KR102611859B1 - overcurrent relay - Google Patents

Abstract

The overcurrent relay 30 includes an overcurrent detection unit 100 that detects overcurrent by comparing the effective value of the input current input from the power system and the set value, a drop detection unit 110 that detects a decrease in the effective value, and an overcurrent detection unit ( It is provided with an output control unit 130 that generates an operation output and a return output based on the detection result of 100), the detection result of the degradation detection unit 110, and predetermined conditions regarding the current waveform of the input current. The output control unit 130 generates a return output regardless of the detection result by the overcurrent detection unit 100 when a decrease in the effective value is detected and when a predetermined condition is established.

Description

overcurrent relay

This disclosure relates to an overcurrent relay.

The overcurrent relay detects a system fault and outputs an operation when the secondary current from the current transformer (CT) provided in the power system is greater than the set value. As a result, a circuit breaker (CB) provided in the power system is opened and a system accident is eliminated. Additionally, the overcurrent relay is configured to provide a return output (i.e., turn the operation output OFF) when the secondary current becomes less than the set value.

For example, Japanese Patent Laid-Open No. 2011-250518 (Patent Document 1) discloses an overcurrent relay including a first overcurrent determination unit and a second overcurrent determination unit. The first overcurrent determination unit makes a return determination by comparing the effective value calculated using current data of a predetermined period with the first set value. The second overcurrent determination unit makes a return determination by comparing the effective value calculated using current data for a period shorter than the predetermined period and the second set value lower than the first set value. The overcurrent relay generates a return output at the earlier timing among the return determination results of each of the first overcurrent determination unit and the second overcurrent determination unit.

Patent Document 1: Japanese Patent Publication No. 2011-250518

In the overcurrent relay according to Patent Document 1, the second set value is changed to a value lower than the first set value in synchronization with the output timing of the operation output, and the second set value is changed to a value lower than the first set value in synchronization with the output timing of the return output. The value is being changed to a higher value than the set value. As a result, the error in the effective value calculation result by the second overcurrent determination unit is suppressed from influencing the precision of the operation determination and recovery determination, while speeding up the operation time and recovery time is attempted.

However, for example, when the fault current contains many harmonic components and distortion wave components, the error in the effective value calculation result by the second overcurrent determination unit greatly affects the accuracy of the recovery determination. In order to suppress this effect, it is necessary to change the second set value to a value significantly lower than the first set value in synchronization with the output timing of the operation output. However, if this is done, the return time becomes longer, and as a result, the return time is not accelerated. There was a problem that it couldn't be realized.

The object of a certain aspect of the present disclosure is to provide an overcurrent relay capable of achieving both appropriate recovery and speeding up the recovery time.

An overcurrent relay according to an embodiment includes an overcurrent detection unit that detects overcurrent by comparing the effective value of the input current input from the power system and a setting value, a drop detection unit that detects a decrease in the effective value, and an overcurrent detection unit. and an output control unit that generates an operation output and a return output based on the detection result, the detection result of the degradation detection unit, and predetermined conditions regarding the current waveform of the input current. The output control unit generates a return output when a decrease in the effective value is detected and when a predetermined condition is established, regardless of the detection result by the overcurrent detection unit.

An overcurrent relay according to another embodiment includes a first overcurrent detection unit including a first digital filter that generates first current data that extracts the rated frequency component of the input current input from the power system, and a filter that is faster than the first digital filter. and a second overcurrent detector including a second digital filter that generates second current data that extracts the rated frequency component of the input current. The first overcurrent detection unit outputs a first detection result of the overcurrent by comparing the first effective value calculated using the first current data of the first period and the first set value. The second overcurrent detection unit outputs a second detection result of the overcurrent by comparing a second effective value calculated using second current data of a second period shorter than the first period and a second set value larger than the first set value. , a third detection result of overcurrent is output by comparing the second effective value and a third set value smaller than the first set value. The overcurrent relay further includes a drop detection unit that detects that the first effective value has decreased, and an output control unit that generates an operation output and a return output based on the first to third detection results and the detection result of the drop detection unit. When a decrease in the first effective value is detected, the output control unit returns a return output at whichever of the first detection results indicate that the overcurrent is not detected and the third detection result that indicates that the overcurrent is not detected, whichever is earlier. creates .

According to the present disclosure, an overcurrent relay capable of achieving both appropriate recovery and faster recovery time is provided.

Figure 1 is a diagram schematically showing the overall configuration of a power system in which a protection relay system is installed.
Figure 2 is a diagram showing an example of the hardware configuration of an overcurrent relay.
Figure 3 is a block diagram showing an example of the functional configuration of the overcurrent relay according to Embodiment 1.
Figure 4 is a schematic diagram showing the input current and effective value from the occurrence of a fault until the circuit breaker is opened.
Figure 5 is a diagram for explaining a method for detecting a decrease in effective value according to Embodiment 1.
Figure 6 is a diagram for explaining the zero cross detection method according to Embodiment 1.
FIG. 7 is a diagram showing an example of operation in the overcurrent relay according to Embodiment 1.
Figure 8 is a diagram showing an example of a DC (Direct Current) attenuation wave.
Figure 9 is a block diagram showing an example of the functional configuration of an overcurrent relay according to Embodiment 2.
Figure 10 is a block diagram showing an example of the functional configuration of the direct current determination unit according to Embodiment 2.
FIG. 11 is a diagram showing an example of operation in the overcurrent relay according to Embodiment 2.
Figure 12 is a block diagram showing an example of the functional configuration of the overcurrent relay according to Embodiment 3.
FIG. 13 is a diagram showing an example of operation in the overcurrent relay according to Embodiment 3.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention will be described with reference to the drawings. In the following description, like parts are given the same symbols. Their names and functions are also the same. Therefore, their detailed description will not be repeated.

Embodiment 1.

＜Configuration of power system＞

1 is a diagram schematically showing an example of the overall configuration of a power system in which a protection relay system is installed. In the power system shown in FIG. 1, electric wires 1 are connected to bus bars 2 and 3. Additionally, the wire 1 is provided with circuit breakers 4, 5, and 6 and a current transformer 7. When the power system in FIG. 1 is for three-phase alternating current, circuit breakers 4, 5, and 6 and current transformers 7 are provided on the wires of each phase.

The protection relay system 10 includes a protection relay 20 and an overcurrent relay 30. In this embodiment, the protection relay 20 functions as a protection relay for detecting accidents in the power system, and the overcurrent relay 30 functions as a CBF relay for countermeasures against Circuit Breaker Failure (CBF). do. In addition, the protection relay 20 includes a main protection relay and a backup protection relay for relay failure of the main protection relay.

Additionally, the CBF relay includes an overcurrent relay element to detect that the fault current has not been interrupted due to a circuit breaker tripping. The CBF relay receives a trip signal from a protection relay that detects an accident in the power system, and when current detection by the overcurrent relay element continues for a certain period of time, it outputs a trip signal to open an adjacent circuit breaker.

The protection relay 20 detects the occurrence of an accident in the power system based on the input current from the current transformer 7 provided on the wire 1, and outputs a trip signal TR1, which is an opening command, to the circuit breaker 4. A trip signal TR2 is output to the overcurrent relay 30. Additionally, the trip signal output from the common digital output circuit may be branched, and the branched signal may be input to the circuit breaker 4 and the overcurrent relay 30, respectively.

The accident determination method by the protection relay 20 is not particularly limited. The protection relay 20 may include, for example, a current differential relay element or a distance relay element. In the case of a current differential relay element, the current detected by another current transformer provided on the wire 1 is also input to the protection relay 20. In the case of a distance relay element, the voltage detected by the voltage transformer provided in the bus bar 2 is also input to the protection relay 20.

The overcurrent relay 30 determines the presence or absence of a fault current based on the input current from the current transformer 7. The overcurrent relay 30 determines that the circuit breaker 4 is inoperable when a fault current is detected even after the time required to open the circuit breaker 4 has elapsed after receiving the trip signal TR2 from the protection relay 20. Thus, a trip signal TR3 is output to the surrounding circuit breakers (5, 6). The trip signal TR3 is branched and input to the circuit breakers 5 and 6, respectively. Additionally, trip signals output from different digital output circuits may be input to the circuit breakers 5 and 6, respectively.

＜Hardware configuration＞

FIG. 2 is a diagram showing an example of the hardware configuration of the overcurrent relay 30. Referring to FIG. 2, the overcurrent relay 30 includes an auxiliary transformer 51, an analog to digital (AD) converter 52, and an operation processing unit 70. The overcurrent relay 30 is configured as a digital protection relay device. In addition, the hardware configuration of the protection relay 20 is the same as the hardware configuration shown in FIG. 2.

The auxiliary transformer 51 receives the input current from the current transformer 7, converts it into a voltage signal suitable for signal processing in the relay internal circuit, and outputs it. The AD converter 52 receives the voltage signal output from the auxiliary transformer 51 and converts it into digital data. Specifically, the AD converter 52 includes an analog filter, a sample hold circuit, a multiplexer, and an AD converter.

The analog filter removes high-frequency noise components from the signal output from the auxiliary transformer 51. The sample hold circuit samples the signal output from the analog filter at a predetermined sampling period. Based on the timing signal input from the calculation processing unit 70, the multiplexer sequentially converts the waveform signal input from the sample and hold circuit into time series and inputs it to the AD converter.

The AD converter converts the signal input from the multiplexer from analog data to digital data. The AD converter outputs a digitally converted signal (i.e., digital data) to the operation processing unit 70. In the AD converter, for example, analog-to-digital conversion is performed at 12 sampling cycles during one cycle (i.e., 360°) of the electrical angle at the rated frequency. In this case, one sampling interval is a time interval corresponding to an electrical angle of 30° at the rated frequency.

The operation processing unit 70 includes a CPU (Central Processing Unit) 72, ROM 73, RAM 74, DI (digital input) circuit 75, DO (digital output) circuit 76, and , includes an input interface (I/F) 77. These are combined into a bus 71.

The CPU 72 controls the operation of the overcurrent relay 30 by reading and executing a program previously stored in the ROM 73. Additionally, the ROM 73 stores various information used by the CPU 72. CPU 72 is, for example, a microprocessor. Additionally, the hardware may be a FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a circuit with other computational functions other than the CPU.

The CPU 72 receives digital data from the AD converter 52 through the bus 71. The CPU 72 performs control operations using the received digital data according to the program stored in the ROM 73.

The DO circuit 76 outputs a trip signal to open the circuit breaker. For example, the trip signal TR2 output from the DO circuit 76 of the protection relay 20 is input to the DI circuit 75 of the overcurrent relay 30. The input interface 77 typically includes various buttons and accepts various setting operations from the system operator.

＜Function configuration＞

FIG. 3 is a block diagram showing an example of the functional configuration of the overcurrent relay 30 according to Embodiment 1. Referring to FIG. 3, the overcurrent relay 30 includes an overcurrent detection unit 100, a drop detection unit 110, a zero cross determination unit 120, and an output control unit 130 as its main functional structure. Typically, each of these functions is realized by the CPU 72 executing a program stored in the ROM 73. Additionally, some or all of these functions may be configured to be realized by using a dedicated circuit.

The overcurrent detection unit 100 detects overcurrent by comparing the effective value of the input current input from the power system and the set value. Specifically, the overcurrent detection unit 100 includes a digital filter 101, an effective value calculation unit 102, and an overcurrent determination unit 103.

The digital filter 101 generates current data by extracting the rated frequency component (i.e., fundamental wave component) of the input current. Specifically, the digital filter 101 removes the harmonic component, direct current component, and distortion component of the input current converted to digital data by the AD converter 52 and generates current data from which the rated frequency component is extracted.

The digital filter 101 uses, for example, data from a period T1 of 1/2 cycle (i.e., 180°) of the electrical angle of the rated frequency. This corresponds to data for 6 sampling lengths, for example, when the sampling number of the AD converter 52 is 12 times in 1 cycle.

The effective value calculation unit 102 performs calculation of the effective value of the input current from which the rated frequency component is extracted. Specifically, the effective value calculation unit 102 calculates the effective value using the current data input from the digital filter 101. The effective value calculation unit 102 calculates the effective value using, for example, the following equation (1).

Ir(t) =sqrt(|I(t-90) ² -I(t)*I(t-180)|)···(1)

Here, Ir(t) represents the effective value at time t. In addition, I(t) represents the instantaneous current value of the input current from which the rated frequency component is extracted at time t, and I(t-90) represents the instantaneous current value 90° before the electrical angle at time t, I(t-180) represents the instantaneous current value 180 degrees electrical angle before time t. Additionally, in equation (1), the time required to obtain data used for calculating the effective value is the time equivalent to 1/2 cycle of the electrical angle.

The overcurrent determination unit 103 determines the presence or absence of overcurrent by comparing the effective value Ir calculated by the effective value calculation unit 102 with the predetermined set value Is.

Figure 4 is a schematic diagram showing the input current and effective value from the occurrence of a fault until the circuit breaker is opened. Referring to FIG. 4, at time tx after the failure occurs, the effective value Ir becomes more than the set value Is. Therefore, the overcurrent determination unit 103 performs an operation determination (i.e., determination of overcurrent detection) at time tx and outputs an output value of "1".

Moreover, at time ty after the circuit breaker 4 is opened, the effective value Ir becomes less than the set value Is. The overcurrent determination unit 103 makes a non-operation or recovery determination (i.e., determination that the overcurrent is not detected) at time ty and outputs an output value of “0”. The output value of the overcurrent determination unit 103 becomes the output value of the overcurrent detection unit 100. The corresponding output value corresponds to the detection result Dx of the overcurrent detection unit 100.

In addition, the overcurrent detection unit 100 generates current data by extracting the rated frequency component of the input current using data of a relatively long period, calculates the effective value Ir using the corresponding current data, and calculates the effective value Ir and the set value. Execute overcurrent detection using Is. Therefore, the overcurrent detection unit 100 is difficult to be influenced by harmonics and distortion waves, and does not return when a fault current occurs, so it has high stability.

Again, referring to FIG. 3, the drop detection unit 110 detects a drop in the effective value Ir. Specifically, the decrease detection unit 110 detects a decrease in the effective value Ir when the decrease rate of the effective value Ir is greater than or equal to the reference decrease rate.

Figure 5 is a diagram for explaining a method for detecting a decrease in effective value according to Embodiment 1. Referring to FIG. 5, the drop detection unit 110 detects a drop in the effective value Ir using the following equations (2) and (3).

Ir(t)<Ir(t-180)···(2)

|Ir(t) -Ir(t-180)|≥Th1*Ir(t-180)···(3)

Here, Ir(t) represents the effective value at time t. Additionally, Ir(t-180) represents the effective value 180° electrical angle before time t.

The decrease detection unit 110 detects a decrease in the effective value Ir when the above equations (2) and (3) hold true. In other words, the condition that the current rms value Ir(t) is smaller than the rms value Ir(t-180) 180° ago, and the rms value Ir(t) and the rms value for the rms value Ir(t-180) When the condition that the ratio of the absolute value of the difference (i.e., degradation rate) of Ir(t-180) is equal to or greater than the threshold Th1 (e.g., Th1=0.15 to 0.5) is met, the degradation detection unit 110 determines the effective value. Detect the decrease in Ir. When the decline detection unit 110 detects a decline in the effective value Ir, it outputs an output value of "1", and when it does not detect a decline in the effective value Ir, it outputs an output value of "0". The corresponding output value corresponds to the detection result of the degradation detection unit 110.

Again, referring to FIG. 3, the zero cross determination unit 120 determines whether a zero cross point of the current waveform of the input current converted to digital data by the AD converter 52 has been detected. Specifically, the zero cross determination unit 120 includes a zero cross detection unit 121 and a return timer 122.

Figure 6 is a diagram for explaining the zero cross detection method according to Embodiment 1. Referring to FIG. 6, the zero cross detection unit 121 is composed of, for example, a comparator with hysteresis, and detects the zero cross point of the input current by comparing threshold values H and L set near the ground level. . In this way, by providing a hysteresis characteristic to the threshold value of the comparator, false detection of the zero cross point due to noise after digital conversion is prevented. Typically, a zero cross point is detected every half cycle.

Again, referring to FIG. 3, when the zero cross detector 121 outputs an output value of “1”, the recovery timer 122 maintains that value for the recovery time Tre. The recovery time Tre is, for example, a time equivalent to 2/3 cycle (i.e., an electrical angle of 240°). The output of the return timer 122 becomes the output of the zero cross determination unit 120. When the zero cross determination unit 120 determines that a zero cross point has been detected, it outputs an output value of "1", and when it determines that a zero cross point has not been detected, it outputs an output value of "0". This output value corresponds to the decision result of the zero cross determination unit 120.

The output control unit 130 generates an operation output and a return output based on the detection result of the overcurrent detection unit 100, the detection result of the degradation detection unit 110, and the determination result of the zero cross determination unit 120. Specifically, the output control unit 130 includes a NOT gate 131, AND gates 132 and 134, and OR gate 133. The output control unit 130 generates an operation output (i.e., output value “1”) and a return output (i.e., output value “0”) of the overcurrent relay 30 by using these logic gates.

The NOT gate 131 performs NOT operation on the output value of the degradation detection unit 110. The AND gate 132 performs an AND operation of the output value of the degradation detection unit 110 and the output value of the zero cross determination unit 120. The OR gate 133 performs an OR operation of the output value of the NOT gate 131 and the output value of the AND gate 132. The AND gate 134 performs an AND operation of the output value of the overcurrent detection unit 100 and the output value of the OR gate 133. The output value of the AND gate 134 becomes the output value of the output control unit 130.

＜Example of operation＞

FIG. 7 is a diagram showing an example of operation in the overcurrent relay 30 according to Embodiment 1. Additionally, the example shown in FIG. 7 shows an example in which the input current rapidly increases due to a fault or the like occurring at time t1, and the input current decreases due to the circuit breaker 4 being opened at time t4. In Figure 7, the current waveform of the input current, the output value of the overcurrent detection unit 100, the output value of the zero cross determination unit 120, the output value of the degradation detection unit 110, and the output value of the output control unit 130 are shown. there is.

At time t2, the zero cross determination unit 120 detects the zero cross point of the input current and outputs an output value of “1”. At time t3, the overcurrent detection unit 100 outputs an output value of “1”. At this time, the output value of the zero cross determination unit 120 is “1”, but the output value of the degradation detection unit 110 is “0”, so the output control unit 130 outputs an output value of “1”. Specifically, the output control section 130 generates an operation output when a decline in the effective value is not detected by the decline detection section 110 and when an overcurrent is detected by the overcurrent detection section 100. That is, the overcurrent relay 30 operates and outputs. The operation time corresponds to the time from time t1 to time t3.

When the circuit breaker 4 is opened at time t4, the input current rapidly decreases. The decrease detection unit 110 detects a sudden decrease in this input current at time t5 and outputs an output value of “1”. Additionally, if the input current suddenly decreases, the zero cross point unique to the alternating current waveform cannot be detected. Therefore, the zero cross determination unit 120 determines that the zero cross point has not been detected at time t6, and outputs an output value of “0”. At time t6, as the output value "1" of the degradation detection unit 110 and the output value "0" of the zero-cross determination unit 120 are established, the output control unit 130 outputs the output value "0". That is, the overcurrent relay 30 provides a return output. The return time corresponds to the time from time t4 to time t6.

At time t6, the output value of the overcurrent detection unit 100 is “1”, and at time t7, the output value is “0”. From this, as shown in FIG. 7, the output value of the degradation detection unit 110 is "1" and the zero cross determination unit ( It can be seen that the restoration time is shortened when the restoration output is performed based on the establishment of the output value "0" in 120). Below, this reason will be explained in detail.

First, in order to accurately determine the overcurrent, the overcurrent detection unit 100 uses current data from which the rated frequency component from which harmonic components, distortion wave components, etc. have been removed by the digital filter 101 is extracted. For this reason, phase shift with respect to the rated frequency component occurs. In addition, in the RMS calculation by the RMS value calculation unit 102, the RMS value is calculated based on the current instantaneous current value and the past current instantaneous value, as shown in equation (1), so the circuit breaker 4 is opened. Later, the effective value does not decrease instantaneously but rather decreases transiently. Therefore, the timing at which the effective value Ir is determined to be less than the set value Is is delayed, and even when the circuit breaker 4 is opened, it takes time for the output value of the overcurrent detection unit 100 to change from "1" to "0".

In addition, the drop detection unit 110 also uses an effective value based on the current instantaneous current value and the past instantaneous current value, but unlike the overcurrent determination, it is sufficient to detect a decrease in the effective value. Therefore, the drop detection unit 110 detects a drop in the effective value at an early stage (for example, time t5) after the circuit breaker 4 is opened, and outputs an output value of “1”.

Here, in the zero cross determination unit 120, a zero cross determination is made based on current data of the input current from which harmonic components, distortion wave components, etc. have not been removed by the digital filter 101, as described above. Therefore, there is no processing delay due to the digital filter 101. Additionally, since the zero cross determination is made based on the current instantaneous value rather than the effective value using the past instantaneous current value, there is no delay in the judgment timing.

In addition, in the zero cross judgment, current data of the input current from which harmonic components, etc. have not been removed, is used, so in the period when the input current is large until the circuit breaker 4 is opened, it is affected by harmonics, etc. After the zero crossing point is detected, a period Ta during which the output value temporarily becomes "0" may occur due to the current not crossing the zero point beyond the return time Tre.

On the other hand, during the period when the input current after opening the circuit breaker 4 is small and the zero cross point characteristic of the AC waveform is not detected, there is almost no influence from harmonics, etc., so zero cross judgment can be performed with high accuracy. there is. Therefore, during this period, the zero cross determination unit 120 will not mistakenly detect a zero cross point unique to the alternating current waveform.

Accordingly, in Embodiment 1, the detection result of the degradation detection unit 110 and the determination result of the zero-cross determination unit 120 are combined to produce a return output. Specifically, the output control section 130 generates overcurrent when a decrease in the effective value Ir is detected by the decrease detection section 110 and when the zero cross determination section 120 determines that the zero cross point has not been detected. A return output is generated regardless of the detection result of the detection unit 100. That is, in a period when the effective value Ir is lowered and the zero cross determination accuracy is high, when a determination is made that the zero cross point is not detected, a return output is generated. In addition, even if the zero cross point is not detected during the period Ta in which a decrease in the effective value Ir is not detected, no recovery output is generated.

As a result, even when the input current contains many harmonic components, it is possible to detect that the circuit breaker 4 is open at high speed with high accuracy. Therefore, it becomes possible to properly restore the overcurrent relay 30 and speed up its restoration time.

In addition, when the breaker (4) is opened and the current suddenly decreases on the primary side of the current transformer (7) to which the overcurrent relay (30) is connected, the energy accumulated in the inductance of the excitation circuit of the current transformer (7) changes the current. As a result of discharge to the secondary side of the transformer 7, an attenuation current of a direct current component may flow for a certain period of time. Even in this case, the overcurrent relay 30 according to Embodiment 1 can speed up the recovery time.

Figure 8 is a diagram showing an example of a DC (Direct Current) attenuation wave. Referring to FIG. 8, it can be seen that a DC attenuation wave is generated even after the circuit breaker 4 is opened. The DC attenuation wave does not affect the judgment accuracy of the zero cross determination unit 120 when a decrease in the effective value Ir is detected by the decrease detection unit 110. Specifically, the zero cross determination unit 120 can appropriately determine non-detection of the zero cross point when the effective value Ir decreases. Therefore, even when a DC attenuation wave is generated, the recovery time can be speeded up by combining the detection result of the degradation detection unit 110 and the judgment result of the zero cross determination unit 120 and performing a recovery output.

In addition, generally, in order to remove the influence of DC attenuation waves, calculations such as differential filters that subtract current data from a certain period of time ago from current current data are necessary, but according to Embodiment 1, the need for such calculations is eliminated.

＜Advantage＞

According to Embodiment 1, by combining the detection result of a decrease in the effective value Ir and the zero-cross determination result, even when harmonic components, distortion components, etc. are superimposed on the fault current and when DC attenuation waves are generated, the overcurrent relay ( 30), proper recovery can be realized, and the recovery time can be accelerated.

Embodiment 2.

In Embodiment 1, a configuration was described that generates a return output when a decrease in the effective value Ir is detected and the condition that the zero cross point of the current waveform of the input current is not detected is met. In Embodiment 2, a configuration for generating a return output will be described when a decrease in the effective value Ir is detected and when the condition that the direct current component of the current waveform of the input current is more dominant than the alternating current component is met. In addition, the configuration of the power system in Embodiment 2 and the hardware configuration of the protection relay 20 and the overcurrent relay 30 are the same as the corresponding configurations in Embodiment 1.

＜Function configuration＞

FIG. 9 is a block diagram showing an example of the functional configuration of the overcurrent relay 30A according to Embodiment 2. The overcurrent relay 30A corresponds to the overcurrent relay 30 shown in FIG. 1, but in order to distinguish it from other embodiments, an additional symbol such as “A” is given for convenience. This also applies to Embodiment 3 below.

Referring to FIG. 9, the overcurrent relay 30A includes an overcurrent detection unit 100, a drop detection unit 110, a direct current determination unit 150, and an output control unit 170 as its main functional structure. Typically, each of these functions is realized by the CPU 72 executing a program stored in the ROM 73. Additionally, some or all of these functions may be configured to be realized by using a dedicated circuit. Since the configurations of the overcurrent detection unit 100 and the degradation detection unit 110 are the same as in Embodiment 1, their detailed description will not be repeated.

The direct current determination unit 150 determines whether the direct current component of the current waveform of the input current converted to digital data by the AD converter 52 is dominant over the alternating current component of the corresponding current waveform.

FIG. 10 is a block diagram showing an example of the functional configuration of the DC determination unit 150 according to Embodiment 2. Referring to FIG. 10, the DC determination unit 150 includes a fundamental wave detection filter 151, an AC effective value calculation unit 152, a DC detection filter 153, and a comparison unit 154.

The fundamental wave detection filter 151 generates current data by extracting the rated frequency component (i.e., fundamental wave component) of the input current. The fundamental wave detection filter 151 uses, for example, data for 1/2 cycle (i.e., 180°) of the electrical angle of the rated frequency. Typically, the fundamental wave detection filter 151 has the same function as the digital filter 101.

The AC effective value calculation unit 152 calculates the AC effective value of the input current from which the rated frequency component is extracted. Specifically, the AC rms value calculation unit 152 uses the current data input from the fundamental wave detection filter 151 to calculate the rms value of the alternating current component (hereinafter also referred to as the “alternating current rms value”). The AC effective value calculation unit 152 calculates the AC effective value using, for example, the following equation (4).

Ira(t)=sqrt(|Ia(t-90) ² -Ia(t)*Ia(t-180)|)···(4)

Here, Ira(t) represents the effective value at time t. In addition, Ia(t) represents the current instantaneous value of the alternating current component of the input current at time t, Ia(t-90) represents the current instantaneous value 90° before the electric angle at time t, and Ia(t -180) represents the instantaneous current value 180° before the time t. Typically, the AC effective value calculation unit 152 has the same function as the effective value calculation unit 102.

The DC detection filter 153 generates current data by extracting the direct current component of the input current. The DC detection filter 153 uses, for example, data for 1/2 cycle (i.e., 180°) of the electrical angle of the rated frequency. Here, the direct current component of the extracted input current at time t is defined as Idc(t).

The comparison unit 154 compares the AC effective value Ira(t) and the direct current component Idc(t), and when the direct current component Idc(t) is significantly larger and dominates the AC effective value Ira(t), the output value is "1". Outputs . For example, the direct current component Idc(t) is greater than the alternating current rms value Ira(t), and the ratio of the direct current component Idc(t) to the alternating current effective value Ira(t) is the threshold Th2 (for example, Th2= 5) In the case above (i.e., when Idc(t) > 5*Ira(t) holds true), the comparison unit 154 determines that the direct current component Idc(t) is more dominant than the alternating current effective value Ira(t). Judge.

Meanwhile, the comparison unit 154 outputs an output value of “0” when Idc(t)≤Th2*Ira holds true. The output of the comparison unit 154 becomes the output of the DC determination unit 150. That is, the DC determination unit 150 outputs an output value of “1” when it determines that the DC component is dominant over the AC component, and outputs an output value of “0” when it determines that this is not the case. This output value corresponds to the decision result of the DC determination unit 150.

Again, referring to FIG. 9, the output control unit 170 generates an operation output and Generates return output. Specifically, the output control unit 170 includes AND gates 171 and 172.

The AND gate 171 performs an AND operation of the output value of the degradation detection unit 110 and the output value of the DC determination unit 150. The AND gate 172 performs an AND operation on the output value of the overcurrent detection unit 100 and the inverted output value of the AND gate 171. The output value of the AND gate 172 becomes the output value of the output control unit 170.

<Example of operation>

FIG. 11 is a diagram showing an example of operation in the overcurrent relay 30A according to Embodiment 2. In addition, the example shown in FIG. 11 shows an example in which the input current rapidly increases due to a fault or the like occurring at time t1a, and the input current decreases due to the circuit breaker 4 being opened at time t3a. In Figure 11, the current waveform of the input current, the output value of the overcurrent detection unit 100, the output value of the DC determination unit 150, the output value of the degradation detection unit 110, and the output value of the output control unit 170 are shown. .

At time t2a, the output value of the degradation detection unit 110 is “0”, so as the overcurrent detection unit 100 outputs the output value “1”, the output control unit 170 outputs the output value “1”. That is, the overcurrent relay 30A operates and outputs. The operation time corresponds to the time from time t1a to time t2a.

When the breaker 4 is opened at time t3a, the input current rapidly decreases. When the input current suddenly decreases, the direct current component becomes more dominant than the alternating current component. Typically, the DC attenuation wave described above is generated. Therefore, the direct current determination unit 150 determines that the direct current component has become dominant over the alternating current component at time t4a, and outputs an output value of “1”. Additionally, the drop detection unit 110 detects a sudden drop in this input current at time t5a and outputs an output value of “1”.

At time t5a, as the output value "1" of the degradation detection unit 110 and the output value "1" of the DC determination unit 150 are established, the output control unit 170 outputs the output value "0". That is, the overcurrent relay 30A provides a return output. The return time corresponds to the time from time t4a to time t5a.

At time t5a, the output value of the overcurrent detector 100 is “1”, and at time t6a, the output value is “0”. From this, as shown in FIG. 11, the output value "1" of the undercurrent detection section 110 and the direct current determination section 150 are lower than in the case where a return output is made based on the output value of the overcurrent detection section 100 becoming "0". ), it can be seen that the return time is shortened when the return output is performed based on the establishment of the output value "1".

In addition, the DC determination unit 150 also performs filter processing and effective value calculation processing, similar to the overcurrent detection unit 100. However, the direct current determination unit 150 just needs to be able to determine that the direct current component has become dominant, unlike the overcurrent determination. Therefore, the direct current determination unit 150 determines that the direct current component has become dominant at an early stage (for example, time t4a) after the circuit breaker 4 is opened, and outputs an output value of “1”. In addition, as described above, the drop detection unit 110 also detects a drop in the effective value at an early stage (for example, time t5a) after the circuit breaker 4 is opened, and outputs an output value of "1".

Here, in the period when the input current after opening the circuit breaker 4 becomes small and the alternating current component becomes relatively smaller than the direct current component, it is hardly affected by harmonic waves and distortion waves, so the direct current determination unit 150 can perform the above judgment with high precision.

Accordingly, in Embodiment 2, the detection result of the degradation detection unit 110 and the determination result of the DC determination unit 150 are combined to produce a return output. Specifically, when the output control unit 170 detects a decrease in the effective value Ir by the decrease detection unit 110 and when the DC determination unit 150 determines that the direct current component is more dominant than the alternating current component, A return output is generated regardless of the detection result of the overcurrent detection unit 100.

In Embodiment 2 as well, even when the input current contains many harmonic components, it is possible to detect that the circuit breaker 4 is open at high speed with high accuracy. Therefore, it becomes possible to properly restore the overcurrent relay 30A and speed up its restoration time.

Additionally, the DC attenuated wave shown in FIG. 8 is an attenuated wave that contains almost no alternating current component. Therefore, even if a DC attenuation wave is generated after opening the circuit breaker 4, it can be detected with high precision by the DC determination unit 150. Therefore, even in this case, the recovery time can be sped up by combining the detection result of the degradation detection unit 110 and the determination result of the DC determination unit 150 and performing a recovery output.

＜Advantage＞

According to Embodiment 2, it has the same advantages as Embodiment 1.

Embodiment 3.

In the above-mentioned Embodiments 1 and 2, a configuration using one overcurrent detection unit 100 was explained, but in Embodiment 3, a configuration using two overcurrent detection units is explained. In addition, the configuration of the power system and the hardware configuration of the protection relay 20 and the overcurrent relay 30 in Embodiment 3 are the same as the corresponding configurations in Embodiment 1.

＜Function configuration＞

FIG. 12 is a block diagram showing an example of the functional configuration of the overcurrent relay 30B according to Embodiment 3. Referring to FIG. 12, the overcurrent relay 30B includes an overcurrent detection unit 100, a degradation detection unit 110, an overcurrent detection unit 200, and an output control unit 210 as its main functional configuration. Typically, each of these functions is realized by the CPU 72 executing a program stored in the ROM 73. Additionally, some or all of these functions may be configured to be realized by using a dedicated circuit. Since the configurations of the overcurrent detection unit 100 and the degradation detection unit 110 are the same as in Embodiment 1, their detailed description will not be repeated.

The overcurrent detection unit 200 includes a digital filter 201, an effective value calculation unit 202, an overcurrent determination unit 203, and an overcurrent determination unit 204.

The digital filter 201 generates current data by extracting the rated frequency component of the input current. Specifically, the digital filter 201 has high-speed filter characteristics with a shorter sampling data length than the digital filter 101. Here, for example, data of a period T2 of 1/4 cycle (i.e., 90°) of the electrical angle of the rated frequency are used. This corresponds to data for 3 sampling lengths, for example, when the sampling number of the AD converter 52 is 12 times in one cycle. That is, the period T2 is shorter than the period T1 of the data used by the digital filter 101.

The effective value calculation unit 202 performs calculation of the effective value of the input current from which the rated frequency component is extracted. Specifically, the effective value calculation unit 202 calculates the effective value using the current data input from the digital filter 201. The effective value calculation unit 202 uses an effective value calculation equation that has transient characteristics that follow changes in input current more quickly than equation (1) used in the effective value calculation unit 102. For example, the effective value calculation unit 202 calculates the effective value using, for example, the following equation (5).

Irb(t)=sqrt(|Ib(t-30)*Ib(t-60)-Ib(t)*Ib(t-90)|)···(5)

Here, Irb(t) represents the effective value at time t. In addition, Ib(t) represents the current instantaneous value of the input current from which the rated frequency component is extracted at time t, Ib(t-30) represents the current instantaneous value 30° before the electrical angle at time t, and Ib (t-60) represents the instantaneous current value 60° before the electric angle at time t, and Ib(t-90) represents the instantaneous current value at 90° before the electrical angle at time t.

Additionally, in equation (5), the time required to obtain data used for calculating the effective value is the time equivalent to 1/4 cycle of the electric angle. Therefore, dynamic responsiveness is high, and compared to equation (1) used in the effective value calculation unit 102, the speed can be increased by a time equivalent to 1/4 cycle of the electric angle.

The overcurrent determination unit 203 compares the effective value Irb calculated by the effective value calculation unit 202 and the set value Is1 to determine the presence or absence of overcurrent. The set value Is1 is set to a value larger than the set value Is (for example, Is1=1.05*Is). The overcurrent determination unit 203 outputs an output value of "1" when the effective value Irb is greater than or equal to the set value Is1, and outputs an output value of "0" when the effective value Irb is less than the set value Is1. The output value of the overcurrent determination unit 203 corresponds to the overcurrent detection result Dy output by the overcurrent detection unit 200.

The overcurrent determination unit 204 compares the effective value Irb calculated by the effective value calculation unit 202 and the set value Is2 to determine the presence or absence of overcurrent. The set value Is2 is set to a value smaller than the set value Is (for example, Is2=0.95*Is). The overcurrent determination unit 204 outputs an output value of "1" when the effective value Irb is greater than or equal to the set value Is2, and outputs an output value of "0" when the effective value Irb is less than the set value Is2. The output value of the overcurrent determination unit 204 corresponds to the overcurrent detection result Dz output by the overcurrent detection unit 200.

In this way, the overcurrent detection unit 200 compares the effective value Irb calculated using the current data of the period T2, which is shorter than the period T1, with the set value Is1, which is larger than the set value Is, and outputs the overcurrent detection result Dy. The overcurrent detection unit 200 compares the effective value Irb with the set value Is2, which is smaller than the set value Is, and outputs the overcurrent detection result Dz.

In addition, because the overcurrent detection unit 200 uses data of a relatively short period of time, it can perform calculations at a higher speed compared to the overcurrent detection unit 100. On the other hand, the error in the effective value calculation result of the overcurrent detection unit 200 is larger than that of the effective value calculation result of the overcurrent detection unit 100. Therefore, the output control unit 210 is configured to suppress the error in the effective value calculation result from affecting the operation and recovery precision of the overcurrent relay 30B.

The output control unit 210 provides operation output and recovery based on the detection result Dx output from the overcurrent detection unit 100, the detection results Dy and Dz output from the overcurrent detection unit 200, and the detection result of the degradation detection unit 110. Generates output. Specifically, the output control unit 210 includes OR gates 211 and 215 and AND gates 212, 213, and 214.

The OR gate 211 performs an OR operation on the output value of the overcurrent determination unit 103 (i.e., detection result Dx) and the output value of the overcurrent determination unit 203 (i.e., detection result Dy). The AND gate 212 performs an AND operation of the output value of the overcurrent determination unit 103 (i.e., detection result Dx) and the output value of the overcurrent determination unit 204 (i.e., detection result Dz).

The AND gate 213 performs an AND operation on the output value of the OR gate 211 and the inverted output value of the degradation detection unit 110. The AND gate 214 performs an AND operation of the output value of the AND gate 212 and the output value of the degradation detection unit 110. The OR gate 215 performs an OR operation of the output value of the AND gate 213 and the output value of the AND gate 214. The output value of the OR gate 215 becomes the output value of the output control unit 210.

According to the above, when a decrease in the effective value Ir is not detected by the decrease detection unit 110, the output value of the overcurrent determination unit 103 (i.e., detection result Dx) and the output value of the overcurrent determination unit 203 (i.e. , the OR operation of the detection result Dy) becomes the output value of the output control unit 210. Specifically, the output control unit 210 generates an operation output at whichever of the detection results Dx indicating that the overcurrent was detected and the detection result Dy indicating that the overcurrent was detected, whichever is earlier.

On the other hand, when a decrease in the effective value Ir is detected by the decrease detection unit 110, the output value of the overcurrent determination unit 103 (i.e., detection result Dx) and the output value of the overcurrent determination unit 204 (i.e., detection result The AND operation of Dz) becomes the output value of the output control unit 210. Specifically, the output control unit 210 generates a return output at whichever of the detection results Dx indicating that the overcurrent is not detected and the detection result Dz indicating that the overcurrent is not detected, whichever is earlier.

As a result, it is possible to suppress the error in the effective value calculation result by the overcurrent detection unit 200 from affecting the operation and recovery precision of the overcurrent relay 30B, while simultaneously speeding up the operation time and recovery time.

Additionally, in a period when the input current after opening the circuit breaker 4 is small and is hardly affected by harmonics, distortion waves, etc., the output value of the overcurrent determination unit 103 and the output value of the overcurrent determination unit 204 By the AND operation of , a return output is generated. Therefore, even if the fault current contains many harmonic components and distortion wave components, there is no need to change the set value Is2 used in the overcurrent determination unit 204 to a value significantly lower than the set value Is, so the recovery time High speed can be realized.

＜Example of operation＞

FIG. 13 is a diagram showing an example of operation in the overcurrent relay 30B according to Embodiment 3. In addition, the example shown in FIG. 13 shows an example in which the input current rapidly increases due to a fault or the like occurring at time t1b, and the input current decreases due to the circuit breaker 4 being opened at time t5b. 13 shows the current waveform of the input current, the output value of the overcurrent detection unit 100 (i.e., detection result Dx), the output value of the overcurrent determination unit 203 (i.e., detection result Dy), and the overcurrent determination unit 204. The output value (i.e., detection result Dz), the output value of the degradation detection unit 110, and the output value of the output control unit 210 are shown.

At time t2b, the overcurrent determination unit 204 outputs an output value of “1” according to the establishment of the effective value Irb≧Is2. At this point, no operational output is generated by the output control unit 210. Next, at time t3b, the overcurrent determination unit 203 outputs an output value of "1" according to the establishment of the effective value Irb≥Is1. At this time, the output control unit 210 outputs an output value of “1”. That is, the overcurrent relay 30B operates and outputs. The operation time corresponds to the time from time t1b to time t3b.

At time t3b, the output value of the overcurrent detector 100 is “0”, and at time t4b, the output value becomes “1”. From this, as shown in Fig. 13, the output value of the degradation detection unit 110 and the overcurrent determination unit 203 are lower than the case where the operation output is made based on the output value of the overcurrent detection unit 100 being “1”. ), the operation time is shortened when the operation output is performed based on the establishment of the output value "1".

Next, when the circuit breaker 4 is opened at time t5b, the input current rapidly decreases. At time t6b, the drop detection unit 110 detects a sudden drop in this input current and outputs an output value of “1”. At time t7b, the overcurrent determination unit 203 outputs an output value of “0” according to the establishment of the effective value Irb < Is1. At this point, no return output is generated by the output control unit 210. Next, at time t8b, the overcurrent determination unit 204 outputs an output value of “0” according to the establishment of the effective value Irb < Is2. At this time, the output control unit 210 outputs an output value of “0”. That is, the overcurrent relay (30B) provides a recovery output. The return time corresponds to the time from time t5b to time t8b.

At time t8b, the output value of the overcurrent detector 100 is “1”, and at time t9b, the output value is “0”. From this, as shown in FIG. 13 , the output value of the degradation detection unit 110 and the overcurrent determination unit 204 are higher than in the case where the return output is made based on the output value of the overcurrent detection unit 100 becoming “0”. ), it can be seen that the return time is shortened when the return output is performed based on the establishment of the output value "0".

In this way, when the input current rapidly increases due to a fault, etc., the overcurrent relay 30B operates at the timing when the output value "1" is output by the overcurrent determination unit 203, and when the input current suddenly decreases, the overcurrent relay 30B operates. Return output is performed at the timing when the output value "0" is output by the determination unit 204. Therefore, it is possible to operate and restore at high speed based on the effective value calculation result obtained by Equation (5), which is the high-speed effective value calculation equation by the overcurrent detection unit 200.

＜Advantage＞

According to Embodiment 3, while suppressing the error in the effective value calculation result by the overcurrent detection unit 200 using a relatively short data length from affecting the operation and recovery precision of the overcurrent relay 30B, the operation time and recovery time can be accelerated together. Moreover, even in the case where the fault current contains many harmonic components and distortion wave components, a faster recovery time can be realized.

Other embodiments.

In the above-described embodiment, a configuration in which the overcurrent relay functions as a CBF relay has been described, but the configuration is not limited to that configuration. The overcurrent relay may be used as a protection relay that detects fault current flowing in a power system (for example, a transmission line) and outputs a trip signal to a circuit breaker.

The configuration illustrated as the above-described embodiment is an example of the configuration of the present invention, and can also be combined with other known techniques, and can be configured by modifying the configuration, such as omitting some parts, as long as it does not deviate from the gist of the present invention. It is also possible.

In addition, in the above-described embodiment, the processing and configuration described in other embodiments may be appropriately adopted and implemented.

The embodiment disclosed this time should be considered as an example in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all changes within the meaning and scope equivalent to the claims.

1: Frontline 2, 3: Mothership
4, 5, 6: breaker 7: current transformer
10: protection relay system 20: protection relay
30, 30A, 30B: Overcurrent relay 51: Auxiliary transformer
52: AD conversion unit 70: Operation processing unit
71: Bus 72: CPU
73: ROM 74: RAM
75: DI circuit 76: DO circuit
77: Input interface 100, 200: Overcurrent detection unit
101, 201: digital filter 102, 202: effective value calculation unit
103, 203, 204: overcurrent determination unit 110: degradation detection unit
120: Zero cross determination unit 121: Zero cross detection unit
122: Return timer 130, 170, 210: Output control unit
131: NOT gate
132, 134, 171, 172, 212, 213, 214: AND gate
133, 211, 215: OR gate 150: DC decision unit
151: Fundamental wave detection filter 152: AC effective value calculation unit
153: DC detection filter 154: comparison unit

Claims (9)

an overcurrent detection unit that detects overcurrent by comparing the effective value and set value of the input current input from the power system;
a decline detection unit that detects a decline in the effective value;
An output control unit that generates an operation output and a recovery output based on the detection result of the overcurrent detection unit, the detection result of the degradation detection unit, and predetermined conditions regarding the current waveform of the input current;
A zero cross determination unit is provided to determine whether a zero cross point of the current waveform of the input current has been detected,
The output control unit generates the return output regardless of the detection result by the overcurrent detection unit when a decrease in the effective value is detected and when the zero cross point is not detected. an overcurrent detection unit that detects overcurrent by comparing the effective value and set value of the input current input from the power system;
a decline detection unit that detects a decline in the effective value;
An output control unit that generates an operation output and a recovery output based on the detection result of the overcurrent detection unit, the detection result of the degradation detection unit, and predetermined conditions regarding the current waveform of the input current;
a determination unit that determines whether a direct current component of the current waveform of the input current is dominant over an alternating current component of the current waveform, wherein the determination unit determines that the direct current component of the current waveform is greater than an effective value of the alternating current component of the current waveform; In addition, when the ratio of the direct current component to the effective value of the alternating current component is greater than or equal to a second threshold, it is determined that the direct current component is more dominant than the alternating current component -
The output control unit generates the return output regardless of the detection result by the overcurrent detection unit when a decrease in the effective value is detected and when the direct current component is dominant over the alternating current component. In claim 1 or claim 2,
An overcurrent relay, wherein the output control unit generates the operation output when a decrease in the effective value is not detected and when an overcurrent is detected by the overcurrent detection unit. In claim 1 or claim 2,
An overcurrent relay, wherein the drop detection unit detects a decrease in the effective value when the rate of decrease in the effective value is greater than or equal to a first threshold. In claim 1 or claim 2,
The overcurrent detection unit is
A digital filter that generates current data by extracting the rated frequency component of the input current,
An overcurrent relay comprising an effective value calculation unit that calculates the effective value using the current data. A first overcurrent detection unit including a first digital filter that generates first current data by extracting the rated frequency component of the input current input from the power system;
a second overcurrent detection unit including a second digital filter that has faster filter characteristics than the first digital filter and generates second current data that extracts a rated frequency component of the input current;
The first overcurrent detection unit outputs a first detection result of the overcurrent by comparing a first effective value calculated using the first current data of the first period and a first set value,
The second overcurrent detector compares a second effective value calculated using the second current data of a second period shorter than the first period and a second set value larger than the first set value, thereby detecting the second overcurrent. Outputting a detection result, outputting a third detection result of overcurrent by comparing the second effective value with a third set value smaller than the first set value,
a decrease detection unit that detects that the first effective value has decreased;
Further comprising an output control unit that generates an operation output and a return output based on the first to third detection results and the detection result of the degradation detection unit,
When a decrease in the first effective value is detected, the output control unit outputs whichever is earlier among the first detection result indicating that the overcurrent is not detected and the third detection result indicating that the overcurrent is not detected. An overcurrent relay that generates the return output in timing. In claim 6,
When a decrease in the first effective value is not detected, the output control unit outputs whichever is earlier among the first detection result indicating that the overcurrent was detected and the second detection result indicating that the overcurrent was detected. An overcurrent relay that generates the operating output in timing. delete delete

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