JPH07241035A - Method for stabilizing single separated system - Google Patents

Abstract

PURPOSE:To calculate a control amount for sustaining the frequency and voltage appropriately at the time of single separation even in case of an intricate system configuration or a feed power flow by determining the necessity of control for every case of single separation being predicted previously. CONSTITUTION:A unit 4 for stabilizing a single separated system prepares a data for calculating power flow based on bus voltages, load amounts, etc., received on control input cables 11a-33a. A finish voltage of each bus and a system frequency are then calculated in case of uncontrollable after single separation and then a decision is made whether a control is required or not. If a control is required, the load of power flow for a system interconnection line or the power supply interrupting amount thereof is calculated followed by calculations of finish frequency and voltage for the case where only a generator 31 or loads b1-b3 is interrupted. A decision is then made whether that control is sufficient and a control pattern for only the effective power is determined if it is sufficient otherwise a control pattern for simultaneous control of effective power and phase modification is determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single isolated system stabilizing method for calculating a control amount for maintaining system frequency, voltage, etc. after system isolation based on information such as system configuration and operation status. It is a thing.

[0002]

2. Description of the Related Art FIG. 5 shows, for example, JP-A-60-255018.
It is a block diagram which shows the conventional system stabilization apparatus shown by the publication, 1 is a substation which belongs to the main system M side, 2
Is a substation that is the center of the separation system L, 3 is a power plant belonging to the separation system L, and 31 is a generator, which are connected by transmission lines 5 and 6 as interconnection lines, respectively.

Reference numeral 4 denotes a separate system stabilizing circuit, a1 to a.
3 is a phase adjusting equipment, b1 to b3 are loads, 22 is a current transformer (CT) as a sensor, 25 is a load current transformer as a sensor, 26 is a voltage sensor, 11 and 21 are at both ends of the transmission line 5. System isolation circuit breakers, 23 and 24 are control system isolation circuit breakers, 23 to 24a and 25a are control input cables, and 47 is an output control cable.

Further, the basic principle of the system stabilizing device is as shown in FIGS. 6 to 8. Here, first, the active power control amount of the local system L which is a system separated from the main system M, that is, The method of determining the load amount to be cut off will be described. After being separated from the main system M, the unbalanced amount of active power in the local system L is the total load active power output amount minus the generator active power amount.

If these line losses are ignored, these are almost equal to the amount of active power supplied from the main system M before the separation. Therefore, the load amount to be interrupted is determined to be equal to the active power amount measured at the separation point.

On the other hand, since the load has not only active power but also reactive power, if control focusing only on the active power balance is performed, the reactive power balance will be disturbed and the load of the cable like the power system in urban areas will be lost. When the charge capacity is large, an overvoltage phenomenon may occur.

It is desirable to predict the overvoltage phenomenon that would occur when the load is cut off, and to execute the reactive power control necessary for preventing it at the same time when the load is cut off. 5 to 8 show the basic principle for determining the reactive power control amount.
I will explain according to. Each state quantity described below is expressed as a unit.

FIG. 6 and FIG. 7 respectively show a power system diagram and its equivalent circuit diagram drawn in a simplified manner for explaining the basic principle. A case will be described as an example in which a local power system L including one power generation station GE having a generator g as shown in FIG. 6 and two substations A and B is separated from the main power system M.

In FIG. 6, a1 to a3 are parallel reactors as phase adjusting equipment, b1 to b6 are loads, and c1 to c11.
Is a circuit breaker, and e1 to e3 are power transmission lines. Generally, when conducting an analysis on a power system of the scale shown in the figure,
Even if the simplified equivalent circuit model shown in FIG. 7 is used, the error is not so large. Therefore, description will be made using the equivalent circuit of FIG.

In FIG. 7, the symbols G, B _C and X _L are
Each has the following physical meaning.

G: A load in the local system L is expressed as a constant impedance characteristic, and the total active power is expressed as a ground conductance.

B _C : The load in the local system L is defined as a constant impedance characteristic, and the total of the reactive power, the ground capacitance of the overhead line, the cable, and other parallel reactors are expressed as a ground susceptance.

X _L : Including the generator transient reactance,
A parallel combination of line (or cable) reactances up to the bus of substation A selected as the representative node.

Generally, as the representative node, a substation bus having a relatively large bank capacity, which is as far away from the power plant that is likely to be affected by the ferrant effect as possible, may be selected.
Here, substation A is the representative node.

In the system shown by the equivalent circuit of FIG. 7, the transient reactance back voltage V'g of the generator _g and the load point voltage V _L
The relationship of V _L = [{1 / (G + jB _C )} / {1 /
_{(G + jB C) + jX} L}] V 'g = {1 / (1-B C ·
X _L + jG · X _L )} V ′ _g .

[0016] The size of the transient reactance behind voltage V _'g of the generator g, since hardly changes even when disturbances such as the system partition and load shedding, to evaluate the overvoltage of the absolute value at the load point Choose as a standard. That is, k = | V ' _L
The quantity | / | V ′ _g | is defined, and this k is hereinafter referred to as an overvoltage coefficient.

As a result, the overvoltage coefficient from the load point voltage V _L is k = | 1 / (1-B _C · X _L + jG · X _L ).
│ = 1 / {(1-BC _{C XL} ) ² + (G _XL ) ² }
Given by ^1/2 . Also, if this equation is transformed, {B <sub>C
- (1 / X L)}</sub> 2 + G 2 = 1 / k 2 · X L 2 is obtained.

This formula is based on the coordinate G-B _C plane with the horizontal conductance G as the horizontal axis and the vertical susceptance B _C as the vertical axis, and the center (0,1 / X) of the region where the overvoltage coefficient k is constant.
_L), indicating that represented by a circle with a radius 1 / k · X _L. And when k = 1, this circle means passing through the origin. FIG. 8 shows a state in which the above-mentioned modified formulas are displayed as coordinates on the G-B _C plane.

On the other hand, assuming that the load has a constant impedance characteristic, the locus of load shedding is represented by a straight line on the G-B _C plane. Therefore, it is possible to predict the overvoltage phenomenon and determine the reactive power control amount necessary to suppress the overvoltage phenomenon based on the locus of the load cutoff and the overvoltage region defined by the modified expression.

That is, when the locus of load shedding falls within the region of k> 1, it is predicted that a bouncing voltage of 1 p · u or more will occur, and the reactive power of the reactive power is adjusted so that the locus falls within the region of k ≦ 1. Take control. A specific method for determining the reactive power control amount will be described below.

In FIG. 8, it is assumed that the locus of load shedding becomes A → B. Here, the coordinates of point A (G ₀ , B _C0 )
Indicates the load state of the local system during steady reverse rotation (including parallel reactors, cable ground capacitance, etc.)
Represents

Now, assuming that all loads are inductive loads, the average power factor angle determined by the load power factor is −Θ _L , and the active power control amount, that is, the active power imbalance amount in the local grid is P _C. Then, the coordinates of the point B are (G ₀ −P _C , B
_C0 + P _C tan Θ _L ). On the other hand, in order to suppress the bouncing voltage generated by load shedding within 1 p · u, a straight line on the B _C axis at the point G = G ₀ −P _C and k = k _C
It is necessary to move the locus to a point C where the circle at intersects.

Here, k _C is an overvoltage coefficient that gives a control target, and since the normal reference generator transient reactance back voltage is greater than 1 p · u, the value of k _C is
A value of 0.8 to 0.9, which is slightly smaller than 1, will be selected. From the above modified formula, the coordinates of the point C are (G ₀
−P _C , − {1 / (k _C · _XL ) ² − (G ₀ −P _C )
² } ^1/2 + (1 / _XL )).

Therefore, the locus A → B only for load shedding is A →
The reactive power control amount Q _C required to move to C is expressed as B → C in the figure, and Q _C = B _C0 + P _C tan
Θ _L + {1 / (k _C · _XL ) ² − (G ₀ −P _C ) ² } ^1/2
It can be determined from − (1 / X _C ).

From this, it is sufficient to cut off the capacitor or turn on the shear reactor and cut off the cable until the total sum of the control amounts of the reactive power reaches Q _C. Therefore, the locus A → C in FIG. 8 is the locus of the sum of the load shedding and the reactive power control.

Next, the operation of the system stabilizing device shown in FIG. 5 will be described. The isolated system stabilizing circuit 4 models the controlled object and the system in the system of one machine and one node by using the information of the current and the voltage input through the control input cables 22a to 26a in advance, and described FIG. The controlled variable is calculated by the method, and the controlled object is selected based on the calculated controlled variable. Then, when the separated system stabilizing circuit 4 receives through the control input cables 11a and 21a that the circuit breakers 11 and 21 open and shifts to the separated system L, the separated system stabilizing circuit 4 receives the output control cable 47, Stabilize the separation system L by outputting a trip command to any of the circuit breakers 23 and 24 on the side to be interrupted that have been selected in advance among the loads b1 to b3 and the parallel reactors a1 to a3 that are phase adjusting equipment. .

[0027]

Since the conventional system stabilizing device is constructed as described above, the control amount must be calculated after the system is contracted into a one-machine one-node system.
If you try to apply it to a complicated system, not only can you not accurately calculate the control amount, but you can not cope with the feed flow,
In addition, since it is reduced to a 1-machine 1-node system, there is a problem that it is difficult to distribute the control amount when there are a plurality of buses.

The invention of claim 1 has been made to solve the above problems, and has a complicated system configuration.
An object of the present invention is to provide a method for stabilizing a single isolated system that can calculate a control amount that can appropriately maintain the frequency and voltage during single isolation even when it is difficult to reduce the number to one node per node, or even during a power flow.

It is an object of the invention of claim 2 to obtain a single isolated system stabilizing method capable of highly accurately performing control execution determination by determining the necessity of control by using a power flow calculation capable of considering frequency fluctuations. To do.

According to the third aspect of the present invention, by calculating the control amount by using the power flow calculation capable of considering the frequency fluctuation, a method for stabilizing the isolated system which can maintain the frequency and the voltage at the values before the independent separation is obtained. The purpose is to

It is an object of the invention of claim 4 to obtain a method for stabilizing an isolated system which can maintain a frequency and a voltage at arbitrary values by calculating a control amount using a power flow calculation.

[0032]

A method for stabilizing a single isolated system according to the invention of claim 1 determines the necessity of control by a control execution determination method using a power flow calculation for each single isolated case assumed in advance. The determination is made, and if necessary, the control amount is calculated by the stabilized control amount calculation method using the power flow calculation to stabilize the separated system.

In the method for stabilizing a single isolated system according to the invention of claim 2, in the control execution judging method for judging the necessity of stabilization control, the finishing frequency and voltage when the control is not executed by the power flow calculation or when the control is executed. Is calculated and the necessity of control is determined.

According to a third independent system stabilizing method of the present invention, in the stabilizing control amount calculation method for calculating the control amount necessary for maintaining the frequency and voltage in the separated system, the frequency and voltage are compared with those before the system separation. The amount of control required to maintain the same value is calculated by power flow calculation.

According to a fourth aspect of the present invention, there is provided a single isolated system stabilizing method, wherein a stabilizing control calculation method for calculating a control amount necessary for maintaining a frequency and a voltage in the separated system has an arbitrary frequency and voltage. The required control amount is calculated by power flow calculation.

[0036]

According to the method for stabilizing an isolated system according to the first aspect of the invention, the necessity of control is judged by the control execution judgment method for each isolated case defined in advance. In order to stabilize the separated system, the control amount is calculated using the stabilized control amount calculation method regardless of the complexity of the system configuration.

In the method for stabilizing an isolated system according to the second aspect of the present invention, the finished frequency and voltage are calculated using power flow calculation without control or when the generator and load are cut off, and the calculated results are constant. Whether or not control is necessary and whether control is sufficient or inadequate is determined by whether or not it is within the allowable range.

In the method for stabilizing an isolated system according to the third aspect of the present invention, the amount of interruption of the generator and the load is made equal to the power flow value of the transmission line even after the independent separation, and the bus of the substation having the phase-adjustment facility is Normally, when calculating the power flow, after changing the PQ designated bus to the PV designated bus, the power flow calculation that can consider the fluctuation of the system frequency using the formula that considers the frequency characteristics and voltage characteristics of the load and generator output is performed. Based on the result, the phase control amount is calculated for each of the substations, and the frequency and voltage are maintained at the values before the independent separation.

In the method for stabilizing an isolated system according to the invention of claim 4, the amount of interruption of the generator and the load is determined, the PQ designated busbar is changed to the PV designated busbar, and the changed one is set as the slack busbar, and the target is set in advance. The output of the load and the generator is set in consideration of the deviation between the frequency to be set and the frequency in advance, and the power flow is calculated by fixing the output to the target frequency, and the frequency and voltage are maintained at arbitrary values.

[0040]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a substation on the side of the main system M, 2 is a substation on the side of the isolated system L as a local system, 11, and 2.
1 is a system isolation circuit breaker put in a transmission line 5 as an interconnection line,
Reference numeral 22 is a current transformer as a sensor for measuring the interconnection power flow, 3 is a power plant (bus), 31 is a generator, 32 is a current transformer as a sensor for measuring generator output and the like, 33
Is the breaker of the generator.

Reference numeral 23 denotes phase adjusting equipment a1 to a of the substation 2.
3 is a circuit breaker, 24 is a circuit breaker for loads b1 to b3,
Reference numeral 25 is a load current transformer as a sensor for taking in the tidal current of the loads b1 to b3, 26A is a current sensor, and 11a, 2a.
1a, 22a, 23-24a, 25a, 26a, 32
a and 33a are control input cables as a transmission line for taking in various system information to the single isolated system stabilizing circuit 4,
47 is an output control cable.

Next, the operation will be described. When the isolated system stabilizing device 4 receives the information that the system L has been systemically separated from the main system M through the control input cables 11a and 22a by performing the calculation as shown in FIG. The independent isolation system stabilizing device 4 through the output control cable 47 uses the control amount determined by the calculation routine of FIG.
1 to a3, loads b1 to b3, and outputs a trip command to a preselected object.

That is, in the calculation routine shown in FIG. 2, first, the power flow is calculated from the bus voltage, the load amount, the generator output, the interconnection line power flow, the phase input amount, etc. input from the control input cables 11a to 33a. Data for use is prepared (step ST1). Next, by the control execution determination method used for this power flow calculation and determining the necessity of stabilizing control, the finished voltage and the system frequency for each bus in the case of no control after single isolation are calculated (step ST2), Then, the necessity of control is determined from the fluctuation range of the frequency and voltage (step ST3), and if control is not necessary, the control pattern is determined to be uncontrolled (step ST8).

On the other hand, if control is required, the load or power cutoff amount for the power flow of the interconnection line is calculated (step ST4),
A finishing frequency and a voltage when only the generator 31 or any of the loads b1 to b3 are cut off by the control execution determination method are calculated (step ST5). Then, it is again determined whether or not this control is sufficient (step ST6), and if it is sufficient, the control pattern is determined to control only active power (step ST9). If it is still not enough, the phase control amount is calculated by the stabilization control calculation method that calculates the control amount necessary for maintaining the frequency and voltage in the isolated system L (step ST7), and the control pattern is set to the active power and the same phase. Time control is determined (step ST10).

In this embodiment, there is no control and loads b1 to b
2. Regarding the control of the generator 31 and the simultaneous phase adjustment control, the control execution determination is performed in order, and the stabilization control amount calculation method is used at the end, but it is possible to proceed from step ST1 to step ST7. , Step ST1 to step ST4, step ST5, step ST6, step ST7 may be performed.

Example 2. Next, the control execution determination method using the power flow calculation in the arithmetic routine of the above embodiment will be described. First, uncontrolled or generator 31, loads b1 to b
Obtain the finished frequency and voltage when only the interruption in 3 is performed. In this case, the power flow calculation that can consider the fluctuation of the system frequency is used, and basically the data used in step ST1 of FIG.
The power flow is calculated assuming that there is no substation 1 and transmission line 5 on the main system side in FIG. The conditions for calculating the power flow are to specify PQ for the bus of a substation with a load, specify PV for the bus of a substation with a generator, and use loads P and Q as expressions that take frequency characteristics and voltage characteristics into consideration. The machine output uses a formula that considers the frequency characteristics.

Further, in the calculation in the case where only the generator 31 and the loads b1 to b3 are cut off, the generator 31, which is cut off,
The calculation is performed excluding the loads b1 to b3. Whether or not control is necessary or sufficient is determined by whether or not the system frequency calculated by performing this power flow calculation and the voltage value of the substation 2 in FIG. 1 are within a certain range.

Example 3. Next, the stabilization control amount calculation method in the calculation routine of the first embodiment will be described with reference to the flowchart of FIG. First, in order to maintain the system frequency and voltage at the same values as before the system isolation even after the independent isolation, the cutoff amounts of the generator 31 and the loads b1 to b3 are set to be equal to the power flow value of the transmission line 5 ( Step ST
11).

Next, the substation 2 having the phase adjusting equipments a1 to a3
Is changed from the PQ designated bus to the PV designated bus (step ST12), and the V (voltage) designated at this time designates the value before the grid separation. Next, a power flow calculation that can consider the system frequency is performed (step ST13), and subsequently, based on this calculation result, for each substation having the phase-adjustment equipment a1 to a3,
The compensator control amount calculated from the equation Q _C = Q-Q _L (step ST14). Here, Q _C is compensator control amount, Q is the result of power flow calculation, reactive energy necessary to maintain the voltage to be calculated for each generatrix, Q _L is a reactive power load after load rejection is there.

Example 4. Next, another stabilization control amount calculation method in the calculation routine of the first embodiment will be described.
In this method, the stabilization control amount calculation method of the third embodiment controls the frequency and voltage before the independent separation as targets, whereas it controls arbitrary frequencies and voltages to target values. This control procedure is shown in the flowchart of FIG.

First, suppose that the generator 31 and the loads b1 to b3.
The amount of interruption of is determined and the total value is P _C (step ST
21). Here, the load shedding is positive and the PQ designated bus bar is P
Change to V designated busbar (step ST22). One of the buses thus changed to the PV designated bus is set as a slack bus (step ST23), and then the loads b1 to b1 are taken into consideration in consideration of the deviation between the target frequency and the previous frequency.
b3 and the output of the generator 31 are set (step ST2
4) The power flow is calculated by fixing the target frequency (step ST25).

As a result, when the power generation amount of the slack bus is P _G , P ′ _C represented by P ′ _C = P _C −P _G is the final sum of the generator 31 and the load shedding amount. The phase control amount is the same as in the third embodiment, the substation 2 having the phase adjusting equipments a1 to a3.
Each of the bus, and can be calculated by the equation Q _C = Q-Q _L (step ST26).

[0053]

As described above, according to the first aspect of the present invention, the necessity of control is determined by the control execution determination method using the power flow calculation for each presumed single separation case,
When necessary, the control amount is calculated by the stabilized control amount calculation method using the power flow calculation, so even if the system configuration is complicated or in the case of sending power flow, the conventional method cannot handle It is possible to calculate the controlled variable with high accuracy,
This has the effect of obtaining a stabilized control amount for each bus of the isolated system.

According to the second aspect of the present invention, in the control execution judging method for judging the necessity of the stabilization control, the finishing frequency and the voltage when the control is not executed by the power flow calculation or when the control is executed are calculated, and the control Since it is determined whether or not it is necessary, there is an effect that it is possible to obtain a highly accurate control implementation determination.

According to the third aspect of the present invention, in the stabilized control amount calculation method for calculating the control amount necessary for maintaining the frequency and voltage in the isolated system, the frequency and voltage are maintained at the same values as before the system isolation. Since the control amount required for the above is calculated based on the power flow calculation, there is an effect that the frequency and voltage can be maintained at the values before the single separation with high accuracy.

According to the fourth aspect of the present invention, in the stabilization control calculation method for calculating the control amount necessary for maintaining the frequency and voltage in the separated system, the control amount necessary for setting the arbitrary frequency and voltage is the flow rate. I decided to calculate based on the calculation,
There is an effect that a system frequency of the separated system after the system separation and a voltage for each bus of each substation can be maintained at an arbitrary value with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a system stabilizing device for implementing a method for stabilizing an isolated system according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a method for stabilizing an isolated system according to an embodiment of the inventions of claims 1 and 2.

FIG. 3 is a flow chart showing a method for stabilizing a single isolated system according to an embodiment of the invention of claim 3;

FIG. 4 is a flow chart showing a method for stabilizing a single axis separated system according to an embodiment of the invention of claim 4;

FIG. 5 is a configuration diagram showing a conventional system stabilizing device by an admittance plane system.

FIG. 6 is a system configuration diagram showing an example of a power system to which the isolated system stabilizing device is applied.

FIG. 7 is a circuit diagram showing an equivalent circuit applied to analysis of the power system in FIG.

8 is a principle operation explanatory diagram showing a state of analysis of the power system in FIG. 5. FIG.

[Explanation of symbols]

 M Main system L Separation system 31 Generator b1-b3 Load

Claims (4)

[Claims] 1. A data preparation step of preparing data for power flow calculation based on bus voltage, load amount, generator output, interconnection line power flow, and amount of phase-modulating equipment input, and based on the above data,
A first calculation step for calculating the uncontrolled control of the finishing frequency and voltage after the separation of the separation system from the main system by the control execution determination method used for the power flow calculation, and the control range from the fluctuation range of the calculated finishing frequency and voltage. First to judge
Necessity determination step, a non-control determination step of determining a control pattern as uncontrolled when control is unnecessary according to the determination, and a control line determination when the above determination determines that the interconnection line power flow component Load, or load that calculates the amount of power interruption
A power cutoff amount calculation step, a second calculation step of calculating a finishing frequency and a voltage when only the generator and load of the interconnection line power flow are cut off by the control execution determination method, and the calculated finishing frequency A second necessity determination step of determining necessity of control from each fluctuation range of the voltage;
If the control is not required in the necessity determination step, the active power control determination step that determines the control pattern to control only active power, and if the control is required in the second necessity determination step Is a phase control amount calculating step for calculating the phase control amount by the stabilized control amount calculation method, and a control pattern based on the calculated phase control amount for active power, active power for determining simultaneous control of phase, A method for stabilizing a single isolated system, which comprises a phase control determining step. 2. A control execution determination method for determining the necessity of stabilizing control, calculating a finishing frequency and a voltage when control is not performed or when it is performed by power flow calculation,
The method for stabilizing an isolated system according to claim 1, wherein the necessity of control is determined. 3. In a stabilized control amount calculation method for calculating a control amount required for maintaining frequency and voltage in a separated system, a control amount necessary for maintaining the frequency and voltage at the same values as before the system separation flows. The method for stabilizing a single isolated system according to claim 1, which is calculated based on calculation. 4. A stabilizing control calculation method for calculating a control amount necessary for maintaining frequency and voltage in a separated system, wherein a control amount necessary for setting an arbitrary frequency and voltage is calculated based on power flow calculation. The method for stabilizing an isolated system as described in 1.