JP2942892B2 - Measurement method of insulation resistance of ungrounded circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring the insulation resistance of an electric circuit, and more particularly to a method for measuring the insulation resistance of an ungrounded electric circuit.

(Prior Art) Various methods have been proposed for measuring or monitoring the insulation resistance of an electric circuit of an ungrounded electric circuit, generating an alarm when the insulation resistance becomes equal to or less than a predetermined value, and notifying a danger.

As a conventional method for measuring the insulation resistance of an ungrounded circuit, a DC power supply or a low-frequency power supply is applied through a neutral point or between the circuits via a high resistance, and a current is fed back from the power supply via the insulation resistance. A neutral point in the electrical circuit, ground the neutral point with a high resistance, and measure the insulation resistance from the leakage current of the commercial frequency that is fed back through the insulation resistance. There is a method to do.

However, the former method requires a DC or low-frequency power supply for measurement, and when insulation deterioration near the ground fault occurs on the electric circuit, there is a danger that the power supply will be damaged and other accidents will occur. The latter method has the drawback that it is difficult to measure the insulation resistance accurately due to the influence of the earth capacitance of the electric circuit, and it is desired to develop a simple and accurate method and apparatus for measuring the insulation resistance of the electric circuit. Was rare.

(Object of the Invention) The present invention has been made to solve the problems of the conventional method for measuring the insulation resistance of an ungrounded electric circuit as described above, and newly measures the electric circuit by using a leakage current of a commercial frequency. It is an object of the present invention to provide an accurate method for measuring insulation resistance which does not require a power supply for use and does not cause a measurement value to vary due to a stray capacitance of a circuit to ground.

(Summary of the Invention) In order to achieve this object, a method for measuring the insulation resistance of an ungrounded electric circuit according to the present invention is to ground one of the ungrounded electric circuits of the electric circuit voltage V via a capacitor having a capacitance C0. Then, the active component current value a1 in phase with the circuit voltage flowing through the capacitor C0 and the reactive component current value b1 orthogonal to the circuit voltage are detected, and the other non-grounded circuit is connected via the capacitor having the capacitance C0. The active component current value a2 in phase with the circuit voltage flowing through the capacitor when grounded and the reactive component current value b2 orthogonal to the circuit voltage are detected, and the sum a of the valid component current values a1 and a2 is detected.
And using the sum b of the reactive current values b1 and b2 to calculate the leakage current i due to only the ground insulation resistance without being affected by the ground capacitance of the ungrounded circuit. Is characterized by being calculated and measured using

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

FIG. 1 is a diagram showing the principle of an insulation resistance measuring method for an ungrounded electric circuit, where T1 is a transformer, and 1 and 2 are transformers T1.
And Z is a load connected to the non-grounded electric circuit.

The insulation resistance of the load Z and the ungrounded electric circuits 1 and 2 are R1 and R2, the ground capacitance is C1 and C2, the commercial frequency is ω / 2π, and the electric circuits 1 and 2 are connected to a capacitor C0 via a switch SW. When the switch SW is connected to the ungrounded electric circuit 1 side as shown in FIG. 2, an equivalent circuit can be represented as shown in FIG.

At this time, the current flowing through the capacitor C0 provided on the ground line 3
i1 Becomes

(However, the circuit voltage is assumed to be V.) An equivalent circuit when the switch SW is connected to the ungrounded circuit 2 side can be represented as shown in FIG. The current i2 flowing through C0 is Becomes

That is, the currents a1 and a2 represented by the formulas and the formulas are components (effective components) in phase with the applied voltage, while the currents b1 and b2 represented by the formulas and the formulas are components (ineffective components) orthogonal to the applied voltage. is there.

Even if the active component currents a1 and a2 and the reactive component currents b1 and b2 are simply detected, these currents are inherently related to the ground insulation resistances R1 and R2 and the ground capacitances C1 and C2. Cannot be obtained.

In order to measure the insulation resistance to the ground without being affected by the capacitance to the ground, the insulation resistance measuring method according to the present invention performs the following calculation.

That is, assuming that the sum of the effective component currents a1 and a2 is a,
From the formula It can be expressed as.

Similarly, assuming that the sum of the reactive currents b1 and b2 is b, from the equation, Becomes

Then the expression is Can be converted to Substituting expressions into expressions and rearranging Becomes

Accordingly, the following equation is established, irrespective of the ground capacitance from the equation.

Furthermore, when rearranging the formula, And from the formula In-phase currents a1 and a2 and quadrature currents b1 and b2
, A and b are obtained by adding the equations to obtain a known V,
If the calculation on the right side of the equation is performed using ω and C0, the insulation resistance R1,
It can be seen that the leakage current can be measured by the parallel combined value of only R2.

The in-phase and quadrature current values can be obtained by synchronously detecting the leakage current of the equation with the circuit voltage or a voltage shifted by 90 ° from the circuit voltage, or by using a known technique. it can.

In the above description, the current flowing through the capacitor C0 is measured, but the voltage across the capacitor C0 may be measured.

Measuring the voltage across the capacitor C0 is equivalent to measuring the voltage between the electric circuit and the ground. For example, when the switch is connected to the electric circuit 1, the voltage between the electric circuit 1 and the ground is measured.

Capacitor when switch SW is connected to circuit 1
The voltage V1 across C0 is The voltage V2 across the capacitor C0 when the switch SW is connected to the circuit 2 is given by It can be expressed as.

If the sum of the common mode voltage Va1, Va2 and Va, the Va = Va ₁ + Va ₂ ··· next ,, formula Becomes

If a and Vb sum of orthogonal partial voltage values Vb1, Vb2 _{Similarly, Vb = Vb 1 + Vb 2} ···, from equation And, furthermore, the equation is Similarly the formula is Becomes Therefore, more The following relationship can be obtained, and the calculation can be performed without the influence of the ground capacitance as shown in the following expression.

If you further organize the formula Becomes

Therefore, the in-phase and quadrature voltages of the voltage across the capacitor C0 (the voltage between the circuit and the ground) are measured when the circuits 1 and 2 are grounded by the capacitor C0, respectively, and the equation is calculated to calculate the insulation resistance of the circuit. Can be calculated and measured.

It should be noted that the formula can be modified, and various modifications can be made based on the principle of the present invention so that the calculation can be easily performed.

FIG. 4 is a view showing the configuration of an apparatus for implementing the above-described insulation resistance measuring method, and the same parts as those in FIG. 1 are denoted by the same reference numerals.

One of the ungrounded circuits 1 and 2 of the circuit voltage V is switched by a switch SW, grounded via a capacitor C0, and the voltage across the capacitor C0 is amplified by a high input impedance amplifier AMP and flows to the capacitor C0. Measure the current.

The output of the amplifier AMP is input to one input terminal of each of a first synchronous detector M1 and a second synchronous detector M2, and the other input terminal of the first synchronous detector M1 is connected to electric circuits 1 and 2. The secondary output of the connected transformer T2 is applied, and the secondary output of the transformer T2 is input to the other input terminal of the second synchronous detector M2 via a 90-degree phase shifter PS.

The output of each of the synchronous detectors M1 and M2 is supplied to an arithmetic circuit CP having a storage circuit provided in the next stage.

First, when the switch SW is connected to the ungrounded electric circuit 1 side as shown in the figure, the output of the amplifier AMP, which is the voltage across the capacitor C0, is an output proportional to the equation, and the output of the amplifier AMP is the first. And the other input terminal of the first synchronous detector M1 is applied with a voltage having the same phase as the circuit voltage via the transformer T2, and thus is applied to the synchronous detector M1 and the second synchronous detector M2. An effective component voltage value Va1 corresponding to the equation is output to the output terminal of the synchronous detector M1. On the other hand, the circuit voltage obtained from the transformer T2 is applied to the other input terminal of the second synchronous detector M2.
Since a voltage shifted by 90 ° is applied through the 90 ° phase shifter PS, an invalid voltage value Vb1 corresponding to the equation is output to the output terminal of the synchronous detector M2. The output of each of the synchronous detectors M1 and M2 is applied to an arithmetic circuit CP provided in the next stage, and is stored in a storage circuit (not shown) provided in the arithmetic circuit CP.

Next, when the switch SW is connected to the ungrounded circuit 2 side, the amplifier
An output corresponding to the expression appears at the output terminal of the AMP.

Therefore, as described above, an effective component voltage value Va2 corresponding to the equation is provided at the output end of the synchronous detector M1, and the synchronous detector M1
An invalid component voltage value Vb2 corresponding to the equation is output to the output terminal of No. 2 and the effective component voltage value Va1 already stored in the arithmetic circuit CP is stored.
And the detected effective component voltage value V2a are added to obtain an effective component voltage value V2a.
a is added to the previously stored invalid component voltage value Vb1 and the detected invalid component voltage value Vb2 to calculate the invalid component voltage value Vb.

Next, the calculated effective component voltage value Va and the invalid component voltage value Vb
By performing the operation of the expression by using, the output terminal OUT of the operation circuit CP That is, a leakage current is output only from the insulation resistance of the electric circuits 1 and 2.

In the embodiment of the present invention, an example using the voltage between both ends of the capacitor C0 has been described.However, a current flowing through the capacitor C0 is detected by a current detector, and an equation is calculated by the same method as in the above embodiment. Also leakage current It is clear that can be measured.

Although the method of obtaining the measurement result by the current value has been described, the measurement result may not be displayed by the current value, but may be directly displayed by the insulation resistance state.

(Effects of the Invention) Since the present invention is constructed and functions as described above, it is not necessary to use a new signal source in measuring the insulation resistance of the ungrounded electric circuit, and the measurement is performed by the capacitance of the electric circuit to ground. Because the insulation resistance measurement result does not change,
It has a remarkable effect in accurately measuring the insulation resistance of an electric circuit without using expensive equipment.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of the insulation resistance measuring method according to the present invention, FIGS. 2 and 3 are equivalent circuit diagrams of the circuit shown in FIG. 1, and FIG. FIG. 2 is a circuit configuration diagram for implementing a method of measuring insulation resistance of a ground circuit. T1, T2… Transformer 1, 2… Ungrounded electric circuit 3… Connection line SW… Switch R1, R2… Insulation resistance to ground C1, C2… Capacitance to ground C0… Capacitor Z… Load AMP… … Amplifier M1, M2 …… Synchronous detector PS …… 90 ° phase shifter CP …… Operation circuit

Claims (1)

(57) [Claims] When one of the non-grounded circuits of the circuit voltage V is grounded via a capacitor having a capacitance C0,
Effective component current value in phase with circuit voltage flowing through capacitor C0
a1 and the reactive component current value b1 orthogonal to the circuit voltage are detected, and the active component current value in phase with the circuit voltage flowing through the other ungrounded circuit when the other non-grounded circuit is grounded via a capacitor having a capacitance C0. Reactive component current value orthogonal to a2 and circuit voltage
b2, and by using the sum a of the effective component current values a1 and a2 and the sum b of the reactive component current values b1 and b2, without being affected by the ground capacitance of the ungrounded electric circuit. 3. A method for measuring insulation resistance of an ungrounded electric circuit, wherein a leakage current i is measured only by a ground insulation resistance.