JPH0578790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for measuring charging current of a capacitive element that can be used, for example, to measure the insulation resistance of a capacitive element such as a capacitor.

"Prior Art" Conventionally, the insulation resistance of a capacitive element has been measured using a measuring circuit as shown in FIGS. 4 and 5. Fourth
The measurement circuit shown in the figure shows the measurement method specified in JIS-C5102. In addition, the measurement circuit shown in Figure 5 is JIS
-This is a measurement circuit specified in C1303.

In the measurement circuit shown in FIG. 4, 1 is the object to be measured;
2 is a protective resistor, 3 is a standard resistor, 4 is a DC power supply, 5 is a galvanometer, 6 is a shunt, _S1 is a shunt switch that switches off galvanometer 5, and _S2 is a changeover switch. .

When measuring, turn off the shunt switch _S1 and turn on the changeover switch _S2 to contact 9. The deflection of the galvanometer 5 at this time is defined as d ₀ . Also, at this time, the flow divider 6
Let the dividing ratio of S 0 be S ₀ . Next, flip the selector switch _S2 to contact b. At this time, the deflection of the galvanometer 5 is d _x , the shunt ratio of the shunt 6 is S _x , and the resistance value of the standard resistor 3 is R _S
Then, the insulation resistance R of the object to be measured 1 is determined by R= _RS ·d ₀ /d _x ·S ₀ /S _x .

In the measurement circuit shown in FIG. 5, 1 is the object to be measured;
3 is a standard resistor, 4 is a DC power supply, 7 is a voltage measuring device with high input impedance, such as a Digivol, and S ₂ is a changeover switch.

In this measurement circuit, the changeover switch S ₂ is normally kept in contact with the contact a to release the charge on the object to be measured 1. During measurement, the changeover switch S ₂ is switched to the contact b and the DC power supply 4 is connected to the object to be measured 1. A DC voltage is applied to a series circuit consisting of a standard resistor 3 and a standard resistor 3. When the charging current to the object to be measured 1 becomes zero, the standard resistor 3
A voltage measuring device 7 measures the voltage generated across the terminal. If the measured value is V ₀ , the insulation resistance value R can be obtained as R=R _S /V ₀ ·(V _B ·V ₀ ). Here, V _B is the voltage of DC power supply 4,
R _S is the resistance value of the standard resistor 3.

"Problem to be solved by the invention" In the measurement method shown in Fig. 4, the deflection of the galvanometer 5
The timing to read _dx must be when the charging current flowing through the object to be measured 1 reaches zero. Therefore, in JIS-C5102, changeover switch S ₂ is set to contact b.
The value read 1 minute ± 5 seconds after the switch was made is used.

Therefore, it takes at least 1 minute for the measurement, so if a capacitor manufacturing factory were to inspect all the capacitors manufactured, the inspection time per unit would be long and many inspectors would have to be assigned. Otherwise, there is an inconvenience that the inspection may not be completed in time. The measuring circuit shown in FIG. 5 has similar drawbacks. In addition, in the case of a capacitor with a large capacity, charging current may still be flowing even after one minute has passed, and there is also the disadvantage that accurate insulation resistance values cannot be measured for a capacitor with a large capacity.

For this reason, the charging current value is measured at multiple timings within a short period of time immediately after charging current starts flowing through the capacitive element, and the current value after a desired time is predicted based on the multiple current measurement values. It would be convenient to be able to calculate the

An object of the present invention is to propose a method for measuring the charging current of a capacitive element, which can measure the current value of the charging current flowing through the capacitive element when it reaches a steady state in a short time.

"Means for Solving the Problem" In the present invention, current values are measured at at least three points at fixed time intervals starting from the point in time when a predetermined period of time has elapsed from the start of the charging current flowing through the capacitive element, and the current values of the at least three current points are measured. The current value after a desired time is predicted and calculated based on the current value.

In other words, in this invention, the current values at three points are measured within a short time after the charging current begins to flow, and the current values at the three points indicate that the charging current flowing through the capacitor reaches 0 after a sufficient period of time has passed since the charging current started flowing. This paper proposes a method of predicting and calculating the steady state current value at a given point in time.

According to the current measuring method of the present invention, charging current values are measured at three points within a short time from the start of measurement.
Measure I ₀ , I ₁ , and I ₂ , and calculate the electric charge value I _x in steady state using the charging current values I ₀ , I ₁ , and I ₂ as I _x = I ₁ ² −I ₀・I ₂ /2I Calculated by ₁ −I ₂ −I ₀ .

As a result, the result can be calculated before the time when the steady state is reached, and by finding the current value in the steady state, the insulation resistance value of the capacitive element can be easily found.

Therefore, according to the charging current measuring method of the present invention, a steady state current value can be determined in a short time, and thereby the insulation resistance value of a capacitive element, etc. can be calculated in a short time.

"Example" FIG. 1 shows an overview of the charging current measuring method according to the present invention. In FIG. 1, reference numeral 11 indicates a charging current waveform of a certain capacitive element. The current starts flowing from time t=0, and the current I ₀ is measured at time t ₀ when time T ₀ has elapsed.

The current I ₁ is measured at time t ₁ after time KT ₀ (K=1, 2, 3...) has elapsed from time t ₀ , and then at time t ₁
The current I ₂ is measured at time t ₂ after a time K·T ₀ has passed since then. The time t ₀ +2KT ₀ up to this point is selected within a short time.

According to the invention, these current measurements I ₀ , I ₁ ,
Using I ₂ , the current value I _x after a time T _x for the charging current flowing through the capacitor 12A to reach 0 is determined by the following equation.

I _x = I ₁ ² −I ₀ · I ₂ /2I ₁ −I ₂ −I ₀ The calculation process of the formula for I _x will be explained below.

FIG. 2 shows an electrical equivalent circuit of the capacitive element.
In FIG. 2, 12 indicates a capacitive element. 12A indicates the capacitance of the capacitive element 12, and C is the capacitance value. 12B represents a series resistor, and its resistance value is _R1 . 12C indicates insulation resistance, and its resistance value is R ₂ .

Figure 3 shows a diagram of the principle of the measurement circuit. In FIG. 3, 13 is a DC source that generates a known voltage value V;
4 represents the internal resistance of the DC source 13, and its resistance value is r. Prior to the start of measurement, the switch 15 is brought into contact with the contact point A to short-circuit both ends of the capacitive element 12, thereby discharging the charge stored in the capacitor 12A. When the discharge of charge is completed, switch 15 is closed to contact B.
voltage V from the DC source 13 to the capacitive element 12.
Apply. A current measuring means 16 is provided in the capacitive element 12.
are connected in series and measure the current value over time. This current measuring means 16 can use, for example, a voltage/current measuring device incorporating a microcomputer or the like, and the current value is measured by an AD converter.
The digital signal can be converted and the digital signal can be taken in by a microcomputer at predetermined intervals.

Current I _x when switch 15 connects to contact B
I _x =V/r+R ₂ +V/r+R ₁ ε ^-t/C(R1+r) (R ₁・R ₂ ≫r).

Let I _x at time t = T ₀ be I ₀ I x _at time t = T ₁ = T ₀ + T _a be I ₁ I _x at time t = T ₂ = T ₀ + 2T _a be I ₂ , I ₀ =V/r+R ₂ +V/r+R ₁ ε ^-T0/ 〓 …(1) I ₁ =V/r+R ₂ +V/r+R ₁ ε ^-1/ 〓 ^(T0+Ta) …(2) I ₂ =V/ r+R ₂ +V/r+R ₁ ε ^-1/ 〓 ^(T0+2Ta) ...(3). Note that τ=C(R ₁ +r).

The general formula for current I _x is I _x =V/r+R ₂ +V/r+R ₁ ε ^-1/ 〓 ^(T0+xTa) Here, if the value of Ta is _{T a =} KT ₀ , then I _x =V/r+R ₂ +V /r+R ₁ ε ^-1/ 〓 ^t0(1+xk) ……(4) If A=ε ^-1/ 〓 ^t0 , then I _x =V/r+R ₂ +V/r+R ₁ A ^(1+xk) ……( _{( 1+ _ _ _ _} ^{_ k)} ……(7) I ₂ =rV r+R ₂ +V r+R ₁ A ^(1+2k) ……(8) I ₁ −I ₀ =V/r+R ₁ A(A ^k −1) ……(9) I ₂ −I ₁ =V/r+R ₁ AA ^k (A ^k −1) ……(10) When formula (10) is divided by formula (9), A ^k =I ₂ −I ₁ /I ₁ −I ₀ ...(11) From equations (5) and (6) I _x −I ₀ = V/r+R ₁ A (A ^xk -1) ...(12) From equation (9) V/r+R ₁ A=I ₁ −I ₀ /A ^k −1 From formula (11), A ^k −1=I ₂ −I ₁ /I ₁ −I ₀ −1 = I ₂ −2I ₁ +I ₀ /I ₁ −I ₀ V/r+R ₁ A =(I ₁ −I ₀ )(I ₁ −I ₀ )/I ₂ −2I
₁ +I ₀ = (I ₁ −I ₀ ) ² /I ₂ −2I ₁ +I ₀ Substituting into equation (12), I _x −I ₀ = (I ₁ −I ₀ ) ² /I ₂ −2I ₁ +I ₀ ( A ^xk −1
) = (I ₁ −I ₀ ) ² /2I ₁ −I ₂ −I ₀ (1−A ^xk ) I _x = (I ₁ −I ₀ ) ² /2I ₁ −I ₂ −I ₀ (1−A ^xk )+I
₀ ...(13) With this, the current I _x after the time T _x when the charging current flowing through the capacitor 12A becomes 0 can be calculated.

When k = 1 (t ₂ - t ₁ = t ₁ - t ₀ = t ₀ ), I _x = (I ₁ - I ₀ ) ² /2I ₁ - I 2 _- I ₀ (1 - A ^x ) + I ₀ …
…(14) In equation (13), when A ^xk ≪1, I _x = (I _{1 −} I ₀ ) ² /2I ₁ −I ₂ −I ₀ +I ₀ =I ₁ ² −I ₀ I ₂ /2I ₁ −I ₂ −I ₀ ……(15) becomes a simple formula.

Here _, the A ^xk ≦1 condition is, from equation (11), A ^xk = (I _{2 −} I ₁ / ^I _{1 − I 0} ) Therefore, since I ₂ −I ₁ /I ₁ −I ₀ =I ₁ −I ₂ /I ₀ −I ₁ <1 A ^xk ≪1, approximately I ₁ −I ₂ /I ₀ −I ₁ ≦ Must be 1/2. The time for the current value found here
Assuming that t _x is to be searched for at least 10 times the measurement time interval KT ₀ (x≧10), A ^xk ≦ (1/2) ¹⁰ = 1.9×10 ^-3 ≪1, and equation (15) holds.Here, I Find the condition that ₁ −I ₂ /I ₀ −I ₁ ≦1/2 2(I ₁ −I ₂ )≦I ₀ −I ₁ I ₀ ≧3I ₁ −2I ₂ ...(16) (6), Rewriting equations (7) and (8) as I ₀ =K ₀ +αA I ₁ =K ₀ +αA ^(1+k) I ₂ =K ₀ +αA ^(1+2k) , equation (16) becomes K ₀ +αA≧ 3 {K ₀ +αA ^(1+k) }−2{K ₀ +αA ^(1+2k) } 2αA ^(1+2k) −3αA ^(1+k) +αA≧0 2A ^2k −3A ^k +1≧0 (2A ^k −1) (A ^k −1) ≧ 0 Since A ^k = ε−KT ₀ /τ, A ^k ≧ 1, but time T ₀ is T ₀ ≦ 0 (k≠0), so it is not a solution. Therefore, A ^k ≦1/2 ε−k/τT ₀ ≦1/2 −K/τT ₀ ≦ln1/2 KT ₀ ≧τln1/2=C(R ₁ +r)ln1/2 KT ₀ ≧0.69C(R ₁ +r) This means something like the following expression. In FIG. 1, after switching the switch 15 to contact B at time t=0, the current I ₀ at time t ₀ after time T ₀ ,
When measuring the current I ₁ after time KT ₀ from t ₀ and the current I ₂ after 2KT ₀ , the current I x after T _x = T ₀ + xKT ₀ is I _{x =} (I ₁ − I ₀ ) ² /2I ₁ −I ₂ −I ₀ {1−I ₂ −I ₁ /I ₁ −
It can be calculated as I ₀ } ^x + I ₀ .

Furthermore, if KT ₀ is chosen to satisfy KT ₀ ≧0.69C (R ₁ +r), it is possible to calculate I _x = I ₁ ² −I ₀ I ₂ /2I ₁ −I ₂ −I ₀ .

"Operations and Effects of the Invention" As described above, according to the present invention, the time interval kt ₀ of current measurement is set by the capacitance value C of the capacitance 12A and the series resistance 1
2B and the internal resistance 4 of the DC source 3 and the time constant of about 70% of the time constant _{C (R 1 +} r) determined by r, the current values I ₀ , I ₁ , _I2
By measuring the current value, it is possible to predict and calculate the current value at the time when, for example, 10 times the time constant has elapsed.

By selecting the time T ₀ to a sufficiently small value, the measurement can be completed in about 1.4C (R ₁ +r). In other words, the measurement can be completed in approximately 1.4 times the time constant, and the current value at the time 10 times the time constant has elapsed can be predicted and calculated. The time constant C (R ₁ +r) corresponds to the time until the charge/discharge waveform 11 drops by about 70%. Therefore, if the time T ₀ is selected to be a small value, the time t ₁ at which the current I ₁ is measured roughly corresponds to the time constant C(R ₁ +r). For example, C=1μF,
When R ₁ +r=10Ω, the time constant becomes 10 μsec.
With this time constant, the time (T ₀ +2KT ₀ ) required to measure the currents I ₀ , I ₁ , and I ₂ is approximately 14 μ. With a measurement time of 14 μs, it is possible to predict and calculate the current value after about 100 μs, which is 10 times the time constant, so it is possible to complete the measurement of the current in the steady state of the charging current in a short time. I can do it. If the value of the capacitance 12A is large, the measurement time interval KT ₀ ≧0.96C (R ₁ +r) is selected according to the capacitance value C, so even if the capacitance value C is large, the steady state current value can be accurately determined. I can do it.

By being able to know the charging current in a steady state in a short time, for example, the insulation resistance of a capacitive element can also be measured in a short time. Therefore, even if all capacitors are checked during the capacitor manufacturing process, there is an advantage that the product can be tested at high speed.

[Brief explanation of the drawing]

Fig. 1 is a graph for explaining the operation of the main part of this invention, Fig. 2 is a connection diagram showing an equivalent circuit of a capacitor to be measured, and Fig. 3 is for explaining an embodiment of this invention. Connection diagram, Figures 4 and 5
The figure is a block diagram for explaining a conventional circuit. 11...Charging current waveform, 12...Capacitive element, 1
2A...Capacity, 12B...Series resistance, 12C...
Insulation resistance, 13... DC source, 14... Internal resistance of the DC source, 15... Switch, 16... Current measuring means.

Claims (1)

[Claims] 1. A known voltage V is applied to a capacitive element having an electrical equivalent circuit in which an insulation resistance is connected in parallel to a capacitor, and the time required for the charging current flowing through the capacitor to reach a zero state. Current value I _x flowing through the above capacitive element after T _x
In the method for measuring the charging current of a capacitive element for determining the insulation resistance value _of the capacitive element by measuring, At three time points t ₀ , t 1 , t ₂ defined by the time interval _{KT 0 (} K=1, 2, 3...) related to the above time _{T 0} , starting from the time t ₀ after a short time T 0 has elapsed. , measure the current values I ₀ , I ₁ , I ₂ flowing through the capacitive element, and calculate the current value I _x after the above time T _x from these three current measurement values I ₀ , I ₁ , I ₂ by I _x
= (I ₁ ² − I ₀ · I ₂ )/(2I ₁ − I ₂ − I ₀ ), and the current for determining the insulation resistance value of the capacitive element within a time shorter than the above time T _x A method for measuring the charging current of a capacitive element to obtain the value I _x .