JPH025627Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an overvoltage suppression device for an AC filter.

For example, at a frequency conversion station in a power transmission system,
An AC filter is connected to the converter bus to absorb high frequencies generated during frequency conversion. Figure 1 shows the wiring, where 1 is the power transmission line, 2 is its short-circuit impedance, 3 is the conversion station busbar, 5 and 6 are the 5th AC filter, and the 7th AC filter.
These are capacitor 7, reactor 8 and resistor 9
It consists of a series circuit. In such a circuit configuration, the value of short-circuit impedance 2 varies greatly depending on the system conditions behind the converter station. For example, as shown in the figure, when a no-load transformer 10 is connected to a converter station bus 3 through a shield breaker 11, the short-circuit impedance 2 and the AC filter are included in the excitation current of the no-load transformer 10. If the parallel resonance condition is satisfied at high frequency, overvoltage will occur on the converter station bus 3.

In order to suppress such overvoltage, a suppression resistor 12 is installed in the AC filter, for example, the 5th AC filter 5.
may be connected in series, and a switch (for example, a switch) 13 may be connected in parallel to the suppression resistor 12. However, conventionally, when connecting the no-load transformer 10, the switch 13 is opened before or at the same time as the disconnector 11 is closed, and the suppression resistor 12 is inserted into the AC filter 5. I was trying to insert the shinoki disconnector 11 at the bottom. Switch 13 is then closed again. However, according to such a control means, the switch 13 is opened and closed even when a resonance state does not occur depending on the value of the short-circuit impedance, so a reduction in the life of the switch 13 and the suppression resistor 12 can be avoided. do not have.

The purpose of this idea is to prevent shortening of the lifespan of the suppressor and switch by avoiding the insertion of a suppressor under conditions where the resonance condition is removed due to a change in system conditions and overvoltage does not occur on the bus bar.

For the above-mentioned purpose, this invention includes a resonance detection circuit. In the embodiment shown in FIG. 1, a voltage distortion detection circuit 14 is connected to the bus bar 3 as a resonance detection circuit, and the switch 13 is opened for a short time by a signal when this detects voltage distortion exceeding a predetermined value. It is equipped with a switch suppression circuit 15 for the purpose of According to this configuration, the transformer 10 is
When connected to the bus 3, if the short-circuit impedance and the AC filter resonate due to harmonics generated by the no-load transformer 10, a large distortion will occur in the voltage of the bus 3. When the voltage distortion detection circuit 14 detects this voltage distortion, the switch control circuit 15 operates based on a signal from this, and the switch 13 is opened. Due to this opening, the control resistor 12 is connected in series to the AC filter 5,
This connection quickly suppresses the high frequency resonance phenomenon and suppresses overvoltage on the bus 3.

FIG. 2 shows a time chart of the above-mentioned operation. Assuming that the voltage distortion expands due to resonance conditions when the shield breaker 11 is turned on, the time t ₁ required for detection by the voltage distortion detection circuit 14 has elapsed. When this happens, the switch 13 is opened. Note that the voltage distortion detection circuit 14
The response speed is desirably as fast as about 0.5 to 1 cycle in order to ensure the overvoltage suppressing effect. The opened switch 13 is automatically closed again at the time t ₂ (approximately 0.5 to 1 second) required for the transient voltage distortion to disappear, shorting the suppression resistor 12. It goes without saying that the switch 13 remains closed at this time, since voltage distortion on the bus bar 3 will not occur even if the circuit breaker 11 is turned on if the resonance condition is not met.

The illustrated embodiment uses a voltage distortion detection circuit 14 as a resonance detection circuit, but in order to detect the occurrence of resonance, the magnitude of the current flowing into the AC filter is detected instead. Switch switch 13
may be made to work. Therefore, the overcurrent detection circuit may be connected to the AC filter, and the switch 13 may be opened when the overcurrent detection circuit detects a current exceeding a predetermined value. Further, in the example shown in the figure, the suppression resistor 12 is connected to the fifth-order AC filter 5, but the AC filter that resonates is not limited to this AC filter, and the seventh-order AC filter 6 may also resonate.
The suppression resistor 12 may be connected to the seventh AC filter 6. Alternatively, since this may also occur with other AC filters, it is necessary to connect a suppression resistor to the AC filter where resonance may occur. For a suppression resistor connected in this way,
Since each switch 13 is connected, the above-described control may be executed for each of these switches 13. In addition, a suppression resistor may be inserted between the neutral point of the three phases and the ground for the three phases in common. Needless to say, this idea can be applied to this case as well.

As detailed above, according to this invention, when a device is connected to a system bus, the AC suppression resistor is connected to the AC filter so as to suppress resonance of the AC filter connected to the system bus and an overvoltage state. In the configuration for connecting to a filter, there is no need to insert a suppression resistor every time a device is connected as in the past, so the suppression resistor and the switch for connecting it are used less frequently than in the past. As a result, it is possible to sufficiently prevent the suppressing resistance and the life of the switch from decreasing.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an embodiment of this invention, Figure 2 is a circuit diagram showing an embodiment of this invention.
The figure is a time chart for explaining the operation. DESCRIPTION OF SYMBOLS 1... Transmission line, 3... System bus, 5, 6... AC filter, 11... Line breaker, 12... Suppression resistor, 13... Switch, 14... Voltage distortion detection circuit (resonance detection circuit), 15...Switch control circuit.

Claims (1)

[Scope of utility model registration request] In an overvoltage suppression device for an AC filter, in which a suppression resistor for overvoltage suppression is inserted into an AC filter connected to a grid bus by the operation of a switch, resonance of the AC filter occurs when power equipment is connected to the grid bus. a resonance detection circuit that detects the occurrence of
An overvoltage suppression device for an AC filter, comprising: a switch control circuit for operating the switch for a predetermined period of time based on resonance detection by the resonance detection circuit.