JP4480647B2 - Power system step-out prediction device - Google Patents

Description

  The present invention relates to a power system step-out prediction apparatus that predicts step-out occurring between generator groups at both ends of a power system interconnection line.

  The conventional power system step-out detection device is an analog / digital converter that takes in the voltage and current of the power system interconnection line, and based on the voltage and current, the voltage and current of a predetermined section up to the point of determination are determined. Mean value calculation means for obtaining an average value, maximum / minimum determination storage means for obtaining and storing the maximum and minimum values of the average value of the voltage and current, and the phase difference from the voltage and current are calculated. When the phase difference calculation means determines that the phase difference exceeds 90 degrees, the average value of the measured current is within a certain range centered on the minimum value of the average value of the stored voltage. Step-out determination means for determining step-out when it is within a certain range centered on the maximum value of the stored average value of currents (see, for example, Patent Document 1).

JP 2003-194863 A

However, in the conventional step-out detection device, when the voltage phase difference at both ends of the interconnection line exceeds 180 degrees and the generator has already stepped out, the phase difference between the voltage at one end and the current flowing through the one end is Since it is detected that the angle exceeds 90 degrees, there is a problem that the generator can only be detached from the system.
In addition, the reactance from one end to the place where the out-of-step locus occurs is obtained from the voltage and current at the one end, and the distance from the one end to the place where the out-of-step locus occurs is calculated using the reactance of the unit length of the interconnection line. There is a problem that it is difficult to determine the center of step-out.
Moreover, since the phase difference between the buses of the power system is not taken into account, there is a problem that erroneous determination is easily performed.

  An object of the present invention is to provide a power system step-out prediction apparatus that can perform step-out prediction and can reliably specify a step-out center.

The power system step-out prediction apparatus according to the present invention is:
A power system step-out prediction device that includes at least one generator and a bus and predicts step-out of the generator in a plurality of power systems that are interconnected by connecting the bus through a connection line. The first-order differential and the second-order differential relating to the phase difference between both ends of the connecting line exceed zero, and the first-order derivative relating to the active power flowing from the connecting line to the one end is less than zero, and the connecting line When all of the four conditions that the center voltage in phase with the current flowing from one end to the other end is smaller than a predetermined threshold are satisfied a predetermined number of times, the generator connected to the one end continues to operate. It is predicted that a step-out will occur and a center of step-out will appear in the connecting line .

  The effect of the power system step-out prediction apparatus according to the present invention is that the phase difference between the buses calculated from the voltage of the bus connected to one end of the connection line and the current flowing from the connection line to the bus, the active power It can be predicted that step-out will occur when all the conditions when the unstable equilibrium point as a branch point where the time series trend and the center voltage continue to operate will result in step-out will be exceeded.

The principle of step-out prediction employed by the power system step-out prediction apparatus according to the present invention will be described.
First, the state in which a generator is stepped out when one generator is connected to an infinite bus will be described. FIG. 1 is a P-δ curve diagram showing the relationship between the phase angle δ _G of the internal voltage of the generator connected to the one-machine infinite bus system and the electrical output Pe. The phase angle δ _G of the internal voltage is a value when the phase angle of the voltage of the infinite bus is zero.
The equation of motion of the generator connected to the one-machine infinite bus system is expressed by equation (1).

However, the mechanical input of Pm generator, Pe is the electrical output of the generator, the [delta] _G phase angle of the internal voltage of the generator, M is the inertia constant of the generator.
The operating point of the generator moves along the P-δ curve when there is a system disturbance due to an accident or the like. The point C in FIG. 1 is an unstable equilibrium point. If the operating point of the generator moves to the side where the phase angle δ _G is larger than the unstable equilibrium point C, if the operation is continued as it is, the operating point cannot be reversed and the generator accelerates. It will lead to step-out.
There are three conditions for the operating point of the generator to move to the larger phase angle than point C.
The first condition is that the phase angle [delta] _G is increased, is that as shown in equation (2), the first derivative of the phase angle [delta] _G of the generator is greater than zero.
The second condition is that the electrical output Pe is less than the mechanical input Pm. Since M on the left side of the equation (1) is a positive real number, as shown in the equation (3), the generator That is, the second derivative of the phase angle δ _G of
The third condition is that the electrical output Pe of the generator tends to decrease, and the first-order derivative of the electrical output Pe of the generator is less than zero, as shown in Equation (4). is there.

As described above, in the generator of the one-machine infinite bus system, when all of the above three conditions are satisfied, if the operation is continued as it is, the step-out occurs (the phase angle δ _G of the generator internal voltage exceeds 180 degrees). That the operating point exceeds the unstable equilibrium point C.
Then, these relationships will be examined in the case where two power systems (A system 1a and B system 1b) as shown in FIG. FIG. 2 is a diagram illustrating a state where two power systems are interconnected by a connection line. In this case, when the phase angle of the internal voltage of the generator 3 of the A system 1a satisfies the above three conditions as in the case of the one machine infinite bus system described above, the generator 3 continues to operate as it is. It can be predicted that step-out will occur. When the connecting line 2 connects the M bus 4a of the A system 1a and the N bus 4b of the B system 1b, the phase difference δ between the voltage of the M bus 4a and the voltage of the N bus 4b and the connecting line 2 are used. Thus, the above three conditions relating to the active power P flowing through the M bus 4a are maintained. And if it determines that the out-of-step center comes to the connecting line 2, it can be predicted that the out-of-step will occur if the generator 3 connected to the A system 1a continues to operate.

Therefore, in order to predict the step-out of the power generator 3, the phase difference δ between the voltage of the M bus 4a and the voltage of the N bus 4b and the effective power P flowing through the connecting line 2 to the M bus 4a are obtained. It may be determined whether or not the above condition is satisfied.
Based on the spiral vector theory, the voltage v _N (t) at the N bus 4b is expressed as shown in Equation (5). Where V _M is the effective voltage value of the M bus 4a, ω is the angular velocity of the rotation vector, I is the effective current value flowing through the connecting line 2, θ is the phase difference between the voltage of the M bus 4a and the current flowing through the connecting line 2, X _MN is the impedance of the connection line 2.

When the time t is zero and the voltage phase of the M bus 4a is zero, Expression (5) is expressed as Expression (6). This expression (6) is divided into a real voltage instantaneous value v _Nre and a voltage imaginary instantaneous value v _Nim of the N bus 4b, and is expressed as expressions (7) and (8).

  Therefore, since the phase of the voltage of the M bus 4a is set to zero, the phase difference δ between the voltage of the M bus 4a and the voltage of the N bus 4b is expressed as in Expression (9).

The fourth condition for detecting whether or not the step-out center enters the connection line 2 is a center voltage V defined as a voltage having the same phase θ as the current I of the connection line 2 as shown in FIG. _C is smaller than a predetermined threshold value. FIG. 3 is a diagram showing a rotation vector on a complex plane.
Thus by obtaining a phase difference [delta], the active power P flows from the contact line 2 to M bus 4a and the center voltage V _C of the voltage of the voltage of the phase and N bus 4b phase of M bus 4a, the first condition, second When all the conditions of 4 are satisfied, it can be predicted that if the generator 3 is operated as it is, a step-out will occur.

Embodiment 1 FIG.
Next, a power system step-out prediction apparatus according to Embodiment 1 of the present invention will be described. This power system out-of-step prediction device 10 predicts out-of-step of the generator G3 using the value measured on the M bus 4a of one power system 1a connected to the connecting line 2 as shown in FIG. Then, the circuit breaker 9 is opened. FIG. 4 shows a power system in which the power system step-out prediction apparatus according to the first embodiment is provided.
In addition, the voltage of the M bus 4a is measured by a voltmeter 7 having a digital voltage output terminal, and the current flowing through the connecting line 2 is measured by an instrument current transformer 8 having a digital current output terminal. Input to the prediction device 10.

  As shown in FIG. 5, the power system step-out prediction apparatus 10 according to the first embodiment includes an actual voltage instantaneous value of the M bus 4a and an actual current instantaneous value flowing from the connection line 2 to the M bus 4a at each predetermined timing. Voltage / current measuring means 11 for measuring the voltage real-time instantaneous value and current real-number instantaneous value, which are measured, are converted into digital voltage real-time instantaneous values and digital current real-time instantaneous values.

  Further, the power system step-out prediction apparatus 10 stores the digital voltage real number instantaneous value and the digital current real number instantaneous value at every predetermined timing, and the voltage effective from the digital voltage real number instantaneous value at every predetermined timing. Voltage, current effective value calculation means 14 for calculating the current effective value from the value, digital real current instantaneous value, and the effective power, voltage effective value from the digital voltage actual value and digital current actual value at each predetermined timing. Active power / reactive power calculation means 15 for calculating reactive power from the current effective value and active power, the voltage of the M bus 4a from the active power and the reactive power at each predetermined timing, and the current flowing from the communication line 2 to the M bus 4a Voltage-current phase difference calculating means 16 for calculating the voltage-current phase difference of the current, the voltage effective value, the current effective value, and the M bus 4a for each predetermined timing. Inter-bus phase difference calculating means for calculating the inter-bus phase difference between the voltage of the M bus 4a and the voltage of the N bus 4b from the phase difference between the voltage and the current flowing from the connecting line 2 to the M bus 4a and a predetermined impedance. 17.

  Furthermore, the power system step-out prediction apparatus 10 includes a bus phase difference first-order differential calculation means 18 for calculating a phase difference between the buses from the phase difference between the buses, and a second-order differential between the buses from the phase difference between the buses first-order differential. Phase difference second-order derivative calculating means 19 for calculating the power, first-order effective power calculating means 20 for calculating the first-order effective power from the active power, center for calculating the center voltage from the voltage effective value and the phase difference between the voltage and current Voltage calculation means 21, step-out prediction means 22 that predicts step-out when all of the phase differences between the bus lines, the second-order differential between the bus lines, the active power first-order derivative, and the center voltage satisfy the conditions; It has system separation command means 23 for transmitting a digital opening operation command when the step-out is predicted.

  Furthermore, the power system step-out prediction apparatus 10 includes a circuit breaker operation command receiving unit 24 that receives a digital opening operation command, and a circuit breaker operation performing unit 25 that transmits a digital switching pole operation command to a target device.

Further, storage means 13, voltage / current effective value calculation means 14, active power / reactive power calculation means 15, voltage / current phase difference calculation means 16, bus phase difference calculation means 17, bus phase difference first-order differential calculation means 18, the inter-bus phase difference second-order derivative calculating means 19, the active power first-order derivative calculating means 20, the center voltage calculating means 21, the step-out prediction means 22, and the system separation command means 23 are constituted by a computer. The computer has a CPU, a RAM, a ROM, and an interface circuit.
The circuit breaker operation command receiving means 24 and the circuit breaker operation executing means 25 are composed of digital quantity processing units.

Next, a procedure for predicting a step-out by the power system step-out prediction apparatus 10 according to the first embodiment will be described with reference to FIG.
The time point (hereinafter referred to as measurement timing) at which the voltage real number instantaneous value and the current real number instantaneous value are measured is determined by determining the sampling period. The sampling period may be a value that can divide one period of the reference wave of the power system into N (N is a positive integer). One period of the reference wave is 2π (radian) expressed in electrical angle. For example, the electrical angle π / 6, π / 12, π / 24, π / 48, etc. of the reference wave is set in advance as the sampling period.

The frequency f _{0 of the} reference wave is 50 Hz, and π / 6 that can divide one period of the reference wave into 12 equal parts is a sampling period. The step size Δt (seconds) is 0.00166666667 seconds. k represents the order of measurement timing, and is 1 to 12 in one cycle of the reference wave. A reference wave electrical angle is rotated by 30 degrees between measurement timings k = 1 and k = 2.

In step 101, the voltage / current measuring means 11 measures the voltage of the M bus 4a to be measured and the current flowing from the communication line 2 to the M bus 4a at each measurement timing. An arbitrary timing among the measurement timings is represented by k. The timing one time before this timing is represented by (k−1), and the next timing is represented by (k + 1). Next, the A / D conversion means 12 A / D converts the measured voltage and current, which are analog signals, into a digital voltage signal and a digital current signal. This value is stored in the storage means 13. This measurement was performed when the voltage instantaneous values v _MA (k), v _MB (k), and v _MC (k) of the M bus are expressed by voltage rotation vectors that rotate counterclockwise around the origin 0 on the complex plane. The voltages are voltage real number instantaneous values v _Are (k), v _Bre (k), and v _Cre (k). The instantaneous current values i _A (k), i _B (k), i _C (k) flowing from the connecting line 2 to the M bus 4a are expressed by current rotation vectors that rotate counterclockwise around the origin 0 on the complex plane. when, the measured current is the current real instantaneous value _{i are (k), i Bre} (k), i Cre (k).

In step 102, the voltage / current effective value calculation means 14 determines one cycle of the reference wave from the voltages measured at the previous 12 timings including its own timing at each timing of the measurement timing. The effective voltage values V _A (k), V _B (k), and V _C (k) are calculated from the equations (10) to (12) using the real voltage instantaneous values v _Are , v _Bre , and v _Cre. To do. Then, the effective voltage value V _M (k) of the M bus 4a is calculated from the equation (13) using the effective voltage values V _A (k), V _B (k), and V _C (k). This value is stored in the storage means 13.

In addition, the voltage / current effective value calculation means 14 calculates the reference wave from the current measured at the previous 12 timings including the own timing for one cycle of the reference wave at each timing of the measurement timing. Current effective values I _A (k), I _B (k), and I _C (k) are calculated from formulas (14) to (16) using current real number instantaneous values i _Are , i _Bre , and i _Cre . Then, the effective current value I (k) flowing from the communication line 2 to the M bus 4a is calculated from the equation (17) using the effective current values I _A (k), I _B (k), and I _C (k). This value is stored in the storage means 13.

In step 103, the active power / reactive power calculation means 15 calculates the effective power P (k) flowing from the communication line 2 to the M bus 4a at each timing of the measurement timing from the equation (18) as a real voltage instantaneous value v _Are ( k), v _Bre (k), v _Cre (k) and current real number instantaneous values i _Are (k), i _Bre (k), i _Cre (k) are used for calculation. This value is stored in the storage means 13.
Further, the active power / reactive power calculating means 15 calculates the reactive power Q (k) flowing from the communication line 2 to the M bus 4a at each timing of the measurement timing from the equation (19), the voltage effective value V _A (k), Calculation is performed using V _B (k), V _C (k), current effective value I _A (k), I _B (k), I _C (k). This value is stored in the storage means 13.

  In step 104, the voltage-current phase difference calculation means 16 calculates the phase difference θ (k) (radian) between the voltage of the M bus 4a and the current flowing through the connecting line 2 at each timing of the measurement timing by the equation (20). From active power P (k) and reactive power Q (k). This value is stored in the storage means 13.

In step 105, the inter-bus phase difference calculating means 17 calculates the phase difference δ (k) (radian) between the voltage of the M bus 4a and the voltage of the N bus 4b from the equation (21) at each timing of the measurement timing. Calculation is performed using the effective value V _M (k), the current effective value I (k), and the phase difference θ (k). This value is stored in the storage means 13. X _MN is a reactance between the M bus and the N bus that is obtained in advance.

  In step 106, the inter-bus phase difference first-order differential calculation means 18 calculates the inter-bus phase difference first-order differential ω (k) from the equation (22) at the measurement timing k and (k−1) at each timing of the measurement timing. Are calculated using the phase differences δ (k) and δ (k−1) between the buses. This value is stored in the storage means 13.

  In step 107, the inter-bus phase difference second-order differential calculation means 19 calculates the inter-bus phase difference second-order differential α (k) from the equation (23) to the measurement timing k and (k−1) at each timing of the measurement timing. Is calculated using the first-order differentials ω (k) and ω (k−1) between the phase differences between the buses. This value is stored in the storage means 13.

  In step 108, the active power first-order derivative calculating means 20 calculates the line effective power first-order derivative P ′ (k) at the measurement timings k and (k−1) from the equation (24) at each timing of the measurement timing. It calculates using electric power P (k) and P (k-1). This value is stored in the storage means 13.

In step 109, the center voltage calculation means 21 uses the effective voltage V _M (k) and the phase difference θ (k) from the equation (25) as the center voltage V _C (k) at each timing of the measurement timing. To calculate. This value is stored in the storage means 13.

In step 110, the step-out prediction unit 22 determines that the phase difference between the buses is the first-order differential ω (k), the phase difference between the buses is the second-order differential α (k), and the active power is the first-order differential P ′. When (k) and the center voltage V _C (k) satisfy the relations of the expressions (26) to (29) at the same time, it is predicted that the step-out will occur if the operation of the generator 3 is left as it is. V _SET is a preset value such as 0.3 PU, for example.
In step 111, when the out-of-step prediction unit 22 predicts that the generator 3 will be out of step, the system separation command unit 23 transmits an opening operation command to the digital quantity processing unit.

  In step 112, upon receiving the opening operation command, the digital quantity processing unit opens the corresponding circuit breaker 9 and closes the communication line 2.

  Such a power system out-of-step prediction device 10 can calculate M from the real-time instantaneous value, that is, the real value of the voltage of the M bus 4a and the current flowing from the connecting line 2 connecting the M bus 4a to the N bus 4b to the M bus 4a. The phase difference of the voltage between the bus 4a and the N bus 4b, the active power flowing through the connecting line 2 and the center voltage are calculated, and the generator 3 in which the time-series tendency of these calculated values is connected to the M bus 4a side is If it is operated as it is, it will be out of step, and it can be predicted that the out-of-step center will appear in the connection line 2 when it indicates that the branch point that cannot be returned is exceeded.

  Further, since the active power is obtained based on the spiral vector theory using the measured voltage of the bus 4a and the current flowing from the connecting line 2 to the bus 4a as a real instantaneous value, the level between the very stable voltage and current is obtained. The phase difference can be calculated.

  Further, by using the rotation vector equation of the spiral vector theory using the voltage effective value obtained at one end of the connection line 4, the current effective value, and the phase difference between the voltage of the M bus 4a and the current flowing from the connection line 2 to the M bus 4a. Since the voltage of the N bus 4b is obtained, the information on the other end can be obtained only from the information on one end of the connecting line 2.

The voltage effective value V _M (k), the current effective value I (k), the active power P (k), and the reactive power Q (k) are obtained over three phases. Also good.

Embodiment 2. FIG.
FIG. 7 shows an EAST10 model system in which the power system step-out prediction apparatus according to the second embodiment of the present invention is provided to simulate the step-out prediction.
The power system step-out prediction apparatus according to the second embodiment of the present invention is installed on the 11 buses of the EAST10 model system, which is one of the power system analysis standard models of the Institute of Electrical Engineers. That is, 11 buses are self-ends, the connection line with the other 21 buses is 11 connection lines, and the generator connected to the 11 buses is the generator G1.
Then, a change in the EAST10 model system is simulated when a three-phase short-circuit accident occurs at point A and recovery is performed after 70 ms. At this time, when the phase angle of the internal voltage of the generators G1 to G10 included in the model system is measured for comparison, the generator G1 connected to the 11 bus is disconnected after 0.9 seconds as shown in FIG. You can see that it is adjusted. Although not shown, other generators did not step out.

The power system step-out prediction apparatus 10 arranged on the 11 bus measures the real number instantaneous value of the voltage of the 11 bus and the current of the 11 connecting line, and then the voltage of the 11 bus and the 21 bus as in the first embodiment. The phase difference between the buses, the first-order differential between the buses, and the second-order differential between the buses are obtained. The results are shown in FIGS.
Moreover, the power system step-out prediction apparatus 10 measures the real number instantaneous value of the voltage of the 11 bus and the current of the 11 connecting line, and uses the real number instantaneous value of one cycle of the reference wave to calculate the voltage effective value and the current effective value. In the same manner as in the first embodiment, the effective power flowing from the 11 connecting lines to the 11 buses is calculated, and the first derivative of the effective power is obtained. The result is shown in FIG.
Moreover, the power system step-out prediction apparatus 10 uses the voltage effective value, the voltage of the 11 buses, and the phase difference between the voltage currents of the current flowing from the 11 connecting lines to the 11 buses to calculate the voltage effective value and the phase difference between the voltage currents. Find the center voltage, which is the product of the cosine. The result is shown in FIG.
Whether or not the equations (26) to (29) are satisfied with respect to the bus phase phase difference first-order differential, bus-phase phase difference second-order differentiation, active power first-order differentiation, and center voltage thus obtained is shown in FIG. Judge as shown. When the four conditions are satisfied, the generator G1 predicts that step-out will occur if it operates as it is, and disconnects the 11 buses from the system.

  According to this simulation, the out-of-step prediction for the generator G1 can be performed in 0.53 seconds, which is as early as 0.5 seconds compared to 1.03 seconds according to the method of detecting the out-of-step of Patent Document 1. Can predict step-out.

Embodiment 3 FIG.
When the generator according to Embodiment 1 loses synchronization with the power system and the phase angle of the internal voltage diverges monotonously is taken as an example, all four conditions for predicting step-out are satisfied simultaneously It is predicted that the generator will step out.
However, some generators have a negative braking torque coefficient and diverge after the internal voltage phase angle oscillates multiple times. In the case of a bus connected to such a generator, when all of the four conditions for predicting the step-out are satisfied a predetermined number of times at the same time, it is predicted that the step-out will occur if the generator continues operating as it is. .

  Such a power system step-out prediction device predicts that step-out will occur when all four conditions for predicting step-out are satisfied a predetermined number of times at the same time. Step-out can be accurately predicted even for generators that diverge after vibration.

Embodiment 4 FIG.
FIG. 15 is a configuration diagram of a power system provided with a power system step-out prediction apparatus according to Embodiment 4 of the present invention. FIG. 16 is a functional block diagram of the power system step-out prediction apparatus according to the fourth embodiment.
As shown in FIG. 15, in the power system according to the fourth embodiment, two generators 3a and 3b are connected to the A system, and the circuit breaker 9b is connected between the generators 3a and 3b and the bus 4a. 9c is different from the power system according to the first embodiment in that the other is the same. When the two generators 3a and 3b are linked in this way, the stability of the power system can be controlled by cutting off the circuit breakers 9b and 9c. The circuit breakers 9b and 9c will be described below as an example of a device for controlling the stability of the power system. However, the stability of the power system such as a braking resistor, a high-speed valve control device, an ultra-high speed excitation device, and a series capacitor will be described. Anything that can be controlled can be applied to the present invention.

Moreover, as shown in FIG. 16, the power system step-out prediction apparatus 10B according to the fourth embodiment has a stability control means 30 added to the power system step-out prediction apparatus 10 according to the first embodiment. Since the other parts are the same, the same reference numerals are attached to the same parts and the description thereof is omitted.
The stability control means 30 according to the fourth embodiment, when the out-of-step predicting means 22 predicts that the generators 3a and 3b are regarded as one generator and will be out of step, one of the generators 3b is connected to the bus 4a. By disconnecting, the unstable equilibrium point is shifted to a larger phase side so that the phase angle of the internal voltage of the generator 3a is closer to the phase side than the unstable equilibrium point. By disconnecting one generator 3b in this way, it is possible to prevent the other generator 3a from being stepped out.

  Further, the power system out-of-step prediction apparatus 10B according to the fourth embodiment simultaneously satisfies all of the four conditions for predicting out-of-step again after controlling the stability of the power system by the stability control means 30. By disconnecting the circuit breaker 9a, the A system 1a is disconnected from the B system 1b.

  Such a power system out-of-step prediction device 10B instructs the device that controls the stability of the power system when it is predicted to be out of step so that a measure for improving the stability is applied to the power system, thus avoiding system separation. be able to.

  Moreover, since the system separation is commanded when it is predicted that a step-out will occur even after the measures for improving the stability are once applied to the power system, the system separation can be performed before the generator steps out.

It is a P-delta curve figure showing relation between phase angle delta _G of an internal voltage of an electric generator connected to one machine infinite bus system, and electric output Pe. It is a figure which shows a mode that two electric power systems are connected by the connection line. It is a figure showing a rotation vector on a complex number plane. 2 is a power system provided with the power system step-out prediction apparatus according to the first embodiment. 1 is a functional block diagram of a power system step-out prediction apparatus according to Embodiment 1. FIG. 3 is a flowchart illustrating a procedure for predicting a step-out by the power system step-out prediction apparatus according to the first embodiment. This is an EAST10 model system in which a power system step-out prediction apparatus according to Embodiment 2 of the present invention is provided and simulation of step-out prediction is performed. It is a figure which shows transition of the phase angle of the internal voltage of the generator G1 of FIG. It is a figure which shows transition of the phase difference between 11 bus lines of FIG. 7, and 21 bus lines. It is a figure which shows transition of the 1st-order differentiation of the phase difference of FIG. It is a figure which shows transition of the 2nd-order differentiation of the phase difference of FIG. It is a figure which shows transition of the 1st-order differentiation of the active electric power which flows into 11 buses from 11 connection lines of FIG. It is a figure which shows transition of a center voltage. It is a figure which shows a mode that four conditions which predict a step-out are satisfied. 5 is a power system provided with a power system step-out prediction apparatus according to a fourth embodiment. FIG. 10 is a functional block diagram of a power system step-out prediction apparatus according to a fourth embodiment.

Explanation of symbols

  1a, 1b Power system, 2 Connection line, 3, 3a, 3b Generator, 4a, 4b Bus line, 7 Voltmeter, 8 Current transformer for instrument, 9, 9a, 9b, 9c Breaker, 10, 10b Power system disconnection Key prediction device, 11 voltage / current measurement means, 12 A / D conversion means, 13 storage means, 14 voltage / current effective value calculation means, 15 active power / reactive power calculation means, 16 voltage-current phase difference calculation means, 17 Phase difference calculating means between buses, 18 Phase difference first order differential calculating means between buses, 19 Phase difference second order differential calculating means between buses, 20 Active power first order derivative calculating means, 21 Center voltage calculating means, 22 Step out prediction means, 23 System separation command means, 24 Circuit breaker operation command receiving means, 25 Circuit breaker operation execution means, 30 Stability control means.

Claims (5)

A power system step-out prediction device that includes at least one generator and a bus and predicts step-out of the generator in a plurality of power systems that are interconnected by connecting the bus through a connection line. There,
The first and second derivatives relating to the phase difference between both ends of the connecting line exceed zero, and the first derivative relating to the active power flowing from the connecting line to the one end is less than zero, and from the connecting line to the one end When all of the four conditions that the center voltage in phase with the current flowing in the current is smaller than a predetermined threshold value are satisfied at the same time, the generator connected to the one end continues to operate. A power step-out prediction apparatus characterized by predicting that a step-out center appears in the connecting line while predicting that the step will be reached. Voltage / current measuring means for measuring the voltage of the bus and the current flowing from the connecting line to the bus in a cycle of N (N is a positive integer) of one cycle of the reference wave;
At each timing when the voltage and the current are measured, a voltage effective value for obtaining a voltage effective value and a current effective value at the own timing from the voltage and the current measured at the past N timings including the own timing. -Current effective value calculation means,
At each timing at which the voltage and the current are measured, from the measured voltage and current at the past N timings including its own timing.

_{(However, v Are, v Bre, v} Cre each voltage measured in the past of N timing including their _{timing, i Are,} i _Bre, i past the N timings _Cre, including their timing , Each measured current in P, P is the active power calculated at its own timing)
To calculate the effective power flowing from the connection line to the bus at each timing according to

(Where V _A , V _B , and V _C are the calculated voltage effective values for each phase at their own timing, I _A , I _B , and I _C are the calculated current effective values for each phase at their own timing, Q Is the reactive power calculated at its own timing)
Active power / reactive power calculating means for calculating reactive power flowing from the connection line to the bus at each timing according to
At each timing when the voltage and the current are measured, the reactive power and the active power are used.

(Where θ is the phase difference between the voltage of the bus at its own timing and the current flowing from the connecting line to the bus)
Voltage-current phase difference calculating means for calculating the phase difference between the voltage of the bus at each timing and the current flowing from the connecting line to the bus according to
The power system step-out prediction apparatus according to claim 1, comprising: At each timing of measuring the voltage and current,

(However, V is the effective voltage value calculated at its own timing, I is the effective current value calculated at its own timing, X is the reactance of the connection line, and δ is the calculated effective value of the connection line at its own timing. Phase difference between both ends)
3. The power system step-out prediction apparatus according to claim 2, further comprising: an inter-bus phase difference calculation unit that calculates a phase difference between both ends of the connection line at each timing according to the above. 4. The apparatus according to any one of claims 1 to 3 , wherein when it is predicted that a step-out will occur, a device for controlling the stability of the power system is instructed to take a measure for improving the stability of the power system. Electric power system step-out prediction device to be described. 5. The power system step-out according to claim 4 , wherein the circuit breaker is instructed to shut off the connection line when it is predicted that the step-out will occur again after taking measures for improving the stability of the power system. Prediction device.

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