KR20240014192A - Protection system and operating method for preventing malfunction by induced current - Google Patents

Abstract

The present invention relates to a protection system that prevents malfunction due to induced current and its operating method. When a power system failure occurs, the induced current generated due to the failure is detected, and the current is blocked or current depending on whether the induced current is detected. Including a protection device that maintains the flow, it has the effect of preventing malfunction of power equipment due to induced currents generated due to failure, protecting power equipment, and preventing power outages due to malfunction of power equipment.

Description

Protection system and operating method for preventing malfunction due to induced current {PROTECTION SYSTEM AND OPERATING METHOD FOR PREVENTING MALFUNCTION BY INDUCED CURRENT}

The present invention relates to a protection system that protects equipment by preventing malfunctions caused by induced currents caused by power system failures and a method of operating the same.

Recently, gas insulated switchgear (GIS) has been miniaturized to reduce installation space and cost, and accordingly, three-phase gas insulated switchgear (GIS) is being introduced.

The three-phase integrated GIS is a gas insulated switch (GIS) and a current transformer (CT) integrated into one device. The bus bar protection current transformer (CT) and the transmission line protection current transformer (CT) are connected to the gas insulated switch (GIS) at an adjacent distance. is connected to

This three-phase integrated GIS has a problem in that mutual interference occurs due to the narrow phase gap between the bus protection current transformer (CT) and the transmission line protection current transformer (CT). In particular, when a fault occurs at the line inlet, an induced current is generated in a phase other than the fault phase.

As a differential current is generated in the normal phase due to the induced current generated in this way, there is a problem of malfunction such as the bus protection relay incorrectly recognizing the differential current caused by the induced current as a fault current and blocking the current.

In order to prevent malfunction of such protection relay, it is possible to check whether induced current is generated in the current transformer and test the characteristics of the current transformer. This test is performed by applying a test current to check whether current is induced in the other phase.

As a related technology, there is Korean Patent No. 10-2211581, “Internal fault detection device for current transformer using induced current.”

However, in the case of the current transformer testing method, the detection sensitivity for high resistance faults is low, so the detection and protection effectiveness is low in the case of multiple faults.

As another method to prevent malfunction of the protection relay, a method of preventing malfunction by changing the settings of the protection relay is being implemented.

However, this method prevents malfunctions by upwardly adjusting the operating value of the protection relay, but there is a problem in that it desensitizes the operation of the system and does not operate when necessary or causes delayed operation.

In addition, to prevent malfunction of the protection relay, an induced current shielded current transformer (CT) can be applied, but in this case, it cannot be applied to the already installed gas insulated switch (GIS), and replacing it requires a lot of cost. .

Accordingly, a method is needed to stably protect power facilities while preventing malfunction of power facilities due to induced current.

Republic of Korea Patent No. 10-2211581

The present invention was created in response to the above-mentioned need, and protects power facilities by detecting induced currents generated due to power system failures and preventing malfunctions of power facilities due to induced currents. The purpose is to provide a protection system and its operation method to prevent it.

In order to achieve the above object, the protection system for preventing malfunction due to induced current according to the present invention analyzes the current transformer (CT) and the current signal flowing from the current transformer (CT) to block the current or stop the current flow when a fault occurs. Maintaining safeguards; Includes, the protection device determines a failure by calculating a differential current according to the total amount of input and output current, detects the induced current based on the maximum and minimum values of the current, and determines that the induced current is a failure. A processor that, when detected, classifies it as an external fault and prevents the current from being cut off; Includes.

The processor is characterized in that when a failure occurs, when the induced current is detected, it controls the circuit breaker not to operate to maintain the flow of current.

The processor is characterized in that it determines a first condition whether a value obtained by dividing the maximum value by the minimum value is greater than a first set value.

The processor is characterized in that it determines a second condition whether the minimum value is greater than a second set value.

The processor detects the maximum value of the current time and the maximum value of the previous time, and determines a third condition whether the value divided by the maximum value of the current time by the maximum value of the previous time is less than a third set value. It is characterized by

The processor is characterized in that it determines that the induced current is included in the current signal when at least one of the first condition and the second condition is satisfied and the third condition is satisfied.

The operating method of the protection system for preventing malfunction due to induced current of the present invention includes the steps of inputting a current signal from a current transformer (CT) to the protection device; determining, by the processor of the protection device, whether there is a failure by calculating a differential current according to the total amount of input and output current; Analyzing the current signal and detecting an induced current based on the maximum and minimum values of the current; When the induced current is detected in a state determined to be a failure, discriminating it as an external failure and maintaining the current without blocking it; and if the induced current is not detected in a state in which a failure is determined, a final determination as a failure is made and the current is cut off; Includes.

Detecting the induced current may include comparing a value obtained by dividing the maximum value by the minimum value with a first set value to determine whether a first condition is satisfied; comparing the minimum value with a second set value to determine whether a second condition is satisfied; and comparing the maximum value of the current time divided by the maximum value of the previous time with a third set value to determine whether the third condition is satisfied. Includes.

Detecting the induced current may include determining that the induced current is included in the current signal when at least one of the first condition and the second condition is satisfied and the third condition is satisfied; It further includes.

In the step of detecting the induced current, it is determined that the first condition is satisfied if the value divided by the maximum value by the minimum value is greater than the first set value, and if the minimum value is greater than the second set value, the second condition is determined to be satisfied. It is determined that the condition is satisfied, and if the value obtained by dividing the maximum value of the current time by the maximum value of the previous time is less than the third set value, the third condition is determined to be satisfied.

The first condition is satisfied when the maximum value exceeds twice the minimum value, the second condition is satisfied when the minimum value is a positive number, and the third condition is satisfied when the maximum value of the current time is greater than that of the previous time. It is characterized as being satisfied if it is less than 70% of the maximum value.

According to one aspect, the protection system and its operating method for preventing malfunction due to induced current of the present invention detect induced current generated by power system failure, prevent malfunction of power equipment due to induced current, and can protect.

According to one aspect of the present invention, it can be easily applied to various power facilities and can prevent power outages due to malfunction of power facilities.

1 is a diagram illustrating the configuration of a protection system that prevents malfunction due to induced current according to an embodiment of the present invention.
Figure 2 is an example diagram referenced to explain induced current due to a power system failure according to an embodiment of the present invention.
Figure 3 is an example diagram referenced to explain a fault current due to a power system failure according to an embodiment of the present invention.
Figure 4 is a diagram referenced to explain a method of detecting induced current in a protection system that prevents malfunction due to induced current according to an embodiment of the present invention.
Figure 5 is a flowchart showing a method of operating a protection system that prevents malfunction due to induced current according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the attached drawings. In this process, the thickness of lines or sizes of components shown in the drawing may be exaggerated for clarity and convenience of explanation. In addition, the terms described below are terms defined in consideration of functions in the present invention, and may vary depending on the intention or custom of the user or operator. Therefore, definitions of these terms should be made based on the content throughout this specification.

1 is a diagram illustrating the configuration of a protection system that prevents malfunction due to induced current according to an embodiment of the present invention.

As shown in FIG. 1, in the protection system of the present invention, the protection device 10 receives current from the power system, detects a fault, and blocks the current when a fault occurs to protect the power system and power facilities.

The protection system includes power equipment and protection devices such as a current transformer (CT) 10 and a gas insulated switch (GIS) including a current transformer (CT).

The protection device 10 analyzes the current signal input from the current transformer (CT) 20 and detects the corresponding fault current when a fault occurs. The protection device 10 protects the power system and facilities by operating a breaker to block the current in order to solve problems such as increased load on other facilities or malfunction due to fault current.

When an induced current is generated in the current transformer (CT) due to an external fault, the protection device 10 detects the fault current by comparing the currents at both ends (D1, D2) when a current containing the induced current flows in, and also induces Detects current and controls the breaker.

The current transformer (CT) 20 may be a current transformer (CT) inside a transformer, a transformer's neutral point current transformer (CT), a current transformer (CT) of an HV gas insulated switch (GIS), or a current transformer (CT) inside a generator.

Current transformers (CTs) may generate induced currents due to fault currents in the process of processing large currents. The generated induced current may flow into the protection device 10, which is a protection relay.

The protection device 10 detects the induced current based on the current signal for each phase and controls the circuit breaker to operate or not operate.

The protection device 10 detects a fault current and detects an induced current generated in response to the fault current. The protection device 10 analyzes the current signal of the power equipment 20 for each phase and detects the induced current.

The protection device 10 is a protection relay. The protection device 10 may use a current differential relay that blocks the current based on the total of input and output currents. Additionally, the protection device 10 may be configured as a separate, independent device connected to a current differential relay.

The protection device 10 includes a communication module 140, an output unit 130, a current sensor 150, a memory 120, and a processor 110.

The memory 120 stores data about the measured current signal, stores data for detecting induced current, and stores detection result data. The memory 120 stores pattern data about the induced current generated by the fault current. The memory 120 stores algorithm data for the operation of the processor 110.

The memory 120 includes storage means such as non-volatile memory such as RAM (Random Access Memory), ROM, and EEPROM (Electrically Erased Programmable ROM), flash memory, SSD, and HDD.

The communication module 140 transmits and receives data with a management server (not shown) that manages other power facilities and power systems using a wired or wireless communication method. When a fault current or induced current is detected, the communication module 140 transmits data about it to the management server.

Additionally, the communication module 140 transmits data to a database (DB) (not shown) and receives data stored in the database according to a request from the processor 110.

The communication module 140 communicates by including at least one module among, for example, short-range communication, mobile communication, and serial communication such as Ethernet, WIFI, and Bluetooth.

The output unit 130 includes at least one of a speaker (not shown), a display (not shown), and a lamp (not shown), and outputs data on the detected fault current and induced current, detection results, and circuit breaker operation status. .

Additionally, the output unit 130 may output a warning about whether the breaker is operating according to the induced current.

The current sensor 150 measures the current flowing into the protection device 10. Additionally, the current sensor 150 is installed at the input or output terminal of the protection device 10 to measure current.

The processor 110 detects a failure by analyzing the incoming current signal.

When a fault current is detected from the incoming current signal, the processor 110 compares the current signals at both input and output ends (D1 and D2) and determines whether the fault is internal or external according to the difference current.

The processor 110 operates a circuit breaker to block current in the event of an internal failure, and prevents the circuit breaker from operating in the event of an external failure.

Additionally, the processor 110 analyzes the current signal and detects the induced current generated due to the fault current. The processor 110 detects an induced current with characteristics different from a general fault current and controls the circuit breaker operation by distinguishing it from the fault current.

The processor 110 detects the induced current from the current signal and stops the operation of the circuit breaker to prevent it from being mistakenly judged to be an internal fault due to the induced current caused by an external fault.

The processor 110 detects the maximum and minimum values for each phase from the current data measured for a certain period of time, calculates the ratio of the maximum and minimum values, and detects the induced current from the current data.

The processor 110 outputs data on the detection result of fault current and induced current detection and the circuit breaker operating state through the output unit 130. Additionally, the processor 110 generates and outputs a warning signal when an induced current is detected and the circuit breaker is stopped.

In addition, the processor 110 stores data on breaker operation due to fault current and breaker operation stoppage due to induced current in a database (DB) or transmits it to the management server through the communication module 140.

Processor 110 includes at least one microprocessor. The processor 110 may operate according to a fault current detection algorithm, an induced current detection algorithm, and a breaker operation control algorithm.

Accordingly, the protection device 10 can operate by ignoring the induced current, stop the operation of the circuit breaker when the induced current is detected, and temporarily change the settings according to the operation.

Figure 2 is an example diagram referenced to explain induced current due to a power system failure according to an embodiment of the present invention.

As shown in FIG. 2, the protection device 10 may receive an induced current generated by other power equipment within a certain area, for example, a current transformer (CT) 20.

Induced current is generated when a fault occurs in a power facility or power system, the fault current flows into the current transformer (CT), and the fault current occurs while the current transformer (CT) processes a large current. For example, induced current may occur when a fault current occurs in phase A and is affected by a fault current in phase B or C.

Induced current can occur in adjacent phases due to the saturation residual magnetic flux of the ring core current transformer (Ring core CT). Induced current can occur in the current transformer (CT) inside the transformer, the transformer's neutral point current transformer (CT), the current transformer (CT) of the HV gas insulated switch (GIS), and the current transformer (CT) inside the generator.

The induced current appears larger as the spacing between phases becomes smaller. As the conductor spacing gets shorter, the magnitude of the magnetic flux increases, so the induced current also increases in magnitude. Additionally, the induced current appears larger as the DC component of the external fault current on the primary side increases.

The induced current has the characteristic of generating a large amount of induced current during the initial 0.5 cycle from the external ground fault current and then rapidly stabilizing to a low current.

In addition, the induced current is in the form of a non-sinusoidal wave and contains a large amount of DC and harmonic components, so it appears in a different form from the fault current. The size of the induced current may vary depending on the manufacturer of the gas insulated switch (GIS), the physical characteristics and fault conditions inside the gas insulated switch (GIS).

As shown in (a) of FIG. 2, such induced current occurs in a section where a fault occurs on another phase. In the first section T1 before a failure occurs, the load current L1 flowing into the protection device 10 flows within a certain range.

However, in the second section (T2) where a fault occurs on the other phase, the load current (L2) changes in waveform by repeatedly increasing and decreasing in size. In the second section (T2) where a fault occurs, the waveform of the load current (L2) does not remain constant and its magnitude decreases.

The protection device 10 detects this load current (L2) as an induced current.

As shown, the protection device 10 increases the load current L2 based on the characteristics of the induced current, which initially increases in size greatly in the second section T2, then rapidly decreases and stabilizes at a low current. It is judged by induced current.

In addition, the protection device 10 detects the maximum and minimum values of the load current and distinguishes the induced current from the fault current by comparing the magnitude according to the detection time.

As shown in (b) of FIG. 2, the load current L3 appears as a sine wave of a certain size in the third section T3 before failure.

However, in the fourth section (T4) when a fault occurs in the other phase, the load current (L4) initially increases greatly in size and the waveform changes, and the increased size is not maintained and the size decreases, returning to the original waveform. do.

The protection device 10 analyzes the current signal and detects the load current L4 as an induced current.

As shown, the protection device 10 determines whether to operate the circuit breaker when an induced current is detected, and controls the circuit breaker to block or not block the current and allow the current to flow accordingly.

When the protection device 10 detects an induced current and stops the circuit breaker, it generates a guide or warning indicating that the operation is stopped due to the induced current, outputs it through the output unit 130, and manages it through the communication module 140. Transmit to server (not shown).

Figure 3 is an example diagram referenced to explain a fault current due to a power system failure according to an embodiment of the present invention.

The protection device 10 detects a fault current by analyzing the current signal.

If a ground fault occurs on phase C among the three phases of the transmission line, a fault current occurs on phase C as shown in (a) of FIG. 3.

In addition, as shown in (b) of FIG. 3, when a short circuit fault occurs in the B phase and C phase among the three phases of the transmission line, a fault current occurs in the B phase and C phase. At this time, the fault current appears in different phases for each phase.

The fault current appears in a different form from the induced current in FIG. 2 described above.

Accordingly, when a fault occurs, the protection device 10 distinguishes between fault current and induced current and operates the circuit breaker in response.

The protection device 10 detects a fault current by analyzing the current signal, and distinguishes between an internal fault and an external fault by comparing the current signals at both ends to calculate a differential current.

The protection device 10 determines it to be an internal failure when the differential current is above a certain value, and determines it to be an external failure when the differential current is less than a certain value. In addition, the protection device 10 determines an external failure when an induced current is detected in a state determined to be an internal failure.

In the case of an internal failure, the protection device 10 operates a breaker to block the current, and in the case of an external failure, it stops the breaker from operating to allow the current to flow. At this time, the range of internal failure and external failure is based on the protection area allocated to the current differential relay, which is the protection device 10.

Figure 4 is a diagram referenced to explain a method of detecting induced current of a protection device that prevents malfunction due to induced current according to an embodiment of the present invention.

As shown in FIG. 4, the processor 110 of the protection device 10 detects the maximum value (PEAK(+)) and minimum value (PEAK(-)) of the measured current signal.

As shown in FIG. 2 described above, the induced current increases to the maximum value in the initial 0.5 cycle and gradually decreases in size, so the processor 110 detects the maximum and minimum values and detects the induced current according to the ratio or size. .

The processor 110 can divide the signal input from the current sensor 150 into sections at regular time intervals and detect the maximum and minimum values for each section.

The processor 110 determines at least three conditions as criteria for classifying induced current.

The processor 110 calculates a value obtained by dividing the maximum value by the minimum value and determines whether the value is greater than the first set value (A) (first condition) (51).

The processor 110 determines whether the minimum value is greater than the second set value (B) (second condition) (52).

In addition, the processor 110 calculates the value obtained by dividing the maximum value (n) of the current time by the maximum value (n-1) of the previous time, and determines whether the value is less than the third set value (C). 3 conditions) (53).

As the first condition 51, the processor 110 determines whether the maximum value detected in the current signal exceeds twice the minimum value because the maximum value is detected in the initial cycle and decreases thereafter according to the characteristics of the induced current, and the flow current Detect. Accordingly, the first set value (A) may be set to about 2.

As a second condition 52, the processor 110 determines whether the minimum value of the induced current is a positive number. Therefore, the second set value (B) can be set to approximately 0. The processor 110 determines whether the minimum value of the current signal is greater than 0 and determines whether it is a positive number.

In addition, in the third condition 53, the processor 110 can detect the induced current based on the degree of decrease in the maximum value for each pole cycle because the magnitude of the induced current increases significantly in the initial cycle and gradually decreases thereafter.

As shown in (a) and (b) of Figure 2, the maximum value of the second cycle is 50% to 60% of the first cycle, and the third cycle is approximately 60% to 70% of the second cycle, so the third cycle is accordingly The setting value can be set to approximately 0.7.

That is, the processor 110 detects the induced current by determining whether the maximum value of 2 cycles is less than 70% of the maximum value of 1 cycle.

The first set value (A) to the third set value (C) may be changed depending on the installation location of the current transformer (CT), the characteristics of the current transformer (CT), and the characteristics of the gas insulated switch (GIS).

With respect to the first to third conditions (51 to 53), the processor 110 determines that the first condition (51) and the second condition (52) are the OR gate 41, and determines the first condition (51) and the second condition (52) as the OR gate (41). 2 Determine whether at least one of conditions (52) is satisfied.

When at least one of the first condition 51 and the second condition 52 is satisfied, the processor 110 processes the satisfied condition and the third condition 53 through the AND gate 42. It is determined whether the third condition (53) is satisfied, and if both conditions are satisfied, the induced current (55) is determined.

The processor 110 determines that it is an induced current when at least one of the first condition 51 and the second condition 52 is satisfied and the third condition 53 is satisfied, and the third condition 53 is satisfied. If it does not, it is judged not to be an induced current. The third condition (53) is an essential condition for determining the induced current.

The processor 110 detects the induced current from the current signal using the characteristics of the induced current.

The processor 110 performs induced current detection for each phase.

When the processor 110 detects an induced current in a state in which a failure is determined based on the differential current between the input and output ends, the processor 110 determines that the differential current is caused by the induced current and stops the circuit breaker from operating.

Meanwhile, if the differential current is greater than a certain level and the induced current is not detected, the processor 110 ultimately determines that it is an internal failure and operates a circuit breaker to block the current.

Figure 5 is a flowchart showing a method of operating a protection device that prevents malfunction due to induced current according to an embodiment of the present invention.

As shown in Figure 5, the protection device 10 detects the input current signal (S310).

The processor 110 detects the maximum and minimum current values for each phase from the current signal (S320). The processor 110 calculates values for the first to third conditions 51 to 53 for detecting the induced current, based on the maximum and minimum values of the current (S330). The processor 110 calculates the value by dividing the maximum value by the minimum value and dividing the maximum value of the current time by the maximum value of the previous time.

The processor 110 determines whether the first condition 51 is satisfied by comparing the maximum value of the current to the minimum value with the first set value (A) (S340).

The processor 110 determines whether the second condition 52 is satisfied by comparing the minimum value of the current with the second set value (B) (S350).

The processor 110 first determines whether at least one of the first condition 51 and the second condition 52 is satisfied. If both the first condition 51 and the second condition 52 are not satisfied, the processor 110 determines that it is not an induced current and outputs the result (S400).

The processor 110 completes the first determination when at least one of the first condition 51 and the second condition 52 is satisfied, and detects the maximum value of the current to check the third condition 53 ( S360). The processor 110 detects the maximum value (n) of the current time and the maximum value (n-1) of the previous time, respectively.

The processor 110 secondly determines whether the third condition 53 is satisfied by comparing the value obtained by dividing the maximum value (n) of the current time by the maximum value (n-1) of the previous time with the third set value (C). Do it (S370).

If the third condition 53 is not satisfied, the processor 110 determines that it is not an induced current and outputs a detection result (S400).

The processor 110 determines that the current signal is an induced current when the third condition 53 is satisfied while at least one of the first condition 51 and the second condition 52 is satisfied (S380 ).

The processor 110 performs induced current detection for each of the three phases.

Since the processor 110 may malfunction due to the induced current, the circuit breaker is stopped and the current is controlled to flow (S390).

In the case of a current differential relay that blocks the current based on the total of input and output currents, a differential current may be generated by the induced current, so the processor 110 prevents the current from being blocked by preventing the circuit breaker from operating when the induced current is detected.

The processor 110 outputs a detection result according to the detection of the induced current (S400). Additionally, the processor 110 transmits the current operating status to the management server.

Therefore, in the present invention, when a failure occurs in the power system, the fault may be mistakenly judged due to the induced current generated by the failure. Therefore, the circuit breaker is controlled to prevent malfunction by detecting the induced current. Accordingly, the present invention can prevent damage to power equipment due to malfunction and prevent power outages.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely illustrative, and those skilled in the art will recognize that various modifications and other equivalent embodiments can be made therefrom. You will understand. Therefore, the true technical protection scope of the present invention should be determined by the patent claims below.

10: Protection device 20: Current transformer (CT)
110: Processor 120: Memory
130: output unit 140: communication module
150: Current sensor

Claims (14)

current transformer (CT); and
A protection device that analyzes the current signal flowing from the current transformer (CT) and blocks the current or maintains the current flow when a failure occurs; Including,
The protective device is,
A failure is determined by calculating the differential current according to the total amount of input and output current, and the induced current is detected based on the maximum and minimum values of the current. If the induced current is detected in a state where it is determined to be a failure, it is classified as a failure that occurred externally. A processor that prevents the current from being cut off; A protection system that prevents malfunction due to induced current, including. According to claim 1,
A protection system for preventing malfunction due to induced current, wherein when a fault occurs, the processor controls the breaker not to operate when the induced current is detected to maintain the flow of current. According to claim 1,
A protection system for preventing malfunction due to induced current, wherein the processor determines a first condition as to whether a value obtained by dividing the maximum value by the minimum value is greater than a first set value. According to claim 3,
A protection system for preventing malfunction due to induced current, wherein the processor determines the induced current when the maximum value exceeds twice the minimum value. According to claim 3,
A protection system for preventing malfunction due to induced current, wherein the processor determines a second condition whether the minimum value is greater than a second set value. According to claim 5,
A protection system for preventing malfunction due to induced current, wherein the processor determines whether the minimum value is a positive number. According to claim 5,
The processor detects the maximum value of the current time and the maximum value of the previous time, and determines a third condition whether the value divided by the maximum value of the current time by the maximum value of the previous time is less than a third set value. A protection system that prevents malfunction due to induced current. According to claim 7,
A protection system for preventing malfunction due to induced current, wherein the processor determines whether the maximum value of the current time is less than 70% of the maximum value of the previous time. According to claim 7,
Malfunction due to induced current, wherein the processor determines that the induced current is included in the current signal when at least one of the first condition and the second condition is satisfied, and the third condition is satisfied. A protection system that prevents. Inputting a current signal from a current transformer (CT) to a protection device;
determining, by the processor of the protection device, whether there is a failure by calculating a differential current according to the total amount of input and output current;
Analyzing the current signal and detecting an induced current based on the maximum and minimum values of the current;
If the induced current is detected in a state determined to be a failure, discriminating it as an external failure and maintaining the current without blocking it; and
If the induced current is not detected in a state in which a failure is determined, a final determination as a failure is made and the current is cut off; A method of operating a protection system that prevents malfunction due to induced current, including. According to claim 10,
The step of detecting the induced current is,
comparing the maximum value divided by the minimum value with a first set value to determine whether a first condition is satisfied;
comparing the minimum value with a second set value to determine whether a second condition is satisfied; and
Comparing a value obtained by dividing the maximum value of the current time by the maximum value of the previous time with a third set value to determine whether the third condition is satisfied; A method of operating a protection system that prevents malfunction due to induced current, including. According to claim 11,
The step of detecting the induced current is,
determining that the induced current is included in the current signal when at least one of the first condition and the second condition is satisfied and the third condition is satisfied; A method of operating a protection system that prevents malfunction due to induced current, further comprising: According to claim 11,
The step of detecting the induced current is,
If the value obtained by dividing the maximum value by the minimum value is greater than the first set value, it is determined that the first condition is satisfied,
If the minimum value is greater than the second set value, it is determined that the second condition is satisfied,
A protection system for preventing malfunction due to induced current, characterized in that it is determined that the third condition is satisfied if the value obtained by dividing the maximum value of the current time by the maximum value of the previous time is less than the third set value. How it works. According to claim 11,
The first condition is satisfied when the maximum value exceeds twice the minimum value,
The second condition is satisfied if the minimum value is a positive number,
The third condition is satisfied if the maximum value of the current time is less than 70% of the maximum value of the previous time.

Images