KR102634381B1 - Apparatus for monitoring insulation of insulation-terra system based - Google Patents

Abstract

The present invention includes a signal applicator that applies a direct current detection signal to the transmission line to monitor a grounding fault in an ungrounded power system that transmits power through a transmission line, and a return to the signal applicator in response to the direct current detection signal in the event of a grounding fault. It includes a calculation unit that calculates a return current, a core disposed on a transmission line, and a first coil wound on the core, and applies an alternating current to the first coil, and a direct current offset current induced by a direct current detection signal in the event of a ground fault. An insulation monitoring device for an ungrounded power system is provided, including a sensor unit that detects and an accident monitoring unit that monitors a grounding fault based on at least one of return current and direct current offset current.

Description

{APPARATUS FOR MONITORING INSULATION OF INSULATION-TERRA SYSTEM BASED}

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

The power system is divided into a grounded power system and a non-grounded power system depending on whether it is insulated from the ground (ground).

The grounded power system is connected to the ground and includes TN (Terra-Neutral) and TT (Terra-Terra). In Korea, the distribution line that supplies power from KEPCO uses TN grounding, and the power supplied indoors after the transformer uses TT grounding.

An ungrounded power system (IT System: Insulation-Terra System) refers to a method of insulating the power system from the ground. Ungrounded power systems are used in solar power plants, ESS (Energy Storage System), electric vehicles, power plant batteries, and on-site power grids.

In an ungrounded power system, even if a grounding fault occurs where one line of the power system is connected to the ground, the entire system is insulated from the ground, so almost no fault current (If) flows. Even if a grounding fault occurs on one line, the system can be used normally, but if a grounding fault occurs on another line while no action is taken, a high fault current will flow, resulting in a blackout of the entire system. Therefore, in order to increase the reliability of the ungrounded power system, grounding detection (insulation monitoring) must be performed before a system power outage occurs, and the fault must be eliminated by identifying which line (point) the grounding fault occurred on.

For this purpose, conventional technologies apply a detection signal to an ungrounded power system to measure voltage and current between ground (PE: Protected Earth) and an ungrounded power system to detect ground fault resistance, and apply a separate detection signal. Instead, a method has been used to intentionally connect the ungrounded power system to the ground, causing a grounding fault due to a known resistance value, and detect the grounding fault resistance by measuring the voltage and current between the grounded and ungrounded power system.

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

The inventors of the present invention have made research efforts to solve the problems of the conventional ungrounded power system insulation monitoring device. After much effort, the present invention was completed to complete an insulation monitoring device and method that can increase the reliability of the detection signal while being easy to install and manage for grounding detection of an ungrounded power system.

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

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, 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-described problem, the present invention includes a signal applicator that applies a direct current detection signal to the transmission line to monitor a grounding fault in an ungrounded power system that transmits power through the transmission line, and a direct current detection signal in the event of a grounding fault. It includes a calculation unit that calculates a return current returning to the signal application unit in response to a signal, a core disposed on a transmission line, and a first coil wound around the core, and applies an alternating current to the first coil and detects direct current in the event of a grounding fault. An insulation monitoring device for an ungrounded power system is provided, including a sensor unit that detects a direct current offset current induced by a signal, and a fault monitoring unit that monitors a grounding fault based on at least one of return current and direct current offset current.

Here, the accident monitoring unit may determine a grounding accident if at least one of the return current and the direct current offset current is greater than or equal to the reference value.

Additionally, in the event of a grounding fault, a coil current obtained by adding a direct current offset current to an alternating current may flow through the first coil.

Additionally, the sensor unit can calculate the direct current offset current by removing the alternating 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 that corresponds to an alternating current and applies a compensation current in the opposite direction to the alternating current to the second coil. can do.

Additionally, the sensor unit may be provided on a plurality of transmission lines located at different locations.

In addition, the calculation unit may transmit the return current to the accident monitoring unit, and the sensor unit may transmit the direct current offset current to the accident monitoring unit.

Additionally, the fault monitoring unit can detect the location of the transmission line where the grounding fault occurred based on the direct current offset current.

Additionally, the accident monitoring unit may determine that a grounding accident occurred at the location of the transmission line where the sensor unit that transmitted the direct current offset current is located.

According to the present invention, by detecting a grounding fault in an ungrounded power system using a direct current detection signal, the system can be simple and provide high reliability compared to the alternating current detection signal application and alternating current detection methods.

In addition, according to the present invention, since a 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 when a DC leakage current is detected, there is no need to distinguish between reactive power and active power, and the ground fault current is immediately detected. It can be judged by

In addition, according to the present invention, insulation resistance can be precisely measured using return current, and the point where a grounding fault occurs can be detected in the form of occurrence or absence regardless of the current measurement precision.

The effects that can be obtained from 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.

Figure 1 is a diagram schematically showing an ungrounded power system.
FIG. 2 is a diagram illustrating a phase synchronization-based insulation monitoring device that monitors insulation in the ungrounded power system of FIG. 1.
Figure 3 is a schematic block diagram of an insulation monitoring device for an ungrounded power system according to an embodiment of the present invention.
Figure 4 is a schematic circuit diagram of an insulation monitoring device for an ungrounded power system according to an embodiment of the present invention.
Figure 5 is a detailed circuit diagram of the sensor unit of Figure 3.
FIG. 6 is a specific circuit diagram for forcibly applying alternating current to the coil in the circuit diagram of FIG. 5.
Figure 7 is a graph showing the waveform of the coil current flowing in the first coil.
FIG. 8 is a graph showing a waveform obtained by removing the alternating current from the coil current of FIG. 7.
FIG. 9 is a specific circuit diagram for compensating the alternating current forcibly applied to the coil in the circuit diagram of FIG. 5.
Figure 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 attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various changes can be made. However, the description of this embodiment is provided to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the present invention of the scope of the invention. In the attached drawings, components are shown enlarged in size for convenience of explanation, and the proportions of each component may be exaggerated or reduced.

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

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

An ungrounded power system refers to a power system that is not grounded to 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, the transmission lines (L1, L2) of the ungrounded power system are insulated from the ground (PE), so theoretically, no current flows between the transmission lines (L1, L2) and the ground (PE). However, in reality, a small leakage current (Ic) flows due to the leakage capacitor (Ce) existing between the transmission lines (L1, L2) and the ground (PE), so that the transmission lines (L1, L2) and the ground (PE) are completely connected. It is not insulated.

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

In order to monitor such ground faults, leakage current (Ic) and ground fault current (If) must be distinguished.

Hereinafter, we will describe a phase synchronization-based insulation monitoring device that monitors ground faults by distinguishing between leakage current (Ic) and ground fault current (If).

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

Here, the detection signal detection units 20, 21, and 22 may include a current transformer (CT) using the principle of alternating current induced electromotive force, and are located at different positions. It may be provided on each of a plurality of transmission lines.

The detection signal generator 10 generates an alternating current detection signal for ground fault detection and transmits it to the transmission lines (L1, L2) of the ungrounded power system, and the detection signal detectors 20, 21, and 22 generate an alternating current detection signal. The current signal corresponding to is detected 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 ground resistance has occurred and the location of the ground fault.

At this time, the alternating current 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. In other words, the leakage current (Ic) caused by the leakage capacitor corresponds to a reactive current in relation to the AC detection signal and is therefore not a detection target.

However, the ground fault current (If) due to the ground fault resistance (R _F ) has the same phase as the alternating current detection signal (Vs).

Using this phase difference, the insulation monitoring device distinguishes between the leakage current (Ic) caused by the leakage capacitor (Ce) and the ground fault current (If) caused by the ground fault resistance ( _RF ) by the phase difference to determine whether ground resistance has occurred and the ground fault current (If). You can determine where an accident occurred.

In order to distinguish between 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, this phase synchronization increases system complexity and, if an error occurs in phase synchronization, the reliability of ground fault detection is lowered.

Figure 3 is a schematic block diagram of an insulation monitoring device for an ungrounded power system according to an embodiment of the present invention. And, Figure 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 may be configured to include.

The signal applicator 110 may apply a direct current detection signal (Vd) to the transmission lines (L1, L2) to monitor grounding faults in the ungrounded power system that transmits power through the transmission lines (L1, L2). .

At this time, if a grounding fault occurs between the transmission lines (L1, L2) and the ground (PE), the grounding fault current (If) corresponding to the direct current detection signal (Vd) is signaled through the grounding fault resistance (R _F ). It returns to wealth (110).

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

Since the insulation monitoring device of the present invention applies a direct current detection signal (Vd) to the transmission lines (L1 and L2) in order to detect a grounding fault, the leakage current (Ic) due to the leakage capacitor (Ce) is zero (0). ) becomes. Accordingly, in determining a grounding fault, there is no need to distinguish between the leakage current (Ic) due to the leakage capacitor (Ce) and the return current (If) due to the grounding fault resistance (R _F ).

The calculation unit 120 includes a detection resistor (Rd) connected between the signal application unit 110 and the ground (PE), and when measuring the voltage (Vr) across the detection resistor (Rd), Ohm's law ( The return current (if) can be calculated by Vr/Rd). And, the calculation unit 120 may transmit the calculated return current (If) to the accident monitoring unit 150 by communication.

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

The signal application unit 110 may be a variable voltage source to ensure that the return current (If) is less than the target current. In this case, if the insulation resistance (R _F ) is relatively low, the magnitude of the direct current detection signal (Vd) is lowered, and the insulation resistance (R F ) is relatively low. If the resistance (R _F ) is relatively high, the magnitude of the direct current detection signal (Vd) can be increased.

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

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

FIG. 5 is a specific circuit diagram of the sensor unit of FIG. 3, and FIG. 6 is a specific circuit diagram for forcibly applying alternating current to the coil in the circuit diagram of FIG. 5. And, FIG. 7 is a graph showing the waveform of the coil current flowing in the first coil, and FIG. 8 is a graph showing the waveform of the coil current of FIG. 7 with the alternating current removed. And, FIG. 9 is a specific circuit diagram for compensating the alternating current forcibly applied to the coil in the circuit diagram of FIG. 5.

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

Meanwhile, when the direct current detection signal (Vd) is continuously applied to the transmission lines (L1, L2) to monitor grounding faults in the ungrounded power system, the core 131 of the sensor unit 130 is saturated and the current transformer no longer operates. cannot perform its role.

Accordingly, the sensor unit 130 prevents the core 131 from being saturated by applying an alternating voltage (alternating voltage) Vs to the first coil 132. At this time, an alternating current (is) flows through the first coil 132 due to the alternating 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, a first current controller 133 is connected to one end of the first coil 132 wound on the core 131, and between one end of the first coil 132 and the first current controller 133, the first and The second resistors (R1, R2) are connected in series. And, 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 turns of the first coil 132 may be adjusted according to the detection range of the return current (If) or the direct current offset current.

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

Referring to FIG. 7, if a grounding accident does not occur, the coil current (i _ST ) flowing in the first coil 132 includes only the alternating current (is) (a). However, when a grounding fault occurs, a coil current (i _ST ), which is an alternating current (is) plus a direct current offset current, flows through the first coil 132 (b).

At this time, in order to measure the coil current ( _iST ), 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) By measuring the voltage (V _ST ) across the shunt resistance (Rs), the coil current (i _ST ) can be measured according to Ohm's law (V _ST /Rs).

The sensor unit 130 may calculate a direct current offset current by removing the alternating current (is) from the coil current (i _ST ). At this time, referring to FIG. 8, it can be seen that if a grounding accident does not occur, the direct current offset current is close to zero (0) (a), and if a grounding accident occurs, a direct current offset current above a certain value appears (a). b).

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

The accident monitoring unit 150 may determine whether a grounding accident has occurred based on the direct current offset current transmitted from the sensor unit 130. In other words, if a direct current offset current is detected, it can be determined to be a grounding fault. At this time, if the direct current offset current is greater than the reference value, it can be judged to be a grounding fault.

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

For this purpose, 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 alternating current (is). can do. Accordingly, the compensation current (i _T ) according to the compensation 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, L2) can be eliminated.

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) through the low-pass filter 142 and the integrator 143, the second coil ( 141), a compensation 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 in the second coil 141 according to Ohm's law (V _T / R _T ) by measuring the voltage (V _T ) across both ends of the measurement resistance (R _T ).

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

Referring to FIG. 10, an ungrounded power system may be configured to include a plurality of transmission lines branched from a bus bar, and the sensor unit 130 may be provided on each of a plurality of transmission lines at different positions.

The accident monitoring unit 150 receives the return current (If) from the calculation unit 120 and the direct current offset current from the sensor unit 130, and can monitor the grounding accident and its location.

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

Meanwhile, it is difficult to determine at which location of a plurality of transmission lines a grounding accident occurred based on the return current (If) alone.

Accordingly, the accident monitoring unit 150 can detect the location of the transmission line where the grounding accident occurred based on the direct current offset current.

Specifically, the accident monitoring unit 150 may determine that a grounding accident has occurred at the location of the transmission line where the sensor unit 130 that transmits the direct current offset current is disposed. At this time, the sensor unit 130 may transmit its own identification code when transmitting a direct current offset current to distinguish each sensor unit 130.

The accident monitoring unit 150 may be provided with a display unit (not shown) that displays the return current (If) and the direct current offset current for each of the plurality of transmission lines in numbers, etc. In this case, the display unit indicates that a normal transmission line and a grounding accident occur. Transmission lines can be distinguished and displayed with LEDs, etc.

As such, the insulation monitoring device of the ungrounded power system according to the embodiment of the present invention detects grounding faults of the ungrounded power system using a direct current detection signal, so the system is simple compared to the alternating current detection signal application and alternating current detection methods. , can provide high reliability.

In addition, since a 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 when a DC leakage current is detected, it can be immediately judged to be a ground fault current without the need to distinguish between reactive power and active power. .

In addition, insulation resistance can be precisely measured using return current, and the point at which a grounding fault occurs can be detected in the form of occurrence or absence regardless of the current measurement precision.

In the detailed description of the present invention, specific embodiments have been described, but of course, 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, but should be defined by the claims described below and equivalents to these claims.

110: signal application unit
120: Calculation unit
130: sensor unit
140: Compensation unit
150: Accident Monitoring Department

Claims (10)

a signal application unit that applies a direct current detection signal to the transmission line to monitor a grounding fault in an ungrounded power system that transmits power through the transmission line;
a calculation unit that calculates a return current returning to the signal application unit in response to the direct current detection signal when the ground fault occurs;
A sensor unit comprising 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 direct current offset current induced by the direct current detection signal when the ground fault occurs. ; and
An accident monitoring unit that monitors the grounding fault based on at least one of the return current and the direct current 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 direct current offset current is greater than the reference value, the grounding fault is determined.
Insulation monitoring device for ungrounded power systems.
According to claim 1,
In the first coil
At the time of the grounding fault, a coil current in which a direct current offset current is added to the alternating current flows.
Insulation monitoring device for ungrounded power systems.
According to claim 3,
The sensor unit
Calculating the direct current offset current by removing the alternating current from the coil current
Insulation monitoring device for ungrounded power systems.
According to claim 1,
A compensation unit comprising a second coil wound around the core and applying a compensation current corresponding to the alternating current and in a direction opposite to the alternating current to the second coil.
An insulation monitoring device for an ungrounded power system further comprising:
According to claim 1,
The sensor unit
provided on each of the plurality of transmission lines at different locations.
Insulation monitoring device for ungrounded power systems.
According to claim 6,
The calculation part is
Transmitting the return current to the accident monitoring unit
Insulation monitoring device for ungrounded power systems.
According to claim 7,
The sensor unit
Transmitting the direct current 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 direct current offset current
Insulation monitoring device for ungrounded power systems.
According to claim 6,
The accident monitoring department
Determining that the grounding accident occurred at the location of the transmission line where the sensor unit that transmitted the direct current offset current is disposed
Insulation monitoring device for ungrounded power systems.

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