JPS5821497B2 - Denryokukeito no Seigiyohouhou Oyobi Souchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a control method and apparatus for a power system in which converters for converting or inverting AC power into DC power are provided at both ends, and the converters are connected through a DC power line for bipolar operation. It is related to.

Looking at a DC transmission system as an example of a DC power system capable of bipolar operation, the configuration of the transmission line is a return-to-ground system in which each converter station at both ends of the transmission line is grounded and the neutral wire is omitted, and the other is a ground return system in which the neutral wire is omitted. ] There is a neutral line return method in which the wire is grounded.

Here, if a direct current is passed to the ground, problems such as induction disturbance and electrolytic corrosion occur, so a single point grounding of the neutral wire is used.

An example of this neutral line single point liquid field system will be explained with reference to FIG.

In the figure, there is a conversion circuit group G1 consisting of a converter transformer T1, a converter B1, and a DC reactor DCL1, and three other similarly configured conversion circuit groups G2. G3. G4 is installed at both ends of the power transmission system, and a DC power transmission line L is connected between these anodes and cathodes.
1. Connect at L2° and L3 to enable bipolar operation.

One end of the neutral line L2 of the DC transmission line is grounded to form a DC transmission system.

If an accident occurs in the converter circuit group G1 while the DC power transmission system is in bipolar operation, the converter B1 is gate-blocked and then the AC side breaker (not shown) is shut off to protect the system.

In coordination with this, the operation of the conversion circuit group G2 is also stopped, and unipolar operation (monopolar) is continued with the conversion circuit group 03 G4 having a healthy pole.

However, if a ground fault occurs at the fault point ■ shown in Figure 1, even if the converter circuit group Gl and G2 of the fault pole is stopped, the healthy pole continues to operate, so that the non-ground end of the neutral wire L2 generates a potential corresponding to the voltage drop of the neutral wire L2,
DC current continues to be shunted to the fault point (■) through converter B1.

In order to stop this branched flow, the healthy pole must also be stopped.

As described above, it is extremely inconvenient to shut down the entire DC power transmission system despite the fault in the converter circuit group G1, since the power transmission capacity will be greatly reduced.

The cause of the above-mentioned inconvenience is that a potential corresponding to the voltage drop of the neutral wire L2 exists at the non-grounded end of the neutral wire L2 during unipolar operation with only a healthy pole, so this potential can be removed.

An object of the present invention is to provide a converter for converting alternating current to direct current or inversely converting it to direct current, and to connect the converters with a direct current line so that bipolar operation can be performed between the converters, and one end of the neutral line of the said direct current line is grounded. In the system, a forced grounding switch is provided at the non-grounded end of the neutral line, and when a ground fault occurs in one pole of the power system and the operation is stopped, this forced grounding switch is installed at the non-grounded end of the neutral line. To provide a control method and device for a power system including a DC line, which removes the potential generated at the non-grounded end of a neutral line by temporarily turning on a power line, and allows continued operation on the healthy pole side. There is a particular thing.

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

In the DC power transmission system shown in FIG. 1, a forced grounding switch, such as a breaker CB, is provided at the non-grounded end of the neutral line L2, that is, at the left end in the figure, between it and the ground.

FIG. 2 shows an enlarged view of the conversion circuit group G1 shown in FIG. 1 and the accident detection device provided therein, and the details thereof will be explained below.

Note that the same parts as in FIG. 1 are denoted by the same reference numerals, and explanations thereof will be omitted.

Current transformers CT1 to C are installed for each phase in the AC side circuit of converter B1.
T3 is provided, and direct current transformers DC-CT, DC-CT2 are also provided in the anode and cathode side electric circuits on the direct current side, respectively.

Both RFi%RF3 are rectifier circuits, and transformers CT11 to C
via T15 the corresponding current transformers CT1-CT2 or direct current transformer DC-.

CT1. Connect to the secondary circuit of DC-CT2 and connect these two
Next, convert the current into a DC amount, 1111, maX (K・1Ial,
K1Ib1. KIIcl), convert to K-1■41.

Here, K is a constant, max(K・IIal, KIIbl,
K1Ic1) is in parentheses.

represents the maximum value of the variable.

DIFl is the current 11 flowing between the anode side and the negative side of the DC circuit.
．． A differential circuit that detects the difference between I4 and the rectifier circuit RF.
i, 1111. to the output of RF3. It inputs K·lI41 and outputs the difference between them.

This output is rectified by the rectifier circuit RF4 and the absolute value I
After becoming K.l 111-K.1I411, it is added to the level detection circuit LDi.

The level detection circuit LDl has its input, that is, the current 11. of the DC circuit. When the difference in I4 exceeds a predetermined value, the DC current transformer DC
It is determined that a ground fault has occurred in the protected area surrounded by -CTi and DC-CT2, and the output 87DG is set to 11. / Make it /.

Also, DIF2 is the AC side current Ia, Ib, I of converter B1.
c and DC side current■.

- A differential circuit that detects the difference between the rectifier circuit RFl
.

RF2 output K −l 111 , max(K ・l
Ia I.

K−I Ib l , -l Ic l) are input, and the difference max(K −l Ial , K・lIb1
, -Icl)-K.■, is output and added to the level detection circuit LD2.

When this input, that is, the current difference between the AC side and the DC side becomes equal to or greater than a predetermined value, the level detection circuit LD2 determines that an arm short circuit has occurred in the converter B1, and sets the output 51DA to 11/l.

Incidentally, the level detection circuit LD2 outputs the output 51DA as XX1. / Make it /.

Figure 3 shows a control circuit that performs various protective operations in response to the accident detection outputs 87DG and 51DA. , its output is used as a gate block command for converter B1 and a cutoff command for an AC side breaker (not shown).

ANDi is an AND gate whose input conditions are the ground fault detection output 87DG and a condition signal when the healthy pole is in operation, and its output is used as a closing command for the forced earthing circuit breaker CB.

AND2 is an AND gate whose input conditions are the ground fault detection output 87DG applied via the inverting circuit NOT and the operation delay circuit TDE, and the normally open auxiliary contact CB-a (closed when CB is turned on) of the forced grounding breaker. The output is used as a forced earthing breaker CB's breaker, that is, a forced earthing release command.

Next, the action will be explained.

In Figure 1, when the converter circuit G1 is operating as a converter, if a ground fault occurs at point 0, the fault point will be connected to the grounding point DC transmission line L2 (neutral line), converter transformer TI A fault current flows between the alternating current Ia shown in Figure 2.
, Ib, Ic and the DC current I4 include the fault current.

However, since the fault current is not included in the DC current 11, the difference detected by the differential circuit DIFi is IK・l 1
11''-11411>0, resulting in imbalance, and the output 87DG becomes the operation ゃ1〃.

Similarly, the difference due to the differential circuit DIF2 is also maX(K・1■a
1. K・1■b1. K・1■c1)−K・I1>0, which causes an unbalance, so that the output 5 i DA also operates as “1”.

When 87DG and 51DA operate, in the control circuit shown in FIG. 3, an OR gate with conditions for 87DG and 51DA operates to operate the gate block of converter B, and is also provided on the primary side of converter transformer T1. An AC breaker (not shown) is tripped to stop the conversion circuit groups G1 and 02, and single-pole operation is performed using only the healthy poles.

At the same time, AND gate AND 1 operates on the condition that 87DG operates and the healthy pole is operating, and the forced grounding breaker CB on the non-grounded side of the neutral wire is turned on, and the non-grounded end ground voltage is also turned on. The shunt to the Tozuku converter B1 is eliminated.

Next, when the ground fault is recovered and g7DG is restored, the delay circuit TDE is activated after a predetermined period of time.

At this time, on the condition that the forced earthing breaker CB has already been turned on, the AND gate AND2 operates to trip the forced earthing breaker DC-CB.

Further, the same operation is performed for a ground fault such as the fault point (2) in FIG.

Next, as shown in FIG.

- When a short circuit [F] occurs, a short circuit current flows on the secondary side of the converter transformer T1 through the converter B1.

Since this short circuit current does not flow to the DC side, the output of the differential circuit DIF2 in FIG. 2 is max(K-lIa I.

Since K·lIb1, 1Icl)Kl■l>0 and unbalance occurs, the output 5lDA becomes inoperable.

On the other hand, since the DC side current is balanced, IK・l 11
1-K·lI411"o, and the output 8γDG is inactive"0. ．． becomes.

Therefore, in the control circuit of FIG. 3, since the output 5 i DA operates, the OR gate is OR.

It operates to operate the gate block of converter B1, and also trips the AC breaker (not shown) on the primary side of converter transformer T1 to stop converter circuit groups G1 and G2, allowing single-pole operation with only healthy poles. Let's do it.

Here, since g7DG is inactive, it is used for forced grounding, and disconnector CB is not turned on.

In this way, the forced earthing breaker D (
, by turning on CB and removing the potential generated at this non-grounded terminal, the follow-on current to the ground fault point is cut off.
It is possible to stop only one pole without stopping both poles and continue operating the healthy pole.

In addition, in the case of an accident such as an arm short circuit that is not a grounding fault even if it is a fault in the conversion circuit, forced grounding is not performed unnecessarily and both ends are not grounded, so damage caused by the flow of earth return current can be minimized.

In addition, the forced grounding circuit breaker CB is turned on to stop the fault pole, but if the shunt current is diverted from the fault pole to DC-CB, the ground can be removed for a short time, so this also suppresses the earth return current to a short time. There is an advantage that it can be done.

In the above embodiment, the forced grounding breaker CB was turned on at the same time as the ground fault occurred, but if the earth return current can be tolerated for a somewhat longer period of time, it is possible to detect the presence of a shunt after the AC breaker is opened. It is also possible to insert a forced grounding circuit breaker CB.

Further, in FIG. 3, it is also possible to add the short circuit fault detection output 51DA as shown by the chain line as the input condition of the ant game-1-ANDl, which is the closing condition for the forced grounding circuit breaker CB.

As described above, according to the present invention, converters for converting alternating current into direct current or inversely converting are provided at both ends, and these are linked by a direct current line so as to be able to perform bipolar operation, and one end of the neutral line of this direct current line In a power system that is grounded, if one pole side is stopped due to an accident, if this is a ground fault, a strong earthing switch installed at the ungrounded end of the neutral line is turned on, and the neutral line is grounded. Since the potential generated at the ungrounded end of the ground line is removed, it is possible to effectively prevent current from being shunted to the ground wire fault point due to this potential. Unipolar operation can be continued.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining a power system control method and apparatus according to the present invention, and FIGS. 2 and 3 are circuit diagrams showing an embodiment of a control section of the present invention. B1 to B4...Converter, Ll, L2. L3...
...DC line, L2...neutral line, CB.
... Forced grounding switch, 87DG... Ground fault detection output, ANDl... AND gate for closing the grounding switch.

Claims (1)

[Scope of Claims] 1. A converter for converting alternating current into direct current or inversely converting it is provided at both ends, and these are connected to each other so that bipolar operation can be performed by a direct current line, and one end of a neutral line of said direct current line is grounded. Control of a power system including a DC line, characterized in that when a ground fault occurs on one pole side of the power system, operation on the fault side is stopped and the ungrounded end of the neutral line is forcibly grounded. Method. 2 A power system that is equipped with a converter that converts alternating current to direct current or inversely converts alternating current to direct current, which is connected to enable bipolar operation by a direct current line, and furthermore, one end of the neutral line of the said direct current line is grounded. a ground fault detection device that compares the anode side current and the cathode side current of the converter and generates an output when the difference exceeds a predetermined value; and a ground fault detection signal from this device and a ground fault detection signal sent to the converter. and an AND gate that operates on the condition that the other pole side of the power system is in operation and gives a closing command to a grounding switch provided at the non-grounded end of the neutral wire. System control device.