JP2021078196A - Protective relay device - Google Patents

Abstract

To provide a protective relay device that has a simple structure and can accurately determine whether or not a CT is saturated.SOLUTION: A protective relay device includes an input unit that receives an input of a power system current detected by a current transformer, a waveform generation unit that generates a first-order differentiation waveform of the current by differentiating the current, a zero-cross detection unit that detects first zero-cross points of the first-order differentiation waveform, and a saturation determination unit that determines whether or not the current transformer is saturated on the basis of a first zero-cross interval indicating an interval between the adjacent first zero-cross points.SELECTED DRAWING: Figure 6

Description

The present disclosure relates to a protection relay device.

In order to detect a failure that has occurred in the power system, the protection relay device takes in the current flowing through the power system via a current transformer (CT). Generally, when the primary current of CT exceeds a certain value due to a failure current generated due to a system failure or the like, the primary current is not correctly converted into a secondary current due to saturation of the CT iron core (for example, also referred to as a CT saturation state). Will be done.) In the CT saturated state, the fault current is not correctly input to the protection relay device, so that there is a possibility that the protection relay device may malfunction or malfunction. Therefore, in the protection relay device, it is necessary to accurately detect the saturation of CT.

Japanese Patent Application Laid-Open No. 2006-523942 (Patent Document 1) discloses a method for compensating for secondary current of a current transformer. In this method, it is examined to prevent the malfunction of the protective relay system caused by the fact that the actual secondary current value cannot be accurately recognized due to the distortion of the secondary current due to the saturation of the current transformer.

Japanese Patent Application Laid-Open No. 2006-523942

In Patent Document 1, in order to appropriately set a critical value for determining whether or not CT is saturated, an actual system state and detailed characteristics of the applied CT are required. However, the calculation for obtaining the critical point of CT saturation from the characteristics of CT is complicated. In addition, detailed CT characteristics are often not available, which is considered impractical.

An object of an aspect of the present disclosure is to provide a protection relay device capable of accurately determining whether or not CT is saturated with a simple configuration.

A protection relay device according to an embodiment includes an input unit that receives an input of a power system current detected by a current transformer, a waveform generator that differentiates the current to generate a first-order differential waveform of the current, and a first-order unit. A zero-cross detection unit that detects the first zero-cross point of the differential waveform, and a saturation determination unit that determines whether or not the current transformer is saturated based on the first zero-cross interval that indicates the interval between adjacent first zero-cross points. To be equipped.

According to the present disclosure, it is possible to accurately determine whether or not CT is saturated with a simple configuration.

It is a figure which shows the electric power system to which the protection relay device according to Embodiment 1 is applied. It is a figure which shows an example of the hardware composition of the protection relay device which follows Embodiment 1. FIG. It is a figure which shows the waveform at the time of CT desaturation. It is a figure which shows the waveform at the time of CT saturation. It is a flowchart which shows an example of the determination method according to Embodiment 1. FIG. It is a block diagram which shows an example of the functional structure of the protection relay device according to Embodiment 1. FIG. It is a figure which shows the waveform at the time of CT desaturation, and the transformer is in an inrush state. It is a figure which shows the waveform at the time of CT saturation, and the transformer is in an inrush state. It is a figure which shows the waveform when the three-phase transformer is in an inrush state. It is a flowchart which shows an example of the determination method according to Embodiment 2. It is a block diagram which shows an example of the functional structure of the protection relay device according to Embodiment 2.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of them will not be repeated.

Embodiment 1.
<Overall configuration>
FIG. 1 is a diagram showing a power system to which the protection relay device according to the first embodiment is applied. In the power system shown in FIG. 1, bus lines 2 and 4 are connected to both ends of the transmission line 3, and three-phase AC power supplies 10 and 11 are provided far from the bus line 2 and the bus line 4, respectively. The AC power supplies 10 and 11 are, for example, generators.

The transmission line 3 is provided with a circuit breaker 5 and a transformer 9. Further, a current transformer (CT) 6 is provided in each phase of the transmission line 3. The CT6 detects the phase current of the transmission line 3 (for example, the A phase current). The current detected by the CT6 is input to the protection relay device 100. The protection relay device 100 has a function of determining whether or not the CT6 is saturated based on the secondary current (hereinafter, also referred to as “CT secondary current”) taken in from the CT6. Although the details will be described later, the protection relay device 100 determines whether or not the CT6 is saturated based on the interval between the zero cross points of the first-order differential waveform of the CT secondary current.

A voltage transformer (VT: Voltage Transformer) 8 is connected to the bus 2. The voltage transformer 8 detects each phase voltage (for example, A-phase voltage, B-phase voltage, C-phase voltage) of the transmission line 3 on the bus 2 side. The voltage detected by the voltage transformer 8 is input to the protection relay device 100.

The protection relay device 100 is a digital protection relay for protecting the power system (for example, the transmission line 3). The protection relay device 100 uses the collected electric energy (for example, voltage and current) to perform operations necessary for protecting the power system such as relay operations, and determines whether or not a system accident has occurred. Then, when the protection relay device 100 detects an accident on the transmission line 3, it outputs a trip signal to the circuit breaker 5. The protection relay device 100 is composed of, for example, a current differential relay device for protecting transmission lines, a directional relay device, and the like.

FIG. 2 is a diagram showing an example of the hardware configuration of the protection relay device 100 according to the first embodiment. With reference to FIG. 2, the protection relay device 100 includes an auxiliary transformer 51, an AD (Analog to Digital) conversion unit 52, and an arithmetic processing unit 70.

The auxiliary transformer 51 takes in the current detected by the CT 6 and the voltage detected by the voltage transformer 8, converts them into a voltage suitable for signal processing in the relay internal circuit, and outputs the voltage. The AD conversion unit 52 takes in the voltage output from the auxiliary transformer 51 and converts it into digital data. Specifically, the AD conversion unit 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 waveform signal of the current output from the auxiliary transformer 51. The sample hold circuit samples the waveform signal of the current output from the analog filter at a predetermined sampling cycle. Based on the timing signal input from the arithmetic processing unit 70, the multiplexer sequentially switches the waveform signals input from the sample hold circuit in chronological order and inputs them to the AD converter. The AD converter converts the waveform signal input from the multiplexer from analog data to digital data. The AD converter outputs the digitally converted waveform signal (that is, digital data) to the arithmetic processing unit 70.

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

The CPU 72 controls the operation of the protection relay device 100 by reading and executing a program stored in the ROM 73 in advance. The ROM 73 stores various information used by the CPU 72. The CPU 72 is, for example, a microprocessor. The hardware may be an FPGA (Field Programmable Gate Array) other than the CPU, an ASIC (Application Specific Integrated Circuit), or a circuit having other arithmetic functions.

The CPU 72 takes in digital data from the AD conversion unit 52 via the bus 71. The CPU 72 executes an operation using the captured digital data according to a program stored in the ROM 73.

The CPU 72 outputs a signal to the outside via the DO circuit 76 based on the calculation result. For example, the DO circuit 76 outputs a trip signal to the circuit breaker 5. The CPU 72 receives a signal from the outside via the DI circuit 75. The input interface 77 is typically various buttons and the like, and receives various setting operations from the system operator.

<CT saturation judgment method>
FIG. 3 is a diagram showing a waveform when CT is not saturated. The vertical axis of FIGS. 3A and 3B is the current (corresponding to “I” in the figure), and the horizontal axis is the time (corresponding to “t” in the figure). With reference to FIG. 3A, the waveform 300 shows the waveform of the CT secondary current when the CT is not saturated (that is, when the CT is not saturated), and the waveform 301 is the first-order differential waveform of the CT secondary current. Is shown. With reference to FIG. 3 (b), the waveform 302 shows the second derivative waveform at the time of CT desaturation. FIG. 3B shows the vertical axis of FIG. 3A changed so as to enlarge the waveform 301.

Here, the waveform of the CT secondary current at the time of CT desaturation (hereinafter, also simply referred to as “current waveform”) is represented by the following equation (1), and the first-order differential waveform is expressed by the following equations (2.1) to (2.1) to The second-order differential waveform is represented by (2.3) and is represented by the following equations (3.1) to (3.3).

_{I (t) = I p ×} sin (ωt + θ) -I P × sin (θ) × exp (-1 / Ts × t) ··· (1)
Here, the first term _{"I p × sin (ωt +} θ)" of the formula (1) is a stationary solution that represents the sin component, the second term _{"-I P × sin (θ)} × exp (-1 / Ts × "t)" is a transient solution representing a DC component. For the sake of explanation, the first term corresponding to the stationary solution is defined as Is (t), and the second term corresponding to the transient solution is defined as It (t).

The first-order differential equation of the stationary solution is shown in Eq. (2.1), and the first-order differential equation of the transient solution is shown in Eq. (2.2). Moreover, the mathematical formula of the waveform which combined the stationary solution and the transient solution is shown in the equation (2.3).

Is ⁽¹⁾ (t) = ωI _p × cоs (ωt + θ) ・ ・ ・ (2.1)
It ⁽¹⁾ (t) =-(1 / Ts) x sin (θ) x exp (-1 / Ts x t) ... (2.2)
I ⁽¹⁾ (t) = Is ⁽¹⁾ (t) + It ⁽¹⁾ (t) ... (2.3)
The second derivative of the stationary solution is shown in Eq. (3.1), and the second derivative of the transient solution is shown in Eq. (3.2). Moreover, the mathematical formula of the waveform which combined the stationary solution and the transient solution is shown in the equation (3.3).

Is ⁽²⁾ (t) = −ω ² I _p × sin (ωt + θ) ・ ・ ・ (3.1)
It ⁽²⁾ (t) =-{1 / (Ts ² )} x sin (θ) x exp (-1 / Ts x t) ... (3.2)
I ⁽²⁾ (t) = Is ⁽²⁾ (t) + It ⁽²⁾ (t) ... (3.3)
I _p is the amplitude value of the current, ω is the angular frequency of the system, θ is the phase angle at the time of failure, and Ts is the time constant of the power system (specifically, the primary side of CT). Comparing Eqs. (1) and (2.1), the current waveform and the first derivative waveform are 90 ° out of phase, and comparing Eqs. (2.1) and Eqs. (3.1) It can be seen that the first-order differential waveform and the second-order differential waveform are 90 ° out of phase. That is, the phase shifts by 90 ° each time it is differentiated.

As the differential calculation method for the sampled digital values, a method based on the difference between adjacent sampled values may be simply adopted. In this case, the first-order differential waveform is represented by the following equation (4), and the second-order differential waveform is represented by the following equation (5).

I ⁽¹⁾ (t) = I (t) -I (t-T) ... (4)
I ⁽²⁾ (t) = I ⁽¹⁾ (t) -I ⁽¹⁾ (t-T) ... (5)
Here, I (t) is the current value sampled at the current time, and I (t−T) is the current value sampled before the current time by time T, and I ⁽¹⁾ (t). Is the first derivative of the current. I ⁽¹⁾ (t-T) is the first derivative value of the current before the current time by time T, and I ⁽²⁾ (t) is the second derivative value of the current.

With reference to FIG. 3A, attention is paid to the time interval (hereinafter, also simply referred to as “interval”) of each zero crossing point E1, E2, E3 of the waveform 301 showing the first-order differential waveform at the time of CT desaturation. The distance between adjacent zero cross points E1 and E2 is T1, and the distance between adjacent zero cross points E2 and E3 is also T1. From this, the interval T1 corresponds to 1/2 of the system period Ts. For example, when the system frequency is 50 Hz (that is, the system period Ts is 20 ms), the interval T1 is 10 ms.

The system frequency may fluctuate slightly from a predetermined frequency. Therefore, the system frequency may be calculated periodically by frequency calculation in consideration of the fluctuation. For example, when CT is not saturated, the interval between the zero cross points of the waveforms 301 and 302 is 1/2 of the system period Ts. Therefore, the system frequency can be calculated by utilizing the interval and the fact that the system frequency is the inverse of the system period Ts.

With reference to FIG. 3B, attention is paid to the interval between the zero crossing points F1, F2, and F3 of the waveform 302 showing the second-order differential waveform when CT is not saturated. The distance between adjacent zero cross points F1 and F2 is T1, and the distance between adjacent zero cross points F2 and F3 is also T1. From this, the interval between the zero cross points of the waveform 301 and the interval between the zero cross points of the waveform 302 are the same.

From this, in the CT unsaturated state, the interval between the zero cross points of the first-order differential waveform and the interval between the zero cross points of the second-order differential waveform are the interval T1 (that is, 1/2 of the system period Ts). It can be seen that it is kept constant.

FIG. 4 is a diagram showing a waveform at the time of CT saturation. The vertical axis of FIGS. 4A and 4B is the current (corresponding to “I” in the figure), and the horizontal axis is the time (corresponding to “t” in the figure). With reference to FIG. 4A, waveform 350 shows the current waveform when CT changes from unsaturated to saturated. Waveform 351 shows the first derivative waveform of the CT secondary current. With reference to FIG. 4B, waveform 352 shows the second derivative waveform of the CT secondary current. FIG. 4B shows the vertical axis of FIG. 4A changed so as to enlarge the waveform 351.

With reference to FIG. 4A, attention is paid to the interval between the zero cross points G1, G2, and G3 after the occurrence of CT saturation in the waveform 351. The distance between adjacent zero cross points G1 and G2 is T3, and the distance between adjacent zero cross points G2 and G3 is T3a. The interval T3 is considerably smaller than the interval T3a and much smaller than 1/2 of the system period Ts. In the example of FIG. 4A, the interval T3 is 4.7 ms and the interval T3a is 10.2 ms. Therefore, unlike the example of FIG. 3A, it can be seen that the interval between the zero cross points is not a constant value (for example, 1/2 of the system period Ts).

With reference to FIG. 4B, attention is paid to the interval between the zero cross points H1, H2, and H3 after the occurrence of CT saturation in the waveform 352. The distance between the adjacent zero cross points H1 and H2 is T4, and the distance between the zero cross points H2 and H3 is T4a. The interval T4 is considerably smaller than the interval T4a and much smaller than 1/2 of the system period Ts. In the example of FIG. 4B, the interval T4 is 2.2 ms and the interval T4a is 9.3 ms. Therefore, unlike the example of FIG. 3B, it can be seen that the interval between the zero cross points is not a constant value (for example, 1/2 of the system period Ts).

Therefore, at the time of CT saturation, the interval between the zero cross points of the first-order differential waveform and the interval between the zero cross points of the second-order differential waveform are not kept constant. In addition, some of the intervals between the zero cross points of the first-order differential waveform deviate significantly from Ts / 2. Similarly, some of the intervals between the zero cross points of the second-order differential waveform also deviate significantly from Ts / 2.

Therefore, when the waveform at the time of CT non-saturation shown in FIG. 3 and the waveform at the time of CT saturation shown in FIG. 4 are compared, the interval between the zero cross points of the first derivative waveform and the interval between the zero cross points of the second derivative waveform There is a difference. Therefore, the protection relay device 100 determines the presence or absence of CT saturation by using the interval between the zero cross points of the first-order differential waveform and the interval between the zero cross points of the second-order differential waveform.

FIG. 5 is a flowchart showing an example of the determination method according to the first embodiment. Typically, each of the following steps is performed by the CPU 72 of the arithmetic processing unit 70 of the protection relay device 100.

With reference to FIG. 5, the protection relay device 100 determines whether or not an abnormality in the current flowing through the transmission line 3 has been detected based on the current taken in from the CT 6 (step S10). Typically, the protection relay device 100 detects a current anomaly by means of a current change width relay element. The current change width relay element determines whether or not the difference between the instantaneous value of the current current and the instantaneous value of the current one cycle before (or two cycles before, three cycles before, etc.) exceeds a specified threshold value, for example. judge. Therefore, the current change width relay element can detect a sudden change in the amplitude of the current or a sudden change in the phase. The protection relay device 100 may detect an abnormality in the current by using an overcurrent relay element instead of the current change width relay element.

If no abnormality in the current is detected (NO in step S10), the protection relay device 100 repeats the process of step S10. When an abnormality in the current is detected (YES in step S10), the protection relay device 100 executes the processes after step S12.

Here, the process of step S10 is executed in order to accurately perform the CT saturation determination described later. Specifically, as described with reference to FIGS. 3 and 4, in the present embodiment, the presence or absence of CT saturation is determined using the interval between the zero cross points of the differential waveform of the current. Therefore, if the zero crossing point of the differential waveform is detected due to the fluctuation of a minute current, it may cause an erroneous determination of CT saturation. When an abnormality in the current is detected (YES in step S10), it is assumed that a relatively large current is generated. Therefore, in such a case, by executing the CT saturation determination using the interval between the zero cross points, it is possible to prevent the erroneous determination of the CT saturation due to the above-mentioned minute current.

The protection relay device 100 detects the zero crossing point of the first-order differential waveform of the current taken in from the CT6 (step S12). The protection relay device 100 stores information (for example, time) indicating the timing of each of the detected zero cross points in the RAM 74. Subsequently, the protection relay device 100 detects the zero cross point of the second-order differential waveform of the current taken in from the CT6 (step S14). The protection relay device 100 stores information indicating the timing of each of the detected zero cross points in the RAM 74. For example, the zero cross point is detected based on the sign inversion of the current data.

The protection relay device 100 determines whether or not the interval between the zero cross points of the first-order differential waveform (hereinafter, also referred to as “interval Tx1”) is within the range R1 (step S16). Here, as shown in FIGS. 3 and 4, in the case of CT unsaturated, the interval between the zero cross points of the first-order differential waveform is 1/2 (that is, half a cycle) of the system cycle Ts of the power system. In the case of CT saturation, the interval deviates significantly from 1/2 of the system period Ts. Therefore, the range R1 applied to the interval Tx1 is set in the range from 1/2 of the system cycle Ts to the positive / negative tolerance. For example, if the margin of error is 10% of Ts (ie, Ts / 10), the range R1 is (Ts / 2-Ts / 10) to (Ts / 2 + Ts / 10).

If the interval Tx1 is not included in the range R1 (NO in step S16), the protection relay device 100 determines that the CT6 is saturated (step S18). In this case, the protection relay device 100 changes the operation characteristics (for example, the operation area, the operation timer, etc.) so as not to malfunction even if the difference current generated by CT saturation is detected at the time of an external failure, for example.

When the interval Tx1 is included in the range R1 (YES in step S16), does the protection relay device 100 have the interval between the zero cross points of the second-order differential waveform (hereinafter, also referred to as “interval Tx2”) within the range R1? It is determined whether or not (step S20). As shown in FIGS. 3 and 4, in the case of CT unsaturated, the interval between the zero cross points of the second-order differential waveform is 1/2 of the system period Ts, and in the case of CT saturation, the interval is the system. It deviates significantly from 1/2 of the period Ts. Therefore, the range R1 is applied to the interval Tx2 as well as the interval Tx1.

If the interval Tx2 is not included in the range R1 (NO in step S20), the protection relay device 100 determines that the CT6 is saturated (step S18). When the interval Tx2 is included in the range R1 (YES in step S20), the protection relay device 100 determines that CT6 is not saturated (step S24). In this case, it is presumed that the abnormality of the current is due to the failure of the power system. Therefore, for example, when a failure of the power system occurs inside the protection target, the protection relay device 100 operates and outputs a trip signal to the circuit breaker 5.

In the flowchart of FIG. 5, the protection relay device 100 determines that CT saturation has occurred when at least one of the interval Tx1 and the interval Tx2 is outside the range R1, and when the interval Tx1 and the interval Tx2 are within the range R1. It is determined that CT saturation has not occurred. Therefore, the protection relay device 100 can determine CT saturation more accurately by using both the interval Tx1 and the interval Tx2.

However, the protection relay device 100 may determine the presence or absence of CT saturation using only the interval Tx1 or the interval Tx2. For example, the protection relay device 100 may determine that CT saturation has not occurred when the interval Tx1 is within the range R1, and may determine that CT saturation has occurred when the interval Tx1 is outside the range R1. .. Similarly, even if the protection relay device 100 determines that CT saturation has not occurred when the interval Tx2 is within the range R1, and determines that CT saturation has occurred when the interval Tx2 is outside the range R1. Good.

(Modification example)
In the above-mentioned CT saturation determination method, a method for determining the presence or absence of CT saturation has been described by focusing on the interval between the zero cross points of the first-order differential waveform and the interval between the zero cross points of the second-order differential waveform. In the modified example, a method of determining the presence or absence of CT saturation will be described by focusing on the interval between the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform.

In order to determine CT saturation using the spacing between zero cross points, it is necessary to detect at least two zero cross points. However, considering the reliability of the determination, it is practically preferable to detect three or more zero cross points. In the following, it is assumed that three zero cross points are detected and the presence or absence of CT saturation is determined using each interval between adjacent zero cross points.

When determining the presence or absence of CT saturation using the interval between the zero cross points of the first-order differential waveform with reference to FIG. 3, the interval between the zero cross points E1 and E2 and the interval between the zero cross points E2 and E3 are in the range. It is necessary to determine whether or not it is within R1. Therefore, it is determined that the CT is unsaturated from the detection of the first zero cross point E1 until the detection of the third zero cross point E3 after one cycle (that is, the system cycle Ts). Can not. Similarly, when determining the presence or absence of CT saturation using the interval between the zero cross points of the second derivative waveform, the third zero cross point F3 one cycle after the first zero cross point F1 is detected. Until it is detected, the determination that CT is unsaturated cannot be confirmed.

Here, attention is paid to the interval between the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform. Specifically, with reference to FIG. 3B, attention is paid to the interval between the zero crossing points E1 to E3 of the waveform 301 and the zero crossing points F1 to F3 of the waveform 302. The distance between adjacent zero cross points E1 and F1 is T2, and the distance between adjacent zero cross points F1 and E2 is also T2. From this, the interval T2 is 1/2 of the interval T1, that is, corresponds to 1/4 of the system period Ts. For example, when the system period Ts is 20 ms, the interval T2 is 5 ms. As described above, in the CT unsaturated state, the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform are kept constant at the interval T2.

With reference to FIG. 4B, attention is paid to the interval between the zero crossing points G1 to G3 of the waveform 351 and the zero crossing points H1 to H3 of the waveform 352. The distance between adjacent zero cross points G1 and H1 is T5, and the distance between adjacent zero cross points H1 and G2 is T5a. The interval T5a is much smaller than the interval T5 and much smaller than 1/4 of the system period Ts. In the example of FIG. 4B, the interval T5 is 4.1 ms and the interval T5a is 0.8 ms. Therefore, unlike the example of FIG. 3B, it can be seen that the interval between the zero cross points is not a constant value (for example, 1/4 of the system cycle Ts).

For this reason, at the time of CT saturation, the interval between the zero cross point of the first derivative waveform and the zero cross point of the second derivative waveform is not kept constant. Further, among the intervals between the zero cross points of the first-order differential waveform and the zero cross points of the second-order differential waveform, there are those that deviate significantly from Ts / 4 (for example, the interval T5a).

Therefore, the protection relay device 100 can determine the presence or absence of CT saturation by using the interval between the zero cross points of the first derivative waveform and the interval between the zero cross point of the first derivative waveform and the zero cross point of the second derivative waveform. Specifically, when the interval between the zero cross points of the first derivative waveform is within the range R1 and the interval between the zero cross points of the first derivative waveform and the zero cross point of the second derivative waveform is within the range R2. , The protection relay device 100 determines that the CT is not saturated.

In the case of CT non-saturation, the interval between the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform is 1/4 of the system period Ts, and in the case of CT saturation, the interval is the system period Ts. It deviates greatly from 1/4 of. Therefore, the range R2 is set in the range from 1/4 of the system cycle Ts to the positive / negative tolerance. For example, if the margin of error is 5% of Ts (ie, Ts / 20), the range R2 is (Ts / 4-Ts / 20) to (Ts / 4 + Ts / 20). The range R2 is smaller than the range R1.

In the case of the example of FIG. 3, since the interval between the zero cross points E1 and E2 is within the range R1 and the interval between the zero cross points E1 and F1 is within the range R2, the protection relay device 100 is saturated with CT. Judge that there is no. In this case, if the zero cross point E1 is detected and then the zero cross point E2 after half a cycle is detected, it can be determined that the CT is unsaturated. Therefore, it is possible to make a judgment at a higher speed than making a judgment using only the interval between the zero cross points of the first-order differential waveform.

Further, when the interval between the zero cross points of the first derivative waveform is outside the range R1 and the interval between the zero cross point of the first derivative waveform and the zero cross point of the second derivative waveform is outside the range R2, the protection relay The device 100 determines that the CT is saturated.

In the case of the example of FIG. 4, since the interval between the zero cross points G1 and G2 is outside the range R1 and the interval between the zero cross points H1 and G2 is outside the range R2, the protection relay device 100 is saturated with CT. Judge that there is. In this case, if the zero cross points G1, H1 and G2 are detected, it can be determined that the CT is saturated. On the other hand, when determining the presence or absence of CT saturation using only the interval between the zero cross points of the first-order differential waveform, it cannot be determined that the CT is saturated unless the zero cross points G1, G2, and G3 are detected. Therefore, according to the modified example, high-speed determination is possible.

<Functional configuration>
FIG. 6 is a block diagram showing an example of the functional configuration of the protection relay device 100 according to the first embodiment. With reference to FIG. 6, the protection relay device 100 includes an input unit 152, an abnormality detection unit 154, a waveform generation unit 156, a zero cross detection unit 158, and a saturation determination unit 160 as main functional configurations. Each of these functions is realized, for example, by the CPU 72 of the protection relay device 100 executing a program stored in the memory (for example, ROM 73, RAM 74). Note that some or all of these functions may be configured to be realized by hardware.

The input unit 152 receives the input of the current of the power system detected by the CT6. The input unit 152 may accept the input of the voltage of the power system detected by the VT8.

The abnormality detection unit 154 detects an abnormality in the current of the power system based on the current taken in from the CT6. Specifically, the abnormality detection unit 154 functions as a current change width relay element, and when the difference between the instantaneous value of the current current and the instantaneous value of the current one cycle before exceeds the specified threshold Th1. Detects abnormal current. The abnormality detection unit 154 may function as an overcurrent relay element and detect an abnormality in the current when the effective value of the current exceeds the threshold Th2.

The waveform generation unit 156 differentiates the current acquired from the CT6 to generate a first-order differential waveform of the current. Further, the waveform generation unit 156 further differentiates the first-order differential waveform to generate the second-order differential waveform of the current.

The zero-cross detection unit 158 detects the zero-cross points of the first-order differential waveform and the second-order differential waveform. The zero-cross detection unit 158 is composed of, for example, a comparator with hysteresis, and detects the zero-cross points of the first-order differential waveform and the second-order differential waveform by comparing with the threshold values H and L set near the ground level. .. In this way, by giving the threshold value of the comparator a hysteresis characteristic, it is possible to prevent erroneous detection of the zero cross point due to noise after digital conversion.

Here, the zero cross point of the first-order differential waveform is referred to as a "first zero cross point", and the zero cross point of the second-order differential waveform is referred to as a "second zero cross point". The interval between adjacent first zero cross points is referred to as "first zero cross interval", and the interval between adjacent second zero cross points is referred to as "second zero cross interval". The interval between adjacent first and second zero cross points is referred to as a "third zero cross interval".

In the case of FIG. 3, the first zero cross point is the zero cross points E1 to E3, and the first zero cross interval is the interval T1. The second zero cross point is the zero cross point F1 to F3, and the second zero cross interval is the interval T1. The third zero cross interval is the interval T2. In the case of FIG. 4, the first zero cross points are the zero cross points G1 to G3, and the first zero cross intervals are the intervals T3 and T3a. The second zero cross points are zero cross points H1 to H3, and the second zero cross intervals are intervals T4 and T4a. The third zero cross interval is the interval T5, T5a.

The saturation determination unit 160 determines whether or not the CT6 is saturated by using the above zero cross interval. In one aspect, the saturation determination unit 160 determines whether the CT6 is saturated or not based on the first zero cross interval. Specifically, when the first zero cross interval is outside the range R1, the saturation determination unit 160 determines that the CT6 is saturated. More specifically, the saturation determination unit 160 determines that the CT6 is saturated when any one of the first zero cross intervals (eg, the interval T3) is outside the range R1. Typically, the range R1 is a tolerance range centered on 1/2 of the system period Ts.

Further, the saturation determination unit 160 may determine whether or not the CT6 is saturated based on the first zero cross interval and the second zero cross interval. Specifically, when at least one of the condition that the first zero cross interval is outside the range R1 and the condition that the second zero cross interval is outside the range R1 is satisfied, the saturation determination unit 160 has the CT6. Determined to be saturated.

In another aspect, the saturation determination unit 160 determines whether the CT6 is saturated or not based on the first zero cross interval and the third zero cross interval. Specifically, when the first zero cross interval is outside the range R1 and the third zero cross interval is outside the range R2 (however, the range R2 is smaller than the range R1), the saturation determination unit 160 sets the saturation determination unit 160. It is determined that CT6 is saturated. Typically, the range R2 is a tolerance range centered on 1/4 of the system period Ts.

Further, when the abnormality detection unit 154 detects an abnormality in the current of the power system, the saturation determination unit 160 may execute the above saturation determination process of the CT6. The saturation determination process includes a process of determining whether or not the CT6 is saturated using the first to third zero cross intervals.

<Advantage>
According to the first embodiment, it is possible to easily and accurately determine whether or not the CT is saturated by using the zero cross point interval of the differential waveform of the current taken in from the CT. Therefore, it is possible to prevent malfunction and malfunction of the protection relay device due to CT saturation. Further, it is not necessary to select an expensive CT having a CT saturation characteristic that does not sufficiently saturate even if a system fault current is generated.

Embodiment 2.
In the first embodiment described above, a configuration for determining the presence or absence of CT saturation using the differential waveform of the current has been described. Here, as shown in FIG. 1, when the transformer 9 is arranged in the power system, the exciting inrush current (or "or" Inrush current) is generated. Therefore, it is necessary to prevent malfunction of the protection relay device 100 due to this inrush current.

In the second embodiment, a method of determining whether or not an inrush current is generated in the transformer 9 in addition to the presence or absence of CT saturation will be described. In the following description, the state in which the inrush current is generated in the transformer 9 is also referred to as an “inrush state”. In addition, in FIG. 7 and FIG. 8 below, for the sake of facilitation of explanation, the current waveform when the single-phase transformer is in the inrush state will be described.

FIG. 7 is a diagram showing a waveform when the transformer is in an inrush state during CT desaturation. The vertical axis of FIGS. 7A and 7B is the current (corresponding to “I” in the figure), and the horizontal axis is the time (corresponding to “t” in the figure). With reference to FIG. 7A, the waveform 400 shows the waveform of the CT secondary current in the CT unsaturated state and in the inrush state, and the waveform 401 shows the first derivative waveform of the CT secondary current. With reference to FIG. 7B, waveform 402 shows the second derivative waveform of the CT secondary current. FIG. 7B shows the vertical axis of FIG. 7A changed so as to enlarge the waveform 401.

With reference to FIG. 7A, attention is paid to the interval between the zero crossing points J1, J2, and J3 of the waveform 401 showing the first-order differential waveform. The distance between adjacent zero cross points J1 and J2 is T6, and the distance between adjacent zero cross points J2 and J3 is T6a. The interval T6 and the interval T6a are values close to 1/2 of the system period Ts (for example, 20 ms). In the example of FIG. 7A, the interval T6 is 8.2 ms and the interval T6a is 11.8 ms.

With reference to FIG. 7B, attention is paid to the interval between the zero cross points K1, K2, and K3 of the waveform 402 showing the second-order differential waveform. The distance between adjacent zero cross points K1 and K2 is T7, the distance between adjacent zero cross points K2 and K3 is T7a, and the distance between adjacent zero cross points K3 and K4 is T7b. The interval T7b is close to 1/2 of the system cycle Ts, but the intervals T7 and T7a deviate significantly from Ts / 2. In the example of FIG. 7B, the interval T7 is 6.4 ms, the interval T7a is 5.6 ms, and T7b is 8.0 ms.

Furthermore, attention is paid to the interval between the zero cross point of the first derivative waveform and the zero cross point of the second derivative waveform. Specifically, with reference to FIG. 7B, attention is paid to the distance between the zero cross points J1 to J3 and the zero cross points K1 to K4. The distance between adjacent zero cross points K1 and J1 is T8, the distance between adjacent zero cross points J1 and K2 is T8a, the distance between adjacent zero cross points K2 and J2 is T8b, and the distance between adjacent zero cross points J2. , The distance between K3 is T8c, and the distance between zero cross points K3 and J3 is T8d.

Here, as described with reference to FIG. 4, when the CT is not saturated and is not in the inrush state, the interval between the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform is T2 ( That is, it was kept constant at Ts / 4). However, in FIG. 7B, the distance between the zero crossing point of the first-order differential waveform and the zero-crossing point of the second-order differential waveform is not kept constant and deviates significantly from Ts / 4 (for example, the distance T8c). Exists. In the example of FIG. 7B, the intervals T8, T8a, T8b, T8c, and T8d are 3.3 ms, 4.5 ms, 3.8 ms, 1.9 ms, and 6.5 ms, respectively.

From this, in the CT unsaturated state, even if the transformer is in the inrush state, the interval between the zero cross points of the first-order differential waveform is kept almost constant at Ts / 2, but the second-order differential waveform The interval between zero cross points often deviates from Ts / 2 and is not kept constant. Further, the interval between the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform often deviates from Ts / 4, and is not kept constant.

FIG. 8 is a diagram showing a waveform when CT is saturated and the transformer is in an inrush state. The vertical axis of FIGS. 8A and 8B is the current (corresponding to “I” in the figure), and the horizontal axis is the time (corresponding to “t” in the figure). With reference to FIG. 8A, the waveform 450 shows the waveform of the CT secondary current at the time of CT saturation and in the inrush state, and the waveform 451 shows the first derivative waveform of the CT secondary current. With reference to FIG. 8B, waveform 452 shows the second derivative waveform of the CT secondary current. FIG. 8B shows the vertical axis of FIG. 8A changed so as to enlarge the waveform 451.

With reference to FIG. 8A, attention is paid to the interval between the zero cross points L1 to L4 after CT saturation occurs in the waveform 451. The interval between the zero cross points L1 and L2 is T9, the interval between the zero cross points L2 and L3 is T9a, and the interval between the zero cross points L3 and L4 is T9b. In the example of FIG. 8A, the intervals T9, T9a, and T9b are 6.0 ms, 9.8 ms, and 4.2 ms, respectively. The interval T9a is close to 1/2 of the system cycle Ts, but the intervals T9 and T9b deviate significantly from Ts / 2.

With reference to FIG. 8B, attention is paid to the interval between the zero cross points M1 to M5 after the occurrence of CT saturation in the waveform 452. The interval between the zero cross points M1 and M2 is T10, the interval between the zero cross points M2 and M3 is T10a, the interval between the zero cross points M3 and M4 is T10b, and the interval between the zero cross points M4 and M5 is T10c. In the example of FIG. 8B, the intervals T10, T10a, T10b, and T10c are 5.8 ms, 7.5 ms, 3.2 ms, and 3.5 ms, respectively. The intervals T10 to T10c deviate significantly from Ts / 2. Similarly, the distance between the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform is not kept constant, and many of them deviate significantly from Ts / 4.

From this, when the transformer is in the inrush state at the time of CT saturation, the interval between the zero cross points of the first derivative waveform and the interval between the zero cross points of the second derivative waveform, and the zero cross point of the first derivative waveform. The distance between the second-order differential waveform and the zero cross point of the second-order differential waveform is not kept constant. Specifically, some of the intervals between the zero cross points of the first-order differential waveform deviate significantly from Ts / 2, and Ts also exists in each interval between the zero cross points of the second-order differential waveform. There is something that deviates significantly from / 2. Some of the intervals between the zero cross point of the first-order differential waveform and the zero cross point of the second-order differential waveform deviate significantly from Ts / 4.

Therefore, comparing the waveform shown in FIG. 7 when the CT is saturated and in the inrush state with the waveform shown in FIG. 8 when the CT is saturated and in the inrush state, the first-order differential waveform There is a difference in the interval between the zero cross points. Further, when the waveform shown in FIG. 3 and the waveform shown in FIG. 7 are compared when the CT is unsaturated and not in the inrush state, there is a difference in the interval between the zero cross points of the first-order differential waveform and the second-order differential waveform. is there. Therefore, the protection relay device 100 uses the interval between the zero cross points of the first-order differential waveform and the interval between the zero cross points of the first-order differential waveform and the second-order differential waveform to determine the presence or absence of CT saturation and the inrush state in the transformer. Determine the presence or absence.

As described above, in FIGS. 7 and 8, the current waveform when the single-phase transformer is in the inrush state has been described, but the same applies to the three-phase transformer.

FIG. 9 is a diagram showing a waveform when the three-phase transformer is in the inrush state. With reference to FIG. 9A, the waveforms 500, 510, and 520 show the current waveforms of the A phase, the B phase, and the C phase at the time of CT desaturation, respectively. With reference to FIG. 9B, the waveforms 550, 560, and 570 show the current waveforms of the A phase, the B phase, and the C phase at the time of CT saturation, respectively. Specifically, in FIG. 9B, it is assumed that the CT provided in the A phase is saturated.

The waveform 500 of FIG. 9A and the waveform 400 of FIG. 7A show the same tendency, and the waveform 550 of FIG. 9B and the waveform 450 of FIG. 8A have the same tendency. It is a waveform showing. Therefore, even in a three-phase transformer, the protection relay device 100 uses the interval between the zero cross points of the first-order differential waveform and the interval between the zero cross points of the first-order differential waveform and the second-order differential waveform to saturate the CT. It is possible to determine the presence / absence of the presence and the presence / absence of an inrush state in the transformer.

FIG. 10 is a flowchart showing an example of the determination method according to the second embodiment. Typically, each of the following steps is performed by the CPU 72 of the arithmetic processing unit 70 of the protection relay device 100.

With reference to FIG. 10, since each process of steps S10 to S16 is the same as each process shown in FIG. 5, the details thereof will not be repeated. When the interval Tx1 between the zero cross points of the first derivative waveform is within the range R1 (YES in step S16), the protection relay device 100 has the interval between the zero cross points of the first derivative waveform and the zero cross points of the second derivative waveform. It is determined whether or not (hereinafter, also referred to as “interval Tx12”) is within the range R2 (step S50).

When the interval Tx12 is within the range R2 (YES in step S50), the protection relay device 100 determines that the CT6 is not saturated and the transformer 9 is not in the inrush state (step S52). In this case, it is presumed that the abnormal current is due to a failure of the power system. Therefore, for example, when a failure of the power system occurs inside the protection target, the protection relay device 100 operates and outputs a trip signal to the circuit breaker 5. On the other hand, when the interval Tx12 is out of the range R2 (NO in step S50), the protection relay device 100 determines that the CT6 is in the unsaturated state and the transformer 9 is in the inrush state (step S54).

Further, when the interval Tx1 is outside the range R1 (NO in step S16), the protection relay device 100 determines whether or not the interval Tx12 is within the range R2 (step S56). When the interval Tx12 is outside the range R2 (NO in step S56), the protection relay device 100 determines that CT6 is saturated (step S58).

When the interval Tx12 is within the range R2 (YES in step S56), the protection relay device 100 returns to the process of step S12. Here, it is considered that the case where the interval Tx1 is outside the range R1 and the interval Tx12 is within the range R2 (that is, NO in step S16 and YES in step S56) does not usually occur. Therefore, the protection relay device 100 returns to the process of step S12 and executes the determination process again.

<Functional configuration>
FIG. 11 is a block diagram showing an example of the functional configuration of the protection relay device 100 according to the second embodiment. With reference to FIG. 11, the functional configuration of the protection relay device 100 according to the second embodiment corresponds to a configuration in which the inrush determination unit 162 is added to the functional configuration of the protection relay device 100 according to the first embodiment shown in FIG. To do.

The inrush determination unit 162 determines the transformer 9 based on the first zero cross interval, which is the interval between adjacent first zero cross points, and the third zero cross interval, which is the interval between adjacent first and second zero cross points. Determines whether or not is in the inrush state.

In the case of FIG. 7, the first zero cross points are the zero cross points J1 to J3, and the first zero cross intervals are the intervals T6 and T6a. The second zero cross point is the zero cross point K1 to K4, and the second zero cross interval is the interval T7 to T7b. The third zero cross interval is the interval T8 to T8d. In the case of FIG. 8, the first zero cross points are the zero cross points L1 to L4, and the first zero cross intervals are the intervals T9 to T9b. The second zero cross points are zero cross points M1 to M5, and the second zero cross intervals are intervals T10 to T10c. The third zero cross interval is an interval between zero cross points L1 and M1, between zero cross points M1 and L2, between zero cross points L2 and M2, and the like.

When the first zero cross interval is within the range R1 and the third zero cross interval is outside the range R2, the inrush determination unit 162 determines that the transformer 9 is in the inrush state. When the abnormality detection unit 154 detects an abnormality in the current of the power system, the inrush determination unit 162 may execute such an inrush state determination process of the transformer 9.

<Advantage>
According to the second embodiment, by using the zero cross point interval of the differential waveform of the current taken in from the CT, it is possible to determine not only the presence or absence of CT saturation but also the presence or absence of an inrush state. Therefore, malfunction and malfunction of the protection relay device due to CT saturation and inrush current can be prevented.

Other embodiments.
The configuration exemplified as the above-described embodiment is an example of the configuration of the present invention, can be combined with another known technique, and a part thereof is omitted as long as the gist of the present invention is not deviated. , Can be modified and configured. Further, in the above-described embodiment, the processing and configuration described in the other embodiments may be appropriately adopted and carried out.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

2,4 Busbar, 3 Transmission Line, 5 Circuit Breaker, 8 Voltage Transformer, 9 Transformer, 10,11 AC Power Supply, 51 Auxiliary Transformer, 52 AD Converter, 70 Arithmetic Processing Unit, 71 Bus, 72 CPU, 73 ROM, 74 RAM, 75 DI circuit, 76 DO circuit, 77 input interface, 100 protection relay device, 152 input unit, 154 abnormality detection unit, 156 waveform generation unit, 158 zero cross detection unit, 160 saturation judgment unit, 162 inrush judgment Department.

Claims (7)

An input unit that receives the input of the current of the power system detected by the current transformer, and
A waveform generator that differentiates the current to generate a first-order differential waveform of the current,
A zero-cross detection unit that detects the first zero-cross point of the first-order differential waveform, and
A protection relay device including a saturation determination unit for determining whether or not the current transformer is saturated based on a first zero cross interval indicating an interval between adjacent first zero cross points. The protection relay device according to claim 1, wherein the saturation determination unit determines that the current transformer is saturated when the first zero cross interval is out of the first range. The waveform generation unit differentiates the first-order differential waveform to further generate a second-order differential waveform of the current.
The zero cross detection unit further detects the second zero cross point of the second derivative waveform, and further detects the second zero cross point.
At least one of the condition that the first zero cross interval is out of the first range and the condition that the second zero cross interval indicating the interval between adjacent second zero cross points is out of the first range. The protection relay device according to claim 1, wherein the saturation determination unit determines that the current transformer is saturated when the condition is satisfied. The waveform generation unit differentiates the first-order differential waveform to further generate a second-order differential waveform of the current.
The zero cross detection unit further detects the second zero cross point of the second derivative waveform, and further detects the second zero cross point.
When the first zero cross interval is outside the first range, and the third zero cross interval indicating the interval between the adjacent first and second zero cross points is outside the second range smaller than the first range. The protection relay device according to claim 1, wherein the saturation determination unit determines that the current transformer is saturated. The first range is a tolerance range centered on 1/2 of the system cycle.
The protection relay device according to claim 4, wherein the second range is a tolerance range centered on 1/4 of the system cycle. A transformer is arranged in the power system.
An in-rush determination unit for determining whether or not the transformer is in an in-rush state based on the first zero-cross interval and the third zero-cross interval is further provided.
When the first zero cross interval is within the first range and the third zero cross interval is outside the second range, the inrush determination unit determines that the transformer is in the inrush state. The protection relay device according to claim 4 or 5, which is determined. Further provided with an abnormality detection unit for detecting the abnormality of the current,
The protection according to any one of claims 1 to 6, wherein when the abnormality detection unit detects an abnormality in the current, the saturation determination unit executes the saturation determination process of the current transformer. Relay device.

Images