JPS6028716A - Dc line protecting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] This invention provides a protection device (1) for protecting a DC power transmission line.
.

Regarding.

Conventional protection devices include (a device that performs a protective operation when it detects a voltage change v 1T in an AL DC transmission line; (b)
There were some that carried out protective operations when an undervoltage relay detected a voltage drop on a DC transmission line.

However, such devices have a high possibility of malfunction, as voltage changes dt or voltage drops in DC transmission lines can occur due to failures other than DC transmission line failures, and this malfunction can reduce the availability of the DC transmission system. This causes a decrease in

Therefore, in recent years, current differential type devices have been used that detect faults by utilizing the difference between the current on the converter side and the current on the inverter side when a DC transmission line fault occurs. FIG. 1 shows a conventional current differential protection device.

In the figure, 1 is a forward converter (hereinafter referred to as converter)
, 2 is an inverse converter (hereinafter referred to as an inverter), 11.2
1 is a DC reactor provided for smoothing the DC current flowing through the power transmission line 100 and suppressing a sudden increase in fault current; 12
．． 22 is a DC current transformer CT that converts the electric current flowing through the power transmission line 100 (2) into a minute amount of electricity proportional to the current value, and 101.202 is CT12.

22 is a transmitting device, 201.102 is a receiving device having a function of receiving the signal of the transmitting device 101.202 and converting it into the original waveform signal, 103°203 is a receiving device 102, 201.203. and a differential relay that inputs the current signal from CT12゜22 and generates a failure detection signal F if the deviation of the current value is greater than or equal to a predetermined value; 105.205 is an adder;
Reference numeral 104.204 indicates a constant current control device that controls the direct current flowing through the power transmission line 100 to a constant value.

Next, the operation will be explained. When the inverter 2 is in good condition, the current IINV on the inverter 2 side is controlled so that the DC voltage is constant by a constant voltage control device (not shown), so the constant current control on the inverter 2 side does not function at all. Therefore, when the power transmission line 100 is healthy, the current value flowing through the power transmission line 100 is controlled to a predetermined value by the constant current control device 104 on the converter 1 side, so that the current value is the same on both the converter 1 side and the inverter 2 side. If a ground fault F occurs at time tf, the DC voltage of the power transmission line 100 will drop significantly, so the inverter 2
The constant voltage control device (not shown) on the side stops functioning, and the constant current control device 204 starts functioning. During this time, the polarity of the DC voltage on the inverter 2 side is reversed. Also, inverter 2
The current IINV on the side decreases, and one time later, at time tr, the current value becomes 'ref'd due to the direct current control of the constant current control device 204. Transmitting devices 101, 202. The receiving devices 201 and 102 transmit the detected currents at both ends to each other, and the difference between the detected current at the own end and the detected current at the opposite end is determined by the differential relay 103, 203, and the difference is greater than a predetermined value. Therefore, the output F is output and DC transmission line accident F
The protection operation corresponding to 1 is executed.

Normally, Δ is called current margin and is 10% of rated DC current.
The differential relays 103, 202 and 202 are set to about
203 is set to output the differential output F under the condition that IREC"INV is 5 or more.

(3) Since the conventional protection device is configured as described above,
The drawback was that the equipment was expensive because high precision was required for differential relays, transmitting/receiving equipment, etc.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and reduces the current command value on the inverter side in response to a current change of more than a predetermined value corresponding to an accident. The object of the present invention is to provide a protection device that can accurately detect accidents by increasing the difference between the DC currents on the sides.

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure, the same reference numerals as in FIG.
A signal that corrects the DC current when it drops below I/
, 1/, current command value circuit, 107.207
is an adder.

Next, the operation when the ground fault F1 occurs will be explained. -Mih (4) The DC voltage value signal of the DC transformer 23 is sent to the current command value circuit 20.
6 is input. The current command value circuit 206 indicates that the DC voltage has decreased to v5 by setting the setting value Vref of the setting device 2061.
A correction signal I'i is output. FIG. 4 shows a voltage/current characteristic diagram of the DC power transmission line 100. As shown in Fig. 4, if the DC voltage V(1 drops to v'd), the correction signal will be output. Therefore, if the DC voltage V(1 drops due to an accident), the correction signal will be 207, and the output of the adder 207 is Iref-
The current on the inverter 2 side becomes Iref-ΔI - I'i due to the action of the constant current control device 204.

Furthermore, the current on the converter 1 side is inputted to the differential relay 203 by the transmitting device 101 and the receiving device 201, and the difference with the current Iref-ΔI −I'i on the inverter 2 side is taken. Here, I/ can take any value depending on the settings, and a differential amount greater than the current margin ΔΔ can be obtained, so that the transmitting device 101. Since it is set according to the accuracy of the receiving device 201゜differential relay 203, etc., the differential relay 20
3 easily detects a fault in the DC line 100 and outputs the differential output F.
Output.

As described above, according to the present invention, the current command value on the inverter side is made smaller in accordance with the drop needle of the DC voltage, which eliminates the need for high-precision equipment and has the effect of reducing the cost of the equipment. .

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional DC transmission line protection device.
Fig. 2 is a diagram showing a DC current waveform at the time of an accident, Fig. 3 is a block diagram of a DC transmission line protection device explaining an embodiment of the present invention, and Fig. 4 is a diagram explaining an embodiment of the present invention. It is a characteristic diagram. 1... Forward converter, 2... Inverse converter, 11.21...
・DC reactor, 12.22...DC current transformer, 10
1゜202... Transmitting device, 201.102... Receiving device, 103.203... Differential relay, 105.20
5...Adder, 107.207...Adder, 104
．． 204... Constant current control device, 100... DC power transmission line, 13°23... DC transformer, 106.206.
...Current command value circuit, 1061.2061...DC voltage setting device. Note that the same reference numerals in the figures indicate the same parts. Agent Masuo Oiwa (7) Figure 1, Figure 3, Figure 4, d a Procedural amendment (spontaneous) Commissioner of the Japan Patent Office 1, Case description 'Vf Application No. 58-187162 2,
Name of the invention: DC line protection device 3, Person making the amendment Representative: Hitoshi Katayama Department 5, Drawing subject to the amendment 6, Details of the amendment Figure 8 of the drawing is corrected as shown in the attached sheet (numbers 1061 and 2061 are added). 7. At least one catalog drawing of attached documents (Figure 8)

Claims (1)

[Claims] A forward converter that converts alternating current to direct current, an inverse converter that is connected to this forward converter via a direct current line and converts direct current to alternating current, and control so that the direct current at each end of the direct current line becomes a reference current value. A DC line protection device that compares each DC current value detected from both ends of a DC transmission system, and performs a protection operation for the DC line when the comparison result exceeds a predetermined value. In the apparatus, a comparison circuit that generates a correction amount signal when it is detected that the DC voltage detected from one end of the DC line is lower than a reference voltage;
A DC line protection device comprising: an adder that corrects a reference current signal of the constant current control device so that the comparison result is increased by the correction amount signal of the comparison circuit.