JPH0121683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protective relay device for DC power transmission lines.

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 conversion 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. A large current that could cause collapse of other systems will not flow. 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) 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) has the disadvantage of malfunctioning when the DC current oscillates or increases 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 2, 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 14 of the detector 14 is
A is supplied to a timer 15 whose time limit is a time T set corresponding to the point in time when the current change point increases when the power transmission line 5 has a ground fault. Timer 15 signal 1
5a is supplied to the sample and hold circuit 16,
It is used to sample and hold the output of the DC current transformer 10. The hold signal 16a of the sample-and-hold circuit 16 is transmitted to the other end via the transmission device 17, detected in the same way at the other end, and input to the differential circuit 19 together with the hold signal received via the transmission device 18. Ru. Differential circuit 19
protects the power transmission line by supplying a signal 19a indicating a ground fault in the power transmission line 5 to a protection interlocking circuit (not shown) and stopping the AC/DC converters 3 and 7 when the difference between the two inputs is greater than a predetermined value. .

The operation will be explained with reference to FIG. When the power transmission line 5 is healthy, the detector 14 does not output the signal 14a, and the differential circuit 19 also does not output the signal 19a.

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 time T, which causes the sample-and-hold circuit 16 to output the output of the DC current transformer 10 (FIG. 4c).
and hold e). DC current of power transmission line 5
Idr shows a value increased from the reference value Iref due to the ground fault at one end (Fig. 4b), and conversely shows a value decreased from the reference value Iref at the other end (Fig. 4d). The hold signal 16a is sent to the transmission devices 17 and 18.
The signals are mutually transmitted to the differential circuit 19 at the opposite end.
Since the difference between the two inputs in the differential circuit 19 exceeds the reference value K as shown in FIG. 4f, the differential circuit 19 outputs a signal 19a. Since the voltage drop in the power transmission line 5 due to the occurrence of a ground fault occurs almost simultaneously at both ends thereof, both differential circuits 19 output the signal 19a substantially synchronously.

FIG. 3 is a block diagram of a protective relay device according to another embodiment of the invention. The difference from the device shown in FIG. 2 is that the timer 20 responds to the signal 14a of the detector 14 and generates a pulse signal 20 at time intervals To starting after time T as shown in FIG. 5c.
The sample/hold circuit 21 stores the output of the DC current transformer 10 using the signals 20a, 20b, respectively, and outputs the hold signals 21a, 21b. The hold signals 21a and 21b are transmitted by the transmission device 2.
2 and 23, the signals are transmitted to the differential circuits 24 at the respective opposite ends. The differential circuit 24 has its own end and the transmission device 22
or hold signal 21a at the other end via 23,
21b is input, the corresponding signals are compared, and when a difference greater than a predetermined value is detected, a signal 24a representing a ground fault in the power transmission line is supplied to a protection interlocking circuit (not shown).

FIG. 5 is a timing diagram showing the operation of the device shown in FIG. 3. In the figure, a shows a state in which a ground fault occurs in the power transmission line 5 at time tf and the DC voltage Vd drops to zero volts, b shows the DC current Id at the own end increasing from time tf, and c shows the situation where the DC voltage Vd drops to zero volts. Hold signal 21 of the sample and hold circuit 21 sampled and held by the signals 20a and 20b of the timer 20 at its own end
a and 21b, d indicates the DC current Id at the opposite end, e indicates the hold signal of the sample-and-hold circuit 21 at the opposite end, and f indicates the comparison result in the comparison circuit 24 at the own end and the opposite end.

In the above embodiment, the number of sample and hold times is up to two, but this may be two or more times, and the intervals may or may not be constant. If 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, after an accident occurs,
Since the DC current flowing through the DC transmission line is sampled at the point when the current difference between both ends of the DC transmission line becomes large, and an accident is determined, the transmission capacity of the transmission equipment can be reduced, and the reliability of the determination can be improved. can also be increased.

[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 showing the operation of the apparatus shown in FIG. 2, and FIG. 5 is a timing diagram showing the operation of the apparatus shown in FIG. 3. 12, 13...DC transformer, 14...detector,
15, 20...Timer, 16, 21...Sample/hold circuit, 17, 18, 22, 23...
Transmission device, 19, 24...differential circuit. Note that in the figures, the same reference numerals indicate the same parts.

Claims (1)

[Claims] 1. A detector that outputs a detection signal when the DC voltage or voltage change rate of the DC transmission line exceeds a predetermined value, and a detector that is activated in response to the detection signal of the detector and detects the current change in the case of a ground fault in the DC transmission line. A timer that outputs a signal after a set time corresponding to the time when the point becomes large, and a memory circuit that samples and stores the current value of the DC power transmission line based on the output signal of the timer are provided at each end of the DC power transmission line. a transmission device that transmits the current value data stored in the storage circuit at each end of the DC transmission line to the other end of the DC transmission line, and the storage at the other end that receives the current value data via the transmission device; A protection joint comprising a differential circuit that generates a signal for protecting the DC power transmission line when a difference between current value data of the device and current value data of the storage device at its own end exceeds a predetermined value. Electrical equipment.