KR20050049573A - Out-of-step detecting method using frequency deviation of the voltage - Google Patents

Abstract

The present invention relates to a method for detecting synchronous synchronization using a frequency shift of a voltage. The method includes extracting a fundamental wave of a voltage received from a generator output stage bus using a DFT filter, and a phase angle of the phaser of the extracted fundamental wave. Estimating each frequency component of the voltage by calculating a rate of change, and estimating a generator phase angle using each frequency of the estimated voltage; The fundamental wave of the voltage Extracted by a phaser equation, and the rate of change of the phaser phase angle is Calculated by the formula; Each frequency of the voltage Characterized by the formula, it is possible to quickly detect the synchronous disengagement in case of instability so that it can cope with the fluctuation of the system accurately, and prevent the malfunction and the malfunction of the relay to contribute to improving the stability of the system.

Description

Out-of-Step detecting method using frequency deviation of the voltage}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power protection system in a power transmission and distribution system such as a power system and a distribution system. In particular, a synchronous outage using a frequency shift of a voltage for detecting a synchronous breakdown by estimating a phase angle of a generator using a frequency shift of a voltage. It relates to a detection method.

Currently, the electric power industry places more emphasis on economics than publicity due to continuous load growth and restructuring of the electric power industry. Therefore, it is expected to focus on the protection of the individual equipment, which inevitably acts as a factor that hinders the stability of the power system, the importance of the stability of the entire power system is increasing.

Generally, the power system in normal operation maintains the equilibrium, but due to sudden disturbances such as load fluctuations, system breakdowns and switching phenomena, the phase angle of some systems increases, causing synchronization of the grid power on both ends of the line. do. The voltage and current during this synchronous degenerating phenomenon are vibrated by the phase angle δ of the power supply. According to the degree of change of phase angle δ, it is classified into stable swing and unstable swing. An unstable swing is a power swing that is severe enough to cause synchronous breakdown and causes system instability, so a trip is required at a predetermined grid separation point for overall system stability. The present invention is used to detect synchronous out-of-season phenomena leading to systemic instability.

Synchronous elimination is a phenomenon in which the power fluctuates due to disturbance, and the vibration of the phase angle δ of the generator is generated. Therefore, as the phase angle δ increases, the apparent impedance passes through the zone region due to the vibration of current and voltage. In this way, it is indirectly determined whether the zone region on the apparent impedance trajectory of the distance relay passes. As a method of detecting a synchronous stoppage there is a domestic patent 1996-037498.

The conventional synchronous step-out relay described in this publication realizes that a power swing blocking relay and a synchronous step-out relay are configured separately in one relay, and utilizes the magnitude of the apparent impedance viewed by each relay and the speed of the apparent impedance trajectory. In this case, three areas are set according to the magnitude of the impedance, and power swing and synchronous outbreak are detected from the speed of the impedance trajectory that changes in the area.

Referring to FIG. 1, the outer largest square is a power swing zone (PSZ), the second square inside thereof is a power swing determination zone Z3 for determining a power swing, and the smallest square is a sync. Out of step zone (OSZ). On this coordinate, the impedance trajectory enters the PSZ from the outside of the first quadrant of the first quadrant. If the home position is approached for a short time after entering the PSZ, it is determined to be in a fault state. If it stays in the area ΔZ and exits to the outside again, it is determined to be in the power swing state, and after entering the PSZ, entering the OSZ through Z3, and exiting to the second quadrant again, it is determined to be a synchronous release.

However, the conventional synchronous stop detection algorithm for detecting synchronous stoppage which greatly affects the system stability is detected only when both the pass zone and the pass time of the zone are satisfied. In this case, detection is not possible because of the fast zone passing time. In addition, in the case of the conventional synchronous detection by the apparent impedance trajectory, only the passage of the apparent impedance region is detected and the generator phase difference δ when passing completely through the zone region is generally detected at 180 degrees or more. It is difficult to detect and the relay may malfunction or not operate correctly because of the rapid fluctuation of the system, and thus there is a problem of worsening the stability of the system.

In addition, in 1995, Virgilio Antonio Centeno Zaldivar installed a PMU (Phasor Measurement Unit) at the output of both generators in Adaptive Out-of-Step Relaying with Phasor Measurement, which was described in the doctoral dissertation. In addition, the phase difference angle of the generator phase angle is estimated by using the Phasor calculated in both generator stages, and the method of detecting the synchronous breakout for the unstable case where the phase difference angle diverges through the estimated phase difference angle is described.

However, in the above method, the PMU is used to estimate the generator phase difference between the two generator stages. This requires additional hardware, PMU, in addition to the relay. In order to use the PMU, communication such as GPS for synchronizing the two generators is required. There is a problem that equipment is necessary.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to estimate a generator phase angle by using the frequency shift of voltage by the Discrete Fourier Transform (DFT) signal processing, With the phase angle method, which is a method of evaluating transient stability with generator phase angle, it detects synchronous outage in case of instability accurately, and cope with the fluctuation of the system accurately, and prevents the malfunction of the relay and the malfunction of the voltage which contributes to the stability of the system. The present invention provides a synchronous stop detection method using frequency shift.

In order to achieve the above object, a synchronous stop detection method using a frequency shift of a voltage according to the present invention includes extracting a fundamental wave of a voltage using a DFT filter from a voltage input from a generator output bus bar, and the extracted fundamental wave. Estimating each frequency component of the voltage by calculating a rate of change of the phaser phase angle of and estimating a generator phase angle using each frequency of the estimated voltage; The fundamental wave of the voltage Extracted by a phaser equation, and the rate of change of the phaser phase angle is Calculated by the formula; Each frequency of the voltage It is characterized by the estimated by the equation.

Each frequency component of the estimated voltage Is the fundamental frequency component And each frequency shift component Consisting of; The generator phase angle is a frequency shift component It is preferable to estimate by using the, each frequency shift component Is the first derivative of the generator phase angle.

And, the present invention is each frequency component of the estimated voltage Is the derivative of each frequency over the time t Calculating a further; The angular acceleration is It is preferably calculated by the formula, and the angular acceleration Is the second derivative of the generator phase angle.

In addition, the present invention is the frequency shift component And angular acceleration Detecting whether the synchronous elimination is stable by using; When synchronous stoppage occurs but is stable, each frequency is caused by vibration of generator phase difference that generates power fluctuations. And angular acceleration It is preferable that the trajectory of is rotated in a circular shape, converges to a value of (0, 120 [pi]) as the power fluctuation becomes stable, and is not tripped by synchronous elimination.

In addition, the present invention is the frequency shift component And angular acceleration Detecting whether the synchronization synchronous is unstable using; Each frequency when synchronous stepping is unstable Is greater than 120π and the angular acceleration It is preferable to detect the moment when is changed from (-) value to (+) value and output a trip signal.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. This embodiment is not intended to limit the scope of the invention, but is presented by way of example only.

Fig. 2 is a power-phase difference angle curve during normal operation and shows the relationship of generator output to generator phase difference angle δ.

In steady state, the generator operates at synchronous speed, but when disturbance occurs in the system, the synchronous speed is changed and the electrical and mechanical output balance is no longer maintained and accelerated. The following [Equation 1] shows the shaking equation of the rotor. . In other words, the rotor equation of the rotor is changed by the difference of input and output in the transient state, and the generator phase difference angle is secondary nonlinear due to the transient difference between the input and output of the generator in the transient state. Change to differential equation form.

[Equation 1]

[Equation 2]

Where δ = phase difference angle of the generator

       Pm: mechanical input of the turbine

       Pe: electrical output of the generator

     Pmax: Maximum value of generator electrical output

       Pa: acceleration power

        M: moment of inertia

In [Equation 2], the electrical output (Pe) from the generator depends on the voltage of the power source, the impedance between the power source and the phase difference angle (δ) of the generator, the maximum power is Pmax when δ is 90 °.

Figure 3 is a first stage infinite bus schematic diagram of the present invention, when the state of the system is changed to the four states as follows to apply the isometric area method shown in Figures 4 and 5.

① 3 phase fault occurs on Line 2

② Continued fault

③ Remove the fault by cutting off the fault line (Line 2)

④ Continue after removing fault

4 is a power of stable when time is changed the system of Fig. 3-phase difference as the respective curves, the area A ₁ interval [Equation 1] acceleration power by (P _m - P _e) the (+) region that is, rotation The angle is the acceleration period, and the area A ₂ is the acceleration angle (P _m -P _e ) is the interval where the rotation angle is decelerated to the (-) interval, and when the system of FIG. 3 is changed as the above four states. It shows the power-phase difference curve and the change of phase difference in a stable case.

That is, as a stable case, the speed of the generator rotation angle becomes 0 at the point where the rotation angle acceleration section (area A ₁ ) and the deceleration section (area A ₂ ) are the same, and then decelerate again. Done.

5 is a power of unstable when time is changed the system of Fig. 3-phase difference as the respective curves, the area A ₁ interval [Equation 1] acceleration power by (P _m - P _e) the (+) region that is, rotation The area where the angle is accelerating and the area A ₂ is the area where the rotation angle decelerates from the acceleration power (P _m -P _e ) to the minus (-) area, is unstable when the system of FIG. The power-phase difference curve and the change of phase difference in the case are shown.

That is, as an unstable case, the area A ₂ becomes smaller than the area A ₁ so that the rotation angle speed does not completely decelerate and continues to accelerate, and the rotation angle diverges.

FIG. 6 is a diagram illustrating a first infinite bus system model for generator phase angle estimation according to the present invention. The voltage measured at bus A is as follows.

[Equation 3]

When [Equation 3] is expressed as instantaneous voltage, it is as follows.

[Equation 4]

here, Is the fundamental angular frequency (2π f ), and δ (t) is the generator phase angle that changes with time during power swing.

The instantaneous voltage of [Equation 4] is obtained by extracting the fundamental wave phaser of the voltage through the Discrete Fourier transform (DFT) using Equations 9]-[Equation 10], which will be described later. Each frequency Can be estimated.

Estimated frequency Is as shown in [Equation 5].

[Equation 5]

here : Is the shift of each frequency.

Angular Acceleration Differentiating Equation 5 with Time t Is as shown in [Equation 6].

[Equation 6]

Therefore, by calculating the frequency shift of the voltage, it is possible to estimate the second derivative of the phase angle of the generator as shown in [Equation 1].

7 is a view showing the trajectory of the generator phase angle with time of the present invention, showing a change in the derivative value (speed) of the generator phase angle according to the change of the generator phase angle.

Referring to FIG. 7, in the case of a stable swing, there is a time when the speed of the rotation angle gradually decreases to zero, but in the unstable swing, the speed of the rotation angle does not fully decelerate and accelerates.

Therefore, after the generator rotation angle does not fully decelerate and starts to accelerate, the phase angle of the generator no longer maintains synchronism, so that the synchronism can be accurately detected when such a point is detected.

FIG. 8 is a diagram showing a power-phase difference angle curve when stable in FIG. 7. In the stable swing in FIG. 7, the phase angle increases after the accident elimination t _c and decreases again at the time t _r . At this time, the derivative of the generator phase angle Becomes 0, acceleration power Has a negative value, as shown in Equation 7 below.

[Equation 7]

Referring to Figure 8, each frequency as the phase angle oscillates up to ①-⑤ And angular acceleration The locus of is as shown in FIG.

FIG. 9 is a diagram illustrating synchronous step-off detection by a trajectory of frequency and acceleration in FIG. 8, when the power-phase difference angle curve is as shown in FIG. 8. Wow It shows the trajectory of.

Referring to FIG. 9, in a stable swing, the trajectory rotates in a circular shape due to the vibration of the generator phase difference that generates a power swing, and gradually converges to a value of (0, 120π) as it becomes stable. .

10 is a power of the, if unstable in the 7-phase difference as each curve also, in some cases 7 labile (unstable swing) is a rapidly rising phase from the moment that decreases the electric output after removing accident (t _c) than the mechanical input each do. At this time, the derivative of the generator phase angle Becomes 0 or more, and the acceleration power Has a value of 0 and is represented by the following [Formula 8].

[Equation 8]

Referring to Figure 10, each frequency as the phase angle oscillates up to ①-③ And angular acceleration The trajectory of is as shown in FIG.

FIG. 11 is a diagram illustrating synchronous step-off detection by a trajectory of frequency and acceleration in FIG. 10. When the power-phase difference angle curve is the same as in FIG. 10, FIG. Wow It shows the trajectory of.

Referring to FIG. 11, a trip signal is output by detecting a moment at a point ② from a point ③, that is, when each frequency is greater than 120 pi and each acceleration changes from a negative value to a positive value.

12 is a flowchart illustrating a synchronous stop detection algorithm using a frequency shift of a voltage according to the present invention.

The input instantaneous voltage was extracted with the fundamental wave as shown in [Equation 10] by using the DFT filter. In order to estimate the frequency shift of the voltage as shown in [Equation 5], the rate of change of the phaser phase angle of the fundamental wave was calculated. By calculating the rate of change of Equation 5, the second derivative of the generator of Equation 6 was estimated.

In more detail, the instantaneous voltage ([Equation 4]) received from the generator output terminal bus of FIG. 6 may calculate the fundamental wave phase of the voltage using the following Discrete Fourier Transform (DFT) filter. If the discrete input signal is v (k) and the number of samples in one period is N , the equation of DFT conversion of this signal is shown in [Equation 9].

[Equation 9]

here,

        v (k): Sampling value of voltage

           N: sampling number

When n = 1, the phaser equation from which the fundamental wave is extracted is as shown in [Equation 10].

[Equation 10]

here,

Each frequency of the voltage using the rate of change of the fundamental wave phaser phase angle of the voltage extracted through the DFT Can be estimated.

Each frequency of the phaser phase angle is shown in Equation 11 below.

[Equation 11]

here,

: Each frequency component of the signal [rad / s]

T : Sampling interval [s]

The frequency component can be estimated by calculating the rate of change of the phaser phase angle as shown in [Equation 11].

Estimated frequency Is as shown in [Equation 5].

[Equation 5]

here : Is the shift of each frequency.

Angular Acceleration Differentiating Equation 5 with Time t Is as shown in [Equation 6].

[Equation 6]

Therefore, by calculating the frequency shift of the voltage, it is possible to estimate the second derivative of the generator phase angle as shown in [Equation 1].

The frequency shift of the voltage is the first derivative of the phase angle of the generator. The second derivative of the phase angle of the generator is calculated by calculating the rate of change of this value. Was estimated.

Thus, each estimated frequency shift component And angular acceleration components Detecting the synchronous out-of-order using the method detects the moment when each frequency is greater than 120 pi and each acceleration changes from a negative value to a positive value and outputs a trip signal.

For the verification of the algorithm, data obtained from 154kV system modeling through the Electromagnetic Transient Program (EMTP) was used.The estimation of voltage frequency shift and the implementation of the synchronous deviation detection algorithm use the language MODELS in EMTP compiled with Fortran for easy hardware implementation. Used.

FIG. 13 is a 345kV two-line system diagram used in the present invention, which shows a system used in the simulation for verification of a synchronous deviation detection algorithm using a frequency shift of a voltage.

Referring to FIG. 13, when the grid voltage is 345 kV and current flows from bus BUS 1 to BUS 2 to which synchronous generator G1 is connected and relay A is connected to bus BUS 1, Line 2 between BUS 1 and bus 2 has failed and the line 2 has been shut off after a certain period of time.

Synchronous generator G1 modeled Uljin N / P with 22kV voltage and 6300MVA capacity using EMTP Type-59 synchronizer model, governor and exciter model using TACS.

The length of the track was 100km and the reference capacity was calculated as 100MVA. In order to simulate the synchronous breakdown condition, three phase failure occurred at 95% of Line 2 in Fig. 12 two seconds after the start of the simulation, and the failure was eliminated after 20 cycles and 35 cycles, respectively. After the fault was eliminated, power fluctuations occurred in the generator G1. The initial phase angle of the synchronous generator G1 was set to 20 degrees.

FIG. 14 is a diagram illustrating an estimated generator angle and an actual generator angle at 20 cycles of failure duration in FIG. 13, wherein the actual generator phase angle δ and the derivative value of the estimated generator phase angle are shown. FIG. And second derivative Indicates.

Referring to FIG. 14, in the schematic diagram of FIG. 13, a three-phase fault was generated at 95% of the line 2 and the fault was cut off after 20 cycles of failure duration. The generator phase angle oscillates, but it is stable. Synchronous lag does not occur, only the power swing occurs. The generator phase angle estimated using the DFT is almost in phase with the derivative value of the actual generator angle. Able to know.

FIG. 15 is a diagram illustrating a trajectory of frequency and acceleration in FIG. 14 and illustrates a trajectory of a generator phase angle estimated at 20 cycles of failure duration.

Referring to FIG. 15, as in FIG. 9, it can be seen that the trajectory is circular around the fundamental frequency (0, 120π).

FIG. 16 is a diagram illustrating an estimated generator angle and an actual generator angle at 35 cycles of failure duration in FIG. 13, wherein the actual generator phase angle δ and the derivative value of the estimated generator phase angle are shown. FIG. And second derivative Indicates.

Referring to FIG. 16, in the schematic diagram of FIG. 13, a three-phase fault was generated at 95% of the line 2 and the fault was shut off after 35 cycles of failure duration. Six seconds after the start of the simulation, the generator phase angle accelerated, causing synchronous out-of-order. It can be seen that the phase angle increases sharply at 6 seconds, when the electrical output becomes smaller than the mechanical input.

FIG. 17 is a diagram illustrating a trajectory of frequency and acceleration in FIG. 16, and illustrates a trajectory of a generator phase angle estimated at 35 cycles of failure duration.

Referring to FIG. 17, unlike in FIG. 15, the differential value of the phase angle (angular frequency) is larger than the fundamental frequency (120π) while the second derivative of the phase angle (angular acceleration) is (−) from (−). It can be seen that there is a time point to move to +). Therefore, the synchronization lag can be detected at the time point of the simulation time of 6 seconds.

The present invention is not limited to the above-described embodiment, and it will be apparent that many modifications are possible by those skilled in the art within the technical spirit of the present invention.

As described above, according to the synchronous stop detection method using the frequency shift of the voltage according to the present invention, the generator phase angle is estimated using the frequency shift of the voltage by the Discrete Fourier Transform (DFT) signal processing, and the estimated When the transient stability is determined by the isometry method, which is a method of evaluating transient stability with the generator phase angle, the first derivative of the generator phase angle and the second derivative of the generator phase angle are analyzed and unstable. By detecting synchronous drift quickly, it is effective to cope with the fluctuation of the system and to prevent the malfunction and the malfunction of the relay and contribute to improving the stability of the system.

In conclusion, the demand for high quality electric power is increasing as an information society, and the quality and stability of electric power are becoming more important issues in the power demand. Therefore, synchronous outage caused by disturbances such as failures affecting the stability of the power system. The occurrence of phenomena should be detected and stopped early. However, as the demand for power increased, the power flowing to the track also increased, increasing the likelihood of system instability. Therefore, if the synchronous outage is correctly detected and the unstable generator is not separated from the grid, the chain generator is out of chain and causes instability of the system.

By the way, the synchronous aeration relay currently used has the possibility of deteriorating the stability of the system due to the limitation of the detection by the synchronous operation and the R-X (apparent impedance) trajectory due to the rapid system fluctuation. In order to solve this problem, it is necessary to estimate the phase difference of the generator directly, evaluate the stability, and if it is unstable, synchronous outage occurs, so the unstable generator should be separated from the system. Since the present invention estimates the phase difference of the generator using the frequency shift of the voltage, it is possible to fundamentally detect the synchronous out-of-order through stability evaluation, and is expected to contribute greatly to the stability of the system.

1 is a view showing the impedance operation characteristics of a conventional synchronous elimination relay;

2 is a power-phase difference angle curve diagram during normal operation;

3 is a diagram of the first stage infinite bus line of the present invention,

4 is a power-phase difference angle curve when stable when changing the system of FIG.

5 is a power-phase difference angle curve when unstable when changing the system of FIG.

FIG. 6 is a diagram illustrating a first infinite bus system model for generator phase angle estimation of the present invention; FIG.

7 is a view showing the trajectory of the generator phase angle over time of the present invention,

FIG. 8 is a power-phase difference angle curve when stable in FIG. 7;

FIG. 9 is a diagram illustrating synchronous stop detection due to a trajectory of a frequency and an acceleration in FIG. 8;

FIG. 10 is a power-phase difference curve diagram when unstable in FIG. 7;

FIG. 11 is a diagram illustrating synchronous stop detection due to a trajectory of a frequency and an acceleration in FIG. 10;

12 is a flowchart implementing a synchronous stop detection algorithm using the frequency shift of the voltage according to the present invention;

13 is a 345kV two-line schematic diagram according to an embodiment of the present invention,

FIG. 14 is a diagram showing an estimated generator angle and actual generator angle at 20 cycles of failure duration in FIG. 13;

FIG. 15 is a diagram illustrating a trajectory of frequency and acceleration in FIG. 14;

FIG. 16 is a diagram showing an estimated generator angle and actual generator angle at 35 cycles of failure duration in FIG. 13;

FIG. 17 is a diagram illustrating a trajectory of frequency and acceleration in FIG. 16. FIG.

       Explanation of symbols on the main parts of the drawings

Frequency component : Fundamental frequency component

Frequency shift component : Acceleration component

Claims (7)

Extracting the fundamental wave of the voltage from the voltage inputted from the generator output bus using a DFT filter, estimating each frequency component of the voltage by calculating a rate of change of the phaser phase angle of the extracted fundamental wave; Estimating a generator phase angle using each frequency of the applied voltage; The fundamental wave of the voltage Extracted by a pager formula, The rate of change of the phaser phase angle is Calculated by the formula; Each frequency of the voltage A synchronous stop detection method using the frequency shift of the voltage, characterized in that estimated by the equation. The method of claim 1, Each frequency component of the estimated voltage Is the fundamental frequency component And each frequency shift component Consisting of; The generator phase angle is a frequency shift component Synchronous departure detection method using the frequency shift of the voltage, characterized in that estimated using. The method of claim 1, Each frequency component of the estimated voltage Is the derivative of each frequency over the time t Calculating a further; The angular acceleration is A synchronous stop detection method using the frequency shift of the voltage, characterized in that calculated by the formula. The method according to any one of claims 1 to 3, The frequency shift component And angular acceleration Detecting whether the synchronous elimination is stable by using; When synchronous stoppage occurs but is stable, each frequency is caused by vibration of generator phase difference that generates power fluctuations. And angular acceleration The trajectory of the synchronous out-of-band detection method using the frequency shift of the voltage, characterized in that the rotation of the circle rotates, converges to (0, 120π) value as the power fluctuations stabilize. The method according to any one of claims 1 to 3, The frequency shift component And angular acceleration Detecting whether the synchronization synchronous is unstable using; Each frequency when synchronous stepping is unstable Is greater than 120π and the angular acceleration And a trip signal is output by detecting a moment when the signal is changed from a negative value to a positive value, and outputting a trip signal. The method according to claim 1 or 2, Each frequency shift component Is a first derivative of the phase angle of the generator. The method according to claim 1 or 3, The angular acceleration Is a second derivative of the phase angle of the generator.