JP2654549B2 - Simple insulation resistance measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a method of measuring the insulation resistance of an electric circuit or the like in a live state, and particularly to the influence of a ground resistance that cannot be ignored when a floating capacitance to the ground is large. The present invention relates to a compensated simple insulation resistance measuring method.

(Prior Art) Conventionally, a method of measuring insulation resistance of a circuit as shown in FIG. 4 has been generally used for early detection of electric leakage or the like.

That is, whether to penetrate the ground line L _E of the power receiving transformer T having a Z becomes load transformer OT connected to an oscillator OSC which oscillates a low-frequency signal for measurements made different frequencies ₁ and the commercial power source frequency, or ground and the like by cutting a line connecting the oscillator in series to apply a low-frequency voltage measurement paths L ₁ and L _2, between the earth and the electrical path through current transformer ZCT that allowed through the ground line L _E A leakage current that returns to the ground line via the existing insulation resistance R ₀ and the ground stray capacitance C ₀ is detected, amplified by an amplifier AMP, and then added to a filter FIL to remove a commercial frequency component and remove only a frequency ₁ component. Is selected, and the insulation resistance of the circuit is measured using the voltage obtained by applying the filter output to the rectifier DET.

This can be displayed in such an equivalent circuit shown in FIG. 5, R ₀ is the insulation resistance of the measured circuit, C ₀ is also a ground stray capacitance, the measured circuit by inducing the ground line L _E the output signal of the measuring low frequency oscillator OSC which flows in indicates a case where re-fed back to the R ₀ and a ground line via a C _0. Note that r is a ground resistance at the ground point E.

Conventionally, the insulation resistance has been determined from the following calculation based on such an equivalent circuit.

That is, the frequency ₁ via a ground point E, E 'In figure
The current flowing to the oscillator OSC and I _1, which is referred to as _{I 1 = (A + jB)} V ....... At this time (However, ω ₁ = 2π ₁ ).

Generally an R ₀ >> R, the equation because it is possible to choose the omega ₁ so that ^{_{(ω 1 C 0 r) 2}} «1 ...... is Since the above equation can be expressed as Bω ₁ C ₀ ..., The above-mentioned A and B were determined by actually measuring the feedback current I ₁ , and the insulation resistance R ₀ was determined from these.

However, according to the conventional insulation resistance measuring method as described above, as is clear from the above equation, when the ground stray capacitance _C0 is large or when the frequency _{1 of the} low-frequency signal is increased, the accurate value of the insulation resistance _R0 cannot be obtained. However, if it becomes larger, the effect of the ground resistance r cannot be ignored, and the measurement itself becomes impossible.

(Object of the Invention) The present invention is intended to eliminate such a defect in the conventional method of measuring the insulation resistance of an electric circuit, and always obtains an accurate measurement result by removing the influence of the ground resistance. It is an object of the present invention to provide a simple insulation resistance measuring method that can perform the method.

(Summary of the Invention) In order to achieve this object, the invention according to claim 1 of the simple insulation resistance measuring method according to the present invention relates to a method of connecting a ground to an electric circuit whose one end is grounded via a ground wire. A low-frequency signal for measurement having frequencies f ₁ and f ₂ (f ₁ ≠ f ₂ , respective frequencies ω ₁ and ω ₂ ) is simultaneously or alternately applied using an injection transformer therebetween, and a current transformer coupled to the ground line is applied. A method of measuring the insulation resistance of an electric circuit by deriving the low-frequency signal for measurement returning to the ground line via a measuring device, wherein the low-frequency signal for measurement is applied to a core of an injection transformer for applying the low-frequency signal for measurement to an electric circuit. In order to apply a signal of the opposite phase of the measured low-frequency signal to the current transformer, a new connection line that penetrates the core of the injection transformer and the current transformer is provided, and the connection line is connected to the variable resistor. terminating Te, low measurement of the frequency f ₁ in the current transformer output Current value of the wave signal is adjusted the variable resistor so as to minimize, and the resistance value R ₁ of the variable resistor at that time, the current of the measuring low-frequency signals of the frequency f ₂ in the current transformer output the variable resistance to adjust, using the resistance value R ₂ of the variable resistor at this time so that the value is minimized, Is used to calculate the insulation resistance R ₀ of the electric circuit.

The invention according to claim 2 of the simple insulation resistance measuring method according to the present invention is characterized in that, in the invention according to claim 1, the connection line is the core of the injection transformer or the current transformer. It is characterized by being wound around either one or both.

(Examples) Hereinafter, the present invention will be described in detail based on illustrated examples.

 FIG. 1 is a block diagram showing one embodiment of the present invention.

In this figure, the same components as those in FIG. 4 are denoted by the same symbols, and the following are newly added.

That is, two oscillators ₁ and ₂ having different frequencies are used as the measurement low-frequency signal oscillator connected to the transformer OT.
It includes a OSC ₁ and OSC ₂ of these as well as as connected switchable via a changeover switch SW _1, as opposite phase to the ground line L _E penetrating the penetrating zero-phase current transformer ZCT the transformer OT these are those that the variable resistor R _v new rata loop connection line L _p provided and to which penetrates configured to insert in series.

The following procedure is used to obtain various characteristics of the electric circuit using the measuring circuit configured as described above.

Now In the figure, the changeover switch SW ₁ of the low-frequency signal to ₁ ungated measurement supplied to the measured circuit is switched to a, through the insulation resistance R ₀ and the stray capacitance C ₀ of the path as described above amplifier AMP connected thereto a current induced in the zero-phase current transformer core by measuring the low-frequency signal fed back to the ground line L _E is
It is obtained as a DC voltage signal at its output terminal OUT via the filter FIL and the rectifier circuit DET. In this case the filter FIL output signal Ig ₁ when no loop connection line L _p is the previous formula (1), (5) and (6) Ig ₁ = [a _{(1 / R 0) + (} ω 1 C 0) ² r + jω ₁ C ₀ ] V...

Meanwhile the current flowing through the variable resistor Rv connected to the case of providing the loop connection line L _p new rata as described above acts in mutually canceling directions for a phase opposite to Ig _1.

If the current at this time is Ig ₁ ′, Becomes Therefore, the rectifier output OUT ₁ is Becomes

Therefore the variable resistor Rv adjusted to the rectifier output OUT ₁ is minimum value R ₁ Tosureba from the equation _{(1 / R 0) - (} 1 / R 1) + (ω 1 C 0) 2 r = 0 ....

The value of the variable resistor Rv of the next time the rectified output OUT ₂ when this is performed similar to that described above operations is minimized to the measuring low frequency oscillator as ₂ signals supplied to the circuit under measurement switched to OSC ₂ Assuming that R ₂ , the following equation is obtained: (1 / R ₀ ) − (1 / R ₂ ) + (ω ₂ C ₀ ) ² r = 0 So from the equation From the formula And rearranging the ratios of the equations To obtain the resistance values R ₁ and R
By substituting R ₂ and the constants ω ₁ and ω ₂ , the insulation resistance value of the measured electric circuit can be obtained.

Further, it is also apparent that the value proportional to both sides of the equation to the V / R ₀ to V / R ₂ from (ω ₁ / ω _{²⁾ 2} times the value subtracting the V / R ₁ if multiplied by V are obtained, The insulation resistance value can be calculated using the current value flowing through the variable resistor Rv.

In the embodiment of FIG. 1, the filter FIL has a frequency of ₁
It should not be explained that it should be able to pass through the _second component and remove the commercial frequency component.

Further, the present invention may be modified as follows. FIG. 2 is a block diagram showing another embodiment of the present invention. The difference from the embodiment shown in FIG. 1 is that the measuring low-frequency oscillators OSC ₁ and OSC ₂ are connected in series. and, and these outputs together with two filters of the filter FIL ₂ for extracting filter FIL ₁ and frequency ₂ components for selecting the filter FIL provided to the signal component detecting circuit for feeding back to the ground line the frequency ₁ components the which are connected to switch by the switch SW _2. Thus is at the measuring circuit connected may be performed to the same measurements and calculations as described above by the switch SW ₂ of the filter side switching examples and are at the signal frequency of the time the first view It's just what you do, nothing else changes.

Note that this may optionally be measured separately by connecting the switch SW ₂ to the two rectifier DET the provided filter FIL ₁ and FIL ₂ respectively instead without providing the will be obvious.

FIG. 3 is a view showing still another embodiment of the present invention.
The application of frequency _{1, 2} of the low-frequency voltage to the electric path is through the application transformer OT in path L _1, L ₂ without passing through the ground line, and also to penetrate the paths L _1, L ₂ current transformer ZCT it is possible to detect the leakage current which returns to the ground line L _E by.

Furthermore, trans-OT a ground line L _p In the above embodiment and current transformer ZC
T penetrated so as to be in reverse phase.
If the connection wire is wound N ₁ times, a voltage of N ₁ V can be obtained at the winding end. In this case, it is clear that the value of the variable resistor Rv should be 1 / N ₁ , a current transformer ZCT may be _twice windings N, also it is obvious that it is also possible to wound the two.

Also, if the cores of the zero-phase current transformer ZCT and the transformer OT are divided cores, the work on site becomes easier.

(Effects of the Invention) The present invention makes it possible to measure the insulation resistance of an electric circuit in a live state by the method as described above, and to easily measure them in the field even when the stray capacitance is large. It has a significant effect on accurate measurement.

In the embodiments of the present invention, the case of a single-phase two-wire circuit has been exemplified for the sake of simplicity. However, the present invention is not necessarily limited to this. For example, a single-phase three-wire system or a three-phase three-wire circuit It will not be necessary to explain that it is equally effective in the case of an electrical circuit.

Further, as described above, the variable resistor Rv is set to the measurement frequency ₁ and
This not only can be simplified measurement if tightened automatically done _{by 2} the feedback signal components to at ground line L _E is provided an automatic adjusting loop circuit it in performing regulation to minimize , The insulation state of the electric circuit can be constantly monitored, and the response to the failure can be promptly performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2 and 3 are block diagrams showing another embodiment of the present invention.
FIG. 1 is a block diagram illustrating a conventional insulation resistance measuring method, and FIG. 5 is an equivalent circuit thereof. T ...... receiving transformer, L ₁ and L ₂ ...... paths, L _E ...... ground line, OS
C, OSC ₁ , OSC ₂ …… Oscillator, AMP …… Amplifier. FIL, FIL ₁ and F
IL ₂ …… Filter, DAT …… Rectifier circuit, ZCT …… Zero-phase current transformer,
OT… Measurement signal application transformer L _p … Connection loop, R ₀ … Insulation resistance, C ₀ … Floating capacitance to ground, R… Variable resistor.

Claims (2)

(57) [Claims] A frequency f ₁ and f ₂ (f ₁ ≠ ₁₎ are set using an injection transformer between an electric circuit whose one end is grounded via a ground line and the ground.
f ₂ , by applying a measurement low-frequency signal of each frequency ω ₁ , ω ₂ ) to derive the measurement low-frequency signal that returns to the ground line via a current transformer coupled to the ground line. In the method for measuring the insulation resistance of an electric circuit, a signal having a phase opposite to that of the low-frequency signal for measurement applied to a core of an injection transformer for applying the low-frequency signal for measurement to an electric circuit is applied to the current transformer. said injection through the transformer core and the current transformer is provided a new connecting lines, the connecting line terminates at the variable resistor, the measuring low frequency of the frequency f ₁ in the current transformer output for current value of the signal is adjusted the variable resistor so as to minimize, and the resistance value R ₁ of the variable resistor at this time, the current value of the low frequency signal for the measurement of the frequency f ₂ in the current transformer output Is adjusted so as to minimize the resistance of the variable resistor at that time. Using the R _2, A simple insulation resistance measuring method, wherein the insulation resistance R ₀ of the electric circuit is calculated by the following formula. 2. A simple insulation resistance measuring method according to claim 1, wherein said connection wire is wound around one or both of a core of an injection transformer and a current transformer.