JPH031890B2 - - 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 step-out protection relay system that detects whether the system fluctuation is stable fluctuation or a step-out when a system fault occurs in the power system and the system is shaken after the fault is cleared will be described below. FIG. 1 is a simulated power system diagram simulating a power system, where 1a shows the power supply at the a-end and 1b shows the power supply at the b-end. 2 is a power transmission line between power sources 1a and 1b, 3a is a bus of power source 1a, 4a is a transformer that introduces current to a protective relay 6a (hereinafter referred to as a relay), and 5a is a transformer that introduces voltage from bus 3a to relay 6a. Show the container. Voltage of power supplies 1a and 1b V〓a・V〓b (=V〓ae ^-j 〓)
The power W=Pa+jQa=Va・I=a (I=a is the conjugate complex number of Ia) is the active power Pa and reactive power Qa of the second As shown in the figure, the active power Pa reaches its maximum value at 90°, the reactive power Qa reaches its maximum value when θ is 180°, and they become equal at point A (θ=90°) in FIG.

Active power Pa and reactive power Qa are obtained as follows. The impedance of the power transmission line is Z＝Ze ^j
If ≒jZ (≒90°), current I〓a=(V〓a−V〓b)
/
From Z=V〓a(1-e ^-j〓 )/Z〓, W〓=V〓a・I〓a=(Va ² /Z) {sinθ +j(1−cosθ)}=Pa+jQa.

In Figure 3, the horizontal axis is active power Pa, and the vertical axis is reactive power Qa.
_The ^{PQ trajectory when _} indicates θ=90°.

In general, in power systems, the magnitude of the synchronization force is also relevant, but if the phase difference angle θ is 90° or more, it can be determined that synchronization has occurred. However, the reactive power Qa at this time 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 obtain the active power P and reactive power Q from the voltage and current at the power supply end, and then determine whether the PQ trajectory exceeds the point where θ = 90°. It turns out.

Now, an example of determining whether the PQ trajectory exceeds 90 degrees will be described. Instantaneous value V(t),i obtained by digital sampling of voltage and current of the grid
From (t), V=v(t)+jv(t-π/2)=Vd+jVq
I〓 =i(t)+ji(t-π/2)=Id+jIq Therefore P
= VdId+VqIq It can be obtained as Q=VqId-VdIq (t and t-π/2 indicate that the sampling times are different by π/2).

FIG _{. 4} shows _the trajectory ₁₀₀ , where _{x 0 ...} , y _o-1 represent straight lines, ie, chords, connecting the coordinates x _o , x _o-1 and the coordinates x _on , x _on-1, respectively. In the example shown, the direction of chord y _o -1 is the direction of the first quadrant, and the chord y _o is the direction of the second quadrant, and the direction changes from the first quadrant to the second quadrant (quadrant change is [1→
2] (hereinafter abbreviated), it can be determined that the point A (phase difference angle 90°) has been exceeded.
In addition, the trajectory 101 shows that the quadrant change of the string is from the second quadrant to the first quadrant, that is, the quadrant change [2→1], and the trajectory 102
It can be determined that point A has been exceeded when the trajectory 103 changes direction to quadrant change [4→3] and the trajectory 103 changes direction to quadrant change [3→4].

Generally, power systems are composed of multiple systems, so
The fluctuations of each system connected to the system to be protected (hereinafter referred to as the main system) influence each other, and the
The PQ trajectory has complex movements.

Figure 5 shows an example of a PQ trajectory (solid line) during local step-out in a small capacity system connected to this system. In the figure, the wavy line indicates the out-of-step locus of this system. Now the strings y _o+1 and y _o in Figure 5
Looking at the trajectory direction of and detect it. In Figure 6, which explains the curvature relationship between strings and arcs, the ratio (curvature) of the chord y _r to the arc Z on the locus 110 of radius R and the chord y r to the arc Z on the locus 111 of radius _r . niy _R /Z＞y _r /
There is a relationship Z(R>r). Therefore, it is possible to determine whether it is local out-of-step or main out-of-step based on the magnitude relationship of curvature=chord/arc size. On the other hand, in the trajectory during stable oscillation from the accident point F shown in FIG. 7, which explains stable oscillation, there is a similar direction change in the quadrant direction [1→2], and it is determined that there is a step-out. In this case as well, it can be determined from the curvature that this system is not out of step, but it is originally a stable oscillation. In this way, a string is always created with a small curvature near the turning point of stable oscillation or when there is a local loss of synchronization.

[Summary of the invention]

This invention focuses on the fact that the curvature decreases both during stable oscillations and local out-of-steps other than when the system loses synchronization, and has been made to process the direction of the string. The purpose is to provide a protection relay method that does not detect detection.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 8 showing the configuration of this invention, 7a
8a is the first calculation unit that calculates active power Pa and reactive power Qa from the input electricity amount, and 8a is the active power Pa at each time.
and a second calculation unit that creates a string from the reactive power Qa, 9
a is a determination unit that determines a change in the direction of the string.

Next, the operation will be explained. 7a is the input electrical quantity V(t),i obtained by digital sampling.
From the instantaneous values Vd, Vq, Id, and Iq of (t), the active power Pa
= VdId + VqIq, reactive power Qa = VdIq - VdIq is determined and output. 8a is the coordinate point x _o (P _o , Q _o ) on the active power P and reactive power Q axes at each sampling time,
Detect the string y _o =x _o −x _on from x _o+1 …. x _o here
indicates a coordinate point obtained by active power Pn and reactive power Qn at time n. Also, Z _o = x _o −x _o-1 , Z _o-1
= x _o-1 −x _o-2 Arc Z, which is the moving distance of the coordinate point from...
=Z _o +Z _o-1 +...+Z _o-n+1 and self-rate value f _o =y _o /Z
Determine 〓F (F is a constant). Then, when the condition of f _o ≧F is satisfied, the direction of y _o is outputted to the determination unit 9a as the direction of the first to fourth quadrants, and when the condition of f _o <F is satisfied, the direction of y o is outputted to the determination unit 9a.
A process is performed in which the direction of y _o is not output to the determination unit 9a.

The determination unit 9a looks at the change in direction of the string output from the second calculation unit 8a and determines the quadrant direction [1→2], [2→1],
Step-out output 1 when pattern is [3→4], [4→3]
Outputs 0a. Since the string direction is not output from the second calculation unit 8a under the condition of f _o <F, in this case, the direction when the string direction is y _{o -1} is treated as the direction of y _o . That is, when f _o <F, it is treated as the same direction as the previous string direction. In the example in Figure 5, y _o to y _o+l
When each curvature value is f _o <F...f _o+l <F,
When the direction of the string y _ol and the direction of the string y _o+l+1 are taken as the first quadrant directions, all directions from y _o-1 to y _o+l+1 are the first quadrant directions.
Treated as a quadrant direction. Therefore, since there is no change in the direction of the string during this period, no out-of-step is detected. In addition, in the example of Fig. 7, each curvature value f _o from y _o to y _{o + l}
<F...f _o+l When <F, the direction of the string y _o-1 is the first
If the quadrant direction and the direction of the chord y _o+l+1 are the third quadrant direction, all the string directions from the chord y _o-1 to y _o+l are treated as the first quadrant. A direction change in the quadrant direction [1→3] occurs between string y _o+l and string y _o+l+1 , but the step out is not detected because it is different from the direction change pattern at the time of step out.

〔Effect of the invention〕

As described above, according to the present invention, the curvature value between the chord between the PQ coordinate points and the arc that is the moving distance between the coordinates during stable oscillation or local step-out is calculated, and the curvature value is smaller than the constant K. In this case, the direction of the string is treated as being the same as the direction of the previous string, and step-out detection is performed.This has the effect of providing a highly accurate and reliable protective relay system.

[Brief explanation of the drawing]

Fig. 1 is a simulated power system diagram, Fig. 2 is a diagram of active power and reactive power with respect to the phase difference angle between ends A and B, Fig. 3 is a trajectory diagram of active power P and reactive power Q, and Fig. 4 is a diagram of the An explanatory diagram of key detection, Fig. 5 is a locus diagram of active power P and reactive power Q at the time of local step-out, Fig. 6 is an explanatory diagram of curvature, Fig. 7 is a stable fluctuation diagram, and Fig. 8 is a diagram of the present invention. FIG. 2 is a configuration diagram showing a protective relay system according to an embodiment. 1...Power supply, 2...Power line, 3...Bus bar, 4,
5... Transformer, 6... Relay, 7... First calculation section, 8... Second calculation section, 9... Judgment section, 10...
output.

Claims (1)

[Claims] 1. A first step that calculates active power and reactive power at each sampling time from the instantaneous values obtained by digitally sampling the voltage signal and current signal of the power system.
A calculation unit inputs the active power and reactive power processed by the first calculation unit, calculates a chord connecting the coordinate points and an arc that is the moving distance between the coordinate points, and calculates a curvature value from the chord and the arc. a second calculation unit that detects the coordinate points of the active power and the reactive power of the second calculation unit, and a determination unit that detects a change in the quadrant direction of the string connecting the coordinate points of the active power and the reactive power of the second calculation unit and sends out an out-of-step output when the string is in a predetermined quadrant direction. A protective relay system comprising: comparing the curvature value with a set value and treating the string direction as the same direction as the previous string direction if the curvature value is less than the set value.