JPS6366131B2 - - Google Patents

Description

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

A DC power transmission system usually has a configuration as shown in FIG. The AC system 1 is connected to an AC system 9 via a conversion transformer 2, an AC/DC exchange device 3, a DC reactor 4, a power transmission line 5, a DC reactor 6, an AC/DC conversion device 7, and a conversion transformer 8. A DC current transformer 10 is installed at both ends of the power transmission line 5 to detect the current.
11 and a DC transformer 1 for detecting its voltage.
2 and 13 are provided, and their outputs are supplied to a protective relay device (not shown).

Since the AC/DC converters 3 and 7 are under constant current control, even if a ground fault or short circuit occurs in the power transmission line 5, an excessive current approximately twice the rated current will flow through the transmission line 5, preventing an accident in the AC system. It will not cause the earth system to collapse like this. However, accidents need to be detected quickly and protective actions taken.
The following methods are known as accident detection methods.

(a) A method of detecting a drop in DC voltage using DC transformers 12 and 13.

(b) A method of detection based on the rate of change dVd/dt of the DC voltage Vd using the DC transformers 12 and 13.

(c) A method of detecting when the difference current between the currents detected by the DC current transformers 10 and 11 exceeds a predetermined value.

(d) A method of detecting that the DC current increases on the forward converter side and decreases on the inverse converter side.

However, (a) and (b) also include a drop in DC voltage due to commutation failure in converters 3 and 7, and (c) constantly transmits the detected current value to the other end for comparison.
The amount of information to be transmitted is also considerable, and compensation for transmission delays is required. (d) had the drawback of malfunctioning when the DC current oscillated or increased only at one end of the transmission line.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above. It is an object of the present invention to provide a protective relay device that can achieve highly reliable operation and reduce the amount of transmitted information by checking the difference current between the two and determining the occurrence of an accident when the difference is greater than a predetermined value.

An embodiment of the present invention will be described below with reference to the drawings. In Figure 3, the same symbols as in Figure 1 indicate the same parts, and since similar parts are provided at both ends of the power transmission line 5, the same symbols are attached to clarify the correspondence. I will focus on and explain. The output of the DC transformer 12 is supplied to a detector (for example, an undervoltage relay) 14 that detects when the output falls below a predetermined level, and the signal 14a of the detector 14 is
is supplied to a timer 15 whose time limit is a time T set corresponding to the point at which the current changes when a ground fault occurs in the power transmission line 5. Timer 15 signal 15
a is supplied to a sample and hold circuit 16 and used to sample and hold the output of the DC current transformer 10. The hold signal 16a of the sample/hold circuit 16 is the reference signal 1 of the current command unit 17.
It is supplied to a comparison circuit 20 for comparison with 7a. Comparison circuit 20 is composed of two circuits, and outputs signal L1 when hold signal 16a is greater than reference signal 17a, and outputs signal S1 when the opposite is true. The signals L1 and S1 are transmitted to the other end by the transmission device 22 and are also supplied to the coincidence detection circuit 24.

The coincidence detection circuit 24 receives signals L2 and S2 generated in the same way from the other end via the transmission device 23.
are input, and the signals L1 and S2, S1 and L2
AND gates A1 and A2 which use AND logic to check whether the outputs of AND gates A1 and A2 match the
The output of gate O1 becomes a signal 24a representing a ground fault in power transmission line 5, which is input to a protection interlocking circuit (not shown), and protects power transmission line 5 by stopping AC/DC converters 3 and 7.

The operation will be explained with reference to FIG. When the power transmission line 5 is healthy, the detection circuit 14 does not output the signal 14a, and the comparator 20 does not output the signals L1 and S1.
Therefore, the coincidence detection circuit 24 also does not output the signal 24a.

When a ground fault occurs in the power transmission line 5 at time tf, the DC voltage Vd of the power transmission line 5 becomes zero as shown in FIG. 4a, so the detector 14 outputs a signal 14a,
Start timer 15. The timer 15 outputs a signal 15a after a time T, which causes the sample-and-hold circuit 16 to hold the output of the DC current transformer 10 (FIG. 4c). At its own end of the transmission line 5, the DC current Idr shows a value greater than the reference value Iref due to the ground fault (Fig. 4b). Comparison circuit 20 compares hold signal 16a of sample-and-hold circuit 16 with reference signal 17a, and keeps signal L1 high and signal S1 low, as shown in FIG. 4d.
The signals L1 and S1 are ANDed with the signals L2 and S2 at the other end by the AND gates A1 and A2 of the coincidence detection circuit 24. On the other hand, the DC current Idi of the transmission line 5 at the other end is at time tf as shown in Figure 4e.
Since it starts to decrease from and is lower than the reference value Iref, the hold signal 16a of the sample-and-hold circuit 16 becomes as shown in FIG. 4f, and the comparator circuit 20 becomes as shown in FIG. 4g.
The signal L2 is held low as shown in FIG.
get high.

Therefore, the AND gate A1 at its own end opens, and the OR gate O1 outputs the signal 24a as shown in FIG. 4h, causing the protection operation to be performed.

In addition, in order to simplify the explanation, the current command device 17
are provided at both ends of the power transmission line 5, but they may be provided at either end and transmitted to the comparison circuit 20 at the other end via the transmission device 22 or 23.

FIG. 3 is a circuit diagram of a protective relay device according to another embodiment of the invention. To explain the differences from FIG. 2, the timer 15 is configured to output signals 15a and 15b having different time limits. The sample-and-hold circuit 16 consists of two circuits having the same configuration, samples and holds signals 15a and 15b, respectively, and outputs the results as hold signals 16a and 16b. Comparison circuit 16 also consists of two circuits with the same configuration, and compares hold signals 16a and 16b with reference signal 17a, and when the former is large, outputs signals L1 and L3 (the other end is L2 and L4), and vice versa. When , signal S1,
S3 (the other end outputs S2 and S4). The coincidence detection circuit 24 has AND gates A1 to A4,
Signals L1, S2; S1, L2; L3, S, respectively
4; Find a match between S3 and L4, that is, a logical product. The output of AND gates A1 and A2 is OR gate O
1, the outputs of AND gates A3 and A4 are OR.
It is led through gate O2 to AND gate A5, and the output of OR gate A5 becomes signal 24a.

In the above embodiment, the number of samples and holds is up to two, but this may be two or more times, and the intervals may or may not be constant. When the number of times is two or more, the determination result of the comparator circuit that is equal to or more than a predetermined number may be output.

Further, in the above embodiment, a drop in the DC voltage of the power transmission line is used as a triggering factor for determining an accident, but a change in DC voltage within a unit time, that is, a rate of change exceeding a predetermined value may be used as a triggering factor.

As described above, according to the present invention, the DC current of the power transmission line is investigated in response to changes in the DC voltage, and an accident is determined. Therefore, the transmission capacity of the transmission device can be reduced, and the determination is reliable. It has the effect of increasing sex.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a power system, FIG. 2 is a block diagram of a protective relay device according to one embodiment of the present invention, and FIG. 3 is a block diagram of a protective relay device according to another embodiment of the present invention. , FIG. 4 is a timing diagram of the operation of the apparatus shown in FIG. 12, 13...DC transformer, 14...detector,
15...Timer, 16...Sample/hold circuit, 20...Comparison circuit, 22, 23...Transmission device, 24...Coincidence detection circuit. In addition, in the figures, the same reference numerals indicate the same parts.

Claims (1)

[Scope of Claims] 1. A detector that outputs a detection signal when the DC voltage at one end of the DC transmission line drops by a predetermined value or more, and a current value of the DC transmission line that is sampled by the detection signal of this detector. A storage circuit for storing, a comparison circuit for comparing a preset reference value with the current value data stored in the storage circuit, and a transmission device for transmitting the comparison result of the comparison circuit to the other end of the DC power transmission line. is provided at each end of the power transmission line, and when the comparison result of the comparison circuit at one end and the comparison result of the comparison circuit at the other end received via the transmission device are opposite to each other, the power transmission line is A protective relay device equipped with a judgment circuit that generates a signal for protection. 2 The storage circuit is composed of a sample-and-hold circuit that responds to the detection signal of the detector and sequentially samples and stores the current value of the DC transmission line multiple times at predetermined time intervals, and the comparison circuit stores the above-mentioned storage at both ends. The judgment circuit is configured to compare multiple pieces of current value data supplied from the circuit with a reference value, and the judgment circuit protects the DC transmission line when the corresponding comparison results of the comparison circuits at both ends are opposite to each other. 2. The protective relay device according to claim 1, wherein the protective relay device is configured to generate a signal. 3. The protective relay device according to claim 1, wherein the detector is configured to output a detection signal when the level of the DC voltage of the DC transmission line falls below a predetermined value. 4. The protective relay according to claim 1, wherein the detector is configured to output a detection signal when the DC voltage of the DC transmission line shows a drop of more than a predetermined value per unit time. Electrical equipment.