KR20070024361A - Low voltage on-line insulation monitoring system - Google Patents

Abstract

A low voltage on-line insulation monitoring device is provided to detect an insulation state of a low voltage line in an uninterruptible live wire state by monitoring resistance components directly related to an electric leakage regardless of the magnitude of capacitance remaining in the line and a load input stage. A low voltage on-line insulation monitoring device(18) detects leakage current correspondent to commercial AC(Alternating Current) frequency components of 60Hz or 50Hz and leakage current correspondent to low frequency components below 20Hz of a low frequency overlapping device(10) installed at a second ground wire(2) of a transformer(1), extracts pure resistance components by removing capacitance components irrelevant to an insulation state by calculating the leakage currents, and displays and monitors 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 f0) 14b: Band pass filter (for f1)

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

16a: analog / digital converter (for f0) 16b: analog / digital converter (for f1)

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.

Low frequency (less than 20Hz) by the leakage current (if0) corresponding to the commercial AC frequency (60Hz or 50Hz) component and the low frequency superposition device separately installed on the 2 types of grounding line of transformer for easy insulation measurement and installation at the site to be monitored. After detecting the leakage current (if1) corresponding to the component, the capacitance component is removed from the leakage current of the two components, if0 leakage current and if1 leakage current, to calculate the pure resistance component. An insulation monitoring apparatus for displaying an effective leakage current value corresponding to a component.

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 measuring the insulation state of the converter with the insulation ohmmeter 6 as shown in Fig. 1, the power supply must be stopped at the place where electricity is continuously used. 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 ground fault alarm in the live state without power failure is performed by the insulation resistance between the converter (4) and the earth. Vector sum of leakage current (Irr, Irs, Irt) and leakage current (Icr, Ics, Ict) due to capacitance generated when the line is long and noise filter inserted into the input of load equipment Because of the detection, no insulation deterioration (leakage) occurs and even if the insulation resistance is very good, 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 electric safety accident and low voltage charge part cannot be connected. 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 to the second type ground line 2, and at this low frequency leakage current, The low frequency superimposition device as a separate synchronization signal input line 11b for synchronizing with the frequency of the low frequency superposition device 10 to remove the reactive component current corresponding to the capacitance component and to detect the active component current corresponding to the insulation resistance ( 10) The low-frequency voltage signal corresponding to the point a of the class 2 grounding line 2 corresponding to the secondary side of the overlap transformer 9, which is interconnected or 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.

Therefore, without connecting the reference voltage input line 11a to the insulation monitoring device or connecting the low frequency power line 11b, it is easy to apply a wide range in the actual field and only the insulation resistance component corresponding to pure insulation resistance can be detected and monitored. Insulation monitoring devices have been required.

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 insulation resistance component, the leakage current (if0) flowing to the ground due to the voltage of the commercial AC (60 Hz or 50 Hz, f0) component and the low frequency side of the low voltage side of the transformer 1 are separately provided. The video current transformer 17 or 19 detects a leakage current if1 flowing to the earth by a low frequency (20 Hz or less, f1) signal voltage caused by the superimposition device 10 and the superimposition transformer 9 or the superimposition resistor 9a. After that, from the leakage current of the two components, if0 leakage current and if1 leakage current, the capacitance is removed to calculate the pure resistance component and display the insulation resistance value or the effective leakage current value corresponding to the resistance component. To provide an insulation monitoring device it is an object.

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 Through the insulation resistance (R) and the capacitance (C) existing between the phase and the ground, the leakage current (if0) corresponding to the commercial alternating frequency (f0) to the ground and the low voltage side of the high-voltage / low-voltage transformer (1) The superposed transformer 9 or the superimposed resistor 9a and the low frequency superimposition device 10, which are separately installed between the neutral point (or one earthing point) and the ground, are superimposed on the second earth line 2 The image current transformer 17 or 19 detects a leakage current if1 corresponding to a low frequency signal at which the low frequency f1 signal flows between the phase 4 and the ground of the converter 4 and the load 5 through the switch 3. The insulation monitoring device 18 amplifies, filters, and calculates the leakage current if0 + if1 corresponding to the two frequency components detected by the current transformer 17 or 19. By removing the capacitance (C) component, the insulation state corresponding to the pure resistance component of the earth leakage, that is, insulation resistance or effective leakage current is monitored.

      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 and the leakage current if1 of the low frequency component detected by the image current transformer 17 or 19 are converted into voltage through the current / voltage converter 12 and the amplifier 13 is converted into a voltage. After amplifying the minute voltage through the component, the component corresponding to the commercial frequency (f0) is extracted only the component corresponding to the commercial frequency (f0) through the bandpass filter for commercial frequency (14a) and the extracted commercial frequency component is commercial frequency If0a is detected through the amplifier 15a. Meanwhile, the component corresponding to the low frequency f1 is extracted only from the component corresponding to the low frequency f1 through the band pass filter 14b for the low frequency f1, and if1b is extracted through the extracted low frequency f1 amplifier 15b. Detect. The voltage component if0a corresponding to the detected leakage current of the commercial frequency and the voltage component if1a corresponding to the leakage current of the low frequency are transmitted to the CPU 41 in the control device 40 through the analog / digital converters 16a and 16b, respectively. When input, the CPU 41 removes the capacitance component corresponding to the reactive component and extracts only the insulation resistance component corresponding to the active component through the following calculation process.

  The symbols used in the following calculations are as follows.

    f0: Commercial AC (60Hz or 50Hz)

    f1: 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 low frequency f1 detected by image transformer 17 or 19

    a: Total amplification factor of current / voltage converter 12, amplifier 13 and amplifier 15a corresponding to commercial frequency f0

    b: Total amplification factor of current / voltage converter 12, amplifier 13, and amplifier 15b corresponding to low frequency f1c.

    E0: Phase-to-earth phase voltage corresponding to commercial frequency (f0)

    E1: Low frequency (f1) 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

    The leakage current of if0a and the low frequency component corresponding to the leakage current of the commercial frequency component corresponding to the input values of the analog / digital converter 16a and the analog / digital converter 16b in the insulation monitoring device 18 The component if1a is

      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.

    Looking at the function related to the insulation resistance R in equation (5), regardless of the capacitance C

식을 사용하여 절연저항치를 저항성분에 의한 유효 누설전류값으로 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.Can be calculated, and the insulation resistance R value calculated above

Using the formula, the insulation resistance value can be calculated as the effective leakage current value by the resistance component. 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.

 Also, as in Eq. (5), if the input values of the analog / digital converters 16a and 16b are adjusted so that the E0 and E1 values are the same by adjusting the amplification degrees a and b, the calculation can be simplified as in the following equation. have.

 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. E0, E1, f0, f1 values necessary 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 E0, E1, f0, f1, calculated on the insulation resistance value R or the effective leakage current value as described above, and the 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.

As described above, the present invention provides a low frequency signal by a superposition transformer or a superimposed resistor and a low frequency superimposition device connected between a ground and two types of ground wires connected to a neutral point or one ground point of a high-voltage / low voltage conversion transformer in a live state of a commercial AC frequency. Is superimposed on a commercial AC converter and has two types of leakage currents (if0) and low-frequency leakage current (if1) detected by the image transformer in the middle of two ground lines or converters. It removes the capacitance component between the phase of the converter and the load and the ground irrespective of irrelevant conditions, and detects only the insulation resistance component or effective leakage current value directly related to insulation degradation (leakage). Insulation monitoring device that solves the problem of detection and measurement and also monitors the insulation state of low-voltage converter in live state It is possible to effectively monitor and measure the insulation state of low-voltage converters in live state easily in any place without difficulty 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 works. In addition, an alarm output unit and a communication unit may be added to configure a device that can be controlled remotely.

Claims (3)

The low frequency signal voltage is superimposed on the low voltage circuit through the ground line connected to the neutral point or ground of the low voltage side transformer, and the low current component leakage current component (if1) leaked between the phase of the converter or load and the ground by the low frequency signal voltage, Leakage current component (if0) of the commercial frequency component leaked between the phase and ground of the converter or load by the commercial frequency alternating current voltage is detected through the image current transformer, and the current / voltage converter, the amplifier and the commercial band bandpass filter, low frequency The capacitance corresponding to the leakage current leaked by the commercial frequency voltage converted using the band pass filter and the analog / digital converter, and the leakage current leaked by the low frequency signal voltage In order to eliminate the influence of components, it is possible to calculate and detect insulation resistance value or effective leakage current value by using the following formula. The low pressure around the live wire of the insulation monitoring system in which

 Where E0 is the voltage across the earth at the commercial frequency. F0 is the commercial frequency and f1 is the low frequency. E1: low frequency signal voltage, a: amplification degree corresponding to commercial frequency, b: amplification degree corresponding to low frequency, if0a: final amplified leakage current value corresponding to commercial frequency component if1a: final amplified leakage current for low frequency component) For commercial AC voltage

Or for low frequency signal voltage

The low-frequency signal voltage is superimposed on the low-voltage circuit through the neutral point of the low-voltage transformer or the ground wire connected to one ground, and the low-frequency leakage voltage component (if1) of the low-frequency component leaked between the phase and ground of the converter or load by this low-frequency signal voltage is commercially available. Leakage current component (if0) of commercial frequency component leaked between phase and ground of converter or load by frequency alternating voltage is detected through image current transformer, current / voltage converter, amplifier, commercial frequency bandpass filter and low frequency Capacitance component by reading the value corresponding to the leakage current leaked by the commercial frequency voltage converted by the band pass filter and the analog / digital converter, and the value corresponding to the leakage current leaked by the low frequency signal voltage, respectively. In order to eliminate the influence and simplify the calculation of the insulation resistance, the amplification degree of the current / voltage converter and the amplifier is electronically adjusted. The analog / digital conversion unit to the input voltage magnitude is formed by isolated following hot-line of low pressure, characterized in that before indicating to calculate the insulation resistance value or the effective leakage current value by using a calculation formula, such as monitoring devices

Where E0 is the voltage across the earth at the commercial frequency. F0 is the commercial frequency and f1 is the low frequency. E1: low frequency signal voltage, if0a: final amplified leakage current value corresponding to commercial frequency component, if1a: final amplified leakage current value corresponding to low frequency component, α: constant related to amplification factor) For commercial AC voltage

Or for low frequency signal voltage

The live wire insulation monitoring device of claim 1 or 2, wherein the alarm output unit (48) or the communication unit (49) is configured to be remotely monitored.

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