KR20070024362A - Low voltage on-line insulation monitoring system - Google Patents

Abstract

A low voltage on-line insulation monitoring device is provided to display an exact insulation resistance value with a low measurement error or an effective leakage current value correspondent to resistance components. A low voltage on-line insulation monitoring device(18) detects a leakage current flowing to electric line and load zones by low frequency signal voltage and a leakage current flowing to electric line and load zones by low frequency signal voltage by overlapping the low frequencies of two components by a low frequency overlapping device(10) installed at a second ground wire(2) disposed at the low voltage side of a transformer(1), calculates pure resistance components by removing capacitance components irrelevant to an insulation state by computing the two leakage currents, and then displays an insulation resistance value or an effective leakage current value directly related to the insulation state.

Description

Low Voltage On-line Insulation Monitoring System {Low Voltage On-Line Insulation Monitoring System}

1 is an explanatory diagram of an insulation monitoring method using an insulation resistance meter in a conventional blackout state

2 is an explanatory diagram of an insulation monitoring method using a leak current meter in a conventional live state.

3 is an explanatory diagram of a conventional insulation resistance measuring apparatus in a live state

4 is an explanatory diagram of an insulation monitoring apparatus using a low frequency method in a conventional live state.

5 is a conceptual diagram illustrating the insulation monitoring device in the live state of the present invention;

Figure 6 is a detailed internal view of Embodiment 1 of the insulation monitoring apparatus in the live state of the present invention;

Figure 7 is a detailed internal view of the second embodiment of the insulation monitoring device in the live state of the invention

8 is another embodiment 1 of the leakage current measuring unit of the present invention

9 is another embodiment 2 of the leakage current measuring unit of the present invention

10 is a conceptual diagram illustrating an insulation monitoring apparatus according to another embodiment in the live state of the present invention;

<Explanation of symbols for the main parts of the drawings>

1: high / low voltage conversion transformer 2: Class 2 ground wire

3: switchgear 4: converter (rail)

5: Load Equipment 6: Insulation Resistance Meter

7: VCT 8: Clamp meter

9: superposition transformer 10: low frequency stacking device

11a: reference voltage input line 11b: low frequency signal input line

12: current / voltage converter 13: amplifier

14a: Band pass filter (for f1) 14b: Band pass filter (for f2)

15a: Amplifier (for f1) 15b: Amplifier (for f2)

16a: analog / digital converter (for f1) 16b: analog / digital converter (for f2)

17, 19: current transformer (ZCT) 18: insulation monitoring device

20: Class 2 Ground 21: Leakage Current Measuring Unit

30: Class 3 Ground 40: Control Unit

41: CPU 42: ROM

43: RAM 44: I / O

45: display section 46: voltage, frequency setting section

47: key input 48: alarm output

49: communication unit

The present invention provides a live wire insulation monitoring device that monitors only a resistance component directly related to an earth leakage, regardless of the magnitude of the capacitance existing in the live wire state in the live state without the interruption of the low voltage converter.

In order to facilitate insulation measurement and installation at the site where insulation is to be monitored, the low frequency superimposition device separately installed on the 2 types of ground wires on the low voltage side of the transformer is superimposed on the AC circuits of commercial frequency by f1 and f2 of two components. The leakage current if1 flowing to the ground of the converter and the load by the low frequency signal voltage of Hz and the leakage current if2 flowing to the ground of the converter and the load by the low frequency signal voltage of f2 Hz are detected and extracted. Insulation resistance value which is directly related to insulation state (leakage) by calculating pure resistance component by removing capacitance component not related to insulation state (leakage) through calculation process from leakage current of two components, if1 leakage current and if2 leakage current. Or it relates to a live insulation monitoring device of a low-voltage converter for displaying and monitoring the effective leakage current value.

Conventionally, in order to detect and monitor the insulation state of the low-voltage converter, as shown in FIG. 1, the switch 3 connected to the high-voltage / low-voltage transformer 1 is turned off, that is, the power is interrupted, so that the resistance R of the converter 4 is changed to the insulation resistance meter 6. Insulation between the S, T phase and the ground (20, 30) is measured, or the neutral point of the transformer (1) in live state without breaking off the switch (3) connected to the high-voltage / low-voltage transformer (1) as shown in FIG. The current transformer 7 detects a leakage current flowing through the general grounded two ground wires 2 to determine whether there is a short circuit or insulation deterioration. In these methods, when the insulation state of the converter is measured by the insulation ohmmeter 6 as shown in FIG. 1, the power supply must be interrupted. Therefore, a problem arises in that the power supply must be stopped at a place where electricity is continuously used. Likewise, the method of monitoring the insulation state by measuring the leakage current flowing through the Class 2 ground wire (2) such as the clamp meter (8) or the earth leakage alarm in the live state without power failure is performed by the insulation resistance between the converter (4) and the earth. Detection by vector sum of leakage currents (Irr, Irs, Irt) and leakage currents (Icr, Ics, Ict) due to capacitance generated when the line is long and capacitance such as noise filter inserted at the input of load equipment Therefore, even if the insulation resistance is very good and the insulation resistance is very good, even if the capacitance is very large, the leakage current caused by the capacitance component also increases, so that the insulation state is poor, that is, Unknown has been a problem that the lock is detected to have occurred is measured.

Due to this problem, in the foreign countries, Japanese Patent No. 2598991 describes a prior art in the same field as the present invention for measuring leakage currents (Irr, Irs, Irt) corresponding to insulation resistance components due to an insulation state in a live state. It is composed of the same configuration as shown in Figure 4 and another method. 3 and 4 are as follows. In FIG. 3, the current transformer 17 detects a leakage current Ig0 flowing in the second grounding line 2 of the transformer 1 once grounded, and separates the low voltage charging section from the insulation monitoring device 18 in the converter 4. The reference voltage Vab corresponding to the phase voltage between the grounded phase and the non-grounded phase is measured through the connected reference voltage input line 11a, and the phase difference θ is obtained from the leakage currents Ig0 and Vab to determine the phase difference θ and The leakage current value corresponding to the resistance component is calculated from the leakage current Ig0. There are many problems of this prior art, but the problem of connecting the reference voltage input line 11a to the live part when using in actual field is that it is inconvenient to apply in actual field because there is a place where it is impossible to connect to the low voltage charger and electric shock safety accident. There is a point. On the other hand, in the method as shown in FIG. 4 of another prior art, the current transformer 17 detects a leakage current such as a low frequency superimposed on the low frequency superposition device 10 flowing through the second type ground line 2, and the electrostatic force is reduced at this low frequency leakage current. The low frequency superimposition device 10 as a separate synchronization signal input line 11b for synchronizing with the frequency of the low frequency superimposition device 10 to remove the reactive component current corresponding to the capacitive component and to detect the active component current corresponding to the insulation resistance. The low frequency voltage signal corresponding to the point a of the second ground line 2 corresponding to the secondary side of the overlap transformer 9, which is the output of the low frequency overlapping signal, should be connected to the insulation monitoring device 18. The connection line used for synchronizing with the low frequency signal has a problem that it is inconvenient to be applied in actual field because many places are difficult to connect in the long distance. Utility Model No. 20-2005-0024581 filed by the present applicant is a device using the method of calculating the insulation resistance R from the leakage current of the commercial frequency component and the leakage current of the low frequency component using the following formula: However, commercial frequency AC phase voltage has some measurement error in calculating insulation resistance R due to fluctuation of voltage value of minimum ± 10% due to voltage fluctuation rate.

Therefore, without the reference voltage input line (11a) connected to the insulation monitoring device, or connected to the low frequency power line (11b), it is easy to apply a wide range in practical field, the measurement error is small, and the insulation resistance corresponding to pure insulation resistance accurately There has been a need for an insulation monitoring device capable of detecting and monitoring delivery.

The present invention has been made to satisfy the above requirements, without using the synchronous signal connecting line (11b) or the reference voltage input line (11a) to exclude the leakage current by the capacitance component and by the pure insulation resistance component In order to detect the leakage current or the insulation resistance component with a small error, two low frequencies by the low frequency superposition device 10 and the superimposed transformer 9 or the superimposed resistor 9a separately provided on the low voltage side two ground lines of the transformer 1 (20 Hz or less, f1 and f2 Hz) An existing live line because the leakage current (if1) of the low frequency component (if1) and the low current component (if2) of the low frequency component (f2 Hz) flowing to the ground by the signal voltage are live. After detecting the leakage current (if0) flowing to the ground at the current transformer (17 or 19) due to the AC voltage of the commercial alternating frequency (60 Hz or 50 Hz), it is f1 Hz from the leakage current (if0 + if1 + if2) of these three components. If1 leakage current of low frequency component The value corresponding to the if2 leakage current of f2 Hz low frequency component is extracted through each band pass filter 14a, 14b, and the capacitance is removed from the extracted leakage current to calculate pure resistance component. Its purpose is to provide an insulation monitoring device with a small measurement error and an indication of the effective leakage current value corresponding to the correct insulation resistance value or resistance component.

Hereinafter, the insulation monitoring device of the low-voltage converter in the live state of the present invention will be described with reference to the accompanying drawings.

     As described above, FIG. 3 and FIG. 4 show explanatory diagrams illustrating an apparatus for monitoring an insulation state of a low-voltage electric current in a live state in a foreign country, and FIG. 5 is a concept of an insulation monitoring apparatus in a live state of the present invention. 6 and 7 show an embodiment of the insulation monitoring device 18 according to the present invention, and FIGS. 8 and 9 show the present invention of the leakage current measuring unit 21 inside the insulation monitoring device 18. According to another embodiment of the present invention, the amplifier is changed and the position is changed, and FIG. 10 is another embodiment of the present invention of FIG. 5. 9) Instead of using a superimposed resistor 9a, the grounding method of the low voltage side connection of the transformer 1 is the one-grounding method of the delta connection. The overlapping transformer 9 and the overlapping resistor 9a can be applied to both grounding methods, such as the low voltage side connection grounding the neutral point of the wire connection or the one-phase grounding of the delta connection. For the sake of brevity, FIG. 10 is a diagram illustrating a single grounding method of the delta connection.

     5 of the present invention will be described in more detail. In the high-voltage / low-voltage transformer 1, the switch 3 is closed, that is, electricity is supplied to the low-voltage converter 4 and the load 5 in the live state, and the electricity of the converter 4 and the load 5 The leakage current (if0) corresponding to the phase voltage (E0) of the commercial alternating frequency (f0) through the insulation resistance (R) and the capacitance (C) existing between the phase and the ground, and a high / low voltage conversion transformer ( The earthing transformer (9) or the earthing resistance (9a) and the low-frequency overlapping device (10) separately installed between the neutral point (or one grounding point) on the low-pressure side and the ground (2) connected between the earth. Two kinds of low frequency (f1, f2) signals superimposed on (2) flow through the switch (3) between the voltage and frequency of f1 and f2 Hz flowing between the phase (4) and the load (5) and the ground. The leakage current if1 and leakage current if2 corresponding to the low frequency signal voltages E1 and E2 designed to be very small are detected by the image current transformer 17 or 19, and the image current transformer 17 The amplification and filtering of the leakage current (if0 + if1 + if2) corresponding to the three frequency components detected in 19) is performed by the insulation monitoring device 18 to remove the leakage current of the commercial AC table frequency component and the low frequency signal f1. By extracting only the leakage current (if1a, if2a) of the two components by, f2), and remove the capacitance (C) through the calculation process, the insulation state corresponding to the pure resistance component of the earth leakage, that is, insulation resistance or effective leakage Monitor the current.

      The method of detecting the insulation resistance component related to the ground fault by removing the capacitance component irrelevant to the insulation state or the ground fault in the insulation monitoring device 18 is shown in FIG. It demonstrates in detail with reference.

      The leakage current if0 of the commercial frequency component detected by the image current transformer 17 or 19 and the leakage currents if1 and if2 of the two low frequency components are converted into voltage through the current / voltage converter 12 and the amplifier ( After amplifying the minute voltage through 13), the component corresponding to the f1 low frequency signal is extracted through the f1 low frequency band pass filter 14a, and only the component corresponding to f1 low frequency is extracted, and the extracted f1 low frequency component is applied to the f1 low frequency amplifier. The value of if1a is detected through (15a). On the other hand, the component corresponding to the low frequency f2 extracts only the component corresponding to the low frequency f2 through the f2 low frequency band pass filter 14b, and detects the value of if2b through the extracted low frequency f2 amplifier 15b. . The leakage current components corresponding to the common frequency component f0 are removed by the band pass filters 14a and 14b, and the voltage components if1a and f2 corresponding to the leakage currents of the low frequency components f1 of the two kinds of low frequency components are detected. When the voltage component if2a corresponding to the leakage current of the low frequency is input to the CPU 41 in the control device 40 through the analog / digital converters 16a and 16b, respectively, the CPU 41 calculates an invalid component through the following calculation process. Remove the capacitive component corresponding to and extract only the insulation resistance component corresponding to the active ingredient.

  The symbols used in the following calculations are as follows.

    f0: Commercial AC voltage frequency (60Hz or 50Hz)

    f1: Low frequency (frequency less than 20Hz) superimposed to converter 4 through Class 2 ground wire (2)

    f2: Low frequency (frequency less than 20Hz) superimposed to converter 4 through Class 2 ground wire (2)

    if0: ground-to-ground leakage current corresponding to the common frequency f0 detected by the image transformer 17 or 19

    if1: ground-to-ground leakage current corresponding to the low frequency of f1 Hz detected by the image transformer 17 or 19

    if2: ground-to-ground leakage current corresponding to the low frequency of f2 Hz detected by the image transformer 17 or 19

    a: Total amplification factor of current / voltage converter 12, amplifier 13 and amplifier 15a corresponding to a low frequency of f1 Hz

    b: Total amplification factor of current / voltage converter 12, amplifier 13 and amplifier 15b corresponding to low frequency of f2 Hz

    E0: Phase voltage of commercial AC frequency (60Hz or 50Hz)

    E1: Low frequency (f1) signal voltage which is superimposed on the converter 4 through the 2 type ground line (2)

    E2: Low frequency (f2) signal voltage which is superimposed on the converter 4 through the 2 type ground line (2)

    R: Parallel composite insulation resistance between phase and ground of converter 4 and load 5

    C: Parallel composite capacitance between phase and ground of converter 4 and load 5

    Low frequency components of if1a and f2 Hz, which correspond to leakage currents of the low frequency components of f1 Hz corresponding to the input values of the analog / digital converter 16a and the analog / digital converter 16b in the insulation monitoring device 18, If2a, a component corresponding to the leakage current, is as follows.

      In order to eliminate the effect of C corresponding to the reactive component (imaginary part),

을 좌우항에 곱하면

Multiply by the left and right terms

     Subtracting equation (1) from equation (3)

   When the insulation resistance R is obtained from Equation (4), it is as follows.

식을 사용하여 절연저항치를 저항성분에 의한 유효 누설전류값 또는 저주파수(f1, f2)의 신호전압에 대한 유효누설전류

으로 계산할 수 있다. 그리고 절연저항R이 계산되면 상기의 계산식에 절연저항R을 대입하면 정전용량C성분도 계산할 수 있을 것이다. 반대로 식(1)과 식(2)에 상수를 곱하여 절연저항R성분을 소거시키고 정전용량C성분을 구한 후, 다시 절연저항R을 계산하는 방법을 사용할 수 도 있을 것이다.The function related to insulation resistance R in Equation (5) shows that it can be calculated irrespective of capacitance C. Also, the insulation resistance R value calculated above is applied to the phase voltage of commercial AC (60Hz or 50Hz). Effective leakage current

Using the formula, the insulation resistance value is the effective leakage current due to the resistance component or the effective leakage current with respect to the signal voltage at low frequencies (f1, f2).

Can be calculated as When the insulation resistance R is calculated, the capacitance C component may be calculated by substituting the insulation resistance R in the above formula. Conversely, by multiplying Equation (1) and Equation (2) by a constant, the insulation resistance R component may be eliminated, the capacitance C component may be obtained, and then the insulation resistance R may be calculated.

 In addition, if the amplification degree a, b is the same as in Equation (5), and the magnitudes E1 and E2 of the low frequency signal voltage are the same, the calculation can be simplified as in the following equation.

여기서 α는 증폭율에 관계되는 상수이다.

Α is a constant related to the amplification factor.

8 and 9 show another embodiment of the leakage measuring unit 21 inside the insulation monitoring device 18 of FIGS. 6 and 7, and FIG. 8 shows the leakage current measuring unit 21 of FIG. 6 or 7. 9 is an embodiment without the amplifier 13, and FIG. 9 is an embodiment without only the amplifiers 15a and 15b in the leakage current measuring unit 21 of FIG. That is, the leakage current measuring unit 21 of FIG. 6 or 7 has two amplifiers, while FIGS. 8 and 9 show only one amplifier. 8 and 9 have been described in detail above, and thus will not be described further. The E1, E2, f1, f2 values required for the calculation of the insulation resistance value R or the effective leakage current value are set in the setting unit 46 by an electronic component such as a setting switch in FIG. 6 and the calculation program equation is stored in the ROM 42. The calculated value or necessary function constant value required for the calculation may be displayed on the display unit 45 via the digital input / output unit I / O 44 and the calculated insulation resistance value or the effective leakage current value temporarily stored in the RAM 43. .

    In addition, in FIG. 7 which is another example, a constant value of a function required for calculation such as E1, E2, f1, f2 calculated on the insulation resistance value R or the effective leakage current value as described above, and using a plurality of insulation monitoring devices 18 are used. In this case, input the necessary values for the device operation such as the device address number by using the key input unit 47.Alarm output when the insulation leakage value or the paid leakage current value is calculated more than the randomly set value or less. The alarm 48 can be output to the outside through the unit 48. Also, if you want to monitor remotely through the communication unit 49 in various forms of communication (RS-232, RS-485, CDMA, power line communication) You can configure the functions that can be used.

According to the present invention, two types of superposition transformers, superimposed resistors, and low frequency superposition devices connected between the earth and two earth wires connected to the neutral point or one ground point of the high-voltage / low voltage conversion transformer in the live state of the commercial AC frequency as described above. Leakage current (if0) and two kinds of low frequency (f1, f2 Hz) of the common frequency components detected by the image transformer in the middle of the two ground lines or converters by superimposing the low frequency signals (f1, f2) of Leakage Current (if1) and Leakage Current (if2) Leakage Current (if1) and Leakage Current (if1) of Low Frequency Component (f1 Hz) corresponding to Low Frequency (f1, f2) Signal Voltage By taking out only the leakage current value corresponding to if2), it removes the capacitance component between the phase and earth of the load and load irrelevant to the insulation drop (leakage), and the insulation low is directly related to the insulation drop (leakage). Insulation monitoring device that detects only the component or effective leakage current value with small measurement error and accurately detects insulation condition but has good capacitance but has a large capacitance, and solves the problem of measurement by short circuit. It is possible to effectively monitor and measure the insulation state of low-voltage converters in live state easily in any place without any trouble to apply live insulation monitoring value in the field without connecting reference voltage input line or low frequency signal synchronization line to insulation monitoring device. It has an effect. In addition, an alarm output unit and a communication unit may be added to configure a device that can be controlled remotely.

Claims (3)

Two kinds of low frequency (f1, f2 Hz) signal voltages are superimposed on the low voltage circuit through the neutral point of the low voltage side transformer or the ground wire connected to one ground, and the two types of low frequency signal voltage Leakage current component (if1) of low frequency component (f1 Hz), leakage current component (if2) of low frequency component (f2 Hz) and leakage frequency of commercial frequency component leaking between the phase of the converter or load by the commercial frequency AC voltage The component (if0) is detected through the image current transformer, and the leakage current (if0 + if1 + if2) of the detected three frequency components is converted into a current / voltage converter, an amplifier, an f1 low frequency band pass filter, and an f2 low frequency band pass. The CPU and the corresponding values of leakage currents of the two low frequency components leaked by the two kinds of low frequency (f1, f2 Hz) signal voltages converted using the filter and the analog / digital converter are respectively obtained from the CPU. Control the capacitance component of the live wire insulated with a low pressure, characterized in that before using the following equation as to eliminate the effect of detection to calculate the insulation resistance value or the effective leakage current monitoring device

 (E0: phase voltage of commercial AC, E1: f1 low frequency signal voltage, f1: low frequency (f1 Hz), f2: low frequency (f2 Hz), E2: f2 low frequency signal voltage, a: low frequency corresponding to f1) Amplification degree, amplification degree corresponding to b: f2 low frequency, if1a: final amplified leakage current value corresponding to f1 low frequency component, if2a: final amplified leakage current value corresponding to f2 low frequency component) For commercial AC voltage

Or for low frequency signal voltage

Two kinds of low frequency (f1, f2 Hz) signal voltages are superimposed on the low voltage circuit through the neutral point of the low voltage side transformer or the ground wire connected to one ground, and the two types of low frequency signal voltage Leakage current component (if1) of low frequency component (f1 Hz), leakage current component (if2) of low frequency component (f2 Hz) and leakage frequency of commercial frequency component leaking between the phase of the converter or load by the commercial frequency AC voltage The component (if0) is detected through the image current transformer, and the leakage current (if0 + if1 + if2) of the detected three frequency components is converted into a current / voltage converter, an amplifier, an f1 low frequency band pass filter, and an f2 low frequency band pass. The CPU and the corresponding values of leakage currents of the two low frequency components leaked by the two kinds of low frequency (f1, f2 Hz) signal voltages converted using the filter and the analog / digital converter are respectively obtained from the CPU. In order to eliminate the influence of the capacitance component and simplify the calculation of the insulation resistance value, the amplification degree and signal voltage for f1 Hz and the amplitude of f2 Hz and signal voltage are configured to be the same. Live insulation monitoring device of low voltage electric line, characterized by calculating and displaying insulation resistance value or effective leakage current value

(E0: phase voltage of commercial AC, f1: low frequency (f1 Hz), f2: low frequency (f2 Hz), E1: f1 low frequency signal voltage, E2: f2 low frequency signal voltage, if1a: f1 low frequency component) Amplified leakage current value, if2a: final amplified leakage current value corresponding to f2 low frequency component, α: constant related to amplification factor) For commercial AC voltage

Or for low frequency signal voltage

The live wire insulation sensation value of the low-voltage converter according to claim 1 or 2, wherein the alarm output unit (48) or the communication unit (49) is configured to be monitored remotely.

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