JPH11289658A - Overvoltage suppressing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure protective reliability with reference to a reversed polarity surface of a power apparatus by a method wherein a second overvoltage suppressing device installed across a first overvoltage suppressing device and an apparatus to be protected is operated only with reference to an overvoltage whose polarity is opposite to that of an AC voltage. SOLUTION: An overvoltage suppressing mechanism, with reference to a reversed polarity surge, which is constituted of a second overvoltage suppressing device 22 whose voltage limit is lower than the voltage limit of a first overvoltage suppressing device 21, reverse-durrent blocking devices 25, 26 and a changeover switch 27 is installed across the first overvoltage suppressing device 21 and an apparatus 23 to be protected. The changeover switch 27 is changed over to the side of the reverse- current blocking device 25 when an AC voltage flowing in a bus 24 for power is positive, and it is changed over to the side of the reverse-current blocking device 26 in synchronization with a polarity change when the AC voltage is negative. Thereby, irrespective of whether the AC voltage is positive or negative, the reversed polarity surface creeps, the second overvoltage suppressing device 22 is operated, and it is possible to suppress the change amount of a voltage creeping into the apparatus to be protected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to protection of power equipment in a substation.

[0002]

2. Description of the Related Art One of the main causes of damage to power equipment in a substation is the intrusion of overvoltage generated by a lightning surge or switching surge into power equipment. Due to the penetration of the overvoltage, electric field concentration occurs inside the power equipment, which leads to dielectric breakdown. As means for protecting the power equipment from such overvoltage intrusion, as shown in FIG. 4, a configuration in which the overvoltage suppression device 21 is installed on the side where the overvoltage 28 enters the protected device 23. , Is now widely used. As the overvoltage suppressing device 21, a zinc oxide type lightning arrester mainly composed of a non-linear resistance element mainly composed of zinc oxide having excellent voltage suppressing ability and high energy withstand capability is used.

[0003]

In the prior art using the above zinc oxide type arrester, since it operates irrespective of the polarity with reference to the ground potential in the substation, it invades protected equipment as shown in FIG. The absolute value of the overvoltage was suppressed to a limit voltage of 1 or less. Therefore, when considering the amount of voltage change based on the commercial AC voltage 4, the voltage change 3 of the limit voltage 1 or more is applied to the so-called reverse-polarity surge 2 in which an overvoltage of the opposite polarity to the AC voltage enters. Sometimes joined. For this reason, there was no particular problem with power equipment that can evaluate the dielectric strength only by the absolute value of the intrusion overvoltage, but power equipment such as a transformer that causes a transient oscillation phenomenon of the potential inside due to a change in the intrusion voltage Regarding the above, if the amount of change in the penetration voltage is large, an overvoltage exceeding the dielectric strength is generated inside the device, which may lead to damage to the device.

An object of the present invention has been made in view of the above-mentioned point, and an object of the present invention is to provide a power device in which a transient oscillation phenomenon of an internal potential occurs due to a fluctuation of an intrusion voltage, in response to a reverse polarity surge. Therefore, the protection reliability of the power equipment is improved, and more stable power supply is enabled.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for limiting a reverse voltage surge between a first overvoltage suppression device typified by a zinc oxide arrester and a device to be protected. An overvoltage suppression mechanism for reducing only the overvoltage suppression device, and more specifically, a second overvoltage suppression device having a lower limit voltage than the first overvoltage suppression device between the first overvoltage suppression device and the protected device. The overvoltage suppression device of
Is operated only for an overvoltage having a polarity opposite to that of the AC voltage.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an overvoltage suppressing method according to the present invention will be described below with reference to FIGS. FIG.
4 schematically shows, with respect to a time axis, a voltage applied to the power device to be protected when the reverse polarity surge 12 has entered in the operation state where the AC voltage 4 is applied. FIG. 2 shows a simplified configuration of a power system around a power device to be protected.

The feature of the present embodiment is that a limit voltage 1 lower than the limit voltage 1 of the first overvoltage suppression device 21 is provided between the first overvoltage suppression device 21 and the protected device 23 having the conventional configuration.
Second overvoltage suppression device 22 with backflow prevention device 2
An overvoltage suppression mechanism for reverse-polarity surges, which is constituted by the switches 5 and 26 and the changeover switch 27, is provided. The backflow prevention device 25 allows a current to flow when the potential of the power bus 24 becomes negative, and the backflow prevention device 26 allows a current to flow when the potential of the power bus 24 becomes positive. Switch 2 for connecting backflow prevention devices 25 and 26 and second overvoltage suppression device 22
7 is switched to the backflow prevention device 25 when the AC voltage 4 flowing through the power bus 24 is positive, and to the backflow prevention device 26 when the AC voltage 4 is negative, in synchronization with the polarity change of the AC voltage 4.

Thus, when the AC voltage 4 is positive, the second overvoltage suppression device 22 operates only when the potential of the power bus 24 becomes negative due to the intrusion of the reverse polarity surge, and the AC voltage 4 becomes negative. In this case, the second overvoltage suppression device 22 operates only when the potential of the power bus 24 becomes positive due to the intrusion of the reverse polarity surge. As a result, the voltage change amount 13 applied to the protected device 23 is suppressed to “(the maximum peak value of the AC voltage 4) + (the limit voltage 11 of the second overvoltage suppression device 22)” at the maximum.

In a power device such as a transformer, in which a transient oscillation phenomenon of a potential is caused internally by a variation of an intrusion voltage, the degree of the internal potential oscillation changes according to the amount of the invading voltage change. By suppressing the amount of voltage change with a simple configuration, the internal potential oscillation can be suppressed, and the reliability of protection against overvoltage intrusion can be improved.

The second overvoltage suppressing device 22 includes a first
The same type as that of the overvoltage suppression device 21 described above, for example, a zinc oxide arrester is suitable. Alternatively, the amount of energy of overvoltage processed by the second overvoltage suppression device 22 is smaller than the amount of energy processed by the first overvoltage suppression device 21 and the number of operation opportunities is reduced to about half. It is also possible to use an inexpensive device that does not have as good operating characteristics as the first overvoltage suppressing device 21 as the suppressing device 22. The limit voltage 11 of the second overvoltage suppression device 22 is:
It is sufficient that the voltage is lower than the limit voltage 1 of the first overvoltage suppression device 21. However, in order to match the maximum change amount of the voltage due to the overvoltage with the limit voltage 1 of the first overvoltage suppression device 21, "(first overvoltage Limiting voltage 1) of suppression device 21
(The maximum peak value of the AC voltage 4) ”is preferable.

The withstand voltage levels of the backflow prevention devices 25 and 26 need to be equal to or higher than the limit voltage 1 of the first overvoltage suppression device 21. As the backflow prevention devices 25 and 26, a device using a semiconductor such as a diode may be used.

The changeover switch 27 for connecting the backflow prevention devices 25 and 26 and the second overvoltage suppression device 22 includes a simple reciprocating mechanical changeover switch and a rotary switch combining a rotor and an electric contact. A type changeover switch, an electronic control type changeover switch using a semiconductor, and the like are conceivable.

Another embodiment of the present invention will be described with reference to FIG. The configuration on the circuit is the same as that shown in FIG. The feature of this embodiment is that the time region 15 in which the second overvoltage suppression device 22 operates is limited to only while the AC voltage 4 exceeds the threshold voltage 14. When the AC voltage 4 is low, the voltage change amount does not become much larger than the limit voltage 1 of the first overvoltage suppression device 21 even if the reverse polarity surge enters. Therefore, when the AC voltage 4 is equal to or lower than the threshold voltage 14, the necessity of operating the second overvoltage suppression device 22 is reduced, and the operation time 15 can be limited.

By performing such an operation, the first
The amount of voltage change applied to the protected device 23 can be suppressed more effectively than the embodiment, and the protection reliability against intrusion of overvoltage can be further improved.

As a guideline of the threshold voltage 14 for operating the second overvoltage suppressing device 22, it is conceivable that about half of the maximum peak value of the AC voltage 4 is provided. Furthermore, “(limit voltage 1 of first overvoltage suppression device 21) + (threshold voltage 14)”
And "(limit voltage 11 of second overvoltage suppression device 22) +
(The maximum peak value of the AC voltage 4), the voltage limit applied to the protected device 23 can be reduced by setting the limit voltage 11 of the second overvoltage suppression device 22 to the second overvoltage suppression. Regardless of the operation of the device 22, it can be suppressed to a certain level or less, and more reasonable protection reliability can be secured.

While the present invention has been described with reference to several embodiments, it is also possible to combine the embodiments and use the conventional configuration.

[0017]

According to the overvoltage suppressing method of the present invention described above, it is possible to suppress the amount of voltage change invading the protected device against an overvoltage having a reverse polarity to the AC voltage, that is, a reverse polarity surge, It is possible to suppress the amount of potential oscillation of a power device having an internal potential oscillation. As a result, the protection reliability of the power equipment against overvoltage intrusion can be improved, and it can contribute to the stable supply of power.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram schematically showing a voltage applied to a power device to be protected according to an embodiment of the present invention with respect to a time axis.

FIG. 2 is a simplified circuit configuration diagram showing a power system configuration around a power device to be protected in FIG. 1;

FIG. 3 is a characteristic diagram schematically showing a voltage applied to a power device to be protected according to another embodiment of the present invention with respect to a time axis.

FIG. 4 is a simplified circuit configuration diagram showing a power system configuration around a power device to be protected according to a conventional example.

FIG. 5 is a characteristic diagram schematically showing a voltage applied to a power device to be protected according to a conventional example with respect to a time axis.

[Explanation of symbols]

1 ... Limited voltage, 2,12 ... Reverse polarity surge, 3,13 ... Voltage change, 4 ... Commercial AC voltage, 5 ... Ground potential, 11 ... Second
The threshold voltage for operating the second overvoltage suppression device, 15 the time range in which the second overvoltage suppression device operates, 21 the first overvoltage suppression device, and 22 the second overvoltage suppression device. 2, overvoltage suppression device, 23 ... protected equipment,
24 ... power bus, 25, 26 ... backflow prevention device, 27 ...
Changeover switch, 28 ... intrusion overvoltage.

Claims (4)

[Claims] In a power substation comprising various power devices such as a bus, a lightning arrestor, a cable, and a transformer, a nonlinear device for protecting a power device such as a transformer from an overvoltage exceeding a commercial AC voltage caused by a lightning surge or a switching surge. First with resistance characteristics
Between the overvoltage suppression device and a protected device such as a transformer, a second overvoltage suppression device having a lower limit voltage than the first overvoltage suppression device is installed, and the second overvoltage suppression device is connected to an AC voltage. An overvoltage suppression device characterized by being operated only for an overvoltage of the opposite polarity. 2. The overvoltage suppression device according to claim 1, wherein the second overvoltage suppression device is operated only when the voltage value of the AC voltage exceeds a certain threshold voltage. 3. A sum of a threshold voltage of an AC voltage for operating the second overvoltage suppression device and a limit voltage of the first overvoltage suppression device, a maximum peak voltage of the AC voltage, and a second overvoltage suppression device. 3. The overvoltage suppressing device according to claim 2, wherein the threshold voltage and the limiting voltage of the second overvoltage suppressing device are set so that the sum of the limiting voltage and the limiting voltage substantially coincides with each other. 4. A means for operating the second overvoltage suppression device only with respect to an overvoltage having a polarity opposite to that of an AC voltage, a device having a current backflow prevention function such as a diode, and a device synchronized with the polarity of the commercial AC voltage. The overvoltage suppression device according to any one of claims 1 to 3, wherein a combination of a switch and a switch is used.