WO2023085697A1

WO2023085697A1 - Insulation monitoring device for insulation-terra system

Info

Publication number: WO2023085697A1
Application number: PCT/KR2022/017212
Authority: WO
Inventors: 박병철; 정규창; 오성문
Original assignee: 한국전자기술연구원
Priority date: 2021-11-09
Filing date: 2022-11-04
Publication date: 2023-05-19
Also published as: KR20230067208A; KR102634381B1

Abstract

The present invention provides an insulation monitoring device for an insulation-terra system, comprising: a signal application unit for applying a direct current detection signal to a transmission line in order to monitor a ground fault in an insulation-terra system transmitting power through the transmission line; a calculation unit for calculating a return current, which returns to the signal application unit in response to the direct current detection signal if a ground fault occurs; a sensor unit, which includes a core disposed in the transmission line and a first coil wound on the core, applies an alternating current to the first coil and detects a direct current offset current induced by the direct current detection signal if a ground fault occurs; and a fault monitoring unit for monitoring a ground fault on the basis of at least one from among the return current and the direct current offset current.

Description

Insulation monitoring device for ungrounded power systems

The present invention relates to a technique for detecting leakage current in an ungrounded power system.

The present invention is derived from research conducted as part of other projects of the Small and Medium Business Technology Information Promotion Agency below.

[Assignment identification number] 1425147376

[Assignment number] S3035699

[Name of Department] Ministry of Small and Medium Venture Business

[Task management (professional) organization name] Small and Medium Business Technology Information Promotion Agency

[Research project name] Other projects

[Research Project Title] Development of DC electricity measurement and relay solution technology for common demand in new energy (electric power) industries

[Contribution rate] 1/1

[Name of project performing organization] Korea Institute of Electronics Technology

[Research period] 2020.12.01 ~ 2022.11.30

The power system is divided into a grounded power system and an ungrounded power system depending on whether or not it is insulated from the ground (ground).

In the grounding power system, the power system is connected to the ground, and there are TN (Terra-Neutral) and TT (Terra-Terra). In Korea, distribution lines supplied with power from KEPCO use TN grounding, and power supplied indoors after transformers uses TT grounding.

The non-grounded power system (IT System: Insulation-Terra System) means a method of insulating the ground and the power system. The ungrounded power system is used in solar power plants, ESS (Energy Storage System), electric vehicles, power plant batteries, and on-site power grids.

In the ungrounded power system, even if a ground fault occurs in which one line of the power system is connected to the ground, almost no fault current (If) flows because the entire system is insulated from the ground. Even if a ground fault occurs in one line, the system can be used normally, but if a ground fault occurs in other lines while no action is taken, a high fault current flows and the entire system is blacked out. Therefore, in order to increase the reliability of an ungrounded power system, it is necessary to perform grounding detection (insulation monitoring) before a system blackout occurs, identify which line (point) has a grounding fault, and eliminate the fault.

To this end, conventional technologies apply a detection signal to an ungrounded power system to measure the voltage and current between the ground (PE: Protected Earth) and the ungrounded power system to detect ground fault resistance, and apply a separate detection signal A method of detecting the ground fault resistance by measuring the voltage and current between the ground and the ungrounded power system by intentionally causing a ground fault by a known resistance value to ground the ungrounded power system without doing so has been used.

However, this method according to the prior art has a problem in that the longer the power wiring, the more difficult it is to install the measurement equipment, and the longer the wiring, the larger the leakage capacitance, so there is an error in measuring the detection signal due to the circulating current caused by this. . In addition, since the detection signal is a small signal with a very small output, it is difficult to distinguish between the detection signal and noise when affected by EMC (Electro-Magnetic Compatibility) noise generated from a peripheral power system, resulting in frequent signal detection malfunctions.

The inventors of the present invention have made research efforts to solve the problems of the prior art ungrounded power system insulation monitoring device. After much effort to complete an insulation monitoring device and method that can increase the reliability of detection signals while being easy to install and manage for ground detection of ungrounded power systems, the present invention has been completed.

In order to solve the problems of the prior art as described above, an object of the present invention is to provide an insulation monitoring device for an ungrounded power system having a simple system and high reliability.

The technical problems to be achieved in the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. There will be.

In order to solve the above problems, the present invention provides a signal applying unit for applying a DC detection signal to a transmission line in order to monitor a ground fault in an ungrounded power system that transmits power through a transmission line, and a DC detection in case of a ground fault. It includes a calculator that calculates a return current that returns to the signal applicator in response to a signal, a core disposed on a transmission line, and a first coil wound around the core, applying an alternating current to the first coil and detecting direct current in case of a ground fault. Provided is an insulation monitoring device for an ungrounded power system including a sensor unit for detecting a DC offset current induced by a signal and a fault monitoring unit for monitoring a ground fault based on at least one of a return current and a DC offset current.

Here, the fault monitoring unit may determine a ground fault when at least one of the return current and the DC offset current is greater than or equal to a reference value.

Also, in the event of a ground fault, a coil current obtained by adding a DC offset current to an AC current may flow through the first coil.

In addition, the sensor unit may calculate the DC offset current by removing the AC current from the coil current.

In addition, the insulation monitoring device of the ungrounded power system of the present invention includes a second coil wound around the core, and further includes a compensation unit for applying a compensation current corresponding to the AC current and in the opposite direction to the AC current to the second coil. can do.

In addition, the sensor unit may be provided in each of a plurality of transmission lines located at different positions.

Also, the calculation unit may transmit the return current to the fault monitoring unit, and the sensor unit may transmit the DC offset current to the accident monitoring unit.

Also, the fault monitoring unit may detect the position of the transmission line where the ground fault has occurred based on the DC offset current.

In addition, the fault monitoring unit may determine that a ground fault has occurred at a location of a transmission line where a sensor unit transmitting a DC offset current is disposed.

According to the present invention, by detecting a ground fault in an ungrounded power system using a DC detection signal, a system compared to the AC detection signal application and AC current detection method is simple and can provide high reliability.

In addition, according to the present invention, since a DC voltage without frequency is applied as a detection signal, there is no effect of leakage capacitance between the transmission line and the ground, so there is no need to distinguish between reactive power and active power, and when a DC leakage current is detected, the ground fault current can be judged by

In addition, according to the present invention, insulation resistance can be precisely measured by return current, and a ground fault occurrence point can be detected regardless of current measurement accuracy in the form of whether or not it has occurred.

The effects obtainable in the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the description below. will be.

1 is a diagram schematically illustrating an ungrounded power supply system.

FIG. 2 is a diagram illustrating a phase synchronization based insulation monitoring device for monitoring insulation in the ungrounded power system of FIG. 1 .

3 is a schematic block diagram of an insulation monitoring device for an ungrounded power system according to an embodiment of the present invention.

4 is a schematic circuit diagram of an insulation monitoring device for an ungrounded power system according to an embodiment of the present invention.

5 is a specific circuit diagram of the sensor unit of FIG. 3 .

FIG. 6 is a specific circuit diagram for forcibly applying an alternating current to a coil in the circuit diagram of FIG. 5 .

7 is a graph showing a waveform of a coil current flowing through a first coil.

FIG. 8 is a graph showing a waveform obtained by removing an alternating current from the coil current of FIG. 7 .

FIG. 9 is a specific circuit diagram for compensating an alternating current forcibly applied to a coil in the circuit diagram of FIG. 5 .

10 is an overall diagram of an insulation monitoring device applied to an ungrounded power system according to an embodiment of the present invention.

In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be implemented in various forms and various changes may be made. However, the description of the present embodiment is provided to complete the disclosure of the present invention and to completely inform those skilled in the art of the scope of the invention to which the present invention belongs. In the accompanying drawings, the size of the components is enlarged from the actual size for convenience of description, and the ratio of each component may be exaggerated or reduced.

Terms such as 'first' and 'second' may be used to describe various elements, but the elements should not be limited by the above terms. The above terms may only be used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a 'first element' may be named a 'second element', and similarly, a 'second element' may also be named a 'first element'. can Also, singular expressions include plural expressions unless the context clearly indicates otherwise. Terms used in the embodiments of the present invention may be interpreted as meanings commonly known to those skilled in the art unless otherwise defined.

1 is a diagram schematically illustrating an ungrounded power supply system. And, FIG. 2 is a diagram showing a phase synchronization based insulation monitoring device for monitoring insulation in the ungrounded power system of FIG. 1 .

The ungrounded power system refers to a power system that is not grounded with the ground (PE), that is, is insulated from the ground, and transmits power to each load through transmission lines L1 and L2.

Referring to FIG. 1 , since the transmission lines L1 and L2 of the ungrounded power system are insulated from the ground PE, theoretically, no current flows between the transmission lines L1 and L2 and the ground PE. However, in reality, since a minute leakage current (Ic) flows due to the leakage capacitor (Ce) existing between the transmission lines (L1, L2) and the ground (PE), the transmission lines (L1, L2) and the ground (PE) are completely not insulated

In addition, when a ground fault occurs between the transmission lines (L1, L2) and the ground (PE), a ground fault resistance (R _F ) is generated, and this ground fault resistance (R _F ) causes the transmission line (L1, L2) and the ground to A large amount of ground fault current (If) flows between (PE). Accordingly, the power is cut off, resulting in a power outage accident.

In order to monitor such a ground fault, it is necessary to distinguish between the leakage current Ic and the ground fault current If.

Hereinafter, a phase synchronization based insulation monitoring device for monitoring a ground fault by distinguishing the leakage current (Ic) and the ground fault current (If) will be described.

Referring to Figure 2, the phase synchronization based insulation monitoring device is composed of a detection signal generator 10 and a plurality of detection signal detectors (20, 21, 22).

Here, the detection signal detectors 20, 21, and 22 may include a Current Transformer (CT) using the AC induced electromotive force principle, and the detection signal detectors 20, 21, and 22 may include a CT at different locations. Each of the plurality of transmission lines may be provided.

The detection signal generator 10 generates an AC detection signal for detecting a ground fault and transmits it to the transmission lines L1 and L2 of the ungrounded power system, and the detection signal detectors 20, 21 and 22 generate an AC detection signal The current signal corresponding to is sensed and transmitted back to the detection signal generator 10.

Then, the detection signal generator 10 compares the current signal received from the detection signal detectors 20, 21, and 22 with the AC detection signal to detect whether or not ground resistance occurs and the location of a ground fault.

At this time, the AC detection signal Vs transmitted by the detection signal generator 10 has a phase difference of 90 degrees from the phase of the leakage current Ic caused by the leakage capacitor. That is, since the leakage current (Ic) caused by the leakage capacitor corresponds to the reactive current in relation to the AC detection signal, it is not a detection target.

However, the ground fault current If caused by the ground fault resistance R _F has the same phase as the AC detection signal Vs.

Using this phase difference, the insulation monitoring device classifies the leakage current (Ic) by the leakage capacitor (Ce) and the ground fault current (If) by the ground fault resistance (R _F ) by the phase difference to determine whether or not ground resistance has occurred and ground. The location of the accident can be identified.

In this way, in order to distinguish the leakage current Ic and the ground fault current If using the phase difference, phase synchronization between the detection signal detector 20 and the detection signal generator 10 is essential. However, there is a problem in that system complexity increases due to such phase synchronization and reliability of ground fault detection is lowered when an error occurs in phase synchronization.

3 is a schematic block diagram of an insulation monitoring device for an ungrounded power system according to an embodiment of the present invention. 4 is a schematic circuit diagram of an insulation monitoring device for an ungrounded power system according to an embodiment of the present invention.

3 and 4, the insulation monitoring device of the ungrounded power system includes a signal application unit 110, a calculation unit 120, a sensor unit 130, a compensation unit 140, and an accident monitoring unit 150. It can be configured to include.

The signal applying unit 110 may apply a DC detection signal Vd to the transmission lines L1 and L2 in order to monitor a ground fault in an ungrounded power system that transmits power through the transmission lines L1 and L2. .

At this time, if a ground fault occurs between the transmission lines (L1, L2) and the ground (PE), the ground fault current (If) corresponding to the DC detection signal (Vd) is applied as a signal through the ground fault resistance (R _F ). It will return to section 110.

The calculation unit 120 may calculate the return current (ground fault current) If returning to the signal applying unit 110 in response to the DC detection signal Vd.

In the insulation monitoring device of the present invention, since the DC detection signal Vd is applied to the transmission lines L1 and L2 to detect a ground fault, the leakage current Ic by the leakage capacitor Ce is zero (0). ) becomes Accordingly, in determining a ground fault, it is not necessary to distinguish between the leakage current Ic caused by the leakage capacitor Ce and the return current If caused by the ground fault resistance R _F .

The calculation unit 120 includes a detection resistance Rd connected between the signal application unit 110 and the ground PE, and when the voltage Vr of both ends of the detection resistance Rd is measured, Ohm's law ( The return current (if) can be calculated by Vr/Rd). Also, the calculation unit 120 may transmit the calculated return current If to the accident monitoring unit 150 through communication.

In addition, the calculation unit 120 uses Kirchhoff's law based on the detection resistance (Rd), the DC detection signal (Vd), and the return current (if) at the location of the transmission line (L1, L2) where the ground fault occurred. Insulation resistance (R _F ) can be calculated.

The signal applying unit 110 may be a variable voltage source so that the return current If is less than the target current. In this case, if the insulation resistance R _F is relatively low, the level of the DC detection signal Vd is lowered and the insulation resistance is relatively low. If the resistance R _F is relatively high, the magnitude of the DC detection signal Vd can be increased.

The sensor unit 130 is disposed on the transmission lines L1 and L2 and can detect a DC offset current induced by the DC detection signal Vs when a ground fault occurs.

The fault monitoring unit 150 may monitor a ground fault based on at least one of the DC offset current and the return current If. That is, if at least one of the DC offset current and the return current (If) is detected by the fault monitoring unit 150, it may be determined as a ground fault, or if the DC offset current and the return current (If) are greater than or equal to a reference value, it may be determined as a ground fault.

5 is a specific circuit diagram of the sensor unit of FIG. 3 , and FIG. 6 is a specific circuit diagram for forcibly applying an alternating current to a coil in the circuit diagram of FIG. 5 . 7 is a graph showing a waveform of a coil current flowing through the first coil, and FIG. 8 is a graph showing a waveform obtained by removing an AC current from the coil current of FIG. 7 . And, FIG. 9 is a specific circuit diagram for compensating the AC current forcibly applied to the coil in the circuit diagram of FIG. 5 .

5 and 6, the sensor unit 130 may be a current transformer (CT) as a current sensor using the principle of alternating current induced electromotive force, and the core 131 disposed on the transmission lines L1 and L2 and a first coil 132 wound around the core 131 .

On the other hand, when the DC detection signal Vd is continuously applied to the transmission lines L1 and L2 to monitor the ground fault of the ungrounded power system, the core 131 of the sensor unit 130 is saturated and no longer operates as a current transformer. cannot fulfill the role of

Accordingly, the sensor unit 130 prevents the core 131 from being saturated by applying the AC voltage (alternating voltage) Vs to the first coil 132 . At this time, an AC current (is) flows in the first coil 132 due to the AC voltage (Vs).

Specifically, the sensor unit 130 includes a first operational amplifier op1, a first resistor R1, a second resistor R2, and a first operational amplifier op1 to apply an alternating current is to the first coil 132. It may be configured to include a current controller 133.

Here, the first current controller 133 is connected to one end of the first coil 132 wound around the core 131, and between one end of the first coil 132 and the first current controller 133, first and second The second resistors R1 and R2 are connected in series. The non-inverting terminal (+) of the first operational amplifier op1 is connected between the first and second resistors R1 and R2, and the inverting terminal (-) of the first operational amplifier op1 is connected to the first coil. It is connected to the other end of (132).

Here, the number of windings of the first coil 132 may be adjusted according to the detection range of the return current If or DC offset current.

As described above, the alternating current (is) is applied to the first coil 132 . In addition, when the signal applying unit 110 applies the DC detection signal Vd to the transmission lines L1 and L2, the primary side of the transmission lines L1 and L2 due to the ground fault resistance R _F when a ground fault occurs. A DC current ip flows, and a DC offset current is induced in the first coil 132 by the primary side DC current ip.

Referring to FIG. 7 , when no ground fault occurs, the coil current i _ST flowing through the first coil 132 includes only the alternating current is (a). However, when a ground fault occurs, a coil current (i _ST ) obtained by adding a DC offset current to an AC current (is) flows in the first coil 132 (b).

At this time, in order to measure the coil current i _ST , a shunt resistor Rs may be connected between the other end of the first coil 132 and the inverting terminal (-) of the first operational amplifier op1, and the sensor unit 130 can measure the coil current (i _ST ) by Ohm's law (V _ST /Rs) by measuring the voltage (V _ST ) across the shunt resistor (Rs).

The sensor unit 130 may calculate the DC offset current by removing the AC current is from the coil current i _ST . At this time, referring to FIG. 8 , if a ground fault does not occur, the DC offset current is almost zero (0) (a), and if a ground fault occurs, it can be confirmed that a DC offset current of a certain value or more appears ( b).

The sensor unit 130 may transmit the calculated DC offset current to the accident monitoring unit 150 through communication.

The fault monitoring unit 150 may determine whether a ground fault has occurred based on the DC offset current received from the sensor unit 130 . That is, when the DC offset current is detected, it can be determined as a ground fault. In this case, when the DC offset current is greater than or equal to the reference value, it may be determined as a ground fault.

Meanwhile, when the alternating current (is) is forcibly applied to the first coil 132, the current (Icc) flowing through the transmission lines (L1, L2) is also affected. Therefore, it is preferable to remove the effect on the transmission lines L1 and L2 by flowing the compensation current i _T in the opposite direction to the AC current is applied to the first coil 132 .

To this end, the compensation unit 140 includes a second coil 141 wound around the core 131, and applies a compensation voltage V _T to the second coil 141 in response to the AC current is. can do. Accordingly, the compensating current i _T according to the compensating voltage V _T flows in the second coil 141 in the opposite direction to the alternating current is, so that the alternating current is flowing in the first coil 131 The influence on the transmission lines L1 and L2 can be removed.

5 and 9, the compensation unit 140 includes a low-pass filter 142, an integrator 143, and a second operational amplifier op2 to apply a compensation current i _T to the second coil 141. ) and a second current controller 144.

One end of the second coil 141 is connected to the second current controller 144, and the second current controller is connected to the output terminal of the second operational amplifier op2. Then, the integrator 143 is input to the non-inverting terminal (+) of the second operational amplifier op2 and the low-pass filter 142 is connected to the integrator 143. And, the other end of the second coil 141 is connected to the inverting terminal (-) of the second operational amplifier op2.

Here, when the voltage (V _ST ) across the shunt resistor (Rs) is input to the non-inverting terminal (+) of the second operational amplifier (op2) via the low-pass filter (142) and the integrator (143), the second coil ( 141), the compensating current (i _T ) flows.

In order to measure the compensation current (i _T ), a measurement resistance (R _T ) may be connected between the other end of the second coil 132 and the inverting terminal (-) of the first operational amplifier (op1), and the sensor unit 130 ) can measure the compensation current (i _T ) flowing through the second coil 141 by Ohm's law (V _T / R _T ) when the voltage ( _VT ) across the measured resistance (R _T ) is measured.

Referring to FIG. 10 , an ungrounded power supply system may include a plurality of transmission lines branched from a bus line, and sensor units 130 may be provided in each of a plurality of transmission lines at different locations.

The fault monitoring unit 150 may receive the return current If from the calculation unit 120 and the DC offset current from the sensor unit 130 to monitor the ground fault and its location.

Specifically, the fault monitoring unit 150 may determine a ground fault when one of the DC offset current and the return current (If) is received or when the received DC offset current and the return current (If) are greater than or equal to a reference value.

On the other hand, it is difficult to determine at which transmission line position among a plurality of transmission lines a ground fault has occurred using only the return current If.

Accordingly, the fault monitoring unit 150 may detect the position of the transmission line where the ground fault has occurred based on the DC offset current.

Specifically, the fault monitoring unit 150 may determine that a ground fault has occurred at a location of a transmission line where the sensor unit 130 transmitting the DC offset current is disposed. In this case, the sensor unit 130 may transmit the DC offset current along with its own identification code in order to identify each sensor unit 130 .

The fault monitoring unit 150 may include a display unit (not shown) that displays the return current If and the DC offset current for each of the plurality of transmission lines in numbers, etc. In this case, the display unit is normal and a ground fault occurs The transmitted transmission lines can be distinguished and displayed with LED lights.

As described above, the insulation monitoring device of an ungrounded power system according to an embodiment of the present invention detects a ground fault in an ungrounded power system using a DC detection signal, so that the system is simple and compared to the AC detection signal application and AC current detection method. , can provide high reliability.

In addition, since DC voltage without frequency is applied as a detection signal, there is no influence of leakage capacitance between the transmission line and the ground, so it is not necessary to distinguish between reactive power and active power. When a DC leakage current is detected, it can be immediately determined as a ground fault current. .

In addition, insulation resistance can be precisely measured by return current, and a ground fault occurrence point can be detected regardless of current measurement accuracy.

In the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention is not limited to the described embodiments, and should be defined by the following claims and equivalents thereof.

The insulation monitoring device of the ungrounded power system of the present invention can be used in ungrounded power systems such as photovoltaic power plants, energy storage systems (ESSs), electric vehicles, power plant batteries, and on-site power grids.

Claims

a signal applying unit for applying a DC detection signal to the transmission line in order to monitor a ground fault in an ungrounded power system that transmits power through the transmission line;

a calculator configured to calculate a return current returning to the signal applying unit in response to the direct current detection signal when the ground fault occurs;

A sensor unit including a core disposed on the transmission line and a first coil wound around the core, applying an alternating current to the first coil and detecting a DC offset current induced by the DC detection signal when the ground fault occurs. ; and

Fault monitoring unit for monitoring the ground fault based on at least one of the return current and the DC offset current

Insulation monitoring device of ungrounded power system including.
According to claim 1,

The accident monitoring department

If at least one of the return current and the DC offset current is greater than or equal to a reference value, determining the ground fault

Insulation monitoring device for ungrounded power systems.
According to claim 1,

In the first coil

In the case of the ground fault, a coil current obtained by adding a DC offset current to the AC current flows

Insulation monitoring device for ungrounded power systems.
According to claim 3,

The sensor part

Calculating the DC offset current by removing the AC current from the coil current

Insulation monitoring device for ungrounded power systems.
According to claim 1,

A compensation unit including a second coil wound around the core and applying a compensating current corresponding to the AC current and in a direction opposite to the AC current to the second coil.

Insulation monitoring device of an ungrounded power system further comprising a.
According to claim 1,

The sensor part

Each of the plurality of transmission lines at different locations is provided

Insulation monitoring device for ungrounded power systems.
According to claim 6,

The calculation unit

Transmitting the return current to the accident monitoring unit

Insulation monitoring device for ungrounded power systems.
According to claim 7,

The sensor part

Transmitting the DC offset current to the accident monitoring unit

Insulation monitoring device for ungrounded power systems.
According to claim 6,

The accident monitoring department

Detecting the location of the transmission line where the ground fault occurred based on the DC offset current

Insulation monitoring device for ungrounded power systems.
According to claim 6,

The accident monitoring department

Determining that the ground fault has occurred at the location of the transmission line where the sensor unit transmitting the DC offset current is disposed

Insulation monitoring device for ungrounded power systems.