JP2002131362A - Leakage current measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure only a leakage current Igr component due to equivalent insulation resistance to the ground so as to be able to judge whether an electric apparatus and the like is in a good condition or not. SOLUTION: This leakage current measurement device is provided with a current trans-sensor 2 for detecting a leakage current flowing through a measured electric line or a ground line, a current-voltage conversion circuit 3, a voltage amplifying circuit 4, a voltage dividing amplifying circuit 6 dividing a circuit voltage of a voltage line in the measured electric line 1 and amplifying it, a multiplication circuit 5 multiplying an output of the voltage amplifying circuit 4 and an output of the voltage dividing amplifying circuit 5 together, a low-pass filter 7, a leakage current displaying circuit 8 displaying the leakage current signal Igr serving as an output signal from the low-pass filter 7, a leakage current comparing judgement circuit 9 judging whether the leakage current signal is above a specified value or below it, a judgement result displaying circuit 10 indicating the judgement result of the leakage current comparison determining circuit 9, and a polarity determining circuit 19 determining whether the current trans-sensor 2 is connected normally or reversely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leakage current measuring device for determining the quality of insulation of electric equipment by measuring the leakage current, and more particularly to a leakage current component which is inversely proportional to the level of equivalent ground insulation resistance. The present invention relates to a leakage current measuring device capable of measuring.

[0002]

2. Description of the Related Art Hitherto, in order to judge the quality of insulation of electric equipment and electric appliances, measurement has been carried out using a leak clamp tester or an insulation resistance meter.

[0003]

By the way, when trying to measure the leakage current using a conventional leak clamp tester, the leakage current (Igc) due to the capacitance to ground and the leakage current (Igr) due to the equivalent insulation resistance to ground are measured. However, there is a problem that only Igr, which is truly related to the quality of insulation of electrical equipment and appliances, cannot be measured.

In order to measure the insulation state of electrical equipment and appliances using an insulation resistance meter, it is necessary to temporarily stop the electrical equipment and measure the insulation resistance between the line and ground.

The present invention has been proposed in order to solve the problems of the prior art, and can perform measurement without stopping the operation of electrical equipment, and can measure the leakage current (equivalent to the equivalent ground insulation resistance). It is an object of the present invention to provide a leakage current measuring device capable of measuring only the Igr) component to determine the quality of the insulation state of the electrical equipment and determining the normal / reverse connection state of the current transformer sensor.

[0006]

In order to achieve this object, a leakage current measuring device according to the present invention detects a leakage current which is clamped on a measured electric wire or a ground wire and flows through the measured electric wire or a ground wire. A current transformer sensor,
A current-voltage conversion circuit for converting the output signal of the current transformer sensor into a voltage signal, a voltage amplification circuit for amplifying the output signal of the current-voltage conversion circuit, and a voltage line of the electric wire to be measured; A voltage dividing circuit that divides and amplifies a circuit voltage, a multiplying circuit that multiplies an output of the voltage amplifying circuit by an output of the voltage dividing amplifying circuit, and a harmonic component from an output signal of the multiplying circuit. A low-pass filter to be removed, a leakage current display circuit for displaying a leakage current signal which is an output signal of the low-pass filter, and a leakage current comparison / judgment circuit for judging whether the leakage current signal exceeds a prescribed value or less than a prescribed value And a judgment result display circuit for displaying the judgment result of the leakage current comparison judgment circuit.

According to the above-described configuration, the leakage current flowing through the measured electric wire or the ground line is converted into a voltage signal, then amplified and added to the multiplying circuit, and the voltage applied to the voltage line of the measured electric wire is divided. The voltage is amplified and input to the multiplication circuit, and the multiplication circuit multiplies both signals to obtain a leakage current signal including harmonics. If harmonics are removed from the output signal of this multiplying circuit through a low-pass filter, it is possible to detect only a leakage current (Igr) component caused by an equivalent ground insulation resistance flowing through the electric line or the ground line to be measured. The leakage current (Igr) component is displayed on the display circuit, and the result of the comparison of the leakage current is displayed on the display circuit.

[0008] Further, the leakage current measuring apparatus according to the present invention comprises:
The output of the voltage amplification circuit and the output of the voltage division amplification circuit are input, the phase difference between the two signals is detected, and the leakage current signal has an opposite phase to the voltage signal of the electric wire to be measured. In this case, a polarity determination circuit for outputting an alarm signal is provided.

According to the configuration described above, an alarm is issued when the leakage current signal has an opposite phase to the voltage signal of the electric line to be measured in the polarity judgment circuit. It can be determined whether the connection state is reverse clamped.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a leakage current measuring device according to the present invention. In this figure, the output (leakage current ig) of the current transformer sensor (CT sensor) 2 clamped on the entire electric wire 1 to be measured.
Is sent to the current-voltage conversion circuit 3. The output of the current-voltage conversion circuit 3 is sent to a multiplication circuit 5 after being amplified by a voltage amplification circuit 4. On the other hand, the switching contact piece RY1-1 of the relay connected to the voltage line of the electric wire 1 to be measured is switched by the circuit voltage determination selection circuit 11. The output of the circuit voltage judgment and selection circuit 11 is sent to the measurement circuit voltage display circuit 12 and the circuit voltage of the voltage line of the electric wire under test 1 becomes 1
When the voltage is 00 V, the green indicator LED 6 is turned on, and when the circuit voltage is 200 V, the red indicator LED 7 is turned on. Further, the circuit voltage of the voltage line of the electric wire under test 1 is sent to the voltage dividing amplifier circuit 6 via the switched contact piece RY1-1 of the relay, and the output of the voltage dividing amplifier circuit 6 is multiplied by the multiplying circuit 5 Sent to

In the multiplication circuit 5 in which the outputs (vy, vz) of the voltage amplification circuit 4 and the voltage division amplification circuit 6 are multiplied,
A leakage current signal including a harmonic component is obtained. In the active low-pass filter 7 connected to the multiplication circuit 5,
This harmonic component is removed, and a leakage current (Igr) component due to the equivalent ground insulation resistance that is truly related to insulation quality is obtained.

The leakage current signal output from the active low-pass filter 7 is displayed on a display circuit 8 and sent to a leakage current comparison / judgment circuit 9. In the judgment result display circuit 10 connected to the leak current comparison and judgment circuit 9, when the leak current (Igr) is equal to or less than the standard value of 30 mA, the indicator LEDs 1 to 5 are turned on in a stepwise manner, and the leak current (Igr) Is more than 30mA, the indicator LED1-5
Is turned on and an alarm is issued.

Next, a circuit configuration for detecting whether or not the polarity of the clamped state of the current transformer sensor 2 to the electric wire 1 to be measured is suitable will be described. The output signal V1 of the voltage amplification circuit 4 obtained by converting the leakage current into a voltage and the output signal V2 of the voltage division amplification circuit 6 for extracting the voltage division signal of the electric wire under test 1 are sent to the addition / subtraction circuit 17. The output signal V of the addition / subtraction circuit 17 is given by the following equation. V = V2−V1 (1) When the polarities of the current transformer sensor 2 are compatible and V1 and V2 are in phase. V1 = Vm1 · sin ωt V2 = Vm2 · sin ωt V = V2−V1 = Vm2 · sin ωt−Vm1 · sin ωt =
(Vm2−Vm1) sin ωt In this equation, if Vm2−Vm1 = 0, that is, if Vm2 = Vm1, then V = 0.

(2) The case where the polarities of the current transformer sensor 2 do not match, and V1 and V2 are in opposite phases. V1 = Vm1 · sin (ωt ± π) V2 = Vm2 · sin ωt V = V2−V1 = Vm2 · sin ωt−Vm1 · sin (ωt ±
π) = (Vm2 + Vm1) sin ωt If Vm2 = Vm1, then V = 2Vm2 · sin ωt.

(3) Judgment of Polarity The output V of the addition / subtraction circuit 17 is sent to a comparison circuit 18 and compared with a reference voltage Vr. When the comparison result satisfies V <Vr, the phases are the same, and the polarities of the current transformer sensors 2 match. On the other hand, when the comparison result is V> Vr, the phases are in opposite phases, and the polarity of the current transformer sensor 2 is incompatible. Emits. When an alarm is given, the clamp state of the current transformer sensor 2 to the electric wire 1 to be measured may be reversed and reconnected. Here, the addition / subtraction circuit 17 and the comparison circuit 18 are connected to a polarity determination circuit 19.
Is composed.

Next, a specific circuit configuration of the leakage current measuring device shown in FIGS. 2 to 4 will be described. In this figure, a resistor R1 to which a current transformer sensor 2 is connected forms a current-voltage conversion circuit 3. A part of the IC1 including the resistors R2, R3, the variable resistor VR1, and the operational amplifier at the next stage to which the current-voltage conversion circuit 3 is connected forms the voltage amplification circuit 4. On the other hand, a part of the IC 3 composed of an operational amplifier connected to the voltage line of the electric wire 1 to be measured, a part of the IC 8, the transistor Tr 3, the relay RY 1, and the peripheral circuit elements constitute a circuit voltage determination selection circuit 11. . In addition, IC8
A part of the transistor Tr5 is an indicator light LED
6. The measurement circuit voltage display circuit 12 for selectively lighting the LED 7 is configured. Further, resistors R10 and R13, a variable resistor VR4, and a resistor R1 that are connected to the voltage line of the electric wire 1 to be measured via the switched contact piece RY1-1 of the relay RY1.
1, a part of the IC 2 including the R73 and the operational amplifier, and peripheral circuit elements constitute a voltage dividing amplifier circuit 6.

Further, a part of the IC 1, the transistor Tr
1, Tr2, a part of the IC2, and peripheral circuit elements constitute a multiplication circuit 5 that multiplies both outputs of the voltage amplification circuit 4 and the voltage division amplification circuit 6. Further, a part of IC2, resistors R20 and R21, capacitors C6 and C7 and circuit elements
Removing harmonic components from the output signal Vout of the multiplication circuit 5,
An active low-pass filter 7 for extracting only a leakage current (Igr) component due to an equivalent ground insulation resistance is configured.

IC7 and 7-segment display elements SE1 to SE1
Reference numeral 4 denotes a display circuit 8 for digitally displaying the leakage current (Igr) output from the active low-pass filter 7. The IC3 and IC4 comprising the operational amplifier, the transistor Tr5, and the peripheral circuit elements constitute a leakage current comparison and determination circuit 9 and a determination result display circuit 10. The IC 9 composed of an operational amplifier and peripheral circuit elements constitute a polarity determination circuit 19. The transistor Tr4 is
The buzzer drive circuit 20 is configured.

Next, the basic concept of the present invention will be described. First, assuming that the instantaneous value of the circuit voltage of the voltage line of the electric line 1 to be measured is v and the instantaneous value of the leakage current is ig, v and ig are given by the following equations. v = Vm · sin ωt (1) ig = Im · sin (ωt + θ) (2) where Vm is the maximum value of the voltage and Im is the maximum value of the current. Subsequently, the output voltage signals vz, vy of the voltage dividing amplifier circuit 6 and the voltage amplifying circuit 4 are as follows: vz = (Vm / n) A1 sinωt
(3) where n is a voltage division ratio, and A1 is a voltage amplification factor of the voltage division amplification circuit 6. vy = (Im / K1) R1 A2 · sin (ωt + θ)
.. (4) where K1 is the current transformer ratio of the current transformer sensor 2 constituting the current transformer, and R1 is the input resistance for voltage conversion. A2 is a voltage amplification factor of the voltage amplification circuit 4.

Subsequently, the output signal Vout of the multiplication circuit which multiplies both outputs vy and vz of the voltage amplification circuit 4 and the voltage division amplification circuit 6 is given by the following equation. Vout = (vy / 10) (vz / vx)) = C ・ vy ・ vz (5) where C = (1 / 10vx). Substituting the equations (3) and (4) into the equation (5), Vout = C (Im / K1) R1 A2sin (ωt + θ) (V
m / n) A1 sin ωt = K0 Vm Im · sin (ωt + θ)
· Sin ωt (6) where the constant K 0 = (C
R1 A1 A2) / (K1 n). If the effective value of the voltage is V and the effective value of the leakage current is Ig, Vm and Im are Vm = 2 · Vim = 2 · Ig. Therefore, if both equations are substituted into (6), Vout = K0
(2VIg) · sin (ωt + θ) · sin ωt. Here, if α = ωt + θ and β = ωt, Vout = 2K0 VIg · sin α · sin β

Subsequently, from the formula for converting the product of trigonometric functions into a sum, Vout = 2K0 VIg ｛cos (α-β) -cos (α +
β)｝ / 2 (7). Here, since α−β = (ωt + θ) −ωt = θ α + β = (ωt + θ) + ωt = 2ωt + θ, the equation (7) is expressed as follows: Vout = K0 VIg ｛cos θ
−cos (2ωt + θ)｝ (8) The signal voltage Vout expressed by the equation (8) is converted to an operational amplifier A
When added to the active low-pass filter 7 using the term 7, the term that fluctuates at twice the frequency 2ωt of the second term in the parentheses in the equation (8) can be cut off, and only the first term is obtained as an output signal. .

Therefore, Vout is only a DC component irrespective of the frequency (time). Vout = K0 VIg · cos θ = K2 Ig · cos θ Here, it is assumed that K2 = K0V. Thus, the output signal V
out is the leakage current (Igr = Ig · c) due to equivalent ground insulation resistance.
os θ). If the input resistance R1, the voltage amplification factors A1 and A2, and the voltage vx are determined so that K2 = 1, then Vout = Igr, and it is possible to directly display the leakage current Igr on the digital meter DP1 and read the indicated value. it can.

As described above, according to the present invention, in principle, the current I due to the ground capacitance included in the entire leakage current Ig is obtained.
Excluding gc, the resistance (effective component) current Igr directly related to the insulation resistance value can be separately measured.

Next, a measuring method of the above-described leakage current measuring device will be described. First, when the power supply connected to the load 13 is a single-phase two-wire system as shown in FIG. 5, the measurement is performed as follows. First, the voltage line (L-phase) and the ground line (N-phase) of the electric line 1 to be measured are identified by the low-voltage detector. Subsequently, the voltage component input terminal T of the leakage current measuring device is
1 and T2 are connected. At this time, the neutral terminal T2 of the voltage component input terminal is connected to the ground line side of the electric line 1 to be measured. Subsequently, the current transformer sensor 2 is clamped to the electric line 1 to be measured, and the display on the display circuit 8 is read. At this time, the current transformer sensor 2 may be clamped to the ground line 16 of the load 13 which is grounded to the D-class.

Next, a case where the power supply connected to the load 14 is a single-phase three-wire system as shown in FIG. 6 will be described. First, each low-voltage detector detects each voltage line (R phase, T
Phase) and neutral line (N-phase). Subsequently, the voltage component input terminals T1, T2 of the leakage current measuring device are connected to the electric line 1 to be measured.
Connect. At this time, the neutral terminal T of the voltage component input terminal
2 is connected to the neutral line (ground line) side of the electric line 1 to be measured.
Subsequently, the current transformer sensor 2 is clamped to the electric line 1 to be measured, and the display on the display circuit 8 is read. At this time,
The current transformer sensor 2 may be clamped to the ground line 16 of the load 14.

Next, a case where the power supply connected to the load 15 is a three-phase three-wire system as shown in FIG. 7 will be described. The procedure is the same as that of the single-phase three-wire system, but the voltage of each of the three phases R, S, and T is checked with a low-voltage detector, and the voltage component input terminal is connected to the grounded phase of zero-type B. Neutral terminal T2.
Subsequently, the current transformer sensor 2 is clamped to the electric line 1 to be measured, and the display on the display circuit 8 is read. At this time,
The current transformer sensor 2 may be clamped to the ground line 16 of the load 15.

[0027]

As described above, according to the present invention, there is an advantage that the quality of insulation of electric equipment or appliances can be determined by measuring leakage current without power failure of the equipment / apparatus itself. is there. In addition, it is possible to measure and display only the component of leakage current that is truly inversely proportional to the level of equivalent ground insulation resistance that is related to the quality of insulation.
There is an advantage that the insulation state of the electric device / equipment can be easily determined without requiring any experience. Further, in the present invention, when the connection state of the current transformer sensor is reverse connection, an alarm is issued from the polarity determination circuit, so that there is an advantage that erroneous measurement can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a leakage current measuring device according to the present invention.

FIG. 2 is a circuit diagram showing a part of a specific circuit configuration of the leakage current measuring device.

FIG. 3 is a circuit diagram showing a part of a specific circuit configuration of the leakage current measuring device.

FIG. 4 is a circuit diagram showing a part of a specific circuit configuration of the leakage current measuring device.

FIG. 5 is an explanatory diagram showing a measuring method when a power supply is a single-phase two-wire system.

FIG. 6 is an explanatory diagram showing a measuring method when the power supply is a single-phase three-wire system.

FIG. 7 is an explanatory diagram showing a measuring method when a power supply is a three-phase three-wire system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric wire to be measured 2 Current transformer sensor 3 Current-voltage conversion circuit 4 Voltage amplification circuit 5 Multiplication circuit 6 Voltage division amplification circuit 7 Active low-pass filter 8 Display circuit 9 Leakage current comparison judgment circuit 10 Judgment result display circuit 11 Circuit voltage judgment selection Circuit 12 Measurement circuit Voltage display circuit 13, 14, 15 Load 16 Ground line 17 Addition / subtraction circuit 18 Comparison circuit 19 Polarity judgment circuit 20 Buzzer drive circuit

Claims (3)

[Claims] 1. A current transformer sensor that is clamped on a measured electric wire or ground line and detects a leakage current flowing through the measured electric wire line or ground line, and a current voltage that converts an output signal of the current transformer sensor into a voltage signal. A conversion circuit; a voltage amplification circuit that amplifies an output signal of the current-voltage conversion circuit; and a voltage division amplification circuit that is connected to a voltage line of the electric wire to be measured and divides and amplifies the voltage of the voltage line. A multiplying circuit that multiplies the output of the voltage amplifying circuit by the output of the voltage dividing amplifying circuit; a low-pass filter that removes a harmonic component from an output signal of the multiplying circuit; a leakage current that is an output signal of the low-pass filter A leakage current display circuit for displaying a signal; and a leakage current comparison / judgment circuit for judging whether the leakage current signal is over a specified value or less than a specified value. , Leakage current measurement apparatus characterized by comprising a determination result display circuit for displaying the determination result of the leakage current comparison judgment circuit. 2. An output of the voltage amplifying circuit according to claim 1 and an output of the voltage dividing amplifying circuit are inputted, a phase difference between the two signals is detected, and a voltage difference between the two signals is detected. 2. The leakage current measuring device according to claim 1, further comprising a polarity determination circuit that outputs an alarm signal when the leakage current signal is out of phase. 3. A transistor when the voltage is 100 V,
A leakage current measuring device characterized in that a relay is driven to automatically switch to a circuit 100V side of a measuring instrument and to turn on a light emitting diode of a 100V display element.