JPH0424934B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a protective relay system for protecting an electric power system.

[Prior art]

A description will be given below of a step-out protection relay system that detects whether the system fluctuation is a stable fluctuation or a step-out when a system fault occurs in the power system and the system oscillates after the fault is cleared. FIG. 1 is a simulated power system diagram simulating a power system, where 1a shows the a-end power supply and 1b shows the b-end power supply. 2 is the power transmission line between power sources 1a and 1b, 3a
4a is a transformer that introduces current to a protective relay (hereinafter referred to as a relay) 6a, and 5a is a transformer that introduces voltage from the bus 3a to the relay 6a.

For the phase difference angle θ between the voltages V〓a, V〓b (=V〓ae ^-j 〓) of the power supplies 1a and 1b, the electric quantity voltage V〓a of the a-end power supply,
Power W〓=Pa+jQa=V〓a・I〓a(I
〓
is the conjugate complex number of I〓) The active power Pa and reactive power Qa are as shown in Fig. 2. The active power Pa has a maximum value when θ is 90°, and the reactive power Qa has a maximum value when θ is 180°. They become equal at point A (θ=90°) in the figure.

The active power Pa and the reactive power Qa are obtained using the following formulas. The impedance of the power transmission line is Z =
If Ze _j ≒jZ (≒90°), current I〓a==(V〓a
−
The following formula is obtained from V〓b)/Z〓=V〓a(1-e _-j )/Z〓.

W〓=V〓a・I〓a=(V ² a/Z) {sinθ +j(1-cosθ)}=Pa+jQa Also, when the horizontal axis is the active power Pa and the vertical axis is the reactive power Qa, the PQ trajectory is The result is as shown in FIG. The locus of active power Pa and reactive power Qa shown in Figure 3 is
It is a circular locus of Pa ² + (Qa-Va ² /Z) ² = (Va ² /Z) ² , and point A in the figure indicates θ = 90°. In general, in power systems, the magnitude of the synchronization force is also relevant, but the phase difference angle θ
If it opens more than 90 degrees, it can be determined that the motor has lost synchronization. however,
At this time, the reactive power Q ₂ increases, that is, d|Qa|/dt>0.

In this way, in order to determine if the power system is out of synch, it is necessary to detect the active power P and reactive power Q from the voltage and current at the power supply end, and determine whether the PQ trajectory exceeds the point where θ = 90°. It turns out.

On the PQ trajectory, the phase difference angle θ between the a-terminal power source and the b-terminal power source is
An example of determining whether the angle exceeds 90 degrees will be described. Instantaneous value V(t), i obtained by digital sampling of the voltage and current of the system shown in Figure 1
From (t), V=v(t)+jv(t-π/2)=Vd+jVq I==i(t)+ji(t-π/2)=Id+jIq. Here, time (t-π/2) represents a time delayed by π/2 in electrical angle from time (t). Therefore, P=VdId+VqIq and Q=VqId-VdIp are obtained.

The coordinate at time n on the PQ coordinate axis is x _o (Pn,
Qn), the out-of-step locus as shown in FIG. 4 can be obtained by connecting the coordinates x _o at each time. In the figure, the string yn that connects the coordinates x _o and x _on =
Let us express the direction x _o − x _on as a quadrant of PQ coordinates. That is, the limits y _o-1 and y _o-2 are in the first quadrant direction, and the chord
y _o is facing towards the second quadrant. The direction of the string is the first
From the quadrant to the second quadrant (here, the quadrant change is [1 →
2)), it can be determined that this is the point A, that is, a loss of synchronization. It can be determined that the phase difference angle exceeds 90°. As shown in Figure 4 (b), the locus of step-out is more likely to be in the 4th case than in the 1st case, so the quadrant change in each of these cases [1→2],
Quadrant changes of the string to [2→1], [3→4], and [4→3] are similarly determined to be out of tune.

Figure 5A shows an example of a stable oscillation after a system accident, and Figure 5B shows an example of a step-out. As mentioned above, in order to detect step-out, it is necessary to create a string and determine the change in direction of the string. Therefore, if there is no oscillation, the coordinate points of active power P and reactive power Q do not move, so a string cannot be created, and a string can only be created after oscillation occurs. Further, the size of the string should be determined by the size of the out-of-step locus, but if the string size is not reached, another string cannot be created.

On the other hand, in a power system, the size and direction of power flow change over time, so the active power P gradually increases.
Move the reactive power Q coordinate point. If we determine the direction of the string by assuming that the PQ locus, which has gradually moved compared to the step-out period, has reached the size of the string, then
It may also be determined that the string is out of synch due to a change in direction from the previous direction of the string.

[Summary of the invention]

In order to avoid erroneously determining that the string is out of synchronization due to the above-mentioned string creation, the present invention creates the string on the condition that the oscillation locus of the system moves within a relatively short period of time. The object of the present invention is to provide a protective relay system that does not make erroneous step-out determinations.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 6, 7 is a first calculation unit that calculates active power and reactive power from the input electrical quantity and outputs a PQ coordinate point, 8 is a second calculation unit that creates a string from the PQ coordinate point, and 9 is a string 10 is a determining unit that locks the direction determination of the logical unit 9 based on the rate of movement of the PQ locus with respect to time.

Next, the operation will be explained. The first calculation unit 7 calculates and outputs the PQ coordinate point x _o of active power and reactive power at time n from the electrical quantities V and I input from the transformers 4 and 5. The second calculation unit 8 is a coordinate point
The string y _o =x _o −x _on is calculated from x _o , x _{o -1 .} . . , and the quadrant direction of the string is output and calculated. Logic part 9 is string y _o
If the change in the quadrant between the direction _of That is, the aforementioned quadrant change directions [1→2], [2→1], [3→4],
This is the case of [4→3]. However, the condition for increasing reactive power |Q _o −Q _o-1 |>0 is required. Judgment section 10
is from the PQ coordinate points x _o , x _o-1 ... as shown in Figure 7.
Calculate Zn=|x _o −x _o-1 |, Zn ₋₁ = |x _o-1 −x _o-1 ..., and find Z=Zn+...+Z _ol . That is, time n-l
The moving distance of the PQ trajectory from −1 to time n is Z. This moving distance Z is Z≧K (K is a constant)
Only in this case, the calculation unit 8 detects the creation of a string, and if the string can be created, outputs the direction of the string to the logic unit 9.
Also, when Z<K, string creation is locked. On the other hand, for the logic section 9, when Z<K, the direction of the string created up to that point is reset. That is, the second calculation section 8 and logic section 9 are set to the same state as the initial state.

Note that in the above embodiment, string creation is locked when the moving distance Z of the PQ locus is Z<K, but the same effect is obtained even if it is treated as an imaginary quadrant direction, for example, an O quadrant direction, without being limited to this. .

〔Effect of the invention〕

As described above, according to the present invention, the moving distance of the active power P and the reactive power Q within a certain period of time is constantly monitored, and the string is not created unless the distance exceeds a predetermined value. This has the effect of providing an extremely accurate protective relay system that makes accurate judgments.

[Brief explanation of drawings]

Figure 1 is a simulated power system diagram, Figure 2 is a
Characteristic diagram of active power and reactive power with respect to power supply phase difference angle at end and b end, Fig. 3 is a PQ trajectory diagram, Fig. 4 is an explanatory diagram of step-out determination, Fig. 5 is a system fluctuation trajectory diagram, Fig. 6 The figure is a configuration diagram of a relay according to the present invention, and FIG.
FIG. 3 is an explanatory diagram of the moving distance of a PQ trajectory. 1... Power source, 2... Power line, 4, 5... Transformer, 6... Relay, 7... First calculation section, 8... Second calculation section, 9... Logic section, 10... Judgment Part, 11
...Output, subscripts a and b indicate the a end and the b end. The same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A first calculation unit that calculates active power and reactive power at each sampling time from instantaneous values obtained by digitally sampling the voltage signal and power signal of the power system and outputs a coordinate point; a second computing unit that computes a string connecting the coordinate points of the first computing unit and outputs the quadrant direction of the string; 1. A protective relay system comprising: a logic unit that sends out a signal; and a determination unit that locks the direction determination of the logic unit based on the rate of movement of the active power and reactive power trajectories with respect to time. 2. The determination unit does not determine step-out when the moving distance of the coordinate point within a predetermined time is less than a predetermined value, and returns to the initial state when the distance is less than a predetermined value. Protective relay method described in scope 1.