JPH07118864B2 - Digital type current fluctuation detection relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a digital type current fluctuation detection relay for detecting fluctuations in a power system.

(Prior Art) An accident occurs in a power system, and after the accident is eliminated, the relevant system is reclosed, but if this reclosing fails,
The stability of the entire system is impaired, causing a so-called upset.

In order to detect fluctuations in this system, a step-out detection relay (56V), which operates when the phase difference between the two points exceeds 180 °, has been used in the past, and a multistage overcurrent relay (51M ) Is used. Fig. 6 shows the characteristic diagram of the 56V relay, and Fig. 7 shows the characteristic diagram of the 51M relay.

(Problems to be Solved by the Invention) Here, it is conceivable to use 51M to detect system fluctuations from changes in current.

However, in this case, the 51M has a drawback that it operates not only when the system is shaking but also when a simple accident occurs.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a digital type current fluctuation detection relay that correctly detects fluctuations in a system from currents in the system and does not operate in a simple accident.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the present invention, an electric quantity of a power system is sampled at a constant time interval and converted into a digital quantity, and then based on the digital data. In a digital relay that performs relay determination, means for obtaining the maximum value and minimum value of the system current within a predetermined time, means for obtaining the difference between the maximum value and the minimum value of the current, and operation when the difference exceeds a predetermined value. A first relay element comprising a judging means, a means for obtaining a current gradient, a means for starting a counter when the gradient of the change in the current exceeds a predetermined value, and an operation when the counter reaches a predetermined value. A second relay element consisting of a judging means and a means for extending the operation output for a predetermined time, and a relay judgment by introducing respective outputs of the first relay element and the second relay element. It was composed of a judging means for.

(Operation) When a fluctuation occurs in the power system, the current fluctuates gently with a constant fluctuation period. Therefore, the system fluctuation is detected by an element that detects that the difference between the maximum value and the minimum value of the current exceeds a predetermined value and an element that detects that the slope of the current change is equal to or greater than the predetermined value for a predetermined time. It can be detected correctly.

(Examples) Examples will be described below with reference to the drawings.

FIG. 1 is a functional block diagram of an embodiment of a digital type current fluctuation detection relay according to the present invention.

In FIG. 1, a digital type current fluctuation detection relay 10
Is a current value calculating means 11 for calculating a current value after converting the current taken from the power system into digital data, and a maximum value calculating means 12 for calculating the maximum value of the calculated current value within a predetermined time. Similarly, the minimum value calculating means 13 for calculating the minimum value within a predetermined time is compared with whether or not the difference between the means 12 and the means 13 is larger than a predetermined value, and if the difference is larger, the output is turned on.
However, the comparison means 14 for turning off the output when it is small and the means 1
The slope calculation means 15 for calculating the slope of the change in the current value calculated in 1 is compared with the slope calculated by the means 15 to determine whether or not the slope is larger than a predetermined value. And a comparison means 16 for turning off the output, and detecting that the output of the means 16 continues for a predetermined time, turning on the output if this continues, and turning on the output if it does not continue, and an operation continuation checking means 17 , When the output of means 17 is ON and from ON to OF
When the output extension means 18 that turns on the output for a predetermined time after changing to F, and both the output of the comparison means 14 and the output of the output extension means 18 are on, the relay operation is turned on, and otherwise It is composed of a judging means 19 for returning to the relay.

FIG. 2 is a diagram showing an example of a change in current when the system fluctuates in a 3-second cycle. A description will be given below with reference to FIG. First, in order to detect a change in the current in the system, the oscillation width of the current is detected. The difference between the current values at points A and B in FIG. 2 is a predetermined value
When it exceeds I _set , it is judged to be abnormal. As shown in Fig. 2, when the current fluctuates every 3 seconds, the current repeats the maximum value and the minimum value every 1.5 seconds.
For example, the width of vibration can be detected by obtaining the difference between the maximum value and the minimum value of the current within the past 3 seconds. Therefore, when this difference exceeds a predetermined value I _set , the relay operation is performed. This relay element is tentatively called an OC element.

FIG. 3 shows a flowchart showing the processing contents of the OC element.

The content shown in FIG. 3 is an example in which each means 12, 13, 14 in FIG. 1 is configured by software.

In FIG. 3, in step S31, the maximum value I _MAX of current values within the past 3 seconds from the present time is obtained. In step S32, the minimum value I _min of current values within the past 3 seconds from the present time is obtained. In step S33, it is determined whether or not I _MAX −I _min is larger than I _set. If it is larger, the process of step S34 is performed, and if it is smaller, the process of step S35 is performed. In step S34, since the current vibration width is larger than I _set , the relay operation is performed. In step S35, since the vibration width of the current is smaller than I _set , the relay is reset.

Next, in order to distinguish between an accident and an agitation, the slope of increase / decrease in current is calculated. As shown in FIG. 2, a relatively slow increase / decrease in current is repeated during shaking.

FIG. 4 is a diagram illustrating the slope of the current when the current vibrates in a cycle of 3 seconds and the vibration width is I _set . This will be described below with reference to FIG.

As can be seen from FIG. 4, the current changes by I _set in 1.5 seconds, so the average slope can be considered as I _set /1.5.
Now, considering the double margin, the change of the current with the slope of I _set / 3 or more continues for at least 500 ms. Therefore, if you confirm that the slope of the current is larger than I _set / 3 for 500 ms or more,
It is determined that the current is fluctuating during fluctuation, and relay operation is performed.
This makes it possible to distinguish between a sudden change in current during an accident and a change in current during shaking. It should be noted that near point C and point D in FIG.
Once it is detected that the current gradient is I _set / 3 or more for 500 ms or more, the continuous operation can be performed by holding the output for 1 second, for example. This relay element is tentatively called a dI / dt element.

FIG. 5 shows a flowchart showing the processing contents of the dI / dt element.

The content shown in FIG. 5 is an example in which each process 15, 16, 17, 18 of FIG. 1 is configured by software.

In FIG. 5, in step S51, the slope of the current is obtained. In step S52, it is determined whether or not the slope of the current is larger than I _set / 3. If it is larger, the process of step S53 is performed, and if it is smaller, the process of S54 is performed. In step S53, if the current slope is greater than I _set / 3, 500
It is determined whether or not to continue for ms. If it continues, the process of step S55 is performed, and if not, the process of S54 is performed. In step S54, the slope of the current is I _set /
After the value of 3 or more continues for 500 ms, the slope of the current I
When the output holding time is smaller than _set / 3, it is determined whether or not one second has passed. If it has passed, the process of step S56 is performed, and if it has not passed, the process of step S55 is performed. In step S55, the current slope is I
Relay operation is performed because the value larger than _set / 3 continues for 500 ms or the output hold time does not exceed 1 second. In step S56, the current slope is I
_{Since it} is smaller than _set / 3 and the output holding time has passed 1 second, the relay is reset.

As described above, the OC element can detect a change in current and the dI / dt element can distinguish between an accident and a sway, and thus, when both the OC element and the dI / dt element operate, a sway is detected. It is determined that the relay has been operated.

In the above-mentioned embodiment, the case where the shaking period is 3 seconds has been described as an example, but the present invention is not limited to this, and the shaking period can take any value, and various times can be changed according to the shaking period. It can take any suitable value.

Further, the detection sensitivity of the dI / dt element is set to double the margin, but it can be set to an appropriate value. The OC element alone can be applied as a motion detection relay. Further, the dI / dt element alone in the first embodiment can be applied as a vibration detection relay.

Although the above contents are all examples configured by software processing, similar functions can be configured by hardware.

[Effects of the Invention] As described above, according to the present invention, system fluctuation is determined on the condition that the variation width of the system current is equal to or greater than a predetermined value and the slope is equal to or greater than the predetermined value and continued for a predetermined time. With this configuration, it is possible to provide a digital type current fluctuation detection relay that does not respond unnecessarily to a simple accident.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a digital type current fluctuation detection relay according to the present invention, FIG. 2 is a diagram for explaining an OC element, and FIG. 3 is a flowchart for wetting the processing contents of the OC element.
FIG. 4 is a diagram for explaining the dI / dt element, FIG. 5 is a flowchart showing the processing contents of the dI / dt element, FIG. 6 is a characteristic diagram of a 56V relay, and FIG. 7 is a characteristic diagram of a 51M relay. 10 ... Digital type current fluctuation detection relay 11 ... Current value calculating means, 12 ... Maximum value calculating means 13 ... Minimum value calculating means, 14, 16 ... Comparison means 15 ... Inclination calculating means, 17 ... Operation Continuation confirmation means 18 …… Output delay means, 19 …… Judgment means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-3528 (JP, A) JP-A-59-209021 (JP, A) JP-A-63-90450 (JP, A)

Claims (1)

[Claims] 1. A digital type current fluctuation detection relay which detects the system fluctuation based on the digital data after sampling the electric quantity of the power system at a constant time interval and converting it into a digital quantity within a predetermined time of the system current. Of the maximum value and the minimum value of, a means for determining the difference between the maximum value and the minimum value of the current, and a first relay element consisting of means for determining the operation when the difference exceeds a predetermined value, A second relay element comprising a means for obtaining a slope of change, a means for determining an operation when the slope of the current change is equal to or greater than a predetermined value and continued for a predetermined time, and a means for extending the operation output for a predetermined time; A digital type current fluctuation detection relay, comprising: a determining unit that detects system fluctuation when both the relay element and the second relay element operate.