JPH01116455A - Measurement of insulation resistance compensated for ground resistance effect - Google Patents

Abstract

PURPOSE:To compensate for effect of an earth resistance by providing a core of a transformer with a low frequency voltage applied thereto and a current transformer for detecting a leakage current with a connection wire piercing in the opposite phase to an electric circuit to terminate it with a first variable capacitor. CONSTITUTION:A first variable capacitor Cv is so adjusted to minimize a low frequency leakage current component contained in an output of a current transformer ZCT and an earth electrostatic capacitance Co is detected to determine the size I1 of a low frequency component obtained after the adjustment. Then, a specified value C of capacitor is forcibly inserted between an electric circuit and the ground and the first variable capacitor Cv is so adjusted to minimize a low frequency leakage current component then contained in the current transformer ZCT and then, the size I2 of the low frequency component obtained is determined. Then, these two components I1 and I2 are used to compute (I1-K<2>I2)/(1-K<2>) [wherein K=Co/(Co+C)], thereby measuring an insulation resistance of the electric circuit.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention provides a method for measuring the insulation resistance of electric circuits, etc. in a live line state, and compensates for the influence of ground resistance, which cannot be ignored when the stray capacitance to ground is large. Concerning the simple insulation resistance method (1 method).

(Prior Art) Conventionally, in order to detect electrical leakage or the like at an early stage, it has been common to use the apparatus shown in FIG. 3 and measure the insulation resistance of an electric circuit by the method described below.

That is, the second type grounding wire LH of the receiving transformer T.

A transformer OT connected to an oscillator O8C that oscillates a low frequency signal for measurement with a frequency fl different from the commercial power supply frequency.
The electric circuit L! can be connected to the oscillator by cutting the grounding wire or cutting the grounding wire and connecting the oscillator in series with it. A low-frequency voltage for measurement is applied to L2 and L2, and the insulation resistance R existing between the electric circuit and the ground is
After detecting the leakage current that returns to the grounding line via O and the ground stray capacitance CO, this is amplified by the amplifier Ia AMP, and the filter F'IL selects only the frequency f1 component from which the commercial frequency component is removed. The voltage obtained by applying this to the rectifier DET is used to measure the insulation resistance of the electric path, and this circuit can be represented by the equivalent circuit shown in FIG.

In Fig. 4, RO is the insulation resistance of the electrical circuit under test, Co
is also a stray capacitance to the ground, and shows the case where the output signal of the measurement low frequency oscillator O8C, which is induced by the ground line LIK and flows into the electrical path to be measured, is returned to the ground line via the Ro and Co mentioned above. R is the grounding resistance between the grounding point E and the earth.

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

That is, in the figure, it is assumed that the current flowing through the oscillator O8CK of frequency f1 via the ground point E is It.

this shall be. At this time (However, ωs = 2wfl) It is.

General Y Ro>r.

(ω5cor)”<1 ・・・・・・・・・・・・
If ω1 is chosen so that By subtracting the feedback current 1 from the actual value 1, the insulation resistance RO'ft can be determined from the above-mentioned A and B.

However, in the conventional insulation resistance measuring method as described above, as is clear from the above equations (5) and (6), the floating capacitance f
When iCo is large or when the frequency ω1/2K of the applied voltage is high, the component related to stray capacitance CO becomes large, making it difficult to obtain an accurate insulation resistance RO value. There was a drawback that the influence of r could no longer be ignored, making the measurement itself impossible.

(Object of the Invention) The present invention has been made to eliminate the defects in the conventional method for measuring insulation resistance of electric circuits, and provides an insulation resistance measuring method that compensates for the influence of ground resistance. It is.

(Summary of the Invention gI) The grounding wire of the transformer or the core of the transformer to which a low-frequency voltage is applied is coupled to a current transformer for detecting leakage current, and the core of the transformer and the current transformer of the transformer are A connecting line passing through the phase trap is provided, and this is terminated with a first variable capacitor.

First, in this state, if the first variable capacitor is adjusted so that the above-mentioned low-frequency leakage current component included in the current transformer output is minimized, the ground capacitance CO is detected across K and !
iI! The magnitude of the low frequency component obtained after adjustment is determined. Next, a capacitor of a predetermined value C is forcibly inserted between the electric circuit and the ground, and the first capacitor is adjusted so that the low frequency leakage current component contained in the current transformer output is minimized. The magnitude factor 2 of the above-mentioned low frequency component obtained by the equation 1 is determined, and the insulation resistance of these two components is determined by 11.

(Example) The present invention will be described in detail below based on an illustrated example.

An embodiment of the present invention is shown in FIG. Symbols that are the same as in Figure 3 shall have the same meaning.

In Figure 1, transformer OT, current transformer ZCT, and busy line L1. Although it passes through Lg, the operations of applying a low frequency voltage to the electric circuit and detecting leakage current are completely equivalent to those in FIG. 3. The difference between this embodiment and that shown in FIG. 3 is as follows.

Electric line Ll, L! Transformer OT and current transformer ZC passed through
TK Furthermore, the connecting line Lp is passed through so as to be in the opposite phase to the electric circuit and terminated with a variable capacitor CvK, and the grounding electric line L! This is the point where the second capacitor C is connected via the pressure switch SW between the ground and the ground.

The operation of this device is as follows.

Adding the output of an oscillator that oscillates a low frequency of frequency f1 = ω1/2π to the transformer OTK, V between the stain road and the ground.
A voltage of sinω11 is applied. First, the connection line Lp
Considering the case where there is no current transformer ZCT, the output of current transformer ZCT is converted to amplifier AM
Filter F that amplifies with P and detects the ″ component of 9 frequency f=
If applied to IL.

It is expressed as

Next, a connecting wire Lp? passing through the current transformer ZCT and lance OT so as to be in opposite phase to the electric circuit. ::If it is terminated with a capacitor Cv, the current flowing through the connection line Lp is -3ωlCV÷, so the output Itl of the filter FIL at this time is as follows (8). Therefore, the filter output 11' is connected to the rectifier DET.
If applied to , the rectifier output at that time will be...
...(9) becomes.

Therefore, by adjusting the variable capacitor Cv so that the output of the rectifier becomes the minimum, the ground capacitance of the stain path, which is minimum when Co=Cv, can be measured from the value of the capacitor Cv, and when Co=Cv. If the rectifier output at that time is It, then the following equation is obtained.

Next, a capacitor C of a predetermined value is inserted between the one-car constant current path and the ground. For example, as shown in the same figure, this is the ground phase (
Here, it is sufficient to connect the capacitor C to the ground via the switch SW, and when the capacitor C is inserted (when the switch SW' is on, the filter FIL output Ig
'Hai! ″=(±+ω1m (Co −)C)” r +
jωt (Co+C−Cv))R.

V ++ ...... (Company) Therefore, if the filter output is applied to the rectifier DET and the variable capacitor Cv is adjusted so that the rectifier output becomes the minimum, it becomes the minimum when Co+C=Cv, If the rectifier output at this time is 2, it will be from the wholesale type. Also, in this case, (Co+C=Cv) (9) formula becomes (goods) formula (to), so if we take the ratio of formula (2), = is...
......(2) If we further transform equation (2), we get the following.

That is, by calculating 9k shown in equation (g) from the measured ground capacitance Co and the value of capacitor C, and substituting the measured values It and I into equation (v), the stain path can be calculated. can measure the insulation resistance of

Similarly, in the above example, a single-phase, two-wire electric circuit was used, but measurements can be made in the same way with other single-phase, three-wire, three-phase, three-wire, etc. electric circuits.

Also, in the above example, the connecting wire is simply a transformer OT and a current transformer ZC.
9 For example, connect the connecting wire to the transformer O.
If only T is wound N times, the current flowing through the connecting wire is -jω
1cvNV, which means the value of capacitor Cv is 1/N
This is equivalent to the fact that it may be The same effect can be obtained even if only the current transformer ZCT is wound N times. Furthermore, by winding both of them a predetermined number of times, it is possible to reduce the value of the capacitor Cv by the product of each.

Furthermore, in the above explanation, the capacitor Cv was used to flow a current that is phase shifted by 0 degrees from the low frequency voltage applied to the connection line Lp, but in order to flow such a current, a capacitor Cv is used to flow through the transformer OT as shown in Fig. 2. The wound conductor Lq is connected to a 90 degree phase shifter p.
To apply sK, generate a voltage with a phase shift of 0 degrees from the applied voltage, apply the output to the power amplifier PAMP, and connect the conductor Lr, which is passed through or wound around the current transformer, with the resistor Rv. If the current flowing through the conductors I and q is in reverse phase with the current flowing through the ground capacitance through the circuit, then adjust the value of the resistor Rv.
It is clear that an equivalent function can be realized by adjusting the capacitor Cv shown in the figure.

Alternatively, the value of the resistor RV may be fixed and the output voltage of the power amplifier may be varied and adjusted.

(Effects of the Invention) As explained above, the method of the present invention can compensate for the influence of grounding resistance, so it is possible to increase the frequency of the applied voltage compared to the conventional method, and it is possible to miniaturize the transformer OT. However, it is effective in realizing a compact measuring instrument.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, and FIG. 3 is a diagram explaining a conventional method.
FIG. 4 is a diagram showing both circuits of a system for measuring insulation resistance of electric circuits. T・・・・・・Power receiving transformer, ZCT・
・・・・・・・・・Current transformer, OT・・・・・・・
··Trance. AMP......Amplifier, FIL...
・・・・・・Filter, DBT・・・・−・
... Rectifier, OSC ...... Oscillator, SW ...... Switch. Patent applicant: Toyo Tsushinki Co., Ltd.b・11JZ Co., Ltd.

Claims (1)

[Scope of Claims] 1. The core of a transformer that applies a low frequency voltage directly to the grounding wire or electrical circuit of the transformer and the current transformer that detects leakage current are passed through, and the core of the transformer and the current transformer are connected to the A new connecting wire is provided that passes through the ground wire or the electrical circuit so as to be in reverse phase, and a first capacitor is inserted into the connecting wire, so that the low frequency component contained in the output of the current transformer is removed. The value of the first capacitor is adjusted to minimize the magnitude of the low frequency component obtained in this state, and the value of the first capacitor is adjusted to minimize the magnitude of the low frequency component obtained in this state. The low frequency component contained in the current transformer output obtained by the size and value of the first capacitor and the state in which a second capacitor of a predetermined value is inserted between the electric circuit and the ground is minimized. The effect of grounding resistance is characterized in that the insulation resistance of the electrical circuit is calculated using the magnitude of the low frequency component obtained by adjusting the value of the first capacitor and the value of the second capacitor. Insulation resistance measurement method that compensates for 2. A method for measuring insulation resistance that compensates for ground resistance as set forth in claim 1, wherein the connecting wire is wound around the core of the transformer or the current transformer, or both. .