KR101989350B1 - Appatus for protecting of microgrid using superimposed reactive energy and method thereof - Google Patents

Abstract

This disclosure discloses a protective relay capable of protecting the microgrid in both power grid interconnected and stand-alone modes and in low resistance, high resistance faults. The protective relay according to the present invention judges whether the fault occurs and the direction of the fault through the invalid superposition energy, and if the fault occurrence area is not the protection area of the main protection area, the protection relay of the fault occurrence area first The blocking operation can be performed after the delay time.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a micro grid protection relay and a method of controlling the micro grid protection relay,

The present invention relates to a micro-grid protection apparatus and method, and more particularly, to a micro-grid protection relay through superposed reactive energy measurement and a control method thereof.

Conventional micro-grid protection schemes can be classified into five types: adaptive protection, distance protection, voltage-based protection, differential protection, and protection for installing external energy devices.

Adaptive protection schemes have drawbacks due to the expense of upgrading all protection devices currently used in the power system. Also, it may be difficult to apply the short-circuit calculation to a microgrid operated in other states.

Distance protection schemes use the admittance of the line, but it is difficult to measure the admittance of a short line like a microgrid. In addition, distance protection schemes introduce errors in the case of high resistance faults.

Voltage-based schemes are only applicable for detecting low resistance faults. Also, the sensitivity of voltage-based schemes is difficult to apply during operation of the grid-connected mode.

Differential protection schemes require synchronized signal measurements at both ends of the power feeder, requiring high investment costs in the device.

The use of an external energy storage device requires a very high investment cost because a protection scheme for installing an external energy device generates a high short circuit current in the event of a failure in a single operation.

Most of the above conventional methods are applicable only for detecting low resistance faults. Thus, these approaches require additional approaches to protect the microgrid in the case of high resistance faults. Furthermore, there is a need for a way to protect the microgrid system against low resistance, high resistance faults in both conventional power grid connection and stand alone modes.

Korean Patent Publication No. 10-0920946

The present disclosure aims to propose a protective relay capable of protecting the microgrid in both power grid interconnected and stand-alone modes and in low resistance, high resistance faults, and its control method.

The solutions described herein are not limited to those mentioned above, and other solutions not mentioned may be clearly understood by those skilled in the art from the following description.

In order to solve the above-described problem, the protection relay according to the present invention determines whether a fault has occurred by using the three-phase current value iabc and determines whether the fault detection signal SDet is in contact with the same power line and the opposite direction A failure detection unit for outputting to other protection relays of the other power lines; A direction determination unit for outputting a failure direction signal SDir indicating a direction in which a failure has occurred by using the three-phase voltage value vabc to other protection relays of another power line contacting the same power line and the opposite direction; A faulty area identification unit for receiving the fault detection signal SDet and the fault direction signal SDir output from the other protection relays and determining whether the fault occurred in the main protection area or the backup protection area; A fault classifying unit for classifying the type of fault by comparing an absolute value of the superposed reactive energy coefficient of each phase with a preset reference value; And a tripping unit for controlling the operation of the circuit breaker in accordance with the signal output from the fault area identification unit and the fault classification unit.

The fault detection unit can detect whether a fault has occurred due to a ratio based on a current before fault occurrence, a superposed normal and a reverse fault current, and a system unbalance ratio.

The system imbalance ratio R _n can be calculated by Equation 1 below.

≪ Formula 1 >

R _n : System unbalance ratio

| I _0pre |: The current before failure, the input current to the protection relay

| I _1pre |: current before fault, normal current input to the protection relay

| I _2pre |: The current before fault occurrence, the reverse phase current input to the protection relay

The failure detection ratio R _FD can be calculated by the following equation (2).

&Quot; (2) "

R _FD : Fault detection ratio

R _n : System unbalance ratio

| I _1pre |: current before fault, normal current input to the protection relay

| I _2pre |: The current before fault occurrence, the reverse phase current input to the protection relay

| Δi _1f |: Normal part of the fault point Invalid RMS (Root Mean Square)

| Δi _2f |: Inverse phase of the fault point Invalid RMS (Root Mean Square)

According to one embodiment of the present invention, the failure detection unit determines that the failure detection ratio is a normal state when the value of the failure detection ratio is '0' (R _FD = 0) When the set limit value is exceeded, it can be judged that a trouble has occurred.

According to an embodiment of the present invention, the direction determination unit can determine whether a type of a fault occurring through the following Equation 3 and Equation 4 is a forward fault or a reverse fault.

&Quot; (3) "

X _u : Reactance of the upstream equivalent circuit

X _a : Reactance between bus B and fault F1

Vm: voltage magnitude at the relay (U)

≪ Equation 4 &

X _d : Reactance of the downstream equivalent circuit

X _ab : reactance between bus A and bus B

X _u2 : reactance between bus B and fault F2

Vm: voltage magnitude at the relay (U)

According to an embodiment of the present invention, the fault area identification unit may be configured such that one protective relay (D) of one power line is connected to another protection relay (U) of the same power line and another power line It is possible to receive the failure detection signal S _Det and the failure direction signal S _Dir from the protection relay U.

According to an embodiment of the present invention, the faulty area identification unit may determine that a fault has occurred in the faulty protected area after a predetermined delay time than when it is determined that a fault has occurred in the main protection area Can be output.

According to an embodiment of the present invention, when the coefficient expressed in Equation (5) is larger than a preset limit value, the fault classification unit can determine that a fault has occurred in the phase.

≪ Eq. 5 &

E _qa , E _qb , E _qc : superimposed reactive energy (SER) on A, B,

_Eqmax = Max (| _Eqa |, | _Eqb |, | _Eqc |)

A control method of a protection relay according to the present invention for solving the above-mentioned problems is characterized in that (a) the fault detection unit judges whether or not a fault has occurred by using the three-phase current value (i _abc ) (S _Det ) to the same power line and other protection relays of the other power line in the reverse direction; (b) The direction determination unit outputs the failure direction signal (S _Dir ) indicating the direction in which the failure occurs by using the three-phase voltage value (v _abc ) to the other power relays of the other power lines contacting the same power line and the opposite direction step; (c) The faulty area identification unit receives the fault detection signal (S _Det ) and the fault direction signal (S _Dir ) output from the other protection relays, and judges which of the main protection area and the rear protection area occurred in the fault step; (d) classifying the type of the fault by comparing the absolute value of the superposed reactive energy coefficient of each phase with a preset reference value; And (e) controlling the operation of the circuit breaker in accordance with the signal output from the fault area identification unit and the fault classification unit by the tripping unit.

A control method of a protection relay according to the present invention for solving the above-mentioned problems can be expressed by a computer program recorded in a computer-readable recording medium which is created to perform each step in the computer.

According to an aspect of the present disclosure, even if a fault occurs while the micro grid is operating in the single operation mode and the grid connection mode, it is possible to detect a failure and protect the power grid.

According to another aspect of the present disclosure, a failure of the microgrid can detect failure and protect the power grid, regardless of low resistance and high resistance failure.

 According to another aspect of the present disclosure, even if the fault-causing area is not smoothly separated, the remaining electric power network can be protected by blocking other areas connected to the fault-causing area.

The effects described in the present specification are not limited to those mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

1 is a block diagram briefly showing the configuration of a protection relay according to the present invention.
2 is a schematic view of a portion of a microgrid according to the present invention.
Fig. 3 is a reference diagram of the area divided by the protection relay -1D.
4 is a reference diagram showing the center of the line 1.
5 is an equivalent circuit diagram according to forward fault.
6 is an equivalent circuit diagram according to reverse fault.
Fig. 7 is a circuit diagram schematically showing a configuration for a shutoff operation of the protection relay.
8 is a block diagram showing the configuration of the protection relay according to the present invention in more detail.
Fig. 9 is a simulation system diagram.
Fig. 10 shows experimental results of the independent mode of the microgrid.
Fig. 11 shows experimental results of the grid connection mode of the micro grid.
Fig. 12 shows experimental results of high impedance failure.
FIG. 13 shows experimental results in which three capacitor banks (500 kvar each) are installed on busbars 4, 6, and 7 of the microgrid.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Wherever possible, the same or similar parts are denoted using the same reference numerals in the drawings.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto.

Means that a particular feature, region, integer, step, operation, element and / or component is specified and that other specific features, regions, integers, steps, operations, elements, components, and / It does not exclude the existence or addition of a group.

All terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Hereinafter, a microgrid protection apparatus and method according to the present invention will be described with reference to the drawings.

The present invention proposes a micro grid protection relay and its control method using superimposed reactive energy generated due to a failure. The change in voltage, current, and energy caused by the failure is called the superposition component, and the change in the reactive component of the energy is referred to as superposed reactive energy. Overlapping reactive energy is a momentary change in reactive power caused by a fault or a sudden change in system.

1 is a block diagram briefly showing the configuration of a protection relay according to the present invention.

1, a protection relay 100 according to the present invention includes a fault detection unit 110, a fault direction unit 120, a fault area identification unit 130, a fault classification unit 140 and a tripping unit 150 ).

The fault detection unit 110 determines whether or not a fault has occurred by using the three-phase current value i _abc and outputs the fault detection signal S _Det to the other power line in the same power line and the other Can be output to protective relays. The failure detection unit 110 can determine whether a failure has occurred by using the superposition component and the failure detection ratio to be described below. The fault detection unit 110 can detect all kinds of faults including high resistance faults in both the grid connection and single operation mode.

The fault direction unit 120 outputs the fault direction signal S _Dir indicating the direction in which the fault has occurred by using the three-phase voltage value v _abc to the other power relays of the other power lines contacting the same power line and the reverse direction can do.

The fault area identification unit 130 receives the fault detection signal S _Det and the fault direction signal S _Dir output from the other protection relays and determines whether the fault occurs in the main protection area or the back protection area can do. In outputting a signal to the tripping unit 150, the faulty area identification unit 130 determines a delay time so that the protection relay having the faulty area as the main protection area may operate first And can output a signal. The signal and time zone output from the faulty area identification unit 130 to the tripping unit 150 will be described below.

The fault classification unit 140 can classify the type of fault by comparing the absolute value of the superposed reactive energy coefficient of each phase with a preset reference value.

The tripping unit 150 may control the operation of the circuit breaker according to the signals output from the fault area identification unit 130 and the fault classification unit 140. The tripping unit 150 can individually block three phases according to the type of failure.

Hereinafter, a description will be given of a micro grid in which the protective relay 100 according to the present invention is installed.

2 is a schematic view of a portion of a microgrid according to the present invention.

Referring to Fig. 2, it can be seen that the main grid shown on the right side of the drawing, the power source, which is composed of the power source, the converter, the transformer, shown on the left side of the drawing. And a power line connecting the power source and the main grid. It can be seen that the power lines are divided into lines 1 and 2 by the buses A, B and C, respectively. It can be confirmed that a load is connected between the line 1 and the line 2. Figure 2 illustrates one example of a power line of a plurality of power lines as part of a microgrid.

Referring to FIG. 2, in the line 1 and the line 2, the protection relay -1U, the protection relay -1D, the protection relay -2U and the protection relay -2D can be identified. In the present specification, assuming that a current flows from a power source to a load or a main grid, the power source is set to 'upstream' and the main grid is set to 'downstream'. Therefore, 'Protection Relay -1U' means protection relay installed in line 1 and 'Protection Relay -1D' means protection relay installed in line 1 in Downstream.

In this specification, microgrid refers to a small power system, which is connected to an existing power grid and receives power from an existing power source, but which is equipped with a small power source (e.g., solar generator, wind generator, etc.). Therefore, the micro grid can be operated in a single operation mode in which power is supplied only by a power source provided in the power grid and in a grid-connected operation mode in which power is supplied from an existing power grid.

In this specification, for convenience of understanding and explanation, a microgrid protection apparatus and method according to the present specification will be described, focusing on a protection relay-1D.

Fig. 3 is a reference diagram of the area divided by the protection relay -1D.

Referring to FIG. 3, the right side of the protection relay -1D is indicated as 'forward area', and the left side of the protection relay -1D is indicated as 'reverse area'. The forward direction and the reverse direction are based on setting the power supply source described above with respect to the protective relay -1D as 'upstream' and setting the main grid as 'downstream'.

4 is a reference diagram showing the center of the line 1.

Referring to FIG. 4, it can be seen that the remaining sections except for line 1 between B and C are replaced by equivalent circuits. It can be seen that the part where the power source and line 2 were located was replaced with the upstream equivalent circuit, and the part where the main grid was replaced with the downstream equivalent circuit. In order to explain the microgrid protection apparatus and method according to the present invention, it is assumed that there are two failures. The first fault location is between protection relay -1U and protection relay -1D (F1), the second fault location is between upstream equivalent circuit and protection relay -1U (F2). The two faults F1 and F2 refer to a forward fault and a reverse fault, respectively, with respect to the protection relay -1D.

5 is an equivalent circuit diagram according to forward fault.

6 is an equivalent circuit diagram according to reverse fault.

The meanings of the abbreviations used in Figs. 5 and 6 are as follows.

L _u : Upstream equivalent inductance

L _d : downstream equivalent inductance

L _a : Line inductance between the fault point and bus B

L _b : Line inductance between fault point and bus C

L _ab : inductance of line 1

i _Bfl : Invalid overlap current on bus B

i _Cfl : invalid overlap current on bus C

v _Bfl : invalid overlap voltage on bus B

v _Cfl : Invalid _{overvoltage on} bus C

v _fpre : the previous fault voltage at the fault point

Δi _f : Current at fault point

Δv _fl : Invalid overlap voltage at fault point

The protection relay 100 according to the present specification can detect whether or not a fault has occurred by a ratio based on a current prior to a fault, a superposed normal and an inverse phase current, and a system unbalance ratio. If the system imbalance ratio R _n is given by Equation 1 below, the expression for the fault detection ratio R _FD is given by:

≪ Formula 1 >

R _n : System unbalance ratio

| I _0pre |: The current before failure, the input current to the protection relay

| I _1pre |: current before fault, normal current input to the protection relay

| I _2pre |: The current before fault occurrence, the reverse phase current input to the protection relay

&Quot; (2) "

R _FD : Fault detection ratio

R _n : System unbalance ratio

| I _1pre |: current before fault, normal current input to the protection relay

| I _2pre |: The current before fault occurrence, the reverse phase current input to the protection relay

| Δi _1f |: Normal part of the fault point Invalid RMS (Root Mean Square)

| Δi _2f |: Inverse phase of the fault point Invalid RMS (Root Mean Square)

The protection relay 100 according to the present invention determines that the value of the base failure detection ratio is in a normal state when the value of the failure detection ratio is '0' (R _FD = 0) When the set limit value is exceeded, it can be judged that a trouble has occurred.

In addition, the protection relay 100 according to the present invention can determine whether the type of failure that occurs through Equation (3) and Equation (4) is forward failure or reverse failure. Meanwhile, Equation 3 corresponds to the failure F1 shown in Fig. 4, and Equation 4 corresponds to the failure F2 shown in Fig.

&Quot; (3) "

X _u : Reactance of the upstream equivalent circuit

X _a : Reactance between bus B and fault F1

Vm: voltage magnitude at the relay (U)

≪ Equation 4 &

X _d : Reactance of the downstream equivalent circuit

X _ab : reactance between bus A and bus B

X _u2 : reactance between bus B and fault F2

Vm: voltage magnitude at the relay (U)

Equations 3 and 4 are negative for forward fault and positive for reverse fault. Therefore, the protection relay 100 according to the present invention can determine the direction of the failure according to the sign of the values of the equations (3) and (4).

The protection relay 100 according to the present specification can output the failure detection signal S _Det and the failure direction signal S _Dir in accordance with the above description. For example, the failure detection signal S _Det can output '1' when a failure occurs in a binary code, and can output '0' if it is not a failure. The failure direction signal (S _Dir ) can be '1' when it is a forward fault in binary code, and can output '0' when it is in reverse fault.

The protection relay 100 according to the present invention is capable of communicating with another protection relay 100 adjacent thereto. Preferably, the one protection relay D of one power line receives the fault detection signal SDet from one protection relay U of another power line in contact with the other protection relay U of the same power line and the other power line in a reverse direction, And the failure direction signal SDir (see Fig. 7). The protection relay 100 can use the failure detection signal SDet and the failure direction signal SDir received from other protection relays to determine an area where a failure has occurred.

Meanwhile, the protection relay 100 according to the present invention is provided with a main protection zone and a backup protection zone. For example, the protection relay -1D shown in FIG. 3 is given a forward protection area as a 'main protection area' and a reverse protection area as a 'protection protection area'. The protection relay 100 immediately performs a shutdown operation (outputting a shutdown operation signal (FF trip signal)) when a failure occurs in the main protection area, and performs a shutdown operation after a predetermined delay time when a failure occurs in the protection area do. The delay time is to give a time for the protection relay having the main protection area to start the blocking operation in the corresponding area where the failure occurs. If the protection relay having the main protection area fails the blocking operation, This is to ensure that the protective relay in the protected area works. The delay time must be greater than the time taken for the shutdown operation to occur when a fault occurs in the primary protected area.

Fig. 7 is a circuit diagram schematically showing a configuration for a shutoff operation of the protection relay.

Referring to FIG. 7, it is a circuit diagram based on the protection relay -1D. The one protection relay D of one power line receives the failure detection signal SDet and the failure direction signal SD from one protection relay U of another power line in contact with the other protection relay U of the same power line and the other power line in the reverse direction, (SDir).

Meanwhile, the protection relay 100 according to the present invention can classify various types of faults through Equation (5).

≪ Eq. 5 &

E _qa , E _qb , E _qc : superimposed reactive energy (SER) on A, B,

_Eqmax = Max (| _Eqa |, | _Eqb |, | _Eqc |)

In the protection relay 100 according to the present specification, if any of the coefficients is larger than a preset limit value, the phase can be determined as a failure.

8 is a block diagram showing the configuration of the protection relay according to the present invention in more detail.

Hereinafter, an experimental example in which the protection relay 100 according to the present invention is implemented in a MATLAB / SIMULINK in a simulated system will be described.

Fig. 9 is a simulation system diagram.

Referring to FIG. 9, failure analysis is performed on all positions of the simulation system. The fault types considered in the above fault analysis are single phase ground fault, line short fault, 2 wire ground fault, 3 phase fault, and high impedance fault. Also, it was confirmed whether or not the protection relay of the protection area of the protection area performs the blocking operation considering the failure of the protection relay of the main protection area.

Fig. 10 shows experimental results of the independent mode of the microgrid.

The table shown in Fig. 10 shows the operation times of the protective relays (MGPR), the protective relay of the main protection area and the protection relay of the protection area, the failure detection ratio, and the independent mode of the microgrid, Represents the SRE coefficient. It can be confirmed that the failure is detected successfully because the proposed failure detection ratio R _FD exceeds the set threshold value (2.5) in the table shown in FIG.

Fig. 11 shows experimental results of the grid connection mode of the micro grid.

The table shown in Fig. 11 shows the operation times of the protection relay of the main protection area and the protection relay of the protection area in the grid protection mode (MGPR), the fault detection ratio, the SRE coefficient, and the micro grid grid connection mode. As in the stand-alone mode, it can be verified that if the protection relay (MGRP) of the primary protected area fails to isolate the fault, the protection relays (MGPR) of the posterior ambiguity region provide adequate post-protection.

Fig. 12 shows experimental results of high impedance failure.

The table shown in FIG. 12 is the result of high impedance failure in the scenario selected for both grid-connected mode and independent mode. It can be seen that the protective relay according to the present invention effectively detects high impedance faults but is relatively slow by comparing the independent mode and the grid-connected mode. However, the operating speed of the protective relay in accordance with the present invention is still less than 0.1 second, which is effective for protection of the distribution system.

FIG. 13 shows experimental results in which three capacitor banks (500 kvar each) are installed on busbars 4, 6, and 7 of the microgrid.

Protection relays in accordance with the present disclosure use the bi-directional nature of the SRE for fault locations and fault classes. Therefore, the protective relay according to the present invention needs to be tested in a system having a reactive power compensation device. It can be seen from the table shown in FIG. 13 that the protective relay according to the present disclosure provides a stable SRE direction when there is a reactive power compensation device.

The embodiments and the accompanying drawings described in the present specification are merely illustrative of some of the technical ideas included in the present invention. Accordingly, the embodiments disclosed herein are for the purpose of describing rather than limiting the technical spirit of the present invention, and it is apparent that the scope of the technical idea of the present invention is not limited by these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

100: Protection Relay
110: Fault detection unit
120: Failure direction unit
130: Failure Zone Identification Unit
140: Fault classification unit
150: Tripping unit

Claims (19)

A fault detection unit for judging whether or not a fault has occurred by using the three-phase current value iabc and outputting the fault detection signal SDet to the same power line and other protection relays of other power lines contacted in the reverse direction according to whether a fault has occurred;
A direction determination unit for outputting a failure direction signal SDir indicating a direction in which a failure has occurred by using the three-phase voltage value vabc to other protection relays of another power line contacting the same power line and the opposite direction;
A faulty area identification unit for receiving the fault detection signal SDet and the fault direction signal SDir output from the other protection relays and determining whether the fault occurred in the main protection area or the backup protection area;
A fault classifying unit for classifying the type of fault by comparing an absolute value of the superposed reactive energy coefficient of each phase with a preset reference value; And
And a tripping unit for controlling the operation of the circuit breaker in accordance with the signal outputted from the fault region identifying unit and the fault classifying unit,
Wherein said fault detection unit detects whether a fault has occurred by a ratio based on a current before fault occurrence, a superposed normal and an inverse phase current, and a system unbalance ratio. delete The method according to claim 1,
Wherein the system imbalance ratio (R _n ) is calculated by: &_lt; EMI ID ₌ 1.0 >
≪ Formula 1 >

R _n : System unbalance ratio
| I _0pre |: The current before failure, the input current to the protection relay
| I _1pre |: current before fault, normal current input to the protection relay
| I _2pre |: The current before fault occurrence, the reverse phase current input to the protection relay The method of claim 3,
And the failure detection ratio (R _FD ) is calculated by the following equation (2).
&Quot; (2) "

R _FD : Fault detection ratio
R _n : System unbalance ratio
| I _{1pre |} : The current before fault occurrence, the normal current input to the protection relay
| I _{2pre |} : Current before fault occurrence, reverse phase current input to the protection relay
| Δi _{1f |} : RMS (Root Mean Square) of the null current of superfluous current at the failure point
|? I _{2f |} : Reverse phase difference of fault point Invalid RMS (Root Mean Square) The method of claim 4,
The failure detection unit determines that the failure detection ratio is a normal state when the value of the failure detection ratio is '0' (R _FD = 0), and when the value of the failure detection ratio exceeds a preset limit value for a predetermined time, The protection relay being characterized in that: The method according to claim 1,
Wherein the direction determining unit determines whether a type of a fault occurring through Equation (3) and Equation (4) is forward fault or reverse fault.
&Quot; (3) "

X _u : Reactance of the upstream equivalent circuit
X _a : Reactance between bus B and fault F1
Vm: voltage magnitude at the relay (U)

≪ Equation 4 &

X _d : Reactance of the downstream equivalent circuit
X _ab : reactance between bus A and bus B
X _u2 : reactance between bus B and fault F2
Vm: voltage magnitude at the relay (U) The method according to claim 1,
The faulty area identification unit is configured such that one of the protection relays (D) of one power line is connected to another protection relay (U) of the same power line and one protection relay (U) of another power line facing the opposite power line And receives a signal (SDet) and a fault direction signal (SDir). The method according to claim 1,
Wherein the faulty area identification unit outputs a blocking operation signal after a preset delay time than when a fault has occurred in the main protection area when it is determined that a fault has occurred in the reserved protection area. The method according to claim 1,
Wherein the failure classification unit determines that a failure has occurred in the phase when the coefficient represented by the following expression (5) is larger than a preset limit value.
≪ Eq. 5 &

E _qa , E _qb , E _qc : superimposed reactive energy (SER) on A, B,
_Eqmax = Max (| _Eqa |, | _Eqb |, | _Eqc |) (a) The fault detection unit judges whether or not a fault has occurred by using the three-phase current value (i _abc ), and the fault detection signal (S _Det ) Outputting to the relays;
(b) The direction determination unit outputs the failure direction signal (S _Dir ) indicating the direction in which the failure occurs by using the three-phase voltage value (v _abc ) to the other power relays of the other power lines contacting the same power line and the opposite direction step;
(c) The faulty area identification unit receives the fault detection signal (S _Det ) and the fault direction signal (S _Dir ) output from the other protection relays, and judges which of the main protection area and the rear protection area occurred in the fault step;
(d) classifying the type of the fault by comparing the absolute value of the superposed reactive energy coefficient of each phase with a preset reference value; And
(e) controlling the operation of the circuit breaker in accordance with the signal output from the fault locating unit and the fault classifying unit,
Wherein the step (a) is a step of detecting whether a failure has occurred due to a ratio based on a current before fault occurrence, a superposed normal and a reverse phase divided current, and a system unbalance ratio. delete The method of claim 10,
Wherein the step (a) is a step in which the failure detection unit calculates the system unbalance ratio (R _n ) by the following equation (1).
≪ Formula 1 >

R _n : System unbalance ratio
| I _0pre |: The current before failure, the input current to the protection relay
| I _1pre |: current before fault, normal current input to the protection relay
| I _2pre |: The current before fault occurrence, the reverse phase current input to the protection relay The method of claim 12,
Wherein the step (a) is a step in which the failure detection unit calculates the failure detection ratio (R _FD ) using the following equation (2).
&Quot; (2) "

R _FD : Fault detection ratio
R _n : System unbalance ratio
| I _1pre |: current before fault, normal current input to the protection relay
| I _2pre |: The current before fault occurrence, the reverse phase current input to the protection relay
| Δi _1f |: Invalid of normal point of fault point RMS (Root Mean Square)
| Δi _2f |: Inverse phase of the fault point Invalid RMS (Root Mean Square) 14. The method of claim 13,
Wherein the step (a) includes the steps of: when the failure detection unit determines that the failure detection ratio is a normal state when the value of the failure detection ratio is '0' (R _FD = 0) And judging that a failure occurs when the voltage exceeds a predetermined voltage. The method of claim 10,
Wherein the step (b) is a step of determining whether a type of a fault occurring in the direction determination unit through the following equations (3) and (4) is a forward fault or a reverse fault.
&Quot; (3) "

X _u : Reactance of the upstream equivalent circuit
X _a : Reactance between bus B and fault F1
Vm: voltage magnitude at the relay (U)

≪ Equation 4 &

X _d : Reactance of the downstream equivalent circuit
X _ab : reactance between bus A and bus B
X _u2 : reactance between bus B and fault F2
Vm: voltage magnitude at the relay (U) The method of claim 10,
In the step (c), one of the protection relays (D) of one power line is connected to the other protection relay (U) of the same power line and one protection relay (S _Det ) and a fault direction signal (S _Dir ) from the fault detection signal (S _Det ). The method of claim 10,
The step (c) includes a step of outputting a blocking operation signal after a predetermined delay time than when a failure has occurred in the main protection area when it is determined that a failure has occurred in the protection area Wherein the protection relay is a control relay. The method of claim 10,
Wherein the step (d) is a step of determining that a failure has occurred in the phase when the coefficient represented by the following equation (5) is larger than a preset limit value.
≪ Eq. 5 &

E _qa , E _qb , E _qc : superimposed reactive energy (SER) on A, B,
_Eqmax = Max (| _Eqa |, | _Eqb |, | _Eqc |) A computer program recorded on a computer-readable recording medium, the computer program being written in the computer to perform the steps of the control method according to any of claims 10 and 13 to 18.

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