JPH06296321A - Protector for direct-current transmission line - Google Patents

Abstract

PURPOSE:To provide a protector which can detect a disconnection accident which brings the grounding of both ends by combining a part of condition for operation at the time of the disconnection accident with the condition for operation at the time of the grounding.short-circuiting accident. CONSTITUTION:Digital signal transmission devices 34, 35 transmit a digital amount of signal corresponding to signals e17, e20, e24 to a counterpart in the case where an overcurrent relay 17 and current differential relays 20, 24 are operated. An operating signal e19 and the signal e17 of a shortage voltage relay 19 are inputted into an OR circuit 26 on a terminal A side, and when one of the signals exists, a signal e26 is outputted and supplied to an AND circuit 28 at a succeeding stage. Also, when the conditions of the operating signal e20 and the unoperating signal e24 at the counterpart end are satisfied, an AND circuit 27 outputs the signal e27 to supply it to the AND circuit 28, and when the input conditions of the operating signal e26 and the operating signal e27 are satisfied, a disconnection accident which brings the grounding of both ends is decided to output a protective operating signal e28 to a controller 32. Similarly on the terminal B side. As a result, the appropriate operation of protecting disconnection can be perform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC transmission line protection device for protecting a DC transmission line from a disconnection accident accompanied by a ground fault.

[0002]

2. Description of the Related Art FIG. 2 shows an example of the configuration of an AC / DC conversion system which interconnects two AC systems. In FIG. 2, when power is transmitted from the AC system 1 to another AC system 11, the AC power is sent to the AC / DC converter 5 via the AC bus 2 and the conversion transformer 3. The AC / DC converter 5 functions as a forward converter (REC) and converts AC power into DC power. This DC power is sent to the AC / DC converter 8 acting as an inverse converter (INV) via the smoothing reactors 4 and 7 and the DC power transmission line 6 (overhead line: 6A, 6B, cable: 6C). The direct-current power is converted back into the alternating-current power by the AC / DC converter 8 and is sent to the AC system 11 via the converting transformer 9 and the AC bus 10.

The DC line 6 is a current differential system in which the current charged and discharged from the cable 6C due to voltage fluctuations at the time of an accident is compensated, that is, the currents at the A terminal and the B terminal are detected by CT13 and CT14, respectively, and mutually detected. Transmitted via transmitter, CT13 and CT14
The current obtained by compensating the charging / discharging current from the cable 6C is compared in the current differential relays 20 and 24 in synchronization. And if the difference is more than a certain value, an internal accident,
If it is less than a certain value, it will be protected by the method of judging as an external accident. This internal / external judgment function is provided in both the current differential relays 20 and 24 installed at each end, and their operations are independent of each other. This current differential relay 20,
24 and CT13, CT14 secondary current input undercurrent relay 21,25, PT12, PT12 secondary voltage input overvoltage relay 18,22, undervoltage relay 19,23, and CT16 flowing to the ground. DC overcurrent relay for inputting secondary current
17 are combined to protect against ground faults, short circuits, and disconnections (including ground faults at only one end) of DC lines. However, it was not possible to detect and protect a wire disconnection accident involving ground faults at both ends as a wire disconnection accident by distinguishing it from a ground fault / short circuit accident.

[0004]

[Problems to be Solved by the Invention] There are ground faults / short circuits and disconnection accidents in DC transmission line accidents. In the case of ground faults / short circuit accidents, do not apply DC current until the arc at the accident point is extinguished. Control the AC / DC converter and restart it, but
In case of a wire breakage accident, the immediate conversion system must be stopped. In other words, the protection operation is different between the ground fault / short circuit accident and the wire disconnection accident, so it is necessary to clearly distinguish and detect and protect.

However, in the case of an accident in which both ends of the wire are connected to the ground fault, the above-mentioned insufficient current relay for detecting the disconnection accident does not operate, but instead the current differential relay for detecting the ground fault / short circuit operates only at one corner. Also, the overcurrent relay at the ground point and the undervoltage relay at both ends operate, and so-called ground fault protection is applied.

That is, at the time of a wire disconnection accident accompanied by ground faults at both ends, this cannot be distinguished from a ground fault / short circuit accident, and detection / protection cannot be applied as the wire disconnection protection. Therefore, an object of the present invention is to obtain a protection device for a DC transmission line that detects a disconnection accident by catching a phenomenon of a disconnection accident accompanied by ground faults at both ends of the DC transmission line.

[0007]

In order to achieve the above object, in the present invention, the internal / external fault judgment of the current differential relays installed at both ends of the DC line protection section does not match at both ends of the protection section. In addition to the above condition, a disconnection detection unit is provided that outputs a control command to the converter by combining at least one of the undervoltage relay and the condition that the overcurrent relay at the ground point is desired to operate to determine a disconnection accident.

[0008]

[Function] By combining a part of the conditions that operate at the time of a wire break accident and the conditions that operate at the time of a ground fault / short circuit accident, a wire break accident with a ground fault at both ends is detected, and a control command is issued to the converter as a wire break protection.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block diagram of a protective device for a disconnection of a DC power transmission line which is accompanied by a ground fault at both ends. In FIG. 1, 34 and 35 are digital signal transmission devices,
When the overcurrent relay 17 at the grounding point and the current differential relays 20 and 24 on the DC transmission line operate, digital signals corresponding to the signals e17, e20, and e24 are transmitted to the other end.

First, on the A terminal side, 26 is an OR circuit, which receives the operation signal e19 of the undervoltage relay 19 and the signal e17, and outputs the signal e26 when at least one of these two signals is present. And supplies it to the AND circuit 28 in the subsequent stage. Reference numeral 27 denotes an AND circuit, which is conditioned on the operation signal e20 of the current differential relay 20 and the non-operation signal e24 of the current differential relay at the other end, and outputs the signal e27 to the AND circuit 28 when this is established. . Further, the operation signal e26 and the operation signal e27 are used as input conditions, and when these are satisfied, it is determined that a disconnection accident involving grounding at both ends is output, and a protection operation signal e28 is output to the control device 32.

Similarly, on the B terminal side, if at least one of the undervoltage relay 23 and the two signals e14 transmitted from the A terminal side exists for the 29 OR circuit,
The signal e29 is supplied to the AND circuit 31 in the subsequent stage. 30 is also an AND circuit, which is conditioned on the operation signal of the current differential relay 24 and the non-operation signal e20 of the current differential relay at the other end, and outputs the signal e30 to the AND circuit 31 when this is established. Further, the operation signal e29 and the operation signal e30 are used as input conditions, and when these are satisfied, it is determined that a disconnection accident accompanied by grounding at both ends,
The protection operation signal e31 is output to the control device 33. As a result, the AC / DC conversion system is stopped in the event of a wire breakage accident.

With such a structure, it is possible to detect a disconnection accident accompanied by a ground fault at both ends of the DC transmission line, and to take an appropriate disconnection protection operation. Note that FIG. 3 simply shows a system configuration diagram of a DC transmission line, and shows cases of disconnection accidents (a) to (d) with ground faults at both ends. The response of the relay to each case is shown in Fig. 4.

In case (a), the REC (forward converter) side is grounded, and at the REC side 6A of the DC main line, there is a disconnection accident that shifts to a ground fault at both ends. In case (b), the REC (forward converter) side is grounded. Then, a disconnection accident that shifts to both ends ground fault on the INV side 6B of the DC main line, in case (c), the INV (inverter) side is grounded, and a disconnection shifts to both ends ground fault on the REC side 6A of the DC main line. The accident, case (d), shows the case where the INV (inverse converter) side is grounded and a disconnection accident occurs in which the INV side 6B of the direct current main line shifts to a ground fault at both ends.

[0014]

As described above, according to the present invention, there is provided a DC transmission line protection device capable of surely detecting a disconnection accident involving ground faults at both ends and performing an appropriate disconnection protection operation in a DC transmission line. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of a DC transmission line protection device according to an embodiment of the present invention.

FIG. 2 is a system configuration diagram of an AC / DC conversion system that connects two AC systems and a DC transmission line.

[Fig. 3] System configuration diagram of a DC transmission line for explaining a case of a disconnection accident

FIG. 4 is a diagram showing the response of each relay to a case of a disconnection accident.

[Explanation of symbols]

1, 11 ... AC system, 2, 10 ... AC busbar, 3, 9 ... Conversion transformer, 4, 7 ... Smoothing reactor, 5, 8 ... AC / DC converter, 6 ... DC transmission line (6A, 6B ... Overhead line) , 6C ... Cable), 12,15 ... DC transformer (DCPT), 13,14,16
… Direct current transformer (DCCT), 17… Direct current overcurrent relay, 1
8,22 ... Overvoltage relay, 19,23 ... Undervoltage relay, 20,2
4… Current differential relay, 21, 25… Under current relay, 26,29
... OR (or) circuit, 27, 28, 30, 31 ... AND (AND) circuit, 32, 33 ... Control device, 34, 35 ... Digital signal transmission device.

Claims (1)

[Claims] 1. A current differential relay for making an internal / external determination of an accident by using a difference between currents detected at both ends of a DC transmission line transmitting an output converted by an AC-DC converter, and a voltage of the DC transmission line. An undervoltage relay that detects a drop, an overcurrent relay that detects an overcurrent that flows to the ground point of the AC-DC converter on the ground side, and operation signals of the current differential relays provided at both ends do not match and Of the direct current transmission line characterized by including a disconnection detection unit that determines a disconnection accident when at least one of the undervoltage relay and the overcurrent relay is operating, and outputs a control command to the AC / DC converter. Protective device.