JPS63151870A - Insulation resistance measurement with phase compensation - Google Patents

Abstract

PURPOSE:To obtain correct results of measurement by correcting phase deviations among measuring signals without requiring costly parts, by inserting a capacitor between an electric circuit to be measured and a ground point of a ground wire to connect and disconnect the connection repeatedly at a fixed cycle. CONSTITUTION:A measuring low frequency signal voltage generated at a phase control circuit PC is applied to a ground wire LE and an output of a current transformer ZCT mounted on the ground wire LE is applied to synchronous detectors MULT1 and MULT2 through a filter FIL. A capacitor C is connected in parallel to the ground wire LE and controlled with the circuit PC through a switch SW. A low frequency signal generated at the circuit PC is further inputted into the detectors MULT1 and MULT2 shifted by 90 deg. in the phase from the former. An output of the detector MULT1 is divided in two and a part thereof is inputted into a subtractor SUB while the other part thereof is inputted into a detector MULT3 to make a signal which is compared with a switching signal output from the circuit PC as reference signal. In addition, an output of the detector MULT3 is inputted into a multiplier MT to be multiplied by an output of the detector MULT2 and the results are inputted into the other end of the subtractor SUB to obtain a desired signal OUT.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of compensating for changes in temperature, changes in circuit characteristics, etc. of a device that measures the insulation resistance of an electric circuit 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.

Does this mean that the second grounding wire Lv of the power receiving transformer T having a load Z is passed through the transformer OT connected to the measuring low frequency signal oscillator O8C having a frequency f1 different from the commercial power supply frequency?

Alternatively, by inserting and connecting the oscillator in series with the grounding line Lx, a low frequency signal voltage for measurement is applied to the electric line 1 and the electric line 2, and a current transformer ZCT passing through the grounding line Lm is used to connect the electric line and the earth. After detecting the leakage current of the measurement low frequency signal that returns to the ground line through the insulation resistance RO and ground stray capacitance QO existing in the ground line and amplifying it with the amplifier AMP, only the frequency f1 component is detected using the filter FIL. The insulation resistance of the electrical circuit is measured by detecting the effective component in the leakage current, that is, the component in phase with the applied low-frequency voltage, by synchronously detecting it with a multiplier MLILT using, for example, the output signal of the oscillator O8C. It was more structured than written.

To help understand the present invention, the measurement theory thereof will be further explained.

If the measurement low-frequency signal voltage applied to the grounding line Lg is, for example, a sine wave and Bs1nω11 (ω1=2πfl), then the leakage current of frequency f1 that returns to the grounding line LE via the grounding point E is as follows. 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 this way, the leakage current that returns to the ground wire is detected by the current transformer ZCT, and the frequency f included in the current transformer output is
In the conventional method of selectively outputting the leakage current component of l using a filter FIL, the phase of the leakage current of frequency fl is shifted in the system of 1 normal current transformer → amplifier → filter, so the output of these synchronous detections is inversely proportional to Ro. In order to obtain the desired value, it is necessary to compensate for this phase shift. For this purpose, as shown in the figure, a phase shifter PS is inserted into the first input terminal or the second input terminal of the synchronous detector MLILT, thereby correcting the phase shift and achieving mutual synchronization. That is, by providing a phase shifter PS with
0) of the synchronous detector. The phase difference between the voltages applied to the second input terminal was set in advance to be zero.

However, in the conventional phase compensation method as described above, the phase characteristics of the current transformer ZCT, filter FII, phase shifter PS, etc. fluctuate due to temperature changes or secular changes in the characteristics of used parts. This has the drawback that a phase error occurs between the two, making it impossible to provide accurate measurement results. Furthermore, current transformers have the disadvantage that their phase characteristics may vary as the primary current increases, and errors may also occur due to this influence. In order to deal with these problems, conventional methods have been to minimize the influence of phase errors by using extremely high-quality current transformers or filters with little variation in characteristics, and to minimize the primary current of the current transformer. However, it was still difficult to completely eliminate that influence.

(Object of the Invention) The present invention has been made in order to eliminate the drawbacks of the conventional insulation resistance measurement method as explained above, and is capable of constantly correcting the phase shift of the measurement signal at low cost without requiring expensive parts. The purpose of the present invention is to provide an insulation resistance measurement method that can always provide accurate measurement results.

(Summary of the Invention) In order to achieve this object, the present invention inserts a reactance element of a predetermined value, such as a capacitor, between the electrical circuit to be measured and the grounding point of the grounding line, and repeatedly connects and disconnects this connection using a signal with a period T. Flip it over or at 90° with the low frequency voltage for measurement.
A current having a predetermined value with a phase shift is changed by a signal with a repetition period T, and the conductor through which this current flows is set to the current transformer wave number f.
l and related leakage current are detected, and this is synchronously detected by a first synchronous detector using a voltage obtained from the measurement low frequency voltage to obtain a first signal. In addition, the above leakage current is determined by using a voltage that has a phase change of 90 degrees with the low frequency voltage for measurement. A second synchronous detector performs synchronous detection and obtains a second signal. Furthermore, a component with a frequency of 1/T contained in the first signal is detected, and a third synchronous detector performs synchronous detection using the signal with the repetition period T to obtain a third signal, and a third signal is obtained. the first to obtain the second signal. The phase of each signal obtained from the measurement low frequency signal voltage applied to the second synchronous detector is automatically adjusted. At the same time, the second signal and the third
The product of the signals is multiplied by a constant and then added to the first signal. The configuration is such that the insulation resistance of the electrical circuit is measured using the addition result obtained in this manner.

(Example) The present invention will be described in detail below based on the illustrated embodiment, but before that, a conventional method and its drawbacks will be described in some detail to help understand the present invention.

In Fig. 4, if the phase shift that occurs when the leakage current component of frequency fl shown by equation (1) passes through the current transformer ZCT, amplifier AMP, and filter FILO system is set to 0, then the filter FIL output 11 is...(2) This is applied to the first input terminal of the synchronous detection device MLILT.

Further, the voltage applied to the second input terminal of the synchronous detector is set to, for example, a constant amplitude a. If sin (ωIt + θ1), then
The output of the synchronous detector is D = I 1x aosin (ω11 + $1) ・
・・・・・・・・・(3) (□ means to remove components with angular frequency of 01 or higher) ・・・・・・・・・(4) Therefore, when 0=01, the output Do is Then, l ■* Since aQ is constant, the insulation resistance R.

A value that is inversely proportional to can be measured. Therefore, the above is true when the phase shift θ-01 is not zero.

The error E of D for is = 1-cos(a-01)-ωt CoRo sin
(θ−01)−・−・・(6).

However, now 9, for example, the phase shift is θ-01 = 1 (degree)
Then, in equation (6), when ft = 25Hz, RO: 20 is Ω, and C0 = 5μF, G) ICORO”15.7
Therefore, the error ε is 27.4%, which means that the measurement error becomes significantly large.

The present invention proposes a method for minimizing the occurrence of errors caused by the above-mentioned phase shift.

FIG. 1 is a circuit diagram showing an embodiment of the insulation resistance measuring method according to the present invention.

In the figure, a low frequency voltage with a frequency f1 generated by a nine-phase control circuit PC is amplified on the ground line LE by a power amplifier PAMP with small phase characteristic fluctuation, and then a voltage of V sinωIt is applied to the electric line via a transformer OT. do. At this time, the output impedance of the transformer OT inserted in series with the grounding line LE is selected to be sufficiently low. Also, a current transformer ZCT is connected to the grounding wire Lz.
are combined and the output is applied to a filter FIL that passes a component including one frequency f1 and removes a commercial frequency component to obtain an output corresponding to the above equation (2). , MULT2 are applied to the input terminals of WJ1.

Also, a capacitor OFF: switch SW is connected in parallel to the grounding wire Lv.
The opening and closing of this switch SW is controlled by a phase control circuit PC.

Furthermore, these two synchronous detectors MULT1 and MULT
The low frequency signal f1 generated in the phase control circuit PC is inputted to the other input terminal of each of the two input terminals, and a 90° phase shifter PSO is inserted into the synchronous detector MULT2. shift.

Of the two synchronous detection outputs obtained in this way, Mt
The output of JLTx is divided into two, and one is applied to one input terminal of subtracter 5LIB, and the other is used as a comparison signal for third synchronous detector MULT3 via filter BP.

Furthermore, the switching signal output generated by the phase control circuit WIIPC is input as the reference signal of the third synchronous detector MtJLT3.

Further, the output of the MULTa is inputted to the multiplier MT via the coefficient circuit COF, and is input to the second synchronous detector MU in the core part.
The output of LT2 is multiplied and the result is input to the other end of the subtracter SOB to obtain the desired signal 01JT.

Further, the switch SW in the series circuit of the capacitor C and the switch 8W connected in parallel with the grounding line Lv is turned ON-OFFy! by the phase control circuit PCK. - Configuring to control. The operation of this configuration will be explained below.

Now, if we consider the case where the switch SW is turned on, an additional current ωtcVcosω1t will flow through the grounding line Lv), and the leakage current Io of the applied low frequency component flowing through the grounding line will be ゛... ... (7) becomes. Therefore, output 2 of filter FIL is (2)
From the relationship of the formula ■ I! = −5ia ('a' 1 t+σ)+(C
o+C)ωtVcoso − (ω1t+θ) (8), and the output DI of the synchronous detector MULT1 at this time is (4
) According to the relationship of the equation, sin (θ−θ1) (91) is obtained.

Here, the switch SW is operated at a period T (that is, T>>-!
! ! ), the value of C included in the second term ω1 of equation (9) changes with the period T, so the synchronous detector MUL
In this case, as can be seen from equation (9), when 0;01, the second term becomes zero, so the frequency 1/T component is generated in the output Dl of the TI. Ingredients frequently occur. Furthermore, if the output of the first synchronous detector ML)LTI is applied to the filter 'BP which extracts only the frequency 1/T component, the output A of the filter BP becomes 2π A=-kcωlV a osln (, t+ψ) sin
It can be expressed as (θ-θl)...where k is a constant and ψ is the filter B
This is the phase determined from the characteristics of P, etc.

Next, the output of this filter BP is sent to a third synchronous detector MUL.
By applying to one input terminal of T3, and applying to the other input terminal a repetitive signal with a period T that turns on and off the switch SW'It generated by the phase control circuit PC, the synchronous detector Mt)
The output So of LT3 can be expressed as 2π So = Axsta-t =-・al), which is also S 6 =-k. cosψ5sii (Ij-01)
−・・−・−−−−02.

Here k. = Cω1va0, which is a constant.

Therefore, if 191〈π/2, 1θ−θII〉π/2, then 5o(0) when 0〉al, or SO〉0 when θ〉al.In the phase control circuit PC to which So is input, the phase The direction of phase adjustment can be determined using the control signal So, and the phase 01 is adjusted using this determination result to
If o is controlled so that it approaches zero, it can be made closer to 0-01→0.

This phase control circuit PC can be realized using existing technology, so a detailed description thereof will be omitted.

By the way, the voltage applied to the second input terminal of the synchronous detector M[JLT2 is the voltage a applied to the second input terminal of the synchronous detector MULTI. Since sin (ω1t+θ1) is phase-shifted by 90', this is now a. cos(ω1t+θl
), the output H of the synchronous detector MLILT2 is when the switch SW is off.

・・・・・・・・・It becomes a mackerel. Also, when the switch SW is on, MLILT2
The output H2 becomes...a4.

Further, the output of the synchronous detector MULT3 and the output of the coefficient circuit are -5 inches (.theta.-.theta.1). (As mentioned above (K.

, cosψ can be considered to be constants) Therefore, the product of the output of the synchronous detector MtlLT2 and the coefficient circuit output is multiplied by the multiplier MT, and the output of the synchronous detector MTJLT1 is subtracted by the subtracter 5tJB. For example, when the switch SW is off, the output 0 [J'rt of the subtracter 8tJB is (4
1. From C13 formula, 0UTI = D+H11sin (
θ−θri・・・・・・(To) On the other hand, when the switch SW is on, the output of the subtracter is 0LI
T2 is (9) from the α4 formula: 10LIT2 = Dt +
Hzsin((j-as)...-(g).

If phase 01 is adjusted by the above method so that 1θ-611<< 1, then 5in(#-θ1)=(
$-01), cos((θ-' ”)”1, sia
” (θ-01): Since it can be set as 0, the output 0 [JT expressed by the formula (to) becomes.

On the other hand, if the output of the synchronous detector MLILTI is simply used as in the conventional case, if 10-011<<1, then from equation (4) when the switch is off, and from equation (9) when the switch is on...・・・・It is important to not make 0-θ1 sufficiently small when the ground capacitance Co is large because it is affected by the phase error (θ-θl). I know it's getting thicker.

As described above, it is clear that the phase compensation method of the present invention is less susceptible to the influence of phase errors than the conventional method.

In the above explanation, the phase control signal So is used for one phase adjustment, but the following signal can also be used as an alternative signal.

That is, the signal obtained by detecting the frequency component of the frequency 1/T contained in the output of the So and the synchronous detector ML with a separately provided filter and performing separate synchronous detection with the signal of the repetition period T. It may also be a signal obtained when taking the product of . Still another method is to detect the frequency 1/T component contained in the outputs of the synchronous detectors MULTI and MULT2, find the product of each, and use the DC component to obtain the same result. The description will be omitted.

Further, in the above description, a case has been described in which the capacitor C is inserted between an electric line and a ground point, but the present invention is not limited to this, and may be inserted between an ungrounded electric line and a ground point, for example.

However, in this case, since commercial power is applied to capacitor C, the current flowing through capacitor C and switch SW becomes significantly large, so it is necessary to use a capacitor that can withstand this.

FIG. 2 is a block diagram of the main parts showing a modified embodiment of the present invention, including the capacitor C and the switch 5w1F.
! : In order to flow a current with a phase shift of 900 from the low-frequency signal voltage for measurement to the primary side of the current transformer ZCT, a second secondary winding is provided in place of the applying transformer OT, and fCOT' is used. A low frequency signal voltage for measurement that can be easily obtained is applied. According to this example, there is no need to connect the capacitor C and the switch SW to the ground wire Lm as in the embodiment shown in FIG. 1, 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 a capacitor C and a switch SW are connected to the primary side of an application transformer OT, and when the voltage on the primary side is higher than the voltage on the secondary side, By reducing the capacitance of capacitor C by that ratio, #
) The operation described in the embodiment of FIG. 1 is the same.

Furthermore, the capacitance of the capacitor can be reduced by winding the conductive wire connected to the capacitor multiple times instead of passing it through the current transformer.・Although the voltage applied to the capacitor is set to V as shown in equation (7), it is clear that this is not restrictive, and there is no problem in operation even if other voltages are used.

In addition, the phases output from the 1-phase control circuit and applied to the second input terminal of the phase locking circuit are adjusted in advance so that they are in the same phase, and only the phase shift due to temperature etc. is compensated for by the automatic phase control described above. By doing so, the time for phase synchronization can be shortened.

Furthermore, in the above explanation, a capacitor element was used to flow a current with a phase 90° different from the low frequency signal voltage for measurement, but this is not necessarily the case, and other circuit networks (for example, inductance and capacitor combined circuit)
You may also use . Obviously, it may also occur in other electrical circuits.

Further, in the above description, the low frequency signal voltage for measurement 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 addition, in the above explanation, when performing phase adjustment, 9,
Synchronous detection irfMtlLT1, ML)LT2 f) fJ
Although the phase of the signal applied to the synchronous detector MtlLTt and MtlLT2 is adjusted in the above example, it is clear that the same result can be obtained by adjusting the phase of the signal applied to the first input of the synchronous detectors MtlLTt and MtlLT2. be.

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, since the present invention measures insulation resistance, it is extremely effective in realizing an extremely stable measuring method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2 and 3 are partial block diagrams showing other embodiments of the present invention. FIG. T......Trans, 1,2...
...Electric circuit. LI!・・・・・・・・・Ground wire, E・・・・・・
...Grounding point. ZC'l'・・・・・・・・・Current transformer, AMP
......Amplifier FIL...Filter. MtlLTl, 2.3... Synchronous detection circuit. O20・・・・・・Oscillator, 0TOT'
......Input transformer, PS...
...Phase shifter. SW......Switch, MT...
・・・・・・Multiplier PC・・・・・・・・・Phase control circuit. BP-74k l, PSO---90' phase shifter, SUB------ subtractor. COP・・・・・・Coefficient circuit, P A
M P・・・・・・Power amplifier. Patent applicant: Toyo Tsushinki Co., Ltd. 1 unit

Claims (1)

[Claims] 1. A low frequency signal voltage for measurement with a frequency f_1 different from the commercial frequency is applied to the electric line via the grounding line of the transformer by electromagnetic induction or series coupling, and the electric line and the grounding line are connected. The value of a predetermined reactance element inserted between the grounding points is varied at a repetition period T to remove the leakage current of the commercial frequency component in the output of the current transformer coupled to the grounding wire, and
A first signal is obtained by synchronously detecting the leakage current containing the component _1 with the measurement low-frequency signal voltage, and the leakage current is synchronized with a voltage whose phase is shifted by 90 degrees from the measurement low-frequency signal voltage. A second signal is obtained by detection, and a third signal obtained by detecting a frequency component with a frequency of 1/T included in the first signal and performing synchronous detection with the signal with the repetition period T. The phase of the low frequency voltage for measurement applied to the synchronous detector to obtain the first and second signals and the voltage whose phase has shifted by 90° from the low frequency voltage for measurement are adjusted so that the signal approaches zero. adjusted and configured to measure the insulation resistance of the electrical circuit using a signal obtained by subtracting from the first signal a signal obtained by multiplying the value of the product of the second signal and the third signal by a constant, A method for measuring insulation resistance with phase compensation, characterized in that phase characteristic fluctuations in a measurement circuit are compensated for. 2. Claim 1, characterized in that the phase of the leakage current applied to the synchronous detector is automatically adjusted in order to obtain the first and second signals.
Insulation resistance measurement method with phase compensation as described in . 3. Changing a current of a predetermined magnitude with a 90° phase shift with the measurement low frequency signal voltage with a signal of a repetition period T,
3. A method for measuring insulation resistance with phase compensation according to claim 1 or 2, characterized in that a conducting wire through which the current flows is passed through or wound around the current transformer.