JPS5910126A - Transformer protecting repeating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] This invention provides a transformer protection relay that takes harmonic suppression measures as a countermeasure against inrush current. This invention relates to a transformer protection relay device with harmonic countermeasures that prevents the transformer from being locked and unable to operate. The most typical type of transformer protection is the ratio differential relay system shown in Figure 1. In the figure, (1) is the transformer to be protected, (2) (, 3) are the high voltage side and low voltage side 0C, respectively.
T (current transformer), (4) is a breaker, (5) is a power supply, and (6) is a ratio differential relay. In the ratio differential relay system shown in Figure 1, when the breaker (4) is turned on and the transformer is excited with no load, a so-called excitation inrush current (inrush current) θX flows in from the electric 11@ side. However, the CT secondary 1[ff1iex of the inrush current generator eX flows into the differential circuit of the ratio differential relay (6), and a differential operation output that appears to be the same as an internal failure of the pressure regulator (1) occurs, causing a ratio difference. Dynamic relay (
6) may malfunction. Ratio differential relay (6)
is a differential relay in which the operating force is the difference between the input and output currents in consideration of the winding ratio of the transformer (1), and the suppressing force is the sum of the input and output currents. As for the suppressing force, the maximum of the input and output currents or the maximum of the input and output currents may be adopted.

Various measures have been taken to counter this inrush, but the most common method worldwide is:
Focusing on the harmonics contained in the inrush current, especially the second harmonic f2, the second harmonic f2 contained in the differential current
is more than a certain ratio to the fundamental wave fl (generally f
z/f ln 0.15) This method determines that it is an inrush current and locks the ratio differential relay (6) to prevent vAvJJ from occurring.

FIG. 2 shows the above method. In the figure, (6) is a ratio differential relay, (7) l- is a harmonic detection circuit, and (8) is an inhibit circuit. 6) is shown to be locked.

As mentioned above, countermeasures against inrush due to the second harmonic have been effective, but recently there have been cases where the ratio differential relay of the second harmonic locking method cannot be used due to the following points. In other words, recently, the transformer body has been designed economically, and the saturation magnetic flux of the iron core has less margin compared to the rated magnetic flux, making it easier to saturate during inrush, and as a result, the basic value contained in the inrush current The ratio of the second harmonic to the wave (f2/fl) is decreasing. In the past, f2/f+ during inrush current did not fall below 15%, but recently, due to the above reasons, cases have occurred where f2/ft becomes less than 15%, and as a result, inrush current when the transformer is turned on has become less than 15%. There have been cases of malfunction.

If this is just the case, use f2/fl for inrush detection.
The percentage of
%) This is a good thing, but the problem is that power systems have recently become larger and more complex, especially due to the expansion of high-voltage cable transmission networks in urban areas and the centralization and remoteization of power sources in 2008. With the advent of long-distance power transmission lines, ground capacitance has increased, and due to the resonance between this ground capacitance and the inductance of the transmission line, harmonic currents with a wide range of frequencies can be generated for a relatively long period of time (several cycles) in the event of an accident. It has become clear. The harmonics generated at the time of this accident include all the same wave number components depending on the system conditions, but in systems with large ground capacitance (cable systems, systems with starboard inserts, etc.), the second harmonic wave is already the fundamental wave. Strains that contain about 30% of the This means that in the event of an internal fault in a transformer, if such a large second harmonic component is included in the fault current, the ratio differential relay with second harmonic countermeasures will lock due to the inrush current countermeasure and cause an internal failure. However, it will not work. In theory, the harmonics generated during this failure will be attenuated by the resistance component and will attenuate after the failure cycle, but if the transformer protection relay becomes locked during that time, there is a risk of major disasters such as destruction of the transformer tank. The sex is great.

Conventional transformer protection relay devices are composed of the ratio differential relay with second harmonic suppression as described above, so in the event of an internal fault in the transformer, it will not be able to operate until the second harmonic is attenuated.
It had drawbacks that could lead to major accidents, such as transformer explosions.

This invention was made for the purpose of eliminating the above-mentioned drawbacks of the conventional ones, and is used when inrush countermeasures are required, that is, after voltage has been applied to a transformer or when the applied voltage increases. By making use of the conventional harmonic suppression circuit for a certain period of time after the current is applied, and by enabling the output of the differential relay before the locking function of the harmonic suppression circuit is activated at other times, the inrush current will not malfunction and the internal The present invention provides a transformer protection relay device that can operate without being affected by second harmonics during an accident.

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure, (9) is a voltage dividing capacitor that detects the voltage applied to transformer (1), and (10) is an undervoltage detector that detects that the voltage applied to transformer (1) is below a predetermined value. , (11) is a delay timer circuit that receives the output of the undervoltage detector (10) and outputs the output after shifting it by a certain time t.
2) is an AND circuit. In the figure, ■ is the grid voltage, V6
, v7, V8, V+o, l/11, V12
, are the outputs of each Glock circuit. Inrush occurs in the transformer (1) when voltage is applied by closing the breaker when the transformer starts, or when the voltage drops due to an external low fault when the transformer starts and is recovered by removing the external fault. This occurs only when voltage is applied, and does not occur at other times.

Therefore transformation! (1) The undervoltage detector (10) identifies whether the condition is such that K inrush current is generated, and the delay timer circuit (11) detects the undervoltage i (10).
By shifting the output of This prevents the ratio differential relay (6) from malfunctioning due to the generation of second harmonics in the event of an internal fault.

For a brief explanation of the operation of the embodiment, Fig. 4 shows the occurrence of an internal fault when voltage is applied to the transformer, and Fig. 5 shows the internal fault including the second harmonic when voltage is applied to the transformer. The times are shown in FIG. 6 as a time chart when a voltage is applied to the transformer combined with the examples shown in FIGS. 4 and 5, and at the same time when an internal accident occurs.

FIG. 4 will be explained.

Initially, the predetermined voltage is not applied to the transformer (1), so the undervoltage detector (10) outputs v+o, and the delay timer (11) also receives VIG and outputs Vll. Transformation 1! (1) When the K voltage is applied, the undervoltage detector (10) stops outputting, but the I erase timer (11)
) and V'to disappears, and Vll is output for a certain period of time t.

When the second harmonic component included in the inrush current accompanying the voltage application is at a predetermined ratio or more with respect to the fundamental wave component, the high illumination wave detection circuit (7) outputs the signal V7.

AND times u' (12) Id Vt ] and V717)
The output V12 is inputted to the inhibit circuit (8) to block the output v6 of the ratio differential relay (6).

Here, the time required for the harmonic detection circuit (7) to fall below the inrush detection level is tl, and the ratio differential relay (6)
t2 is the time it takes for
Then, the fixed time tF of the delay timer circuit (11)
It is necessary to set it longer than the shorter of 'it+ and t2.

FIG. 5 will be explained.

Since the transformer voltage drops when an internal failure occurs, an undervoltage detector (10) outputs Vlo, and a delay timer (11) receives VIO and outputs Vll after a certain period of time. The harmonic detection circuit (7) outputs v7 during a period in which the second harmonic component included in the fault current is at a certain ratio or more with respect to the fundamental wave component, but the AND circuit (1
2) Fi is not output for a certain period of time t, thereby invalidating the output v7 of the harmonic detection circuit (7). In the case of Fig. 5, the delay timer (11) has a delay time of t.
) t3, there is no risk that the relay will malfunction due to malfunction of the undervoltage detector (10).

Furthermore, the method of introducing the voltage condition of the undervoltage detector (10) is not limited to the method using the voltage dividing capacitor (9).
Transformer (1) FT (, FD) installed on the primary and secondary sides
Another possible method is to introduce it from

As described above, according to the present invention, the inrush countermeasure circuit is utilized only when voltage is applied where inrush occurs, and is configured so as not to be involved in the operation in the event of an internal fault in the transformer.
It is possible to obtain a transformer protection relay device that can operate normally even if any harmonics (including second harmonics) occur during a system fault.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing an application example of a conventional ratio differential relay to protect a transformer, Fig. 2 is a block diagram showing an inrush countermeasure circuit of the system diagram shown in Fig. 1, and Fig. 3 is a system diagram showing the inrush countermeasure circuit of the system diagram shown in Fig. 1. FIG. 4 is a time chart of the relay device of the present invention during an inrush, and FIG. Figure 6 is a time chart of the relay device of the present invention at the time of an internal accident of the transformer at the same time as an inrush, and Figure 7 is a time chart showing another embodiment of the transformer protective relay device of the present invention. It is a diagram. In the figure, (1) is a transformer, (6) is a differential relay such as a ratio differential relay, (7) is a harmonic detection circuit, (8) is an inhibit circuit, (10) is an undervoltage detector, ( 11
) is a tiller timer circuit, and (12) is an AND circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Makoto Kuzuno - Figure 1 Figure 2 Figure 3 Figure 4 EpθU: vB'-111---1---Figure 5, “゛Figure 6 6p5o Simultaneous $F V □ Figure 7

Claims (1)

[Claims] an undervoltage detector that detects that the voltage applied to the transformer is less than a predetermined value; a delay timer circuit that receives the output of the undervoltage detector and outputs the output after a certain period of time;
a harmonic detection circuit that detects that the ratio of the harmonic components of the transformer current to the fundamental wave components is greater than or equal to a predetermined value;
A differential relay that responds to the difference between the input current and output current of the transformer is installed, and the delay timer circuit and the harmonic detection circuit are connected to each other.