JP2002311074A - Leakage current measurement method for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten charging time before a leakage current measuring operation in leakage current measurement of a capacitor. SOLUTION: During charging before leakage current measurement of a capacitor 4, a charging voltage where an alternating voltage va is superimposed on a direct voltage Vp of a measuring direct current power source 1 is applied to converge a dielectric absorption current in a short time, so that a true leakage current is measured in a short time. During the discharge of an electric charge of the capacitor 4, the alternating voltage va with no direct current component is applied to converge a leakage current of dielectric absorption in a short time, and during charging before leakage current measurement, a charging voltage where the alternating voltage va is superimposed on the opposite direct voltage vm of a measuring negative direct current power source 10 is applied to converge a dielectric absorption current in a short time, so that a true leakage current in the opposite direction is also measured in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a leakage current by applying a DC voltage to a capacitor.

[0002]

2. Description of the Related Art As one of the characteristic tests for determining the quality of a capacitor, there is an item for measuring a leakage current one minute after a DC voltage is applied. Depending on the material of the insulator forming the capacitor, the characteristic of the leakage current Io with respect to time after voltage application is such that it quickly converges as shown by the curve A in FIG. Some currents slowly increase. It is considered that the time constant of the dielectric absorption current is apparently increased in the case of the curve B because the dielectric absorption phenomenon of the insulator has a slow convergence. In a capacitor having a characteristic such as a B curve, the pre-charging time for measuring the leakage current becomes long, and in a production machine for inspecting this characteristic, the production tact becomes long, so that the production efficiency of the capacitor becomes long. And the cost increases.

Conventionally, in order to solve this problem, in a method described in Japanese Patent Application Laid-Open No. Hei 10-115651, a voltage Vh higher than the measured voltage Vc is temporarily applied to a capacitor during a charging period before measuring a leakage current. After the voltage is applied, the applied voltage is reduced to the measurement voltage Vc, and a reverse dielectric absorption current is generated in the discharge direction. The reverse dielectric absorption current and the current in the charge direction generated by charging the capacitor are canceled out, so that the dielectric absorption current is reduced. A method of early measuring the true leakage current by shifting the state to the converged state early has been proposed and put into practical use.

[0004]

SUMMARY OF THE INVENTION The above-mentioned conventional method comprises:
The charging time is shortened by increasing the charging voltage to be higher than the measurement voltage and charging the battery for a certain period of time to generate a reverse dielectric absorption current when the measurement voltage is applied. Depending on the type of capacitor material, some of them have very long dielectric absorption time constants. In this case, the charging time effect becomes insufficient unless a charging voltage whose charging voltage value exceeds the absolute rating is applied. However, since a voltage cannot be applied beyond the absolute rating, the effect of shortening the charging time is limited. In addition, when measuring the leakage current in the reverse direction or when inspecting other characteristics such as the dielectric loss tangent (tan δ) of the capacitor, it is necessary to discharge the electric charge accumulated in the capacitor. As a method thereof, a method of short-circuiting both ends of a capacitor via a resistor or the like is general. In this case, also due to the dielectric absorption phenomenon, the discharge characteristics are slow and take a long time, but no method for making the discharge quick is disclosed.

[0005]

According to the present invention, in order to solve the above-mentioned problems, a sequence for measuring a leakage current of a capacitor is as follows. In the first step, a DC voltage for measurement is measured in advance for each type of capacitor, and a charging voltage obtained by superimposing an AC voltage having a predetermined amplitude and frequency without DC component is measured in advance for each type of capacitor. The predetermined voltage is applied for Ta seconds, and at the timing when the AC voltage becomes zero, the AC voltage is turned off. In the second step, the voltage is switched to the DC voltage for measurement and measured for each capacitor type. The measurement is waited for Tb seconds while the DC voltage for measurement is applied. In the third step, the leakage current is measured by the leakage current measuring device in Tc seconds, which is the measurement time. The execution of the inspection is completed by the above three steps. Since the dielectric absorption phenomenon can be converged early by performing the second step,
The total inspection time (Ta + Tb + Tc) can be reduced.

Next, a fourth step for discharging the capacitor is started. During this period, by preliminarily measuring for each capacitor type, measuring for each predetermined capacitor type for Td seconds, and applying a predetermined AC voltage and amplitude having no DC component, Discharge is terminated by turning off the AC voltage at a timing when the AC voltage becomes zero, by converging the leakage current of the dielectric absorption at an early stage.

Next, a step of measuring a reverse leakage current is started. In the fifth step, a charging voltage obtained by superimposing an AC voltage having a predetermined amplitude and frequency on a DC voltage for measurement in a direction opposite to the above direction is applied for a predetermined Ta time or more. Converge the absorption phenomenon early. By performing the sixth and seventh steps in the same manner as in the second and third steps, the total time for measuring the leakage current in the reverse direction can be reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention relates to a capacitor leakage current measuring method for applying a DC voltage to a capacitor and measuring its leakage current.
A charging voltage obtained by superimposing an AC voltage on a DC voltage for measurement is applied for Ta seconds determined for each type of capacitor, and the AC voltage is turned off at a timing when the AC voltage becomes zero; Then, switch to the DC voltage for measurement, and for Tb seconds determined for each capacitor type,
Waiting for measurement while applying DC voltage for measurement,
In the step, the leakage current is measured by a leakage current measuring device, which is characterized in that a capacitor having a large time constant of dielectric absorption is compared with a case where only a DC voltage for measurement is used for charging. Has the effect that charging is completed in a shorter time in the total time of the first step and the second step.

According to a second aspect of the present invention, there is provided a capacitor leakage current measuring method for measuring a leakage current by applying a DC voltage to a capacitor, wherein Td determined for each type of the capacitor after completion of the leakage current inspection. It is characterized by applying an AC voltage with no DC component for 2 seconds to discharge the capacitor.In a capacitor with a large time constant of dielectric absorption, the AC voltage is not applied and the resistance of both ends of the capacitor is changed. This has the effect that the discharge is completed in a short time as compared with the case where the short circuit occurs via the switch.

According to a third aspect of the present invention, there is provided a method for measuring a leakage current of a capacitor, in which positive and negative DC voltages are applied to the capacitor to measure the positive and negative leakage currents. A charging voltage in which an AC voltage is superimposed on a DC voltage is applied for Ta seconds determined for each type of capacitor, and the AC voltage is turned off at a timing when the AC voltage becomes zero. Switch to voltage, wait for measurement while applying DC voltage for measurement for Tb seconds determined for each capacitor type, measure the positive leakage current with a leakage current measuring instrument in the third step, and perform the fourth step T determined for each capacitor type
The capacitor is discharged by applying an AC voltage having no DC component for d seconds, and in a fifth step, a charging voltage obtained by superimposing an AC voltage on a negative DC voltage for measurement is determined for each capacitor type. The AC voltage is turned off at the timing when the AC voltage becomes zero, and is switched to the DC voltage for measurement in the sixth step, and the DC voltage for measurement is switched for Tb seconds determined for each type of capacitor. And measuring the positive leakage current with a leakage current measuring device in a seventh step, wherein the time constant of dielectric absorption is measured. The total time of the first step and the second step and the total time of the fifth step and the sixth step are different from the case where the capacitor having a large value is charged with only the DC voltage for measurement. And has the effect of discharge time of the fourth step is completed in a short time.

Hereinafter, the first embodiment of the present invention will be described.
This will be described with reference to FIGS.

FIG. 1 is a block diagram of a leakage current measuring device used for measuring a leakage current of a capacitor according to a first embodiment of the present invention. FIG. 5 is a block diagram of a leakage current measuring device of a capacitor according to a second embodiment of the present invention. It is a block diagram.

Reference numeral 4 denotes a capacitor to be inspected, 1 denotes a positive DC power supply for measurement, 10 denotes a negative DC power supply for measurement, and 2 denotes a leak current measuring device for measuring the leak current of the capacitor 4. 6
Is an AC power supply, and 7 is a transformer, which acts to superimpose an AC voltage on the capacitor 4 on a DC voltage for measurement. The superimposition of the AC voltage allows a capacitor having a large time constant of dielectric absorption to be charged in a short time, and to set the DC voltage after the leakage current measurement to zero volt to discharge the capacitor. You can also shorten it.
Reference numeral 8 denotes a semiconductor relay which has an operation of controlling ON / OFF of the AC voltage at a timing when the AC voltage becomes zero volt. SW1, SW2, SW3, SW4, SW5
Is a control relay contact having the function of controlling the timing of the leakage current measuring device.

Hereinafter, a method of measuring a leakage current of a capacitor according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit block diagram of a capacitor leakage current measuring device according to this embodiment. FIG. 2 shows FIG.
5 is an operation timing chart of the capacitor leakage current measuring device shown in FIG. In FIG. 1, 1 is a positive DC power supply for measurement, 2 is a leak current measuring device, 3 is a shielded cable, 4 is a capacitor of an inspection object, 4a and 4b are electrodes thereof, and 5a and 5b are electrodes of the capacitor. Measurement probe (electric needle), 6 is an AC power supply, 7 is a transformer, 8 is a semiconductor relay,
Reference numeral 9 denotes a control DC power supply. SW1, SW2, and SW3 are relay contacts whose timings are controlled by a separate programmable controller (not shown), and R1 is a limiting resistor for charging current of the capacitor.

FIG. 4 shows an inflow current characteristic curve for the capacitor shown by the curve B in FIG. 3 during leakage current measurement. The leakage current Io after 60 seconds is the current value for the judgment of the inspection.

The operation will be described below with reference to these figures. The voltage Vp (V) of the DC power supply 1 for measurement is connected to the capacitor 4 via the resistor R1 and the transformer 7 and the measurement probe 5a,
6b, the current i flowing into the capacitor 4
(A) is measured by flowing into the leakage current measuring device 2. Here, the resistor R1 is for limiting the maximum value of the current i. The total of the resistance R1 and the internal resistance of the transformer 7 is about 1 MΩ at the maximum, and is negligible as compared with the insulation resistance of the capacitor 4 of 1 to several tens GΩ. In addition, (insulation resistance) =
It is a value calculated by (applied voltage Vp) / (leakage current i). Further, the leakage current Io is about 1 nA or less, which is very small, so that it is easily affected by noise. The shielded cable 3 is wired close to the measurement probe 5a to reduce the influence of noise. AC power supply 6 is
A sine wave alternating current having a frequency of 0 to several KHz is output. The semiconductor relay 8 uses a semiconductor component such as a triac and a photocoupler. The input side and the output side are insulated, and the input side DC voltage is turned on and off. The AC voltage can be turned on and off. Therefore, the relay contact SW1
Is turned on, a voltage is applied to the primary side of the transformer 7 as shown in FIG. E is applied to the capacitor 4. Also, set the relay contact SW1 to OF
F, the action of the semiconductor relay 8 causes Δ shown in FIG.
T When the AC voltage becomes zero with a delay of ₁ second, the AC voltage va
Disappears.

Now, the procedure for measuring the leakage current configured as described above will be described with reference to FIGS.

In the first step, the relay contacts SW1 and S
The W2 turned ON, continuing this state T ₁ seconds. Then, the voltage E on which AC is superimposed is applied to the capacitor 4.
Initially, a current i in which the charging current and the AC current are superimposed flows through the capacitor 4 with a time constant determined by the limiting resistor R1 and the capacitance of the capacitor 4, and the time characteristic at this time is a curve C in FIG. On the other hand, when the relay contact SW1 is kept OFF, the waveform becomes a B curve.

After ₁ second has elapsed, the relay contact SW1 is turned off.
And enters the second step. As for the time characteristic of the current i, the current fluctuates transiently as shown in FIG. 4, but the current value of Δi is smaller than that of the conventional B curve in which the relay contact SW1 is kept OFF from the start. It becomes small and quickly approaches the true leakage current Io. Until the time T ₂ seconds to stabilize the fluctuation has elapsed, the relay contact SW1 O
FF is performed, the relay contact SW2 is kept ON, and DC voltage application is continued. The above-mentioned time T ₁ second, T ₂ second, and the frequency and amplitude of the AC power supply have effective values for shortening the inspection time depending on the type of the insulating material and the capacitance value of the capacitor. Decide in advance.

After a lapse of T ₂ seconds, a third step is entered. By turning on the relay contact SW3, the leakage current measuring device 2
The start of measurement is signaled to start the measurement. After the measurement,
The relay contacts SW2 and SW3 are turned off. The measurement ends
It is determined by a completion signal (not shown) of the leak current measuring device 2 or by a timer (T ₃ ) as in the present embodiment.

Next, as a second embodiment of the present invention, a description will be given of an example in which a charge is discharged quickly by dielectric absorption once stored in the leakage current measurement, and a third embodiment will be described. A description will be given of an inspection apparatus which performs high-speed measurement of leakage current in the reverse direction with reference to FIGS.

FIG. 5 is a block diagram of an apparatus for inspecting the forward and reverse leakage current of a capacitor. FIG. 6 is an operation timing chart, and FIG. 7 is a partially enlarged view of the fourth step in FIG. 6, for explaining the discharge voltage characteristics of the capacitor.

In FIG. 5, components having the same numbers and symbols as those in FIG. 1 are components having the same functions and performances as the components shown in FIG. Reference numeral 10 is a negative DC power supply for measurement for measuring leakage current in the reverse direction. SW4 and SW5 are control relays controlled by a programmable controller (not shown). R1, R2, and R3 are a positive charging current limiting resistor, a discharging current limiting resistor, and a negative charging current limiting resistor, respectively.

Now, the procedure for measuring the leakage current according to the present invention thus configured will be described with reference to FIGS.

The first to third steps are performed as shown in FIG.
The description is omitted because it is exactly the same as FIG. In the fourth step, while turning off the relay contacts SW2 and SW3,
Turn on the relay contact SW4. Then, the AC voltage va whose DC voltage component is zero is applied to the capacitor 4. First, the charge of the capacitor 4 is discharged with a time constant determined by the current-limiting resistor R2 and the capacitance of the capacitor 4.
At this time, the time characteristic of the voltage Er across the capacitor 4 is a curve D in FIG. T after ₄ seconds, OFF the relay contact SW4 Then, appears a slight voltage vo that remained for dielectric absorption phenomenon of the capacitor 4. This value does not apply an AC voltage, as in the prior art simply compared with the case where discharged by short-circuiting both ends of the capacitor 4 by the resistors R2, depending on the length of time T _4, the fraction of Reduced.

From the fifth step, a reverse leakage current measuring step is started. First, only the relay contact SW4 is turned on, and the other relay contacts SW1, SW2, and SW5 are turned off.

[0028] T ₅ seconds for (T ₅ may be zero), to ON the turned ON at the same time SW5 the relay contacts SW1 again. Then, a charging current in which the alternating current and the current in the direction opposite to the first step by the DC voltage Vm are superimposed flows through the capacitor 4. The application of the AC voltage to the capacitor 4 has the effect of accelerating the convergence of the dielectric absorption phenomenon, as in the first step.

After ₁ second elapses, the relay contact SW1 is turned off.
Then, the process enters the sixth step. Until the time T ₂ seconds to stabilize the fluctuation of the current has passed, the relay contact S
W1 is turned off, the relay contact SW5 is kept on,
Continue applying negative DC voltage. The time T ₁ , T ₂ and
The frequency and amplitude of the AC power supply may be the same numerical values as in the first and second steps.

After a lapse of T ₂ seconds, a seventh step is entered. By turning on the relay contact SW3, the leakage current measuring device 2
The start of measurement is signaled to start the measurement. After the measurement,
The relay contacts SW3 and SW5 are turned off. The measurement ends
It is determined by a completion signal (not shown) of the leak current measuring device 2 or a timer (T ₃ ) as in the present invention.

After the measurement is completed, an eighth step is entered. The relay contacts SW1 and SW4 are turned on, and the electric charge stored in the capacitor 4 is quickly discharged as in the fourth step.

In this embodiment, an example in which positive and negative leakage currents are continuously measured has been described. Subsequently, as a characteristic test of the capacitor, the capacitance value of the capacitor and the dielectric loss tangent (tan) are determined.
When it is necessary to continuously perform the measurement such as δ), it is very effective to perform the above-described eighth step before the start of the measurement in order to eliminate the influence of the leakage current test.

[0033]

According to the leakage current measurement, which is one of the characteristics for judging the quality of a capacitor, a DC voltage is applied to the capacitor, and in many cases, the capacitor reaches a true value in a few seconds. Depending on the material of the insulator, the dielectric absorption phenomenon of the insulator has a slow convergence, so that the value of the insulator finally becomes a true value several tens seconds to several minutes after the application of the voltage. Also, when the charging voltage is discharged after the measurement is completed, the discharging time is similarly long. A capacitor having such a property requires a long charging time and a long discharging time for measuring a leakage current. As a result, the time required for testing the capacitor is prolonged, resulting in low productivity.

As described above, according to the present invention, in the capacitor having such characteristics, the dielectric absorption phenomenon can be quickly converged by superposing the AC voltage on the DC voltage and charging the capacitor. Leakage current can be measured in a short time. In addition, even during discharging, by discharging while applying an AC voltage, it is possible to discharge in a short time the charge due to the dielectric absorption phenomenon stored in the capacitor after the leakage current measurement, so that the capacitor inspection time is reduced. Can be shortened. As a result, the productivity of the capacitor can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a capacitor leakage current measuring device according to a first embodiment of the present invention.

FIG. 2 is a timing chart of the leakage current measuring device for a capacitor shown in FIG. 1;

FIG. 3 is a characteristic diagram of a current flowing through a capacitor when a DC voltage is applied to the capacitor to be inspected;

FIG. 4 is a characteristic diagram of a current flowing through a capacitor.

FIG. 5 is a block diagram of a capacitor leakage current measuring device according to a second embodiment of the present invention.

FIG. 6 is an operation timing chart of the capacitor leakage current measuring device shown in FIG. 5;

FIG. 7 is an enlarged view of a discharge step in FIG. 6;

[Explanation of symbols]

 Reference Signs List 1 Positive DC power supply for measurement 2 Leakage current measuring device 4 Capacitor of inspection object 6 AC power supply 7 Transformer 8 Semiconductor relay 10 Negative DC power supply for measurement SW1, SW2, SW3, SW4, SW5 Relay contact R1, R2, R3 Resistance

Continued on the front page (72) Inventor Yasuhiko Miyamoto 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 2G028 BB06 2G036 AA21 AA27 BB02 CA10 5E082 MM35

Claims (5)

[Claims] In a capacitor leakage current measuring method for applying a DC voltage to a capacitor and measuring the leakage current, in a first step, a charging voltage obtained by superimposing an AC voltage on a DC voltage for measurement is supplied to the capacitor. Is applied for Ta seconds determined for each product type, and when the AC voltage becomes zero,
The AC voltage is turned off, and in the second step, the measurement is switched to the DC voltage for measurement, and the measurement is waited while the DC voltage for measurement is applied for Tb seconds determined for each type of capacitor. A method for measuring leakage current of a capacitor, wherein the leakage current is measured by a current measuring device. 2. A capacitor leakage current measuring method for applying a DC voltage to a capacitor and measuring its leakage current, wherein after the leakage current inspection is completed, an alternating current without a DC component for Td seconds determined for each capacitor type. A method for measuring leakage current of a capacitor, comprising discharging a capacitor by applying a voltage. 3. A method for measuring a leakage current of a capacitor, in which positive and negative DC voltages are applied to a capacitor to measure a reverse leakage current thereof, wherein an AC voltage is superimposed on a positive DC voltage for measurement in a first step. The applied charging voltage is applied for Ta seconds determined for each type of capacitor, and the AC voltage is turned off at a timing when the AC voltage becomes zero. In the second step, the voltage is switched to a DC voltage for measurement, and the type of capacitor is changed. Wait for measurement while applying DC voltage for measurement for Tb seconds determined every time, measure positive leakage current by leakage current measuring device in the third step, and decide for each capacitor type in the fourth step For Td seconds, an AC voltage without a DC component is applied to discharge the capacitor,
In a fifth step, a charging voltage obtained by superimposing an AC voltage on a negative DC voltage for measurement is applied for Ta seconds determined for each type of capacitor, and the AC voltage is turned off at a timing when the AC voltage becomes zero. In the sixth step, the voltage is switched to the DC voltage for measurement, and T is determined for each type of capacitor.
A method for measuring a leakage current of a capacitor, comprising: performing a measurement wait while applying a DC voltage for measurement for b seconds; and measuring a positive leakage current with a leakage current measuring device in a seventh step. 4. The capacitor leakage current measuring method according to claim 1, wherein the AC voltage is turned off at a timing when the AC voltage becomes zero by a semiconductor relay. 5. The method for measuring a leakage current of a capacitor according to claim 1, wherein an AC voltage and a DC voltage are superimposed via a transformer.