JP2618902B2 - Power system stabilizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention eliminates the phenomenon that a plurality of generators step out due to a system failure by disconnecting some generators from the system. The present invention relates to a system stabilization device capable of stabilizing a power generator.

(Prior art) Conventionally, a control amount applied to this type of system stabilization device, that is, a method of calculating the number of generators to be disconnected, is obtained from the generator output before the system failure and information about the circuit breaker. The main method is to determine the number of disconnected generators based on a preset control amount calculation curve (parameter) based on the determined failure type.

FIG. 7 shows an example of an electric power system to which such a system stabilizing device is applied. That is, the seventh conventional system stabilizer as shown in the figure, a power detection unit 1 detects the total output P ₀ of the plant before the failure, after system failure, open circuit breaker information (CB6, CB7 Failure condition determination unit 2 that determines a failure condition (fault point, failure type) based on pole information)
Based on the power plant total output P ₀ before the occurrence of the failure detected by the power detection unit 1 and the failure condition determined by the failure condition determination unit 2, a control amount calculation curve as shown in FIG. The control unit includes a control amount calculation unit 3 for calculating a control amount and determining an optimal number of generators to be disconnected, and a control unit 4 for shutting off the generator.

However, in such a system stabilization device, a means for determining a failure condition is required, and since the system has been expanded and the step-out mode has been diversified, such a method is used for all the step-out modes. In such a case, it is necessary to input circuit breaker information and the like of all transmission lines, and the scale of the apparatus including the transmission system increases.

(Problems to be Solved by the Invention) As described above, the conventional system stabilization device requires a means for determining a failure condition (fault point, failure type), and is intended for all step-out modes. If this is attempted, there is a problem that the scale of the apparatus becomes large, which results in uneconomical results.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an economical and highly reliable system stabilization device which does not need to judge a fault condition.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a system stabilization device according to the present invention provides an electric output of each generator in a power system including a plurality of generators. A power station terminal means comprising a power detection section for detecting each, and a control section for outputting a disconnection command to the generator, and an electrical connection between each generator transmitted from the power station terminal means via the transmission means. A computing means for calculating and predicting the kinetic energy and potential energy of the entire system based on the output, and the stability of the system based on the kinetic energy and potential energy of the entire system predicted by the computing means Judgment is made, and the system is unstable under the condition that the predicted value of kinetic energy increases, the predicted value of potential energy decreases, and the difference between the two exceeds a preset threshold. A stability judging means for judging,
Under the condition that the stability is judged to be unstable by the stability judgment means, necessary for stabilizing the system based on the difference between the predicted value of the kinetic energy and the predicted value of the potential energy when the generator is cut off. A power limiting amount determining means for calculating a generator cutoff amount as a power limiting amount and sending a disconnection command for the corresponding generator to a power plant terminal means via a transmitting means. .

(Operation) In the above-described system stabilization device, when a failure occurs in the power system including a plurality of generators, the electrical output of each generator is detected by the power detection unit of the power station terminal device, respectively.
The data is transmitted to the calculation means via the transmission means. When the system fault is removed, the calculation means calculates and predicts the kinetic energy and the potential energy of the entire system based on the electric output of each generator. In the stability determination means, the stability of the system is determined based on the kinetic energy and the potential energy predicted by the calculation means, and the difference between the predicted value of the kinetic energy and the predicted value of the potential energy exceeds the threshold. If so, it is determined that the system is unstable. Further, in the power control amount determining means, when the stability determining means determines that the system is unstable, the power system control amount determining means determines the system based on the difference between the predicted value of the kinetic energy and the predicted value of the potential energy when the generator is shut off. A generator cutoff amount, which is a power supply restriction amount necessary for stabilization, is calculated, and a disconnection command for the generator is transmitted to the power station terminal means via the transmission means. Then, the control unit of the power station terminal means outputs a disconnection command to the corresponding generator, thereby disconnecting some generators from the system and stabilizing the system.

(Embodiment) First, the concept of stability determination and power supply restriction amount calculation according to the present invention will be described.

Methods for determining the stability of the power system include a method using an internal phase angle difference between generators and a method using energy stored in the system due to a power system failure or the like. In particular, the latter is known as the energy method or the Lyapunov method. The stability determination and the calculation of the power supply restriction amount according to the present invention are based on this energy method. In the following description, when a plurality of generators are arranged in parallel at the same power plant, they will be treated as equivalent single-machine generators. Also, for simplicity of explanation,
It is assumed that generators in parallel with the same power plant have the same capacity.

That is, equation (1) shows an example of the energy function.
In equation (1), the first term on the right side is the kinetic energy of the entire system, and the second term on the right side is the potential energy of the entire system.
The subscript i indicates each generator, and the subscript COI indicates various amounts of the center of inertia weighted by the inertia constant of the generator.

θ _i = δ _i −δ _CI (2a) P _ai = P _INi −P _ei … (2e) The symbols on the right side of the equations (2a) to (2f) mean the following, respectively.

M: inertia constant of generator, ω: angular velocity of generator, δ: internal phase angle of generator, PIN: mechanical input to generator, Pe: electrical output of generator, n: generator parallel to system The number of vehicles operated.

FIGS. 2 (a) and 2 (b) show an example of the temporal movement of kinetic energy (hereinafter, referred to as KE) and potential energy (hereinafter, referred to as PE) when a three-phase short circuit fault or the like occurs in the power system. 2 (a) shows a case where the system is stable, and FIG. 2 (b) shows a case where the system is unstable (a part of the system loses synchronism). Now, as a characteristic of the energy method, it is known that the total energy obtained by adding KE and PE is constant. As can be seen from FIGS. 2 (a) and 2 (b), the energy accumulated due to the system failure is After the failure is eliminated, KE and PE share each other. Then, in a stable case, the faulty KE is absorbed by the system, so that the PE increases and the KE decreases. On the other hand, in the case of instability, the KE increases, the PE decreases, and the KE becomes unstable because the system has no ability to absorb the KE during the failure. Therefore, by quickly capturing such characteristics of the energy method by means of prediction, it is possible to quickly and appropriately perform stability determination and power supply limit calculation. As shown in FIG. 3 in particular, the prediction value (KE-PE) ₀ at the present time (t ₀ point) than a predetermined time later (te time) of (KE-PE),
If a predetermined threshold value _El is exceeded, it is determined to be unstable, and a predicted value (KE-PE) c of (KE-PE) when a part of the generator is cut off is obtained. There is for calculating a power limit amount so as not to exceed E _l.

Next, a specific calculation method of the energy value will be described.

First, in a steady state before the occurrence of a failure, the electrical output Pei (0) of each generator is detected, and the value is used as the mechanical input PINi of each generator. Next, if a fault occurs in the system, using the electrical output Pei of each generator detected at intervals of Δt, the angular velocity ωi, from the equation of motion shown in equations (3a) and (3b).
Calculate the internal phase angle δi.

ω _i (t) = ω _i (t−Δt) + (P _INi− P _ei (t)) Δt / M _i (3a) δ _i (t) = δ _i (t−Δt) + (ω _i ( t) + ω _i (t−Δt)) Δt / 2M _i (3b) Next, if the system fault is removed, the above-described angular velocity ω
i, using the calculation result of the internal phase angle δi, , And finally calculate KE (t) from equation (4),
PE (t) is obtained from equation (5).

Next, a specific method of predicting the energy value will be described.

In order to obtain a predicted value of energy from the equations (2), (3), (4), and (5), an estimated value of the electrical output of each generator is required. On the other hand, if this estimation value is to be obtained strictly, a power flow calculation is required and cannot be applied to the system stabilization device. Therefore, the electric output Pei of each generator is approximated as shown in FIG. To Narachi, from the present time t ₀ to shut assumed time tc, it calculates the coefficient of using measured values of the electric output Pei previously set as shown in FIG. 5 estimation formula, on an extension of the estimation formula Find the estimated value as a point. On the other hand, Pei is approximated to be constant from the cutoff assumed time tc to the energy prediction time te, and the following equation is obtained using the estimated value Pei (tc) at the time tc and the rate of change Ki of the electrical output at the time of the generator cutoff. Calculate from

Pei (t) = Ki · Pei (tc) (6) Here, since it is impossible to obtain the exact solution of Ki, Ki of the power plant not subject to interruption has a small change in electrical output. Therefore, it is set to 1.0, and the Ki of the power plant to be cut off is approximately calculated using Expression (7).

Here, XG: a value obtained by adding the reactance of the step-up transformer and the d-axis transient reactance when the power generation target power plant is an equivalent generator, and XD: a driving point when the system is viewed from the high voltage bus of the power generation target power generation target. Reactance, n: Number of operating power stations before interruption, m: Number of interrupting power stations. Note that Ki when the number of interrupted units is 0 is
As can be seen from equation (7), it is 1.0.

Based on the electrical output Pei ^* of each generator estimated by the method described above, the predicted values ωi ^* and δi ^* of the angular velocity and the internal phase angle are obtained from the equation of motion shown in Expression (3).
From equation (2) , PcI is calculated from Eqs. (4) and (5).
Calculate the predicted value of E.

Determination of stability is performed by comparing KE in case of not carrying out interruption, it calculates a predicted value of PE, with a threshold set in advance and the difference between them _{(KE-PE) 0 E l} . That is, as shown in FIG. 3, it is determined that (KE-PE) when the predicted value of ₀ is larger than the threshold value E _l is unstable.

On the other hand, the calculation of the power supply restriction amount is performed by calculating the predicted values of KE and PE when a part of the generator is cut off in accordance with the cutoff priority of the power plant, and setting a difference (KE-PE) c between the two. performed by comparing the threshold value E _l, as shown in FIG. 3, and calculates the (KE-PE) power limit amount as the predicted value is less than the threshold value E _l of c. The interruption priority of the power plant is the angular velocity deviation from the center of inertia calculated from equations (2a) and (2b). Is determined using That is, angular velocity deviation The larger the is, the easier it is to lose synchronism, so priorities are given in descending order.

FIG. 6 shows an overall flowchart of the above-described stability determination method and power supply limit amount calculation method according to the present invention.

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

FIG. 1 shows a configuration example of a power system to which the system stabilizing device of the present invention is applied. In FIG. 1, P is a target power system, G11 / G12 / G13, G21 / G22 / G23 are power plants connected to the power system 1, a generator parallel to the power plant 2, and B1 and B2 are power plants. These are the buses on the 1 and 2 sides.

On the other hand, 51a and 51b are instrumentation transformers PT1 and PT2 and current transformer CT.
Each generator G11 via 11 ・ CT12 ・ CT13, CT21 ・ CT22 ・ CT23
Power detection units for detecting the electrical outputs of G12, G13, G21, G22, and G23, respectively, and 52a and 52b are control units that output a disconnection command to the shutoff generator, and the power station terminal means 5
a, 5b. Also, 6a, 6b are power station terminal means 5a,
Transmission means for transmitting the electrical output of each generator from 5b. Further, 7 is an input which receives the electrical output of each generator transmitted via the transmission means 6a and 6b, and calculates and predicts the kinetic energy and potential energy of the entire system based on the input. The stability of the system is determined based on the kinetic energy and the potential energy of the entire system predicted by the calculation means 7, and the predicted value of the kinetic energy increases, the predicted value of the potential energy decreases, and the difference between the two is determined in advance. Stability determining means 9 for determining that the system is unstable on condition that the set threshold value is exceeded is provided on condition that the stability determining means 8 determines that the system is unstable. Based on the difference between the predicted value of the kinetic energy and the predicted value of the potential energy when the generator is shut off, calculate the generator cutoff amount, which is the power supply limit required for system stabilization, and Transmission means 6 a disconnecting command to
The power supply limiting amount determining means sends the power source terminal means 5a and 5b to the power station terminal means 5a and 5b via a and 6b.

Next, the operation of the system stabilizing device configured as described above will be described.

First, in a steady state, the electric output of each of the generators G11, G12, G13, G21, G22, G23 connected to the power plant 1 and the power plant 2 connected to the power system P is detected by the power detection of the power plant terminal means 5a, 5b. Parts 51a, 5
1b, and transmitted to the calculating means 7 via the transmitting means 6a, 6b. Then, in the arithmetic means 7, each of the generators G11, G12, G13, G21, G22, G23 to be incorporated in the power plant 1 and the power plant 2
, And this value is stored as the machine input PINi when the power plant is treated as an equivalent single-machine generator (step S1 in FIG. 6).

Next, when a failure occurs in the power system P in such a state, the generators G11, G12, G13, G21, G
The electric output Pei (t) of 22 · G23 is connected to the power station terminal means 5a, 5
The power detection units 51a and 51b of b detect the power at intervals of Δt, and transmit the detected power to the calculation means 7 via the transmission means 6a and 6b. Then, in the arithmetic means 7, the transmitted generators G11 and G12 are transmitted.
Calculate the total output of G13, G21, G22 and G23, and use this value as the electric output Pei of the equivalent single-generator,
The angular velocity ωi and internal phase angle δi of the equivalent generator
Is calculated.

Next, when the system fault is removed, step S3 in FIG.
, The kinetic energy KE and the potential energy PE of the entire system are calculated. Further, when a certain period of time has passed after the elimination of the system failure, the predicted values KE ^* ₀ , PE ^* of the kinetic energy KE and the potential energy PE when the generator is not cut off, according to the operations of steps S4, S5, S6 in FIG. ₀ is calculated, and the stability determination means 8 determines the stability of the system by the operation of step S7 in FIG. As a result, the predicted value PE ^* ₀ predictive value KE ^* ₀ increases and potential energy of the kinetic energy is reduced, and the difference KE ^* ₀ -PE ^* ₀ both exceeds a preset threshold value E _l In this case, it is determined that the system is unstable. In addition, the power limit amount determining means 9
In the case where it is determined by the stability determining means 8 that the system is unstable, the steps S8, S9, S10 in FIG.
By the action, the kinetic energy when the shut off a part of the generator according to interruption priority of the plant, the potential energy KE, the predicted value of the PE KE ^{* *,} PE ^{* c} is calculated. Then, according to the operation of step S11 in FIG. 6, the difference (KE
^{* C,} PE ^{* c)} calculates a generator cutoff amount is a power limit amount necessary for stabilization of the system to be equal to or less than the threshold value E _l,
A disconnection command for the generator is transmitted to the control units 52a, 52b of the power station terminal means 5a, 5b via the transmission means 6a, 6b. Thereby, in the control units 52a, 52b of the power station terminal means 5a, 5b,
By the operation of step S12 in FIG. 6, the corresponding generator is disconnected from the system to stabilize the system.

When the stability determining means 8 determines that the system is stable, the process returns to step S2 in FIG. 6, and the above-described processing is continuously performed for a certain period of time.

As described above, in the system stabilizing apparatus according to the present embodiment, it is possible to quickly determine that a plurality of generators lose synchronism due to the occurrence of a failure in the power system P without determining failure conditions (fault points and failure types). In this manner, the system stabilization control is performed using the system stabilization device, so that step-out can be prevented in advance. In addition, since means for determining a failure condition (failure point, failure type) is not required, the scale of the apparatus is not increased, which is extremely economically advantageous.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an economical and highly reliable system stabilization device that does not need to determine a failure condition.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a power system to which the system stabilizing device of the present invention is applied, and FIGS. 2 (a) and 2 (b) show temporal changes in energy when a three-phase short-circuit fault or the like occurs in the power system. FIG. 3 is a diagram illustrating a movement, FIG. 3 is a diagram for explaining a stability determination method based on a predicted value of energy and a method of calculating a power supply limit amount, and FIG. 4 is an approximation of an electrical output of a generator used for energy prediction. FIG. 5 is a diagram for explaining the method, FIG. 5 is a diagram for explaining a method of estimating a future electric output based on the electric output up to the present time, and FIG. 6 is a stability judging method and a power supply limit calculation. FIG. 7 is a block diagram showing a conventional system stabilizing device, and FIG. 8 is a diagram for explaining a control amount determining method applied to the conventional system stabilizing device. FIG. 5a, 5b ... power station terminal means, 51a, 51b ... power detection unit, 52
a, 52b control section, 6a, 6b transmission means, 7 calculation means, 8 stability determination means, 9 power limit amount determination means, P power system, G11, G12, G13 , G21, G22, G23 …… Generator, B1, B2 …… Bus.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Eiji Hioki Inventor at Kita-Kanzan 20 at Odaka-cho, Midori-ku, Nagoya-shi, Aichi 1 Inside Chubu Electric Power Research Institute (72) Inventor Kazuya Omata Fuchu-shi, Tokyo No. 1, Toshiba-cho, Toshiba Fuchu Plant Co., Ltd. (72) Inventor, Masahiro Sato No. 1, Toshiba-cho, Fuchu City, Tokyo Toshiba Fuchu Plant, Inc.

Claims (1)

(57) [Claims] In a power system having a plurality of generators,
A power detection unit for detecting an electrical output of each of the generators,
And a power station terminal means comprising a control unit for outputting a disconnection command to the generator, and an electric output of each of the generators transmitted from the power station terminal means via transmission means as inputs. Calculating means for calculating and predicting the kinetic energy and potential energy of the entire system based on this; and determining stability of the system based on the kinetic energy and potential energy of the entire system predicted by the calculating means. Stability determining means for determining that the system is unstable on the condition that the predicted value of the energy increases and the predicted value of the potential energy decreases and the difference between the two exceeds a preset threshold value; Based on the difference between the predicted value of the kinetic energy and the predicted value of the potential energy when the generator is shut off, provided that the stability determination means determines that the system is unstable. Power limit amount determining means for calculating a generator cutoff amount, which is a power limit amount necessary for stabilizing the power generation, and sending a disconnection command to the power generator to the power station terminal means via the transmission means. A system stabilization device comprising: