JP2003255011A - Effective leakage current measuring circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure a resistance content current IR of a leakage current I<SB>g</SB>which becomes a cause for dielectric breakdown or electrical leakage fire of an electric device, without being effected by the influence of changes in the voltage or the frequency. <P>SOLUTION: An effective leakage current measuring circuit comprises a zero-phase current transformer 2, having a leakage current detecting winding Nd and a feedback wiring Nf in a single-phase wiring circuit, and a transformer T connected between wirings of a power source side to generate a reference vector e at a secondary voltage by the transformer 2. A 90° dividing voltage detecting circuit TD and an in-phase content voltage detector circuit RD, in which a detected voltage e<SB>g</SB>of an amplifier connected to the wiring Nd and the reference vector are input, first, second multipliers M1, M2 for multiplying the reference vector by detected voltages EC, ER of the detector circuits to obtain the 90° dividing voltage multiplied voltage eC and the in-phase content multiplied voltage eR are automatically balanced with an electric leakage current by negatively feeding back the multiplied voltages to the feedback wiring Nf via a converter for converting the multiplied voltage into a current. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a circuit that can measure an effective leakage current in a leakage current of a single-phase device during operation and constantly monitor deterioration of insulation resistance. [0002] Leakage current I _g of the Prior Art Electrical equipment, a resistor component I _R and capacitance component I _C, is generally I _C>> I _R. Which cause dielectric breakdown and leakage fire is an increase in I _R due to a decrease in the insulation resistance R _g. Also, recently now includes more noise and harmonic components in the power supply voltage from the widely used devices of the inverter drive, the I _C by these high frequency components is increasingly larger tendency. Therefore the conventional leakage current meter has become difficult to measure the effective leakage current I _R and the insulation resistance R _g. SUMMARY OF THE INVENTION [0003] The present invention is intended to prevent the resistance component current and the insulation resistance in the leakage current from being affected by the power supply frequency or the power supply voltage, and by the offset or drift of the operational amplifier in the circuit. It is intended to provide an automatic measurement circuit capable of performing measurement without receiving the signal. A circuit according to the present invention detects a leakage current flowing through a wiring connected to a device by a zero-phase current transformer ZCT and supplies a current corresponding to a resistance component in the leakage current to the current transformer. Then, the current for the capacity is fed back to form a current comparison type transformer bridge using the current transformer itself as a current comparator to measure and monitor the insulation deterioration of the electric equipment during operation. [0005] Figure 1 DETAILED DESCRIPTION OF THE INVENTION A block diagram of the inventive circuit, voltage e by the electrical machine 1 is wiring L _1, L _2, such as a motor
Connected to _S power supply. R _g is the insulation resistance of the device, C _g is the capacitance, and I _g is the leakage current. 2 is a zero-phase current transformer (ZCT)
In addition, wirings L ₁ and L ₂ are penetrated in the annular iron core 3, and a leakage current flux detection winding Nd and a feedback winding Nf are provided.
Nf is wound in a negative feedback direction with respect to Nd. Transformer T connected between the wiring on the power supply side from ZCT is used to insulate and protect the measuring instrument from the power supply, and uses a low voltage e (for example, 1/10 of e _S ) without phase shift on the secondary side. Occurs. JD is 90 ° from the reference vector e and the magnetic flux detection voltage e _g proportional to the leakage current.
A 90-degree voltage detecting circuit that outputs the divided voltage E _C , and RD is a common-mode component detecting circuit that outputs the common-mode voltage E _R. M1, M2
Are multipliers for obtaining multiplied voltages of e × E _C = e _C and e × E _R = e _R , respectively. C _O is the output voltage e _C of the multiplier M1
A capacitor for converting a current I _CO for canceling the I _C, R _O is the resistance for converting a current I _RO for canceling the I _R. These combined currents _IgO are negatively _{fed back} to the winding Nf. In this circuit, if the amplification degree of the operational amplifier A is infinite, the magnetic flux in the iron core of the ZCT becomes zero and is balanced regardless of the magnitude of the leakage current. In the present invention, the zero-phase current transformer is a clamp type,
It can be applied to either split type or annular iron core type CT,
A synchronous rectification circuit or a multiplication rectification circuit is used as JD and RD. Here, the detection output E _C is proportional to the current I _{C corresponding} to the capacitance of the leakage current, and similarly, E _R is proportional to the current I _{R corresponding} to the resistance. And
There is a feature that the values of E _C and E _R are not affected by the change of the power supply voltage e _S. E _C of FIG, E respectively connecting the instrument to _R I _C, directly from the instrument reading by performing the scaling corresponding to I _R I _C, it is possible to know the I _R. Further, it is possible to obtain an insulation resistance by obtaining the reciprocal of the I _R, and I _C and more equipped with a data processing function
The tan δ can also be determined from the ratio of I _R. In addition, if a transmission circuit is added, remote monitoring and mobile operation are possible. The measuring circuit of the present invention eliminates the influence of the power supply voltage and the power supply frequency by adding a feedback winding to the zero-phase current transformer to form a magnetic flux self-balancing bridge, and also increases the operation amplification. Highly accurate measurement values can be obtained without being affected by the offset and drift of the detector. Of course, the feedback winding Nf may be divided into a resistance current winding and a 90 ° component winding. The device incorporating the circuit of the present invention is small and lightweight and can be used as a portable diagnostic device.

[Brief description of the drawings] FIG. 1 is a configuration diagram of a circuit of the present invention.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Hirofumi Asai             3-57-124 Kamiishihara, Chofu-shi, Tokyo Total             Ken Electric Co., Ltd. F term (reference) 2G014 AA17 AB02 AB26 AC18                 2G025 AA17 AB14 AC04

Claims (1)

Claims: 1. A zero-phase current transformer having a leakage current detection winding and a feedback winding and penetrating a single-phase wiring to which a device under test is connected,
A transformer connected between the wires on the power supply side from the zero-phase current transformer and generating a reference vector in a secondary voltage, a detection voltage of an amplifier connected to the detection winding and the reference vector are input. 90 ° component voltage detection circuit and common mode component voltage detection circuit,
The reference vector is multiplied by the detection voltage of each of the detection circuits to obtain a 90 ° multiplication voltage and an in-phase multiplication voltage, through first and second multipliers and a conversion element that converts each multiplication voltage into a current. An effective leakage current measuring and monitoring circuit, wherein a negative feedback is made to the feedback winding.