JPH01206819A - Judging method for operation of digital relay - Google Patents

Abstract

PURPOSE:To operate at an arbitrary phase shifting angle by employing the momentary value of a system current one sampling period backward in its sampling period and present momentary value as data. CONSTITUTION:A momentary value am is employed in formula I and III at an arbitrary sampling timing (m) of a vector A represented by the formula I. In order to obtain a current value phase-shifted, for example, 60 deg., 60 is substituted in alpha, an arbitrary sampling period (angle) is substituted in beta, thereby determining K1 and K2, a present current data im and data one sampling period backward i.e., data im-1 an angle beta backward is multiplied by them to obtain it. Mho characteristic having an arbitrary maximum sensitivity angle is obtain by such a phase shifting calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for determining the operation of a digital relay used to protect a power system.

[Conventional technology]

A power system is usually equipped with a protective relay, that is, a relay, in order to protect the system by cutting off current when an abnormality occurs.

As an example of the conventional technology of such a relay, there is a digital type that is published in Volume 41, No. 4 (January 21, 1986) of Electric Kyodo Research published by Electric Kyodo Research Association, No. 47.48. Explanation will be made regarding the multi-layer distance relay.

FIG. 1 is a block diagram showing the basic configuration of a digital relay.

1 in the figure is the A/D input voltage and current of the power system to be protected.
A for converting and sampling digital data
/D converter, 2 is a memory for storing calculation programs and various data, 3 is a CPU as a control center,
Reference numerals 4 and 5 are interfaces for exchanging on/off signals with the outside, and 6 is a signal bus connecting each of them.

Figure 3 is a vector diagram showing the Moh characteristics of the relay, where α is the maximum sensitivity angle of the Moh characteristics, ! is a current vector, 9 is a voltage vector, and 2I is a settling vector.

In Figure 2, the sampling period for current ■ and voltage ■ is 30"
FIG. 2 is a schematic diagram showing the sampling timing with respect to the reference frequency of the power system in the case of FIG. Here, since the object to be protected by the relay is an AC power system, both voltage and current are sinusoidal waves, and one period is 360 degrees in electrical angle.

Further, FIG. 4 shows a flowchart of a conventional calculation procedure for a digital type distance relay.

For example, as shown in Figure 3, any voltage vector ♀
If the voltage vector 9 is within the circle shown in FIG. 3, the relay will operate, ie, shut off the system, and conversely, if the voltage vector 9 is outside the circle, the relay will be inoperative.

That is, person = 2.・↑-9 White = 9 However, 21 is the two resultant vectors represented by the settling vector. The phase difference θ between human and white is (1) Operates when θ<90 degrees, that is, cosθ>0 (2)
When θ>90 degrees, that is, cos θ<0, it is determined as an operation.

Specifically, let the instantaneous values of vectors A and B at arbitrary sampling timing m be a, ll, and bIYl, respectively, and express them as sampling values of voltage and current at a 30° cycle as shown in (1) and (2) below. Becomes the second.

a+a=Z+' 1+a*t Vs...(1
)b=9. ...(2) Here, 1@
+i is the sampling value obtained by advancing i by 60°, and the fourth
This corresponds to the phase shift calculation (step Sl) in the flowchart in the figure. This phase calculation is performed using the sampling value i shown in FIG.
This can be obtained by sampling two more sampling periods, that is, sampling values 1m+2 at 60° ahead.

This angle of 60° is the maximum sensitivity angle of this conventional relay, and corresponds to α in FIG.

The calculations of +11 and equation (2) above correspond to the vector composition calculation (step S2) in the flowchart of FIG.

Next, the phase difference calculation (step S3) in FIG.
)2 calculation, and determining whether the result is positive or negative becomes the operation determination formula for the Moh characteristic.

1 person 1.1 white 1 cosθ=am' bl1, am-
3'tlm-+..."(3) Here, am-ff+
bm-3 are as shown in Fig. 2, afilb, respectively.
This is a sampling value three sampling periods (90°) before ll.

From the above equations (11, +21 and (3)), the basic operation determination equation for the Moh characteristic is expressed as the following equation (4).

(Z+ '?+t VJ' Vs+(Z+ ・t
@-+ Vm-:l) V+n-1>Q...(4) After this, in step S4, the positive/negative determination of the above equation (4) is executed, and as a result, in step S5 or S6, the relay is actually activated. A signal indicating whether the device is operating or not is output.

[Problem to be solved by the invention]

As mentioned above, conventional relays use a phase shift calculation method, so they can only handle data that depends on the sampling period, such as 11+2, and specifically, is an integral multiple of the angle of the sampling period. . Therefore, it is not possible to deal with a case where the maximum sensitivity angle is 64 degrees and does not depend on the sampling period. For this reason, there is a problem in that the relay cannot meet the requirement of operating at a finely tuned maximum sensitivity angle commensurate with the characteristics of the power system that the relay is intended to protect.

The present invention has been made to solve these problems, and it is an object of the present invention to provide a method for determining the operation of a digital relay that can operate at an arbitrary phase shift angle that does not depend on the sampling period.

[Means to solve the problem]

The digital relay operation determination method of the present invention performs calculation for an arbitrary phase shift angle using the instantaneous value of the system current one sampling period before the arbitrary sampling period and the current instantaneous value as data.

[Effect]

In the method for determining the operation of a digital relay according to the present invention, since calculation is performed for an arbitrary phase shift angle, a mho characteristic having an arbitrary maximum sensitivity angle can be obtained.

[Embodiments of the invention]

Examples of the present invention will be described in detail below. Note that the method of the present invention is executed using the digital relay configured as shown in FIG. 1 and using the calculation procedure shown in FIG. 4.
The phase shift calculation in step S1 is distinctive.

Now, the instantaneous value i of current vector i at any sampling timing is ilI=Im−sinωt ・(5) However, 1m is i
, and if the current phase-shifted by an arbitrary angle α from this 11 is i, +6, then t+a++ = 1m 5in(ωt+α)...
(61.Here, if one sampling angle with an arbitrary sampling period is β, then 1m ・5in(ωt+ (r) = 1m・(K, -5inωt−Kg ・5in(ω is one β
) ) ・(7)

Expressing this equation (7) as an instantaneous value that can be processed by a digital relay, from equations (1), (21 and (3)), -i, 7Kz Hi, -ρ... (8 ).However, β is an angle determined in the sampling period, and i,−1 is the sampling value one sampling period before i, so it is expressed as !+s−1.

Therefore, iva+,,L=KI' 1m KN・1M−1・
...(9) becomes (60° phase shift equation 1 included in equation 11
When 1ya is replaced with equation (9), a,=Z, H(Kt ・iea Kz ・1m−1
) V+s...am.

For example, to obtain a current value with a phase shift of 60",
By substituting an arbitrary sampling period (angle) into , β, and 2 are determined, and the current current data i is respectively determined. This is realized by multiplying by 1+*-1, which is data from one sampling period before, that is, data from β° before.

Further, for example, in the case of a 62° phase shift, the same calculations as described above may be performed by substituting 62 for α, finding , and.

By substituting the value obtained by such a phase shift calculation into the above-mentioned equation (4), it is possible to obtain a mho characteristic having an arbitrary maximum sensitivity characteristic.

In the above embodiments, a relay that operates based on the Moh characteristic was described, but the present invention is also applicable to a reactance characteristic as shown in FIG.

〔Effect of the invention〕

As described above, according to the digital relay operation determination method of the present invention, it is possible to perform any current phase shift in any sampling period, so it can accurately respond to any case where maximum sensitivity characteristics are required. Therefore, accurate protection operation is realized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic configuration of a digital relay, Fig. 2 is a schematic diagram showing the sampling timing for an AC fundamental waveform by a digital relay, Fig. 3 is a vector diagram for explaining the Moh characteristics, and Fig. 4 is a FIG. 5 is a flowchart showing the procedure of calculation based on the Moh characteristic, and FIG. 5 is a vector diagram for explaining the reactance characteristic. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The instantaneous value of the current vector obtained by sampling the AC amount of the power system to be protected at a sampling angle m times the predetermined sampling period angle is i_m, the instantaneous value of the voltage vector is v_m, and the settling vector is Z_1, when the maximum sensitivity angle is a phase angle that is n times the sampling period, the formula a_m・v_m+a_m_-_3・v_m_-_3 However, a_m=Z_1+i_m_+_m-v_m is determined to be positive or negative and the predetermined operation is executed. In the operation judgment method of a digital relay, an arbitrary sampling period angle is β,
When an arbitrary phase shift angle is α, the above a_m is expressed as the formula Z_1・(K_1・i_m−K_2・i_m_−_1)
−v_m However, K_1=sin(α+β)/sinβK
A method for determining the operation of a digital relay, characterized in that the determination is made at an arbitrary maximum sensitivity angle α by replacing _2=sin α/sin β.