KR102452127B1 - Apparatus for monitoring overcurrent and earth leakage for both ac and dc, and method thereof - Google Patents

Abstract

The present invention relates to an AC/DC combined overcurrent blocking and leakage monitoring device. In the prior art, an AC and DC overcurrent blocking device and an earth leakage monitoring device are separately operated, a sensor and a control unit are galvanically isolated and a detection signal is used to By monitoring the leakage current, it is possible to provide an overcurrent blocking and leakage monitoring device capable of simultaneously monitoring AC/DC, thereby simplifying the overcurrent and leakage monitoring device.

Description

AC and DC combined overcurrent and leakage monitoring device and method

The present invention relates to a technology for blocking overcurrent or short circuit of a low voltage power supply.

In order to safely use low voltage electricity from fire or electric shock, an overcurrent circuit breaker and an earth leakage circuit breaker are essential. Korea's low voltage extension regulations stipulate that a circuit breaker that can monitor and block overcurrent and short circuit to prevent electric fire or electric shock must be installed in the switchboard or distribution board of a home or factory.

In the past, power grids such as Korea Electric Power Corporation (KEPCO) send electricity and consumers use them, so TN (Terra-Neutral) grounding was used for the supplier's distribution line, and TT (Terra-Terra) grounding was used indoors after the low-voltage step-down transformer. . Here, the overcurrent and earth leakage breaker were standardized and set at 60Hz AC, 220V, and 500mA or less of leakage current.

However, as many distributed power sources such as renewable energy generation, electric vehicle charging, and energy storage system (ESS) are connected to the power grid, the power system cannot be defined as a single standard as in the past. In particular, as the DC power grid (LVDC: Low Voltage Direct Current) is increasing, there is a need for a product that detects and blocks overcurrent and short circuit in DC electricity as well as AC electricity.

However, in the past when only AC was used, products that blocked AC overcurrent and short circuit could not block overcurrent and leakage of DC electricity, so there is a problem that a DC circuit breaker must be added separately. Also, in the case of a DC circuit breaker, there is a problem that there is no product capable of monitoring overcurrent and leakage at the same time. Therefore, it is necessary to separately install devices for monitoring and interrupting AC and DC overcurrent and leakage current, which inevitably increases the complexity and cost of installation.

The inventors of the present invention have been researching and trying to solve the problems of such prior art AC and DC overcurrent, leakage monitoring and interruption devices. The present invention was completed after much effort to complete a device and method capable of electronically monitoring short circuit and overcurrent of DC and AC power while simultaneously monitoring leakage current.

An object of the present invention is to provide an electronic overcurrent and leakage monitoring device and method that can be used for both AC and DC.

On the other hand, other objects not specified in the present invention will be additionally considered within the range that can be easily inferred from the following detailed description and effects thereof.

AC and DC combined overcurrent and leakage monitoring device according to the present invention,

a current sensor installed in a line of each phase of the power grid; an analog-to-digital converter for converting the value measured by the current sensor into digital; a detection signal generator generating a signal for detecting a leakage current; a detection signal detection unit for detecting the generated detection signal; and a control unit including one or more processors and a memory; including, wherein the current sensor and the control unit are galvanic isolation, and the control unit is measured by the current sensor and converted to a digital current or voltage value. It is characterized in that the DC or AC overcurrent protection function is performed and the leakage current protection function is performed by the signal detected by the detection signal sensing unit.

The current sensor is characterized in that it is a current sensor using a shunt resistor.

The controller calculates a frequency of a current measured by the current sensor and converted by the analog-to-digital converter to classify the current into alternating current or direct current.

The control unit calculates the magnitude of only the AC current by removing the DC offset component of the current when the current for which the frequency is calculated is AC, and operates a blocking circuit when the magnitude of only the AC current exceeds a preset value characterized by doing.

The control unit calculates only the magnitude of the DC current from which the intrinsic DC offset component is removed from the current when the current for which the frequency is calculated is DC, and operates the blocking circuit when the magnitude of the DC current exceeds a preset value characterized.

The control unit operates a blocking circuit when the value of the signal detected by the detection signal detection unit exceeds a preset value, and the detected signal has the same frequency and phase as the detection signal generated by the detection signal generation unit. It is characterized in that the blocking circuit is operated only when it has.

AC and DC combined overcurrent and leakage monitoring method according to another embodiment of the present invention.

receiving a current or voltage measured by a current sensor installed in a line of each phase and galvanically isolated from the control unit; generating a detection signal for detecting leakage current; detecting the detection signal in the line; performing an overcurrent protection function by the current or voltage measured by the current sensor; and performing a leakage current protection function according to the sensed detection signal.

It is characterized in that by calculating the frequency of the current or voltage measured by the current sensor, the measured current is divided into alternating current or direct current.

When the measured current is AC, calculating the magnitude of only the AC current by removing the DC offset component of the current, and operating a blocking circuit when the magnitude of only the AC current exceeds a preset value; further comprising characterized in that

When the measured current is DC, calculating the magnitude of the DC current from which the intrinsic DC offset component is removed from the current, and operating the blocking circuit when the magnitude of the DC current exceeds a preset value; characterized.

When the value of the detected detection signal exceeds a preset value, the blocking circuit is operated, but the blocking circuit is operated only when the detected detection signal has the same frequency and phase as the detection signal generated by the detection signal generator characterized by doing.

According to the present invention, since one device can be used for both AC and DC, installation is simple and cost can be saved.

In addition, there is an advantage in that a circuit breaker of a DC electric network, which has been implemented with two conventional circuit breakers, can be implemented as one.

On the other hand, even if it is an effect not explicitly mentioned herein, it is added that the effects described in the following specification expected by the technical features of the present invention and their potential effects are treated as described in the specification of the present invention.

1 and 2 are schematic structural diagrams of a conventional DC/AC overcurrent or earth leakage monitoring device.
3 is a structural diagram of an AC and DC combined overcurrent and leakage monitoring device according to a preferred embodiment of the present invention.
4 is a more detailed structural diagram of an earth leakage detecting unit according to a preferred embodiment of the present invention.
5 shows a leakage capacitor and a leakage current of an ungrounded power system.
6 is a diagram illustrating a phase relationship of signals for monitoring an electric leakage according to a preferred embodiment of the present invention.
7 is a flowchart of a method for monitoring overcurrent and leakage according to another preferred embodiment of the present invention.
8 is a flowchart of an overcurrent protection method according to another preferred embodiment of the present invention.
9 is a flowchart of a leakage current protection method according to another preferred embodiment of the present invention.
※ It is revealed that the accompanying drawings are exemplified as a reference for understanding the technical idea of the present invention, and the scope of the present invention is not limited thereby

Hereinafter, the configuration of the present invention guided by various embodiments of the present invention and effects resulting from the configuration will be described with reference to the drawings. In the description of the present invention, if it is determined that the subject matter of the present invention may be unnecessarily obscured as it is obvious to those skilled in the art with respect to related known functions, the detailed description thereof will be omitted.

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 term may be used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a 'first component' may be termed a 'second component', and similarly, a 'second component' may also be termed a 'first component'. can Also, the singular expression includes the plural expression 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 of ordinary skill in the art.

Hereinafter, the configuration of the present invention guided by various embodiments of the present invention and effects resulting from the configuration will be described with reference to the drawings.

1 to 3 are schematic structural diagrams of a conventional DC/AC overcurrent or earth leakage monitoring device.

Current measuring sensors include a current transformer (CT), a Hall effect sensor, a Rogowski coil current sensor, and a current sensor using a shunt resistor.

Hall effect sensor can be used for both DC and AC, but it is difficult to use for leakage measurement because the sensor price is high and a slight current offset value changes whenever a large current flows.

1 is an example of a sensor using a CT (Current Transformer).

The CT sensor measures the current flowing in the line on the principle that when the current flowing in the line generates a magnetic flux 2 in the iron core 1 , an induced current is generated in the secondary coil 2 . However, since this uses the principle of induced electromotive force generated by alternating current, there is a problem that it cannot be used for direct current.

1 is an example of using a current sensor using a shunt resistor.

Since the current sensor 4 using the shunt resistor calculates the current flowing through the resistor by measuring the voltage across the resistor based on Ohm's law, it can be used for both direct and alternating current. However, since the current directly flows through the current sensor 4 using the shunt resistor, Joule heat (I2R) is generated by the flowing current, so that it is difficult to use in a device through which a large current flows. In order to reduce the Joule heat, the resistance value should be lowered to the level of several tens to tens of microohms (uΩ).

In addition, both ends of the current sensor (4) using a shunt resistor must be connected to the measurement circuit (5). However, if a high-voltage grid voltage is directly connected to the measurement circuit (5), there is a risk of electric shock, and multi-phase (3-phase, 2-phase) If each phase of the power grid is connected to the common measurement circuit 5 without circuit isolation, there is also a problem in that each phase is short-circuited (short-circuited).

Therefore, the present invention solves this problem by electrically insulating the current sensor and the measuring circuit using a shunt resistor.

3 is a structural diagram of an AC and DC combined overcurrent and leakage monitoring device according to a preferred embodiment of the present invention.

AC and DC combined overcurrent and leakage monitoring device 10 according to the present invention includes a current sensor 110, an AC/DC converter 120 (ADC: Analog to Digital Converter), a detection signal generator 130, and a detection signal detection unit. 140 , a control unit 160 , and a blocking unit 170 .

The current sensor 110 is composed of a current sensor using a shunt resistor. Since it measures the current flowing directly through the line, both direct current and alternating current can be measured.

The ADC 120 converts the current or voltage measured by the current sensor 110 into a digital signal. The converted digital signal is transmitted to the controller 160 and used for overcurrent determination.

Unlike FIG. 2 , the current sensor 110 and ADC 120 for measuring current are electrically insulated from the controller 160 . In the present invention, the current sensor 110 and the ADC 120 are characterized in that the control unit 160 and galvanic isolation (Galvanic isolation). As described above, galvanic isolation is a technology that electrically insulates the sensor unit and the measurement unit to prevent electric shock or short circuit. As the galvanic isolation method, an isolation transformer, a coupling capacitor, an optocoupler, or the like may be used. A separate power supply from the control unit 160 is supplied to the galvanically isolated current sensor 110 and ADC 120 .

The controller 160 may include one or more processors and memories. A program code for operating the processor and data for determining AC/DC and overcurrent or leakage current may be stored in the memory.

The controller 160 determines the overcurrent based on the current or voltage data measured by the current sensor 110 and converted into a digital value by the ADC 120 .

First, the frequency value of the measured voltage or current data is calculated. If the calculated frequency value is in the range of 30~90Hz, it is judged as AC, and if the frequency is not recognized or less than 1Hz, it is judged as DC.

When it is determined as AC, since the DC component included in the voltage or current data is noise, the DC offset component is removed at every cycle to calculate the magnitude of the AC current or voltage.

If it is determined as DC, the unique DC offset value on the circuit must be removed. It means a DC offset value that occurs due to the characteristics of the current sensor 110 or ADC 120 even in a state where no electrical signal is applied to the overcurrent and leakage monitoring device 10, and is measured in a state of no current and no voltage in the manufacturing stage. Thus, it is a value stored in advance in the control unit 160 . Therefore, the intrinsic DC offset value is removed from the measured current or voltage value.

The current or voltage value calculated according to alternating current or direct current is compared with a predetermined overcurrent reference value, and when the current state satisfies the condition in consideration of the cut-off delay time, the cut-off unit 170 is controlled to protect the electric line and the connected circuit. .

4 shows the detection signal generating unit 130 and the detection signal detecting unit 140 for detecting leakage current according to the present invention in more detail.

The method using a general CT sensor as shown in FIG. 1 has a problem in that direct current cannot be detected.

Therefore, in the present invention, a method of generating a detection signal for use in both DC/AC, injecting it into the line, sensing it again, and measuring the leakage current was used.

The detection signal generator 130 generates a signal for detecting the leakage current and injects it into the line. The detection signal is a signal for measuring the leakage of a line by injecting a high-frequency minute signal irrespective of the current flowing in the line into the line. Since CT is used to generate or sense a detection signal, an alternating current is used for the detection signal. Preferably, an AC signal of 5 Hz or more and less than 30 Hz is used.

The generated detection signal is transmitted to the transmission line by the induced electromotive force principle through the CT.

The detection signal detection unit 140 senses the detection signal generated and inserted by the detection signal generation unit 130 through CT similarly using the principle of induced electromotive force. The induced electromotive force generated by the detection signal, which is an AC signal, is sensed through the coil.

The control unit 160 should separate only the effective signal from the detected signal.

5 shows a schematic structure of an ungrounded power supply system for the description of the reactive component. Since the ungrounded power system is not connected to the ground (PE), in theory, the ground current (If) should not flow. However, in reality, the transmission line and the ground are not completely insulated because a minute leakage current (Ic) is generated between the transmission line and the ground due to the leakage capacitor (Ce). Therefore, negligible leakage current occurs due to the leakage capacitor or the Y-capacitor installed to reduce the noise of the ungrounded power load.

Therefore, the controller 160 must distinguish the leakage current Ic from the current generated by the detection signal. This is the reason that it cannot be determined whether leakage has occurred simply by the magnitude of the sensed current or voltage.

The controller 160 may distinguish an invalid component from an active component according to the phase of the signal.

6 shows the phase relationship between the detection signal Is inserted into the transmission line, the current signal If detected by the detection signal, and the leakage current Ic generated by the leakage capacitor.

6A shows the phase difference between the three signals, the detection signal Is and the current signal If sensed by the detection signal Is have the same phase and the leakage current Ic generated by the leakage capacitor ) can be seen to have a phase difference of 90 degrees.

6(b) shows the waveform relationship of the three signals. It is shown that the leakage current Ic is transmitted 90 degrees later than the other two signals.

Accordingly, the control unit 160 may separate only a signal having the same phase as the detection signal from among the signals detected by the detection signal detection unit 140 , and monitor the leakage using this signal. When a current or voltage value of a signal having the same frequency and the same phase as the detection signal among the detected signals is greater than a predetermined value and exceeds a predetermined delay time, it is determined as a short circuit and the blocking unit 170 may be operated.

As described above, the AC and DC combined overcurrent and leakage monitoring device 10 according to the present invention has the advantage of being able to monitor both AC and DC in one device.

7 is a flowchart of a method for monitoring overcurrent and leakage according to another preferred embodiment of the present invention.

The overcurrent and leakage monitoring method of the present invention may be performed by a controller including one or more processors and memories.

First, a voltage or current signal of a line measured by a current sensor is received to prevent overcurrent (S10). The current sensor and control unit must be galvanically isolated.

Next, a detection signal for monitoring the leakage current is generated (S20), transmitted to the line, and a signal generated by the detection signal is detected (S30). Since the detection signal is generated and sensed by the CT, it is irrelevant whether the electricity of the transmission line is AC or DC. The detection signal may be an AC signal of 5 to 30 Hz.

The overcurrent protection is performed by the voltage or current signal measured by the current sensor (S40), and the leakage current protection is performed according to the detection signal.

8 is a flowchart of an overcurrent protection method according to another preferred embodiment of the present invention.

For overcurrent protection, first, the frequency of the current measured by the sensor is calculated (S41).

If the calculated frequency value is in the range of 30 to 90 Hz, it is determined as AC, and if the frequency is not recognized or less than 1 Hz, it is determined as DC (S42).

If it is determined as DC, a unique DC offset value on the circuit must be removed (S43). Even in a state where no electric signal is applied, the DC offset value generated due to the characteristics of the current sensor or ADC is removed and the current size is compensated (S44).

When it is determined as AC, the DC component included in the voltage or current data is noise, so the DC offset component is removed every cycle (S45) to calculate the magnitude of the AC current or the current that compensates for the magnitude and phase of the voltage ( S46).

If the magnitude of the AC or DC current is calculated, it is determined whether the magnitude of the current is equal to or greater than the reference value (S47), and when the magnitude of the current is greater than the reference value, it is determined as overcurrent and the blocking circuit is operated (S48).

9 is a flowchart of a leakage current protection method according to another preferred embodiment of the present invention.

First, a signal generated by the detection signal is detected to calculate the phase and frequency of the signal (S51).

Since the leakage current generated by the leakage capacitor on the transmission line is an invalid component, it is determined whether the detected signal is in the same phase as the detection signal (S52). S54) Cut off the leakage current.

As described above, the present invention can prevent overcurrent in both direct and alternating current of high current by maintaining galvanic isolation from the measuring circuit while using a current sensor using a shunt resistor, and by generating and detecting a detection signal using a CT, leakage current There is also a detectable effect.

The protection scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the protection scope of the present invention cannot be limited due to obvious changes or substitutions in the technical field to which the present invention pertains.

Claims (11)

a current sensor installed on a line of an ungrounded power system;
an analog-to-digital converter for converting the value measured by the current sensor into digital;
a detection signal generator generating an AC detection signal for detecting leakage current and applying it to a line of the ungrounded power system;
a detection signal detection unit for detecting a current signal flowing through the line of the ungrounded power system after the AC detection signal is applied to the line of the ungrounded power system; and
A control unit including one or more processors and memory; including,
The current sensor and the control unit are galvanic isolation (Galvanic Isolation),
The control unit performs a DC or AC overcurrent protection function by the digitally converted current or voltage value measured by the current sensor and performs a leakage current protection function by the current signal detected by the detection signal detection unit,
the control unit
Separating a first current signal having the same phase as the AC detection signal from among the current signals, and determining that the leakage current has occurred when the value of the first current signal exceeds a preset value
AC and DC combined overcurrent and leakage monitoring device.
According to claim 1,
The current sensor is a current sensor using a shunt resistor, AC and DC combined overcurrent and leakage monitoring device.
According to claim 1, wherein the control unit,
AC and DC combined overcurrent and leakage monitoring device, characterized in that by calculating the frequency of the current measured by the current sensor and converted by the analog-to-digital converter to divide the current into alternating current or direct current.
According to claim 3, wherein the control unit,
When the current for which the frequency is calculated is AC, the magnitude of only the AC current is calculated by removing the DC offset component of the current, and the blocking circuit is operated when the magnitude of only the AC current exceeds a preset value. AC and DC combined overcurrent and short circuit monitoring device.
According to claim 3, wherein the control unit,
When the current for which the frequency is calculated is DC, only the magnitude of the DC current from which the intrinsic DC offset component is removed from among the current is calculated, and when the magnitude of the DC current exceeds a preset value, the blocking circuit is operated, AC and DC combined overcurrent and leakage monitoring device.
According to claim 1, wherein the control unit,
AC and DC combined overcurrent and leakage monitoring device, characterized in that the operation of the blocking circuit when the value of the first current signal exceeds a preset value.
In the AC and DC combined overcurrent and leakage monitoring method performed by a control unit including one or more processors:
receiving a current or voltage measured by a current sensor installed on a line of an ungrounded power system and galvanically isolated from the control unit;
generating an AC detection signal for detecting leakage current and applying it to a line of the ungrounded power system;
detecting a current signal flowing through the line of the ungrounded power system after the AC detection signal is applied to the line of the ungrounded power system;
performing an overcurrent protection function by the current or voltage measured by the current sensor; and
Including; performing a leakage current protection function by the sensed current signal;
The step of performing the leakage current protection function is
Separating a first current signal having the same phase as the AC detection signal from among the current signals, and determining that the leakage current has occurred when the value of the first current signal exceeds a preset value
A method for monitoring overcurrent and leakage current for both AC and DC.
8. The method of claim 7,
AC and DC combined overcurrent and leakage monitoring method, characterized in that by calculating the frequency of the current or voltage measured by the current sensor to classify the measured current into AC or DC.
9. The method of claim 8,
When the measured current is AC, calculating the magnitude of only the AC current by removing the DC offset component of the current, and operating a blocking circuit when the magnitude of only the AC current exceeds a preset value; further comprising characterized in that, AC and DC combined overcurrent and leakage monitoring method.
9. The method of claim 8,
When the measured current is DC, calculating the magnitude of the DC current from which the intrinsic DC offset component is removed from the current, and operating the blocking circuit when the magnitude of the DC current exceeds a preset value; Characterized, AC and DC combined overcurrent and leakage monitoring method.
8. The method of claim 7,
The step of performing the leakage current protection function,
The step of operating a blocking circuit when the value of the first current signal exceeds a preset value, the AC and DC combined overcurrent and leakage monitoring method.

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