JPH0467719A - Ratio differential relay for protecting transformer - Google Patents

Abstract

PURPOSE:To prevent a malfunction by conducting outputting to another phase under conditions, in which the detecting level of the content of the second harmonic of excitation rush current is a detecting value or higher even in one phase out of three phase, and locking a relay under the conditions. CONSTITUTION:Excitation rush current at a time when a power supply is turned ON is made to flow into a relay, and the levels of a ratio differential detecting element deciding an internal or external fault and a second harmonic detecting element detecting excitation inrush current are decided. When the second harmonic detecting element is returned at a time faster than the ratio differential detecting element, the second harmonic detecting element receives a second harmonic detecting signal from another phase and outputs a novel lock signal, thus preventing the malfunction of the relay. Accordingly, the malfunction of the relay, which may be generated by the time coorporation of the ratio differential detecting element and the second harmonic detecting element by an excitation rush-current waveform, and a malfunction due to the lowering of the content of a second harmonic generated by the delta connection of the current transformer of a system can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a ratio differential relay for protecting a transformer, and more particularly to a ratio differential relay for protecting a transformer that prevents malfunctions caused by magnetizing inrush current. .

[Prior art J Ratio differential relays are generally used to protect transformers, and when a transformer is connected to the grid, an inrush current of more than 10 times the rated current flows through the transformer, and these Since the magnetic energy on the primary and secondary sides of the transformer is not equal, it is the same as that of a reactor, so it appears as if there is an internal fault and the differential relay malfunctions.

Therefore, there is a conventional ratio differential w1 electric appliance with second harmonic suppression as a device for distinguishing and determining these inrush currents and internal fault currents. FIG. 4 is a circuit diagram showing a conventional ratio differential relay with second harmonic suppression disclosed in, for example, Japanese Unexamined Patent Publication No. 53-111451.

In the figure, (4) is a CT differential circuit, (42) is an input transformer, (43) is a second harmonic blocking R-wave filter, (44) is an operating coil, and (45) is a fundamental wave blocking circuit. A second harmonic passing P-wave device, (46) a suppression coil, and (47) a relay element composed of an operating coil (44m suppression coil (46)).

Next, the operation of the conventional ratio differential relay shown in FIG. 4 will be explained. When an internal fault current or excitation inrush current is input to the CT difference 1 circuit (41), the DC component of these differential currents is removed by the input transformer (42). After that, L-
The harmonic components outside the fundamental wave and the second harmonic are removed by the second harmonic blocking device (43) by the operating coil (44).
> flows to On the other hand, since the second harmonic component flows into the second harmonic pass filter (45) with fundamental wave blocking, only the second harmonic flows into the suppression coil (46). Since the magnetizing inrush current contains more second harmonics than the fault current, the fault current flows to the operating coil (44) and the magnetizing inrush current flows to the suppression coil (46). Therefore, it is possible to distinguish between the internal fault current and the excitation inrush current, and the operating coil (44)
This caused the system to trip in the event of an internal accident.

[Problem to be solved by the invention] Since the conventional ratio differential relay for transformer protection is configured as described above, it has a second harmonic blocking r-wave device and a second harmonic passing r-wave device with fundamental wave blocking. Depending on the delay and time coordination of the transformer, the application conditions of the excitation inrush current when the power is turned on, and the specification conditions of the system, components other than the second harmonic may flow into the operating coil side and malfunction may occur.In particular, protect the transformer. CT of
Because the connection does not circulate the zero-sequence current, it is a Δ (telta) connection, so the inflow current to the relay becomes a difference current between each phase, and the content of the second harmonic decreases, causing problems such as malfunction.

This invention was made to solve the above problems, and provides a ratio differential relay for protecting transformers that can detect the second harmonic in the excitation inrush current when the power is turned on and effectively lock the relay. The purpose is to obtain.

[Means for Solving the Problems] A ratio differential relay for protecting a transformer according to the present invention includes a ratio differential detection element that determines an internal or external fault of the transformer, and a ratio differential detection element that detects an excitation inrush current when the power is turned on. If the detection level of the content rate of the second harmonic of the excitation inrush current exceeds the detection value in one of the three phases, it outputs to the other phases under that condition and locks the relay. It is.

[Function] In this invention, if a content rate higher than the level detection value of the second harmonic detection element is detected in even one of the three phases in the CTΔ connection, there is a possibility of malfunction in other phases. - Outputs the same lock signal as when detecting the second harmonic for a fixed period of time. However, if the second harmonic is detected in the phase in which the output lock signal is received, the temporary lock signal from the other phase will be invalidated, and if the second harmonic is not detected, the temporary lock signal from the other phase will be invalidated. The temporary lock signal is activated to lock the relay for a certain period of time to prevent malfunction.

Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
Figure 6 is a circuit configuration diagram showing an embodiment of the present invention. In Figure 6, (1), (3), and (5) are ratio differential detection elements for determining internal and external faults of the transformer; (2) ,(4),(
6) is the second harmonic detection element that detects the excitation inrush current when the power is turned on - (7) is the second harmonic detection element (2), (4)
, (6) is an OR circuit that takes the logical sum of each output, and (8) is O
An operation timer circuit provided on the output side of the R circuit (7), (
9) is an inhibit circuit that receives the output of the OR circuit (7) and the output of the operation timer circuit (8), and (10) is an inhibit circuit that receives the output of the second harmonic detection element (2) and the output of the inhibit hint circuit (9). (11) is an inhibit circuit that receives the output of the second harmonic detection element (4) and the output of the inhibit circuit (9); (12) is a circuit that receives the output of the second harmonic detection element (6) and the inhibit circuit (9); ) is the inhibit circuit that receives the output of 13) is the ratio differential detection element 1
(14) receives the output of the ratio differential detection element (3), the output of the second harmonic detection element (2), and the output of the inhibit circuit (10); (4) output and inhibit times 1 (11
), (15) is the output of the ratio differential detection element (5), and the second harmonic detection element (
6) and the output of the inhibit circuit (12); (16) is an OR circuit that ORs the outputs of the inhibit circuits (13), (14> and (15)); (17), ( 1) and (21) are the signal lines after determining the level of the ratio differential detection element, (18), 20) and (22) are the signal lines after determining the level of the second harmonic detection element, and (23) is the signal line after determining the level of the second harmonic detection element. 2nd harmonic detection element 3 phase ○R output signal line, (24) is the output signal line after passing the operation timer, (25)
indicates that one of the three phase second harmonic detection elements has detected the second harmonic above the level, and (26), (27) and (28) are the signal lines for each phase. Lock signals to the elements, (29), (30) and (31) are the output signals of each phase, and (32) is the relay trip signal.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained. Figure 1 shows the state after the excitation inrush current flows into the relay when the power is turned on, and the level is determined by the ratio differential detection element that determines internal and external faults and the second harmonic detection element that detects the excitation inrush current. This is what I did. Each element output signal line 17), (18), (19), (20), (21)
And (22) is expressed as -H-5-L-, then -
H means that it is detected to be above the level, and -L- means that it is judged to be below the level. When the signal line (25) detects the second harmonic in any one of the three phases, the -14- signal is continued for a predetermined time by the operation timer circuit (8),
It means a signal line that becomes -I-1 after its duration. or,
The signal line (26) is not detecting the second harmonic detection element (2) of that phase, but the other phase is detecting the second harmonic.
That is, it means a signal line that becomes -H when the signal line (25) is H-, locking the relay, and becomes -L- under other conditions. Also, the signal lines (two) carry the operation signal ~H- of the element.
-L- means non-operation. Figure 2 shows a typical example when there is no problem when the power is turned on, and Figure 3 shows the level of the excitation inrush current determined by the ratio differential detection element and the second harmonic detection element, and the level of the excitation inrush current is determined by the ratio differential detection element and the second harmonic detection element. This shows the case where the ratio returns earlier than the differential detection element. In response to the second harmonic detection signal from this special phase, a new lock signal is output to prevent the relay from malfunctioning.6 In addition, in the above embodiment, if the second harmonic is detected even in one phase, the relay will operate. Timer circuit (
8) to issue a lock signal, but if an internal accident occurs and the ratio differential detection element detects the level and operates, the lock time will become a problem. Malfunction mode, for example, when the power is turned on, when the second harmonic is detected on all three phases, when the second harmonic is detected on only two phases, when the second harmonic is detected on only one phase, the operation will occur in the most likely state. It may also be driven by a timer circuit (8).

Further, the waveform shaping circuit constituted by the OR circuit (7), the operation timer circuit (8), and the inhibit circuit (9) may be constituted by a one-shot circuit or the like. For example, by using the set terminal and reset terminal of a flip-flop, 3
A method may also be used in which the output of the second harmonic detection element which is the earliest among the phases is set, a lock signal is outputted, and the lock signal is reset by the slowest signal of the ratio differential detection element to release the lock signal. Also, as a setting method, AND the output of the ratio differential detection element and the output of the second harmonic detection element.
You can also take

Further, other harmonics may be used as long as it is easier to detect the difference between an excitation inrush current and an internal fault depending on the specifications of the system.

[Effects of the Invention] As described above, according to the present invention, the ratio differential detection element for determining internal and external faults of the transformer and the detection element for detecting the magnetizing inrush current at power-on are provided, and the magnetizing inrush If the detection level of the content rate of the second harmonic of the current is higher than the detection value for any one of the three phases, the output is output to the other phase and the relay is locked under that condition, so depending on the excitation inrush current waveform, A ratio difference for protecting transformers that can prevent malfunctions of relays caused by time coordination between ratio differential detection elements and second harmonic detection elements, and malfunctions due to a decrease in the content of second harmonics caused by delta connections of current transformers in the grid. There are effects that can be obtained from dynamic relays.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a timing chart when the lock signal from the waveform shaping circuit according to the present invention is invalid, and FIG. FIG. 4 is a timing chart when the lock signal is valid, and is a circuit configuration diagram showing a conventional ratio differential m electric device 3 for protecting a transformer. In the figure, (1), (3), and (5) are ratio differential detection elements, (2), (4), and (6) are second harmonic detection elements, and (
7), (16) are OR circuits, (8) are operation timer circuits,
(15) are inhibit circuits. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] Comprising a ratio differential detection element for determining internal and external faults of the transformer, and a detection element for detecting magnetizing inrush current at power-on, the content rate of the second harmonic of the magnetizing inrush current is A ratio differential relay for protecting a transformer, characterized in that if the detection level of any one of the three phases exceeds the detection value, the output is output to the other phases under that condition and the relay is locked.