JP3235224B2 - Digital overvoltage relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage / frequency (V / f) for detecting over-excitation of a generator and performing a protection operation.
The present invention relates to a digital type overvoltage relay having characteristics.

[0002]

2. Description of the Related Art Some overvoltage relays have a voltage / frequency characteristic in which an operating voltage changes according to the frequency of an AC input voltage. FIG. 3 shows this voltage / frequency characteristic, where f ₀ is the rated frequency of the AC input voltage, V _s is the voltage set value, and the hatched portion in the figure is the operating region. This overvoltage relay detects V / f> K (K is a set value) and performs a protection operation. As is apparent from FIG. 3, as the frequency f increases, the operating voltage V also increases. f
Is smaller, the operating voltage V is smaller.

In a conventional analog overvoltage relay, a circuit called a V / f filter 10 is provided at an input stage of a voltage relay 20 as shown in FIG. When the input voltage of the V / f filter 10 is V
_I , when the output voltage is V _O , the input / output gain (V _O
/ V _I ) is approximately inversely proportional to the frequency f as shown in FIG. 5, and Equation 1 is obtained. Based on Equation 1, Equation 2 is obtained. In Equations 1 and 2, K ₂ is a constant.

[0004]

## EQU1 ## V _O / V _I = K ₂ / f

[0005]

## EQU2 ## V _O = K ₂ V _I / f

Here, the output voltage V of the V / f filter 10
_{When O} is compared with the set value K ₁ and V _O > K ₁ , Equations 3 and 4 are obtained from Equation 2 above, and from Equation 4, an overvoltage relay having a desired voltage / frequency characteristic is realized. be able to.

[0007]

## EQU3 ## K ₂ V _I / f> K ₁

[0008]

[Number 4] _{V I / f> K 1 /} K 2 (= K)

[0009]

The conventional overvoltage relay requires special hardware such as the V / f filter 10 as described above, which causes the circuit configuration to be complicated and the cost to be high. . Also, since it is difficult to make the input / output gain (V _O / V _I ) of the V / f filter 10 completely inversely proportional to the frequency f, the voltage / frequency characteristics are also
As shown in FIG. 6, the calculated characteristics (indicated by broken lines) have considerable errors such as a, b, and c, resulting in a reduction in overvoltage detection accuracy. The characteristics a, b, and c in FIG. 6 are obtained when the capacitances of the capacitors constituting the V / f filter 10 are set to different values.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a voltage / frequency characteristic without using hardware such as a V / f filter. An object of the present invention is to provide a digital overvoltage relay having high detection accuracy and high reliability.

[0011]

In order to achieve the above object, the present invention relates to a digital overvoltage relay which generates a relay operation output when the ratio between the magnitude of an AC input voltage and its frequency exceeds a set value. Frequency detecting means for detecting the frequency of the AC input voltage, voltage detecting means for detecting the magnitude of the AC input voltage, first calculating means for calculating the product of the frequency of the AC input voltage and the voltage set value, The second to calculate the product of the magnitude of the AC input voltage and its rated frequency
And the outputs of the first and second arithmetic means are compared, and the output of the first arithmetic means is compared with the output of the second arithmetic means.
Comparison means for generating a relay output when also large, the
Provided on the input side of the frequency detecting means and the voltage detecting means.
Analog filter and the gain of this analog filter
Gain stored in correspondence with the frequency of the AC input voltage
A table and a frequency corresponding to the frequency detected by the frequency detecting means.
Analog filter read from the gain table
The voltage detected by the voltage detecting means is determined by the gain of the
And voltage correcting means for correcting the voltage .

[0012]

[0013]

According to the present invention, the product of the frequency of the AC input voltage output from the first calculating means and the voltage set value, and the second
By comparing the magnitude of the product of the magnitude of the AC input voltage, which is the output of the arithmetic means, with the rated frequency, it is determined whether the ratio between the AC input voltage and the frequency is greater than a predetermined set value. Thus, the voltage / frequency characteristics of the overvoltage relay can be realized without using a V / f filter. In addition, an analog filter corresponding to the frequency of the AC input voltage
The magnitude of the AC input voltage is corrected by the filter gain
By using for the calculation in the calculation means of 2, the analog
Excellent detection accuracy without being affected by the frequency characteristics of the filter
Overvoltage relay can be realized.

[0014]

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram showing a configuration of a main part of a digital overvoltage relay according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an input of an AC input voltage and its frequency f
A voltage detecting means for receiving an AC input voltage and detecting the magnitude V of the frequency detecting means;
3 a first arithmetic means for multiplying the voltage set value V _S and the frequency f inputted from outside, 4 second multiplying the rated frequency f ₀ and the voltage value V of the AC input voltage inputted from the outside
Is the output of each of the calculation means 3 and 4 (f ×
This is a comparing means for comparing the magnitude relationship between (V _S ) and (V × f ₀ ) and generating a relay operation output according to the result.

In the above configuration, the desired characteristic to be realized is V / f> K, where the set value K is given by equation (5).

[0017]

## EQU5 ## K = V _S / f ₀

Therefore, the characteristic of the above equation (5) can be transformed into the equation (6). If this is transformed into the equation (7), the comparing means 5 is the output of each of the computing means 3 and 4 (f ×
V _S ) and (V × f ₀ ) are compared, and if Expression 7 is satisfied, a relay output may be generated.

[0019]

V / f> V _S / f ₀

[0020]

V × f ₀ > f × V _S

As described above, according to the present embodiment, the overvoltage is detected by detecting the frequency and magnitude of the AC input voltage, and performing the calculation and comparison processing using the detected value and the voltage set value and the rated frequency. A desired voltage / frequency characteristic of the relay can be realized. That is, V / f as in the prior art
Even without using a filter, the voltage / frequency characteristics can be realized by software such as a voltage detecting means and a CPU constituting an existing digital relay, and there is no danger of complicating the circuit configuration and increasing the cost. Also, the frequency f
It is not necessary to consider the input / output gain V _O / V _I of the V / f filter, which is not completely inversely proportional to the above, which can contribute to improvement of detection accuracy.

Next, FIG. 2 is a functional block diagram showing the present embodiment in more detail . Although not shown in FIG. 1, the AC input voltage is taken into each of the detecting means 1 and 2 via an analog filter 6 for removing harmonic components and DC components. In this case, since the analog filter 6 has frequency characteristics, the magnitude V of the voltage detected by the voltage detecting means 2
May be affected by the frequency characteristics. Therefore
In this embodiment , the output voltage value of the voltage detecting means 2 is corrected according to the frequency of the AC input voltage.

In FIG. 2, a gain table 7 is provided on the output side of the frequency detecting means 1. The gain table 7 stores a known gain of the analog filter 6 as a table corresponding to the frequency of the AC input voltage. On the other hand, a divider 8 is provided on the output side of the voltage detecting means 2.
, And the analog filter gain from the gain table 7 are input. The divider 8 divides the voltage value V ′ by an analog filter gain and outputs the result as a corrected true voltage value V to the second calculating means 4. Here, the gain table 7 and the divider 8 constitute a voltage correction means 9.

According to the above configuration, the magnitude V 'of the original voltage is corrected by the analog filter gain corresponding to the frequency f of the AC input voltage, and is used as a true voltage value V in the calculation by the calculation means 4. Therefore, the comparison process by the comparison means 5 can be performed accurately, and an overvoltage relay excellent in detection accuracy and reliability can be realized without being affected by the frequency characteristics of the analog filter 6.

[0025]

As described above, according to the present invention, the product of the frequency of the AC input voltage which is the output of the first calculating means and the voltage set value, and the AC input which is the output of the second calculating means. By comparing the magnitude of the product of the magnitude of the voltage and its rated frequency, it is possible to compare whether the ratio between the AC input voltage and the frequency is greater than a predetermined set value, which was conventionally required. The voltage / frequency characteristics of the overvoltage relay can be realized without using a V / f filter. For this reason,
The circuit configuration can be simplified, and the accuracy and reliability of overvoltage detection can be improved. Also, AC input
Switching by analog filter gain according to the frequency of voltage
The magnitude of the current input voltage and
Since it is used for calculation, the frequency of the analog filter
High accuracy of overvoltage detection and high reliability without being affected by numerical characteristics
An overvoltage relay can be provided.

[0026]

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of a main part of an embodiment of the present invention .

FIG. 2 is a functional block diagram showing a more detailed configuration of an embodiment of the present invention .

FIG. 3 is an ideal voltage / frequency characteristic diagram of an overvoltage relay.

FIG. 4 is a configuration diagram of a conventional analog overvoltage relay.

FIG. 5 is a gain characteristic diagram of a V / f filter.

FIG. 6 is a voltage / frequency characteristic diagram of a conventional overvoltage relay.

[Explanation of symbols]

1 frequency detecting means 2 voltage detector 3 first calculating means 4 second calculation means 5 comparison means 6 analog filter 7 gain table 8 the divider 9 voltage correcting means f frequency f ₀ rated frequency V voltage value V _S voltage settling value

Claims (1)

(57) [Claims] 1. A digital overvoltage relay for generating a relay operation output when a ratio between the magnitude of an AC input voltage and its frequency exceeds a set value, a frequency detecting means for detecting a frequency of the AC input voltage; Voltage detecting means for detecting the magnitude of the input voltage; first computing means for computing the product of the frequency of the AC input voltage and the voltage set value; computing the product of the magnitude of the AC input voltage and its rated frequency compares the second calculating means, the outputs of the first and second operation means, first computation hand
A comparing means for generating a relay output when an output of the stage is larger than an output of the second calculating means; and an input side of the frequency detecting means and the voltage detecting means.
And the gain of the analog filter is set to the frequency of the AC input voltage.
A gain table storing in correspondence with the gay in response to the detection frequency by the frequency detection means
To the gain of the analog filter read from the
Voltage for correcting the voltage value detected by the voltage detecting means
A digital overvoltage relay , comprising: a correction unit .