JP3225768B2 - Method and device for correcting AC electric quantity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various devices for performing protection control and the like using an electric quantity composed of a single frequency sine wave alternating current,
For example, the present invention relates to a correction method and a correction device for an AC electric quantity used in a digital protection relay or the like that protects an electric power system by using an electric quantity such as a voltage or a current at a commercial frequency as an input in the power field.

[0002]

2. Description of the Related Art An example of this kind of prior art is described in Japanese Patent Application No. 5-190807 "Analog Amount Measurement Apparatus" by the present applicant. FIG. 3 schematically shows the electric quantity correction device 1 as the above-mentioned prior art.
01 frequency detecting means of the input electrical quantity V _in a digital amount, 102 correction value retrieving means for retrieving the correction value corresponding to the detected frequency value f _x (the amplification gains) E _x from the correction value table 103, 104 input quantity of electricity V _in the correction value E
_This is correction means for obtaining a corrected output electric quantity V _out by multiplying _{x by x} .

Then, an electric quantity such as a vector scalar quantity and impedance is detected from the output electric quantity _Vout, and a protection control operation in a digital protection relay is performed. Incidentally, the above-described conventional art has corrected further added according to the level of an input electrical quantity V _in, but since the portion is not directly related to the present invention, not illustrated and described.

[0004] The above prior art calculates a vector scalar quantity, impedance, and the like of an input electric quantity such as a voltage and a current (in the figure, a case where a voltage is input), and executes protection control. Calculates correction values for various errors caused by the frequency and magnitude of the input electric quantity (various errors caused by frequencies in the instrument transformer, current transformer, filter, and the like (not shown)). In this way, a high-precision protection control is realized by correcting the amplification degree.

[0005]

According to the above-mentioned prior art, if the input electric quantity is a waveform that is stationary and invariable, correction for detecting the electric quantity such as the vector scalar quantity and impedance with high accuracy can be performed. . However, when the input electric quantity suddenly changes and a transient error increases or decreases, a problem arises in correction accuracy and detection accuracy.

In general, the detection error in the frequency detecting means 101 increases remarkably due to a sudden change in the amount of input electric power, and its influence continues mainly during the time according to the time constant of the filter circuit in the protection control device. This means that the effect of correcting the error due to the frequency cannot be expected at the time of the sudden change in the input electric quantity, but rather, the error may be increased. That is, these phenomena appear as problems such as an increase in the detection error of the electric quantity of the protection relay or the like and a delay in the detection response time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. It is an object of the present invention to correct various kinds of electric quantities with high accuracy and high speed even when input electric quantities suddenly change. An object of the present invention is to provide a method for correcting an AC electric quantity which can be detected and a correction device used for the method.

[0008]

In order to achieve the above object, a method of correcting an AC electric quantity according to the present invention detects a frequency of an AC input electric quantity as a digital quantity, and generates a correction value according to this frequency value. in the AC electric quantity correction method for obtaining an output electrical quantity by correcting the input electrical quantity by using a signal when the difference between the frequency value before a predetermined time and the frequency value at the present time exceeds the set value Output and output signal
In this method, the frequency value is latched at a frequency value before a predetermined time over a period longer than the period, and the input electric quantity is corrected using a single correction value corresponding to the frequency value before the predetermined time.

Further, the AC electric quantity correction device for realizing the above-mentioned correction method comprises a frequency detecting means for detecting the frequency of the input electric quantity, and a first means for storing a current frequency value for a predetermined time.
A storage memory; frequency change detection means for outputting a signal when a difference between a current frequency value and a frequency value stored in the first storage memory before a predetermined time exceeds a set value; A timer for outputting a latch signal based on an output signal from the detection means for a longer time than the output signal; and a timer for latching the frequency value stored in the first storage memory while the latch signal is output. A second storage memory to be output, a correction value table storing a correction value corresponding to the frequency value, and a correction for searching for a correction value corresponding to the output frequency value of the second storage memory with reference to the correction value table It is provided with a value searching means and a correcting means for correcting the input electric quantity using the correction value.

The correction value is, for example, an amplification gain for the input electric quantity, and the output electric quantity is calculated by multiplying the input electric quantity and the amplification gain by a multiplying means as a correcting means.

[0011]

In the method for correcting an AC electric quantity according to the first aspect or the correction apparatus according to the third aspect, a frequency value before the input electric quantity is suddenly changed is latched, and a correction value corresponding to the frequency value is latched. The output electric quantity is obtained by correcting the input electric quantity using the above. Thereby, the fluctuation of the frequency that occurs at the time of the sudden change of the input electric quantity does not affect the correction value,
The fluctuation of the output electric quantity is only caused by the time constant of the filter circuit or the like. Therefore, the output electric quantity is stabilized in a short time, and it becomes possible to detect various electric quantities using this output electric quantity with high accuracy and high speed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an electric quantity correction device 2 for realizing the correction method of the present invention. Note that the same components as those in FIG. 3 are denoted by the same reference numerals.

[0013] In FIG 1, the frequency value f _x input electrical quantity V _in outputted from the frequency detecting means 101 is input to the frequency variation detecting means 201 and the first storage memory 202. In the memory 202, the input frequency value is stored for use in comparison with the current frequency value after a predetermined time (referred to as Δt), and at the time of comparison, the stored frequency value is output as f _x ′. I do. Note that the frequency detecting means 10
As the frequency detection method in 1, for example, a sine wave linear approximation period measurement method is used. Said frequency value f _x 'and the detected current frequency value f _x is input to the frequency variation detecting means 201, the amount of change in the absolute value | f _x -f _x' | whether exceeds the set value K Is detected.

[0014] | f _x -f _x '| if exceeds the set value K, the signal "1" is output from the frequency variation detecting means 201,
This signal is input to the off-delay timer 205. The timer 205 has a function of holding an input signal for a fixed time and outputting a latch signal. The first storage memory 202 is connected to a second storage memory 204 via a switch 203. When a latch signal “1” corresponding to an input signal “1” is output from an off-delay timer 205, the switch 203 is opened.

The second storage memory 204 includes a switch 203
When the switch 203 is closed, the same frequency value f _x ′ as that of the first storage memory 202 is stored, but when the switch 203 is opened by the latch signal, the stored data is latched,
It does not change until the next time the switch 203 is closed. The frequency value stored in the second storage memory 204 is output to the correction value search means 102 as f _x ″, and the search means 102 refers to the correction value table 103 and corresponds to the frequency value f _x ″ as in the related art. Find the correction value E _x as the amplifier gain to be outputs.

[0016] The correction value E _x is inputted to the correction means 104, the output electrical quantity V _out after the correction by multiplying the input electrical quantity V _in "is calculated. Then, the output electrical quantity V _out" with Then, an electric quantity such as a vector scalar quantity and impedance is detected for protection control calculation.

Next, a specific operation of the electric quantity correction device 2 will be described with reference to a waveform diagram of FIG. First, the waveform of the input electrical quantity V _in is a sine wave AC waveform, time t
_It is assumed that the amplitude value suddenly changes at ₁ (see FIG. 2A). The output of the frequency detection means 101 by the sudden change is transiently fluctuates, the frequency value that has been detected as f ₁ until it varies up and down (see Fig. 2b).

At time t ₁ , the first storage memory 202
Stores the detection frequency before Δt, that is, f ₁ ,
When the time t ₁ after the current frequency value f _x varies every moment, resulting in a difference between the frequency value f _x and each Δt preceding frequency value (output of the first storage memory 202) f _x 'at each time . Then, the absolute value of the difference | f _x -f _x '| if exceeds the set value K, the time t ₂ after the pulse-like signal "1" is output from the frequency variation detecting means 201 (FIG. 2
c).

The signal "1" is output to the off-delay timer 20
5 is input. As a result, the timer 205 sets the time t
₂ since, from the end of the output pulse of the frequency change amount detecting means 201 until after a predetermined timer time? Td, i.e., for longer than the time which the signal "1" from the frequency change amount detecting means 201 is output, The latch signal “1” is continuously output (see FIG. 2D).

As described above, since the switch 203 is opened when the latch signal “1” is output from the timer 205, the storage frequency f _x ”of the second storage memory 204 is set.
, The contents of the first storage memory 202 at time t ₂ the output of the timer 205 becomes "1", i.e., the time t ₂ -
It is latched by the frequency value at the time of Δt (see FIG. 2e). Therefore, f _x "it is latched by f ₁ in the illustrated example.

The correction value searching unit 102, and outputs the search for one of the correction value E _x corresponding to "constant frequency value f _x as described above from the correction value table 103, the correction unit 104
Calculates an output electrical quantity V _out by using the correction value E _x.

Here, f in FIG. 2 is the same as FIG.
Shows vectors scalar output electrical quantity V _out by, g in FIG. 2 indicates a vector scalar quantity of output electrical quantity V _out "according to the present embodiment. As can be seen from these figures,
They differ in the end time of the transient change period of the vector scalar quantity.

[0023] As a reason, in the prior art, because during the transient period of the output f _x of the frequency detection means 101 for changing the correction value E _x with respect to the input electrical quantity V _in sequential, vector results to Figure 2f scalar The transient period of the quantity is also longer. In contrast, in the present embodiment, since the amplitude of the frequency value of the input electrical quantity V _in it is latched at the previous value, i.e. f ₁ to a sudden change stably the correction value E _x with respect to the input electrical quantity V _in I have. For this reason, the transient change period shown in FIG. 2G is only due to the delay caused by the time constant of the filter circuit output due to the sudden change _in the amplitude of the input electric quantity Vin, and FIG.
Compared to the prior art.

The above-described delay caused by the time constant of the output of the filter circuit is a transient error factor inherent in the prior art shown in FIG. 2F. In Figure 2g, only the conventional (transient change in frequency values for retrieving the correction value E _x) Transient change in frequency in the technical minute no error factor of the length and the change width of the transient period of the vector scalar (change Amount) is suppressed,
As a result, good characteristics can be obtained.

In the above embodiment, the latch signal is obtained by using the off-delay timer 205. Here, it is noted that the timing for releasing the latch signal, in other words, the length of the latch signal is to be determined according to the time constant of the filter circuit that is expected in advance, and in addition to the above-described off-delay timer, For example, an output signal of a monostable timer that is started when the frequency variation exceeds a set value may be used as a latch signal. In the power system, the sudden change in the input electric quantity is mainly due to the sudden change in the amplitude or phase of the electric quantity. Considering that the sudden change in the frequency is small, even if the frequency data is latched for a short period, the actual As a result, immediately after a sudden change in the amount of electricity, more accurate detection of the amount of electricity than in the related art becomes possible.

In the above embodiment, the case where the input amount of electricity is a voltage has been described.
Applicable.

[0027]

As described above, in the method and apparatus for correcting an AC electric quantity according to the present invention, the frequency value before the input electric quantity is suddenly changed is latched, and the correction value corresponding to this frequency value is used. The output electric quantity is obtained by correcting the input electric quantity. For this reason, the fluctuation of the frequency that occurs at the time of a sudden change in the amplitude of the input electric quantity does not affect the correction value, and the output electric quantity is stabilized in a short time. Therefore, it is possible to increase the accuracy and speed of the detection calculation of various electric quantities using the output electric quantity, and to improve the performance of the digital protection relay as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform chart showing the operation of FIG.

FIG. 3 is a block diagram showing a conventional technique.

[Explanation of symbols]

 2 Electricity quantity correction device 101 Frequency detection means 102 Correction value search means 103 Correction value table 104 Correction means 201 Frequency change amount detection means 202 First storage memory 203 Switch 204 Second storage memory 205 Off delay timer

Claims (4)

(57) [Claims] 1. A method for correcting an AC electric quantity by detecting a frequency of an AC input electric quantity as a digital quantity and correcting the input electric quantity by using a correction value corresponding to the frequency value to obtain an output electric quantity. A signal is output when the difference between the current frequency value and the frequency value before a predetermined time exceeds a set value, and the frequency value is changed by a predetermined time for a longer period than the output signal . And correcting the input electric quantity using a single correction value corresponding to the frequency value before the predetermined time. 2. The method according to claim 1, wherein an amplification gain for the input electric quantity is used as a correction value, and the correction value is multiplied by the input electric quantity to obtain an output electric quantity. 3. A correction device for an AC electric quantity which detects a frequency of an AC input electric quantity as a digital quantity and corrects the input electric quantity by using a correction value corresponding to the frequency value to obtain an output electric quantity. A frequency detecting means for detecting a frequency of the input electric quantity; a first storage memory for storing a current frequency value for a certain period of time; and a frequency value for a current time and a frequency stored in the first storage memory for a predetermined period of time. Frequency change detection means for outputting a signal when the difference from the value exceeds a set value, and a timer for outputting a latch signal for a longer time than the output signal based on an output signal from the frequency change detection means And a second storage memory for latching and outputting the frequency value stored in the first storage memory while the latch signal is being output, and storing a correction value corresponding to the frequency value. Correction value table, correction value search means for searching for a correction value corresponding to the output frequency value of the second storage memory with reference to the correction value table, and correcting the input electric quantity using the correction value A correction device for an AC electric quantity, comprising: a correction unit. 4. The AC electric quantity correction device according to claim 3, wherein the correction value is an amplification gain for the input electric quantity, and the correction means is a multiplication means.