JPH0522459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a thyristor type current limiting device connected between the neutral point of a power transmission transformer and earth.

BACKGROUND OF THE INVENTION In general, a current limiting device connected between the neutral point of a transmission transformer and the ground is used to prevent abnormal voltages caused by grounding faults when a fault such as grounding occurs in a power system, and to It detects ground fault fault voltage and current, and automatically selects and disconnects the faulty section using the related protective relay, thereby preventing damage to power equipment and the spread of accidents. As such a neutral point grounding type current limiting device, a high resistance neutral point grounding resistor has conventionally been used.

Such a conventional neutral point grounding type resistor (NGR) requires a large number of resistance grids, that is, grids, to be connected in series or in series and parallel.
In addition, mica washer is used as the grid insulation material.
Mica tube etc. are used. like this
NGR has a low initial cost, but
Over time, as the temperature rises, the material of the grid changes, resistance changes, contact resistance increases, and insulation properties deteriorate. Furthermore, NGR is not used for applications where the speed control characteristics change as the resistance value changes over time, as is the case with speed control resistors. Unless something goes wrong, they are normally used for long periods of time without maintenance or inspection.

On the other hand, in the general use of thyristors in high-voltage circuit specifications, when thyristors are connected in series in multiple stages, for example, when two thyristors are assembled on one installation frame, the thyristors are connected in the opposite polarity direction to the installation frame. It is structurally relatively easy to connect the thyristors in parallel, but to assemble them in series with the same polarity, it is necessary to construct the installation frame as an insulating frame, or to connect the thyristors to each other electrically. It requires some ingenuity. However, when the installation frame is constructed with an insulating frame like this, the mechanical strength is lower than that of a conductive metal frame, and there is a problem with its safety. The disadvantages are that the material must be carefully selected, the installation frame is complicated, and it is expensive.

Purpose of the Invention In view of the above-mentioned circumstances, the present invention uses a thyristor instead of a neutral grounding resistor (NGR), which makes it less susceptible to aging and is more effective than the conventional method. The object of the present invention is to provide a current limiting device in a neutral point grounding type that combines the features of a high resistance grounding type and a direct grounding type, and is suitable for handling in a field department where no maintenance or inspection is required.

In addition, the present invention adopts a new assembly structure for multi-stage connection of thyristors, thereby strengthening the structure, improving insulation performance, improving maintenance safety, and reducing installation space. The object of the present invention is to provide a current limiting device according to the present invention.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is an electrical circuit diagram of a power system including a thyristor current limiting device of the present invention.

The Y-connected windings of each phase of the transmission transformer 1 are as follows:
It is connected to a three-phase high pressure source 3 via a system disconnector 2 . A current limiting device 4 is connected between the neutral point N of the transformer 1 and the ground, and is made up of a group of thyristors connected in series in multiple stages and further connected in parallel. Specifically, the neutral point N of the transformer 1 is grounded via a plurality of thyristors SCR ₁₁ to SCR _1o connected in series in the forward direction and an inductance L ₁ . Thyristor SCR ₁₁
, a capacitor C ₁₁ and a resistor γ ₁₁ connected in series, and a resistor γ′ ₁₁ are connected in parallel, and in the other thyristors, a series circuit of a capacitor and a resistor is connected in parallel with a resistor. be done. Additionally, multiple thyristors connected in series (e.g.
SCR ₁₁ and SCR ₁₂ ), a series-connected capacitor and a resistor (eg, capacitor C′ ₁₁ and resistor R ₁₁ ) are connected in parallel. On the other hand, the neutral point N of the transformer 1 also has an inductance L ₂ and a plurality of thyristors SCR ₂₁ connected in series in opposite directions.
to ground via SCR _2o . Similar to the forward connected thyristor group, the thyristor SCR ₂₁ includes a capacitor C ₂₁ and a resistor γ ₁₁ connected in series.
and a resistor γ' ₁₁ are connected in parallel, and a series circuit of a capacitor and a resistor and a resistor are also connected in parallel to the other thyristors. Furthermore, as described above, the capacitors and resistors connected in series are connected in parallel across the plurality of thyristors connected in series in multiple stages.

A current transformer CT for current detection is connected between the current limiting device 4 and the ground, and the detection signal of this current transformer CT is transmitted to the grid and disconnector 2 via a waveform shaper 5. , a disconnection operation signal input terminal, and an auto-shift operation signal input terminal of the thyristor gate of the gate ignition control device 6, respectively.

The thyristor group of the current limiting device 4 and the ignition control circuit 6 of its gate circuit are configured so that the power system circuit voltage can withstand, for example, insulation class No. 80 insulation, and the shared voltage of each thyristor is This is reduced by the novel assembly structure described below in connection with FIG.

Further, the gate ignition control circuit 6 may be a divided multi-stage ignition method known as a thyristor ignition method. For example, as an ignition method from low voltage to high voltage, an optical signal method using optical fiber or a tridal ignition method may be used. One example is a magnetic method that uses a core.

The operation of the system shown in FIG. 1 will be explained with reference to the signal waveforms shown in FIG.

Normally, in normal conditions (section T ₁ ), the load conditions between the three phases are not completely balanced, but are in a slightly unbalanced state, and current flows into the neutral point N of the transformer 1 (zero). phase current). At this time, the conduction angle of the thyristor group of the current limiting device 4 is set to 180°, and a zero-sequence current, for example, a current of about 5 amperes, is passed as a leakage current I ₁ between the neutral point N and the earth. There is. In this way, in order to maintain the conduction angle of the thyristor group at 180 degrees, the conduction current is not limited, and the current limiting device 4 is in a ready state before a failure occurs.

Next, when a ground fault occurs at time t ₁ and a fault current I _s is applied to the neutral circuit, the conduction angle of the thyristor group is set to 180°, so that the ground fault occurs at the beginning of section T _2. The raw fault current is passed through (directly grounded) during 1/2 cycle of the current transformer.
Detected by CT. The detection signal of the current transformer CT is given to a gate firing control circuit 6 via a waveform shaping circuit 5. In the gate ignition control circuit 6, the conduction angle α of the thyristor is set according to the circuit constant of the power system, from the next 1/2 cycle until time t ₂ when the system disconnector 2 operates (section T During ₃ ), the fault current is quantified and limited to the current set between the neutral point N and the ground (high resistance grounding state). When the gate ignition control circuit 6 detects the operation of the breaker,
The conduction angle of the thyristor group is again set to 180°, and the current limiting device 4 is again placed in a ready state for normal operation.

The signal waveform of the fault current detected by the current transformer CT is a distorted sinusoidal waveform with a steep rise, as shown in section _T2 of FIG. Therefore,
Even if a detection signal is directly input to the circuit breaker operating circuit to operate an existing system disconnector operated by a current limiting device using a conventional resistor, the circuit breaker will not be able to operate. It is simply treated as a nozzle, and it is not detected as a fault current and does not cause malfunction. For this reason, even if the conventional resistor group is replaced with a thyristor group by connecting the waveform shaper 5 to the secondary side of the current transformer CT and applying a waveform signal with a small distortion factor to the disconnector, The system is configured so that it can be used as is without any modification to the system or disconnector 2.

FIG. 3 schematically shows the installation structure of thyristor groups connected in series in multiple stages in the current limiting device 4 of FIG. Even in circuit specifications, it is possible to reduce the voltage shared by one thyristor.

The installation frame is a conductive metal frame 30a that has sufficient mechanical strength compared to an insulating frame.
30d. 3 insulators between each metal frame
1. Two thyristors provided on each metal frame, e.g. SCR ₁ ,
SCR ₂ is structurally installed in the same polarity direction, but
Electrically, one thyristor SCR ₁ is directly connected to the metal frame 30a, and the other thyristor
The SCR ₂ is separated from its metal frame by an insulator 32 and is attached to the metal frame 3 of the next installation frame.
It is connected in series to the thyristor provided at 0b.
Similarly, the metal frames 30 of the four installation stands
All the thyristors provided in a to 30d are connected in series in multiple stages.

In this way, for example, if the assembly structure shown in Figure 3 is used in a 22KV/√3 power system, the shared voltage of one thyristor can be approximately 1600V, making it possible to use the thyristor economically. becomes.

According to the present invention, it is possible to provide a neutral point grounding type current limiting device that uses a thyristor group instead of a conventional resistor group, and for this reason, it is possible to provide a neutral point grounding type current limiting device that uses a thyristor group instead of a conventional resistor group. This eliminates the need to use insulators, etc., thereby reducing costs, and also eliminates the need for measures against deterioration of insulation properties due to aging.

Furthermore, according to the present invention, in order to directly limit the fault current, consideration must be given to high voltage and high current. A second circuit including a multi-stage series-connected circuit and a plurality of thyristors.
By connecting the thyristor multi-stage series connected circuit in parallel between the neutral point of the transformer and the ground, the voltage sharing value is reduced, and it can easily cope with excessive fault current. It is possible to do so.

Further, according to the present invention, since the installation frame is formed of a metal frame having a simple structure and sufficient mechanical strength, the installation space can be reduced and maintenance is easy.

Furthermore, according to the present invention, it is easy to install the current limiting device itself in a tank of insulating oil or SF ₆ gas to improve insulation performance, and maintenance can be reduced by setting the installation tank at ground potential. safety can be improved.

[Brief explanation of the drawing]

FIG. 1 shows the neutral point grounding method of the present invention.
FIG. 2 is an electrical circuit diagram of a power system including a thyristor current limiting device. FIG. 2 is a signal waveform diagram for explaining the operation of the electric circuit diagram of FIG. 1. Figure 3 shows
FIG. 2 is a diagram schematically showing an installation structure of a group of thyristors connected in series in multiple stages of the current limiting device of FIG. 1; (Explanation of symbols), 1: Transmission transformer, 2: System disconnector, 3: Three-phase high voltage source, 4: Current limiting device,
5: Waveform shaper, 6: Gate firing control circuit, 30
a to 30d: metal frame, 31: insulator, 32:
Insulator, N: neutral point, CT: current transformer, SCR: thyristor, γ, γ', R: resistance, C, C': capacitor, L: inductance.

Claims (1)

[Claims] 1 A plurality of thyristors connected in series in a first polarity direction, and a plurality of thyristors connected in parallel to the thyristors,
a first thyristor multi-stage series connection circuit consisting of a series circuit of a resistor and a capacitor and a resistor; a plurality of thyristors connected in series in a second polarity direction opposite to the first polarity direction; A parallel connection circuit consisting of a series circuit of a resistor and a capacitor connected in parallel, a second thyristor multi-stage series connection circuit consisting of the resistor, and the resistor is connected between the neutral point of the transmission transformer and the ground. constitute a neutral point grounding circuit, and the plurality of thyristors of the first and second thyristor multi-stage series connection circuits have a conduction angle when normal.
180°, and when a fault current is applied to the neutral point grounding circuit due to a ground fault in the power system, raw fault current flows for the first 1/2 cycle, but for the next 1/2 The ignition is controlled so that a current limited to a predetermined value flows according to a conduction angle set to a circuit constant of the power system from the second cycle until the system disconnector operates. A thyristor type current limiting device in a neutral point grounding type.