JPH05273285A - Surge protective device of partial-discharge measuring instrument - Google Patents

Abstract

PURPOSE:To obtain a low-loss, largely-surge-resistant and high-response lightning-arresting element for very weak signal use by combining the following: a low-loss and largely-surge- resistant lightning-arresting element which is provided with an operation delay; and a low-loss, high-speed-response and small-surge-resistant lightning-arresting element. CONSTITUTION:When lightning intrudes into a cable 2 and a switching operation is performed, a surge is caused and a high surge voltage is generated across both sides of a sheath insulating tube 3. However, it is suppressed to a minimum of about 10 kV by means of a sheath- bridged surge arrester 4. As a result, the voltage of 10 kV is applied to the input side of a detection impedance Zd 7 via the electrostatic capacity of an electrode. At this time, the voltage is suppressed to 60 V by means of a gas lightning-arresting tube 6. However, a voltage of about 600 V is generated during this time due to the delay of an operating time of about 1mum, the voltage is applied to the input side of a high-frequency wide-band amplifier 10, and there is a danger that its semiconductor amplification element is damaged. Then, a series resistance 8 is installed, and an electric current is made to flow to one side of high-speed switching diodes 9 which have been connected in the forward direction and the reverse direction. Thereby, it is possible to protect that a semiconductor element on the input side of the amplifier 10 is damaged due to the surge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure prevention device for a partial discharge measuring instrument installed on a cable line due to a lightning surge, a switching surge voltage or the like that has entered the line.

[0002]

2. Description of the Related Art Table 1 shows the characteristics of a conventional surge protection device for communication.

[0003]

[Table 1]

The input signal level of the partial discharge measuring instrument is usually in the range of several mV, while when a surge enters the cable line, a surge voltage of about 10 kV may be generated between both sheaths of the insulating connection ( A bridge arrester is installed between both sheaths, and a maximum of 10 kV when the arrester operates.
Reach a degree). In the partial discharge measuring instrument, it is necessary to amplify this low level signal voltage to several volts, and a semiconductor amplifier is used. This amplifier is easily destroyed by the intrusion of surge voltage. Since the frequency band of this amplifier is required to be about 0.01 to 100 MHz, the surge protection element is also required to operate at high speed.

[0005]

In Table 1, the gas arrester has a small electrostatic capacitance of 1 pF and a discharge withstand voltage of 10 ³
Although it is as large as A, the response time is as slow as 1 μs, which is not suitable for a high frequency minute signal circuit.

Although the zinc oxide element has a fairly fast response time, it has a large capacitance of 10 ⁴ pF and is not suitable for a high frequency minute signal circuit. On the other hand, a surge protection element using a silicon diode has a fast response time and a capacitance of 10p.
It has excellent responsiveness at about F but has a surge tolerance of 1
It is as low as 0A.

FIG. 2 is a circuit diagram of an example of a conventional composite type low voltage lightning arrester for short-distance lightning, and FIG. 3 is a graph showing its characteristics. That is, it is a lightning arrester that uses an air gap G of 0.4 mm, a non-inductive resistance R, and a zinc oxide element Z and exhibits a considerable discharge withstand capability. However, here, the non-inductive resistance R of 1Ω and the zinc oxide element Z are connected in series and used, which causes a large reduction in signal energy.

As described above, there is a big problem in using the conventional lightning arrester in the amplifier input stage of high frequency weak energy into which a large surge enters.

As described above, a lightning arrester which can be installed on the input side of a minute high frequency amplifier into which a large surge enters has not been developed yet. That is, the conventional element has problems such as a decrease in signal level due to element insertion, a large operation delay of the element, and a small discharge withstand capability of the element.

An object of the present invention has been made in view of the above points, and it is an object of the present invention to develop a lightning protection device for weak signals, which has a low loss, a large surge resistance and a high speed response.

[0011]

According to the present invention, a gas discharge arrester having a low discharge starting voltage is connected in parallel to the output side terminal of the detection impedance, and 0.1 to 2 are also connected to the internal terminal side thereof.
A fixed resistance of 0Ω is connected in series, then connected to the input terminal of the partial discharge measuring instrument, and one or more pairs of high-speed diodes for switching operation are connected across the input terminal in both forward and reverse directions. This is a surge protection device for partial discharge measuring instruments.

[0012]

[Operation] A combination of a low loss, large surge withstanding lightning arrester with operation delay and a low loss, high speed, small surge withstanding lightning arrester provides a low loss, large surge withstanding, high speed response type lightning arrester.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a partial discharge measuring instrument with a surge protection device according to an embodiment. For example, CV of 275kV
If a partial discharge occurs in the insulation connection portion 1 of the cable line 2, a minute high-frequency pulse is generated on both sides of the metal foil electrode 5. The metal foil electrodes provided on both sides of the sheath insulating cylinder 3 detect a high frequency component through the electrostatic capacitance between the copper tube of the connecting portion and the foil electrode 5, and amplify the high frequency component by the partial discharge detector 11. Is configured to measure.

Here, if lightning enters the cable line 2 or an opening / closing operation of the system is performed, a surge occurs due to this and a high surge voltage is generated on both sides of the sheath insulating cylinder 3. Here, when the sheath bridge surge arrester 4 is installed, the voltage during this period can be suppressed to a maximum of about 10 kV. Therefore, this voltage of 10 kV is applied to the input side of the detection impedance Zd7 via the electrostatic capacitance of the electrode. Here, it is suppressed to 60V by the gas arrester 6, but about 1V
Due to the delay of the operating time of μs, a voltage of about 600 V is generated during that time, which is applied to the input of the high frequency wide band amplifier 10 through the detection impedance Zd7 and damages this semiconductor amplifying element.

That is, in FIG. 1, a pulse voltage having a width of 1 μs and 600 V is generated on the output side of the detection impedance Zd7. If the series resistance 8 is 5Ω,
A current will flow to one side of the fast switching diode 9 connected in the forward and reverse directions. If a switching diode IS1588 having a rating of 5 A is used as the diode 9, the capacitance thereof is about 2 pF, and 120 A,
It could withstand a current of 1 μs. In this case, the diode limit voltage is about 25V, and the high frequency wide band amplifier 1
The input semiconductor amplifier of 0 did not fail.

On the other hand, the signal level was reduced by about 10% because of the amplifier input impedance of 50Ω. The length between the detection impedance Zd7 and the high frequency wide band amplifier 10 can be set to about 10 cm, and the effect of mismatching due to this can be practically ignored.

In this example, the case where the series resistance is 5Ω has been described, but it is desirable to appropriately change this value depending on the size of the inrush surge. In addition to the diode varistor using the forward direction, it is also possible to use the reverse direction Zener diode.

[0018]

As described above, according to the surge protective device for the partial discharge measuring instrument of the present invention, stable lightning measurement of partial discharge can be performed by the development of the lightning arrester having high discharge withstand capability, high speed response and low loss. It will be possible. That is, in the case of partial line hot line measurement, although it is rare, the measuring instrument fails due to switching operation of the system, intrusion of lightning surge, etc., and subsequent partial discharge measurement becomes impossible, and it is necessary to replace the amplifier. It was With the development of this lightning protection device, it becomes possible to measure the partial discharge characteristics of a live cable stably and continuously for a long time.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a surge protection device for a partial discharge measuring instrument according to an embodiment of the present invention,

FIG. 2 is a circuit diagram showing a configuration of a conventional compound type lightning arrester,

FIG. 3 is a graph showing characteristics of the composite type arrester of FIG.

[Explanation of symbols]

 1 Insulation connection part 2 CV cable 3 Sheath insulation cylinder 4 Sheath bridging arrester 5 Metal foil electrode 6 Gas arrester 7 Detection impedance 8 Series resistance 9 High speed switching diode 10 High frequency wide band amplifier 11 Partial discharge measuring instrument

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hiroshi Suzuki 5-1-1 Hidakacho, Hitachi City, Ibaraki Prefecture "Inside the Power System Laboratory, Hitachi Cable, Ltd." (72) Inventor Tomoaki Imai Hitachi, Ibaraki Prefecture 5-1-1 Hidaka-cho, Higashi City "Inside the Hitachi Power Cable Co., Ltd. Power System Laboratory" (72) Inventor Mikio Hagiya 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture "Hitachi Cable Power System Research" In-house "

Claims (1)

[Claims] 1. A detection arrester output side terminal is connected in parallel with a gas discharge arrester having a low discharge starting voltage, and a fixed resistor of 0.1 to 20 Ω is also connected in series to the internal terminal side thereof, and then a partial A surge protection device for a partial discharge measuring instrument, characterized in that it is connected to an input terminal of a discharge measuring instrument, and one or more sets of high-speed diodes for switching operation are connected across the input terminal in both forward and reverse directions.