JP2001215247A - Leakage current measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine whether the state of insulation of an electric apparatuses is defective by measuring only a leakage current (Igr) component owing to equivalent insulation resistance to the ground. SOLUTION: This instrument has a current-transformer sensor 2 for detecting a leakage current flowing through a measured electric line 1 or a grounding line, a current/voltage converting circuit 3 for converting an output signal of the sensor 2 into a voltage signal, a voltage amplifying circuit 4 for amplifying the output signal of the circuit 3, a voltage dividing/amplifying circuit 6 connected to a voltage line of the line 1 to divide and amplify the circuit voltage of the voltage line, a multiplying circuit 5 for multiplying the output of the circuit 4 by the output of the circuit 6, a low-pass filter 7 for removing harmonic components from the output of the circuit 5, a leakage-current displaying circuit 8 for displaying a leakage current signal Igr or output signal of the filter 7, a leakage-current comparing/determining circuit 9 for determining whether the current signal is above or below a prescribed value, and a determined result displaying circuit 10 for displaying a result determined by the circuit 9.

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 an insulation state of an electric device by measuring the leakage current, and more particularly to a leakage current component which is inversely proportional to the equivalent ground insulation resistance. The present invention relates to a leakage current measuring device capable of measuring the leakage current.

[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 and determining whether the insulation state of electric equipment is good or not.

[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]

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 a current transformer sensor (CT sensor) 2 clamped on the entire electric line 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 00V, the green indicator LED3 is turned on, and when the circuit voltage is 200V, the red indicator LED4 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 both 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 determination result display circuit 10 connected to the leakage current comparison determination circuit 9, when the leakage current (Igr) is equal to or less than the standard value of 30 mA, the green indicator LED1 is turned on, and the leakage current (Igr) exceeds 30 mA. At this time, the red indicator light LED2 is turned on to issue an alarm.

Next, a specific circuit configuration of the leakage current measuring device shown in FIG. 2 will be described. In this figure, the resistors R1 and R2 to which the current transformer sensor 2 is connected constitute a current-voltage conversion circuit 3. The operational amplifier A2 and the circuit element at the next stage to which the current-voltage conversion circuit 3 is connected constitute a voltage amplification circuit 4. On the other hand, the operational amplifier A12 and the circuit element, the NAND circuit D2, and the relay RY1, which are connected to the voltage line of the electric wire 1 to be measured, are connected to the circuit voltage judgment selection circuit 1
1. Further, the switched contact piece RY1 of the relay
-2 and the resistance constitute a measurement circuit voltage display circuit 12 for lighting the indicator lamps LED3 and LED4. Further, the switching contact piece RY of the relay RY1 is connected to the voltage line of the electric wire 1 to be measured.
Resistances R3, R4, R5, VR connected via 1-1
1, the operational amplifier A1, the circuit element is a voltage dividing amplifier circuit 6
Is composed.

The operational amplifiers A3, A4, A5, A
6. The transistors Tr1 and Tr2 and the circuit elements constitute a multiplication circuit 5 for multiplying both outputs of the voltage amplification circuit 4 and the voltage division amplification circuit 6. In this multiplication circuit 5, the resistance R
6, VR2 gives a voltage vx to be described later. Further, the operational amplifier circuit A7 and the circuit elements constitute an active low-pass filter 7 for removing harmonic components from the output signal Vout of the multiplying circuit 5 and extracting only a leakage current (Igr) component due to an equivalent ground insulation resistance.

The digital meter DP1 constitutes a display circuit 8 for digitally displaying the leakage current (Igr) output from the active low-pass filter 7. The operational amplifiers A8, A9, and A10 and the circuit elements constitute a leakage current comparison and determination circuit 9. The operational amplifier A11 to which the leakage current comparison and determination circuit 9 is connected, the circuit element, and the NAND circuit D1 constitute a determination result display circuit 10 for selectively turning on one of the indicator lights LED1 and LED2.

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 and vy of the voltage dividing amplifier circuits 6 and 4 are as follows: vz = (Vm / n) A1 sin ωt (3) where n is a voltage dividing ratio and A1 is a voltage. Voltage dividing amplifier 6
Is the voltage amplification factor. vy = (Im / K1) R1 A2 .sin (.omega.t + .theta.) (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 vz and vy 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). By substituting equations (3) and (4) into equation (5), Vout = C (Im / K1) R1A2.sin (.omega.t + .theta.) (Vm / n) A1 sin.omega.t = K0 Vm Im.sin (Ωt + θ) · sin ωt (6) Here, the constant K0 = (CR1 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 · V Im = √2 · Ig. Therefore, when 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 the trigonometric functions into a sum, Vout = 2K0 VIg {cos (α-β) -cos (α + β)} / 2 (7) Here, .alpha .-. Beta. = (. Omega.t + .theta.)-. Omega.t = .theta..alpha. +. Beta. = (. Omega.t + .theta.) +. Omega.t = 2.omega.t + .theta. (8) When the signal voltage Vout expressed by the equation (8) is added to the active low-pass filter 7 using the operational amplifier A7, the term that fluctuates at a frequency 2ωt that is twice the second term in the parentheses in the equation (8) is 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). Here, it is assumed that K2 = K0 V. 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, 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 contained 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. 3, 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 of the digital meter DP1 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. 4 will be described. First, the 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 of the digital meter DP1 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. 5 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 of the digital meter DP1 is read. At this time, the current transformer sensor 2 may be clamped to the ground line 16 of the load 15.

[0022]

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.

[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 specific circuit configuration of the leakage current measuring device.

FIG. 3 is an explanatory diagram showing a measuring method when a power supply is a single-phase two-wire system.

FIG. 4 is an explanatory diagram showing a measurement method when a power supply is a single-phase three-wire system.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 and 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 wire LED1, LED2 Indicator light

Claims (1)

[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.