JPS593101B2 - Synchronous connection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronous connection method, and more particularly to a synchronous connection method suitable for synchronous connection between a power transmission line and an electric station bus line that are charged from one end and are in a standby state, or for a low-speed reclosing method.

15 As is well known, in order to connect two electric stations, it is essential that both electric stations be in a synchronized state.

Therefore, when turning on a power transmission line or disconnector connecting two electric stations, for example, it is necessary to check whether there is a power transmission route connecting both electric stations in addition to the route to be connected. Determine the synchronization and then insert the finger into the disconnector◆
Apply voltage or turn on the disconnector at one end of the transmission line to be connected in advance, derive the voltage at the other end of the transmission line and the power station bus line, and create a bead voltage by matching both voltages. 5
From this, the phase difference between the two voltages is detected, and it is confirmed that the phase difference is below a predetermined value and is decreasing, and it is determined that both electrical stations are in a synchronized state, and the remaining circuit breakers are In some cases, the use of 30 In this case, even if both electric stations are in a synchronous state, if the phase difference is excessive, a large disturbance will be caused by connecting the open power transmission line between the two electric stations.

Therefore, regardless of the case where connection 35 is made only on the condition that there is another power transmission route to connect,
When controlling the switching on of a shield breaker by focusing on the phase difference between the two electrical stations, the connection is locked if the phase difference is excessive. Of course, even when connecting due to the existence of another power transmission route, it is preferable to control the closing of the circuit breaker by paying attention to the phase difference between the two electric stations in addition to this condition. However, if we assume that the open transmission lines of both electric stations are locked under the condition that the phase difference is too large even in a synchronized state, then if the system reaches a stable state with an excessive phase difference between the two electric stations, then The open power transmission line between the two electric stations will remain disconnected, which is not favorable for system operation.

FIGS. 1 and 2 show examples in which the phase difference becomes excessive even though electric stations at both ends of the power transmission line to be connected are in a synchronous state. In FIG. 1a, electric stations A and B are connected by a power transmission line L2 and are in a synchronous state. On the other hand, the power transmission line L1 and disconnector CB are open and in a standby state. Electrical stations A and B under such system operating conditions
If we pay attention to the phase difference between the voltages Vl and V2, we can see that
become that way. Here, b is the tidal current of power transmission line L2 at electric station A.
c is the time when moving from to B, and c is the opposite. Under normal stable operation conditions, the larger the tidal current, the larger the phase difference θ becomes. Figure 2a
In , electric stations A and B are connected via electric station C by power transmission lines L2 and L3, and are in a synchronous state.

On the other hand, the power transmission line L1 and disconnector CB are open and in a standby state. Electrical stations A, B and C under such system operating conditions
Focusing on the phase difference between voltages 1, 2, and V3, a combination such as B, c, or d is obtained. Here, b is a case where the tidal current of the power transmission line L2 is directed from electric station A to C, and in L3 is directed from C to B, and c is the case where it is vice versa. d is a case where the direction is from C to A in L2, and from C to B in L3. in this case,
The phase differences θ and θ2 between the voltages at each electric station increase as the tidal current increases.
The phase difference between voltages 1 and V2 is θ+θ' in the case of B and c.
, d, the angle is θ-θ5, so these are naturally affected by the tidal current. In this way, if operation is continued with a large phase difference in a state where the tidal current is large,
There will be no chance to use the breaker CB.

This is not a good thing from the standpoint of system operation, and if possible, a cylindrical disconnector CB should be installed as soon as possible so that the power transmission line L1 between electric stations A and B can also be used.

For this purpose, for example, corresponding to the case of Fig. 1b, the third
As shown in Figure a, the power generation capacity at electric station B is strengthened,
Alternatively, it is effective to reduce the tidal current on the power transmission line L2 by transferring the load of electric station B to the system of another electric station.

In other words, a small tidal flow in L2 means that the phase difference between Vl, V2 and θ becomes smaller like V1', V2' and α, so it is possible to insert the shingle breaker CB. . In addition, for example, as shown in Figure 3 b, corresponding to the case in Figure 2 b, the power generation capacity at electric station B may be strengthened, or the load of electric station B may be transferred to another system. , the tidal current on the power transmission line L3 is reversed, and the phase difference is changed from θ+θ7 to β
It is effective to make it so that In this way, even when the phase difference between the voltages at both ends of the power transmission line to be connected is large, if the relationship between phase lead and lag is known, the phase difference can be corrected by controlling the power generation or changing the load distribution. Since it can be made small, it is possible to prevent the use of the power transmission line to be connected to be inhibited simply due to a large phase difference.

The present invention focuses on this point, and detects the phase difference by using the phase of one voltage as a reference to detect the phase of the other voltage, rather than simply detecting the phase difference using the bead voltage. By doing so, it is possible to derive the relative phase lead/lag relationship between both voltages, and it provides a synchronous connection method that allows synchronous connection as long as the grid is in a synchronous state, no matter what the situation is. be.

FIG. 4 is a block diagram for conceptually explaining the object to which the present invention is applied.

In the figure, B is an electric station, BB is the bus line of the electric station, L1 is a power transmission line to be connected to the bus line BB, and CB is a bridge connecting the two. PTB and PTL are voltage transformers for deriving voltages Vl and V2 of the bus line BBl power transmission line L1, respectively. A-D is an analog-to-digital converter, which outputs a digital signal corresponding to the instantaneous value of the voltage at a given time point of the sampling signal. The CPU is a processing unit with digital calculation and logic decision functions. P/O is an input/output device that connects A-D, CB, and CPU. In the example in the figure, A-D is PI/D according to the CPU's finger ◆.
Analog-to-digital conversion is performed using a sampling signal given from 0, and this digital signal is
is assumed to be introduced into the CPU via the . Of course, as is well known, the sampling signals for A to D may be provided by independent timing circuits by coordinating with the CPU, for example by using an interrupt method. When the CPU determines that the input command should be given to the CB based on the digital signal introduced to the CPU, this is transmitted to the CB via the PI/O, and the input is executed by a predetermined circuit. That will happen. As is clear from FIG. 4, according to the present invention, the beat voltage of both the voltages of the bus line and the power transmission line is not required, and the voltage phase of the other is determined based on one voltage phase independently derived as a digital signal. Since lead/lag and phase differences can be obtained, the idea of the present invention can be immediately put into practical use by introducing the idea of the present invention into a computer installed for other control purposes in an electric station, and a special control circuit for synchronous connection is not required. It will also be possible to do this.

Hereinafter, a description will be given of how to determine from the voltage converted into a digital signal whether or not the conditions for synchronous connection are satisfied.

FIG. 5 is a diagram illustrating an example of the zero point of the sinusoidal AC voltage v(t), that is, the point at which the voltage changes from negative to positive or from positive to negative, and the concept of deriving the voltage phase and phase difference based on this. be.

As shown in Figure 5a, the sinusoidal AC voltage v(t) is
When sampling at t, the previous sampling time Tn-1 and the current sampling time T. There is a zero point of v(t) (the figure shows when it changes from negative to positive; hereinafter, in the present invention, only this zero point will be used and it will be expressed as zero point (1)). When doing so, the value v at each time point is
The product of (Tn-1) and v(Tn) is always negative or zero. Whether or not the zero point is the zero point (g) can be determined by whether or not the previous v(Tn) at the current sampling time is positive. Of course, when v(Tn) is zero, the determination is impossible, so the determination may be made on the condition that v(Tn-1) is negative. At this time, the times Δt1 and ΔT2 from each sampling time point to the zero point (1) are determined as follows. Of course, as is clear from the figure, there is an error ε, but this is due to the sampling period Δt
It is so small that it can be ignored if it is set to a small value less than a micrometer.

Thus, as shown in FIG. 5b, Δt at sampling times Tk and tl for voltages Vl and V2, respectively.
By calculating l'TJt2', ΔTl, and ΔT2, and counting the number of sampling points P that do not include the zero point (t) between Tk and tl, the phase difference ψ between the voltages V and 2 can be calculated as Δ'. be.

As can be easily understood by focusing on Figure 5,
For example, if the phase difference is always calculated using the zero point (g) of voltage V1 as a reference, not only will the phase difference between voltages V1 and V2 be ψ, but if ψ>π, the voltage will be ψ−π. It can be seen that 2 is ahead of v in phase, and ψ minus π
Then, it can be seen that voltage 1 is ahead of voltage 2 by ψ and is in phase.

Of course, each time the zero point (g) of voltage V1 or 2 is detected, in the example of FIG.
is the time TI! , to Trn (not including the zero point...), and ψ5 minus π, so the voltage V
It goes without saying that it may be determined that V2 is in a phase that is ahead of V1 by ψ. In this way, the present invention is able to calculate the phase difference between the voltages at both ends of the circuit breaker to be turned on and the phase lead/lag relationship in FIG. 1B, c or FIG.
, c, and d, and determine whether it is in the third case.
This is intended to enable synchronous connection even when the phase difference is large by controlling the phase difference to decrease as shown in Figures A and b. FIG. 6 is a diagram showing an example of a processing flow when implementing the present invention.

The example shown in FIG. 6 for deriving the phase difference ψ will be explained with reference to FIG. As briefly mentioned above, in Figure 6, the phase difference and lead-lag relationship are determined by measuring the time from the zero point (1) of one voltage V1 to the zero point (G) of the other voltage 2. This is an example. Each time the voltages Vl and V2 are introduced at a predetermined sampling period Δt, first, step 1 is performed.
Whether or not the zero point (G) of the voltage V1 was included between that sampling point and the previous sampling point, in other words, whether the sampling point included the zero point (G) of the voltage V1. Determine.

Now, if this sampling point is time Tk in FIG. 5, the determination at this step will be YES.
Proceed to step 2 and calculate ΔT2'. Next step 3
Then, the counter that counts the number of sampling points that do not include the zero point (g) is cleared to zero. Next, proceeding to step 4, it is determined whether or not the sampling point includes the zero point (T) of the voltage V2. If this determination is YES, it means that it has been determined that the voltages Vl and V2 also include a zero point (g) at one sampling time, so that the phase difference is at most less than the sampling period Δt. The sampling period Δt can be arbitrarily selected, but if it is set to, for example, about 300 or less, the magnitude of the phase difference and V
It is possible to ignore the lead/lag relationship between l and V2 and proceed to step 5, where a closing command is given to the disconnector. Judgment in step 4 is N.
When the result is O, it waits for the next sampling point. Next, when a new sampling is performed after a period Δt,
The determination in step 1 is made again.

If step 1 was determined to be YES at the previous sampling time, the next determination will naturally be NO, so proceeding to step 6, the counter is incremented by one from P to P+1. Next, proceeding to step 7, it is determined whether or not there is a zero point (G) for the voltage V2. At this time, if the determination is NO, the process waits for the next sampling. Fifth
In the case shown in the figure, steps 1, 6, and 7 are repeated until the sampling point Tt is reached.
Then, at the sampling time point Tt, step 7 determines YES, and in step 8, where the calculation of the phase difference proceeds as described below, Δ
Calculate t1. Next, proceed to step 9 and voltages Vl, V2
Calculate the time instant phase difference ψ between the zero points (g) of . At this time, the phase difference ψ is calculated from the data obtained in the previous steps as ψ=ΔT2'+(p-1)Δt+Δt1. That is, at time Tt, the counter is further incremented by 1 at step 6, which is a sampling time error that does not include a zero point for voltage V1. At this point, Δt1 is calculated in step 8, so by finding the product of the count value P of the counter minus 1 and the period Δt, the zero points for voltages Vl and V2 are calculated. The sum of sampling periods not including . Once the phase difference ψ is determined in this way, the process proceeds to step 10 where ψ≧
Determine π. That is, when voltage V1 is in phase leading than 2 (for example, the case in Figure 1 b), ψ should be smaller than π, and when V2 is in phase leading than V1 (for example, in the case in Figure 1 c), ψ should be smaller than π. ψ is larger than π. In other words, depending on whether the determination at step 10 is YES or NO, the relationship between phase lead and lag of 1 and V2 can be determined. Regardless of the decision made in step 10, the phase difference θ can be set to allow the closing of the disconnector in the next step 11 or 12. Determine whether it is within the range. If the determination in step 10 is NO1, that is, 1 is in a leading phase with respect to V2 as shown in FIGS. It is determined whether ψ〉θo. If the judgment in step 10 is YES, that is, Fig. 8A, b
As shown in , when V2 is in a leading phase with respect to V1, the phase difference ψ is a lagging phase angle of V1 with respect to V2, so proceed to step 12 and calculate 2π - ψ and θ. It is determined whether 2π−ψ〉θo. In either step 11 or 12, if the determination is NO, the voltages Vl, V
Since the phase difference of 2 is a small value that allows closing, the process proceeds to step 5 and a closing command is given to the disconnector. If the determination in step 11 is YES, it means that the power generation capacity of electric station B is insufficient for the load in Figure 1, so this load should be transferred to another system or the power generation capacity should be reduced. Outputs a request to increase the size and prepares for full sampling. If the determination in step 12 is YES, it means that the load is too light relative to the power generation capacity, so either reduce the power generation capacity of electric station B or shift the load of other systems to electric station B. Output the request and prepare for the next sampling. In response to the requests in steps 13 and 14, depending on the system configuration, it is possible to automatically perform the operation by the magnitude corresponding to the phase difference, or to have the operator perform the operation manually. You can decide.

In this way, when the required system operation is performed, the phase difference becomes smaller, so that by repeating the sampling and determination steps described above until the synchronous connection is completed, the synchronous connection is always possible.

Next, in the present invention, the value of the phase difference ψ itself does not need to be exact.

The point is that it can be determined that the phase difference between the voltages Vl and V2 in FIGS. 1 and 2 is below a certain value. Therefore, if the sampling period ΔT is set appropriately small, steps 2 and 8 may be omitted, and steps 9 and below may be determined based on the count value P of step 6. That is, as shown in the first , = 2π9 diagram, the count value P is P <= I lower -] (an integer 2π number), so if P <= m or P ≥ (J7f-1) - m, Similar to the NO judgment in steps 11 and 12, Vl and V2
Alternatively, it can be determined that the phase difference is small, such as Vl and V2', and that the injection is possible.

On the other hand, m<P2π 1
When 2.pi. In addition, in order to change the ratio of power generation and load, for example, in the system shown in Figure 2 a, the operation must be equivalently performed at electric station C instead of at electric station B. Also good.

That is, as is clear with reference to FIG.
, A may be increased to reduce the phase difference between Vl and V2. In other words, the problem is whether control is impossible in the target system where this method is adopted, and whether or not it is a controllable electric station is also a limiting condition. The above explanation assumes that the power transmission line is being charged from one power station and is on standby, and that the system is in a steady state and the phase difference is stable.

However, as a practical matter, even in a steady state, the tidal current is constantly changing, and the phase difference is also necessarily changing. Even in such a case, the present invention can be applied by only modifying some steps. As an example of this, the present invention will be described below in a case where the present invention is applied to a case such as a low-speed reclosing circuit in which the phase difference may vary greatly. FIG. 10 illustrates a change in phase difference after a system fault is removed, in order to consider applying the present invention to a so-called system restoration device.

Case a is an example in which both electric stations have already lost synchronization and are in different systems at the time of accident removal, and cases B and c are cases in which they are operated stably even though the phase difference oscillates. In case b, the phase difference is as large as θ2, and in case c, the phase difference is stabilized as small as θl. As you can see in this example, case a
Of course, synchronous connection should not be made in case b, and also in case b, when the phase difference changes rapidly, synchronous connection should not be made.

FIG. 11 shows only the essential parts of an embodiment of the present invention that takes such considerations into consideration. As is clear from comparing FIG. 11 with FIG. 6, this embodiment also takes into account the rate of change in phase difference.

That is, when the current phase difference ψi is derived in step 9, the next step 15 is to calculate the phase difference ψi- at the point in time when the phase difference was derived n times before. Compare with. That is, 1q) i-
. ψIikuψ. is determined, and the change in phase difference is ψ. If the above is the case, all judgments will be stopped. Here, the comparison with the phase difference n times ago means how much the phase difference has changed over the time indicated by T in FIG. 10, in other words,
This is intended to determine whether the rate of change in phase difference is below a predetermined value. Therefore, the sizes of N and ψo are determined as appropriate depending on the system to which the present invention is applied. However, if the rate of change is monitored only by the difference in phase difference before and after time T in FIG. 10, in case b, when the change in phase difference is at an extreme value, there is a possibility of erroneous judgment. In order to avoid this, it is necessary to monitor changes in the phase difference over a long period of time, for example, before and after T, and only when the change rate is below a predetermined value, step 10 is performed.
It is better to move to The embodiment at this time is the first
Shown in Figure 2. In Figure 12, ψi? r is the phase difference before time T' by the number of times of convection. Also, ψ'o is the determination reference value at this time. As described above, the present invention is capable of simultaneously determining not only the phase difference between the voltages at both ends of the disconnector and the disconnector that is about to be turned on, but also the relationship between lead and lag, and also outputs requests for necessary system operations. There is an effect that can be done.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams for explaining the application of the present invention, Figure 4 is a diagram showing the concept of arrangement of devices for realizing the present invention, and Figure 5 is an illustration of an AC as a premise of the present invention. Figure 6 is a diagram explaining the method of deriving the voltage zero point, Figure 6 is a diagram showing the flow of data processing as an embodiment of the present invention, Figures 7 to 9 explain the concept of some of the steps in Figure 6. Figure 10
FIGS. 12 to 12 are diagrams illustrating examples of other embodiments to which the present invention is applied. Explanation of symbols, A, B, C...Electric station, Ll, L
2, L3...Power transmission line, Vl, V2, V3...
...Voltage, CB...Shiya breaker, PT...
...Voltage transformer, A-D...Analog-digital converter, PI/O...Input/output device, CPU...
...Processing unit.

Claims (1)

[Claims] 1. A synchronous connection method comprising the following steps. a) Deriving the voltage of the busbar of an electric station and the voltage of the transmission line to be connected to the busbar by sampling it synchronously at a fixed period. b. For the busbar and transmission line voltage signals derived in the step, performing a product operation of two successive voltage signals at each sampling time. c. Since the result of the product operation is negative, it is determined that a zero point of the sampled voltage exists between the two sampling points that gave the two voltage signals of the operation. d. Determining the phase difference and relative phase lead/lag relationship between the two voltages by comparing the presence of a zero point of one voltage with the presence of a zero point of the other voltage as a reference. e. Determine that the phase difference is below a predetermined value and allow the connection of the power transmission line to the bus bar. to provide a signal to modify the ratio of load to power generation behind the bus or transmission line. 2. Paragraph 1 is characterized in that a signal for modifying the ratio of load to power generation is given to other electric stations connected to the bus and the transmission line via other transmission lines, respectively. Synchronous connection method.