JPH0320968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a distance relay with inrush countermeasures that does not respond to the inrush current of a transformer but responds correctly to a system fault.

[Prior art]

A conventional device of this type is shown in FIG. In the figure, 1 is the introduction terminal of the system voltage;
Reference numeral 2 denotes a system current introduction terminal, and 3 and 4 represent fundamental wave passing filters that remove harmonics contained in the system voltage and system current, respectively, and allow the fundamental wave to pass through. 5 and ₆ are the first _and second arithmetic circuits, respectively. 〓 ₂ I〓 is found and a square wave is created using the zero point as the boundary. 7 is an AND circuit which calculates the logical product of each calculation output V ₁ and V ₂ . 8 is an on-delay timer, which is selected for a time equivalent to 90 degrees in electrical angle. 9 is off-delay timer, electrical angle
Selected as 360° or more. Reference numeral 10 denotes an on-delay timer, which is not shown, but is used to coordinate operation time with other protective relays and the like. Reference numeral 11 denotes an output terminal of a distance relay, not shown, which is connected to a disconnector and performs a response to disconnect the system.

FIG. 2 shows the waveforms when a transformer is connected to the power grid, where a shows the grid voltage applied to the transformer, and b shows the waveform of the inrush current flowing into the transformer. The system voltage signal shown in FIG. 1A is applied to terminal 1 in FIG. 1, and the inrush current signal shown in FIG. 1B is applied to terminal 2. 1C shows the fundamental wave component extracted from the inrush current waveform shown in FIG. 1B, and is the output waveform of the fundamental wave passing filter 4 in FIG. The waveform of the fundamental wave passing filter 3 in FIG.
Since the voltage waveform in FIG. 2a is already a fundamental wave, it can be obtained as is as an output waveform. Therefore,
In FIG. 1, the voltage and current waveforms shown in FIG. 2 a and c are outputted from the fundamental wave passing filters 3 and 4, respectively.

The phase of the current I is advanced by θ and the magnitude is Z ₁ I,
When Z ₂ I is calculated between voltage E and V〓 ₁ = Z〓 ₁ I〓−E〓, V〓 ₂ = E〓−Z〓 ₂ I〓,
The vector shown by the solid line in FIG. 3 is obtained. The overlap width α is determined by the AND circuit 7 in FIG. 1 as the phase difference between the calculated output signals V ₁ and V ₂ . If this overlap width α is longer than _t1 hour of the on-delay timer 8, the off-delay timer 9 converts it into a continuous signal, and then the on-delay timer 10 waits for a time and sends the output signal to the output terminal 11. put out.

FIG. 4 is a timing diagram showing this situation, and a and b in the figure are respectively the arithmetic circuit 5 and the arithmetic circuit 5 in FIG.
6, and c in the same figure is the output signal of AND circuit 7,
In the figure, d is the output signal of the on-delay timer 8, e is the output signal of the off-delay timer 9, and h is the output signal of the on-delay timer 10.

In this way, a conventional distance relay can be used with V ₁ and
In order to detect that the phase difference of V ₂ is within a certain value, if the period α of the same polarity is larger than a certain time t ₁ , it is predicted that a system fault will occur, and this state continues for a specified time t ₃ . At times, it was determined that an accident occurred in a protected area.

Conventional distance relays are configured as described above, so in-rush current flows like when a transformer is being charged, but it may accidentally generate a disconnection output command signal in response to a phenomenon that is not an accident. In this case, consideration must be given to identifying that the problem is due to charging rather than an accident, and installing an interlock to prevent the distance relay from malfunctioning, which inevitably makes the device complicated. There were flaws.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and when it is detected that the temporal change in the overlap width of the outputs of two arithmetic circuits exceeds a predetermined value, charging is stopped. It is an object of the present invention to provide a distance relay that is configured to determine that there is an in-rush current due to a distance relay and to disable the operation of the distance relay.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 2, the inrush current waveform is shown in Fig. 2b, but as shown in the figure, this is a half-wave rectified waveform, and moreover, it attenuates with the passage of time.
This decay time is about several seconds determined by the system constant. Therefore, when the fundamental wave component is extracted, the inrush current waveform of the fundamental wave also attenuates with the passage of time, as shown in c.

Figures 5 and 6 are voltage and current vector diagrams shown in the same way as Figure 3, but the magnitude of the current I becomes smaller as shown in Figures 5 and 6. , representing the passage of time. In the vector diagram of FIG. 5, the phase difference between the two vectors V ₁ and V ₂ is larger than that of the vectors V ₁ and V ₂ shown in FIG. 3, and is even larger in FIG. 6. This is because when the voltage E is kept constant and the current I is decreased, Z ₁ I and Z ₂ I become smaller.

FIG. 7 is a block diagram of a distance relay according to an embodiment of the present invention.
Since the same reference numerals as those in the figures indicate the same parts, detailed explanation will be omitted. 12 is the output signal V ₁ of the AND circuit 7,
This is a change width detection circuit that compares the waveform width of V ₂ before and after one cycle and outputs an output signal when the width is a predetermined value. Further, reference numeral 13 denotes an inhibit circuit, in which the output of the off-delay timer 9 is not inverted, and the output of the change width detection circuit 12 is inverted.

FIG. 8 shows a signal timing diagram of each part of the embodiment of FIG. 4, a, b, c, d, e and h are the same as the output signals of each section shown in FIG. Further, in the same figure, f is a timing diagram of the output signal of the change width detection circuit 12, and g is a timing diagram of the output signal of the inhibit circuit 13.

Next, the operation of this embodiment will be explained. As already explained, the phase difference between the output signals V ₁ and V ₂ in Figure 7 a and b increases with time, so the overlapping width α of the same polarity period is Make a change that becomes smaller. When the output signal shown in FIG. 7c is shortened by _t1 using the on-delay timer 8, it becomes smaller as time passes as shown in FIG. 7d, and eventually there is no output. The limit at which this output disappears is the operating limit value of the distance relay.
With the off-delay timer 9, as shown in FIG. 7e,
If the signal is stretched out _{for 2} hours, the signal will continue as a continuous waveform while the next output appears, as shown in Figure 7d.

In order to detect that the width of the signal shown in FIG. 7d is gradually changing, it can be realized by the change width detection circuit 12 that checks the change in the pulse width before and after, as shown in FIG. 7f. As such, the detection signal can be obtained when the second signal ends. Therefore, by using the timer output signal of f in the same figure,
It becomes possible to stop the continuous signal appearing as . That is, the waveform of the inhibit circuit 13 is stopped by the rising edge of the output signal of the variation range detection circuit 12, as shown in g in the figure. Therefore, if the required time _t3 of the on-delay timer 10 is longer than the waveform width shown in g in the same figure, no output signal will be output to the output terminal 11 as shown in h in the same figure, and a shrunken command will be generated. I won't let you.

In the case of an actual system fault rather than an inrush current to a transformer, both the fault current and fault voltage are stable in the state at the time of the fault, so no temporal changes occur.

Therefore, in this case, the output signal of the AND circuit 7
Since V ₁ and V ₂ do not change over time, there is no output from the change width detection circuit 12, and the signal is not blocked by the inhibit circuit 13, so the output signal of the off-delay timer 9 is transmitted as is to the on-delay timer 10. be done. So, after the required time t ₃ has elapsed,
By outputting an output operation command to the output terminal 11, a disconnector (not shown) can be disconnected, thereby eliminating a system fault.

Although the above embodiment has been described as inputting the output of the AND circuit 7 to the change width detection circuit 12, the output signal of the on-delay timer 8 may also be input.

Further, in the above embodiment, a configuration example in which determination is performed using an analog circuit has been described, but a digital distance relay that processes digitally may be used and the same effects as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the operation of the distance relay is disabled by detecting the temporal change in the phase difference between two vectors. This has the effect of being able to reliably prevent this, and also making it possible to realize the entire relay at a low cost.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional distance relay.
Figure 2 is a waveform diagram of the voltage and current signals during inrush to the transformer, Figures 3, 5, and 6 are vector diagrams of the signals of each part of the distance relay that change over time, and Figure 4. 1 is a timing diagram of each part of the distance relay shown in FIG. 1, FIG. 7 is a block diagram of a distance relay according to an embodiment of the present invention, and FIG. 8 is a timing diagram of each part of the embodiment of FIG. 1... Grid voltage introduction terminal, 2... Grid current introduction terminal, 3, 4... Fundamental wave passing filter, 5, 6...
...first and second arithmetic circuits, 7...AND circuit, 8,
10...On-delay timer, 9...Off-delay timer, 11...Output terminal, 12...Change width detection circuit, 13...Inhibit circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 first and second arithmetic circuits that obtain arithmetic vectors from the system voltage and system current;
an AND circuit that calculates the logical product of the output signals of the arithmetic circuit; and a first circuit that receives the output signal of the AND circuit.
an on-delay timer, an off-delay timer into which the output signal of the first on-delay timer is input, and a waveform width of the output signal of the first on-delay timer or the AND circuit about one cycle. a change width detection circuit that compares and outputs an output signal when the waveform width is a predetermined value; and one of the output signals of the off-delay timer and the change width detection circuit is not inverted and the other is inverted and inputted for a predetermined time. A distance relay comprising a second on-delay timer that generates an on-delay command after a lapse of time.