JP6165086B2 - Step-out prediction apparatus and step-out prediction method - Google Patents

Description

  The present invention relates to a step-out prediction apparatus and a step-out prediction method for predicting occurrence of step-out in an electric power system.

  As the power flow in the power system becomes more complex, it is required to supply power with high reliability and quality. Within the power system, failures can occur for various reasons. For example, when a ground fault occurs in the power system, current flows in a concentrated manner at the point of failure, so the balance between the generated power and power consumption of the synchronized AC power system is lost, and If it is not removed early, the phase difference between some of the generators may increase and cause step-out.

  Conventionally, an apparatus for detecting a step-out that may occur in such a power system has been devised and put into practical use. As a typical detection principle, a method of determining the occurrence of step-out from the impedance change rate is used, as in the impedance change rate relay disclosed in Japanese Patent Application Laid-Open No. 59-169334 (Patent Document 1). ing. According to the impedance change rate relay disclosed in Patent Document 1, it is possible to detect the occurrence of step-out from only the information on the voltage and current at its own end.

  The inventor of the present application has also invented a power system step-out prediction apparatus as disclosed in Japanese Patent Application Laid-Open No. 2007-60870 (Patent Document 2), which employs a detection principle different from the above-described detection principle. In addition, the inventor of the present application disclosed in Japanese Patent No. 4874438 (Patent Document 3) using the concept of a symmetry group that is a group having symmetry that is rotating on a complex plane. We propose a method to calculate

  Furthermore, the inventor of the present application has proposed a technique for measuring various types of electricity in the power system using the concept of a symmetric group as disclosed in Japanese Patent No. 5214074 (Patent Document 4).

JP 59-169334 JP 2007-060870 A Japanese Patent No. 4874438 Japanese Patent No. 5214074

  In the impedance change rate relay disclosed in Patent Document 1 described above, the process of measuring the impedance change rate is complicated, and there is a possibility of making an erroneous determination due to the influence of characteristic changes in the power system and fluctuations in the system. is there.

  Moreover, in the electric power system step-out prediction apparatus disclosed in Patent Document 2 described above, it is necessary to calculate the first-order derivative and the second-order derivative regarding the phase difference between both ends of the connecting line, and the calculation process is somewhat complicated. It has become.

  In particular, when a fault occurs in the power system, the rated frequency (typically 50 Hz or 60 Hz) is not always maintained, and the impedance is calculated on the assumption that the rated frequency is constant. This technique causes an error.

  The present invention has been made in view of the above, and the purpose of the present invention is to be within the power system without being affected even if the rated frequency in the power system is deviated from the original frequency. It is an object of the present invention to provide a step-out prediction apparatus and a step-out prediction method capable of predicting the occurrence of step-out.

  In order to solve the above-described problems and achieve the object, a step-out prediction device according to an aspect of the present invention samples voltage instantaneous value data and current instantaneous value data by sampling at a first sampling frequency from a target power system. 4 that are continuous with the time series extracted from the instantaneous voltage value data acquired by the acquisition means at a second sampling frequency that is smaller than the first sampling frequency and equal to or higher than the frequency of the power system. For the voltage instantaneous value data at the point, three differential voltage instantaneous value data corresponding to the respective differences between two points adjacent in time series are acquired, and the second current instantaneous value data acquired by the acquiring means is Differences between two points adjacent to each other in time series with respect to four points of current instantaneous value data extracted in time series at the sampling frequency Difference value acquisition means for acquiring the corresponding three differential current instantaneous value data, the first gauge value is calculated based on the three differential current instantaneous value data, and the three differential voltage instantaneous value data and the three differential currents First calculation means for calculating a second gauge value indicating active power corresponding to the three differential voltage instantaneous value data and the three differential current instantaneous value data based on the instantaneous value data, the first gauge value, And a second calculating means for calculating a system state value indicating the magnitude of the phase difference between two different points of the power system based on the second gauge value.

  According to the present invention, even when the rated frequency in the power system is deviated from the original frequency, it is possible to predict the occurrence of step-out in the power system without being affected by the rated frequency.

It is a schematic diagram which shows the electrical behavior in case the electric power system is stably operated. It is a schematic diagram which shows the electrical behavior in case some disturbance has generate | occur | produced in the electric power grid | system. It is a figure which shows the gauge voltage group and gauge differential voltage group on a complex plane. It is a figure which shows the gauge current group and gauge differential current group on a complex plane. It is a figure which shows the gauge difference electric power group on a complex plane. It is a schematic diagram which shows the structural example of the step-out prediction apparatus according to embodiment of this invention. It is a flowchart which shows the process sequence of a step-out prediction according to embodiment of this invention. It is a flowchart which shows the process sequence of the calculation process of a step-out center voltage shown to step S2 of FIG. It is a schematic diagram for demonstrating the model system | strain used for simulation. It is a figure which shows the time change of the internal phase angle of the generator obtained by simulation. It is a figure which shows the time change of the bus voltage instantaneous value obtained by simulation. It is a figure which shows the time change of the transmission line current obtained by simulation. It is a figure which shows the time change of the frequency coefficient obtained by simulation. It is a figure which shows the time change of the power system frequency obtained by simulation. It is a figure which shows the time change of the gauge differential current obtained by simulation. It is a figure which shows the time change of the gauge difference active power obtained by simulation. It is a figure which shows the time change of the gauge differential reactive power obtained by simulation. It is a figure which shows the time change of the proportionality coefficient of the active power and reactive power which were obtained by simulation. It is a figure which shows the time change of the step-out center voltage obtained by simulation, and the calculation result of an estimation curve. It is a figure which shows the time change of the calculation result of the step-out estimation time obtained by simulation.

A step-out prediction apparatus and a step-out prediction method according to an embodiment of the present invention will be described below with reference to the accompanying drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and description thereof will not be repeated. In addition, this invention is not limited by embodiment shown below.
[A. Definition of terms]
First, terms used in this specification will be described when describing a step-out prediction apparatus and a step-out prediction method according to the present embodiment.

(1) Complex number A value represented in the form of a + jb using real numbers a and b and an imaginary unit j. In electrical engineering, since i is a current sign, the imaginary unit is expressed using j = √ (−1). In this specification, a rotation vector is expressed using complex numbers.

(2) Complex plane A complex number is a point on a two-dimensional plane, and is generally a plane representing a complex number in rectangular coordinates with the real part (Re) on the horizontal axis and the imaginary part (Im) on the vertical axis. . In principle, the real part (Re) may be the vertical axis and the imaginary part (Im) may be the horizontal axis.

(3) Rotation vector A rotation vector is defined as a vector that rotates counterclockwise on a complex plane related to the electric quantity (voltage or current) of the power system. The real part of the rotation vector corresponds to the instantaneous value.

(4) Differential voltage rotation vector This is a difference vector of two rotation vectors around the sampling frequency of one cycle. The real part of the differential voltage rotation vector is the difference between the instantaneous values of two points before and after one cycle of the sampling frequency.

(5) Symmetric group This is a group having symmetry rotating on the complex plane.

(6) Invariant A parameter that does not change before and after the symmetry group rotates. Invariants assumed in the present embodiment include, but are not limited to, a rotation phase angle, a frequency coefficient, a gauge voltage, a gauge differential voltage, a gauge differential current, and a gauge differential active power. If the invariants are known, the characteristics of the symmetric group can also be known.

(7) Power system frequency It means the rated frequency in the power system, and is typically 50 Hz or 60 Hz.

(8) Data collection sampling frequency This is a sampling frequency (first sampling frequency) at the time of data collection, and is represented by “f _1” . The data collection sampling frequency f ₁ is higher is better accuracy. Similar to the gauge sampling period T, the data collection sampling period T ₁ is represented by T ₁ = 1 / f ₁ as the reciprocal of the data collection sampling frequency f ₁ .

(9) Gauge sampling frequency This is a sampling frequency (second sampling frequency) used to calculate the gauge symmetry group, and is represented by “f _S ”. Therefore, the gauge sampling period T is expressed as T = 1 / f _S as the reciprocal of the gauge sampling frequency f _S. Note that there is a relationship of T> T ₁ between T and T ₁ . The gauge sampling frequency f _S is set to be equal to or higher than the rated frequency (power system frequency) in the power system.

(10) Rotation phase angle A voltage rotation vector (sometimes simply referred to as a “voltage vector”) or a current rotation vector (sometimes simply referred to as a “current vector”) on a complex plane during one gauge sampling frequency cycle The rotated phase angle, represented by α. Note that the rotational phase angle α is a frequency-dependent amount. As will be described later, when α is a positive number, α = 2π (f / f _S ) is calculated, and when α is a negative number, α = Calculated as 2π {(f / f _S ) −1}. When α is zero, there is a relationship of f = f _S / 2 between the gauge sampling frequency f _S and the real time frequency f.

(11) Frequency coefficient This is a cosine function value of the rotational phase angle α and is represented by f _C. Each gauge symmetry group can be defined with a formula for calculating its frequency coefficient. Note that if the frequency coefficient f _C is used as a symmetry index, it is possible to determine whether or not the current is AC.

(12) Moving average process This is a simple average process using a predetermined number of recent data. Note that the influence of measurement error and additive Gaussian noise can be reduced by performing moving average processing.

(13) Gauge voltage group This is a symmetric group composed of three voltage rotation vectors continuous in time series. The same symmetrical group concept can be defined for currents other than voltage and power (active power and reactive power).

(14) Gauge differential voltage group This is a symmetric group composed of three differential voltage rotation vectors continuous in time series.

(15) Gauge differential current group A symmetric group composed of three differential current rotation vectors continuous in time series.

(16) Notation Method In the following description, among lowercase letters in the alphabet, those with parentheses (for example, “v (t)”) represent vectors (phasors) and those without parentheses (for example, “v ₂ ”). Represents an instantaneous value. In addition, alphabetic capitalization (for example, “V _g ”) represents an effective value or an amplitude.

Moreover, since the method described in the above-mentioned patent document 4 can be used for the measurement method of the voltage rotation vector and the current rotation vector, the entire contents thereof are incorporated herein, and the detailed description thereof will not be repeated. .
[B. Summary]
In the out-of-step prediction algorithm according to the present embodiment, the “out-of-step center voltage” is calculated and monitored using the electric quantity measurement formula proposed by the present inventor in the above-mentioned Patent Document 4 and the like. The details of the “step-out center voltage” will be described later, but its physical meaning corresponds to a system state value indicating the magnitude of the phase difference between two different points in the power system. As a specific procedure for calculating the “step-out center voltage”, the gauge differential voltage group is used to calculate the gauge differential voltage, the gauge differential current group is used to calculate the gauge differential current, and the gauge differential power group is calculated. Use to calculate gauge differential active power. Then, the step-out center voltage is calculated based on the gauge differential current and the gauge differential active power. In such a calculation procedure (measurement formula), the transmission line impedance calculated depending on the rated frequency of the power system is not used. For this reason, the frequency of the power system may be greatly deviated from the rated frequency at the time of step-out, but high-accuracy calculation can be realized without being affected by such influence. That is, the calculation method of “step-out center voltage” according to the present embodiment has a power system frequency correction function, and the influence of the DC component and the harmonic component contained in the voltage waveform / current waveform of the power system. It can be made as small as possible.

  Also, in the step-out prediction algorithm according to the present embodiment, the temporal change of the step-out center voltage is assumed to be a time function equation (primary estimation curve and quadratic estimation curve), and the least squares method is used using the actual calculation results. Each estimated curve is determined by fitting with the above. The primary estimation curve coefficient, which is the estimated coefficient of the primary estimation curve, is used to determine whether or not it is proceeding in the step-out direction based on its sign. Further, the estimated secondary estimation curve is used to calculate a step out estimation time which is a time from the current time to the step out point. Specifically, the intersection of the secondary estimation curve and the time axis is regarded as a step-out point, and the time out to the step-out point is evaluated to predict the step-out of the power system. Note that the primary estimation curve and the secondary estimation curve change with time. However, since the functions of the primary estimation curve and the secondary estimation curve are different from each other, only one of them may be calculated.

  Also, in the step-out prediction algorithm according to the present embodiment, when a step-out estimation time can be calculated for each of a plurality of transmission lines included in the power system, the calculated step-out estimation times are calculated. Among them, the transmission line corresponding to the out-of-step estimation time with the smallest value is determined to be the out-of-step center. That is, it is determined that some failure has occurred in the power transmission line having the calculated estimated step-out estimation time.

The accuracy of the step-out prediction algorithm according to the present embodiment was evaluated by simulation (details will be described later).
[C. Step-out prediction algorithm]
First, an outline of the step-out prediction algorithm according to the present embodiment will be described. In the present embodiment, a “step-out center voltage”, which will be described in detail later, is defined, and the occurrence of step-out is predicted based on the temporal change of the “step-out center voltage”.

  “Predicting the occurrence of a step-out” is a concept that includes determining whether or not a step-out has already occurred. Typically, in the situation where a step-out has not yet occurred, Determining whether or not a step-out occurs and / or determining at what timing the step-out is expected to occur.

  FIG. 1 is a schematic diagram showing an electrical behavior when a power system is stably operated. FIG. 2 is a schematic diagram showing the electrical behavior when some disturbance occurs in the power system.

(C1: When the power system is stably operated)
First, the behavior of the step-out center voltage when the power system is stably operated will be described with reference to FIG. FIG. 1A shows one transmission line of interest in the power system, and it is assumed that a power flow exists between the bus A end and the bus B end. Here, the end of the bus A is the target end, and is also referred to as “own end” below. On the other hand, the bus B end is also referred to as “partner end”.

In FIG. 1 (a), v _A (t) represents the voltage rotation vector (bus voltage instantaneous value) at its own end, v _B (t) represents the voltage rotation vector (bus voltage instantaneous value) at the other end, and i _A (t) represents the current rotation vector (transmission line current instantaneous value) of the transmission line current flowing from the own end to the other end.

  When the power system is stably operated, the voltage rotation vectors at both ends of the transmission line rotate at substantially the same rotation angular velocity (that is, frequency). This rotational angular velocity ω is defined according to the following equation (1).

ω = 2πf (1)
Here, f is a power system frequency, and is the same as or close to the rated frequency (typically 50 Hz or 60 Hz) of the power system.

FIG. 1B shows the result of the voltage rotation vector v _A (t) at the end and the voltage rotation vector v _B (t) at the other end on the complex plane.

The voltage rotation vector v _A (t) at its own end is defined according to the following equation (2). In the equation (2), V _A represents the voltage amplitude of the own-end bus voltage, and φ represents the phase difference between the own-end bus voltage and the own-end transmission line current. Further, ω _A indicates the rotational angular velocity of the voltage rotation vector v _A (t) at its own end, and is defined according to the following equation (2). In the equation (3), f _A is the self-end bus frequency.

The current rotation vector i _A (t) of the transmission line current at the end is defined according to the following equation (4). (4) In the equation, I _A represents the current amplitude of the transmission line current local end.

Further, the voltage rotation vector v _B (t) at the other end is defined according to the following equation (5). In the equation (5), V _B represents the voltage amplitude of the bus voltage at the other end. ω _B indicates the rotation angular velocity of the voltage rotation vector v _B (t) at the other end, and is defined according to the following equation (6). In equation (6), f _B is the bus frequency at the other end.

Here, the voltage rotation vector v _C (t) of the step-out center voltage calculated from its own end is defined according to the following equation (7). In the equation (7), V _C represents a step-out center voltage amplitude and is defined according to the following equation (8).

For convenience of explanation, broad step-out center voltage amplitude V _C also referred to as "step-out central voltage".
(C2: State where some disturbance has occurred in the power system)
Next, with reference to FIG. 2, the behavior of the step-out center voltage when some disturbance occurs in the electric power system will be described. Typically, as shown in FIG. 2 (a), a situation is assumed in which some kind of system failure F occurs in the transmission line and the power system is stepped out due to the disturbance. FIG. 2B shows the voltage rotation vector v _A (t) at the other end, the voltage rotation vector v _B (t) at the other end, and the voltage rotation vector v _C ( The result which showed t) on the complex plane is shown. That is, FIG. 2B shows the behavior of the step-out center voltage when the power system is in a state immediately before step-out.

  Comparing the case where the power system as shown in FIG. 1B is stably operated and the case where some disturbance occurs in the power system as shown in FIG. 2B, the following can be said. .

  In a state where the power system is stably operated, the voltage rotation vector at both ends of the transmission line has almost the same rotational angular velocity (same or close to the rated frequency), and the measured step-out center voltage is constant. It is larger than the value. Here, the phase difference (2φ) between both ends of the transmission line shown in FIG. 1B is a value within a predetermined range and does not become a large value.

On the other hand, in a state where some disturbance has occurred in the power system as shown in FIG. 2B, that is, in a state where the power system is going to step out, an increase in the frequency difference between both ends of the transmission line (that is, At the same time, the phase difference (2φ) between both ends of the transmission line becomes larger. Along with this, the step-out center voltage gradually decreases. Finally, the state where the phase difference (2φ) between both ends of the transmission line reaches 180 degrees and the step-out center voltage becomes zero is defined as “the power system has stepped out”. When the own-end bus frequency f _A is larger than the counterpart bus frequency f _B , the step-out is referred to as “acceleration step-out”, and the own-end bus frequency f _A is the opposite-end bus frequency f _B. When it is smaller, the step-out is called “deceleration step-out”.

  In this way, by measuring the out-of-step center voltage of the power system and monitoring its movement (that is, temporal change), occurrence of out-of-step in the power system can be predicted.

  The active power P and the reactive power Q flowing through the transmission line are defined according to the following equation (9).

According to FIG. 1 and FIG. 2 and the above equation (9), in the state where the power system is out of phase, the phase angle for voltage and current increases, and the effective power of the transmission line decreases and becomes invalid. It can be seen that the power increases. Therefore, in the step-out prediction apparatus according to the present embodiment, as a fail-safe condition (that is, a precondition for operation to prevent erroneous determination), “the proportional coefficient between active power and reactive power is continuously reduced. Is adopted. That is, the step-out prediction is performed only when the ratio of the active power to the reactive power is decreasing with time.
[D. Step-out center voltage calculation process]
(D1: Outline of step-out center voltage calculation)
It is a general measurement means that assumes that the power system frequency matches the rated frequency, and obtains the voltage amplitude at the end and the phase angle between the voltage and current, and then uses the above equation (8) to step out. The center voltage can be calculated.

  However, when the power system is out of step, the power system frequency is greatly deviated from the rated frequency, which can be a significant error factor with respect to the measurement result by a general measuring means. Furthermore, direct current components and harmonic components existing in the power system have a great influence on the measurement results.

  In consideration of such facts, the out-of-step prediction algorithm according to the present embodiment has a step-out center voltage having a frequency correction function that minimizes the influence of the DC component and the harmonic component existing in the power system. The measurement formula is adopted.

  In addition, please refer to the above-mentioned patent document 4 etc. about the basic calculation formula of various invariants about a symmetry group.

  In the following calculation procedure, the gauge difference power group is calculated using “three difference voltage rotation vectors” indicating the gauge difference voltage group and “three difference current rotation vectors” indicating the gauge difference current group. A step-out center voltage is determined from the calculated gauge differential power group. Furthermore, the temporal change of the step-out center voltage for predicting the occurrence of step-out is also calculated.

  A gauge power group is calculated using “three voltage rotation vectors” indicating a gauge voltage group and “three current rotation vectors” indicating a gauge current group, and a step-out center is calculated from the calculated gauge power group. The voltage may be determined.

Hereinafter, the calculation procedure will be described in order.
(D2: Calculation of frequency coefficient)
First, the frequency coefficient is calculated from the gauge differential voltage group.

FIG. 3 is a diagram illustrating a gauge voltage group and a gauge differential voltage group on a complex plane. Referring to FIG. 3, three differential voltage rotation vectors on the complex plane are defined according to the following equation (10). Where V is the AC voltage amplitude, ω is the rotational angular velocity, T is the gauge sampling frequency time step (gauge sampling period), and α is the rotational phase angle at T. The gauge sampling period T is calculated according to the following equation (11). Where f _S is the gauge sampling frequency.

The differential voltage instantaneous values v21, v22, v23 in FIG. 3 are calculated according to the following equation (12). Here, v11, v12, v13, v14 are voltage instantaneous values corresponding to the gauge sampling frequency. And according to the above-mentioned Patent Document 4, the frequency coefficient f _C that is an invariant of the gauge differential voltage group is calculated according to the following equation (13).

In calculating the frequency coefficient f _C , a gauge voltage group or a gauge current group can be used instead of the gauge differential voltage group described above. However, since the time difference of the gauge differential voltage group is relatively small, the influence of the direct current component can be suppressed by calculating the frequency coefficient using the gauge differential voltage group, which is more preferable.

(D3: Calculation of gauge differential current)
Next, a gauge differential current is calculated from the gauge differential current group.

  FIG. 4 is a diagram illustrating a gauge current group and a gauge differential current group on a complex plane. Each current instantaneous value shown in FIG. 4 corresponds to a value obtained by replacing each voltage instantaneous value shown in FIG. 3, and in any case, the symmetry relationship is unchanged. Three differential current rotation vectors on the complex plane are defined according to the following equation (14). Here, I is the alternating current amplitude, ω is the rotational angular velocity, T is the gauge sampling frequency time interval (gauge sampling period), and α is the rotational phase angle at T. The gauge sampling period T is calculated according to the above equation (11).

  The differential current instantaneous values i21, i22, i23 in FIG. 4 are calculated according to the following equation (15). Here, i11, i12, i13, and i14 are instantaneous current values corresponding to the gauge sampling frequency. And according to the above-mentioned patent document 4, the gauge differential current that is an invariant of the gauge differential current group is calculated according to the following equation (16).

  The current amplitude and the gauge differential current have a relationship defined by the following equation (17).

It should be noted that a gauge current group or the like can be used for calculating the gauge differential current I _gd instead of the above-described gauge differential current group. However, since the gauge differential current group has a relatively small temporal change, calculating the gauge differential current _Igd using the gauge differential current group is more preferable because the influence of the direct current component can be suppressed.

(D4: Calculation of gauge differential active power and gauge differential reactive power)
Next, gauge difference active power and gauge difference reactive power are calculated from the gauge difference power group.

  FIG. 5 is a diagram illustrating a gauge differential power group on a complex plane. In FIG. 5, three differential voltage rotation vectors on the complex plane are calculated according to the following equation (18). Where V is the voltage amplitude, ω is the rotational angular velocity, T is the symmetric group calculation sampling time step size, α is the rotational phase angle at T, and φ is the phase angle between the voltage and current. Also, the three differential current rotation vectors on the complex plane are calculated according to the following equation (19). Here, V is a voltage amplitude.

  The real part instantaneous value of the differential voltage rotation vector shown in the above equation (18) is calculated according to the following equation (20). Further, the real part instantaneous value of the differential current rotation vector shown in the above equation (19) is calculated according to the following equation (21). Also,

  The gauge difference active power and the gauge difference reactive power are calculated according to the following equations (22) and (23), respectively.

  Here, the active power and reactive power flowing through the transmission line are calculated according to the following equations (24) and (25), respectively.

  In addition, it can replace with the gauge difference electric power group mentioned above, and can evaluate alternating current power using a gauge electric power group. However, it is more preferable to use the gauge differential power group because the influence of the DC component can be suppressed.

(D5: Calculation of step-out center voltage)
The above equation for measuring the step-out center voltage is developed as the following equation (26). When this equation (26) is arranged, equation (27) is derived.

Thus, the step-out center voltage can be calculated from the frequency coefficient, the gauge differential current, and the gauge differential active power. That is, the step-out center voltage calculation unit 102 of the step-out prediction apparatus 100 in FIG. 6 calculates the gauge difference current I _gd (first gauge value) based on the three pieces of instantaneous difference value data (i21, i22, i23). Based on the three differential voltage instantaneous value data (v21, v22, v23) and the three differential current instantaneous value data (i21, i22, i23), the three differential voltage instantaneous value data and the three differential current instantaneous values are calculated. A gauge differential active power (second gauge value) indicating active power corresponding to the value data is calculated. In addition, the step-out center voltage calculation unit 102 is effective to correspond to the three differential voltage instantaneous value data and the three differential current instantaneous value data based on the three differential voltage instantaneous value data and the three differential current instantaneous value data. A gauge differential active power (second gauge value) indicating power is calculated.

  In Patent Document 3 described above, for example, a formula for calculating the step-out center voltage using the gauge differential current and the gauge differential power is disclosed in Formula (111). Since the equation for calculating the step-out center voltage disclosed in Patent Document 3 includes the gauge differential reactive power, the step-out center voltage shown in the above-described equation (27) is used in the present embodiment. That is, in the present embodiment, a simpler calculation formula that does not include the gauge differential reactive power is derived based on the knowledge of the symmetry of the symmetry group and used.

  The step-out center voltage calculation unit 102 then determines the magnitude of the phase difference between two different points in the power system based on the gauge differential current (first gauge value) and the gauge differential active power (second gauge value). A step-out center voltage (system state value) is calculated.

In the step-out prediction algorithm according to the present embodiment, based on the step-out center voltage calculated according to the above-described equation (27), it is determined whether or not there is a possibility of step-out and / or a margin until step-out. Processing such as time calculation is performed.
[E. Implementation example]
Next, an implementation example of the step-out prediction apparatus according to the present embodiment will be described. FIG. 6 is a schematic diagram showing a configuration example of the step-out prediction apparatus 100 according to the embodiment of the present invention. Referring to FIG. 6, step-out prediction apparatus 100 includes, as its functional configuration, voltage / current instantaneous value data input unit 101, step-out center voltage calculation unit 102, fail-safe condition calculation unit 103, and primary estimation curve coefficient. Calculation unit 104, step-out possibility determination unit 105, secondary estimated curve coefficient calculation unit 106, step-out estimation time calculation unit 107, calculation information transmission unit 108, control signal transmission unit 109, interface 110, And a storage unit 111.

  These functions are realized by known hardware and software. Specifically, all or part of the functions shown in FIG. 6 may be realized using LSI (Large Scale Integration) or the like, or in addition to or instead of a CPU (Central Processing Unit) or the like. You may implement | achieve by running a program with a processor. Further, it can be implemented as a single device, or a configuration that realizes the function shown in FIG. 6 as a whole by linking a plurality of devices via a network or the like can be adopted. Furthermore, the step-out prediction apparatus 100 shown in FIG. 6 can be implemented as a partial function of a larger apparatus (for example, a power monitoring apparatus). How to implement the step-out prediction apparatus 100 shown in FIG. 6 is appropriately designed according to the application destination.

The voltage / current instantaneous value data input unit 101 collects voltage / current instantaneous value data in time series. That is, the voltage / current instantaneous value data input unit 101 acquires voltage instantaneous value data and current instantaneous value data by sampling from the target power system at the data collection sampling frequency f ₁ (first sampling frequency). More specifically, the voltage / current instantaneous value data input unit 101 collects the bus voltage instantaneous value from an instrument transformer (PT) provided in the electric power system, and converts the instantaneous voltage of the instrument provided in the electric power system. Collect the instantaneous value of the transmission line current from the current transformer (CT). The step-out center voltage calculation unit 102 accumulates instantaneous value data of the voltage group and current group according to the gauge sampling frequency, and calculates the step-out center voltage. More specifically, the step-out center voltage calculation unit 102 extracts the time-series data extracted from the voltage instantaneous value data acquired by the voltage-current instantaneous value data input unit 101 at the gauge sampling frequency (second sampling frequency). Three voltage instantaneous value data (v21, v22, v23) corresponding to respective differences between two points adjacent to each other in time series with respect to four consecutive voltage instantaneous value data (v11, v12, v13, v14). get. Further, the step-out center voltage calculation unit 102 has four points continuous in time series extracted from the instantaneous current value data acquired by the step-out center voltage calculation unit 102 at the gauge sampling frequency (second sampling frequency). For the instantaneous current value data (i11, i12, i13, i14), three differential current instantaneous value data (i21, i22, i23) corresponding to the respective differences between two points adjacent in time series are acquired. The gauge sampling frequency (second sampling frequency) is smaller than the data collection sampling frequency (first sampling frequency) and is equal to or higher than the frequency of the power system.

  The fail-safe condition calculation unit 103 calculates a fail-safe condition that is a precondition for the operation to prevent erroneous determination. As an example, the fail safe condition calculation unit 103 calculates a proportional coefficient between active power and reactive power and uses it as a fail safe condition. A method for calculating the proportionality coefficient between the active power and the reactive power will be described later.

  The primary estimation curve coefficient calculation unit 104, the step-out possibility determination unit 105, the secondary estimation curve coefficient calculation unit 106, and the step-out estimation time calculation unit 107 respond to temporal changes in the step-out center voltage (system state value). This corresponds to a prediction means for predicting occurrence of step-out in the power system.

  The primary estimation curve coefficient calculation unit 104 and the step-out possibility determination unit 105 determine the possibility of step-out from the primary estimation curve coefficient of the step-out center voltage. That is, the primary estimation curve coefficient calculation unit 104 calculates a primary estimation curve in which a temporal change in the step-out center voltage (system state value) over a predetermined period is estimated as a primary time function. More specifically, the primary estimated curve coefficient calculation unit 104 calculates the primary estimated curve coefficient of the step-out center voltage using the least square method. The step-out possibility determination unit 105 determines whether or not there is a possibility of step-out in the power system based on the calculated sign of the coefficient of the primary estimation curve.

  When it is determined that there is a possibility of step-out, the secondary estimation curve coefficient calculation unit 106 and the step-out estimation time calculation unit 107 calculate a margin time until the step-out is reached. The allowance time until the step out is defined as “step out estimated time”. That is, the secondary estimation curve coefficient calculation unit 106 calculates a secondary estimation curve in which a temporal change in the step-out center voltage (system state value) over a predetermined period is estimated as a secondary time function. More specifically, the secondary estimation curve coefficient calculation unit 106 calculates the secondary estimation curve coefficient of the step-out center voltage using the least square method. The step-out estimated time calculation unit 107 calculates a margin time (step-out estimated time) until a step-out is reached based on a temporal change of the secondary estimation curve. That is, the step-out estimated time calculation unit 107 calculates the step-out estimated time using the calculated secondary estimation curve.

  The calculation information transmission unit 108 transmits calculation information including an estimation result to other step-out prediction devices and control devices in order to realize the cooperative operation of the circuit breakers in the power system. The control signal transmission unit 109 transmits a trip command to the target circuit breaker when it is determined that a failure leading to step-out has occurred in the monitored transmission line.

  In the case where a plurality of step-out prediction apparatuses 100 are provided in the same power system, a function of identifying a step-out center transmission line in one or a plurality of step-out prediction apparatuses 100 may be implemented. More specifically, the step-out prediction device 100 performs step-out to the transmission line having the smallest value among the respective margin times (step-out estimation time) calculated for the plurality of transmission lines included in the power system. It may have a function of specifying that the disturbance to be generated is occurring. By mounting such a function, the cooperative operation of a plurality of circuit breakers can be realized more easily.

The interface 110 has an interface function such as digital display. That is, the interface 110 mediates data exchange with an external device for monitoring and data analysis. The storage unit 111 stores measurement data, calculation information, and the like.
[F. Failsafe condition calculation process]
Next, the fail safe condition calculation process in the fail safe condition calculation unit 103 of the step-out prediction apparatus 100 in FIG. 6 will be described. As such a fail-safe condition, in this embodiment, a proportional coefficient between active power and reactive power is used. More specifically, the proportionality coefficient K _PQ between active power and reactive power is calculated according to the following equation (28).

Thus, the proportionality coefficient K _PQ , which is an example of the fail-safe condition, can be calculated using the frequency coefficient, the gauge difference active power, and the gauge difference reactive power. In a situation where more active power flows than reactive power, the value of the proportional coefficient K _PQ increases. In other words, it is possible to determine whether or not a certain failure has occurred in the power system, and more power flows to the ground.

Note that as the fail-safe condition, the voltage amplitude of the bus voltage at its own end may be used in addition to the proportional coefficient K _PQ described above. In a situation where some kind of failure has occurred and the target transmission line is grounded, the bus voltage does not rise, and therefore, based on the magnitude of the absolute value of the voltage amplitude of the local bus voltage (for example, the threshold value is set to 0). .2PU), it may be determined whether a failure has occurred.
[G. Judgment process of possibility of step-out]
Next, the determination process of the possibility of step-out in the primary estimated curve coefficient calculation unit 104 and the step-out possibility determination unit 105 in the step-out prediction apparatus 100 in FIG. 6 will be described.

First, to set the step-out center voltage _{V C} in accordance with the following equation (29). Here, V is the voltage amplitude at its own end, and φ is the phase angle between the voltage and current.

Primary estimation curve of the step-out center voltage V _C is calculated by the following procedures.
In this embodiment, in order to reduce the processing amount, the exponential function is approximated using four arithmetic operations. As a typical method, an exponential Taylor expansion is used. This Taylor expansion is defined by the following equation (30).

Using this Taylor expansion, defining the primary estimation curve of step-out center voltage V _C in accordance with the following equation (31). Here, V _C0 is the current step-out center voltage, λ is the attenuation coefficient, t is time, and P ₁₁ is the primary estimation curve coefficient.

In the equation (31), V _C0 and P ₁₁ change from moment to moment as the state in the power system changes. Therefore, the equation of the primary estimation curve as shown in the following equation (32) is adopted.

  Furthermore, time-series data having the same time interval is generated as shown in the following equation (33). Here, t1, t2,..., Tn are time values having the same time width.

From the above equation (33), a matrix shown in the following equation (34) is generated. Here, in the equation (34), the actual measurement time series matrix [V _C ] is defined by the following equation (35), and the time value matrix [A ₁ ] is defined by the following equation (36).

Finally, according to the theory of the least squares method, the primary estimated curve coefficient P ₁₁ of step-out center voltage V _C can be calculated according to the following equation (37).

The primary estimation curve coefficient calculation unit 104 of the step-out prediction apparatus 100 in FIG. 6 calculates the primary estimation curve coefficient P ₁₁ according to the above-described equation (37), and the step-out possibility determination unit 105 calculates the primary order curve coefficient P _11. determining the sign of the estimated curve coefficient _{P 11.} In other words, the fact that the primary estimation curve coefficient P ₁₁ is a negative value, it indicates that the absolute value of the step-out center voltage V _C is decreasing, in this case, if is advanced in the direction of the step-out I can judge.
[H. Calculation process of estimated step-out time]
Next, the process of calculating the step out estimation time in the secondary estimated curve coefficient calculation unit 106 and the step out estimation time calculation unit 107 of the step out prediction apparatus 100 in FIG.

The calculation process of step-out estimated time, using secondary estimation curve of step-out center voltage V _C. Specifically, a quadratic estimation curve is defined according to the following equation (38) using Taylor expansion. Here, V _C0 is the current step-out center voltage, λ is an attenuation coefficient, t is time, and P ₂₁ and P ₂₂ are secondary estimation curve coefficients.

In the equation (38), V _C0 , P ₂₁ and P ₂₂ change from moment to moment as the state in the power system changes. Therefore, a quadratic estimation curve equation as shown in the following equation (39) is adopted as the equation of the primary estimation curve.

Furthermore, time-series data having the same time interval as shown in the following equation (40) is generated.
Here, t1, t2,..., Tn are time values having the same time width.

From the above equation (40), the matrix shown in the following equation (41) is generated. Here, in the equation (41), the actual measurement time series matrix [V _C ] is defined in the following equation (42), and the time value matrix [A ₂ ] is defined in the following equation (43), The next estimated curve coefficient [P ₂ ] is composed of two values P ₂₁ and P ₂₂ as shown in the following equation (44).

According the theory of the least squares method, the secondary estimation curve factor of step-out center voltage V _C [P _2] can be calculated according to the following equation (45).

  Here, assuming that the intersection of the secondary estimation curve and the time axis is the step-out point, the following equation (46) is established.

  When the equation shown in the equation (46) is developed, the equation shown in the following equation (47) is obtained. That is, the position of the intersection between the secondary estimation curve and the time axis can be calculated according to the following equation (47).

Finally, the step-out estimated time T _EST is calculated according to the following equation (48). Here, T _NOW is the current time.

The secondary estimation curve coefficient calculation unit 106 of the step-out prediction apparatus 100 in FIG. 6 calculates the secondary estimation curve coefficient [P ₂ ] according to the above equation (44), and the step-out estimation time calculation unit 107 Using the calculated second-order estimated curve coefficient [P ₂ ], the step-out estimated time T _EST is calculated according to the above-described equations (47) and (48). An example of calculating the step-out estimated time T _EST will be described later with reference to FIG.
[I. Processing procedure]
Next, a step-out prediction processing procedure executed by the step-out prediction apparatus 100 shown in FIG. 6 will be described. FIG. 7 is a flowchart showing a step-out prediction processing procedure according to the embodiment of the present invention. Each step shown in FIG. 7 is typically executed in the configuration shown in FIG.

  Referring to FIG. 7, voltage / current instantaneous value data input unit 101 reads an instantaneous value of the bus voltage from an instrument transformer (PT) provided in the power system, and also converts an instrument variable provided in the power system. The instantaneous value of the transmission line current is read from the current collector (CT) (step S1). Note that the read instantaneous value data is stored in the storage unit 111.

  Subsequently, the step-out center voltage calculation unit 102 accumulates the instantaneous value data of the voltage group and the current group at the gauge sampling frequency, and calculates the step-out center voltage (step S2). Details of the process of calculating the step-out center voltage will be described later. The calculated step-out center voltage is sequentially accumulated and used for subsequent estimation processing.

  Subsequently, the fail safe condition calculation unit 103 calculates a proportional coefficient between active power and reactive power (step S3). The calculated proportionality coefficients are sequentially accumulated and used as fail-safe conditions in subsequent processing. Specifically, the out-of-step estimation time (margin time) is calculated only during the period in which the proportionality coefficient between active power and reactive power flowing through the power system is continuously decreasing.

Subsequently, the primary estimation curve coefficient calculation unit 104 calculates a primary estimation curve coefficient of the step-out center voltage (step S4). More specifically, the primary estimated curve coefficient calculation unit 104, according to the above (37) equation, to calculate the primary estimation curve coefficient P ₁₁ of step-out center voltage V _C.

Subsequently, the step-out possibility determining unit 105, based on the sign of the calculated primary estimation curve coefficient P _11, it is determined whether the possibility of step-out. More specifically, the step-out possibility determining unit 105 determines whether the primary estimation curve coefficient P ₁₁ is less than or equal to zero (step S5).

The primary estimated curve coefficient P ₁₁ is the greater than zero (NO in step S5), and is determined not toward the out-, the process returns to the step S1.

On the contrary, if the primary estimation curve coefficient P ₁₁ is less than or equal to zero (YES in step S5), it was judged to be toward the out-of, the step S6 and subsequent steps are executed. That is, the secondary estimation curve coefficient calculation unit 106 typically using a least squares method to calculate the quadratic estimation curve factor of step-out center voltage V _C [P _2] (step S6).

Subsequently, the step-out estimated time calculation unit 107 calculates the step-out estimated time using the calculated secondary estimated curve [P ₂ ] (step S7). More specifically, the step-out estimated time calculation unit 107 calculates the step-out estimated time T _EST according to the above-described equations (47) and (48).

  Subsequently, the calculation information transmission unit 108 outputs calculation information including an estimation result in order to realize the cooperative operation of the circuit breakers in the power system (step S8). For example, in the power system including the transmission line AB and the transmission line BC as shown in FIG. 6, it is assumed that a step-out prediction device is arranged on each of the A bus and the B bus. In such a power system, when it is assumed that the step-out center (failure occurrence point) is in the transmission line BC, the step-out estimation time calculated by the step-out prediction device arranged in the A bus is arranged in the B bus. This is longer than the estimated out-of-step time calculated by the out-of-step prediction apparatus. In this case, the trip command from the step-out prediction device arranged on the A bus is blocked, and only the circuit breaker connected to the step-out prediction device arranged on the A bus is tripped. By performing such a cooperative operation, it is possible to further limit the spillover range of the influence due to the failure.

  Subsequently, the control signal transmission unit 109 outputs a control signal (step S9). More specifically, the control signal transmission unit 109 transmits a trip command to the target circuit breaker when it is determined that a failure leading to step-out has occurred in the monitored transmission line. . As shown in the following equation (49), the control signal transmission unit 109 compares the estimated out-of-step time with the set value, and when this equation (49) is satisfied, a failure that leads to out-of-step is monitored. Judge that it is occurring in the target transmission line, and send a trip command to the breaker of the self-end transmission line.

  Finally, the step-out prediction apparatus 100 determines whether or not the end of the process has been instructed (step S10). If the end of the process has not been instructed (NO in step S10), the process proceeds to step S10. Return to S1. On the other hand, when the end of the process is instructed (YES in step S10), the process ends.

  Next, a specific procedure of the step-out center voltage calculation process in step S2 will be described.

  FIG. 8 is a flowchart showing a processing procedure of the step-out center voltage calculation processing shown in step S2 of FIG.

First, out-of-step center voltage calculation unit 102, from the group of voltage instantaneous value and the current instantaneous value stored in the storage unit 111 (acquired by the data acquisition sampling periods T _1), the gauge sampling a voltage instantaneous value and the current instantaneous value By reading out with the period T, a gauge differential voltage group, a gauge differential current group, and a gauge differential power group are generated (step S200).

  Subsequently, the step-out center voltage calculation unit 102 determines whether or not the symmetry of the gauge differential voltage group is broken (step S201). That is, the step-out center voltage calculation unit 102 determines whether or not the measured amount of electricity is an appropriate alternating current. One object of determining symmetry breaking is to reduce harmonic components contained in the power system.

  More specifically, the step-out center voltage calculation unit 102 determines the presence or absence of symmetry breaking using the following equation (50). Here, v21, v22, and v23 are differential voltage instantaneous values.

  When the above equation (50) is satisfied, it can be determined that the symmetry of the gauge differential voltage group is broken. That is, when it is determined that the symmetry of the gauge differential voltage group is broken (in the case of YES in step S201), the process of step S202 is executed, and it is determined that the symmetry of the gauge differential voltage group is not broken. If so (NO in step S201), the process of step S203 is executed.

  In step S202, the step-out center voltage calculation unit 102 latches the previous measurement value without calculating the frequency coefficient because it is determined that the symmetry is broken. Then, the process proceeds to step S204.

In step S203, the step-out center voltage calculation unit 102 calculates the frequency coefficient f _C. The step-out center voltage calculation unit 102 calculates the frequency coefficient f _C that is an invariant of the gauge differential voltage group according to the above-described equation (13). Then, the process proceeds to step S204.
In step S204, the out-of-step center voltage calculation unit 102 performs a moving average process on the frequency coefficient _{f C.} Specifically, the step-out center voltage calculation unit 102 performs a moving average process on the frequency coefficient f _C according to the following equation (51). M in the formula (51) is the number of data collection sampling points (moving average length), and the relational expression shown in the following formula (52) is established. Here, f ₁ is a data collection sampling frequency, T ₁ is a data collection sampling period, and T _AVG is a moving average processing time.

  Next, the step-out center voltage calculation unit 102 determines whether or not the symmetry of the gauge differential current group is broken (step S205). That is, the step-out center voltage calculation unit 102 determines whether or not the measured amount of electricity is an appropriate alternating current. One object of determining symmetry breaking is to reduce harmonic components contained in the power system.

  More specifically, the step-out center voltage calculation unit 102 determines the presence / absence of symmetry breaking using the following equation (53). Here, i21, i22 and i23 are differential current instantaneous values.

  When the above equation (53) is satisfied, it can be determined that the symmetry of the gauge differential current group is broken. That is, when it is determined that the symmetry of the gauge differential current group is broken (in the case of YES in step S205), the process of step S206 is executed, and it is determined that the symmetry of the gauge differential current group is not broken. If so (NO in step S205), the process of step S207 is executed.

  In step S206, the step-out center voltage calculation unit 102 latches the previous measurement value without calculating the gauge differential current because it is determined that the symmetry is broken. Then, the process proceeds to step S207.

In step S207, the step-out center voltage calculation unit 102 calculates a gauge differential current. The step-out center voltage calculation unit 102 calculates the gauge differential current _Igd , which is an invariant of the gauge differential current group, according to the above equation (16). Then, the process proceeds to step S207.
In step S207, the step-out center voltage calculation unit 102 performs a moving average process on the gauge differential current _Igd . Specifically, the step-out center voltage calculation unit 102 performs a moving average process on the gauge differential current _Igd according to the following equation (54). Here, M is the number of data collection sampling points (moving average length).

  Next, the step-out center voltage calculation unit 102 determines whether or not the symmetry of the gauge differential power group is broken (step S209). That is, the step-out center voltage calculation unit 102 determines whether or not the measured amount of electricity is an appropriate alternating current. One object of determining symmetry breaking is to reduce harmonic components contained in the power system.

  More specifically, the step-out center voltage calculation unit 102 determines the presence or absence of symmetry breaking using the following equation (55). Here, v21, v22, v23 are differential voltage instantaneous values, and i21, i22, i23 are differential current instantaneous values.

  When the above equation (55) is satisfied, it can be determined that the symmetry of the gauge differential power group is broken. That is, when it is determined that the symmetry of the gauge differential power group is broken (in the case of YES in step S209), the process of step S210 is executed, and it is determined that the symmetry of the gauge differential power group is not broken. If so (NO in step S209), the process of step S211 is executed.

  In step S210, the step-out center voltage calculation unit 102 latches the previous measurement value without calculating the gauge difference active power because it is determined that the symmetry is broken. Then, the process proceeds to step S211.

In step S211, the step-out center voltage calculation unit 102 calculates the gauge difference effective power P _gd . The step-out center voltage calculation unit 102 calculates the gauge difference active power P _gd that is an invariant of the gauge difference power group according to the above-described equation (22). Then, the process proceeds to step S211.
In step S211, the step-out center voltage calculation unit 102 performs a moving average process on the gauge difference active power P _gd . Specifically, the step-out center voltage calculation unit 102 performs a moving average process on the gauge difference active power P _gd according to the following equation (56). Here, M is the number of data collection sampling points (moving average length).

Finally, the step-out center voltage calculation unit 102 uses the gauge difference current I _gd and the gauge difference effective power P _gd obtained by the above-described moving average process, according to the above-described equation (27), calculating the voltage _{V C} (step S212). Then, the process returns to the main flow shown in FIG.
[J. simulation result]
The inventor of the present application verified the estimation accuracy by the step-out prediction algorithm according to the present embodiment using simulation. The simulation result will be described below.

  FIG. 9 is a schematic diagram for explaining a model system used in the simulation. The model system shown in FIG. 9 is “The Institute of Electrical Engineers of Japan EAST 10 machine model”. The Institute of Electrical Engineers of Japan EAST 10 machine model is a simulation test model system composed of 10 generators and a plurality of transformers and transmission lines.

  The power transmission line <11> is a power transmission line operated in parallel with two lines and six phases. The buses at both ends of the power transmission line <11> are (11) and (21). In this simulation, the step-out prediction apparatus according to the present embodiment is arranged at the bus node (11) of this system. Then, a one-phase three-phase ground fault occurs at an intermediate point of the transmission line <11>, and after the failure continues for 80 ms, one-line three-phase of the transmission line <11> operating in parallel trips. Simulation was performed under the scenario. The prerequisites for this simulation are as follows.

・ Power system rated frequency: 50 Hz
Data collection sampling frequency f ₁ : 1200 Hz
・ Gauge sampling frequency f _S : 200Hz
-Moving average length in frequency coefficient calculation: 80 ms
-Moving average length for calculation of various currents: 20 ms
-Moving average length in calculation of active power / reactive power: 20 ms
-Length of step-out prediction calculation data: 80 ms
・ Failure duration: 80 ms
The simulation results obtained by this simulation are shown in FIGS.
(J1. Internal phase angle of generator)
FIG. 10 is a diagram showing temporal changes in the internal phase angle of the generator G1 obtained by simulation. Referring to FIG. 10, generator G1 was stably operated until a failure occurred, but it can be seen that the internal phase angle increases with time after the failure occurs and steps out. .
(J2. Bus voltage instantaneous value)
FIG. 11 is a diagram showing a temporal change in the bus voltage instantaneous value obtained by the simulation. For convenience of explanation, FIG. 11 shows only the time waveform of the A-phase voltage. Although a stable value was measured until the failure occurred, it can be seen that the amplitude and frequency of the voltage change due to the influence of the failure.
(J3. Transmission line current)
FIG. 12 is a diagram illustrating temporal changes in the transmission line current obtained by simulation. For convenience of explanation, FIG. 12 shows only the time waveform of the A-phase current of one line transmission line out of two line transmission lines. It can be seen that a stable value is measured until a failure occurs. After the occurrence of the failure, it can be seen that the transmission line current in the remaining lines is increased because one line and three phases have tripped along with the removal of the trouble. It can also be seen that the amplitude and frequency of the current change due to the influence of the failure.
(J4. Frequency coefficient)
FIG. 13 is a diagram illustrating temporal changes in frequency coefficients obtained by simulation. The frequency coefficient f _C before the occurrence of the failure is calculated according to the following equation (57).

The rotational phase angle α corresponding to the frequency coefficient f _C calculated by the above equation (57) is 90 degrees. Referring to FIG. 13, it can be seen that a stable value is measured until a failure occurs. It can be seen that after the failure occurs, the frequency coefficient f _C generally decreases with time, except before and after failure removal. This means that the rotational phase angle α continuously increases beyond 90 degrees, that is, the power system frequency increases. It is assumed that the fluctuation of the fundamental frequency is relatively small, and the moving average time is 80 ms.
(J5. Power system frequency)
FIG. 14 is a diagram illustrating temporal changes in the power system frequency obtained by simulation. In the out-of-step prediction algorithm according to the present embodiment, the power system frequency is not required for out-of-step prediction, but the time waveform of the power system frequency is shown in FIG. Referring to FIG. 14, it can be seen that a stable value is measured until a failure occurs. It can be seen that the frequency of the power system increases after the failure occurs.
(J6. Gauge differential current)
FIG. 15 is a diagram illustrating a temporal change in the gauge differential current obtained by the simulation. Although not required in the step-out prediction algorithm according to the present embodiment, the temporal change in the current amplitude of the transmission line current is also shown for reference. Referring to FIG. 15, it can be seen that a stable value is measured until a failure occurs. It can be seen that the gauge differential current is fluctuated after the failure occurs. It is assumed that the current change is relatively fast, and the moving average time in the process of calculating the gauge differential current is 20 ms.
(J7. Gauge differential active power)
FIG. 16 is a diagram illustrating a temporal change in gauge differential active power obtained by simulation. Although not required in the step-out prediction algorithm according to the present embodiment, the temporal change of the active power of the transmission line is also shown for reference. Referring to FIG. 16, it can be seen that a stable value is measured until a failure occurs. It can be seen that the gauge differential active power is shaken after the failure occurs. It is assumed that the power change is relatively fast, and the moving average time in the process of calculating the gauge differential effective power is 20 ms.
(J8. Gauge differential reactive power)
FIG. 17 is a diagram illustrating a temporal change in gauge differential reactive power obtained by simulation. Although not required in the step-out prediction algorithm according to the present embodiment, the temporal change of the reactive power of the transmission line is also shown for reference. Referring to FIG. 17, it can be seen that a stable value is measured until a failure occurs. It can be seen that the gauge differential reactive power is upset after the failure occurs. However, in calculation, the sign is inverted between the gauge differential reactive power and the reactive power of the transmission line. It is assumed that the power change is relatively fast, and the moving average time in the process of calculating the gauge differential reactive power is 20 ms.
(J9. Proportional coefficient between active power and reactive power)
FIG. 18 is a diagram illustrating temporal changes in the proportionality coefficient between active power and reactive power obtained by simulation. Referring to FIG. 18, as the step-out progresses in the power system, the proportional coefficient between active power and reactive power decreases with time. As described above, in the present embodiment, the proportional coefficient between the active power and the reactive power is set as the fail safe condition.
(J10. Step-out center voltage and estimated curve)
FIG. 19 is a diagram illustrating temporal changes in the step-out center voltage and the calculation result of the estimated curve obtained by the simulation. FIG. 19 shows, as an example, the primary estimation curve, the secondary estimation curve, and the intersection of the secondary estimation curve and the time axis (estimated step-out point) when 0.3383 s has elapsed since the occurrence of the failure.

As shown in FIG. 19, at a certain point in time, if the primary estimation curve is downward (that is, the primary estimation curve coefficient is negative), it is determined that the step-out is progressing. At this time, the intersection (estimated step-out point) between the secondary estimation curve and the time axis is the point when 0.7208 s has elapsed from the occurrence of the failure, and the step-out estimated time is 0.3825 s (= 0.7208 s− 0.3383 s).
(J11. Step-out estimated time)
FIG. 20 is a diagram illustrating a temporal change in the calculation result of the step-out estimation time obtained by the simulation. Referring to FIG. 20, in this simulation example, the estimated step-out time can be calculated when 0.2508 s has elapsed since the occurrence of the failure.

  According to the temporal change of the internal phase angle of the generator shown in FIG. 10 described above, the internal phase angle of the generator G1 still maintains a small value when 0.2508 s has elapsed since the occurrence of the failure. Therefore, in the general method of calculating the internal phase angle of the generator by integrating the temporal change of the active power and performing the step-out determination, it is determined whether there is a step-out at such an early timing. I can't. That is, according to the step-out prediction algorithm according to the present embodiment, the possibility of step-out can be determined at an early timing immediately after the occurrence of a failure. When it is determined that there is a high possibility of stepping out, it becomes possible to instruct necessary measures in advance.

In addition, it demonstrates that the step-out prediction apparatus according to the present embodiment can cope with a plurality of continuous step-outs. For example, if the second step out occurs for some reason (such as when the circuit breaker of the power transmission line did not work), calculate the second step out estimated time using the above formula, By shutting off the distant grid connection line, a major power outage can be prevented by a chained power line trip.
[K. Other Embodiments]
The configuration illustrated as the above-described embodiment is an example of the configuration of the present invention, and can be combined with another known technique, and a part of the configuration is omitted without departing from the gist of the present invention. It is also possible to change the configuration.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 100 Step out prediction apparatus, 101 Voltage current instantaneous value data input part, 102 Step out center voltage calculation part, 103 Fail safe condition calculation part, 104 Primary estimation curve coefficient calculation part, 105 Step out possibility determination part, 106 Secondary estimation Curve coefficient calculation unit, 107 step-out estimated time calculation unit,
108 calculation information transmission unit, 109 control signal transmission unit, 110 interface, 111 storage unit.

Claims (6)

Acquisition means for acquiring voltage instantaneous value data and current instantaneous value data by sampling at a first sampling frequency from a target power system;
From the voltage instantaneous value data acquired by the acquisition means, four voltage instantaneous voltage points that are extracted in time series are extracted at a second sampling frequency that is smaller than the first sampling frequency and equal to or higher than the frequency of the power system. For the value data, three differential voltage instantaneous value data corresponding to respective differences between two points adjacent in time series are acquired, and the second sampling frequency is obtained from the current instantaneous value data acquired by the acquiring means. Then, difference value acquisition means for acquiring three differential current instantaneous value data corresponding to respective differences between two points adjacent to the time series for the extracted current instantaneous value data of four points continuous in the time series,
The first gauge value is calculated based on the three differential current instantaneous value data, and the three differential voltage instantaneous value data is calculated based on the three differential voltage instantaneous value data and the three differential current instantaneous value data. And calculating a second gauge value indicating active power corresponding to the three differential current instantaneous value data, and based on the three differential voltage instantaneous value data and the three differential current instantaneous value data, First calculation means for calculating a third gauge value indicating reactive power corresponding to the differential voltage instantaneous value data and the three differential current instantaneous value data ;
Second calculation means for calculating a system state value indicating a magnitude of a phase difference between two different points of the power system based on the first gauge value and the second gauge value ;
Based on the temporal change of the system state value, the occurrence of a step-out in the power system is predicted under the condition that the proportionality coefficient between the active power and the reactive power flowing through the power system continuously decreases. A step-out prediction apparatus comprising a prediction means. The prediction means includes
Means for calculating a primary estimation curve obtained by estimating a temporal change of the system state value over a predetermined period as a primary time function;
The step-out prediction apparatus according to claim 1 , further comprising: means for determining whether or not there is a possibility of step-out in the power system based on a sign of a coefficient of the primary estimation curve. The prediction means includes
Means for calculating a secondary estimation curve obtained by estimating a temporal change of the system state value over a predetermined period as a secondary time function;
The step-out prediction apparatus according to claim 2 , further comprising: means for calculating a margin time until step-out based on a temporal change of the secondary estimation curve. Before SL predicting means, only during a period in which the ratio Example coefficient decreases continuously, it calculates the margin time, out-prediction apparatus according to claim 3. The system further comprises a specifying unit that specifies that a disturbance that causes a step-out occurs in a transmission line having the smallest value among the respective margin times calculated for the plurality of transmission lines included in the power system. Item 4. The step-out prediction apparatus according to item 2 or 3 . Acquiring voltage instantaneous value data and current instantaneous value data by sampling at a first sampling frequency from a target power system, and storing the data in storage means;
From the voltage instantaneous value data stored in the storage means, four voltage instants that are consecutive in time series extracted at a second sampling frequency that is smaller than the first sampling frequency and equal to or higher than the frequency of the power system. As to the value data, three differential voltage instantaneous value data corresponding to respective differences between two points adjacent in time series are obtained, and the second sampling frequency is obtained from the current instantaneous value data stored in the storage means. And obtaining three differential current instantaneous value data corresponding to respective differences between two points adjacent to the time series for the extracted four current instantaneous value data continuous in the time series;
Calculating a first gauge value based on the three differential current instantaneous value data ;
Based on the previous SL three differential voltage instantaneous value data and the three differential current instantaneous value data, a second gauge that indicates the effective power corresponding to the three differential voltage instantaneous value data and the three differential current instantaneous value data Calculating a value;
A third gauge value indicating reactive power corresponding to the three differential voltage instantaneous value data and the three differential current instantaneous value data based on the three differential voltage instantaneous value data and the three differential current instantaneous value data Calculating steps,
Calculating a system state value indicating a magnitude of a phase difference between two different points of the power system based on the first gauge value and the second gauge value ;
Based on the temporal change of the system state value, the occurrence of a step-out in the power system is predicted under the condition that the proportionality coefficient between the active power and the reactive power flowing through the power system continuously decreases. And a step- out prediction method.

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