JPS5920260B2 - Transformer protection relay device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a transformer protective relay device, and in particular, it securely locks and prevents malfunctions during transformer excitation inrush without impairing the high-speed operation capability in the event of an internal failure of the transformer. The present invention relates to a transformer protection relay device that does not occur.

Generally, for transformer protection, the ratio differential relay system shown in FIG. 1 has been most typically used.

In Fig. 1, 1 is a protected transformer, 2 and 3 are current transformers inserted on the power supply side and load side of this transformer, 4 is a breaker,
5 is a power supply, and 6 is a ratio differential relay.

In Fig. 1, when the breaker 4 is turned on and the protected transformer 1 is excited with no load, a so-called magnetizing inrush current (inrush current) A current iex flows through the secondary side of the transformer, causing a differential operation output that appears to be the same as an internal failure of the transformer, which may cause the ratio differential relay 6 to malfunction.

Various measures have been taken in the past to counter this inrush, some examples of which will be explained below.

(1) The method shown in FIG. 2 that avoids malfunctions due to inrush sequentially.

Figure 2 is a trip circuit diagram, in which 4a is a pallet switch that is turned off when the breaker 4 is closed, 7 is a timer, and 7 is a trip circuit diagram.
6a is the operating closed contact of the ratio differential relay 6.

That is, in order to avoid the inrush that occurs when the breaker is turned on, the trip circuit of the ratio differential relay is locked by the timer 7 activated by the pallet switch 4a provided in the breaker 4 in advance until the inrush current disappears. (i.e. ratio differential relay 6
The output contact 6a of the timer is T-locked for a predetermined time by the contact 7a of the timer.

(2) A method of slowing down the operating time of the ratio differential relay 6 and expecting the inrush to disappear.

(3) A method in which a CT is provided on the neutral point side of the transformer to operate a differential circuit, thus making it theoretically unaffected by inrush current.

(4) Utilizing the fact that the inrush current waveform has a unique shape as shown in Figure 3, whether it is an inrush current by detecting the second harmonic included in the inrush current waveform, etc. If it is determined that there is an inrush current, the operation of the ratio differential relay 6 is locked.

The conventional methods shown above are each effective, but in each case, the inrush countermeasure either kills the operating speed of the ratio differential element itself or sacrifices some of its protection ability. I have to.

This will be explained next. First, the method (1), that is, the sequential method, is true that if a transformer failure occurs during normal operation, it will operate at the speed of the ratio differential relay element itself. It is also possible to speed up the process.

However, if an internal failure occurs at the same time as the transformer is turned on, the second
Since the operation is forcibly locked for time T by the timer 7 shown in the figure, even if the ratio differential relay element operates, it cannot be tripped, and there is a risk of burning out the transformer.

Since this timer one hour T needs to be settled longer than the inrush duration time, it must be locked for a fairly long time (several hundreds of cycles or thousands of cycles).

Needless to say, high-speed operation is not possible with method (2).

Method (3), as shown in Figure 4, involves inserting a current transformer 9 on the neutral point side of the autotransformer 8 (C phase) (only the A phase is shown in Figure 4). The same applies to C phase and C phase)
In principle, it is not affected by in-rush current or tap fluctuation by a tap changer, so a high-sensitivity, high-speed ratio differential relay can be obtained.

However, since interlayer faults cannot be detected in principle, it cannot be said to be a perfect ratio differential relay.

When using the method (4), that is, the phenomenon peculiar to the inrush waveform, a circuit as shown in FIG. 5 is used.

In FIG. 5, when an inrush current is generated due to the breaker being turned on, the inrush waveform determination element 10 is 1 c/s or more necessary for waveform observation (the first half cycle of the inrush waveform is the first half cycle of the inrush waveform). As shown in Figure 7, it is indistinguishable from the sine wave that is the fault current, and it can only be determined that it is an inrush current by looking at the latter half cycle, so in principle a determination time of lc/s or more is required. After the time, a determination output 100 as shown in FIG. 6 is output.

Therefore, the output 60 of the ratio differential relay element 6 is output by the timer 11 as a timer output 110 (FIG. 6).
Must be delayed by 1.

That is, at this time, as shown in FIG. 6, the output 60 of the ratio differential relay element 6 is inhibited by the inhibit circuit 12, the inhibit output 120 does not change, and malfunction is prevented.

Note that FIG. 7 shows operating waveforms at the time of failure in the method of FIG. 5.

Since the inrush current contains many second harmonic components in addition to the fundamental wave component, the inrush waveform determining element 10 is generally determined by the ratio of the second harmonic component and the fundamental wave component in the current. A method of making a determination (second harmonic suppression method) is adopted.

In other words, this second harmonic suppression method means that if the ratio of the second harmonic component to the fundamental wave component in the current exceeds a certain value (for example, 15%), the current is an inrush current. Judgment, inrush waveform judgment element 10
This is a method that outputs an output of 100 and locks the relay.

As explained above, methods (1) to (3) have sacrificed a lot of characteristics in order to prevent inrush, so method (4), which is currently a relatively good method,
This method is widely used.

However, recent transformers are becoming more economically designed, and in order to reduce the amount of transformer core, the saturation magnetic flux of the transformer core is low (
As a result, the iron core is becoming more easily saturated.

As a result, the second harmonic component in the inrush current tends to decrease, and for this reason, there are an increasing number of cases in which the second harmonic suppression method described above cannot adequately cope with the problem.

Therefore, it has become desirable to reliably determine inrush current and prevent malfunctions of transformer protective relay devices due to inrush current.

The purpose of the present invention is to eliminate the drawbacks of the conventional method as described above,
It is an object of the present invention to provide a relay device that does not malfunction due to inrush current.

The purpose of the above is to focus on the repetition of large discontinuities in the current waveform, which rarely occur when a transformer fails and only occur during inrush, to detect this phenomenon and lock the relay using the judgment output. achieved by

The details of the invention will be explained below.

First, the inrush current waveform when inrush occurs will be described.

Figure 8a shows the 8th circuit of the system to which the transformer is connected.
The figure shows a phenomenon diagram when an inrush occurs.

In FIG. 8, e is the power source, Xt is the impedance of the power source and line, Xt is the excitation impedance of the transformer, S is the breaker, Ie or current, ■ is the transformer terminal voltage, and φ is the magnetic flux of the transformer core.

In Figure 8a, when the breaker S is turned on, the magnetic flux φ of the transformer core is 90 degrees behind the transformer terminal voltage V, so the residual magnetic flux of the transformer core before the circuit breaker S is turned on is O.
Then, as shown in FIG. 8, φ rises from 0 at 1=0.

If the saturation magnetic flux of the transformer core is φm, the transformer has a magnetic flux φ
saturates when becomes φm (1=11).

When the transformer is saturated, the excitation impedance Xt of the transformer becomes small, so a large current Iex flows.

After that, when φ becomes less than φm (1=12), the transformer is no longer saturated, so the excitation impedance Xt of the transformer
becomes large again and current Iex no longer flows.

As described above, during the in-rush period, the current Iex has a wide discontinuity (a period in which no current flows), and this occurs repeatedly.

That is, the inrush current Iex flows only during the period when the transformer is saturated, as shown in the figure.

An economically designed transformer has a reduced amount of transformer core, which lowers the saturation magnetic flux φm of the transformer core, making it easier for the core to become saturated.

As the iron core becomes more likely to become saturated, the period during which the iron core is already saturated becomes longer, as shown in FIG.

As the conduction angle of the inrush current widens, the second harmonic component in the inrush current decreases.

Since the second harmonic component is included in the fault current to some extent (generally less than the 10th factor of the fundamental distribution), the conventional second harmonic suppression method has reached its limit.

However, even if the transformer becomes more likely to become saturated in this way, the saturation of the transformer will still cause interruptions in the inrush current Iex.The present invention is economically designed with this point in mind. To provide a transformer protection relay device that can reliably determine even the inrush of a transformer and prevent malfunctions.

FIG. 9 is a block diagram showing an embodiment of the transformer protection relay device according to the present invention.

In FIG. 9, an output 130 of a comparator circuit 13 that detects the ratio between the transformer terminal voltage and the differential current between both terminals of the transformer is inputted to an OR circuit 22 via a rectangular wave conversion circuit 14.

Further, the transformer terminal voltage is inputted to the other terminal of the OR circuit 22 via the rectangular wave conversion circuit 20 and the NOT circuit 21.

The output 220 of the OR circuit 22 is input to the inhibit terminal of the inhibit circuit 17 via a time limit circuit 15 that delays the signal for a fixed time period (T2) and a time limit circuit 16 that holds the signal for a fixed time period (T3).

The output 60 of the ratio differential relay element 6 is connected to the inhibit circuit 1
7 is input to the other terminal.

An instantaneous relay that operates instantly when the differential current exceeds a certain value (normally several times to several tens of times the rated current, a value that does not work with differential current due to inrush current) The output 180 of element 18 and the output 170 of inhibit circuit 17 are applied to OR circuit 19, which outputs trip signal 6a.

The operation of the protective relay device having the above configuration is as follows.

First, if a major fault occurs inside the transformer when the transformer is in operation or turned on, the instantaneous relay element 18 operates and instantly outputs a trip signal.

Next, consider the case where inrush current occurs when the transformer is turned on.
It is shown in FIG.

Since the inrush current has an interrupted waveform that repeats periodically as shown in the figure, the output 130 of the comparator circuit 13 that detects the ratio between the transformer terminal voltage (V) and the inrush current (I)
The output 140 of the rectangular wave conversion circuit 14 receiving the signal periodically generates a rectangular wave.

Also, a rectangular wave conversion circuit 20 receiving transformer terminal voltage (V)
The output 200 of provides a signal after the transformer is turned on.

The output 210 of the NOT circuit 21 receiving this output 200 and the output 140 of the rectangular wave conversion circuit 14 are connected to an OR circuit 2.
2, the output 220 of the OR circuit 22 periodically generates a square wave after the transformer is turned on.

In other words, the reason why the rectangular wave conversion circuit 20 is provided to determine the presence or absence of the transformer terminal voltage is because the output 130 of the comparator circuit 13 cuts the level for a moment when the transformer terminal voltage is reversed from a negative polarity wave to a positive polarity wave. The output 140 of the rectangular wave conversion circuit 14 becomes a periodic rectangular wave with that portion missing, but this missing portion is filled with the output 210.

After the output 220 is output, an output 150 is output to the timer circuit 15 after a time period T2 (This time period T2 is for determining the interrupted waveform peculiar to inrush current. For example, T2 is 60 in electrical angle. (Choose according to degree)

Here, depending on the installation location of the potential transformer (corresponding to FIG. 13, 23), the phase of the transformer terminal voltage may shift with respect to the differential current.

In that case, the missing portion of the output 140 also changes due to the phase shift, and coordination with the time T2 of the timer circuit 15 may not be achieved.

However, as described above, since the inrush current is determined by the OR output 220 of the output 140 and the output 210, there is no possibility of malfunction due to a phase shift between the terminal voltage of the transformer and the differential current.

Even when the output 150 becomes O, the output 160 is extended by the time limit T3 (for making the rectangular wave continuous, about one cycle) of the time limit circuit 16, and becomes a continuous signal.

Therefore, even if the output 60 of the ratio differential relay element 6 outputs an output due to inrush current, the output 170 of the inhibit circuit 17 becomes 0, so that the trip signal 6a is not erroneously output.

Next, when the transformer is in operation, a transformer internal failure (instantaneous relay element 1
FIG. 11 shows a case where a failure (failure in which part 8 does not operate) occurs.

In this case, when an internal failure occurs, the voltage decreases and a differential current is generated, so the output 130 of the comparator circuit 13 that detects the ratio of voltage and differential current decreases, so the output 140 of the rectangular wave conversion circuit 14 becomes It becomes O.

Further, the output 200 of the rectangular wave conversion circuit 20 receiving the transformer terminal voltage periodically generates a rectangular wave.

The output 220 of the OR circuit 22 which introduces the output of the NOT circuit 21 which receives this output 200 and the output 140 of the rectangular wave conversion circuit 14 is in a narrow range (T2 time limit rise small) after the internal failure of the transformer occurs. ) Since it is a pulse output, the output 150 of the timer circuit 15 becomes O.

After the internal failure occurs, the trip signal 6a is output after the T3 time limit of the time limit circuit 16.

FIG. 12 is a time chart when a transformer internal failure (failure in which the instantaneous relay element 18 does not operate) occurs when the transformer is turned on.

In FIG. 12, when an internal failure occurs, the voltage becomes smaller than the rated voltage and a differential current is generated, so the output 130 of the comparator circuit 13 that detects the ratio of voltage and differential current becomes small, so the rectangular wave conversion circuit The output 140 of 14 remains at 0.

Further, the output 200 of the rectangular wave conversion circuit 20 receiving the transformer terminal voltage periodically generates a rectangular wave after a failure occurs.

The output 220 of the OR circuit 22 which introduces the output of the NOT circuit 21 receiving this output 200 and the output 140 of the rectangular wave conversion circuit 14 has a narrow width (T
2 o'clock time limit rise small) Since it is a pulse output, time limit circuit 15
The output 150 of becomes 0.

After the internal failure occurs, the trip signal 6a is output after the T3 time limit of the time limit circuit 16.

FIG. 13 shows an example of a specific circuit diagram of the present invention, and the same reference numerals as in FIG. 9 indicate the same contents.

High voltage side and low voltage side signals of the transformer 1 are applied to the transformers 24, 25, and 26 through the current transformer 2.3.

Further, the terminal voltage of the transformer 1 is applied to the transformer 27 through the instrument transformer 23.

Furthermore, the comparator circuit 13 is connected to the secondary side of the transformer 26 and the transformer 27.
A signal is applied to.

The above-mentioned connection-related operations can be fully imagined from the explanation of the embodiment shown in FIG. 9, so the details will be omitted.

Now, the inrush current waveform shown in the above embodiment is a typical waveform example for convenience of explanation, but in reality, depending on the characteristics of the current transformers 2 and 3, etc., the attenuation time will vary as shown in FIG. As time passes, the waveform may oscillate into both positive and negative polar waves.

At this time, if some other method that detects only the breaks in the current waveform is used, there is a risk of erroneous determination.

However, if the ratio of the transformer terminal voltage to the differential current is determined as a means of detecting discontinuities in the current waveform as in this embodiment, the inrush current waveform shown in FIG. This means that we can expect a highly efficient transformer protection relay device.

The reason for this will be explained in detail below.

First, FIG. 15 shows a conventional device that detects only the breaks in the current waveform.

In the figure, 23 is a NOT circuit, and other symbols indicate the same contents as the same symbols in FIG.

Even with this conventional device, when a normal inrush current occurs when the transformer is turned on (corresponding to Fig. 10), the first
As shown in FIG. 6a, since the output 60 can be blocked by the output 160, the trip signal 6a will not be issued by mistake.

In addition, if an internal failure of the transformer occurs during operation of the transformer (
(corresponding to Fig. 11), T as shown in Fig. 16C.
A trip signal 6a is issued after three time limits.

Further, although not shown, if an internal failure occurs in the transformer when the transformer is turned on (corresponding to FIG. 12), the trip signal 6a will be issued as in the case of FIG. 16C.

However, if an inrush current that swings into both positive and negative polar waves occurs when the transformer is turned on, T
A trip signal 6a is erroneously issued after the third time limit.

This means that when the inrush current swings into positive and negative polar waves,
This is because the current waveform becomes uninterrupted and cannot be detected using a method that detects only the discontinuities in the current waveform.

Since a rectangular wave signal corresponding to the negative polarity wave of the inrush current appears at the output 140 in FIG. 16, the next stage circuit malfunctions and the inhibit signal 160 disappears after the T3 time limit, causing the trip signal 6a to be output by mistake. That will happen.

On the other hand, if the ratio of the transformer terminal voltage and the differential current is calculated, if an inrush current that swings into both positive and negative polar waves occurs when the transformer is turned on (corresponding to the diagram in Figure 16)
However, as shown in FIG.
If the waveform of the dotted line portion becomes smooth as shown by the solid line, the output 140 of the rectangular wave circuit 14 at the next stage is not affected, and the output 160 can be blocked thereafter.

In other words, by finding the ratio between the terminal voltage and the differential current, it is possible to absorb signal waveform distortion (for example, when the inrush current swings into both positive and negative polar waves as shown in Figure 14). Compared to converting the current directly into a square wave,
This has the effect of removing the influence of waveform distortion of the input signal.

As explained above, by using the transformer protection relay device of the present invention, it is possible to prevent malfunctions even in inrush of an economically designed transformer, such as the conventional second harmonic suppression type relay device. No protective relay device can be obtained.

[Brief explanation of the drawing]

Figure 1 shows a conventional ratio differential relay system, Figure 2 shows an example of a conventional inrush malfunction prevention measure, and Figure 3 shows an example of a conventional inrush malfunction prevention measure.
The figure is an inrush current waveform diagram, Figure 4 is a diagram showing a conventional ratio differential relay that does not require inrush countermeasures, Figure 5 is a block diagram of a conventional ratio differential relay, and Figures 6 and 7 are Figure 5 is a time chart of a ratio differential relay, Figure 8a is an equivalent circuit diagram of a system to which a transformer is connected, Figure 8 is a phenomenon diagram when inrush occurs, and Figure 9 is a diagram of the present invention. A block diagram showing an embodiment of the relay device, FIG.
1 and 12 are time charts of the relay device shown in FIG. 9, and FIG. 13 is a specific example of a circuit diagram of the present invention. Further, FIG. 14 is a diagram showing an example of an actual in-rush current waveform. Furthermore, Fig. 15 is a block diagram of a conventional ratio differential relay device that detects interruptions in current, Fig. 16 is a diagram showing the operation of the relay device shown in Fig. 15, and Fig. 17 shows that the relay device swings into both positive and negative polar waves. 10 is a diagram showing the operation of the relay device of FIG. 9 with respect to inrush current; FIG. In the figure, 1 is the transformer to be protected, 2, 3.9 are current transformers, 4 is a breaker, 6 is a ratio differential relay element, 10 is an inrush waveform determination element, 11, 15.16 is a time limit circuit , 12.1
7 is an inhibit circuit, 13 is a comparison circuit, 14.20 is a rectangular wave conversion circuit, 18 is an instantaneous relay element, 19 and 22 are OR circuits, and 23 is a voltage transformer. Note that the same reference numerals in the figures indicate the same or similar parts.

Claims (1)

[Claims] 1. A rectangular wave conversion circuit that converts a comparison value between a terminal voltage of a transformer and a differential current between the terminals into a rectangular wave signal, and means for generating a rectangular wave signal when the polarity of the terminal voltage is reversed. and a time limit circuit for giving a predetermined time limit to the OR signal of the rectangular wave signal produced by this means and the rectangular wave signal of the rectangular wave conversion circuit, and a differential relay that responds to the differential current by the output of this time limit circuit. and means for locking the output of the electrical element. 2. The means for generating a rectangular wave signal when the polarity of the transformer terminal voltage is reversed includes a rectangular wave conversion circuit that determines the presence or absence of the terminal voltage, and a NOT that inverts the output of this rectangular wave conversion circuit.
The transformer protection relay device according to claim 1, characterized in that it consists of a circuit. 3. A patent characterized in that the timer circuit comprises a first timer circuit that continuously outputs the OR signal for a predetermined time period T2, and a second timer circuit that maintains the output of the first timer circuit for a predetermined time period T3. A transformer protective relay device according to claim 1.