JP2750690B2 - Leakage current detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring insulation resistance of an electric circuit or the like by detecting leakage current of the electric circuit or the like.

(Prior Art) Conventionally, it has been general to detect a leakage current by a method as shown in FIGS. 5 and 6, for example, in order to find a trouble due to an insulation failure of an electric circuit at an early stage.

These oscillators OSC in different frequencies ₁ and commercial frequency ground line L _E or path 2 of the transformer T with the load Z
Connected to or penetrated by the injection transformer OT connected to the
Ground line zone leakage current which returns to the ground line L _E of the transformer via the earth capacitance C is detected by the current transformer ZCT that penetrates the path, after amplifying the output by the amplifier AMP, the filter FIL
Select only the component of frequency ₁ by L and use the output signal of the oscillator OSC, for example, to synchronously detect it with the synchronous detector MULT, detect the leakage current component in phase with the injection voltage, and measure the insulation resistance of the circuit. Or when the ground capacitance C is sufficiently small and the frequency ₁ is sufficiently low, the output of the filter FIL is simply rectified to estimate the insulation resistance R of the electric circuit.

However, in the conventional method as described above, the current transformer ZCT is used to detect the leakage current, so that it is not only extremely expensive, but also has a problem such as a change in phase characteristics due to a temperature change. Therefore, there is a disadvantage that a complicated compensation circuit is required.

(Object of the Invention) An object of the present invention is to provide a method for correctly detecting a leakage current without using a current transformer, which is necessary for the conventional leakage current detection as described above.

SUMMARY OF THE INVENTION The present invention in order to achieve the object, comprising a frequency f ₁ to the primary winding is inserted connecting the transformer secondary winding directly or electrical path of the connecting line between the tracks and ground AC connects the voltage source and resistor R ₁ in series, it connects the output of the AC voltage source to the resistor r ₀ and the series circuit composed of a capacitor c ₀ Prefecture,
The resistance R ₁ of the voltage across e and the voltage across the capacitor c ₀
In this configuration, the insulation resistance between the electric circuit and the ground is obtained using the difference e-ep from ep.

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

First, the theory of the present invention will be described in a little more detail prior to the description of the embodiments to assist understanding of the present invention.

Fig. 3 shows leakage when the secondary winding of the injection transformer OT connected to the oscillator OSC is inserted and connected to the ground line of a transformer or the like and the output voltage is applied to the circuit, and returns to the ground line via the circuit. FIG. 3 is a diagram illustrating an equivalent circuit of a system through which current flows.

As shown in the figure, the signal applied to the electric circuit from the secondary side of the injection transformer OT flows to the ground via the insulation resistance R and the ground capacitance C, and further reaches the transformer via the ground line. On the other hand, the primary side of the transformer is an oscillator O with an oscillation frequency of ₁ and output voltage e _s
SC is connected via a resistor R _1. Now, the injection transformer OT
Let L _{1 be the} primary inductance and L be the secondary inductance.
If L ₂ , M is the mutual inductance, n is the turns ratio, i _{1 is the} primary current of the injection transformer, and i _{2 is} the secondary current, the oscillator
Loop voltage across the voltage v _s and the transformer secondary circuit OSC is expressed as the respective following formula.

Vs = (R ₁ + jω ₁ L ₁ ) i ₁ + jω ₁ Mi ₂ ... (Z ₂ + jω ₁ L ₂ ) i ₂ + jω ₁ Mi ₁ = 0... Where Z ₂ is the loop impedance of the transformer primary side circuit so Is represented by

And erasing the current i ₂ Assuming that the coupling coefficient between the primary and secondary of the injection transformer OT is 1, Therefore, if the above equation is substituted into the equation and L ₂ and M are eliminated, It is expressed as

Substituting the equation into the above equation to eliminate Z ₂ further And the voltage e between both ends of the resistor R ₁ is e = R ₁ i ₁ ... In general, since the insulation resistance R of the electric circuit is relatively large, the winding ratio n of the transformer is increased and the frequency ω1 / 2π
If you lower Since the relationship is established, Becomes Toba Becomes

On the other hand, as shown in FIG. 4, the addition of the oscillator output V _s in series circuit of the resistor r ₀ and capacitor C _0, the voltage across ep of the capacitor C ₀ is And the values of the capacitor C ₀ and the resistance r ₀ are If you choose to become Becomes Thus the voltage across e and the capacitor C ₀ of the resistor R ₁
The difference between the voltage across e _p of the, from the formula Expressed as the measured value inversely proportional to the insulation resistance R by detecting the voltage e-e _p that can be obtained can be seen.

Further, the voltage across the at resistor r ₀ in FIG. 4 e _r, the voltage across the primary winding of the at injection transformer OT in Fig. 3 if e _o Thus, e-e _p = e _{and r} becomes -e _o ........., detects the voltage across e ₀ of the voltage across e _r and the primary winding of the resistance r _0, the relationship be determined the difference Is obtained.

 Hereinafter, embodiments of the present invention will be described in detail.

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

In the figure, T is a receiving transformer, and 1 and 2 are 2 of the transformer T.
A next-side electrical path, the power line 2 is grounded by a ground line L _E,
Bonded or otherwise connected to the secondary winding of the injection transformer OT to the ground line L _E. The primary side of the injection transformer OT has a frequency
With an oscillator OSC that generates _a composed signal voltage is connected through a resistor R _1, said oscillator OSC resistor r ₀ and capacitor C ₀ is connected in series, the amplifier A ₂ at both ends of the capacitor C ₀ is Provided. Further, the output terminal of the amplifier A ₂ is one other input terminal connected to the first input terminal of the subtracter SUB connects the output terminal of the amplifier A ₁ which is connected to both ends of the resistor R _1.

A filter FIL and a rectifier DET are connected to an output terminal of the subtractor SUB.

Thus At a configuration the circuit, the output of the amplifier A ₁ which is connected to both ends of the resistor R ₁ is the voltage e applied occurs in the above formula, wherein the output of the amplifier A ₂ on both ends of the capacitor C ₀ A voltage e _p given by the equation results.

As mentioned earlier here That is (Where L ₁ is the primary inductance of the injection transformer OT)
If the values of the resistor r ₀ and the capacitor C ₀ are selected so that the output voltage of the amplifier A ₂ becomes as shown in the above equation, Given by

Furthermore, each output of amplifier A ₁ and the amplifier A ₂ s subtraction circuit SUB
If applied to the output of the cited calculation circuit SUB e-e _p becomes voltage corresponding to the formula is obtained by applying the output to the filter FIL to detect only a component of frequency _1, by rectifying the output For example, the output OUT1 can obtain a voltage inversely proportional to the insulation resistance R as is apparent from the above equation. Here, the filter FIL is for removing a commercial frequency component from the leakage current returning to the ground line.

FIG. 2 is a block diagram showing another embodiment of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals.

In this figure, the difference from the embodiment of FIG. 1 described above is that the output of the filter FIL is connected to one input terminal of a synchronous detector MULT.
The point that the output of the oscillator OSC is applied to the other input terminal of the MULT to detect an in-phase component with the injection voltage in the output of the filter FIL, thereby obtaining an output inversely proportional to the insulation resistance R.

If the circuit is configured as described above, the insulation resistance R can be known without using a current transformer.

In this embodiment, the secondary side of the injection transformer OT has been described as being connected to the ground line. However, the present invention is not limited to this. The measurement may be performed by using a method, and the type of the electric circuit is described using a single-phase two-wire system in the present embodiment. However, it may be used for other electric circuits such as a single-phase three-wire system. it is obvious. Further, the electric circuit is not limited to the electric power transmission line, but can be widely applied to a conductive path used for other purposes such as an antenna.

Further, the resistor r ₀ and the capacitor C ₀ are used to generate the voltage e _p in the equation, but the present invention is not limited to this.
-E _p is clear that it is possible but with differences in the resistance R ₁ and the capacitor C ₀ Each of the voltage across obtain a voltage corresponding to the voltage e-e _p in other detection methods.

(Effect of the Invention) Since the present invention is constructed and functions as described above, it is possible to measure the insulation resistance without using a current transformer. Since the phase characteristic does not fluctuate due to the temperature change and aging of the current transformer which must be considered when using the current transformer, the present invention is extremely effective in obtaining a highly accurate measurement result.

[Brief description of the drawings]

1 and 2 are block diagrams showing an embodiment of the present invention, FIGS. 3 and 4 are block diagrams for explaining the principle of the present invention, and FIGS. 5 and 6 are conventional measurement methods. It is a block diagram showing a method. T ...... receiving transformer, 1, 2 ...... paths, L _E ...... ground line, MULT
…… Synchronous detector, AMP, A ₁ , A ₂ …… Amplifier, OSC …… Oscillator,
OT …… Injection transformer, ZCT …… Current transformer, DET …… Rectifier, FIL
…… Filter, Z …… Load.

Claims (1)

(57) [Claims] 1. A a path directly between ground or an AC voltage source comprising a frequency f ₁ to the primary winding with the secondary winding of the transformer to the power line of the connection line is inserted and connected between the resistor R ₁ in series connected in series circuit comprising the output of the alternating voltage source from the resistor r ₀ and a capacitor c ₀ Metropolitan with connecting, the difference e-ep the voltage across ep across voltage e and the capacitor c ₀ of the resistor R ₁ A method for detecting a leakage current, wherein an insulation resistance between the electric circuit and the ground is obtained by using a method.