JP2016205921A - Signal processing device, signal processing method, and electric power system protection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discriminate an exciting rush current with higher accuracy than before.SOLUTION: In a signal processing device (exciting rush current discrimination device) 100, momentary-value data derived by sampling with a first frequency an input signal that could include a DC component in its fundamental wave component is inputted to an input unit 101. A DC amplitude calculation unit 106 calculates the amplitude of the DC component on the basis of first extracted data at three points that are contiguous in time series, the data being extracted with a second frequency smaller than the first frequency from among the momentary-value data. A fundamental wave amplitude calculation unit 103 calculates the amplitude of the fundamental wave component on the basis of second extracted data at three points that has been obtained by calculating a difference between two adjacent points in the first extracted data at four points that are contiguous in time series. A determination unit 109 determines whether or not the ratio of the amplitude of the DC component to the amplitude of the fundamental wave component exceeds a threshold.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a signal processing device, a signal processing method, and a power system protection device, and is suitably used for, for example, signal processing for the purpose of discriminating excitation inrush current and power system protection using the signal processing. It is.

  The inrush current is a large current that temporarily flows when power is supplied to an electrical device. The inrush current is apparently input to the protection relay device like an accident, and thus causes a malfunction of the protection relay device (the protection relay operates even if it is not an accident). Therefore, it is necessary to distinguish inrush current and accident current.

  For example, Patent Document 1 (Japanese Patent No. 3875575) pays attention to the fact that the inrush current includes many second harmonics, and the ratio of the second harmonic to the fundamental wave included in the alternating current input is greater than or equal to a predetermined value. An inrush current detection element that sometimes determines an inrush current is disclosed. Another example is a transformer protection relay (ratio differential relay). In the transformer protection relay, when the second harmonic content rate is equal to or higher than a predetermined value, a method of determining an excitation inrush current and locking (second harmonic lock method) is generally employed.

  By the way, the inventor of the present application has so far proposed a method of calculating various electric quantities with high accuracy and simpleness by utilizing the symmetry of the alternating voltage current. For example, Patent Document 2 (Japanese Patent No. 5214074) discloses a calculation method using a gauge voltage group and a gauge differential voltage group (the meaning of this term will be described later).

Japanese Patent No. 3875575 Japanese Patent No. 5214074

  The second harmonic content corresponding to excitation inrush currents of energization angles of 60 °, 90 °, and 120 ° can be calculated as 27.5%, 21%, and 9%, respectively. Therefore, for example, when the second harmonic content rate used as the determination threshold is 10%, an excitation inrush current with a conduction angle of 120 ° cannot be detected. As a countermeasure, a method of lowering the determination threshold is conceivable. However, since the fault current also includes a certain amount of second harmonic current, it becomes difficult to distinguish the fault current from the inrush current.

  The present invention has been made in consideration of the above-mentioned problems, and one of its purposes is to use an excitation inrush current by using a calculation method using symmetry that has been proposed by the present inventors. It is to provide a new way of determining. This makes it possible to determine the magnetizing inrush current with higher accuracy than in the past. The new determination method proposed below can be applied to other than the inrush current.

  The present invention is a signal processing device, and includes an input unit, a direct current amplitude calculation unit, a fundamental wave amplitude calculation unit, and a determination unit. Instantaneous value data obtained by sampling an input signal that can include a direct current component in the fundamental wave component at the first frequency is input to the input unit. The DC amplitude calculation unit calculates the amplitude of the DC component based on the first extracted data of three points continuous in time series extracted from the instantaneous value data at the second frequency smaller than the first frequency. To do. The fundamental wave amplitude calculating unit is based on the second extracted data of three consecutive points obtained by calculating the difference between two adjacent points of the first extracted data of the four consecutive points in time series. Calculate the amplitude of the fundamental wave component. The determination unit determines whether the ratio of the amplitude of the direct current component to the amplitude of the fundamental wave component exceeds a threshold value.

  According to the present invention, excitation rushing is performed with higher accuracy than before by using a method different from the conventional method using the first extracted data (instantaneous value of the gauge current group) and the second extracted data (instantaneous value of the gauge differential current group). The current can be determined.

It is a figure which shows the gauge difference electric current group on a complex plane. It is a figure which shows a gauge current group in the case of having a direct-current component on a complex plane. It is a conceptual diagram of gauge sampling frequency selection. It is a block diagram which shows the functional structure of an excitation inrush current discrimination device. It is a flowchart which shows the procedure which discriminate | determines a magnetizing inrush current. It is the figure which showed the parameter of the magnetizing inrush current discrimination device in a tabular form. FIG. 4 is a diagram showing an instantaneous current value waveform in case 1. 6 is a current rotation vector diagram on a complex plane in case 1. FIG. It is a figure which shows the sine wave instantaneous value waveform in case 1, a fundamental wave amplitude, and a direct-current amplitude measurement result. The calculation result of the Fourier coefficient when the conduction angle (α in Equation 18) is 60 degrees, 90 degrees, and 120 degrees is shown. It is a figure which shows the magnetizing inrush current instantaneous value waveform in case 2 (energization angle 60 degree | times). It is an excitation inrush current rotation vector figure on the complex plane in case 2 (energization angle 60 degrees). It is a figure which shows the magnetizing inrush current instantaneous value waveform in Case 3 (energization angle 90 degree | times). It is an excitation inrush current rotation vector figure on the complex plane in case 3 (energization angle 90 degrees). It is a figure which shows the magnetizing inrush current instantaneous value waveform in case 4 (energization angle 120 degree | times). It is an excitation inrush current rotation vector figure on the complex plane in case 4 (energization angle 120 degrees). It is a figure which shows the fundamental wave amplitude and DC amplitude measurement result in case 2 (energization angle 60 degree | times). It is a figure which shows the fundamental wave amplitude and DC amplitude measurement result in case 3 (energization angle 90 degree | times). It is a figure which shows the fundamental wave amplitude and direct current | flow amplitude measurement result in case 4 (electric conduction angle 120 degree | times). FIG. 6 is a diagram showing a measurement result of a direct current amplitude ratio in case 2. FIG. 6 is a diagram showing a measurement result of a direct current amplitude ratio in case 3. FIG. 6 is a diagram showing a measurement result of a DC amplitude ratio in case 4. It is a block diagram which shows the structure of an electric power system protection apparatus.

  Hereinafter, embodiments will be described in detail with reference to the drawings. In the following embodiments, Definition of terms, 2. 2. Arrangement of calculation formulas of group theory method and explanation of algorithm. 3. Configuration diagram of excitation inrush current discriminating device 4. Flow chart of excitation inrush current discrimination calculation 5. Simulation result of excitation inrush current 6. Application example to protection relay device 7. Other application examples This will be explained in the order of summarization. In the following description, the same or corresponding parts are denoted by the same reference numerals, and the description thereof may not be repeated.

[1. Definition of terms]
First, terms used in this specification will be described.

(1) Exciting inrush current When a current is applied to a transformer or the like, a significantly large exciting current (non-sinusoidal wave) may flow. This large current is called the magnetizing inrush current.

(2) Energization angle In the excitation inrush current waveform, the time zone width during which current flows in the rated 1 period is expressed in electrical angle. The greater the energization angle, the greater the time zone width during which current flows.

(3) group theory
Includes mathematical theories to study symmetry.

(4) Symmetry group
A group composed of a plurality of complex vectors having symmetry rotating on the complex plane. A group composed of a plurality of complex vectors having symmetry that is stationary on the complex plane is included.

(5) Data collecting rate
This is a sampling frequency at the time of data collection, and is also referred to as a first frequency. Higher accuracy is better. Data collected at the sampling frequency is referred to as instantaneous value data. In this specification, the data collection sampling frequency is represented by f ₁ and the data collection sampling period is represented by T ₁ . There is a relationship of T ₁ = 1 / f ₁ . In application to an actual protection relay device, it is necessary to select an appropriate data collection sampling frequency in consideration of hardware (H / W) limitations and data synchronization requests in a plurality of channels. In general, Japanese protective relay devices use sampling at an electrical angle of 30 degrees or sampling at 15 degrees. In this specification, sampling at an electrical angle of 15 degrees (in a power system with a rated frequency of 50 Hz, the data collection sampling frequency is 1200 Hz) is used.

(6) Gauge sampling frequency
This is a sampling frequency used for calculation of the gauge symmetry group, and is also referred to as a second frequency. The gauge sampling frequency is smaller than the data collection sampling frequency. The gauge sampling frequency is expressed by a symbol f _g and its unit is hertz (Hz). When representing the data sampling period at T _g, a relationship of T _g = 1 / f _g.

(7) means a symmetric group constituted by three current rotation vector continuous in a time series with the time interval of the gauge current group together T _g. The measured current instantaneous value corresponds to the real part of the current rotation vector, and the unit of current is ampere (A). As described below, the present application uses a gauge current group having a DC component. The magnitude of the DC component is referred to as DC amplitude.

(8) means a symmetric group constituted by three differential current rotation vector continuous in a time series with the time interval of the gauge differential current group together T _g. Here, the differential current rotation vector refers to a difference between adjacent current rotation vectors having a time interval Tg constituting a gauge current group. Although not used in this specification, a gauge voltage group and a gauge differential voltage group can be defined in the same manner as described above by using a voltage rotation vector that rotates on a complex plane.

(9) Invariant
Invariants are the properties of systems that a symmetric group has that does not change under certain transformations. Invariants assumed in the present embodiment include, but are not limited to, a gauge rotation phase angle, a frequency coefficient, a gauge differential current, and the like. If the invariants are known, the characteristics of the symmetric group can also be known.

(10) Gauge rotation phase angle The rotation vector rotating on the complex plane means the angle (electrical angle) actually rotated in the gauge sampling period, and is expressed by the symbol α.

(11) System nominal frequency
It means the rated frequency in the electric power system and is expressed by the symbol f ₀ and is typically 50 Hz or 60 Hz.

(12) Frequency coefficient This means the cosine function value of the gauge rotation phase angle α, and is expressed by the symbol f _C. That is, f _C = cos (α).

(13) the fundamental wave instantaneous amplitude one gauge differential current group (i.e., three differential current rotation vector continuous in a time series with the time interval T _g of each other) a fundamental wave amplitude calculated by.

(14) Fundamental wave amplitude average value This is a value obtained by performing time moving average processing of the fundamental wave amplitude instantaneous value.

(15) DC amplitude instantaneous value A DC amplitude calculated by one gauge current group having a DC component (that is, a current rotation vector having three DC components consecutive in a time series having a time interval of T _g from each other). .

(16) DC amplitude average value A value obtained by performing time moving average of DC amplitude instantaneous values.

(17) DC amplitude ratio The DC amplitude average value is obtained by dividing the DC amplitude average value by the fundamental wave amplitude average value, and is an index used to determine the excitation inrush current.

(18) Exciting inrush current threshold This is the threshold value for determining the DC amplitude ratio proposed in this specification.

[2. Arrangement of calculation formulas of group theory method and explanation of algorithm]
First, with reference to FIG. 1 to FIG. 3, various calculation formulas used for determining the inrush current will be described.

(2.1 Calculation of fundamental current amplitude)
FIG. 1 is a diagram showing a gauge differential current group on a complex plane. As shown in FIG. 1, each of the differential current rotation vectors i ₂ (t), i ₂ (t−T _g ), and i ₂ (t−2T _g ) has a time interval of T _g on the complex plane. Defined as the difference in current rotation vector. The gauge differential current group is a differential current rotation vector that is continuous in three time series, and is assumed to be expressed by the following equation.

Here, I is the alternating current amplitude, ω is the rotational angular velocity, T _g is the gauge sampling period, and α is the rotational phase angle at T _g .

The instantaneous values (differential current instantaneous values) of the differential current rotation vectors i ₂ (t), i ₂ (t−T _g ), i ₂ (t−2T _g ) constituting the gauge differential current group are respectively i ₂₁ , i ₂₂ and i ₂₃ . These differential current instantaneous values i ₂₁ , i ₂₂ , and i ₂₃ are expressed by the following equations.

Using the instantaneous value of this gauge differential current group, the gauge differential current I _gd represented by the following equation can be calculated.

Here, α is called a gauge rotation phase angle. The gauge differential current I _gd is an invariable amount of the gauge differential current group (that is, an amount that does not depend on time and does not change according to the rotation of the current rotation vector).

In this specification, to simplify the problem, it is assumed that the fundamental frequency is constant while the magnetizing inrush current is occurring. For example, the fundamental frequency is assumed to be equal to the rated frequency f ₀ of the power system, and is referred to as a known value. Using the symmetry, the gauge rotation phase angle α can be expressed as follows using the gauge sampling frequency f _g and the power system rated frequency f ₀ . Further, a frequency coefficient f _C that is a cosine function value of the gauge rotation phase angle α is defined as follows.

  By using the above equations (3) and (5), the fundamental current amplitude I can be calculated as follows.

The gauge differential current I _{gd in} the above formula (6) can be calculated using time-series current instantaneous value data (see formula (3)), and the frequency coefficient f _C (cosine function value of the gauge rotation phase angle α) is Can be set in advance. That is, the fundamental wave current amplitude I can be calculated using time-series current instantaneous value data and the frequency coefficient f _C which is a pre-settling value.

(2.2 Calculation of DC amplitude)
FIG. 2 is a diagram showing a group of gauge currents when a DC component is present on the complex plane. In FIG. 2, the gauge current group includes three current rotation vectors i ₁ (t), i ₁ (t−T _g ), i ₁ (t−2T _g ) having a time interval of T _g on the complex plane. Is defined as The instantaneous values i ₁₁ , i ₁₂ , i ₁₃ of the current rotation vectors i ₁ (t), i ₁ (t−T _g ), i ₁ (t−2T _g ) are expressed by the following equations.

Here, I is the alternating current amplitude, ω is the rotational angular velocity, and α is the rotational phase angle. By using the above equations (5) and (7), the DC amplitude I _DC is calculated as follows.

The frequency coefficient f _C (the cosine function value of the gauge rotation phase angle α) in the above equation (8) can be set in advance. That is, the DC amplitude I _DC can be calculated using time-series current instantaneous value data and the frequency coefficient f _C which is a pre-settling value.

Thus, based on the symmetry group when the fundamental wave is a sine wave, the calculation formula of the direct current amplitude and the calculation formula of the fundamental wave amplitude necessary for discriminating the magnetizing inrush current are shown. The calculation method is summarized as follows. First, instantaneous value data obtained by sampling an input signal that can include a direct current component in a fundamental wave component at a first frequency (data collection sampling frequency f ₁ ) is input. Next, the first three consecutive points in time series extracted from the instantaneous value data at the second frequency (gauge sampling frequency f _g ) smaller than the first frequency (data collection sampling frequency f ₁ ). Based on the extracted data (ie, instantaneous values i ₁₁ , i ₁₂ , i _{13 of} the gauge current group), the amplitude I _{DC of the} DC component is calculated. Further, the second extracted data of three consecutive points obtained by calculating the difference between two adjacent points of the first extracted data of the four consecutive points in time series (that is, the instantaneous value of the gauge differential current group) Based on the values i ₂₁ , i ₂₂ , i ₂₃ ), the amplitude I of the fundamental wave component is calculated.

(2.3 selection of the gauge sampling frequency f _g)
FIG. 3 is a conceptual diagram of gauge sampling frequency selection. Referring to FIG. 3, in general, the magnetizing inrush current is a non-sinusoidal wave having a fundamental wave, a DC component, and many even-order waves. However, when observing the waveform of a simulation described later, it can be said that a certain symmetry exists also for a non-sinusoidal wave such as a magnetizing inrush current.

In order to find the symmetry, it is important to select an appropriate gauge sampling frequency f _g . As the larger gauge sampling period T _g (that is, smaller gauge sampling frequency) is selected, it is expected that the influence of harmonics of each order is reduced. However, if the scale is too large, there is a problem that the startup time of the magnetizing inrush current discriminating apparatus and the time until the inrush current is discriminated are delayed. Therefore, it is necessary to select an appropriate value as a gauge sampling period T _g.

For example, FIG. 3 shows a selection of T _g = 4 × T ₁ . Here, T _g is a gauge sampling period, and T ₁ is a data collection sampling period. When a sine wave is assumed as the fundamental wave, the gauge rotation phase angle α is not limited to less than 180 degrees (may be 180 degrees or more).

In practice, several gauge sampling frequencies f _g are selected in advance, a comparison simulation is performed, an appropriate one is selected as the gauge sampling frequency f _g , and used in the magnetizing inrush current discriminating apparatus. In the following simulation, 150 Hz was selected as the gauge sampling frequency f _g . Of course, other gauge sampling frequencies that can find the symmetry of the excitation inrush current may be selected. In this way, by selecting an appropriate gauge space at the pre-design stage, the influence of the harmonic component of the excitation inrush current is reduced, and the stable equivalent fundamental amplitude and stable equivalent DC amplitude component are measured. It becomes possible to do. Since there are two types of power system rated frequencies of 50 Hz and 60 Hz, a gauge sampling frequency is selected for each rated frequency.

(2.4 Outline of algorithm)
In general, the magnitude of each frequency component of the magnetizing inrush current is in the order of fundamental wave, DC component, and second harmonic. In view of this point, the algorithm of the present specification detects the magnetizing inrush current at a high speed by detecting the ratio between the direct current component and the fundamental wave component at a high speed.

  Specifically, the fundamental wave amplitude is calculated using the instantaneous value of the gauge differential current group (see the above equation (6)), and the DC amplitude is calculated using the instantaneous value of the gauge current group (the above equation). (See (8)). If the ratio of the DC component (time moving average value) to the fundamental wave amplitude (time moving average value) is equal to or greater than a predetermined threshold value, it is determined that the excitation inrush current is included in the input signal. . As is clear from the above description, the calculation of the fundamental wave amplitude using the gauge differential current group is not affected by the DC component. Furthermore, the calculation of the DC amplitude using the gauge current group is not affected by the fundamental wave component. Therefore, according to this algorithm, it is possible to accurately determine the magnetizing inrush current to some extent.

  However, the magnetizing inrush current includes various harmonic components including the second harmonic in addition to the fundamental wave and the direct current component. In the above calculation, these harmonic components are ignored. Therefore, the measurement results of the fundamental wave amplitude and the direct current amplitude by this algorithm are approximate values corresponding to a certain scale, and are different from the fundamental wave amplitude and the direct current amplitude (true value) calculated by the fast Fourier transform (FFT). However, it is possible to determine the magnetizing inrush current with sufficient accuracy in practical use.

[3. Configuration diagram of magnetizing inrush current discrimination device]
FIG. 4 is a block diagram showing a functional configuration of the magnetizing inrush current discriminating apparatus. The magnetizing inrush current discriminating device 100 is configured based on a known digital protection relay device in hardware. The digital protection relay device includes, for example, an input converter, an A / D (Analog to Digital) converter, an arithmetic processing unit, and an input / output unit.

  The input converter receives an instantaneous current value detected by a current transformer (CT) installed on the line 11 of the power system 10. The A / D converter converts the input current instantaneous value into digital instantaneous value data. The arithmetic processing unit is a computer including a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory).

  From a functional viewpoint, as shown in FIG. 4, the magnetizing inrush current discriminating apparatus 100 includes an instantaneous value data input means 101, a gauge differential current group symmetry breaking discriminating means 102, a fundamental wave amplitude calculating means 103, a fundamental wave amplitude and a direct current. Amplitude latch means 104 and fundamental wave amplitude moving average means 105 are included. Further, the excitation inrush current discriminating apparatus 100 includes a DC amplitude calculation means 106, a DC amplitude moving average means 107, a DC amplitude ratio calculation means 108, an excitation inrush current discrimination means 109, a calculation information transmission means 110, an interface 111, and a storage means 112. including.

  The interface 111 corresponds to an input / output unit of the digital protection relay device, and inputs / outputs digital signals to / from the outside. The storage unit 112 corresponds to the RAM and ROM of the arithmetic processing unit of the digital protection relay device. The storage unit 112 stores time-series current instantaneous value data input to the current instantaneous value data input unit 101.

  The other components 101 to 110 in FIG. 4 are realized by executing a program by the CPU of the arithmetic processing unit of the digital protection relay device. The function of these components will be described next with reference to the flowchart of FIG.

[4. Excitation inrush current discrimination calculation flowchart]
FIG. 5 is a flowchart showing a procedure for determining the magnetizing inrush current. Referring to FIG. 5, first, in step S101, the current instantaneous value data input means 101 is a current obtained by sampling the current instantaneous value detected by a current transformer (CT) at a data collection sampling frequency f _1. Receives input of instantaneous value data.

In the next step S102, the gauge differential current group symmetry breaking determination means 102 determines whether or not the gauge differential current symmetry index I _BRK is greater than zero. That is, it is determined whether or not the following expression (9) is satisfied.

The gauge difference current group symmetry breaking determination unit 102 proceeds to the next step S103 when the above equation (9) is satisfied. If the gauge difference current group symmetry breaking discriminating means 102 does not satisfy the above equation (9), the gauge difference current I _gd in equation (3) is 0 or there is no real solution. In this case, the gauge difference current group symmetry breaking determination unit 102 determines that the symmetry is broken and advances the process to step S105.

In step S103, the fundamental wave amplitude calculating unit 103 calculates an instantaneous value of the fundamental wave amplitude I using the above-described equation (6). Since the absolute value of the frequency coefficient f _C is smaller than 1 and the gauge differential current I _gd is always larger than zero, it can be seen that the fundamental wave amplitude I is always a positive number. When only the fundamental wave is input in step S101, the fundamental wave amplitude I calculated by the equation (6) coincides with the analytical solution of the AC amplitude and becomes a constant value. When the fluctuating DC component and the harmonic component are included, the calculated fundamental wave amplitude I is approximate.

In the next step S104, the DC amplitude calculating unit 106 calculates the instantaneous value of the DC amplitude I _DC using Equation (8) described above. The frequency coefficient f _C in equation (8) is given as a set value in advance. For example, in the simulation case described later in this specification, since the power system rated frequency f ₀ is 50 Hz and the gauge sampling frequency f _g is 150 Hz, the frequency coefficient f _C is calculated as follows.

According to Equation (8), the instantaneous value of the DC amplitude I _DC can be positive or negative. After calculating the instantaneous value and the instantaneous value of the DC amplitude I _DC of the fundamental wave amplitude I, the process proceeds to step S106.

If the gauge differential current symmetry index I _BRK is zero or less in step S102 described above (NO in step S102), the calculation of the instantaneous value of the fundamental wave amplitude I (step S103) and calculation of the instantaneous value of the DC amplitude I _DC (Step S104) is not executed. In this case, in step S105, the fundamental wave amplitude and the DC amplitude latch means 104 is used directly as the value of the current step by latching the instantaneous value and the instantaneous value of the DC amplitude I _DC of the fundamental wave amplitude I in the preceding step . That is,
I (t) = I (t−T ₁ ), I _DC = I _DC (t−T ₁ ) (11)
The following relational expression holds. By the above processing, the instantaneous value of the instantaneous value and the DC amplitude I _DC of most recently successfully computed the fundamental wave amplitude I is used as a value at the current step. That is, since the fundamental wave amplitude and the DC amplitude when the gauge differential current symmetry index I _BRK is less than or equal to zero are not used in subsequent steps, the influence of harmonics can be reduced. Thereafter, the process proceeds to step S106.

  In step S106, the fundamental wave amplitude moving average means 105 performs a time moving average of the fundamental wave amplitude I. The fundamental amplitude average value is given by the following equation.

Here, M is the number of points used in the time moving average process. This time moving average can further reduce the influence of higher harmonics.

In the next step S107, the DC amplitude moving average means 107 performs a time moving average of the DC amplitude _IDC . The DC amplitude average value is given by the following equation.

Here, M is the number of points used in the time moving average process. This time moving average can reduce the influence of harmonics. There are two types of exciting inrush currents, positive and negative. Since the fundamental wave amplitude average value must always be a positive number for both positive waves and negative waves, the absolute value of the calculated DC amplitude average value (negative number) is taken in the case of a negative wave. This ensures that the DC amplitude ratio calculated next is always a positive number.

  In the next step S108, the DC amplitude ratio calculation means 108 calculates a DC amplitude ratio. The DC amplitude ratio is a ratio of the DC amplitude average value to the fundamental wave amplitude average value, and is calculated by the following equation.

In the next step S109, the excitation inrush current discriminating means 109 determines that the DC amplitude ratio ΔI _DC (t) exceeds the excitation inrush current threshold ΔI _DCSET , that is,
ΔI _DC (t)> ΔI _DCSET (15)
When satisfying, it is determined that the magnetizing inrush current is included in the input current. When the above equation (15) is not satisfied, the magnetizing inrush current determining unit 109 determines that the magnetizing inrush current is not included in the input current.

  In the next step S110, the calculation information transmission unit 110 transmits the calculation information (the determination result of the magnetizing inrush current determination unit). For example, when the above equation (15) is satisfied, the calculation information transmission unit 110 outputs a signal for locking the differential protection unit of the transformer, and prevents the protection relay from malfunctioning.

In the next step S111, the magnetizing inrush current discriminating apparatus 100 determines that the discriminating process has ended when, for example, an input to end the process is received from the user (YES in step S111), and ends the process. Otherwise, the procedure of the above step S101 is repeated for each data collection sampling period T _1.

[5. Simulation result of excitation inrush current]
Hereinafter, the effectiveness of the above-described excitation inrush current determination means will be demonstrated by showing numerical simulation results.

(5.1 Case 1: Sine wave input)
First, it was confirmed that no malfunction occurred when the input current was a sine wave.

FIG. 6 is a table showing parameters of the inrush current discrimination device in a table format. Current input data i (t) and its real part (measured instantaneous value) i _re (t) and imaginary part i _im (t) in case 1 are given by the following equations.

Hereinafter, the simulation result of Case 1 will be described.
FIG. 7 is a diagram showing an instantaneous current value waveform in case 1. FIG. As shown in FIG. 7, in case 1, an instantaneous current value waveform consisting only of the fundamental wave is input.

  FIG. 8 is a current rotation vector diagram on the complex plane in Case 1. As shown in FIG. 8, it can be seen that the motion trajectory of the current rotation vector vertex consisting only of the fundamental wave is a circle whose center is the origin of the complex plane.

  FIG. 9 is a diagram showing the sine wave instantaneous value waveform, the fundamental wave amplitude, and the DC amplitude measurement result in Case 1. FIG. In FIG. 9, the current instantaneous value waveform A is a sine wave. The calculated value (the average value is the same) of the fundamental wave amplitude instantaneous value B matches the theoretical value of the amplitude of the input sine wave. The calculated value (the average value is the same) of the DC amplitude instantaneous value C is zero. Therefore, since the DC amplitude ratio is also zero, it is determined that the magnetizing inrush current is not included in the input current.

(5.2 Cases 2 to 4: including excitation inrush current)
Next, it was confirmed that a correct discrimination can be made in the case of an inrush current. In the following, first, the theoretical formula of the excitation inrush current waveform will be described. In general, the magnetizing inrush current i _inrush (t) in a steady state can be expressed by the following equation.

In the above equation, f is the power system frequency, α is the conduction angle, and k is the excitation inrush current peak value coefficient. The current input data i (t) and its real part (measured instantaneous value) i _re (t) and imaginary part i _im (t) are obtained as follows by expanding the above equation (18) by Fourier series. Can do. However, the excitation inrush current peak value coefficient k is 1, and the real part and the imaginary part are represented up to N = 9 harmonics.

Here, coefficient a _n of Fourier series can be determined by the Fourier transform of equation (18).

FIG. 10 shows the calculation result of the Fourier coefficient when the conduction angle (α in Expression 18) is 60 degrees, 90 degrees, and 120 degrees. In the simulation, Case 2 has a conduction angle of 60 degrees, Case 3 has a conduction angle of 90 degrees, and Case 4 has a conduction angle of 120 degrees. In the simulation, the symmetry principle described so far was applied on the assumption that the real value i _re (t) of the excitation inrush current in the above equation is the measured instantaneous value and corresponds to the real part of the rotational current vector. Hereinafter, simulation results of Case 2 to Case 4 will be described.

  First, with reference to FIGS. 11 to 16, the instantaneous value of the magnetizing inrush current and the magnetizing inrush current rotation vector on the complex plane in cases 2 to 4 will be described.

  FIG. 11 is a diagram showing the instantaneous waveform of the magnetizing inrush current in Case 2 (energization angle 60 degrees). FIG. 12 is an excitation inrush current rotation vector diagram on the complex plane in case 2 (energization angle 60 degrees). FIG. 13 is a diagram showing an excitation inrush current instantaneous value waveform in Case 3 (energization angle 90 degrees). FIG. 14 is an excitation inrush current rotation vector diagram on the complex plane in case 3 (energization angle 90 degrees). FIG. 15 is a diagram showing an excitation inrush current instantaneous value waveform in case 4 (conduction angle of 120 degrees). FIG. 16 is an excitation inrush current rotation vector diagram on the complex plane in Case 4 (conduction angle 120 degrees).

  11 to 16 as a whole, it can be seen that symmetry also exists in the magnetizing inrush current. Note that the magnetizing inrush current flows only when energized. The larger the energization angle, the longer the energization time. According to the Fourier analysis of such a waveform, there are many DC components and even harmonics in addition to the fundamental wave. For this reason, in the existing magnetizing inrush current discriminating device, the second harmonic lock method is mainstream.

  Next, the fundamental wave amplitude and DC amplitude measurement results of cases 2 to 4 will be described with reference to FIGS.

  FIG. 17 is a diagram showing the fundamental wave amplitude and DC amplitude measurement results in Case 2 (60 ° conduction angle). FIG. 18 is a diagram showing measurement results of fundamental wave amplitude and DC amplitude in Case 3 (conduction angle of 90 degrees). FIG. 19 is a diagram showing fundamental wave amplitude and DC amplitude measurement results in Case 4 (conduction angle of 120 degrees). In FIGS. 17 to 19, graph A shows the fundamental wave amplitude instantaneous value, graph B shows the DC amplitude instantaneous value, graph C shows the fundamental amplitude average value, and graph D shows the DC amplitude average value.

  17 to 19 as a whole, it can be seen that the fundamental wave amplitude instantaneous value and the DC amplitude instantaneous value have symmetry. Therefore, it can be said that the symmetry of the excitation inrush current has been successfully found by the symmetry measuring method described so far.

  In each case, the start cycle time (20 ms) is the data accumulation time of the magnetizing inrush current. Thereafter, it can be seen that the fundamental wave amplitude and the DC amplitude fluctuate periodically. By performing the time moving average process, the fundamental wave amplitude and the DC amplitude became constant values. As described above, it was confirmed that the influence of the harmonic component was greatly reduced in the measurement of the fundamental wave amplitude and the direct current amplitude. The reason is considered as follows.

  In the above calculation, since the gauge sampling frequency is 150 Hz (that is, the gauge rotation phase angle is 120 degrees), only four points of instantaneous value data are used in one cycle of the fundamental wave. For this reason, it is considered that the fluctuation of harmonics was absorbed on a large scale, and the stable fundamental wave amplitude and DC amplitude could be calculated.

  It is also possible to further expand the scale and further reduce the influence of harmonic components. However, since the startup time of the apparatus is also an important parameter, a detailed comparison calculation is required to determine its validity. On the other hand, when it is desired to start at a higher speed, it is conceivable to increase the gauge sampling frequency, that is, to reduce the gauge rotation phase angle. However, the influence of harmonics becomes large on the measurement of the fundamental wave amplitude and the DC amplitude, and the measurement value becomes unstable. Therefore, a detailed comparison calculation is also required when judging the appropriateness of the reduction of the gauge scale.

  In addition, the above measurement results are different from true values (frequency components calculated by performing fast Fourier transform), and fundamental wave amplitudes and direct currents measured in a defined gauge space (selected gauge sampling frequency). Note that it is an approximation of the amplitude.

  Next, the measurement results of the DC amplitude ratio in cases 2 to 4 will be described with reference to FIGS.

  FIG. 20 is a diagram illustrating a measurement result of the DC amplitude ratio in Case 2. In FIG. FIG. 21 is a diagram showing the measurement result of the DC amplitude ratio in Case 3. FIG. 22 is a diagram showing the measurement result of the DC amplitude ratio in Case 4.

  As shown in FIGS. 20 to 22, in each case, a stable DC amplitude ratio is obtained after 20 msec when data accumulation is completed. Here, the excitation inrush current discrimination threshold is 30%. Therefore, in each case, it can be normally determined that the input current is a magnetizing inrush current. Therefore, according to the method for discriminating the magnetizing inrush current proposed in this specification, it has been proved that it is possible to discriminate that the magnetizing inrush current is included in the input current at high speed and with high accuracy. In addition, since the data collection sampling frequency is 1200 Hz (15 degrees), which is not different from the normal frequency, it is possible to realize a magnetizing inrush current discriminating apparatus at a low cost.

[6. Application example to protection relay device]
Hereinafter, an example in which the method for determining the magnetizing inrush current described so far is applied to a protection relay device will be described.

  FIG. 23 is a block diagram illustrating a configuration of the power system protection device. Referring to FIG. 23, the power system protection device 200 includes a digital protection relay device 210, a high-speed switch 220 inserted in the line 11 of the power system, and a current reducer 222 connected in parallel with the high-speed switch 220. including.

  The digital protection relay device 210 includes a protection calculation unit 212 and an excitation inrush current determination unit 100. The protection calculation unit 212 performs, for example, a current differential relay calculation based on the input from the current transformer CT. The protection calculation unit 212 outputs a signal for turning off the circuit breaker 230 when the failure of the power system is determined by the current differential relay calculation.

  The magnetizing inrush current discriminating unit 100 discriminates the magnetizing inrush current according to the procedure described with reference to FIGS. 4 and 5 based on the input from the current transformer CT. When it is determined that the magnetizing inrush current is included in the current detected by the current transformer CT, the magnetizing inrush current determining unit 100 outputs a signal for turning off the high-speed switch 220. As a result, the path of the alternating current flowing through the line 11 is switched to the path passing through the current reducer 222, so that the magnetizing inrush current can be suppressed and the malfunction of the protection calculation unit 212 can be prevented.

  Since the generation of the magnetizing inrush current is temporary, when the magnetizing inrush current is not included, the magnetizing inrush current discriminating unit 100 switches the high-speed switch 220 on again. Therefore, according to the said structure, there exists a merit that it is not necessary to lock a protection calculating part like the conventional relay apparatus. Of course, as in the prior art, the magnetizing inrush current discriminating unit 100 may be configured to lock the protection arithmetic unit 212 when the magnetizing inrush current is discriminated.

[7. Other application examples]
The discrimination method described in this embodiment is not limited to the discrimination of the transformer inrush current. For example, it can be used to determine whether or not a current transformer (CT) is saturated. Furthermore, it can be used to determine the occurrence of a zero transition phenomenon in the power cable.

  Furthermore, the method of this embodiment can be used not only for current signals but also for voltage signals. More generally, it can be used for the purpose of determining at high speed whether or not a DC component is included in an input signal mainly composed of a fundamental wave component.

[8. Summary]
The following is a summary of the above explanation. First, according to the present embodiment, it has been possible to show that the group-theoretic calculation method proposed by the present inventor can be applied to the calculation of a non-sinusoidal wave including a DC component (for example, excitation inrush current). .

  Second, it has been shown that the influence of harmonic components can be reduced by selecting an appropriate gauge sampling frequency (scale), whereby the fundamental wave amplitude and the DC amplitude can be calculated at high speed. Note that as the ratio of harmonic components increases, the gauge sampling frequency needs to be set smaller (that is, the gauge sampling period is increased).

  Thirdly, the effectiveness of the proposed algorithm could be verified by simulation of instantaneous values. Case 1 is a case of a sine wave, and cases 2 to 4 are cases of a magnetizing inrush current. Since the input formula and the calculation formula are clearly shown in the four cases, a third party can immediately confirm the effectiveness of the algorithm by simulation.

  Fourthly, the rotation vector of the magnetizing inrush current on the complex plane could be shown for the first time. As a result, it is possible to intuitively (geometrically) understand that the analysis method using the symmetry principle is effective for the magnetizing inrush current when the DC component and the plurality of harmonic components are included.

  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 10 Electric power system, 11 track | line, 100 Excitation inrush current discrimination apparatus, 101 Current instantaneous value data input means, 102 Gauge differential current group symmetry breaking discrimination means, 103 Fundamental amplitude calculation means, 104 Fundamental amplitude latch means, 105 Fundamental wave Amplitude moving average means, 106 DC amplitude calculating means, 107 DC amplitude moving average means, 108 DC amplitude ratio calculating means, 109 excitation inrush current discriminating means, 110 arithmetic information transmitting means, 200 power system protection device, 210 digital protection relay device, 212 protection calculation unit, 220 high-speed switch, 222 current reducer, 230 circuit breaker, I fundamental wave amplitude, I _BRK gauge differential current symmetry index, I _DC direct current amplitude, _Igd gauge differential current, T ₁ data collection sampling period, T _g gauge sampling period, f ₀ rated frequency, f ₁ data collection sampling frequency, f _C frequency Number coefficient, f _g gauge sampling frequency.

Claims (8)

An input unit to which instantaneous value data obtained by sampling an input signal that may include a direct current component in a fundamental wave component at a first frequency;
DC amplitude for calculating the amplitude of the DC component based on the first extracted data of three points that are continuous in time series extracted from the instantaneous value data at a second frequency smaller than the first frequency. A calculation unit;
Based on the second extracted data of three consecutive points obtained by calculating the difference between two adjacent points of the first extracted data of the four consecutive points in time series, the fundamental wave component A fundamental wave amplitude calculator for calculating amplitude;
A signal processing apparatus comprising: a determination unit configured to determine whether a ratio of an amplitude of the DC component to an amplitude of the fundamental wave component exceeds a threshold value. The input signal includes harmonic components in addition to the DC component,
The signal processing apparatus according to claim 1, wherein the second frequency is set to a smaller value as the proportion of the harmonic component increases.   The signal processing apparatus according to claim 1, wherein the determination unit performs determination using a time moving average value of the amplitude of the fundamental component and a time moving average value of the amplitude of the direct current component. The DC amplitude calculating unit sets the three consecutive extracted first extracted data as i ₁₁ , i ₁₂ , i ₁₃ from the later in time, sets the rated frequency of the fundamental wave component as f _0, and When the frequency of 2 is f _g , the amplitude i _{DC of the} DC component is
According to
The fundamental wave amplitude calculating unit sets the amplitude I of the fundamental wave component as i ₂₁ , i ₂₂ , i ₂₃ from the time point of the second extracted data at three consecutive points.
The signal processing device according to claim 1, wherein the signal processing device is calculated according to: The signal processing apparatus according to claim 4, wherein the determination unit does not use the amplitude of the direct current component and the amplitude of the fundamental component when the value of i ₂₂ ² −i ₂₁ × i ₂₃ is 0 or less for determination. The input signal is an AC current of a power system to which a transformer is connected,
The said discrimination | determination part determines that the excitation inrush current of the said transformer is contained in the said input signal, when the ratio of the amplitude of the said DC component exceeds the said threshold value. 2. The signal processing device according to item 1. A signal processing device according to claim 6;
By performing a protection relay calculation based on the input signal, a protection calculation unit that detects an abnormality in the power system,
The determination unit is a power system protection device that prevents an abnormality from being detected by the protection calculation unit when a ratio of amplitudes of the DC components exceeds the threshold value. Receiving an input of instantaneous value data obtained by sampling an input signal that may include a DC component in a fundamental wave component at a first frequency;
Calculating the amplitude of the direct current component based on three points of first extracted data continuous in time series extracted from the instantaneous value data at a second frequency smaller than the first frequency; ,
Based on the second extracted data of three consecutive points obtained by calculating the difference between two adjacent points with respect to the first extracted data of four consecutive points in time series, the fundamental wave component Calculating the amplitude;
Determining whether the ratio of the amplitude of the direct current component to the amplitude of the fundamental wave component exceeds a threshold value.