JPH01143973A - Simplified method for measuring insulation resistance - Google Patents

Abstract

PURPOSE:To remove the influence of a grounding resistance and to execute a correct measurement by inserting-connecting a variable resistor to a new loop connecting line to penetrate so that signals induced to the cores of a zero phase current transformer and a transformer can be made into phases opposite to each other in series. CONSTITUTION:A transformer OT is equipped with oscillators OSC1 and OSC2 with frequencies f1 and f2, a loop connecting line LP to connect them so as to be made into a phase opposite to a grounding line LE to penetrate the OT and a current transformer ZCT is provided, and a variable resistor RV is connected to it in series. First, a changeover switch SW1 is switched to the OSC1 side, a low frequency signal f1 is supplied to measured circuits L1 and L2, and by a signal to be fed back through an insulating resistance R0 and a floating capacity C0 of the circuits to the grounding line LE, a current induced to a ZCT core is obtained through an amplifier AMP, a filter FIL and a rectifier DET at an output terminal OUT as a voltage signal. At such a time, the resistor RV is adjusted, and a resistance value in which a output OUT1 is made minimum is made into an R1. Next, the SW is switched to the OSC2 side, a resistance value R2 in which an output OUT2 is made minimum is obtained, and the resistance R0 value can be calculated based on the values R1 and R2.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for measuring the insulation resistance of electrical circuits, etc. in a live line state, and particularly for measuring the influence of ground resistance, which cannot be ignored when the stray capacitance to ground is large. This invention relates to a compensated simple insulation resistance measurement method.

(Prior Art) Conventionally, for early detection of electrical leakage, etc., it has been common to use a method for measuring the insulation resistance of electrical circuits as shown in FIG.

That is, the grounding line LE of the power receiving transformer T having two loads is connected to the transformer OT connected to the oscillator 08CK which oscillates a low frequency signal for measurement having a frequency fs different from the commercial power supply frequency.
Or cut the ground wire and connect the oscillator in series with it? A current transformer Z to which a low frequency voltage for measuring the electric line L1 and LzK is applied by connecting, etc., and the grounding line Lie is passed through.
CTK detects the leakage current that returns to the ground 11sT/c through the insulation resistance RO existing between the electric path and the ground and the ground stray capacitance CoI, amplifies it with the amplifier AMP, and then adds it to the filter FIL.

The commercial frequency component is removed and only the frequency f1 component is selected, and the insulation resistance of the electrical circuit is measured using the voltage obtained by applying the filter output to the rectifier DET.

This can be expressed by an equivalent circuit as shown in FIG. 5, where the insulation resistance of the ROFi circuit to be measured, C.

is also a stray capacitance to the ground, and indicates the case where the output signal of the measurement low frequency oscillator O8C induced in the ground line LE and flowing to the electrical circuit under test returns to the ground line via the Re and CO. .

R is the grounding resistance of the grounding point E.

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

That is, in the figure, the current flowing through the ground points E and E + to the oscillator O8C of frequency f1 is It, and this is set as It=(A+jB)V . . . 1. (2). At this time (however, ω1=2πfl).

Generally it's Roar.

(ωxcor)” (1...scream...■ω
Since l can be chosen, the above equation 0 and the above equation (■) can be expressed as BmiωICO. , Furthermore, from these, the insulation resistance RO? :I was looking for it.

However, with the conventional insulation resistance measuring method as described above, as is clear from the above equations (1) and (2), it is not possible to obtain an accurate value of insulation resistance RO when the floating capacitance to ground 1ico is large or when the frequency fl of the low frequency signal becomes too large. However, if the resistance becomes larger, the influence of the grounding resistance r cannot be ignored, and the measurement itself becomes impossible.

(Object of the Invention) (The present invention has been made in order to eliminate the defects in the conventional method of measuring insulation resistance of electric circuits, and to eliminate the influence of grounding resistance to always obtain accurate measurement results. The purpose of this invention is to provide a simple method for measuring insulation resistance.

(Summary of the Invention) In order to achieve this object, the present invention applies low frequency signals for measurement with frequencies fl and fl directly to the electric line through the grounding line of the transformer, and Equipment ZC
A new loop connection line is provided that passes through so that the signals induced in 'l' and the core of the transformer OT are in opposite phases to each other, and a variable resistor is inserted and connected in series to this loop, and the frequencies f1 and fx The reciprocal K (fl/fg) of the value of the variable resistor that minimizes the rectifier D ET output obtained by applying measurement signal voltages of
By weighting them and taking the difference between the two, the insulation resistance value can be easily calculated while the wire is in a live wire state.

Embodiments) The present invention will be described in detail below based on illustrated embodiments.

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

In this figure, the same components as in FIG. 4 are given the same symbols, and the following new components have been added.

That is, two oscillators 08Cs and 08Ct with different frequencies, fl and fl0, are provided as measurement low-frequency signal excavators connected to the transformer OT, and these are connected by a changeover switch SW.
1, and a grounding line L passing through the transformer OT and passing through the zero-phase current transformer ZCT.
A new loop connecting line Lp is provided passing through these so as to have an opposite phase to E, and a variable resistor Rv is inserted and connected in series to this new loop connecting line Lp.

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

In the same figure, the changeover switch SWl is now set to a to set the measurement low frequency signal fl to be supplied to the electrical circuit under test, and the grounding wire Lm is transmitted via the insulation resistance R6 of the electrical circuit and the stray capacitance Cod as described above. The current induced in the zero-phase current transformer core by the measurement low-frequency signal fed back to the amplifier AMP, filter FIL, and rectifier circuit DE'l connected to this
' through its output terminal OUT Kl is obtained as a current voltage signal. In this case, when the loop connecting line Lp is not present, the filter FIL output signal Ig1 is calculated using the formula % (6). The current flowing to Igr
Since they are in opposite phase to lc, they act in a direction that cancels each other out.

Let the current at this time be Igx'.

ig/l= (T---F + (ωtCo) r+j
ωtcoJV-...■. Therefore, the rectifier output 0LIT t is...
・・・・・・■ becomes.

Therefore, by adjusting the variable resistor Rv, the rectifier output is 0TJ.
If the value that minimizes T 1 is R1, then from the above formula (1) (1/RO) (1/R1) + (ωtCo) r=o
-Can be expressed as @.

Next, the measurement low frequency oscillator is switched to O8C2 and the signal supplied to the cable under test is S2, and the same operation as described above is performed, and the rectifier output at this time is 01JT! If the value of variable resistor Rv when is the minimum is R2, then (1/RO) (1/R1)+(ωtco) r=0
We obtain the formula , , , , ■. Therefore, the [phase] equation is υ (0゛0°)′=■−了 ゛°°°°°°゛°■ Also, from the ■ equation, taking the ratio of the @ and o equations and rearranging, we get By substituting the resistance values R1 and R2 obtained as above and the constants ωl and ω2, the insulation resistance value in the electrical circuit to be measured can be obtained.

It is also clear that the following can be obtained, which means that the insulation resistance value can also be calculated using the current value flowing through the variable resistor Rv.

In the embodiment shown in FIG. 1, the filter FIL has a frequency f
It is unnecessary to explain that it should be possible to pass the 1 and fl components and remove the commercial frequency component.

Furthermore, the present invention may be modified as follows. That is, FIG. 2 is a block diagram showing another embodiment of the present invention.
The difference from the embodiment shown in the figure is that the measurement low frequency oscillators 08C1 and O8C! The filter FIL has nine signal component detection circuits connected in series and fed back to the ground line.
The filter FIL1 that selects the frequency f1 component and the frequency f! Filter FIL that extracts acid components! It is equipped with two filters, and switches these outputs to SW! It is connected by switching. In the measurement circuit connected in this way, measurements and calculations similar to those described above can be performed, but in this case, the difference from the embodiment shown in FIG. 1 is that the signal frequency is switched by the switch SWz on the filter side. Other than that, nothing else has changed.

In this case, the switch SW! W is not provided and the allowance υ is 2
Filters FILt and FILs with two rectifiers DET
It is obvious that it is also possible to connect each of the two and measure them individually.

FIG. 3 is a diagram showing still another embodiment of the present invention, in which low-frequency voltages of frequencies fx and fz are applied to the lines Ll and L without going through the ground wire, and a transformer OT is applied to the lines Ll and L. The current transformer ZCT is also passed through the electric lines Lt, L! It is possible to detect the leakage current that returns to the ground line Lm by passing it through the ground line Lm.

In the above embodiment, the connecting wire Lp is passed through the transformer OT and the current transformer ZCT'e so that they are in opposite phases.1 For example, if the connecting wire is wound N1 times around the transformer OT, the end of the 9th winding has NIV. In this case, the variable resistor R
It is clear that the value of v may be 17N1, and it is also obvious that the current transformer ZCTKNt times may be wound, or both may be wound.

In addition, if the cores of the zero-phase current transformer Z(,'T) and transformer OT are each split cores, the work on site will be much easier.

(Effects of the Invention) The present invention makes it possible to measure the insulation resistance of an electrical circuit in a live state using the method described above, and also allows for extremely easy and accurate measurement in the field even when stray capacitance is large. It is extremely effective in measuring

In the embodiments of the present invention, the case of a single-phase two-wire electric circuit is illustrated for ease of explanation; however, the present invention is not necessarily limited to this in any way; for example, a single-phase three-wire or three-phase three-wire It is unnecessary to explain that this method is similarly effective in the case of a type electric circuit.

Furthermore, as mentioned above, the variable resistor Rv is connected to the measurement frequencies fl and f! In order to minimize the feedback signal component to the ground line Lx, it is possible to automatically perform this adjustment by providing an automatic adjustment loop circuit, which would simplify the measurement. If the voltage is applied intermittently, it is possible to constantly monitor the insulation state of the electrical circuit, and it is possible to respond quickly to failures.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIGS. 2 and 3 are block diagrams showing other embodiments of the present invention, and FIG.
The figure is a block diagram illustrating a conventional insulation resistance measuring method, and FIG. 5 shows both circuits. T......Power transformer, L! and L
!・・・・・・・Electric circuit, Lg・・・・・・
...Grounding wire. O8C, 08CI, O8C*......Emitter. AMP・・・・・・Amplifier, FIL, F
ILl and FILl...Filter,
DET・・・・・・・・・ Rectifier circuit, zc
'l'・・・・・・Zero phase current transformer. OT...--Measurement signal application transformer. Lp...Connection loop, R6...
・・・・・・Insulation resistance, Co・・・・・・
...Floating capacitance above ground. R・・・・・・Variable resistor. Patent applicant: Toyo Tsushinki Co., Ltd.

Claims (2)

[Claims] (1) A connecting wire is provided through the injection transformer and the current transformer connected to the electrical circuit to be measured or the grounding wire of the electrical circuit so that the phase is opposite to that of the electrical circuit or the grounding wire, and the connecting wire is connected to a variable resistor. and applying low frequency signals with frequencies f_1 and f_2 to the electric line via the injection transformer so that the current value of each of the low frequency signals f_1 and f_2 in the output of the current transformer is minimized. An insulation resistance measuring method characterized in that the insulation resistance of the electric circuit is calculated from the value of the variable resistor when the variable resistor is adjusted. (2) The simple insulation resistance measuring method according to claim 1, wherein the connecting wire is wound around the core of the injection transformer or the current transformer, or both.