JPH0332287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a protective relay system that detects a step-out phenomenon in a system and protects a system to avoid a power outage of the entire system due to system separation.

[Prior art]

In order to maintain the stability of power systems, it is effective to use a system outage prediction separation method that detects the initial phenomenon of a system outage and performs system separation before the disturbance progresses.
For this reason, the inventor took advantage of the fact that when the locus of active and reactive power is captured, it exhibits circular motion at the time of a step-out, to predict and detect the step-out in the system in the initial state of the step-out, and to locate the electrical center point of the step-out. We proceeded with research and development on a completely new method for grasping information.

Consider a case in which active power P and reactive power Q are directly calculated and traced on the PQ plane without calculating the back power supply end voltage vector from the measured voltage vector as in the conventional protective relay system. In Figure 1, the line l shows the voltage and current vectors of the protective relay system.
Points a, b, c, s, and s' above indicate the electrical positional relationship in the system, where point a is power source A, point b is power source B, point c is the electrical center point, and point s and s' Points indicate measurement points. Furthermore, the measured current Is leads the electrical center point voltage vector by θ=90°−α, assuming that the impedance angle of the system is α.
When the PQ locus is obtained from this current vector I〓 _S and the measured voltage vectors V〓 _S and V〓 _S ′ at the measurement points s and s', it becomes as shown in FIG.

As can be understood from FIG. 3, there is a drawback that the PQ locus is compressed in the Q-axis direction of the reactive power depending on the measurement position and is expressed as a circular shape.

[Summary of the invention]

This invention detects system out-of-step by processing the PQ locus on the PQ plane to detect system fluctuations, and when the measured voltage vector is at the midpoint of the system, the gain of active power Q decreases and accurate out-of-step is detected. This was done to prevent failure of detection, and the purpose is to provide a protective relay system that can detect synchronization with high accuracy by calculating the PQ locus of the power supply terminal behind.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3 showing an input/output flow diagram of the back power supply terminal voltage vector calculation device of the present invention, 1 is an input section for each vector of voltage and current, and 2 is a first logical operation for calculating a back voltage vector from each of these vectors. Section 3 is a second logic operation section that creates trajectories of active power and reactive power PQ from the back power supply end voltage vector obtained by the first logic operation section 2 and the current vector from the vector input section 1, and detects step-out. , 4 is a memory buffer, and 5 is a step-out output section.

In Fig. 4, point s indicates the electrical position of the measurement point in a two-machine system consisting of power supply A and power supply B, and 10 indicates the voltage vector V at power supply B with respect to the voltage vector V at power supply _A A and the voltage vector V at power supply _B 20 shows the trajectory of the voltage vector V〓 _S at the measurement point s at that time, and in Fig. 5,
40 is the PQ trajectory with respect to the voltage vector V〓 _A of power supply A, and 50 is the PQ locus with respect to the voltage vector V〓 _S of the measurement point s.
Shows PQ trajectory. Also, Fig. 6 shows the relationship between the measured voltage and current vector when the voltage vector V〓 _B has an open phase θ ₁ with respect to the voltage vector V〓 _A , and Fig. 7 shows the convergence process due to vector correction. show.

FIG. 8 is a block diagram showing a protective relay system according to an embodiment of the present invention, in which 7a is a first logical operation section, 8a
9 is a second logic operation section, and 9a is a determination section. The first logical operation section 7a includes a rotation processing section 71a and a convergence operation section 7.
2a, comparison circuit 73a and PQ calculation processing section 74a
Consists of.

Next, the operation will be explained.

At the electrical position s between the power sources A and B during the two-machine system oscillation shown in FIG. 4, the data from the input section 1 is subjected to graph processing by the first logic operation section 2.

Voltage vector V〓 _S and current vector I〓 _S shown in Fig. 6
When two vectors are input, the current vector I〓 _S
is rotated by the line angle θ, and the current vector I is determined as shown in equation (1) below.

I = (I _sd × cos θ + I _sq × sin θ) + j (−I _sd × sin θ + I _sq × cos θ) ... (1) Next, the current vector I = obtained here and the set impedance Z _S are calculated as follows. Make corrections.

V〓′=V〓 _S +I〓×Z _S It is determined as the square difference value ΔV between the vector voltage V〓′ and the absolute value U of the voltage at the power supply end, and the convergence is judged. If it does not converge, the following equation is corrected.

V〓′=V〓′+ΔV×2 ^nm ×I〓×Z _S (n: number of consecutive same signs of ΔV, m: number of consecutive times of different signs of ΔV) Below, detect the voltage vector V〓′ in the same way,
When the squared difference value ΔV converges, the voltage vector V〓' is used as the back power supply end voltage vector, the active power P and the reactive power Q are calculated, and step-out is detected.

FIG. 8 is a block diagram of a protective relay system according to an embodiment of the present invention, in which the first logic operation section 7a calculates active power Pa and reactive power Qa from current 4a and voltage 5a as input electric quantities, The power is input to the second logic operation section 8a, and the string is measured from the active power Pa and the reactive power Qa at each time in the second logic operation section 8a. The determination unit 9a inputting this string signal determines the change in direction of the string and sends out an output signal. The first logic operation section 7
A rotation processing unit 71a performs rotation processing on the current I _S by a line angle amount θ to detect the current I〓. The convergence calculation section 72a inputs the voltage V〓 _S and the current I〓 of the rotation processing section 71a, calculates V〓=V _S +I〓Z _S from the current I〓 and the set impedance Z _S , and calculates the voltage.
Convergence calculation is performed until the vector absolute value of V〓' becomes the back power supply voltage absolute value. The PQ arithmetic processing section 74a converts the output of the convergence arithmetic section 72a into the input signal V〓' via the comparison circuit 73a and the output signal of the rotation processing section 71a.
I〓' is input, active power Pa and reactive power Qa are calculated and supplied to the input of the second logic operation section 8a.

In addition, in the above example, the back power supply end voltage vector at the measurement point was calculated, but the invention is not limited to this, and the voltage vector that moves from the measurement point to either Z _l ′ in terms of impedance can be measured from the measured value. , the same is true when finding the area behind the virtual measurement point. Furthermore, in the above embodiment, the impedance was doubled and 1/2 times in the convergence process, but the magnification may be determined depending on the characteristics of the system. In addition, here, all the power sources are located at the rear, but the power sources may be located at the front.

〔Effect of the invention〕

As described above, according to the present invention, convergence calculation is performed on the power supply terminal voltage vector behind the measured voltage vector and current vector without using a square root function, and in addition, parameters that change depending on the degree of convergence are given in the convergence calculation process, so the speed is high. This has the effect of obtaining a more accurate back power supply terminal voltage vector and obtaining a more accurate and highly reliable protective relay system as a step-out detection device based on the power supply terminal PQ locus.

[Brief explanation of drawings]

Fig. 1 is a vector diagram of the protective relay system, Fig. 2 is a characteristic diagram showing the trajectory of active power and reactive power, and Fig. 3 is an input/output flow of a back power supply end voltage vector calculation device according to an embodiment of the present invention. 4 is a vector relationship diagram showing the model system of two machines in which one embodiment of the present invention is set, and FIG. 5 is a PQ at the measurement position.
A characteristic diagram showing the locus, FIG. 6 is a vector diagram when the measured current vector is rotated according to an embodiment of the present invention, and FIG. 7 is a vector diagram when the measured current vector is corrected and converged with respect to the measured voltage vector. FIG. 8 is an explanatory diagram for explaining the process, and is a block diagram of a protective relay system according to an embodiment of the present invention. 1... Vector input section, 2... First logic operation section,
3...Second logical operation unit, 4...Memory buffer, 5...
Step-out output section, 7a...first logic operation section, 8a...second
Logic operation section, 9a... Judgment section, 71a... Rotation processing section, 72a... Convergence operation section, 73a... Comparison circuit, 7
4a...PQ calculation processing unit.

Claims (1)

[Claims] 1. When the active power and reactive power of a power system are plotted in orthogonal plane coordinates and their transition locus is noted, there is a protection joint that detects synchronization by detecting the circular movement of the transition locus when the system goes out of synchronization. In the power system, the first voltage vector measured from the power system is
A third voltage vector obtained by adding the current vector and the second voltage vector calculated using a predetermined impedance is detected, and it is determined that the absolute value difference with the back power supply end voltage vector is within the tolerance, and the above-mentioned absolute value difference converges. Repeat the above detection operation until the active power and reactive power are measured as the power supply end voltage vector,
A protective relay system characterized by detecting system out-of-step. 2. The protection set forth in claim 1, wherein the predetermined impedance has a set value for each relay installation position, and the impedance from the installation position to the rear power supply terminal is set during normal system operation. Relay method.