JPS6327924B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protective relay device for a transformer with measures against magnetizing inrush current.

When a transformer is connected to a large-capacity system, a magnetizing inrush current containing harmonic components flows, causing a differential relay for protecting the transformer to malfunction.

Various countermeasures have been taken to address this problem in the past, but currently the most effective countermeasure is a method that utilizes the second harmonic component, which is largely contained in the excitation inrush current. It is being

There are two types of protective relay devices that utilize this second harmonic component: a digital type and a conventional analog type.

Figure 1 is a circuit diagram showing a digital protective relay device with a countermeasure against magnetizing inrush current malfunction using the second harmonic belonging to the former category. In response, the normally open contact 1a is closed and a trip signal is sent to protect the transformer (not shown). On the other hand, when the second harmonic detection circuit 3 detects the second harmonic component in the fault current, it sends out a lock signal to prevent the ratio differential relay 1 from responding via the signal line 4. The normally open contact 1a of the ratio differential relay 1 therefore remains open. That is, the ratio differential relay 1 maintains a non-operating state and does not malfunction in response to the excitation inrush current that contains a large amount of second harmonic components.

FIG. 2 is a circuit diagram showing an analog protective relay device with second harmonic suppression that belongs to the latter category.
Due to the second harmonic of the magnetizing inrush current, the main differential element 5
is activated and the normally open contact 5a is closed, the second harmonic suppression element 6 is not activated, and the normally open contact 6a is opened, so the entire system is inoperative, and there is no risk of malfunction due to the excitation inrush current. do not have.

Here, the principle of second harmonic detection will be explained with reference to FIGS. 3 and 4. First, as shown in FIGS. 3 and 4, sampling values of currents shifted by 180 degrees are taken, and the sum of the values is calculated and detected.
That is, in the fundamental wave current shown in FIG. 3, if the current value at sampling point 7 is i(t-180) and the current value at sampling point 8 is i(t), and the sum is taken, the following equation is obtained.

i(t)+i(t-180)=0...(1) Next, for the second harmonic current shown in FIG. ) and take the sum, i(t)+i(t-180)≠0...(2). Therefore, if the sum of equation (2) is not 0, the second
It is determined that there is a harmonic component.

By the way, the frequency of transformers in power plants varies from 0 to about twice the rated frequency. Therefore, when using the digital protective relay device described above,
There is a frequency where the sum of the sampled values of the current shifted by 180° does not become 0, and even if an internal failure occurs in such a case, the detection circuit 3 will lock the ratio differential relay 1 and send out a trip signal. There is a possibility that it will not be done. Further, in the case of an analog type protective relay device, the second harmonic suppression element 6 is activated at a frequency approximately twice the rated frequency, and does not operate even in the event of an internal failure, and no trip signal is transmitted.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional technology, and when operating at the rated frequency, the locking mechanism using the second harmonic and the second harmonic suppressing element are activated, and when operating at a frequency other than the rated frequency. The purpose of the present invention is to provide a protective relay device for a transformer that operates reliably in the event of an internal failure even during frequency operation.

Hereinafter, one embodiment of the present invention will be described based on FIG. 5.

1, 2, 3, and 4 shown in the figure are the ratio differential relay 1, input line 2, detection circuit 3, and signal line 4 explained in FIG. It is a frequency relay that opens.

In the case of rated frequency operation, the frequency relay 11 shown in the figure is inactive and the normally closed contact 11b remains closed, so the detection circuit 3
Therefore, there is no possibility of malfunction due to the second harmonic. On the other hand, in the case of operation at a frequency other than the rated frequency, the normally closed contact 11b is opened by the operation of the frequency relay 11, and the signal line 4 is cut off, so that the operation of the ratio differential relay 1 is not locked. Therefore, in the event of an internal failure, it operates reliably and sends out a trip signal.

Note that since the transformer (not shown) is not turned on at frequencies other than the rated frequency, there is no malfunction due to magnetizing inrush current when operating at a frequency other than the rated frequency.

In the above embodiment, the lock signal is cut off by opening the normally closed contact 11b of the frequency relay 11, but as shown in FIG. The normally closed contact 12b of the activated auxiliary relay 12 may be opened to disconnect the signal line 4 of the detection circuit 3, or the normally closed contact 12b of the auxiliary relay 12 may be opened as shown in FIG.
Even if the input line 2b is inserted into the input line 2 of the detection circuit 3, the same effect as in the above embodiment can be obtained.

Furthermore, as shown in FIG. 8, for the ratio differential relay with second high frequency suppression, the auxiliary relay 12
It goes without saying that the second harmonic suppressing element 6 may be kept in the operating state by closing the normally open contact 12a of the second harmonic suppressing element 6.

As described above, according to the present invention, the trip signal of the ratio differential relay is locked or the suppressing force of the second harmonic suppressing element is prevented from working when operating at a frequency other than the rated frequency. Therefore, a protective relay device for a transformer that can reliably detect an accident can be obtained.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams showing a conventional protective relay device for a transformer, Figures 3 and 4 are explanatory diagrams of a second harmonic detection method, and Figure 3 shows the basic waveform. Fig. 4 is a diagram showing the second harmonic waveform, Fig. 5 is a circuit diagram showing an embodiment of the protective relay device for a transformer according to the present invention, and Figs. FIG. 7 is a circuit diagram showing another embodiment. 1 is a ratio differential relay, 1a is a normally open contact, 2 is an input line, 3 is a detection circuit, 4 is a signal line, 11 is a frequency relay, 12 is an auxiliary relay, and 11b and 12b are normally closed contacts. Note that the same reference numerals in each of the above figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A ratio differential relay that sends a trip signal in response to a fault current in a transformer; The second one sends out the lock signal of the trip signal.
Protection of a transformer characterized by comprising a harmonic detection circuit, and a frequency relay that detects when the excitation frequency of the transformer deviates from the rated frequency and prevents the second harmonic detection circuit from sending out a lock signal. Relay device. 2. The protective relay device for a transformer according to claim 1, wherein the frequency relay cuts off the input to the second harmonic detection circuit when the frequency relay detects an out-of-rated frequency. 3. A protective relay device for a transformer according to the first claim, characterized in that the output of the second harmonic detection circuit is cut off when the frequency relay detects an out-of-rated frequency.