JPS6074924A - Ratio differential relay for protecting transformer - 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] [Technical Field of the Invention] The present invention relates to a ratio differential relay for protecting a transformer, and particularly to a ratio differential relay for protecting a transformer.
This invention relates to a ratio differential relay for protecting a transformer, which shortens the trip time in the event of a disconnection.

[Technical background of the invention]

FIG. 1 shows a conventional ratio differential relay for protecting a transformer, in which a current is provided at each terminal across a power transformer 1 and flows through a current transformer 2 to each terminal.

A current IX, (2) which is more proportional to VC is introduced so that the ratio differential relay 3 can discriminate between internal and external faults and trip the circuit breaker 4.

FIG. 2 is a block diagram of a conventional ratio differential relay. In FIG. 2, the ratio differential element 6 is (r, , +
I'B)-Kt(II'AI+IIQl)≧KO (KHIKO is a constant), and the amount of suppression is II
%l+lx'Bl (7) In addition, use the maximum value of knee and ■t.

There are various methods.

FIG. 3 is a characteristic diagram of the ratio differential relay, and the characteristic of the differential element 6 is shown by 10. In Fig. 2, the high setting overcurrent element 5-wire A4. , I N ≧ is a 2 operation formula (K2 is a constant), and its characteristic is shown in 11 of the 3rd IνI. The second harmonic detection element 7 is, for example, an element that operates when the prefecture co=1 harmonic current with respect to the fundamental wave end current of the differential current property + engineering t reaches a predetermined value of 3 (Ks is a constant) or more. This is an element used to lock the output of the ratio differential element 6 so that the ratio differential relay does not malfunction when the excitation inrush current generates a full differential current that apparently causes an internal fault in the transformer. . That is, as can be seen from the waveform example of the transformer magnetizing inrush current in Figure 4, the ratio of the second harmonic component, which is largely included in the transformer magnetizing inrush current, is detected to determine whether it is the transformer magnetizing inrush current. This is an element that determines whether or not.

As mentioned above, the ratio differential relay 3 has a high setting overcurrent element 5.
, a ratio differential element 6 and a second harmonic detection element 7, and the output of the ratio differential element 6 is the same as that of the OR circuit 9 only when there is no output from the second harmonic detection element 7. Since the output of the high-settling overcurrent element 5 is also input to the OR circuit 9, if at least one of the two inputs is input, the OR circuit 9 outputs the input, and thereby the ratio differential Relay 3 outputs a rip command to keep the transformer cool.

[Problems with background technology]

In the conventional ratio differential relay 3 having the above configuration, when the circuit breaker 4 is turned on while there is an accident inside the transformer, the second harmonic detection element 7 is activated to detect the magnetizing inrush current and the ratio difference is Since the dynamic element 7 operates and locks the output direction of the ratio differential element 6, the ratio differential relay 3 does not operate and no trip output is derived. This state continues until the excitation inrush current attenuates and the content ratio of the second harmonic current to the fundamental wave current becomes a predetermined value of 3 or less. When this content ratio becomes less than the predetermined value, the ratio difference The dynamic relay 3 operates for the first time and outputs a trip command to the circuit breaker 4. Therefore, the trip time was significantly delayed compared to a normal accident, and the damage to the transformer was extremely large.
The hydraulic pressure inside the transformer exceeded the strength of the tank and there was a risk of an explosion. This danger has traditionally been regarded as a major problem, but there has been no effective countermeasure, and solving the problem of protection during power-on failures in transformers has been a major challenge for many years.

``Purpose of the Invention'' The present invention has been made with the aim of solving the above problems, and even when a breaker is turned on and voltage is applied to a transformer in a state where an accident has occurred, the trip time can be reduced. The purpose of this invention is to provide a ratio differential relay for transformer protection without delay.

[Summary of the invention]

In the present invention, the phase of the differential current is determined by introducing the terminal voltage in addition to the current at each terminal across the transformer. Only time,
It attempts to lock the second harmonic wave detection element to the ratio differential element. That is, when voltage is applied to the transformer, if the transformer has an internal Y-fault, the phase of the differential current is far from the phase region when there is only an excitation inrush W, so the second t'l The wave detection element does not interfere with the ratio differential element, and there is no delay in the trip operation time.

Embodiments of the Invention] Examples will be described below with reference to the drawings. FIG. 5 is an application diagram of an embodiment of a ratio differential relay for protecting a transformer according to the present invention. The symbols 1, 2, 4 and 〇/, 〇, 〇 in the figure correspond to those in Fig. 1. J2 is a ratio differential relay, in which a current 1 proportional to t rB flows through each terminal via a current transformer 2 placed between the power transformer 1.
:, , 工′, are introduced.

Also, a voltage V proportional to the A terminal voltage V of the power transformer 1
' is connected to the ratio differential relay 12 via the opening voltage transformer 13.
It was introduced in 9.

FIG. 6 is a block diagram of an embodiment of a ratio differential relay.

Reference numerals 5 to 9 in the figure correspond to those in FIG. In FIG. 6, the input current from the current transformer 2 is introduced into the high setting fixed overcurrent element 5, the ratio differential element 6, the second harmonic detection element 7 and the vector sum generation circuit 14, respectively. . The output of the vector sum generation circuit 14 and the input voltage V' are determined by the phase determination circuit 1.
5 will be introduced. The output of the second harmonic detection element 7 and the output of the phase determination circuit 15 are introduced into an AND circuit 16, and the output of the AND circuit 16 is used as the inhibition side input of the inhibit circuit 8 and as the output of the ratio differential element 6. is introduced as the non-inhibition side input of the inhibit circuit 8. The output of the inhibit circuit 8 and the output of the high setting element 5 are introduced into an OR circuit 9, and the output of the OR circuit 9 becomes the output of the ratio differential relay 12.

That is, as is clear from the above configuration, the difference between this embodiment and the conventional example is that the output of the phase determination circuit 15 is added to the output of the second harmonic detection element 7, and the other configurations are the same. It is. Here, the phase determination circuit 15 determines the phase of the differential current based on the input voltage V', and locks the output of the second harmonic detection element 7 only when this is near the phase region when only the excitation inrush current is present. Lively. The other operations are the same as those of the conventional example described above, so they will be omitted.

FIG. 7 is a characteristic diagram of the phase determination circuit. As is clear from the figure, the operating range indicated by diagonal lines is determined by considering that the excitation inrush current lags approximately 90° with respect to the excitation voltage, and the input current ■'. When the vector sum current 4 of , 1, and 4 is in the operating range, the phase determination circuit 15 outputs "1", and the second harmonic detection element 7 can lock the ratio differential element 6.

Figure 8 is a characteristic diagram at the time of an internal accident. In this case, at the time of excitation inrush current i. The vector sum current I of and faulty current I,
is outside the operating range of the phase determination circuit 15, the phase determination circuit 5 remains inoperative, the second harmonic detection element 7 does not lock the output of the ratio differential element 6, and the ratio differential relay 12 It operates without delay in operation time and can protect the transformer.

FIG. 9 is a vector diagram of a fault current caused by a fault point resistance, and the phase of the fault current will be briefly explained using this diagram. Furthermore, FIG. 9(a) shows the case where the resistance at the fault point is small, and similarly FIG. 9(b) shows the case when the resistance at the fault point is large. Generally, in most transformer faults, the high-settling overcurrent element and the ratio differential element are operable, and a fault in which only the ratio differential element responds is an accident with a large fault resistance (Figure 9 (b)).
reference). The internal accidents that are a problem due to the excitation inrush current are the internal accidents in the perspective area of Figure 10 where the high settling overcurrent element 5 cannot be relied upon, and most accidents occur in this area where the resistance at the fault point is large. It is. Moreover, since the vector of the fault current I flowing in this case is close to the phase of the vector of the input voltage V', it can be seen that the ratio differential relay 12 can detect a fault at the time of the magnetizing inrush current according to the above operating range. .

FIG. 11 shows another embodiment of the phase determination circuit, and in this embodiment, it is an impedance determination circuit. In this case, it is particularly effective when the voltage fluctuates during an accident.

In addition to the current of the same phase, the input of the second harmonic detection element described above may be of a type that takes in an amount of electricity related to a current of another phase.

In the above embodiment, a two-winding transformer has been described, but it goes without saying that a transformer with three or more windings can be constructed in the same way.

〔Effect of the invention〕

As explained above, according to the present invention, the method locks the cutoff command by detecting that the excitation inrush current is generated according to the proportion of the second harmonic component flowing in the differential circuit of the ratio differential relay. In the transformer protection device of It is possible to provide a ratio differential relay for protecting a transformer, which does not delay its operation time even in most accidents when it is turned on.

[Brief explanation of drawings]

Figure 1 is an application diagram of a conventional ratio differential relay for protecting transformers.
Figure 2 is a block diagram of a conventional ratio differential relay;
Figure 4 is a characteristic diagram of a ratio differential relay, Figure 4 is a waveform diagram of magnetizing inrush current, Figure 5 is an application diagram of an embodiment of the ratio differential relay for transformer protection according to the present invention, and Figure 6 is a diagram of the ratio differential relay. A block diagram of one embodiment of the relay, Figure 7 is a characteristic diagram of the phase determination circuit, Figure 8 is a characteristic diagram of the phase determination circuit.
The figure is a characteristic diagram at the time of an internal fault, and Figure 9 is a vector diagram of fault current due to fault point resistance. 1... Power transformer 2... Current transformer 3.12...
Ratio differential relay 4... Breaker 5... High setting constant overcurrent t, 1 element 6... Ratio differential element 7... Second harmonic detection element 8... Inhibit circuit 9... OR circuit 13... Voltage transformer for can opening 14... Vector sum current detection circuit 15... Mu gamma phase determination circuit 16... AND circuit Patent applicant Tokyo Shibaura Electric Co., Ltd. Agent Patent attorney Ishii Norio Figure 1 Figure 3 Figure 5 Figure 6 . Fig. 7 906 Fig. 8 2'''70' ↓JF Tanika Fig. 11 Hand Itotome Amendment Book (Method) % Formula % (1Mrfi Unihouse 2101 Name 75.'(li j4i Ri 1 Ishii Ki) Man Te
1. (03) 586-55565, Sodome no Mikoto・'')
[Attachment 1, January 11, 1980 (shipped)] January 31, 1982) I), The death of the drawing subject to amendment, the tank lua of the explanation of r door'fr, of the amendment '6 Separate 4th amendment [... is a vector diagram] described in the 9th line of the brief description of the drawing section on page 10 of the contents specification box. ] to [...vector diagram, 1 and then add the following. ``Figure 10 is a characteristic diagram of a ratio differential relay to explain internal faults that cannot rely on high-settling overcurrent elements.
FIG. 1 is another characteristic diagram of the phase comparison and determination circuit. ” From

Claims (1)

[Claims] A ratio differential relay is equipped with a magnetizing inrush current determining element that suppresses or prevents the operation of the relay when a magnetizing inrush current occurs, in which a differential current due to the current at each end is introduced into a current transformer that is placed between two transformers. , the terminal voltage of the transformer is introduced into the ratio differential relay to determine the phase with the differential current, and only when the differential current enters a predetermined lag power factor region from the terminal voltage, excitation is performed. A ratio differential relay for protecting a transformer, characterized in that the output of an inrush current determination element is enabled.