JPS5947916A - Neutral 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 The present invention relates to a protection device for a neutral line provided between bipolar DC transmission lines.・Diagram $1 shows a bipolar DC transmission system with a neutral line. In the figure (1),
(2) is an AC system, (a), (4), (5)
(6) is a converter transformer, (7) and (9) are Cyrisk, and are configured as a three-phase bridge forward converter (hereinafter referred to as RE).
(abbreviated as C) (8), σ0 is RE C(7), (
9) Inverse converter (hereinafter abbreviated as INV) configured similarly to
, αυ, (2), a, Q4) is a DC reactor,
ση is a high-voltage DC transmission line, 00 is a neutral line, and (g) is a surge capacitor.

Konoyouna lineage Teti normal RE C (7) and I N V
(8), RE C (9) and INVQO are -
They are operated as a pair, and the current command values for both are the same.

That is, the current value i+ of the DC system composed of RE C (7) and I N V (8), and the current value i + of the DC system consisting of RE C (9) and I N V
(The current value is of the DC system with the 10f configuration is equal to the current value is. Therefore, the current value 11 and i cancel each other out in the neutral line a, so no current flows at all times, and therefore the potential difference between both ends remains almost unchanged. Current flows through the neutral line α when unipolar DC transmission is performed for some reason.For this reason, even if a ground fault or disconnection occurs on the neutral line aQ, bipolar DC transmission will not occur. It is not possible to detect an accident on the neutral line α because it has no effect. However, if the neutral line α is left as it is, it will have the following negative effects. First, the neutral line Ql19 will be disconnected. Considering the case of an accident, the converter station on the non-grounded side (REC side) of the neutral line αQ is designed on the assumption that it is completely grounded, so if it becomes floating due to a disconnection, the high voltage DC transmission line (to) ,
Insulation is threatened by surges and the like that enter from Qη. Further, even if an abnormality is detected in one of the converters and an attempt is made to perform unipolar operation, it is impossible because a closed loop cannot be formed in the neutral line αQ and there is no path for direct current. Next, looking at the ground fault accident on the neutral line Qf5, in normal bipolar operation, the neutral line Q
There is no particular problem as there is no current flowing through the l, but when switching to unipolar operation as mentioned above, a ground fault current equivalent to a ground fault on the high-voltage DC transmission line flows through the ground, causing electrical corrosion and harmonics. This may cause noise, etc.

Conventional bipolar DC transmission systems are configured to have a neutral line, so it is effective to constantly monitor the neutral line 0Q, but there is always a current/voltage difference in the neutral line θQ. Since there is almost no detection, it is almost impossible to detect using differential methods such as those used to protect high-voltage DC transmission lines.

This invention was made with the aim of eliminating the drawbacks of the conventional ones as described above, and provides a neutral line protection device that can detect an abnormality by forcing a current to flow through the neutral line. It is.

An embodiment of the present invention will be described below with reference to FIG.

In the same figure, 4 is a coupling capacitor, ? ) is the neutral wire @QQ
and the ground through a coupling capacitor 00, Qη is a DC transformer installed at the non-grounded end of the neutral line αQ, and N) is a DC transformer also installed at the non-grounded end.
■ is a simulating circuit of the neutral line Q8 connected to the secondary output side of the DC current transformer ■υ, which has a filter and outputs a voltage according to the AC frequency component of the current value detected by the DC current transformer Qυ. do. (C) is an input circuit connected to the secondary output side of the DC transformer (E), which has a filter and outputs a voltage according to the AC frequency component of the voltage value detected by the DC transformer (F). (C) is a differential relay that will be used previously if there is a difference between the output voltages of the simulated circuit (C) and the input circuit (product).

During bipolar DC power transmission In this configuration, the current value flowing when the neutral line Qf9 is normal is the voltage value Vs of the AC power supply (E).
The equivalent value of this Zl, which is found from the line impedance Zl of the neutral line α, is set as the impedance of the neutral line Qt9), and the current flowing through the neutral line Qf9 during normal operation is introduced, and the input circuit ■ If you adjust the output voltage of the simulated circuit @ so that the voltage difference with the output voltage is zero,
When a fault occurs on the neutral line αQ, the DC current transformer e
The detected current increases and the output voltage from the simulating circuit (c) rises, creating a voltage difference between the output voltage of the input circuit (c) and the differential relay (c) operating to detect a failure. In addition, if the neutral line a is disconnected, the detected current becomes zero, so the output voltage from the simulated circuit () becomes zero, creating a voltage difference between the output voltage of the input circuit (c) and the differential relay (). operates and detects failures.

Here, even if unipolar DC power transmission is performed and DC current flows through the neutral line QQ, the DC component is cut by the filters in the simulation circuit (E) and input circuit (C), so the differential relay )
does not malfunction.

As described above, according to this embodiment, it is possible to detect an abnormality in the neutral line a, the influence of the neutral line abnormality on the system can be removed, and a highly accurate bipolar DC power transmission system can be obtained.

In addition, in the above example, the DC current transformer Qp1)
are installed at the non-grounded end (power supply end), but the protection zone is from these current/voltage detectors to the grounded end.

As described above, according to the present invention, since the configuration is such that a current is forced to flow through the neutral line and the current and voltage of the neutral line are compared, abnormalities in the neutral line can be easily detected. This has the effect of providing a sexual track protection device.

[Brief explanation of the drawing]

Figure 1 is a diagram of a conventional bipolar DC power transmission system with a neutral line.
FIG. 2 is a diagram of a bipolar DC power transmission system equipped with an embodiment of the neutral line protection device according to the present invention. In the figure, (7) and (9) are forward converters, (g),
(10 is the inverter αυ, @, (to), αXu is the DC reactor, (to), Q71 is the high-voltage DC transmission line, α is the neutral line, αe is the coupling capacitor, the wire is the AC power supply, eA
) is a DC current transformer, (A) is a DC transformer, (2) is a simulated circuit, (2) is an input circuit, and (C) is a differential relay. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Shin Kuzuno −

Claims (1)

[Claims] A series circuit formed by inserting a power source between one end of a neutral line of a bipolar DC transmission system and the ground, and grounding the other end of the neutral line to the ground, a voltage based on the current of the series circuit, and a voltage of the series circuit. and means for detecting the difference between the neutral line protection device and the neutral line protection device.