KR102666279B1 - Malfunction prevention method for current transformer - Google Patents

Abstract

The present invention relates to a method for preventing current transformer malfunction, which is processed by a processor, comprising: a) detecting current transformer saturation using instantaneous value and root-square-square (RMS) value, and b) negative-sequence Detecting whether there is an external failure using , c) Detecting whether there is an external failure using the phase difference for each phase, d) Detecting whether CT saturation has occurred using the magnitude of the second harmonic compared to the standing wave, and e) The above It may include the step of checking the CT saturation state due to an external failure using the judgment results of steps a) to d).

Description

Malfunction prevention method for current transformer}

The present invention relates to a method for preventing malfunction of a current transformer, and more specifically, to a method for preventing malfunction of a current transformer that can determine current transformer saturated state and other state failures by identifying current characteristics.

In general, a current transformer (CT) is used for transformers, etc., by insulating them from high-voltage circuits and transforming the current in the main circuit into an appropriate input current for measuring instruments and protection relays, which can be used as a measurable input power for measuring instruments and protection relays. I'm doing it.

In a current transformer, when the primary current exceeds a certain limit, the magnetic flux density is saturated and the excitation current rapidly increases.

In the event of a system failure, it may be saturated by the direct current component of the fault current, and power CTs may burn out or cause fire, and may also cause malfunctions in operations such as ratio differential relay, low current relay, and low power relay.

Therefore, when current transformer saturation occurs, it is necessary to block relay elements such as current ratio differential relay.

Registered Patent No. 10-2104835 (registered on April 21, 2020, 29KV GIS with CT secondary open prevention system for remote monitoring) describes a device that actively protects instruments connected to the CT.

However, conventionally, CT saturation detection was performed, but there was a problem in that the cause of CT saturation could not be identified.

The problem to be solved by the present invention in consideration of the above problems is to detect current transformer malfunction that CT saturation occurs due to an external fault using the negative-sequence element and current characteristics of the first and second winding sides of the transformer. It provides a prevention method.

The current transformer malfunction prevention method of the present invention for solving the above technical problems is a current transformer malfunction prevention method processed by a processor, comprising the steps of: a) detecting current transformer saturation using instantaneous value and root-square-square (RMS) value; b) detecting an external failure using the negative sequence, c) detecting an external failure using the phase difference for each phase, d) detecting whether CT saturation has occurred using the magnitude of the second harmonic compared to the standing wave, and , e) may include the step of confirming the CT saturation state due to an external failure using the determination results of steps a) to d) above.

In an embodiment of the present invention, in step a), if the instantaneous value is 150% or more of the RMS value, it may be determined that CT saturation has occurred.

In an embodiment of the present invention, in step b), the magnitude of the vector sum of the negative-sequence portion on the first winding side of the transformer and the negative-sequence portion on the second winding side of the transformer is greater than or equal to the set value, and the negative-sequence portion on the first winding side of the transformer and the negative-sequence portion on the second winding side of the transformer are equal to or greater than the set value. If the phase difference is within ±45 degrees of 0 degrees, it is judged as an internal fault; b-2) If the magnitude of the negative sequence is less than the set value, if the slope of the current ratio differential is more than 70% for all three phases, it is judged as a three-phase fault. Step b-3) may include a step of determining an external failure, except when at least one of the determination results of step b-1) and the determination result of step b-2) is determined to be a failure.

In an embodiment of the present invention, step c) includes c-1) determining a single-phase ground fault internal fault when the phase difference between phases A-B, B-C, and C-A is ±45 degrees based on 0 degrees, and c-2) A-B, B-C, If the phase difference between phases C-A is ±45 degrees based on 180 degrees, a line-to-line short circuit is judged to be an internal fault, and c-3) at least one of the judgment results of step c-1) and c-2) is judged to be a fault. Except in cases where failure occurs, a step of determining that it is an external failure may be included.

In an embodiment of the present invention, step d) calculates the 2nd harmonic difference current and obtains the value of (calculated 2nd harmonic difference current/standing wave difference current) * 100. If the result is 15% or more, CT in the 2nd harmonic situation. It can be judged that it is saturated.

In an embodiment of the present invention, step e) is performed when both the determination results of steps a) and d) are determined to be CT saturation, and both steps b) and c) are determined to be external failures. It can be judged that CT saturation occurs due to .

In an embodiment of the present invention, if it is determined that CT saturation has occurred due to an external failure as a result of step e), the step of blocking the relay element may be further included.

The current transformer malfunction prevention method of the present invention detects CT saturation due to an external fault by using the negative-sequence element and current characteristics of the first and second winding sides of the transformer, and blocks relay elements when CT saturates to prevent malfunction. There is an effect that can be done.

In particular, the present invention has the effect of identifying the cause of an internal failure and responding to it.

1 is a flowchart of a method for preventing malfunction of a current transformer according to a preferred embodiment of the present invention.
Figure 2 is a detailed flow chart of step S20.
Figure 3 is a detailed flow chart of step S30.

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.

Hereinafter, a method for preventing malfunction of a current transformer according to a preferred embodiment of the present invention will be described with reference to the drawings.

1 is a flowchart of a method for preventing malfunction of a current transformer according to an embodiment of the present invention.

Referring to FIG. 1, the present invention includes a step of detecting CT saturation using instantaneous value and root-square-square (RMS) value (S10), a step of detecting external failure using negative-sequence (S20), and phase difference for each phase. A step of detecting whether an external failure occurs using (S30), a step of detecting whether CT saturation has occurred using the size of the second harmonic compared to the standing wave (S40), and a step of detecting whether CT saturation has occurred using the determination results of steps S10 to S40. It includes a step of checking the CT saturation state (S50) and a step of blocking relay elements such as current ratio differential relay when CT saturation occurs due to an external fault as a result of the determination in step S50 (S60).

Hereinafter, the structure and operation of the current transformer malfunction prevention method of the present invention configured as described above will be described in more detail. The present invention is a process that is processed by a processor that receives the negative-sequence elements and current characteristics of the first and second windings of a transformer detected from various sensors such as a current sensor, and the processor is assumed to be the subject of the present invention.

First, in step S10, the processor detects CT saturation using the instantaneous value and RMS (root mean square) value.

This utilizes the characteristic that current distortion causes errors in the discrete Fourier transform (DFT) calculation value when CT saturation occurs. If the instantaneous value is 150% or more of the RMS value, it is judged that CT saturation has occurred, and the instantaneous value is RMS. If it is less than 150% of the value, it is considered a normal situation.

More specifically, since distortion occurs in the current waveform when CT saturation occurs, when performing a DFT operation, distorted data is included in one cycle data and the RMS value is calculated as a lower value than the normal waveform.

Therefore, when calculating RMS after restoring a sine wave of the same size using the instantaneous peak value for the saturation waveform, it can be confirmed that it is larger than the RMS value calculated by DFT. In other words, if the instantaneous peak value is more than 150% of the RMS value, CT saturation is determined to have occurred.

This judgment result is provided as CT saturation or normal.

Next, in step S20, the processor detects whether there is an external failure or an internal failure using the negative sequence.

Figure 2 is a detailed flow chart of step S20.

First, in step S21, if the size of the vector sum of the negative-sequence portion of the transformer's 1st winding side and the negative-sequence portion of the transformer's 2nd winding side is greater than the set value, and the phase difference between the negative-sequence portion of the transformer's 1st winding side and the negative-sequence portion of the transformer's 2nd winding side is located within ±45 degrees of 0 degrees, the internal It is judged to be a malfunction.

Next, in step S22, if the magnitude of the negative-sequence is less than the set value and the slope of the current ratio differential is more than 70% for all three phases, it is determined to be a three-phase fault.

Next, in step S23, it is determined that it is a normal or external failure, except in cases where one or more of the judgment results of step S21 and the judgment result of step S22 are determined to be a failure.

Next, in step S30, the presence of an external or internal failure is detected using the phase difference for each phase.

Figure 3 is a detailed flow chart of step S30.

First, in step S31, if the phase difference between phases A-B, B-C, and C-A is ±45 degrees from 0 degrees, it is judged to be a single-phase ground fault internal fault.

In step S32, if the phase difference for each phase A-B, B-C, and C-A is ±45 degrees based on 180 degrees, it is judged to be a line-to-line short circuit internal failure.

In step S33, it is judged as normal or external failure, except in cases where one or more of the judgment results of step S31 and step S32 are judged to be a failure.

Next, in step S40, whether CT saturation has occurred is detected using the size of the second harmonic compared to the standing wave.

More specifically, the processor calculates the 2nd harmonic difference current and obtains the value of (calculated 2nd harmonic difference current/standing wave difference current) * 100. If the result is 15% or more, it is judged to be a 2nd harmonic situation. If the result is less than 15%, It is judged to be in normal condition.

Next, in step S50, the CT saturation state due to external failure is confirmed using the judgment results of steps S10 to S40.

The determination in step S50 is that CT saturation occurs in step S10, external failure is determined in both steps S20 and S30, and CT saturation occurs due to the final external failure when it is determined that it is a 2-harmonic situation in step S40. It is judged by

In other words, if there is even one case where an internal failure or normal condition is determined, it is determined that CT saturation is not due to an external failure.

If it is determined that the CT is not saturated, the block for the relay element in the block state is released.

Through this process, the present invention can detect CT saturation caused by an external fault and block relay elements when CT saturation occurs, thereby preventing malfunction.

In addition, the present invention has the feature of enabling clearer cause detection and response by detecting CT saturation caused by internal failure and external failure separately.

Although embodiments according to the present invention have been described above, they are merely illustrative, and those skilled in the art will understand that various modifications and equivalent scope of embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the following claims.

Claims (7)

As a method for preventing malfunction of a current transformer processed by a processor,
a) detecting current transformer saturation using instantaneous value and root-square-square (RMS) value;
b) detecting whether an external failure exists using the negative sequence;
c) detecting whether there is an external failure using the phase difference for each phase;
d) detecting whether CT saturation has occurred using the magnitude of the second harmonic compared to the standing wave;
e) Confirming the CT saturation state due to an external failure using the judgment results of steps a) to d) above,
In step b),
b-1) Internal failure occurs when the vector sum of the negative-sequence division on the 1st winding side of the transformer and the negative-sequence division on the 2nd winding side of the transformer is greater than the set value, and the phase difference between the negative-sequence division on the 1st winding side of the transformer and the negative-sequence division on the 2nd winding side of the transformer is within ±45 degrees of 0 degrees. A step of determining;
b-2) If the magnitude of the negative-sequence is less than the set value and the slope of the current ratio differential is more than 70% for all three phases, determining a three-phase fault; and
b-3) A method of preventing malfunction of a current transformer including the step of determining an external failure, except when one or more of the determination results of step b-1) and the determination result of step b-2) are determined to be a failure. According to paragraph 1,
In step a),
A current transformer malfunction prevention method characterized by determining that CT saturation has occurred when the instantaneous value is 150% or more of the RMS value. delete According to paragraph 1,
In step c),
c-1) If the phase difference between AB, BC, and CA phases is ±45 degrees based on 0 degrees, determining a single-phase ground fault internal fault;
c-2) If the phase difference between AB, BC, and CA phases is ±45 degrees based on 180 degrees, determining a line-to-line short circuit internal failure; and
c-3) A method of preventing malfunction of a current transformer including the step of determining an external failure except when one or more of the determination results of step c-1) and the determination result of step c-2) are determined to be a failure. According to paragraph 1,
In step d),
A method of preventing malfunction of a current transformer, characterized by calculating the 2-harmonic difference current (calculated 2-harmonic difference current/standing wave difference current) * 100, and determining that the CT is saturated, which is a 2-harmonic situation, if the result is 15% or more. . According to paragraph 1,
In step e),
If the judgment results of steps a) and d) are both determined to be CT saturation, and both steps b) and c) are determined to be external failures,
A current transformer malfunction prevention method characterized by determining that CT saturation occurs due to an external fault. According to paragraph 1,
If it is determined that CT saturation occurred due to an external failure as a result of the determination in step e),
A method for preventing malfunction of a current transformer further comprising the step of blocking the relay element.