JPH03243114A - Current differential protective relay for transmission line - Google Patents

Abstract

PURPOSE:To surely judge a faulty phase by a method wherein a second operating section judges the phase relation between an output current and a zere-phase voltage and a third operating section judges the one-line ground fault phase in a transmission line based on the logical product of outputs from first and second operating sections. CONSTITUTION:When a one-line ground fault occurs, the phase of differential current in the fault phase is reversed from that of zero-phase voltage whereas it is in-phase for the sound phase, and thereby only second operating section 27A produces an output signal and other second operating sections 27B, 27C do not produce output signal. Since the output level of the second operating section 27B is L even when the first operating section 26B of a sound phase, e.g. phase B, produces an output signal through erroneous operation, output level of a third operating section 28B for taking a logical product goes L, and thereby the sound phase is not erroneously judged as a faulty phase resulting in the improvement of reliability as a protective unit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power transmission line current differential protection device that protects a power system based on current differential calculation.

[Conventional technology]

Figure 3 is a block diagram showing a general high-resistance grounding power system protection system. In Figure 9, (1) is the power transmission line of the power system to be protected, which is shown as a single line for convenience.
Actually, it consists of three phase wires: A phase, B phase, and C phase.

(2) is the terminal station installed at one end of the transmission line (1), and (3) is the other end of the transmission line (1) located a predetermined distance ahead of the transmission line (2). The other end is the terminal station installed at the other end, (4) is the busbar of the own end electric station installed at the own end (2), and (5) is the bus bar of the other end electric station installed at the other end (3). Bus bar, (6) is own end CT for detecting own end current 11 as own end current information, (7) is opposite end CT for detecting opposite end current I2 as opposite end current information, (8) is Own-end bus PT for detecting the bus voltage v1 of the own-end electrical station as own-end voltage information, (9) is the bus voltage of the opposite-end electrical station■
The other end bus line P for detecting 2 as the other end voltage information
T, (10) is a self-end circuit breaker for disconnecting the power transmission line (1) at its own end (2), and (11) is a counter-end circuit breaker for disconnecting the power transmission line (1) at the opposite end (3). It is a vessel.

(12) is an own-end relay device as a transmission line current differential protection device installed at the own end (2), (13) is the other end (3)
These relay devices (12) and (13) are normally connected to their own end CT (6) and their own end bus P, respectively.
T (8), the other end CT (7), the other end bus PT (9
)It is connected to the.

(]4) is the own-end communication device connected to the own-end relay device 1ifi (12), (15) is the other-end relay device (13)
The other end communication device (16) is a transmission path connecting the own end communication device (14) and the other end communication device (15), and the own end relay device (12) and the other end relay device (16) are connected to the other end communication device (16).
13) mutually transmit digital data related to current information.

Figure 4 shows the conventional self-end relay installation! (12) is a functional block diagram showing the internal configuration of the device (12), and the other end relay device (13), not shown, also has the same configuration.

In the figure, (17) and (18) are the input converter to which the terminal current ■ and the bus voltage V1 are input, respectively, (
19) and (20) are filter circuits connected to input converters (17) and (18), respectively, and (21) converts self-end current and voltage information from the filter circuits (19) and (20) into self-end digital data. A/D converter to convert, ku2
2) is a transmission interface connected to the own end communication device (14), which derives the own end digital data to the other end (3) and introduces the other end digital data. (23) is a calculation unit that calculates the difference current Id from the own end current 2 and the opposite end current 2, and (24) is a ratio protection calculation unit that determines a fault in the transmission line (1) from the difference current Id. .

Although only current, voltage, and 61 phases are shown here, in reality, if there is a three-phase or zero-phase circuit, the configuration will be a total of four phases.

Next, assuming that a one-line ground fault occurs in the A phase of the power transmission line (1), for example, the situation in which the fault current flows and the protection detection operation in this case will be explained with reference to FIG.

In Fig. 5, (IA) (IB) (IC> is the conductive line for each phase, (61A>(61B>(61C) is the self-end CT (6
1 secondary winding for each phase, (62Aj (62B>(62c)
are the tertiary windings for each phase of the self-end CT (6). Normally, these secondary and tertiary windings are wound around the same core for each phase as an integrated CT structure, which is economical and compact. is being planned. Similarly, (71A) (71B>(71C) means that the other end CT (
7) Secondary windings for each phase, (72A) (72B) (72C)
are the tertiary windings of each phase of the opposite end CT (7).

As is well known, the fault current at the time of a one-wire ground fault is three times the zero-sequence current at the time of the fault. Now, if the fault current flowing from the own end (2) side to the fault point is 3*1, and the fault current flowing from the opposite end (3) side to the fault point is 3*2, then both CTs (6) (7)
The current flowing through each winding is as shown in FIG. However, for convenience, the turns ratio of each winding of each CT (6) (7) is set to 1.

Therefore, the difference current Td input to the ratio protection calculation unit (24) of the A-phase self-end relay device (12) has a value expressed by the following equation.

I d= T A, 2 I A, =2 I , +2 I
2 = 2 (T, + I 2)≠O However, IA+ is the phase secondary winding (61
The current flowing out from A), IA2 is the A of the other end CT (7)
This is the current flowing out from the phase secondary winding (7 tA).

Therefore, the magnitude of this difference current Id is calculated by the ratio protection calculation unit (2
4) makes it possible to determine the fault phase of a one-wire ground fault.

[Problem to be solved by the invention]

By the way, if we pay attention to the operations of the other phases, B and C phases in the above case, for example, the ratio protection calculation unit (24) of the B phase
The difference current Id input to is a value expressed by the following equation.

I d= I Q, + I B2=-I l-I 2 (
11÷I2)≠0 However, IB+ is the B-phase secondary winding (61B
), IB2 is a current flowing out from the B-phase winding (71B) of the other end CT (7). The reason why current also flows through the secondary windings of phases other than the fault phase of the self-end CT (6) is as follows.

That is, the self-end CT (6> has a tertiary winding (
62A), (62B), and (62C) are wound, and these phase windings are connected to each other externally to form a closed circuit. Therefore, each phase winding (62A) (62B) (62C
), the zero-sequence current ■1 will equally flow through them. As a result, current flows through the secondary windings wound on the same core as these tertiary windings due to the so-called equal ampere turn of the transformer, as shown in FIG. In addition, in the A phase, the current of the primary winding (3I), which is the power transmission line, and the current of the secondary winding (61A), 2
Equal ampere-turns are established between I1 and the current T of the tertiary winding (62A).

As described above, the polarity is opposite to that of phase A, which is the fault phase, and the magnitude is 1/2, but the difference current Id also flows to phase B (same as phase C), and the ratio protection calculation unit (24) There was a problem that the relay device could malfunction.

This invention was made to solve the above-mentioned problems, and the purpose is to obtain a transmission line current differential protection device that does not malfunction and can reliably determine the fault phase of a single-wire ground fault. shall be.

[Means to solve the problem]

The transmission line current differential protection device according to the present invention is a conventional power transmission line current differential protection device that calculates the difference in output current of CT secondary windings at both ends of the transmission line for each phase and outputs an output signal when the difference exceeds a predetermined set value. In addition to the first calculation section, the output current from the CT secondary winding and the PT
A second calculation unit that determines the phase relationship with the zero-phase voltage from the above-mentioned calculation unit, and a third calculation unit that determines the one-line ground fault phase in the power transmission line from the logical product of the outputs of both calculation units. It is.

[Effect]

The difference current and zero-sequence voltage are in opposite phases in the fault phase and in phase in the healthy phase, so the target for discrimination is clear.
The second arithmetic unit will not mistakenly operate on a healthy phase as a faulty phase. Therefore, the third calculation unit reliably identifies the accident phase.

1 Embodiment] FIG. 1 is a functional block diagram showing the internal configuration of a self-end relay device (25) as a power transmission line current differential protection device according to an embodiment of the present invention. In the figures, the same reference numerals as those in Figs.
6A) (26B) (26C) is a first calculation unit that calculates the difference Td between the own end current and the opposite end current and outputs an output signal when this difference current Id exceeds a predetermined set value; (27A) )
<27B) (27C) is the own-end current ■1 and the own-end bus PT (
8) Zero-sequence voltage obtained from ■. Specifically, as shown in FIG. 2, the second calculation unit that determines the phase relationship between If they are in phase, no output signal is output.

(28A) (28B>(28C) is the first calculation unit (26
This is a third calculation unit that calculates the AND of the outputs of A), etc., and the second calculation unit (27A>, etc.).

In this embodiment as well, the self-end C of the integrated secondary and tertiary windings is
Since T(6) etc. are used, as explained in the prior art, when a one-wire ground fault occurs, a differential current will flow not only in the faulty phase but also in the healthy phase. As shown, the phase of the difference current is opposite to the zero-sequence voltage in the fault phase, and in the same phase in the healthy phase, and the second calculation unit (27
Reliable discrimination is possible with A> etc. That is, only the second arithmetic unit (27A) outputs an output signal, and the other second arithmetic unit (27A) outputs an output signal.
27B>(27C) does not output an output signal.

Therefore, depending on the magnitude of the difference current, for example, B, which is a healthy phase,
Even if the first arithmetic unit (26B) of the phase outputs an output signal due to a malfunction, the output level of the second arithmetic unit (27B) is “L”, so the third arithmetic unit (26B) that takes the AND The output level of 28B) becomes "°L°", which eliminates the possibility of erroneously determining a healthy phase as a failure phase, and greatly improves reliability as a protection device.

In the above embodiment, the zero-sequence voltage is introduced from the outside, but a method may also be adopted in which each phase voltage is introduced and the zero-sequence voltage is determined internally.

Further, by performing differential calculation of the zero-sequence current and performing a logical product including the results, it is possible to further improve the reliability of ground fault detection.

Further, in the above embodiments, the protection device is configured in a digital form, but the protection device is not limited thereto.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to accurately and reliably detect the fault phase of a single-wire ground fault even though a CT equipped with a tertiary winding for zero-phase current detection is used. can do.

[Brief explanation of drawings]

Fig. 1 is a functional block diagram showing the internal configuration of a self-end relay device according to an embodiment of the present invention, Fig. 2 is a vector diagram showing the phase relationship between differential current and zero-sequence voltage, and Fig. 3 is a general FIG. 4 is a functional block diagram showing the internal configuration of a conventional self-end relay device; FIG. 5 is an explanatory diagram showing current distribution in the event of a single-wire ground fault. . In the figure, (1) is the transmission line, (2) is the own end of the transmission line,
(3) is the other end of the transmission line, (6) is the own end CT, (61A
), etc. are secondary windings, (62A), etc. are tertiary windings, (8) is own-end bus PT, (25) is a self-end relay device as a transmission line current differential protection device, (26A> etc. are The first calculation unit, (2
7A), etc. are second calculation units, and (28A), etc. are third calculation units. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A CT equipped with a PT for zero-sequence voltage detection, a secondary winding for positive-sequence current detection, and a tertiary winding connected to a three-phase closed circuit for zero-sequence current detection is connected to the own end of the transmission line and the other end. and a first calculating section installed at each end of the CT secondary winding, and further calculating the difference between the output currents of the CT secondary windings at both ends for each phase and outputting an output signal when the difference exceeds a predetermined set value; A second calculation unit that determines the phase relationship between the output current from the CT secondary winding and the zero-sequence voltage from the PT, and a one-wire ground fault phase in the power transmission line from the logical product of the outputs of both calculation units. A power transmission line current differential protection device including a third calculation unit that makes a determination.