JP7159990B2 - Single-line ground fault overvoltage suppressor for ungrounded systems - Google Patents

Description

TECHNICAL FIELD The present invention relates to a single-line ground fault overvoltage suppression device that suppresses overvoltage caused by an intermittent arc ground fault or the like in an ungrounded system.

Conventionally, as a ground fault detection method for detecting a single-line ground fault in an ungrounded system, as shown in Patent Document 1, a grounded potential transformer (EVT) is installed on the bus of the ungrounded system, and a zero-phase current transformer is installed on each feeder. (ZCT) is considered.

In this ground fault detection method, when a minor ground fault (a minor ground fault that does not cause the relay to operate) or an intermittent arc ground fault (periodically occurring single line ground fault) occurs in the ungrounded system, the EVT's tertiary A ground-fault feeder is specified by the detected value of ZCT in that case, using the voltage appearing in the side open delta circuit.

However, when a slight ground fault or an intermittent arc ground fault occurs, if the ground fault is eliminated in a short period of time, it may be difficult to detect it even with the above configuration. Moreover, the above method is intended only for detecting a ground fault, and cannot suppress an overvoltage when a ground fault occurs. Furthermore, if there is concern about intermittent arc ground faults due to an increase in charging current to the ground due to an increase in the charging current to the ground due to an ungrounded customer, changing the grounding method to a resistance grounding method will require a complete change in the protection method. becomes.

JP 2013-113632 A

Hiroshi Kitajima: "Thinking about Three-Phase Symmetrical Coordinate Method 2nd Symmetrical Coordinate Method Calculation for Low-Voltage Circuits and Examination of EVT Circuits", Denki Keizai September 2006, Denki Shoin

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and its main object is to suppress the overvoltage caused by a short-time single-line ground fault such as an intermittent arc ground fault by using only a passive element. .

An ungrounded system is usually provided with an EVT for detecting a ground fault when it occurs. A single-line ground fault overvoltage suppression device for an ungrounded system according to the present invention suppresses an overvoltage caused by a single-line ground fault in an ungrounded system. Equipped with a resistor, a transformer having an iron core whose primary side is connected in parallel to the shunt resistor or a reactor having an iron core, and the overvoltage caused by the one-line ground fault causes the transformer or the reactor to be magnetically saturated, The overvoltage is suppressed by bypassing the shunt resistor, reducing the resistance value on the open delta side, and increasing the burden capacity.

With such a single-line ground fault overvoltage suppression device for an ungrounded system, the overvoltage caused by a single-line ground fault causes the transformer to become magnetically saturated, increasing the resistance burden and suppressing the overvoltage. It is possible to realize detection and suppression of overvoltage caused by a short-time one-line ground fault by only passive elements at once. In addition, when the overvoltage disappears, the magnetic saturation disappears and the resistor returns to a high-resistance state. Therefore, during normal operation, the advantage of the non-grounded system, such as prevention of induced interference, can be maintained.

In order to prevent erroneous detection of voltage fluctuations during normal operation, it is desirable to further include an antiparallel diode directly connected to the transformer.

According to the present invention configured as described above, overvoltage caused by a short-time single-line ground fault such as an intermittent arc ground fault can be suppressed only by the passive element.

1 is a schematic diagram showing the configuration of a single-line ground fault overvoltage suppressing device according to an embodiment of the present invention; FIG. It is a schematic diagram which shows the one-line ground fault circuit in the conventional ungrounded system. It is a figure which shows the voltage rise waveform of (A) phase voltage and (B) zero phase voltage at the time of an intermittent arc ground fault. It is a schematic diagram which shows the structure of the one-line ground fault overvoltage suppression apparatus of deformation|transformation embodiment. It is a schematic diagram which shows the structure of the one-line ground fault overvoltage suppression apparatus of deformation|transformation embodiment.

An embodiment of a single-line ground fault overvoltage suppression device for an ungrounded system according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the one-line ground fault overvoltage suppression device 100 of the ungrounded system suppresses overvoltage caused by a one-line ground fault such as an intermittent arc ground fault in an ungrounded system such as a 6.6 kV distribution line. It is something to do.

Specifically, the one-line ground fault overvoltage suppression device 100 is a transformer having an iron core 21 whose primary side is connected to an open delta circuit 41 of a grounded potential transformer (EVT) 4 connected to the bus 10 side of an ungrounded system. 2 and a shunt resistor 6 connected in parallel to the primary side of the transformer 2 .

Specifically, the burden resistor 5 and the shunt resistor 6 are connected in series to the tertiary side open delta circuit 41 of the grounded potential transformer 4 .

Here, the saturation characteristics of the transformer 2 are such that the iron core 21 of the transformer 2 does not magnetically saturate with the divided voltage applied to the shunt resistor 6 in a normal single line ground fault, and the magnetic saturation caused by an intermittent arc ground fault or the like occurs. It is designed to be magnetically saturated when an abnormal voltage occurs. In addition, the resistance value of the shunt resistor 6 is about the same as the resistance value of the burden resistor 5 (for example, about 1/2 to 2 times), and is about enough to magnetically saturate the iron core 21 of the transformer 2 when an abnormal voltage occurs. is a value that can ensure the partial pressure of For example, the resistance value of the burden resistor 5 is 50 to 100Ω (Non-Patent Document 1 mentioned above), and the resistance value of the shunt resistor 6 is about the same.

In this one-line ground fault overvoltage suppression device 100, the iron core 21 of the transformer 2 is magnetically saturated due to the overvoltage caused by the one-line ground fault, thereby bypassing the resistor 6 and increasing the load, thereby suppressing the overvoltage. That is, the transformer 2 functions as a switch to switch whether or not the resistor 6 is inserted.

Here, when there is a grounding capacitance _Cst in the ungrounded system (see Fig. 2), when the discriminant by the inductance and resistance constants existing in the same system becomes insufficient damping (voltage is oscillatory) It is known that an intermittent arc ground fault (one line ground fault occurs periodically) causes a phase voltage having an amplitude about five times the normal voltage (see FIG. 3A).

A voltage proportional to the zero-phase voltage of the bus 10 appears in the tertiary side open delta circuit 41 of the EVT 4 . Integrating the partial voltage across the shunt resistor 6 of this voltage results in the magnetic flux of the transformer 4 . During normal operation, nothing happens because there is no zero-phase voltage, but with an intermittent arc ground fault, the zero-phase voltage increases stepwise (see Fig. 3(B)), so the zero-phase voltage with a large amplitude remains constant. As time continues, the magnetic flux saturates and the inductance drops sharply.

As a result, the resistor 6 connected to the primary side of the transformer 2 is bypassed. For example, if resistors 5 and 6 have the same resistance value, the load is temporarily doubled. As a result, the high-frequency vibration required for the build-up of the zero-phase voltage is suppressed, and the overvoltage is suppressed.

Note that even if the inductance of the transformer 2 suddenly decreases and a short circuit occurs, the load resistor 5 is connected to the open delta circuit 41 on the tertiary side of the grounded potential transformer 4, so a short circuit accident occurs. There is nothing. Also, since the intermittent ground fault is a phenomenon that is resolved in a short time, the load resistor 5 only needs to have a heat capacity that withstands the short-time rating when the resistor 6 is bypassed.

According to the one-line ground fault overvoltage suppression device 100 of the ungrounded system of the present embodiment configured in this way, the transformer 2 is magnetically saturated due to the overvoltage caused by the one-line ground fault, thereby bypassing the resistor 6 and Since the burden on the conductor is strengthened and the overvoltage is suppressed, the detection and suppression of the overvoltage caused by a short-time single-line ground fault such as an intermittent arc ground fault can be realized at once with only passive elements. In addition, when the overvoltage disappears, the magnetic saturation disappears and the resistor returns to a high-resistance state. Therefore, during normal operation, the advantage of the non-grounded system, such as prevention of induced interference, can be maintained.

It should be noted that the present invention is not limited to the above embodiments.

For example, as shown in FIG. 4, on the secondary side of the transformer 2, a neutral point grounding resistor 7 connected to the neutral point of the primary side Y-connection 31 of the transformer 3 connected to the same bus as the EVT. (for example, several kΩ) may be connected in series. In this case, a zero-phase voltage discharge circuit is formed to suppress overvoltage.

Furthermore, an anti-parallel diode 8 connected directly to the transformer 2 may be provided, as shown in FIG. With this configuration, when the voltage fluctuates below the operation start voltage (Vth) of the diode 8, the circuit becomes open, and no voltage is applied to the transformer 2, so that it does not saturate. Therefore, unnecessary operations during normal operation can be avoided by setting the operation start voltage higher than the zero-phase voltage that appears due to the three-phase unbalance during normal operation.

Moreover, when nothing is connected to the secondary side of the transformer 2, a reactor having an iron core may be used instead of the transformer 2.

The one-line ground fault overvoltage suppression device of the above embodiment was configured using a tertiary side open delta circuit in a three-winding EVT, but a secondary side open delta circuit in a two-winding EVT (Y-open Δ) may be configured using

In addition, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications are possible without departing from the spirit of the present invention.

100 Single line ground fault overvoltage suppressor 10 Bus 2 Transformer 4 Grounded potential transformer 41 Tertiary side open delta circuit 5 Burden resistor 6・Shunt resistor 8 ・・・Anti-parallel diode

Claims (3)

It suppresses overvoltage caused by a single-line ground fault in an ungrounded system,
A transformer or core-containing reactor comprising a load resistor and a shunt resistor connected in series to the bus line side of the ungrounded system, and having an iron core whose primary side is connected in parallel to the shunt resistor,
A one-line ground fault overvoltage suppressing device, wherein the transformer or the reactor is magnetically saturated due to the overvoltage caused by the one-line ground fault, thereby bypassing the shunt resistor and suppressing the overvoltage. 2. The line according to claim 1, wherein said burden resistor, said shunt resistor, and said transformer or said reactor are connected to a tertiary side open delta circuit of a grounded potential transformer connected to said bus. Ground fault overvoltage suppressor. 3. The one-line ground fault overvoltage suppression device according to claim 1, further comprising an anti-parallel diode connected in series with said transformer or reactor.

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