JPH0424932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a protective relay system for detecting a step-out phenomenon in a power system and protecting the power system to avoid a power outage of the entire system due to power 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 understanding information.

[Summary of the invention]

In this invention, when the measurement point is located near the electrical center point or in a place where the voltage gain is small during power system fluctuations, the locus of the active power P and reactive power Q based on the measurement value will be circular like the power supply end. This was done to prevent the ellipse from becoming a contracted circle in the reactive power Q direction, and no matter where the measured voltage vector is electrically located in the system, the power source end behind the measurement point It is an object of the present invention to provide a protective relay system that detects a voltage vector and detects step-out using active power P and reactive power Q at the power source end.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is an input section for each vector of voltage and current, 2 is a first logic operation section that calculates a back voltage vector from each of these vectors, and 3 is a back power supply terminal voltage calculated by the first logic section 2. A second logic operation section creates trajectories of active power P and reactive power Q from current vectors from the vector and vector input section 1 and detects step-out; 4 is a memory buffer; and 5 is a step-out output section. Next, the basic principle of this invention will be explained using vector relationship diagrams. In Figure 2, 6
7 is the voltage vector at the power source A end V〓 _A in the two model systems, and 7 is the voltage vector at the other power source end _B in the model system V〓 _B 8 is the voltage vector V〓 _S at the electrically intermediate point S on the model system, and 9 is the vector voltage V〓 at the power supply end B when _B moves along the locus 7 when it rotates. The locus of the voltage vector V〓 _S rotated by Also, Figure 3 shows
Voltage vector at measurement point S during a certain system oscillation
It is a principle diagram showing the relationship between V〓 _S 〓, current vector I〓, and back power supply terminal voltage vector V〓 at that time. FIG. 4 is a configuration diagram showing the protective relay system, where 7a is a first calculation section, 8a is a second calculation section, 9a is a determination section, and 7a is a first calculation section, 8a is a second calculation section, 9a is a determination section,
1a is a back power supply voltage vector processing unit, and 72a is a
This is a PQ calculation processing unit.

Next, the operation will be explained. The voltage and current at the electrical point S between the power supplies A and B during the two-machine system oscillation shown in Fig. 2 are inputted from the input section 1 and converted into voltage and current signals, which are processed graphically by the logic operation section 2 as data. . Voltage = V〓 _S = V _sd + jV _sq , current I〓 = I _d +
When the power supply terminal voltage vector V 〓 behind the absolute value u to be determined from jIq and these vectors is taken on the xy plane, it becomes as shown in Fig. 3.

In Figure 3, the straight line l passes through the point (V _sd , V _sq ),
It has an angle of (90°-θ) with respect to the vector I〓. Here, the angle (90°-θ) is a line impedance angle and a set value.

When the line impedance Z is set as Z=R+jX and tan(90°-θ)=X/R=α, the following equation holds true.

l=I _q +α・I _d /I _d −α・I _q・x+V _sq −I _q +α・I
_d /I _d −α・I _q・V _sd () Moreover, the locus of the vector V〓 whose absolute value is u is represented by a circle whose radius is u, and the following equation is obtained.

x ² +y ² =u ² ... () When the intersection of the straight line and the circle is found from these equations () and (), the two equations are solved by setting the coefficient of x in equation () to a and the constant b.

x=-ab±√u ² +a ² u ² −b ² /1+a ² y=-a ² b±a√u ² +a ² u ² −b ² /1+a ² +b, and the intersection of the two points is solved. . Of these two points, the one in the rear direction at point S is output as the rear power supply end voltage vector V=V _d +jV _q . In this case, the backward direction at point S is the straight line l in Figure 3.
In the above, a direction with point S relative to point C is meant, and a direction beyond point C without point S means the direction of the forward power supply.

FIG. 4 is a block diagram of a protective relay system according to an embodiment of the present invention, in which a first logic operation section 7a calculates active power P _a and reactive power _{Q a} from a current 4 a and a voltage 5 a as input electric quantities. This first logic operation section 7a
The back power supply voltage vector processing section 71a provided in
Detects the background power supply voltage vector V〓 as the root of the quadratic equation from the above equations () and () and performs arithmetic processing. The current 4a and the output of the back power supply voltage vector processing section 71a are supplied to the input of the PQ calculation processing section 72a, and the PQ calculation processing section calculates the active power P _a and the reactive power Q _a . is fed to the input of The second logic operation unit 8a creates a string from the above-mentioned active power P _a and reactive power Q _a at each time, and the determination unit 9a determines a change in direction of the string based on the output of this string.

In addition, in the above embodiment, the back power supply end voltage vector is detected, but the third
By measuring another intersection point between the circle in the figure and the straight line l, a front power supply end voltage vector can be obtained using the same algorithm. Furthermore, by changing the radius u of the circle used in FIG. 3, the voltage vector at the system midpoint can also be detected. Further, in the above embodiment, each vector is input digitally, but by providing an S/H, an A/D, etc. in the input section 1, analog input may be made directly from the measurement point.

[Effects of the Invention] As described above, according to the present invention, no matter where the voltage is at any position in the power system, the back power supply end voltage vector is calculated from the voltage and current vector at that position. This has the effect of providing a protective relay system that can supply highly accurate information for protection, monitoring, and control during turbulence.

[Brief explanation of drawings]

FIG. 1 is a simple input/output flow diagram of a back power supply terminal voltage vector calculation device according to an embodiment of the present invention.
Fig. 2 is an explanatory diagram showing the relationship between each vector depending on the electrical position of the system used to explain the algorithm of one embodiment, Fig. 3 is a principle diagram used to explain the algorithm of one embodiment, and Fig. 4 The figure is a configuration diagram of the protective relay system of the present invention. DESCRIPTION OF SYMBOLS 1...Vector input section, 2...First logic operation section, 3...Second logic operation section, 4...Memory buffer, 5...Step-out output section, 7a...First logic operation section, 8a... ...Second logic operation section, 9a...Judgment section,
71a...backward power supply voltage vector processing section, 72a
...PQ calculation processing section.

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, the above-mentioned detection method detects synchronization by detecting the circular movement of the transition locus when the system goes out of synchronization. The detected current vector is rotated by the line angle, and the absolute value of the straight line orthogonal to the current vector that is in phase with the voltage vector at the electrical center point and the vector of the back power supply terminal voltage is defined as the radius. The intersection point with the circle is calculated, and the vector whose end point is the intersection point in the rear direction between the two intersections is used as the rear power supply end voltage vector, and the active power and reactive power at the rear power supply end are calculated and detected. Features a protective relay system.