JPH0429295B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for preventing the progression of synchronization in an electric power system, which is capable of detecting synchronization in an electric power system at high speed and suppressing system fluctuations.

[Prior Art] Generally, when an accident such as a three-phase short circuit or a one-line ground fault occurs in an electric power system, each generator connected to the system is accelerated or decelerated and oscillates. Depending on the severity of the accident, some generators may be unable to maintain synchronization and may go out of step. If this is not detected early and disconnected from the grid, so-called power restriction (hereinafter simply referred to as power shedding) is not carried out, the grid will continue to fluctuate, and other generators will also step out (hereinafter referred to as power restriction). (referred to as a step-out progression phenomenon) occurs, resulting in a significant drop in power supply and even a major power outage. Therefore, it is necessary to early detect the generator that is out of step for the first time and perform the above-mentioned power control.

On the other hand, whether or not a step-out has occurred in the system is determined by looking at the movements of all generators in the system (power plants are treated as equivalent generators) for several seconds to several tens of seconds after the accident. To do this, it is necessary to solve the equation of motion for each generator, but since this equation is a nonlinear differential equation, for example, in a case where several dozen generators are interconnected in a grid, Even if a large computer is used to detect the step-out, it will take tens of seconds to several minutes. This is much slower than the real phenomenon and cannot be applied to online operations.

[Problem to be solved by the invention] Conventionally, in Japan's main power system, the voltage phase at both ends of a power transmission line (substations, switching stations, or power plants are connected to each other at both ends) is monitored, and the voltage phase is If the phase difference is, for example, 180 degrees or more in terms of electrical angle, it is determined that there is a loss of synchronization, and the power line disconnector is opened. However, with this method, by the time a step-out is determined, the voltage phase difference between the generators is often already 180 degrees or more, and the step-out can spread to other generators. There is a fear. For example, as shown in Figure 1, if the voltage phase difference (θ ₁ - _{θ 2} ) exceeds 180 degrees at time t ₁ , the phase difference between the generators (θ ₁ - θ ₃ ) becomes t<t _1. At time t, the angle may already exceed 180 degrees.

The present invention has been made in view of these circumstances, and can detect out-of-step in a system at high speed and prevent the progression of the out-of-step, making it possible to greatly contribute to maintaining the stability of the system. The purpose of the present invention is to provide a device for preventing the progression of out-of-step in a power system.

[Means for Solving the Problems] In order to solve the above problems, in the power system out-of-step progression prevention device of the present invention, after an accident occurs in a power system in which a plurality of generators are interconnected, each generator is A power amount detection means for detecting the output power amount, an angular velocity/phase difference angle calculation means for calculating the angular velocity and phase difference angle of each generator from the output power amount detected by the power amount detection means, and an angular velocity/phase difference angle calculation means. Based on the calculated angular velocity and phase difference angle, it is determined that there is a step-out when the relative difference in the phase-difference angle between each generator exceeds the threshold value that is scheduled to be the step-out determination criterion, and and a step-out detection/determination means for disconnecting the step-out generator from the power system.

In addition, in the power system step-out progression prevention device of another invention, in addition to the above-mentioned power usage detection means and angular velocity/phase difference angle calculation means, the angular velocity and phase difference angle calculated by the angular velocity/phase difference angle calculation means are used. Then, when the difference in relative angular velocity and the difference in phase difference angle between the generators exceeds the threshold value that is scheduled to be used as the criterion for determining step-out, it is determined that step-out has occurred, and the generator that has lost step is and step-out detection/judgment means for disconnecting the power supply from the power system.

[Function] Therefore, in the step-out progression prevention device of the present invention, when an accident occurs in the power system, the output power amount of each generator is detected by the power amount detection means, and the angular velocity is further determined from this output power amount. - The angular velocity and phase difference angle of each generator are determined by the phase difference angle calculating means.

Next, based on this angular velocity and phase difference angle, the step-out detection and determination means determines that the relative fluctuation between the generators, that is, the difference in the relative phase difference angle, is greater than a threshold value that is scheduled to be the step-out determination criterion. The presence or absence of step-out is determined by whether or not.

As a result, since the voltage exceeds the threshold value, it is determined that there is a loss of synchronization, and the generator that has lost synchronization is disconnected from the power system. This makes it possible to detect synchronization in the system at a high speed and prevent the synchronization from progressing.

In still another invention, the presence or absence of step-out is determined based on whether the difference in relative angular velocity between the generators and the difference in the phase difference angle are greater than or equal to a threshold value that is scheduled to be a step-out determination criterion. be done.

[Operating Principle of the Invention] First, the concept of the present invention will be described. It is possible to detect out-of-step in the system by using the internal phase difference angle of each generator connected to the system and finding the relative difference in phase difference angle for each pair of generators. First, the means for determining this phase difference angle will be described below.

Generally, the equation of motion of generator i is expressed by equation (1).

Mid ² δ _i /dt ² = P _INi − Pi (t) (1) ω _i = dδ _i /dt (2) where, δ _i : Internal phase difference angle of generator i P _INi : Mechanical input of generator i (Constant for several seconds) P _i : Electrical output of generator i M _i : Inertia of generator i ω _i : Angular velocity of generator i (however, the change from the periodic angular velocity) In addition, above (1), (2) ), d ² δ _i /dt ² =dω _i /dt =P _INi −P _i (t)/M _i ≡P _ai (t) (3) is obtained.

P _i (t) is a quantity that fluctuates over time during system oscillation after an accident, but can be regarded as a constant value for a very short period of time. Here, the time step Δt is assumed to be approximately 0.01 to 0.02 (s).
Since it can be regarded as a constant value in the minute time step t _K < t < t _K+1 = t _K + Δt, from the above equation (3), Δω _i (t _K )=∫ ^tK+ 〓 ^t _tK P _INi −P _i (t)/M _i =P _INi −P _i (t _K )/MΔt (4). Here, Δω _i (t _K ) is the speed that increases during t _K < t < t _K + Δt, so the speed at time t = t _K + Δt is the sum of Δω _i from t ₀ to t when the accident occurs. ω _i (t _K ) = ω _i (t _K-1 ) + [P _INi − P _i (t _K )
]Δt・1/M _i (5)

Δδ _i (t _K )=∫ ^tK+ 〓 ^t _tK ω _i (t _K )dt=ω _i
(t _K )・Δt(6).

Therefore, the phase difference angle is δ _i (t _K ) = δ _i (t _K-1 ) + [ω _i (t _K ) + ω _i
( _K-1 )]Δt・1/2(7). In this equation (7), the phase difference angle δ _i (t ₀ ) at the time t ₀ , that is, at the time the accident occurs, is an initial value, and is a value that can be obtained from the calculation result of the power flow in the system state before the accident occurs. It can be seen that in this case, since the amount of calculation is small, it is possible to grasp the fluctuation of the system with almost no time delay.

Next, a means for determining whether or not a system step-out has occurred will be described. As is well known, in the case of a single-machine infinite system, the generator oscillates after an accident occurs, and if the internal phase difference angle of the generator becomes 180 degrees or more in electrical angle, it is determined that the generator has lost synchronization. However, in the case of a multi-machine system, the relative fluctuation of each generator must be considered, and a concrete means for determining this has not been established.

Therefore, here, the relative movement of the phase difference angle between the generators and the determination means using the angular velocity will be described. That is, this means determines that the generator 1 has stepped out in the following cases, assuming that n generators are interconnected in the system, for example. In other words, δ _li (t _K )=δ _l (t _K )−δ _i (t _K ) (8) ω _li (t _K )=ω _l (t _K )−ω _i (t _K ) (9) In this case, if δ _li (t _K )>J (10) ω _li (t _K )>K (11) holds for all generators i except generator 1, it is determined that generator 1 has lost synchronization. . Here, it is appropriate to set J=180° and K=0°/sec. Further, in the above equation (10), the phase difference angle between the generator 1 and the other generators is J or more than 180 degrees apart in terms of electrical angle. In other words, the difference in relative phase difference angle is
This indicates that the angle is 180° or more.

On the other hand, equation (11) shows that the difference in phase difference angle between generator 1 and other generators further increases.
This is because, using equation (7) above, the relative phase angle difference δ _li (t) between generator 1 and other generator i is calculated as δ _li (t _K )=δ _l (t _K ) −δ _i (t _K ) = δ _l (t _K-1 ) + [ω _l (t _K ) −ω _l (t _K-1 )] Δt/2 −δ _i (t _K-1 ) + [ω _i (t _K ) −ω _i (t _K-1 )]Δt/2 = δ _l (t _K-1 )−δ _i (t _K-1 ) + [ω _l (t _K )−ω _i (t _{K- 1} )]Δt/2 + [ω _l (t _K-1 ) −ω _l (t _K-1 )]Δt/2 (12). Here, equation (12) is replaced by equation (8), δ _li (t _K ) in equation (9),
ω _li
(t _K ), δ _li (t _K )=δ _li (t _K-1 )+[ω _li (t _K )−
ω _li (t _K-1 )]Δt/2, and applying the relationships of equations (10) and (11), δ _li (t _K )>J+K・Δt, and the difference between generator 1 and other generator i This is because it shows that the phase difference angle with

In addition, in the step-out judgment conditional expressions (10) and (11) above, if the judgment criterion J is set to a small value and K is set to a large value, a step-out generator will be predicted more quickly, making it more effective. Become a means. (For example, J=150°,
(180°/sec) Here, K = 180°/sec means that if the value of the actual angular velocity ΔW _Ki continues for 1 second, the phase difference angle will open by 180°. In actual application, J and K may be selected to appropriate values depending on the system conditions.

Next, the reason why step-out can be determined based on the phase difference angle and angular velocity of each generator will be explained in more detail. For the sake of simplicity, a one-machine infinite bus system shown in FIG. 3 will be described here.

In Figure 3, the line impedance is jX,
When the voltage of the infinite bus is V ₁ (phase difference angle = 0) and the voltage of the generator is V ₂ (phase difference angle = δ), the generator output P is P = (V ₁ V ₂ /X) sin δ expressed. Assume that the vehicle is currently operating at point A in FIG.

Next, considering the case where an accident (3LG) occurs, the generator output becomes zero, the generator is accelerated, and the phase difference angle δ increases. This is expressed as P− in Figure 4.
Looking at the δ curve, the state is A→B→C. C
If the accident is removed at the point, the phase difference angle δ is δ ₀ →
Since δ is expanded to ₁ , the generator output becomes P _E ,
Since P _E is larger than the mechanical input P ₀ , the speed is decelerated.

However, the deceleration force is insufficient (in Figure 4, when the area of ABCD > the area of DEF using the equal area method),
If the phase difference angle δ becomes more than δ ₂ at point F, the generator output P will be
P becomes less than ₀ , and it becomes impossible to accelerate again and return to the original point A. Therefore, if the phase difference angle δ exceeds δ, it can be determined that synchronization has occurred.

Here, if δ ₀ is 20°, δ ₂ is (180−δ ₀ )=160°. In this example, it can be said that step-out occurs if the phase difference angle δ exceeds 160°. In other words, as described in claim 1, it means that step-out can be determined by looking at the phase difference angle.

On the other hand, when considering angular velocity, the phase difference angle is the integral of the angular velocity (difference from the rated velocity).
Furthermore, since the generator has large inertia, the angular velocity changes smoothly without discontinuous changes. Therefore, if the angular velocity reaches a certain level, the phase difference angle will increase over time.
Therefore, as described in claim 2, the angular velocity and the phase difference angle can be used to determine step-out.

The above description has been made using a single-machine infinite bus system, but the same applies to a multi-machine system. For example, in a two-machine system as shown in Figure 5, the internal voltage of one machine system is E ₁ (phase difference angle = δ ₁ ), and the internal voltage of the other machine system is E ₂ (phase difference angle = δ ₂ ). Looking at these changes, if the phase difference angle difference (δ ₂ −δ ₁ ) increases to 180° or more as shown in FIG. 7, it can be determined that synchronization has occurred. Furthermore, the influence of angular velocity is the same as in the case of a single-machine infinite bus system.

In this way, the present invention detects the amount of power of each generator after an accident occurs in the power system, calculates the internal phase difference angle and angular velocity from this, and calculates the relative relationship between each generator based on this. The difference between the phase difference angle and the angular velocity is calculated, and step-out is determined under each condition as described in claims 1 and 2.

[Embodiment] Hereinafter, an embodiment of the present invention based on the above concept will be described with reference to the drawings.

FIG. 2 is a diagram showing a schematic configuration of a system to which the step-out progression prevention device according to the present invention is applied. In Figure 2, 1 and 2 are generators at each end (the power plant is treated as an equivalent generator), and these generators 1 and 2 are interconnected by the transmission line L via the breakers CB1 and CB2. are doing. In addition, in the figure, two generators G1 and G2 and one power transmission line L are shown for simplification of explanation. Moreover, 21 and 22 are power amount detection units provided on each of the generators 1 and 2. The power amount detection units 21 and 22 detect the (effective) power amount at the output end of each generator 1 and 2 via transformers PT1 and PT2 and current transformers CT1 and CT2 provided at the output end. Further, the power amount detection units 21 and 22 transmit the power amount as an analog amount or a digital amount to a local power supply station or a central power supply station, for example, via transmission systems 31 and 32 by a transmission device (not shown).

On the other hand, on the central power supply station side, the angular velocity/phase difference angle calculation unit 4 introduces each electric energy transmitted from the electric energy detection units 21 and 22, and based on it, the above-mentioned (4) and (5) are carried out.
The angular velocity ω _i (t) of each generator 1, 2 is calculated from the formula, and the phase difference angle δ _i (t) is calculated from the formula (6) and (7).

Further, the step-out detection determination section 5 detects each angular velocity ω _i (t) and phase difference angle δ _i in the angular velocity/phase difference angle calculation section 4 .
Based on the calculation result of (t), the relative phase difference angle difference and angular velocity difference between each generator 1 and 2 are detected from the above equations (8) and (9), and further based on the detection result. (10), (11) above
Determine whether there is a generator that is out of step using the formula.
Furthermore, this step-out detection/judgment unit 5 issues a command T _p to open a breakout switch (for example, breakout switch CB1) of the power transmission line L connected to the generator determined to be out of step (for example, generator 1). Send.

That is, in this case, the out-of-step detection and determination unit 5 determines that the generator 1 is out of step because equations (10) and (11) hold between it and the other generators 2, as described above. Then judge. In this embodiment, the values of the step-out determination criteria J and K in the step-out detection and determination section 5 are J=
180°, K=0°/sec.

Further, in the above, after an accident occurs in the system, the power amount detection units 21 and 22 are activated by an operation signal of a failure detection relay such as an overcurrent relay or an undervoltage relay (not shown), and start measuring the amount of power.

Next, the operation of such a step-out progression prevention device will be described.

For example, when an accident such as a three-phase short circuit occurs in a system as shown in FIG. 2, a failure detection relay (not shown) is activated, and the power detection units 21 and 22 are activated by the activation signal. As a result, the power detection units 21 and 22 start detecting the amount of electric power at the output end of each generator G1 and G2 via the transformers PT12 and PT2 and the current transformers CT1 and CT2 (however, each The mechanical input of generators G1 and G2 is equal to the electrical output before the accident, so use it).
Then, each of the detected generators G1 and G2
The amount of electric power is transmitted to transmission system 3 by a transmission device (not shown).
1 and 32, respectively, to the central power supply station as analog or digital quantities.

On the other hand, on the central power supply station side, the power amount signal transmitted from the above system is transmitted to the angular velocity/phase difference angle calculation unit 4.
will be introduced in As a result, the angular velocity/phase difference angle calculation unit 4 calculates the angular velocity ω _i (t) of each generator G1, G2 based on the introduced power amount signal.
From equations (4) and (5), the phase difference angle δ _i (t) is also the same.
They are calculated from equations (6) and (7), respectively, and introduced into the step-out detection/judgment section 5.

Next, the step-out detection determination unit 5 determines whether there is a step-out generator based on the angular velocity ω _i (t) and phase difference angle δ _i (t) of the introduced generators G1 and G2. A determination is made. That is, first, based on the above equations (8) and (9), the difference δ _li in the phase difference angle of each generator G1, G2, respectively,
The difference in angular velocity ω _li is calculated. Next, the calculated phase difference angle difference δ _li and angular velocity difference ω _li are compared with the step-out judgment criteria J (180°) and K (0°/sec) as described in (10) and (11).
) is compared and judged based on the formula. (In this case, there are two generators in the diagram, but in reality, generators not shown are interconnected. For example, if we look at generator G1, it is connected to generator G2 and all other generators not shown. As a result, for example, if equations (10) and (11) hold between generator G2 and all other generators for generator G1, , that is, when δ _li 180° and ω _li 0°/sec are established at the same time, it is determined that the generator G1 is out of step, and the power transmission line L connected to the generator G1 is finally disconnected. Command to open device CB1
The progress of step-out is prevented by applying T _p to the grid side through the transmission system. In addition, in the above, generator G2
Even when it is determined that the step-out has occurred, the progress of the step-out phenomenon is prevented by opening the disconnector CB2 through exactly the same process.

As described above, in the step-out progression prevention device of the embodiment corresponding to claim 2, the output of each generator G1, G2, etc. is activated by the operation signal of the failure detection relay due to the occurrence of a system accident. Detects the end electric energy and transmits it to the central power supply station side 31, 32
Electric energy detection units 21, 22, which are transmitted via...
Based on the transmitted power amount of each generator G1, G2..., each generator G is calculated based on the above equations (4), (5), (6), and (7)
An angular velocity/internal phase difference angle calculation unit 4 that calculates the angular velocity ω _i (t) and (internal) phase difference angle δ _i (t) of 1, G2..., and the angular velocity ω _i ( t), from the phase difference angle δ _i (t), calculate the relative phase difference angle and angular velocity difference δ _li・ω _li between each generator based on the above equations (8) and (9), and further calculate this difference δ _li・ω _li as above
Judgment criteria J (180°), K (0°/
sec) to determine whether there is a generator that has gone out of synchronization, and if there is a generator that has gone out of synchronization, it will issue a command to open the transmission line or disconnector CB connected to that generator. Step-out detection determination unit 5 that sends out T _p
A step-out prevention device has been constructed and prepared to take measures after a system accident.

Therefore, after an accident such as a three-phase short circuit in the power system, it is possible to detect a generator that has lost its synchronization at high speed and disconnect it from the grid, thereby eliminating the problem caused by one generator's loss of synchronization. It is possible to reliably prevent the spread (progress) of the out-of-step phenomenon, i.e., out-of-step of other generators, and greatly contribute to maintaining the stability of the system.

In addition, as described above, the device has a power amount detection section 2.
1, 22. Since it is composed of only the angular velocity/internal phase difference angle calculation section 4 and the step-out detection/judgment section 5, the above-mentioned great effects can be obtained with a simple configuration, and its reliability is further improved. be able to. Further, an angular velocity/internal phase difference angle calculation section 4 and a step-out detection determination section 5
If these functions can be performed all at once by an analog or digital computer, it can be extremely advantageous economically.

Next, an embodiment corresponding to claim 1 will be described.

That is _, in the _embodiment described above, the step-out detection determination section 5 determines whether each generator is The difference in the relative phase difference angle and the difference in angular velocity between 1 and 2 are detected using the above formulas (8) and (9), and based on the detection results, the generator that has lost synchronization is determined from the above formulas (10) and 〓. It was determined whether or not there was.

However, in this embodiment, the step-out detection/judgment unit 5 determines the phase difference angle δ _i of each of the introduced generators G1 and G2.
Based on (t), it is determined whether or not there is an out-of-step generator. That is, the difference δ _li between the phase difference angles of the respective generators G1 and G2 is calculated based on the above equation (8). Next, this calculated phase difference angle difference δ _li is calculated based on the step-out judgment criterion J (180°)
Comparison and judgment are made based on the above equation (10).

As a result, for example, if equation (10) holds between generator G2 and all other generators for generator G1, that is, if δ _li 180° holds true, generator G1 will step out of step. It was determined that the power transmission line L connected to this generator G1 was finally
A command T _p is given to the system side through the transmission system so as to open the signal 1, thereby preventing the step-out from progressing.

In this way, in the previous embodiment, the step-out determination in the step-out detection and determination section 5 is performed based on the conditions of both the angular velocity ω _i (t) and the (internal) phase difference angle δ _i (t). However, when the judgment criterion J is set to a large value, such as 200°, as in this example, the judgment is based only on the (internal) phase difference angle δ _i (t). However, it can be implemented as well.

In other words, the determination of step-out detection is based on the condition of the (internal) phase difference angle δ _i (t), the (internal) phase difference angle δ _i (t) and ω _i
Although it is possible to perform the determination based on any of the conditions (t) and (t), it goes without saying that the reliability of the determination based on the conditions (t) is higher.

It should be noted that the present invention is not limited to the embodiments described above, but can also be implemented as follows.

(1) In the previous embodiment, the step-out detection determination unit 5
The judgment conditions for equations (10) and (11) are J = 180°, K = 0°/sec.
We have described the case where J is a smaller value and K is a larger value, for example, J = 150°, K
= 180°/sec, it is possible to predict a generator out-of-step at an earlier point in time. This value can be selected as appropriate depending on the system conditions.

(2) In the above embodiment, when determining step-out, the power amount signal at each end is transmitted to the central power supply station, and the determination calculation is performed there based on this, but the present invention is not limited to this. For example, on the grid side, based on the power amount of each generator, its angular velocity ω _i (t)
and (internal) phase difference angle δ _i (t), and transmits this as a signal of angular velocity ω _i (t) and (internal) phase difference angle δ _i (t) to the central power supply station, and based on this, the It may be configured to perform key determination.

In addition, the present invention can be implemented with various modifications without changing the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, the output power amount of each generator after an accident occurs in a power system in which a plurality of generators are interconnected is detected, and each power generation amount is determined based on this output power amount. The angular velocity and phase difference angle of the generator are calculated, and based on the angular velocity and phase difference angle, the relative difference in phase difference angle between each generator, or the difference in angular velocity and the difference in phase difference angle is scheduled to be the standard for determining step-out. When it exceeds the threshold value, it is determined that there is a step out, and the generator that has lost its step is disconnected from the power grid. Therefore, it is possible to detect out-of-step in the power grid at high speed and prevent the progression (spread) of the out-of-step phenomenon, thereby greatly contributing to maintaining the stability of the power grid. A device for preventing system step-out progression can be provided.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the drawbacks of the conventional method, Figure 2
The figure is a schematic configuration diagram showing one embodiment of the present invention, and FIGS. 3 to 7 are diagrams for explaining the concept regarding step-out determination of the present invention. 21, 22...Power detection unit, 4...Angular velocity/internal phase difference angle calculation unit, 5...Step-out detection determination unit.

Claims (1)

[Scope of Claims] 1. In an electric power system in which a plurality of generators are linked, an electric power detection means for detecting the output amount of each of the generators after an accident occurs in the electric power system; and detection by the electric power amount detection means. angular velocity/phase difference angle calculation means for calculating the angular velocity and phase difference angle of each of the generators from the output power amount; When the difference in the relative phase angle between the two exceeds a predetermined threshold value as a step-out determination criterion, it is determined that there is a step-out, and the step-out generator is disconnected from the power grid. What is claimed is: 1. A power system step-out progression prevention device, comprising: a detection/judgment means; 2. In a power system in which a plurality of generators are linked, a power amount detection means for detecting the output amount of each of the generators after an accident occurs in the power system; An angular velocity/phase difference angle calculation means for calculating the angular velocity and phase difference angle of each of the generators, and a calculation of the relative angular velocity between the generators based on the angular velocity and phase difference angle calculated by the angular velocity/phase difference angle calculation means. Out-of-step detection determination that determines that there is a step-out when the difference between the difference and the phase difference angle exceeds a threshold value that is scheduled to be a step-out determination criterion, and disconnects the out-of-step generator from the power grid. What is claimed is: 1. A power system step-out progression prevention device, comprising: means;