KR101989459B1 - Apparatus and method for measuring leakage current of three-phase four-wire type power line - Google Patents

Abstract

The present invention relates to a leakage current measuring device and a leakage current measuring method of a three-phase four-wire power line. Leakage current measuring device according to the present invention includes a signal input unit for applying an injection signal of a frequency different from the driving frequency of the power line to each phase; A current measuring unit installed in a neutral wire and measuring a magnitude and phase of a signal current flowing to the neutral wire according to the injection signal; And controlling the signal input unit to sequentially input the injection signal to each phase, and based on the magnitude and phase of the signal current measured according to each of the injection signals by the current measuring unit, And a controller configured to calculate a leakage current, wherein the controller uses the magnitude of the signal current measured by the current measuring unit at the same phase as the phase of the injection signal and the signal voltage of the injection signal. The impedance is calculated, and the leakage current of each phase is calculated based on the leakage impedance of each phase and the driving voltage of each phase. Accordingly, by installing one current measuring unit such as a CT (Current Transformer) sensor, the leakage current generated in each phase can be measured by sequentially inputting an injection signal of a specific frequency into each phase.

Description

Leakage current measuring device and measuring method of three-phase four-wire power line {APPARATUS AND METHOD FOR MEASURING LEAKAGE CURRENT OF THREE-PHASE FOUR-WIRE TYPE POWER LINE}

The present invention relates to a leakage current measuring apparatus and a measuring method of a three-phase four-wire power line, and more particularly to a three-phase four-wire power line capable of measuring in real time the leakage current generated in each phase of the three-phase four-wire power line. It relates to a leakage current measuring device and a measuring method.

In general, when the covering of wires and insulation of electrical equipment are aged or damaged and the insulator is damaged, leakage current flows from the wire path to the ground through the location. If the human body touches the place where leakage current flows, there is a risk of electric shock.In the place where excessive leakage current flows, overheating occurs due to the arc, and it may be ignited by flammable material around, causing leakage fire.

In order to prevent such leakage accidents, Article 52 (Insulation performance of low voltage lines) of the 2006.65.2006 "65 Electrical Equipment Technical Standards" of Ministry of Commerce, Industry and Energy, "When the ground voltage exceeds 150V and below 300V The insulation resistance between the voltage-side wire and the middle conductor or earth shall be at least 0.2MΩ. " It is described.

If the insulation resistance is 0.2MΩ or more in 220V commercial power supply, the leakage current is (220V / 0.2MΩ = 0.0011A) 1.1mA or less.If the leakage current can be measured accurately in live state without shutting off the power, the insulation resistance between wire and earth However, a commercially available live leakage current clamp (Leakage Clamp) has a technical disadvantage that can not accurately measure the leakage current.

In particular, the measurement of leakage currents in three-phase four-wire power lines has more complex aspects. 1 and 2 are diagrams showing an example of the configuration of a three-phase four-wire power line. Referring to FIGS. 1 and 2, in order to obtain an unknown impedance, voltage and current, that is, two physical quantities must be measured. In the case of a three-phase four-wire power line, there are six unknown impedances. Twelve independent physical quantities shall be measured.

However, as shown in Figs. 1 and 2, the physical quantities measurable in the three-phase four-wire power line are V ₁ , I ₁ , V ₂ , I ₂ , V ₃ , I ₃ , and I _N. It is measurable (where V _N is determined by circuit analysis and the measurement is meaningless), and real-time voltage and current measurements alone cannot yield leakage impedance, ie leakage resistance and leakage current.

In order to solve such a problem, in the '4CT combined portable leakage measuring apparatus and method' disclosed in Korean Patent No. 10-0907566, four separate current transformers (CT: Current Transformers) are installed on a three-phase four-wire power line, respectively. Has been proposed, and a method of measuring leakage current by integrating the current measured by four separate current transformers according to a predetermined calculation formula has been proposed, but has four drawbacks.

Accordingly, the present invention has been made to solve the above problems, by installing one current measuring unit, such as CT (Current Transformer) sensor, by sequentially inputting the injection signal of a specific frequency on each phase It is an object of the present invention to provide a leakage current measuring apparatus and measuring method of a three-phase four-wire power line capable of measuring the leakage current generated.

According to the present invention, there is provided a leakage current measuring apparatus for a three-phase four-wire power line, comprising: a signal input unit for applying an injection signal having a frequency different from a driving frequency of the power line to each phase; A current measuring unit installed in a neutral wire and measuring a magnitude and phase of a signal current flowing to the neutral wire according to the injection signal; And controlling the signal input unit to sequentially input the injection signal to each phase, and based on the magnitude and phase of the signal current measured according to each of the injection signals by the current measuring unit, And a controller configured to calculate a leakage current, wherein the controller uses the magnitude of the signal current measured by the current measuring unit at the same phase as the phase of the injection signal and the signal voltage of the injection signal. The impedance is calculated, and the leakage current of each phase is achieved by a leakage current measuring apparatus of a three-phase four-wire power line, characterized in that it is calculated based on the leakage impedance of each phase and the driving voltage of each phase.

Wherein the signal input includes a contactless inductive coupler; The injection signal is applied to the phase through the inductive coupler; The signal voltage may be calculated based on the voltage induction ratio of the inductive coupler and the voltage of the injection signal.

In addition, the leakage impedance of each phase is: R _i = V _si / I _si (R _i is the leakage impedance of phase i, V _si is the signal voltage of phase i, I _si is the signal in phase i The magnitude in the phase equal to the phase of the injection signal of the magnitude of the current); The leakage current of each phase may be calculated by a formula I _GRi = V _i / R _i , wherein I _GRi is the leakage current of phase i and V _i is the driving voltage in phase i. .

On the other hand, the above object is, according to another embodiment of the present invention, in the leakage current measurement method of a three-phase four-wire power line, (a) step of sequentially inputting the injection signal of a frequency different from the driving frequency of the power line on each phase Wow; (b) measuring the magnitude and phase of a signal current flowing in response to the injection signal on a neutral line of the power line; (c) For each phase, the leakage impedance is calculated by using a signal voltage of the injection signal and a magnitude at a phase equal to the phase of the injection signal among the magnitudes of the signal current measured in step (b). Steps; (d) measuring leakage current of each phase based on the leakage impedance calculated for each phase and the driving voltage of each phase; and measuring leakage current of the three-phase four-wire power line. It is also achieved by the method.

Wherein in step (a) the injection signal is applied via a contactless inductive coupler for each phase; In the step (c), the signal voltage may be calculated based on the voltage induction ratio of the inductive coupler and the voltage of the injection signal.

Further, in the step (c), the leakage impedance of each phase is R _i = V _si / I _si (R _i is the leakage impedance of phase i, V _si is the signal voltage of phase i, I _si Is the magnitude in phase equal to the phase of the injection signal of the magnitude of the signal current in phase i); In step (d), the leakage current of each phase is represented by the formula I _GRi = V _i / R _i (wherein I _GRi is the leakage current of phase i and V _i is the driving voltage in phase i). Can be calculated by

According to the configuration as described above, according to the present invention, by installing one current measuring unit, such as a CT (Current Transformer) sensor, by inputting the injection signal of a specific frequency in each phase sequentially the leakage current generated in each phase Provided is an apparatus and method for measuring leakage current of three-phase four-wire power lines that can be measured.

1 and 2 are views showing an example of the configuration of a three-phase four-wire power line,
3 and 4 is a view for explaining the leakage current measuring device of a three-phase four-wire power line according to the present invention,
5 is a view for explaining a leakage current measuring method of a three-phase four-wire power line according to the present invention.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention;

3 and 4 are diagrams for explaining the leakage current measuring device 100 of the three-phase four-wire power line according to the present invention. 3 and 4, the leakage current measuring apparatus 100 according to the present invention includes a signal input unit 121, 122, 123, a current measuring unit, and a controller.

The signal input units 121, 122, 123 are provided in respective phases, as shown in Figs. That is, the signal input units 121, 122, and 123 include a T-phase signal input unit 121 installed in a T phase, an R-phase signal input unit 122 installed in an R phase, and an S-phase signal input unit 123 provided in an S phase. .

Each signal input unit 121, 122, 123 inputs an injection signal having a frequency different from the driving frequency of the power line to each phase under the control of the controller. For example, in the case of a general three-phase four-wire power line, since the AC frequency is 50/60 Hz, an injection signal having a frequency different from this, for example, 100 Hz, is applied to each phase.

In the present invention, for example, each signal input unit 121, 122, 123 is provided as a non-contact inductive coupler, according to the circuit configuration of the power line when installing the leakage current measuring device 100 according to the present invention on a three-phase four-wire power line Installation is possible without change.

As illustrated in FIG. 3, the current measuring unit measures the magnitude and phase of the signal current flowing through the neutral line according to the injection signal installed in the neutral line and sequentially applied from each phase. In the present invention, for example, the current measuring unit is provided in the form of a CT (Current Transformer) sensor.

The control unit controls each of the signal input units 121, 122, and 123 to sequentially input the injection signal to each phase. The control unit receives the magnitude and phase of the signal current measured according to each injection signal by the current measuring unit.

For example, the control unit controls the T-phase signal input unit 121 to input an injection signal of 100 Hz as described above to the T phase, and then a signal current flowing through the center line according to the injection signal of the T-phase signal input unit 121. The magnitude and phase of is received from the current measuring unit. The control unit controls the R phase signal input unit 122 to input a 100 Hz injection signal to the R phase, and then controls the magnitude and phase of the signal current flowing through the center line according to the injection signal of the R phase signal input unit 122. Received from the measurement unit. Similarly, the control unit controls the S-phase signal input unit 123 to input the 100 Hz injection signal as described above, and then, according to the injection signal of the S-phase signal input unit 123, the magnitude of the signal current flowing through the center line. And the phase is received from the current measuring unit. Here, of course, the order of applying the injection signals to the T-phase, R-phase and S-phase is not limited to the above-described order.

As described above, when the magnitude and phase of the signal current is measured for each phase, the controller calculates the leakage impedance and leakage current of each phase based on the magnitude and phase of the signal current measured for each phase.

In more detail, the controller extracts a magnitude at a phase equal to the phase of the injection signal among the magnitudes of the signal current accumulated by the current measuring unit, and calculates a leakage impedance using the extracted magnitude and the signal voltage of the injection signal. do. Here, when the signal voltage according to the present invention is provided as the inductive coupler as described above, the signal voltage can be calculated according to the voltage induction ratio of the inductive coupler and the voltage of the injection signal applied to the inductive coupler.

Here, the leakage impedance of each phase can be calculated through [Equation 1].

[Equation 1]

R _i = V _si / I _si

Where R _i is the leakage impedance of phase i, V _si is the signal voltage of phase i, and I _si is the magnitude in phase equal to the phase of the injection signal of the magnitude of the signal current in phase i.

When the leakage impedance of each phase is calculated as described above, the controller calculates the leakage current of each phase based on the calculated leakage impedance and the driving voltage of each phase. Here, the leakage current for each phase may be calculated through [Equation 2].

[Equation 2]

I _GRi = V _i / R _i

Where I _GRi is the leakage current of phase i and V _i is the drive voltage in phase i.

According to the configuration as described above, by installing one current measuring unit such as a CT (Current Transformer) sensor, and sequentially input the injection signal of a specific frequency to each phase, it is possible to measure the leakage current generated in each phase.

In particular, the midline current for the main power of 60 Hz is used to almost zero, which can lower the maximum current requirement of the current measuring unit, which is advantageous for low current measurement.

More specifically, the electrical safety manager job regulation notice (Ministry of Trade, Industry and Energy Notice No. 2016-16) stipulates that leakage current should be kept below 1 mA for low voltage lines that cannot measure insulation resistance. However, in the digital industrial age, there are many electronic and electric devices that use SMPS or inverter, and most of them come out in excess of 1mA when measured by a general type leakage current meter in a low voltage line. . On the other hand, in the present invention, since the resistive leakage current (Igr) is measured instead of the leakage current I _o (resistive leakage current Igr + capacitive leakage current Igc) as a criterion for defective determination, the best leakage current management is possible, and electric shock or fire accident is prevented. Becomes possible.

Hereinafter, a leakage current measuring method of a three-phase four-wire power line according to the present invention will be described with reference to FIG. 5.

First, an injection signal is applied on T (S50). Here, as described above, the injection signal of a frequency different from the frequency of the main power, for example, 100 Hz, is input to the T phase as described above. Then, the magnitude and phase of the signal current according to the injection signal in the neutral line is measured (S51).

Similarly, an injection signal is applied on R (S52). Here, an injection signal of 100 Hz is input to the R phase as the injection signal. Then, the magnitude and phase of the signal current according to the injection signal in the neutral line is measured (S53).

Then, an injection signal is applied to S phase (S54). Here, as the injection signal, an injection signal of a frequency different from the main power frequency, for example, 100 Hz, is input to the S phase. Then, the magnitude and phase of the signal current according to the injection signal in the neutral line is measured (S55).

As described above, when the magnitude and phase of the signal current for each phase are measured, leakage impedance and leakage current for each phase are measured through [Equation 1] and [Equation 2] (S56 and S57).

In the above-described embodiment, the injection signals are sequentially input to each phase, the magnitude and the phase of the signal current for each phase are measured, and the leakage impedance and the leakage current for each phase are described as an example. In addition, after the injection current is applied to one phase, the magnitude and phase of the signal current, the leakage impedance and the leakage current are calculated, the leakage impedance and the leakage current may be measured for another phase. to be.

In the above-described embodiment, the signal input units 121, 122, and 123 have been described as an example in which each phase is installed. However, the signal input units 121, 122, and 123 may be provided to sequentially apply injection signals to each phase using one signal input unit.

Although some embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that modifications may be made to the embodiment without departing from the spirit or spirit of the invention. . It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

100: leakage current measuring device 110: control unit
121: T-phase signal input unit 122: R-phase signal input unit
123: S-phase signal input unit 130: current measuring unit

Claims (6)

In the leakage current measuring device of a three-phase four-wire power line,
A signal input unit for applying an injection signal having a frequency different from a driving frequency of the power line to each phase;
A current measuring unit installed in a neutral wire and measuring a magnitude and phase of a signal current flowing to the neutral wire according to the injection signal;
And controlling the signal input unit to sequentially input the injection signal to each phase, and based on the magnitude and phase of the signal current measured according to each of the injection signals by the current measuring unit, A control unit for calculating a leakage current,
The control unit
The leakage impedance is calculated by using the magnitude of the signal current measured by the current measuring unit at the same phase as the phase of the injection signal and the signal voltage of the injection signal.
The leakage current of each phase is calculated based on the leakage impedance of each phase and the driving voltage of each phase,
The signal input unit includes a contactless inductive coupler,
The injection signal is applied to the phase through the inductive coupler,
And the signal voltage is calculated based on the voltage induction ratio of the inductive coupler and the voltage of the injection signal. delete The method of claim 1,
The leakage impedance of each phase is the formula R _i = V _si / I _si (R _i is the leakage impedance of phase i, V _si is the signal voltage of phase i, and I _si is the signal current of phase i Of magnitude in phase equal to the phase of the injection signal);
The leakage current of each phase is calculated by the formula I _GRi = V _i / R _i (wherein I _GRi is the leakage current of phase i and V _i is the driving voltage in phase i). Leakage current measuring device for three-phase four-wire power lines. In the leakage current measurement method of a three-phase four-wire power line,
(a) sequentially inputting an injection signal having a frequency different from a driving frequency of the power line on each phase;
(b) measuring the magnitude and phase of a signal current flowing in response to the injection signal on a neutral line of the power line;
(c) for each phase, a leakage impedance is calculated using the magnitude of the signal current measured in the step (b) at the same phase as the phase of the injection signal and the signal voltage of the injection signal; Wow;
(d) calculating a leakage current for each phase based on the leakage impedance calculated for each phase and the driving voltage of each phase,
In the step (a) the injection signal is applied via a non-contact inductive coupler for each phase,
In the step (c), the signal voltage is calculated based on the voltage induction ratio of the inductive coupler and the voltage of the injection signal, the leakage current measurement method of a three-phase four-wire power line. delete The method of claim 4, wherein
In the step (c), the leakage impedance of each phase is R _i = V _si / I _si (R _i is the leakage impedance of phase i, V _si is the signal voltage of phase i, and I _si is phase is the magnitude in phase equal to the phase of the injection signal among the magnitudes of the signal current;
In step (d), the leakage current of each phase is represented by the formula I _GRi = V _i / R _i (wherein I _GRi is the leakage current of phase i and V _i is the driving voltage in phase i). Leakage current measuring method of a three-phase four-wire power line characterized in that calculated by.

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