JPS6361852B2 - - Google Patents

Description

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

Conventionally, transmission line protection methods for DC power transmission include methods that constantly monitor the DC voltage of the power line and determine an accident if it drops below a set value, or a method that transmits the power line currents at both ends and takes the differential. A method has been widely used in which an accident is determined when the output exceeds a set value.

However, with DC undervoltage relays, in the case of a slight ground fault involving resistance, the voltage does not drop much, making it difficult to detect.Furthermore, with both DC undervoltage relays and current differential relays, it is difficult to determine the distance to the fault point. That is impossible.

The present invention has been made in view of this point, and it is an object of the present invention to provide a device that is capable of not only detecting an accident but also determining the distance to the accident point using voltage and current values at both ends.

An embodiment of the present invention will be described below with reference to the drawings. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. In Figure 1, 1 is a thyristor valve, 2 is a DC reactor, and 3 is a DC voltage transformer.
DCPT, 4 is a DC current transformer DCCT, 5 is a transmission line resistance simulation circuit, 6 and 7 are adders, 8 is a transmission device,
9 is a comparator, and 10 is a power transmission line resistance calibration device.
In Figure 2, Vs is the voltage at the sending end, Is is the current at the sending end, Vr is the voltage at the receiving end, Ir is the current at the receiving end, Vx is the fault point voltage, R is the resistance value of the transmission line between the two converter stations,
I is the DC current before the accident.

First, to explain with reference to FIG. 2, when a ground fault accompanied by resistance occurs, the voltage Vx at the fault point becomes somewhat lower than in a normal state. As a result, the sending end current Is increases a little, and the receiving end current Ir decreases a little. When calculating the estimated voltage at the receiving end from the sending end |Vs-Is・R|, since Is=I in a healthy state, |Vs-Is・R|=|
Vr | However, in the event of an accident, I < Is, so |
Vs−Is・R|<|Vr|. The reason why the absolute value is taken here is to take into consideration the case where the polarity of the voltage is reversed due to power flow reversal control. Therefore,
Always compare |Vs−Is・R| and |Vr|, |Vs−
When Is・R｜<｜Vr｜, it is sufficient to judge it as an accident.

A specific example of a protective relay device based on this principle is shown in FIG. R is obtained and added to adder 6.
By adding the output of DCPT3 with opposite polarity,
Obtain Vs−Is・R. On the other hand, the receiving end voltage is transmitted from the other end by the transmission device 8, and by the comparator 9 |
Accidents are detected by comparing the magnitudes of Vs−Is·R| and |Vr|. In addition, since the transmission line resistance value R changes depending on the season, temperature difference between day and night, and load current value, it can be made even higher by periodically calculating R = (Vs - Vr) / 1 and correcting the resistance value in step 5. Sensitivity detection becomes possible.

Similarly, the discriminant for detection at the receiving end is |
Vr+Ir·R|<|Vs|, and a protective relay device based on this principle can be realized with the specific example shown in FIG. 1b.

As described above, transmitting the voltage and current values at both ends has the effect of not only being able to detect a power line fault at both ends, but also being able to determine the distance to the fault point.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an implementation of a protective relay device according to the present invention, and FIG. 2 is an explanatory diagram of an accident detection method. In the figure, 1 is a thyristor valve, 2 is a DC reactor, 3 is a DCPT, 4 is a DCCT, 5 is a transmission line resistance simulation circuit, 6, 7, 10, 11 are adders,
8 is a transmission device, and 9 is a comparator. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a DC transmission line, compare the absolute value of the voltage drop obtained from the product of the DC current at the own end and the resistance value of the transmission line by adding or subtracting it from the DC voltage at the other end, and the absolute value of the DC voltage at the other end, A protective relay device for a DC power transmission line, characterized in that when the absolute value of the DC voltage at the other end is larger, it is determined that an accident has occurred in the DC power transmission line.