JPH0736668B2 - Digital type protective relay - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a digital protective relay, and more particularly to a digital protective relay having a small error over a wide frequency range and improved frequency characteristics.

[Technical background of the invention]

A protective relay is provided to protect the power system,
In this case, it may be necessary to calculate the amplitude value of the input AC amount of the power system to be protected. In this case, in the digital protective relay, the sine wave current or voltage of the power system or both of them are sampled at a predetermined time interval, the sampled value is converted into digital data, encoded, and transmitted. This digital data is used as it is to calculate the amplitude value of the input AC amount. When the amplitude value is calculated from this digital data input, generally, as shown in FIG.
And the digital filter process 2 for attenuating the DC component and the second harmonic component, and then the amplitude value calculation operation 3 is performed. Here, if the sampling frequency is 12 times the input AC frequency, that is, the sampling frequency is 720 Hz for 60 Hz input, the sampling data is i _m , i _m-1 , i _m-2, ... Time series), and the Z conversion is used as the digital filter processing. A filter represented by the following function is used, and as a result, data I _m after digital filtering is obtained. An amplitude value calculation operation for obtaining the amplitude value I _e is, for example, Japanese Patent Publication
54-41513, a rectifying addition method represented by a function of I _e = K ₁ {| I _m | + | I _m-3 || + K ₂ || I _m |-| I _m |}, Or as disclosed in Japanese Patent Laid-Open No. 55-88514 The square method represented by the following function has been conventionally used.

[Problems of background art] Since the above-mentioned conventional system is considered on the premise that the input AC is in the vicinity of the commercial frequency, sufficient accuracy is obtained in terms of performance when the input AC is in the vicinity of the commercial frequency, for example, near 60 Hz. However, the error is large for inputs that are far from the commercial frequency.

Therefore, like a generator protection relay, 20Hz-100Hz
It could not be used for applications where a sufficiently small error is required for the input (when the commercial frequency is 60Hz).

This will be described below. Here, the angular frequency at the commercial frequency is ω ₀ , the angular frequency of the input AC is ω, the amplitude is I, and the time is t. When the sampling cycle is 1/12 of the commercial cycle, the input AC i _m , i _{m- 6} is represented by the following equation (1).

However, R _e {} is an operation that extracts the real part When the digital filter processing of the function is performed, the output I _m is as follows.

That is, the amplitude Becomes a sine wave of. Therefore this Figure 10 shows the gain-frequency characteristics of this function.

here, Then, I _m , I _m-3 , and I _m-6 are given by the following expression (3).

Next, as an amplitude value calculation operation, Considering the case where the square method is used as an example, the following Expression (4) is obtained.

Therefore, the above-described gain of the square method, that is, the ratio of the amplitude I ′ of the input alternating current to the obtained amplitude value I _e is And the gain-frequency characteristic is as shown in the eleventh.

From the above, The digital processing of the function The total gain A in combination with the square method is expressed by the following equation (5), and its gain-frequency characteristic is as shown in FIG.

The amplitude value obtained by the above method represents the amplitude of the input AC when the frequency of the input AC is in the vicinity of the commercial frequency.However, as the frequency moves away from the commercial frequency, the fluctuation range at each frequency is smaller than that at the commercial frequency. , The amplitude will be underestimated.

Next, as another example, Considering the case of the square method expressed as follows, the result is as follows.

I _e ² is t ′, that is, a value between the following two values although it changes depending on the sampling shimming.

Therefore, I _e becomes a value between the following two values (6) and changes with time.

Therefore, the gain-frequency characteristics are as shown in Fig. 13,
Depending on the timing of sampling, it will be any value within the diagonal line.

From the above, The digital filtering of the function The total gain A obtained by combining the above-mentioned square method becomes a value between the gain A1 expressed by the following equation (7) and the gain A2 expressed by the following equation (8), and its gain frequency characteristic is It looks like Figure 14.

That is, the amplitude value obtained by the above-described method represents twice the input AC when the frequency of the input AC is near the commercial frequency, but as the frequency becomes farther from the commercial frequency, the fluctuation range is larger than that at the commercial frequency. Become. Further, even when the rectification and addition method is used as the amplitude value calculation, the variation range of the amplitude value becomes larger as the frequency of the input AC deviates from the commercial frequency, as compared with the case of the commercial frequency.

When a digital protective relay using the above digital filter processing and amplitude value calculation calculation is used for protection of a transmission line or a transformer, etc., the commercial frequency is always input, and therefore it is separated from the commercial frequency. There is no need to consider the increase in the error due to the problem, and this does not pose a problem. However, in protecting the generator, the frequency of the output AC changes depending on the number of revolutions.
Like z, a relay judgment method with the smallest possible error in a wide frequency band, and eventually an amplitude value calculation method, are required.The combination of digital filter processing and amplitude value calculation operation as described above is separated from the commercial frequency. This is a problem because the error is large with respect to the input.

[Object of the Invention]

The present invention has been made to solve the above problems, and an object thereof is to provide a digital protective relay having a small error in a wide frequency band including a commercial frequency.

[Outline of Invention]

The present invention has a frequency characteristic that the gain increases when the input AC signal deviates from the commercial cycle when the sampling cycle is 1 / 4n (where n is a natural number) of the commercial cycle, and by the Z conversion. (Where K and k are constants | k | <1) or when the digital filter of the function expressed by an approximate expression and the data after digital filtering are I _m (m is a sampling time series),
Amplitude value , The gain is reduced when the input signal deviates from the commercial cycle. By using the amplitude value calculation, the amplitude value is complemented to reduce the error.

Example of Invention

Embodiments will be described below with reference to the drawings. FIG. 1 is a flow chart of an embodiment showing a procedure of digital filter processing and amplitude value calculation calculation applied to a digital protective relay according to the present invention. Since the other components of the digital protective relay are well-known circuits and procedures, their description will be omitted.

In FIG. 1, a digital data input process 1A converts a sample value obtained by sampling from an input AC signal into a digital signal, and digital data i _m , i _m-1 , i _m-2 resulting therefrom. ... (m is a time series) is read and processed. Therefore, the sampling period is 1 / 4n (n is a natural number) of the commercial period (reciprocal of frequency). In the next digital filter processing 2A, Z conversion (However, | k | <1)
Data I _m after filtering (m is a time series) is obtained and passed to the next amplitude value calculation calculation 3A.

In the amplitude value calculation operation 3A described above, the amplitude value I _e is calculated by the square method represented by the following equation (10).

Next, the operation will be described. If the amplitude of the AC signal input here is I, the angular frequency is ω, the time is t, the commercial angular frequency is ω ₀ , and the sampling cycle (reciprocal of frequency) is 1 / 4n of the commercial cycle, then the above digital Data i _m , i
_m-2n is expressed by the following equation (11).

This equation (11) is substituted into the equation (9).

here, Then, the filtered data I _m , I _mn , I
_m-2n can be expressed as the following equation (12).

The data I _m , I _mn , and I _m-2n after these filter processing are
It is input to the amplitude value calculation calculation 3A, and the amplitude value I _e is obtained by the above-mentioned equation (10).

From equation (10) and equation (12) Becomes Therefore, the ratio of the amplitude value _Ie to the amplitude I of the input AC signal, that is, the gain A is expressed by the following formula (14), and its gain-frequency characteristic is, for example, according to the value of k, It becomes like FIG. 2 to FIG.

As described above, in this embodiment, Z conversion is used. After the digital filter processing represented by
Calculation of amplitude value by multiplication Since seeking amplitude value at, for example, in the case of k = 0.2, the range of 0.41ω ₀ ≦ ω ≦ 1.59ω ₀ as shown in FIG. 2, i.e., the commercial frequency is 50 Hz 20.5Hz～79.5 Hz, 60Hz
Then, in the range of 24.6 Hz to 95.4 Hz, 0.8 ≦ A ≦ 1.0, that is, the gain error is within + 0% and −20%. Further, for example, when k = 0.25, as shown in FIG. 3, 0.5ω ₀ ≦ ω
In the range of ≤1.5ω ₀ , that is, when the commercial frequency is 50Hz, 25Hz ~
At 75 Hz and 60 Hz, 0.97 ≦ A ≦ 1.04, that is, the gain error is within ± 4% in the range of 30 Hz to 90 Hz. Furthermore, k = 0.3
In the case of, as shown in FIG. 4, 0.37ω ₀ ≤ω≤1.6
3ω ₀ range, that is, 18.5Hz to 81.5 when the commercial frequency is 50Hz
In the range of 22.2Hz to 97.8Hz for Hz and 60Hz, 0.9≤A≤1.1,
That is, the gain error is within ± 10%.

Therefore, the error becomes smaller for a wider frequency band including the commercial frequency than that of the conventional method shown in FIGS.

FIG. 5 is a flow chart showing the procedure of digital filter processing and amplitude value calculation operation according to another embodiment of the present invention. In addition,
Similar to FIG. 1, the other components of the digital protective relay have well-known circuits and procedures, and therefore their explanations are omitted.

In this embodiment, in the digital filter processing 2B, Z conversion is performed. The data I _m after filtering (I _m is a time series) is obtained by the following equation (15), which is expressed as follows, and is passed to the amplitude value calculation processing 3A. Other processes are the same as those in FIG.

Next, the operation will be described. Similar to the embodiment described above,
Digital data i _m , i _m-2n , and i _m-4n are expressed by the equation (16).

This equation (16) is substituted into equation (15).

Here, assuming that ωt ′ = ωt + β−π / 2, the data I _m after the filter processing can be expressed by the following expression (17).

Alternatively, the gain of the digital filter expressed by the equation (16) is expressed by the following equation (18).

As can be seen from the equation (4), the gain of the amplitude value calculation operation 3A represented by Therefore, the gain A of the amplitude value I _e obtained in the present embodiment with respect to the amplitude I of the input AC signal is as follows.
It is expressed by the equation 9).

This gain-frequency characteristic becomes, for example, as shown in FIGS. 6 to 8 according to the value of k.

As described above, in this embodiment, Z conversion is used. After processing the digital filter represented by
By the square method And the amplitude value calculating operation by, for seeking the amplitude value I _e, for example, in the case of k = 0.37 is, 0.425Omega as shown in FIG. 6 ₀
≦ ω ≦ 1.575 ω ₀ range, that is, 2 when commercial frequency is 50Hz
1.25Hz ~ 78.85Hz, 60Hz in the range of 25.5Hz ~ 94.5Hz,
0.85 ≦ A ≦ 1, that is, the gain error is within + 0% and −15%. Also as in the case of k = 0.4 is shown in FIG. 7, the range of 0.395ω ₀ ≦ ω ≦ 1.605ω _0, i.e., the commercial frequency is 50 Hz, 19.75Hz～80.25Hz, the 60 Hz 23.7Hz～96.3
0.85 ≦ A ≦ 1 in the range of Hz, that is, the gain error is +0
%, Within -15%.

Furthermore, when k = 0.46, as shown in FIG.
range of ω ₀ ≦ ω ≦ 1.705ω _0, i.e., the commercial frequency is 50 Hz, 14.75Hz～85.25Hz, in the range of 17.7Hz~102.3Hz At 60Hz, 0.8 ≦ A ≦ 1, i.e., an error of gain + 0% , -2
It falls within 0%.

Therefore, the error becomes smaller in a wider frequency band than in the first embodiment.

In each of the above-described embodiments, the sampling cycle is set to 1 / 4n (n is a natural number) of the commercial cycle of the input AC signal, but if this is a sampling cycle that can obtain 1/4 interval of the commercial cycle, for example, It indicates that any of 1/4, 1/8, 1/12, 1/16, etc. of the commercial cycle may be used. Further, the commercial frequency is not limited to 50 Hz or 60 Hz, and any frequency can be applied.

Furthermore, using the Z transform as a function of the digital filter processing, Although each case has been described, the present invention is not limited to this. Or its approximation, eg It is clear that the error of the gain becomes smaller in a wider frequency band as the approximation becomes more accurate. Furthermore, if a constant K is multiplied as each function of these digital filter processes, the gain is only K times, and the value of k is not limited to the value shown in each of the above embodiments, and other It is clear that the gain-frequency characteristics differ only for the value of.

In each of the above examples, the amplitude value I _e is However, the present invention is not limited to this, and it is needless to say that at least the calculation of I _e ² = ▲ I ² _mn ▼ -I _m · I _{m -2n} may be used.

〔The invention's effect〕

As described above, according to the present invention, the sampling period of the input alternating current is set to 1 / 4n (n is a natural number), and the transfer function of the digital filter processing is Z-transformed. (Where K and k are constants | k | <1) or an approximate product and the digital data is I _m , the amplitude value I _e
² = ▲ I ² _mn ▼ -I _m · I _{m -2n} is configured so that the error is small in a wide frequency band including the commercial frequency and the amplitude value of the AC signal can be obtained. Can provide a protective relay.

[Brief description of drawings]

FIG. 1 is a flow chart of an embodiment showing a procedure of digital filter processing and amplitude value calculation calculation applied to a digital protective relay according to the present invention, FIGS. 2 to 4 are gain-frequency characteristic diagrams, and FIG. 6 is a flow chart showing a procedure of a digital filter processing and an amplitude value calculation operation of another embodiment of the present invention, FIGS. 6 to 8 are gain-frequency characteristic diagrams, and FIG.
FIG. 10 is a flow chart showing a procedure of a conventional digital filter processing and an amplitude value calculation calculation, and FIGS. 10 to 14 are gain-frequency characteristic diagrams. 1,1A… Digital data input processing 2,2A, 2B… Digital filter processing 3,3A… Amplitude value calculation operation

Claims (3)

[Claims] 1. Inputting an AC signal such as current or voltage,
A digital type which performs a digital filter processing and an amplitude value calculation operation on digital data obtained by sampling the AC signal at a constant cycle and performing analog / digital conversion, thereby calculating the amplitude of the AC signal and performing a protection operation. In the protective relay, the sampling cycle is 1 / 4n of the commercial cycle (the reciprocal of the frequency) of the AC signal, and the transfer function of the digital filter processing is Z conversion. (Where K and k are constants | k | <1) or an approximation function thereof, and the amplitude value calculation operation is performed on the digitally processed data by I _m (m is a sampling time series), When the value is I _e , at least ▲ I _e ² ▼ = ▲ I ² _mn ▼
A digital protective relay characterized by using the operation −I _m · I _m-2n . 2. The transfer function of digital filtering is Z
By conversion (Where K and k are constants and | k | <1), and the digital protective relay according to claim 1 is characterized in that: 3. The transfer function of digital filtering is Z
By conversion The digital protective relay according to claim 1, wherein (K, k is a constant and is a function expressed as | k | <1).