JPS6327767A - Position compensation method in insulating resistance measuring apparatus - Google Patents

Abstract

PURPOSE:To always perform accurate measurement by correcting the phase shift of a measuring signal, by a method wherein a switch means is repeatedly turned ON and OFF at a predetermined interval and the phase theta1 of voltage applied to the second input terminal of a synchronous detector so that the predetermined frequency component contained in the output of the synchronous detector always becomes zero. CONSTITUTION:The value of the predetermined resistor inserted between electric circuit 1, 2 and the ground is changed at random at a repeated cycle T and a time interval tau. A leak current component is synchronously detected on the basis of voltage shifted by 90 deg. in a phase from low frequency signal voltage by a synchronous detector MULT2 separately provided to obtain output and, so as to allow the frequency component of frequency 1/T contained in said output to approach zero, the low frequency signal voltage applied to the synchronous detector MULT2 and the phase of voltage shifted by 90 deg. in a phase from low frequency signal voltage are adjusted automatically. By this method, accurate and stable measurement can be always performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of compensating for temperature changes, secular changes in circuit constants, etc. of a device that measures the insulation resistance of electrical circuits or the like in a live line state.

(Prior Art) Conventionally, it has been common practice to monitor the condition of an electrical circuit using a method of measuring the insulation resistance of the electrical circuit, as shown in FIG.

This is done by passing the grounding wire LE of the power receiving transformer T with the load Z through the transformer OT connected to the low frequency signal generator O8C having a frequency f1 different from the commercial power supply frequency, or by connecting the grounding wire LE in series with the grounding wire LP: A low frequency voltage is applied to the electrical circuits 1 and 2 by inserting and connecting the oscillator, etc., and the insulation resistance Ro existing between the electrical circuit and the ground and the grounding are Stray capacitance C
After detecting the leakage current caused by the low-frequency voltage that returns to the grounding line via O and amplifying it with the amplifier AMP, only the frequency f1 component is selected by the filter FIL, and this is used as the output of the oscillator O8C, for example. The structure was such that the insulation resistance of the electrical circuit was measured by synchronously detecting the signal using a multiplier MULT and detecting the effective component (ie, the component in phase with the applied low-frequency voltage) in the leakage current.

Ninth, the measurement theory will be further explained to help understand the present invention.

If the low frequency signal voltage applied to the ground line LE is a sine wave, for example, E sin ω11 (ω1 = 2πfl), then the frequency f1 returned to the ground line Lz via the ground point E is
The leakage current is expressed as the component that is in phase with the applied AC voltage.

In other words, if a value proportional to the first term on the right-hand side of equation (1) is detected using a means such as synchronous detection, this value will be inversely proportional to the insulation resistance Ro. You can ask for it.

However, in the conventional method, the leakage current returning to the ground line is detected by the zero-phase current transformer ZCT, and the leakage current component of the frequency f1 included in the output of the zero-phase current transformer is selectively outputted by the filter FIL. , the phase of the leakage current at frequency f1 usually shifts in the zero-phase current transformer → amplifier → filter system, so it is necessary to compensate for this phase shift in order to obtain a value inversely proportional to RO from these synchronous detection outputs. be. 1 For this purpose, as shown in the figure, a fixed phase shifter PS is inserted into the first input terminal or second input terminal of the synchronous detector MtJLT, thereby correcting the above phase shift and achieving mutual synchronization. Ta. That is, by providing a phase shifter PS with
In the state where there is no Co=O, the first . Second
The phase difference between the voltages applied to the input terminals was set in advance to be zero.

However, in the conventional method as described above, zero-phase current transformation 15Z
The phase characteristics of cT, filter FIL, phase shifter PS, etc. fluctuate due to temperature changes and secular changes in the characteristics of the parts used, resulting in a phase error with the initial setting value.
Please note that there is a drawback that it may not be possible to provide accurate measurement results. In order to deal with these problems, the influence of phase errors has traditionally been minimized by using extremely high-quality zero-phase current transformers or filters with little characteristic variation, but it is still difficult to completely eliminate the influence. was difficult.

(Object of the Invention) The present invention has been made to eliminate the drawbacks of the conventional insulation resistance measurement method as explained above, and it is possible to constantly correct the phase shift of the measurement signal at low cost without requiring expensive parts. The purpose of the present invention is to provide a method for measuring insulation resistance that always provides accurate measurement results.

(Summary of the Invention) In order to achieve this object, the present invention forcibly inserts a resistance of a predetermined value between the electrical circuit to be measured and the ground, and repeats this connection randomly at a fixed period or at a predetermined interval. At the same time, a low frequency leakage current signal flowing to the ground through the resistor and flowing back to the ground wire is detected by synchronous detection with a voltage shifted by 90' from the low frequency voltage, and the signal contained in this output signal is detected. Further, the phase of the voltage shifted by 90° from the low frequency voltage applied to the second input terminal of the synchronous detector is adjusted so that a predetermined frequency component determined by the intermittent period of the resistor becomes zero. Configure adjustments to occur automatically.

(Example) First, before explaining the measuring method according to the present invention, a conventional method and its drawbacks will be explained in some detail in order to facilitate understanding thereof.

If the phase shift that occurs when the leakage current signal of frequency f1 shown in equation (1) passes through the zero-phase current transformer ZCT, amplifier AMP, and filter FILO system shown in Fig. 4 is θ, then the filter FIL is The output If becomes (2) and is applied to the first input terminal of the synchronous detector MULT.

Further, the voltage applied to the second input terminal of the synchronous detector MULT is set to, for example, a constant amplitude a. If sin (ωIt+θ1), then the output of the synchronous detector is (□ means that components with an angular frequency of 01 or higher are removed) ・・・・・・・・・(4) Therefore, when θ=01 The output Do is as follows, and since v and ao are constant, it is possible to measure a value that is inversely proportional to the insulation resistance RO. Therefore, when the phase shift θ-01 is not zero, the error E of D with respect to the above DO is = 1 → S(θ-01)-ωs CoRo sin(θ-
01)...(6).

Now, in order to examine the influence of phase shift, for example, if the phase error is θ - θ1 = 1 (degree), then jt = 25 in equation (6).
Hz, Ro=20, Ω, C0=5/JF, then ω
ICoRo ”E 15.7, so the error ε is 2
It can be seen that the measurement error becomes 7.4 yen, which significantly increases the measurement error.

The present invention proposes a method for suppressing the occurrence of errors due to the above-mentioned phase shift as much as possible.

FIG. 1 is a circuit diagram showing an embodiment of the insulation resistance measuring method according to the present invention, and the same symbols as in FIG. 4 have the same meanings.

That is, in the same figure, T is the transformer, 1 and 2 are the secondary low-voltage electric lines of this transformer, and the -2 side is connected to the grounding line LE which has undergone type 2 grounding work. Furthermore, the ground wire LE
A low-impedance transformer OT connected to a Kfi low-frequency oscillator O8C is coupled to a zero-phase current transformer ZCT.

Further, the output of this zero-phase transformer ZC'l' is guided to one input terminal of a multiplier MULTI via an amplifier AMP and a filter FIL.

In this embodiment, in addition to what has been described above, a series circuit consisting of a resistor R and a switch means 8W is further inserted between the grounding conductor 2 and the earthing point E.

The switch means SW is controlled by a phase control circuit PC controlled by the output of the low frequency signal generator O8C.

Further, a part of the output obtained from the zero-phase current transformer output via the amplifier AMP and the filter FIL is sent to the second synchronous detector MULT2.
, a bandpass filter BP and a rectifier circuit DET in series, and the phase control circuit PC is controlled by the output of the rectifier circuit.

Furthermore, the first and second synchronous detectors MULT1 and MU
At the other input terminal of LT2, the output obtained from the phase control circuit PC is directly connected to the former, and the 90° phase shifter PS is connected to the latter.
8, and the output of the former first synchronous detector MULTI is connected to one input terminal of the phase control circuit PC.
The configuration is such that a desired output signal 0UT2 is derived through a subtracter SUB to which one output of 0UT2 is input.

The operation of the apparatus configured as described above and the functions of each block will be explained in detail below using mathematical formulas.

That is, when the switch means SW inserted between the grounding line 2 and the grounding point 8 is on, the grounding line LE current flows additionally, and the leakage current 0 of the applied low frequency component flowing through the grounding line LE is 'O""(' +-riVsinω1t
+ω1CoVcosωtt −−−−−−(71Ro
It becomes R. Therefore, output 2 of filter FIL is (2)
From the relationship of the formula, it becomes 10) ・・・・・・・・・(8).

Therefore, the voltage applied to the second input terminal of the synchronous detector MULTI is a. 5 inches (ω1 is 1001) and voltage a obtained by applying this voltage to the 90° phase shifter PSS. cos(ωz t+a t ) as a synchronous detector MU
If applied to the second input terminal of LT2, the synchronous detector Mt
The output Dt of JLT2 is ωS(θ−01) (the meaning of □ is the same as in equation (3)).

Here, if 2π T (here T >> -) is the opening/closing period of the switch means SW, then W in equation (9),
Since the value of R included in the first term ω1 changes with the period T, the synchronous detector MULT
In the output D1 of 2, a component of frequency 1/T is generated.

Therefore, if the output of the synchronous detector MULT2 is applied to a filter BP that extracts only the frequency 1/T component, the output A of the filter BP can be expressed as follows. Here k is a constant, ψ is filter B
This is the phase determined from the phase characteristics of P, etc.

Therefore, if the output of the filter BP is rectified by the rectifier circuit DET, the output B will be as follows. Therefore, a voltage a is applied to the second input terminal of the synchronous detector MULTI so that the output of the rectifier circuit DgT becomes zero. If the phase 01 of sin (ω1t+θ1) is adjusted by the phase control circuit PC, the output B can be made zero, so that θ-01-+Q is obtained, so the phase shift can be brought close to zero.

Therefore, the switch means SW is turned on and off at predetermined intervals.
If the phase of θ1 is adjusted so that the frequency 1/T component included in the output of the synchronous detector MtlLT2 is always zero by repeatedly turning it off, one phase shift will disappear.

The phase control circuit PC and automatic phase control circuit required here can be easily realized using existing technology, so detailed description thereof will be omitted.

On the other hand, when the phase shift is compensated by the above method, θ
-θ1 → 0, so the output of the synchronous detector ~IULT1 is when the switch means SW is on, as can be seen from equation (4).

Furthermore, when the switch SW is off, the formula 2 is O. Therefore, when the switch is on, the output OUT of the subtraction circuit can be accurately measured by subtracting the same amount (a constant value).

Further, for example, the output A of the filter BP is connected to the switch means SW.
When synchronous detection (not shown) is further performed using a signal that turns on and off, the output So of this synchronous detector becomes as follows. (Here, ko is a constant.) Then, when θ>θ1, 5o) O, and when θ<θ1, S.

<0. When θ=θ0, S o = 0, and the phase adjustment direction (advance or lag) can be determined using So, and by using this determination result, efficient automatic phase control is possible.

In the above explanation, the resistor R was simply turned on and off at a period T.
The above phase control method can also be applied by changing the value of the resistance R continuously (eg, sinusoidally) with a period T.

Alternatively, the above phase adjustment may be performed for a certain period of time and θ1 is fixed since θ-σl;O is obtained, and the above-mentioned phase adjustment may be performed intermittently such that the phase adjustment is performed after a certain period of time.

In the above description, a case has been described in which the resistor R is inserted between a grounded electric path and the earth, but the present invention need not be limited to this, and the resistor R may be inserted between an ungrounded electric path and the earth, for example. However, in this case, since commercial power is applied to the resistor R, the current flowing through the resistor R and switch SW becomes significantly large, so it is necessary to use a resistor that can withstand this.

FIG. 2 is a block diagram of the main parts of a modified embodiment of the present invention, in which an application trough 3010 is used to supply current to the zero-phase current transformer ZCT via the resistors R and switch SW.
Instead, an OT' provided with a second secondary winding is used, and a low frequency voltage for measurement obtained from this is applied.

According to this example, unlike the embodiment shown in FIG. 1, it is not necessary to connect the resistor R and the switch SW to the grounding line LE, so that the installation work can be simplified.

Note that the operation is exactly the same as that described in the explanation of FIG.

FIG. 3 shows another embodiment in which the resistance R.

The switch SW is connected to the primary side of the application transformer OT, and if the voltage on the primary side is higher than the voltage on the secondary side, the value of the resistor R is increased by that ratio, so that the voltage shown in Fig. 1 is This is the same operation as described in the embodiment.

Note that the voltage applied to the resistor R is as shown in equation (7).
However, it is clear that there is no restriction to this, and there is no problem in operation even if other voltages are used.

In addition, the output from the two-phase control circuit PC is output from the synchronous detection circuit MT.
The phase applied to the second input of JLTI is Co =
If the phases are adjusted in advance so that they are in the same phase when O, and only the phase shift due to temperature or the like is compensated for by the above-mentioned automatic phase control, the time for phase synchronization can be shortened.

Furthermore, in the above explanation, a resistance element is used to flow a low frequency voltage and a common-mode current, but the invention is not limited to this, and other circuit networks (for example, a circuit combining an inductance and a capacitor) may be used. It is clear that it is good.

(9) In the above description, the low frequency signal voltage has been explained as a sine wave, but it is not limited to this, and it may be a rectangular wave, for example, and its fundamental wave component or harmonic component may be used.

In the above explanation, when performing phase adjustment, the phase of the signal applied to the second input of the synchronous detector is adjusted, but the output of the filter FIL applied to the first input of the synchronous detector It is clear that the same result can be obtained by adjusting the phase of the signal.

Further, in the above explanation, the resistance R is interrupted at a period T, but the present invention is not limited to this, and the same result can be obtained even if the resistance R is interrupted at a predetermined interval T. In this case, it would be convenient to take measures to automatically correct even if a slight phase shift occurs.

In addition, although the above example shows the case of a single-phase two-wire electric circuit,
It may be a single-phase three-wire electric circuit or a three-phase three-wire electric circuit.

(Effects of the Invention) As explained above, the present invention enables automatic phase adjustment of fluctuations in phase characteristics of an insulation resistance measuring circuit, and is therefore very effective in realizing an extremely stable measuring method. .

[Brief explanation of drawings]

gg1 is a block diagram showing one embodiment of the present invention, FIGS. 2 and 3 are partial block diagrams showing other embodiments of the present invention, and FIG. 4 shows a conventional method for measuring insulation resistance. It is a block diagram. T......Trans, 1.2...
...Electric circuit. LE・・・・・・Grounding wire, E・・・・・・−
...Grounding point. ZCT・・・・・・Zero phase current transformer, AMP
・・・・・・・・・Amplifier, FIL・・・・・・
····filter. MULT, MULTl, MULT2...
Synchronous detection circuit, OSC...Oscillator. OT, OT'・・・・・・・Ipplication transformer,
PS... Phase shifter, SW...
·······switch. PSS・・・・・・90° phase shifter, PC・
...... Phase control circuit, BP...
·····filter. DET・・・・・・・・・ Rectifier circuit, SUB・
・・・・・・・・・Subtraction circuit. Patent applicant: Toyo Tsushinki Co., Ltd. K. 3g

Claims (1)

[Claims] 1. A low-frequency signal voltage having a frequency f_1 different from the commercial frequency is applied to the electric line via the grounding wire of the transformer by electromagnetic induction or series coupling, and a zero-phase signal is coupled to the grounding wire. In the apparatus for measuring the insulation resistance between the electric line and the ground from the output obtained by synchronously detecting the leakage current component of the frequency f_1 contained in the output of the current transformer with the low frequency signal voltage, the insulation resistance between the electric line and the earth is measured. The value of a predetermined resistor inserted in
° The low frequency signal is applied to the synchronous detector so that the frequency component of frequency 1/T included in the output obtained by synchronous detection with a phase-shifted voltage approaches zero. 1. A phase compensation method for an insulation resistance measuring device, characterized in that a voltage and a phase of a voltage whose phase is shifted by 90 degrees from the low frequency signal voltage are automatically adjusted. 2. From the output obtained by synchronously detecting the leakage current component with the low frequency signal voltage, an increase due to the value of the resistance randomly changed at the repetition period T or the time interval τ is corrected at the time interval τ. 2. A phase compensation method for an insulation resistance device according to claim 1, characterized in that the insulation resistance between the electrical circuit and the ground is measured by: 3. Applying the low frequency voltage to a predetermined resistor, randomly changing the value of the resistor with a repetition period T or time interval τ, and passing the connecting wire connected to the resistor through the zero-phase current transformer. A phase compensation method for an insulation resistance measuring device according to claim 1, characterized in that: 4. The present invention is characterized in that the magnitude of the current in phase with the low-frequency voltage is randomly varied at a repetition period T or time interval τ, and a connection line through which the current flows is passed through the zero-phase current transformer. A phase compensation method for an insulation measuring device according to scope 1. 5. Leakage of the frequency f_1 applied to the synchronous detector so that the frequency component of frequency 1/T included in the output obtained by synchronous detection with a voltage shifted by 90 degrees from the low frequency signal voltage approaches zero. 2. A phase compensation method for an insulation resistance measuring device according to claim 1, wherein the phase of the current component is automatically adjusted.