JPH01277747A - Deterioration detecting circuit for zinc oxide type lightning arrester - Google Patents

Abstract

PURPOSE:To reduce cost, by a method wherein voltage and a current are detected to extract the fundamental waves of both of them and a resistance current is calculated from the relation between the phase difference between both fundamental wave signals and the resistance current of a leaked current to detect the deterioration of a zinc oxide type lightning arrester. CONSTITUTION:The outputs of amplifiers 5, 6, that is, the signals of voltage and a current are passed through the first and second filters 7, 8 to become only fundamental waves, because an external noise is blocked by said filters and the phase difference theta between both waves is detected by a phase difference detection circuit 9. Thereafter, the operation based on the relation between the phase difference theta and a resistance current IR is performed by an operation circuit 10 to calculate the resistance current IR. By this method, the deterioration of a zinc oxide type lightning arrester is detected and cost reduction can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a deterioration detection circuit for detecting deterioration of a zinc oxide type surge arrester used, for example, as a gapless power surge arrester.

B1 Summary of the Invention The present invention provides a deterioration detection circuit for a zinc oxide lightning arrester, which includes a filter circuit that extracts the fundamental wave of power and current, a phase detection circuit that detects the phase difference between both fundamental wave signals, and a phase detection circuit that detects the phase difference and leakage current. By providing an arithmetic circuit that calculates the resistance current from the relationship with the resistance current, the resistance current is calculated using the fundamental wave component, eliminating the influence of external noise and simplifying the circuit configuration. This is what I did.

C0 conventional technology As is well known, the leakage current I of zinc oxide type arresters.

As shown in Fig. 3, the capacitance current 1c and the resistance current [
R is synthesized.

It is known that when a zinc oxide type lightning arrester deteriorates due to various damages (lightning surge, switching surge, AC overvoltage, long-term energization, etc.) that it receives during its use, the resistance current 1a increases significantly. Therefore, measuring the resistance current IR can be said to be the most effective means of detecting deterioration of zinc oxide type arresters.

Generally under normal use conditions! Since R<IC, it is necessary to remove the capacitance current IC in order to measure the resistance current 1vt. Conventionally, the circuit configuration was as shown in FIG. 4.

In FIG. 4, 2■ is a bus bar, 22 is a lightning arrester, and 23 is an instrument transformer (P) for detecting the voltage V of the bus bar 21.
D or +i P T ), 24 is a current transformer (CT) for detecting the current flowing through the lightning arrester 22, 25 is an amplifier for amplifying the detection output of the voltage transformer 23, and 26 is the current transformer 24. 27 is a phase shift circuit provided after the amplifier 25; 28 is a gain control circuit provided after the phase shift circuit 27; 29 is an amplifier for the gain control circuit 28 and the amplifier 26; This is a differential amplifier that calculates the difference in output, and subtracts the capacitance current Ic based on the voltage signal from the leakage Ti current 1o to find the resistance current IR. 30 is a display circuit that displays the value of this resistance component current IR.

D9 Problem to be solved by the invention If the resistance current is determined in this way, the leakage current I
Since the capacitance current Ic included in o changes depending on the system voltage, etc., it is necessary to gain control the lc multiplied signal magnitude depending on the situation. Furthermore, since the resistance current IR has a distorted waveform that includes high frequencies, a circuit design that takes into consideration the frequency of the distorted wave (a circuit design with good frequency characteristics) is required.

However, if the frequency characteristics are improved, it becomes difficult to use a low-pass filter to remove noise containing many high frequency components, and there is a problem that it becomes more susceptible to the influence of external noise.

21 Means for Solving the Problems The present invention includes a voltage detection unit that detects the voltage of a bus to which a zinc oxide type lightning arrester is connected, a current detection unit that detects the current flowing through the lightning arrester, and extracts the fundamental wave of the voltage. A first filter circuit, a second filter circuit that extracts the fundamental wave of the current, a phase detection circuit that detects the phase difference between both fundamental wave signals, and a resistance based on the relationship between the phase difference and the resistance current of the leakage current. The present invention is characterized in that it includes an arithmetic circuit that calculates a divided current.

20 The detection signals of the operating voltage and current have external noise removed and become only the fundamental wave, and the phase difference between them is detected by a phase detection circuit.

Thereafter, calculations are performed based on the correlation between the phase difference and the resistance current, and the resistance current is calculated. The degree of deterioration is determined based on the magnitude of this value.

G. EXAMPLES The present invention will be explained in detail below based on illustrated examples.

FIG. 1 shows an embodiment of the present invention, where l is a bus bar and 2
is a lightning arrester, 3 is a voltage transformer for detecting the voltage of the bus 1, 4 is a current transformer for detecting the current flowing through the lightning arrester 2, and 5 is a detection circular horn of the voltage transformer 3. An amplifier for amplification, 6 an amplifier for amplifying the detection output of the current transformer 4, 7 a fundamental wave extraction filter provided after the amplifier 5, and 8 a fundamental wave extraction filter provided after the current transformer 6. 9 is a phase difference detection circuit that detects the phase difference θ between the outputs (voltage signal and current signal) of both filters 7 and 8;
O is an arithmetic circuit that calculates the resistance current IR from the relationship between the phase difference θ and the resistance current 1[t, and 11 is a display circuit that displays the result of this calculation (resistance current IR).

The above-mentioned phase relationship is as shown in FIG. That is, when the resistance current 1a is zero, the phase difference between the leakage current Io and the voltage V is 90°, and as the resistance current IR increases, the phase difference θ becomes smaller.

With such a configuration, the outputs of amplifiers 5 and 6, that is, the voltage, ? When the 'lli style signal passes through the filter 7.8, external noise is blocked and only the fundamental wave remains, and the phase difference thereof is detected by the phase difference detection circuit 9.

Thereafter, the arithmetic circuit 10 performs a calculation based on the relationship between the phase difference θ and the resistance current IR to obtain the resistance current IR.

H. Effects of the Invention As described above, according to the present invention, voltage and current are detected and their fundamental waves are extracted, and the resistance component current is calculated from the relationship between the phase difference between the two fundamental wave signals and the resistance component current of the leakage current. Since deterioration of the zinc oxide lightning arrester is detected by calculating This reduces costs. Furthermore, since only the fundamental wave is detected, external noise can be effectively removed using a filter circuit. Furthermore, if the circuits from the filter circuit to the arithmetic circuit are configured digitally, there are advantages in that they can be easily digitized and can be directly connected to the integrated control system of the substation.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of a deterioration detection circuit for a zinc oxide lightning arrester according to the present invention, and Fig. 2 is a circuit diagram showing the phase difference of voltage and current and the resistance component, which are the basis for calculating the resistance component current in the same embodiment. FIG. 3 is a characteristic diagram showing the relationship between currents, FIG. 3 is a waveform diagram of leakage current and voltage of a zinc oxide type lightning arrester, and FIG. 4 is a circuit diagram showing a conventional example. ■...Bus bar, 2...Zinc oxide type lightning arrester, 3...Instrument transformer, 4...Current transformer, 5, 6...Amplifier, 7
．． 8... Fundamental wave extraction filter, 9... Phase detection circuit, 10... Arithmetic circuit. Figure 1 Figure 2 θ (d e g) Figure 3 Figure 4

Claims (1)

[Claims] (1) A voltage detection unit that detects the voltage of the bus to which the zinc oxide lightning arrester is connected, a current detection unit that detects the current flowing through the lightning arrester, a first filter circuit that extracts the fundamental wave of the voltage, and A second filter circuit that extracts the fundamental wave, a phase detection circuit that detects the phase difference between both fundamental wave signals, and an arithmetic circuit that calculates the resistance current from the relationship between the phase difference and the resistance current of the leakage current. A deterioration detection circuit for a zinc oxide type lightning arrester, characterized by comprising: