c decreases. Therefore, as shown in FIG. 4, the output of the adder 12 becomes greater than or equal to the predetermined value, so the detector 13 outputs a signal 13a.

In addition, since the polarity for detecting the current of the power transmission lines 1P, 1N and the neutral line 1G is positive in the direction of the arrow shown in the figure, the DC current transformer 11c of the neutral line 1G is a bipolar one using, for example, a Hall element. is appropriate.
Since the detector 13 outputs the signal 13a even in the case of a ground fault in the transmission lines 1P and 1N, in order to distinguish it from the ground fault in the neutral line 1G, the signal 13a is output in synchronization with the closing of the contact 6. All you have to do is judge the output level.

In addition, in the above embodiment, a bias current is added to the current of the power transmission line at both the positive and negative ends in order to detect a ground fault, but the same effect can be obtained even if the bias current is added to either one or both at different times. It has the effect of

As described above, according to the present invention, the currents in the power transmission line and the neutral line on the power transmission side are detected, the appropriate polarities are selected and added, and the level of the addition result is judged to prevent a ground fault in the neutral line. Since the detection is performed, the configuration can be simplified and there is no need for synchronization control with the other end.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional ground fault detection device, FIG. 2 is a block diagram of a ground fault detection device according to an embodiment of the present invention, and FIGS. 3 and 4 are block diagrams of a conventional ground fault detection device.
FIG. 3 is a timing diagram of the operation of the device shown in the figure. 1N, 1P...Power line, 1G...Neutral line, 3a
~3d... AC/DC converter, 4a, 4b... Setting device,
5a, 5b, 12...adder, 6a, 6b...control circuit, 11a-11c...DC current transformer, 13...
…Detector. Note that the same reference numerals in the figures indicate the same parts.

Claims (1)

[Claims] 1. In a ground fault detection device for a neutral wire for DC power transmission in a DC power transmission line consisting of a positive power transmission line that transmits positive polarity current, a negative power transmission line that transmits negative polarity current, and a neutral wire. , a first DC current transformer that detects a load current flowing through the positive power transmission line;
a second DC current transformer that detects the load current flowing through the negative polarity power transmission line; a third DC current transformer that detects the current flowing through the neutral wire; the positive polarity power transmission line;
or a setting device for adding a bias current to at least one of the negative polarity power transmission lines, the load current of the positive polarity and negative polarity power transmission lines detected by the first and second DC transformers; Add in the direction of cancellation, and add the third value in the direction of cancellation of the output.
The adder adds the detection signal of the DC current transformer, and compares the output of the above calculator with the reference level in synchronization with the timing when the bias current is added by the above setter, and based on the comparison result, the neutral A ground fault detection device for a neutral line for direct current power transmission, characterized by comprising a detector for detecting a ground fault in a line.