JPH01287472A - Measuring method for capacitor insulation resistance - Google Patents

Abstract

PURPOSE:To prevent a fault from occurring owing to overdeflection by connecting a capacitor and a negative characteristic thermistor in series and measuring the insulation resistance of the capacitor by an insulation resistance measuring instrument. CONSTITUTION:When a measurement voltage is applied to electrodes at both ends while the capacitor 1 and negative characteristic thermistor 2 are connected in series, the resistance value of the thermistor 2 decreases in the beginning by the self-heating of the thermistor 2 although the voltage is applied to the thermistor 2 because the resistance value is large, but the voltage is not applied to the thermistor any more as a result and the voltage is applied to the capacitor 11. Thus, when the measurement voltage is applied while the capacitor 1 and thermistor 2 are connected in series as mentioned above, the composite resistance value of the the thermistor 2 comes not to vary, so the generation of a surge current can be suppressed, and while the trouble of a meter owing to overdeflection is prevented, the insulation resistance value of the capacitor 1 can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of measuring insulation resistance of a capacitor.

<Prior Art> Conventionally, the insulation resistance of a capacitor has been measured by using an insulation resistance measuring device and applying a measurement voltage with both measurement terminals sandwiching the picture electrode of the capacitor.

Incidentally, since capacitors have charging characteristics, as shown in FIG. 5, when measuring insulation resistance, a large measurement current (surge current) initially flows, and the current gradually stabilizes as time passes.

<Problems to be Solved by the Invention> Since a large surge current initially flows, when measuring insulation resistance, there is a problem that the meter of the insulation resistance measuring device swings out, causing the meter to malfunction.

Another problem is that when measuring insulation resistance, the measurement range of the insulation resistance measuring device must be changed.

This invention was made to solve the above-mentioned problems, and can suppress the generation of surge current when measuring the insulation resistance of a capacitor, prevent meter failure, and improve the measurement range. The purpose of this invention is to provide a method for measuring capacitor insulation resistance that eliminates the need for switching operations.

<Means for Solving the Problems> In order to solve the above-mentioned problems, the present invention provides a method in which a capacitor is connected to a negative characteristic thermistor in a series circuit, and the insulation resistance of the capacitor is measured using an insulation resistance measuring device. It is composed of

When a capacitor and a negative thermistor are connected in series and a measurement voltage is applied to both electrodes, the time change in the insulation resistance of the capacitor and the time change in the resistance of the negative thermistor are exactly opposite, and at first Since the resistance value of the negative characteristic thermistor is large, voltage is applied to the negative characteristic thermistor,
A negative characteristic thermistor's resistance value decreases due to self-heating, and voltage is applied to the capacitor, and the combined resistance value does not change during this time, so the meter of the insulation resistance measuring device moves less and can prevent the meter from swinging out. .

<Embodiments> Hereinafter, embodiments of the present invention will be described based on FIGS. 1 to 4 of the accompanying drawings.

As shown in Figure 1, a negative characteristic thermistor 2 is connected in a series circuit to a capacitor 1 whose insulation resistance is to be measured.
The insulation resistance of the capacitor 1 is measured by connecting the terminals of an insulation resistance measuring device to the electrodes at both ends of the capacitor 1 and the negative characteristic thermistor 2 and applying a measurement voltage.

FIG. 2 shows the relationship between the insulation resistance and time when voltage is applied to the capacitor 1, and the insulation resistance value increases with time and then becomes stable.

Figure 3 shows the relationship between resistance and time when voltage is applied to the negative characteristic thermistor 2, and the resistance value decreases over time due to self-heating, creating a relationship with characteristics opposite to those of the capacitor described above. .

As shown in Figure 1, when capacitor 1 and negative characteristic thermistor 2 are connected in a series circuit and a measurement voltage is applied to the electrodes at both ends, the voltage will initially be negative because the resistance value of negative characteristic thermistor 2 is large. A voltage is applied to the characteristic thermistor 2, but the resistance value decreases due to self-heating of the negative characteristic thermistor 2, and as a result, no voltage is applied to the negative characteristic thermistor 2, and a voltage is applied to the capacitor 1.

As mentioned above, when a measurement voltage is applied with capacitor 1 and negative characteristic thermistor 2 connected in series, the time change of the insulation resistance value of capacitor 1 shown in Figure 2 and the negative characteristic thermistor shown in Figure 3 result. As shown in FIG. 4, the composite resistance of the two resistances changing over time has a characteristic that does not change substantially.

Therefore, since the combined resistance value of the capacitor 1 and the negative characteristic thermistor 2 does not change due to the application of the measurement voltage, it is possible to suppress the generation of surge current when the measurement voltage is applied.
The movement of the meter needle in the insulation resistance measuring device is small, and the insulation resistance value of the capacitor 1 can be measured while preventing the meter from malfunctioning due to run-out.

As described above, according to the present invention, the insulation resistance of the capacitor is measured by placing the capacitor in a series circuit with the negative thermistor, so the combined resistance of the capacitor and the thermistor is the opposite of the two. Characteristics that do not change substantially can be obtained, surge current can be suppressed when a measurement voltage is applied, the deflection of the meter of an insulation resistance measuring device is reduced, and failures due to swing out can be prevented.

Further, since the meter in the insulation resistance measuring device does not swing out and the combined resistance remains almost unchanged, the work of switching the measuring range of the measuring device can be omitted.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the measurement method of the present invention, Fig. 2 is a characteristic graph showing the relationship between capacitor insulation resistance and time.
Figure 3 is a characteristic graph showing the relationship between the resistance of a negative characteristic thermistor and time, Figure 4 is a graph showing the combined resistance of a capacitor and negative characteristic thermistor, and Figure 5 is a graph showing the relationship between current and time depending on the voltage applied to the capacitor. 3 is a graph of characteristics shown in FIG.

Claims (1)

[Claims] (1) A method for measuring capacitor insulation resistance, which comprises placing the capacitor in a series circuit with a negative characteristic thermistor and measuring the insulation resistance of the capacitor with an insulation resistance measuring device.