JPH0452051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a step-out prediction device that predicts step-out in a power system in advance.

[Technical background of the invention and its problems] Bus voltages at multiple substations or power plants are sampled at high speed, transmitted and received via a transmission system, and voltage phase angle differences are detected to determine each other's voltage phase angles. Conventionally, a method has been used to detect that the difference exceeds a certain value, for example by 180 degrees, and determine that system step-out has occurred. However, there is a method that detects the grid voltage phase angle difference without using a transmission system, and predicts and calculates the future voltage phase angle difference from the voltage phase angle difference at several points in the past to detect grid step-out early. has not yet been realized.

If system out-of-step can be predicted and detected in advance, it becomes possible to perform various system stabilization controls based on this condition and prevent system out-of-step in advance. That is, in order to prevent synchronization, it is absolutely necessary to predict and detect synchronization in advance rather than detect synchronization.

[Object of the invention] The present invention detects the bus voltage phase angle difference at both ends of a power transmission line connected to a substation or power plant without using a transmission system, and calculates the future bus voltage phase angle difference from the values at several points in the past. An object of the present invention is to provide an out-of-step prediction device for an electric power system that predicts and calculates the occurrence of a system out-of-step in advance.

[Summary of the invention] The present invention measures the magnitude of the bus voltage V _A on one side of a transmission line, the current vector I and the recorded bus V) of that transmission line at regular intervals, and calculates the bus voltage vector V and _B at the other end. Then, the voltage phase angle difference θ at both ends of the power transmission line is detected, and the future voltage phase angle difference θt is predicted and calculated based on the voltage phase angle difference at several points in the past, and step-out can be detected early based on the trend and value. It is something.

[Embodiments of the Invention] First, the concept (principle) of step-out prediction will be explained using an example of a power system with reference to FIG. 4 and subsequent figures.

Figure 4 shows an example of a power system. In the figure, 1 and 2 indicate a large power supply system consisting of a plurality of generator groups, and 3 indicates a large capacity long-distance transmission line connecting the large power supply systems 1 and 2.

Next, due to a system fault, etc., the bus voltage V・_A , V・_B phase angle difference between both ends of long-distance transmission line 3 becomes 180 degrees or more, causing a situation where system 1 and system 2 go out of synch. This will be explained using the movement of the bus voltage vectors at both ends of the distance transmission line 3 and the movement of the voltage phase angle difference between the two.
Generally, when a power grid failure occurs in a power system as shown in Figure 1, the weakest interconnection line in the system, i.e., the long-distance transmission line 3, is affected by an out-of-step locus (the busbar voltage phase angle difference at both ends of the transmission line exceeds a certain value). For example, it means opening more than 180 degrees), and inter-system out-of-sync occurs.
Therefore, by understanding the movement of the bus voltage phase angle difference at both ends of the long-distance transmission line 3, it is possible to
It is possible to detect the out-of-step phenomenon.

In Figure 5, V・_A is the busbar voltage of an electric station such as a connecting substation or power plant on the system 1 side of the long-distance transmission line 3, and V・_B is a tangential substation or power station on the system 2 side of the long distance transmission line 3. represents the bus voltage vector of an electric station such as

Figure 5a shows the normal situation, and the long-distance transmission line 3
It is operated with a phase angle difference θ _a between the bus voltages V・_A and V・_B at both ends.

Next, Fig. 5b shows that system 1 is affected by system disturbance etc.
The behavior of the generator group in system 2 and the generator group in system 2 is different, and the bus voltage V・_A at both ends of long-distance transmission line 3 gradually increases.
This shows how the phase angle difference between V and _B increases. Fig. 5c shows a case where the bus voltage phase angle difference between both ends of the long-distance transmission line 3 increases and the angle reaches a certain value or more, for example, 180 degrees. System 1 and system 2 lose synchronization and go out of synchronization.

Furthermore, FIG. 5d shows the tendency of the bus voltage phase angle difference at both ends of the long-distance transmission line 3 to increase over time. For example, in the case of a transient first wave step-out, the tendency becomes monotonically divergent.

In this way, when two large groups of generators are interconnected via a long-distance transmission line and lose synchronization due to grid disturbance, it can be determined by observing the change in the bus voltage phase angle difference at both ends of the long-distance transmission line. It is possible to detect out-of-step phenomena.

Next, a method of detecting the bus voltage phase angle difference between both ends of the long-distance power transmission line 3 will be explained.

The magnitude of the connected bus voltage on the system 1 side of the long-distance transmission line 3 is V _A , the current vector of the long-distance transmission line 3 when V _A is the reference phase is I, and the line impedance of the long-distance transmission line 3 is Z. The voltage vector _I.B of the connecting bus on the system 2 side of the long-distance transmission line 3 and its phase angle θ are determined by equations (1) and (2). still,
θ is a phase angle when V _A is used as a reference phase, and is equivalent to the bus voltage phase angle difference between both ends of the long-distance power transmission line 3.

V・_B =V・_A +Z・I・(1) θ=tan ^-1 I _n {V/・_B }/R _e {V・_B }(2) Here, R _e {V・_B } is V・Indicates the size of the real part of _B ,
I _n {V· _B } indicates the imaginary part of V· _B .

As described above, according to the present invention, the bus voltage phase angle difference θ between both ends of the power transmission line can be detected without using a transmission system.

Next, a method for predicting the bus voltage phase angle difference at a future point in time will be described from the bus voltage phase angle difference at several points in the past detected at intervals of ΔT.

Generally, after the faulty power transmission line is disconnected by a protective relay, the busbar voltage phase angle difference at both ends of the long-distance transmission line 3 changes discontinuously due to the large inertia of the generator groups of system 1 and system 2. Changes smoothly without any changes. Therefore, by finding a higher-order equation that passes through the bus voltage phase angle differences at several points in the past, it is possible to find the future bus voltage phase angle difference from that higher-order equation.

Hereinafter, step-out prediction when the higher-order equation is a quadratic equation will be explained using FIG. 3.

If the bus voltage phase angle differences at both ends of the long-distance transmission line 3 detected at intervals of ΔT are θ(t _K ), θ(t _K-1 ), and θ(t _K-2 ), the curve passing through these three points is ( It is defined by equations 3) and (4).

θ(t)=θ( _tK-2 )+ _Δθ12 (t- _tK-1 )+Δ
θ ₀₁₂ (t-t _K-1 ) (t-t _K-2 ) (3) Δθ ₁₂ = (θ(t _K-1 )−θ(t _K-2 ))/ΔT Δθ ₀₁ = (θ(t _K ) − θ (t _K-1 )) / ΔT Δθ ₀₁₂ = (Δθ ₁₂ − Δθ ₀₁ ) / 2ΔT (4) Here, t _K is the current time, t _K-1 is the time before ΔT, t _{K -2} indicates the time before 2ΔT, respectively.

Bus voltage phase angle difference θ(τ) at future time τ
is obtained by substituting τ for t in equation (3).

Next, a method for determining step-out will be explained. The out-of-step judgment is based on the long-distance transmission line 3 at the future point determined by equations (3) and (4).
This is determined based on whether the bus line voltage phase angle difference between both ends of the line shows a tendency to diverge and exceeds a preset boundary value. That is, the bus voltage phase angle difference at future time τ ₁ <τ ₂ <...<τ _P is θ(τ ₁ )<θ(τ ₂ )<...<θ(τ _P ) (5) and θ(τ _P ) > θlimit (6), it is determined that the step is out of step. Here, θlimit is the boundary value explained earlier.

This step-out determination method is such that when system 1 and system 2 are out-of-step at the first wave, for example, and the locus enters long-distance transmission line 3, the bus voltage phase angle difference at both ends monotonically diverges, and It takes advantage of the physical property of exceeding boundary values.

An embodiment of the present invention will be specifically described using FIG. 1.

Reference numeral 11 denotes a connection bus on the system 1 side of the long-distance power transmission line 3, and 12 represents a connection bus on the system 2 side. 13
inputs the secondary voltage of the potential transformer PT connected to the busbar and the secondary current of the current transformer CT installed on the transmission line, samples these electrical quantities at regular intervals, and converts them A/D. This is a sampling device that outputs. 14 is based on the sampling values of the voltage of the connection bus 11 on the grid 1 side and the current of the long-distance transmission line 3.
This is a voltage/current vector detection device that detects the voltage magnitude V _A of the connection bus 11 and the current vector I of the long distance power transmission line 3. 15 calculates the bus voltage phase angle difference at both ends of the long distance transmission line 3 from the voltage magnitude V _A of the connection bus 11 and the current vector I of the long distance transmission line 3, and calculates the bus voltage phase angle at the past several points. This is a step-out detection device that predicts and calculates the bus voltage phase angle difference at a future point in time based on the difference, and detects step-out. Note that the voltage/current vector detection device 14 and the step-out detection device 15
This is carried out using, for example, the functions of a digital computer.

The operation of the invention will be explained below.

If a system disturbance such as a transmission line failure occurs and the failure is removed by the protective relay, the voltage/current vector detection device 14 detects the connection on the system 1 side output from the sampling device 13, as shown in FIG. Voltage sampling values for one period of the bus 11 V ₁ , V ₂ ,
..., V _o-1 , V _o and the current sampling values I ₁ , I ₂ , ..., I _o-1 , I _o during one cycle of the long-distance transmission line 3 are input, and the voltage of the connection bus 11 is calculated. Calculate the magnitude V _A from equation (7), and calculate the current vector I of the long-distance transmission line 3 by (8),
Calculate from equations (9) and (10). In addition, the formula (8) is a formula for calculating the magnitude I of the current vector of the long-distance transmission line 3,
Equation (9) is an equation for determining the phase ψ of the current vector when the voltage of the connection bus 11 is referenced. Also, equation (10) is an equation for determining the current vector I. from I and ψ.

ψ＝360×f×Δξ ……(9) I・=I _cps 〓+jI _sio 〓 ……(10) Here, Δξ is the connection bus 1 as shown in Figure 2.
It is the time difference between the bus line voltage sampling value of 1 and the current sampling value of the long-distance transmission line 3, and f is the frequency of the system. In addition, the above V _A , I・
The calculation is performed every cycle, that is, every ΔT=1/f.

The step-out detection device 15 determines the bus voltage vector V of the connecting bus 12 on the system 2 side of the long-distance transmission line 3 using the equation (1) from the V _A , I and the line impedance Z of the long-distance transmission line 3 .・Calculate _B , and further calculate the phase angle θ of V· _B using equation (2). This phase angle θ is V _A
This is the phase angle of the connection bus 12 when the reference phase is taken as the reference phase, and is equivalent to the bus voltage phase angle difference between both ends of the long-distance power transmission line 3.

Next, the operation of the step-out detection device 15 will be explained using FIG. 3. First, in step _S1 , the current t _K ,
For each time point t _K-1 before ΔT time and t _K-2 before 2ΔT time (1),
Using equation (2), the bus voltage phase angle difference θ (t _K ), θ
(t _K-1 ) and θ(t _K-2 ), and then in step S ₂ , equations (3) and (4) are used to calculate the long distance at future points τ ₁ , τ ₂ , ...τ _P The bus voltage phase angle difference between the connecting buses 11 and 12 of the power transmission line 3 is predicted and calculated. Furthermore, in step _S3 , it is determined whether the predicted value satisfies equations (5) and (6), and if it is determined that step-out has occurred in step S4, control is sent to a system stabilizing device (not shown) via step _S4 . Send a command (step _S5 ). On the other hand, if it is not determined that step-out has occurred, the calculations and determinations in steps _S1 to _S4 are repeated after a certain time delay in step _S6 .

[Effects of the Invention] As described above, according to the present invention, the bus voltage phase angle difference at both ends of the power transmission line is sequentially detected serially, and the future bus voltage phase angle difference is predictively calculated from the values at several past points. This makes it possible to detect synchronization at an early stage, and by performing system stabilization control using the determination conditions of such a device, synchronization can be prevented in advance. Furthermore, the present invention is advantageous in terms of equipment compared to the prior art, since the busbar electric phase angle difference at both ends of the power transmission line is detected without going through a transmission system.

In the embodiment of the present invention, the prediction calculation of the bus voltage phase angle difference at a future point in time is performed using a quadratic equation, but the same effect can be obtained even if it is performed using an N-order equation that is a cubic equation or higher. However, in this case, (N+1) bus voltage phase angle differences up to the present time are required.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing an embodiment of the present invention;
Figure 2 is a diagram for explaining the method of calculating the magnitude of the bus voltage and the vector value of the current from the sampled values of the bus voltage and current on one side of a long-distance transmission line.
Figure 4 shows an example of a power system; Figure 5 shows the voltage vector at both ends of a long-distance transmission line and the time of bus voltage phase angle difference during steady state and step-out conditions. FIG. 6 is a diagram for explaining a method of calculating a bus voltage phase angle difference at a future point in time and a method of determining step-out. 3...Power line, 11, 12...Bus bar, 13...
Sampling device, 14... Voltage/current vector detection device, 15... Step-out detection device, CT... Current transformer, PT... Potential transformer.

Claims (1)

[Claims] 1. Sampling the bus voltage and line current at any one electric station out of multiple electric stations connected by a power transmission line at a fixed period, and calculating the magnitude of the bus voltage and the current vector of the transmission line at the electric station. is detected, and the bus voltage vector of another electric station facing the arbitrary electric station is determined from the magnitude of the bus voltage, the current vector, and the line impedance of the transmission line, and from the real part and imaginary part of this bus voltage vector. The busbar voltage phase angle difference between the two electric stations is determined moment by moment, the future voltage phase angle difference is predicted and calculated from the voltage phase angle difference at multiple points, and system out-of-step is detected according to the value obtained by the calculation and the trend of change. An out-of-step prediction device for a power system is characterized by predicting in advance that the occurrence of a power outage will occur.