How to determine the substation connection direction

Abstract

To provide a substation connection direction determination method using an automatic voltage regulator installed on a distribution line.SOLUTION: The substation connection direction is determined by comparing the magnitudes of primary and secondary impedances of an automatic voltage regulator. Data is sampled m1 times in the calculation range before tap switching, data is sampled m2 times in the calculation range after tap switching, and determination is performed m3 times. When the condition of (n / m3)>(1 / 2) is satisfied between the same value determination n times among m3 determinations, the determination accuracy of the substation connection direction is enhanced by using the final determination result.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for determining the connection direction of an automatic voltage regulator installed on a distribution line to a substation. [Background technology]

[0002] Figure 1 shows a simplified equivalent circuit of a power distribution system equipped with an automatic voltage regulator (SVR: Step Voltage Regulator). The SVR installed on the distribution line controls the tap to maintain the voltage on the load side, on the opposite side, at an appropriate voltage (operating voltage) based on the connection direction of the substation. The connection direction of the substation can be changed by switching the system.

[0003] An example of how to determine the connection direction of a substation is disclosed in Patent Document 1 below. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-102128

[0005] The determination method described in Patent Document 1 calculates the impedances Z1 and Z2 on the primary and secondary sides from the SVR and determines the connection direction of the substation by comparing their magnitudes. Since the substation connection side is considered to be connected to an infinite bus, the connection direction of the substation is determined based on the fact that the impedance on the substation connection side is smaller than the impedance on the load side.

[0006] Specifically, when a tap is changed, the primary voltage V1, secondary voltage V2, and secondary current I2 are measured before and after the tap change, and the change ΔV1 in the primary voltage V1, the change ΔV2 in the secondary voltage V2, and the change ΔI2 in the secondary current are calculated from each measurement value.

[0007] Then, by substituting the primary side voltage V1, secondary side voltage V2, and secondary side current I2 into a specified formula, the primary side current I1 is found, and its change ΔI1 is calculated. The primary side impedance is found as Z1 = ΔV1 / ΔI1, and the secondary side impedance Z2 = ΔV2 / ΔI2, and the magnitudes of both Z1 and Z2 are compared. Summary of the Invention [Problem to be solved by the invention]

[0008] However, when a synchronous generator or induction generator used in a hydroelectric generator or the like is connected as a distributed power source on the secondary side of the SVR, the determination method described in Patent Document 1 may result in a small change ΔV2 in the secondary-side voltage V2 and a large change ΔV1 in the primary-side voltage V1, which may lead to an incorrect determination of the connection direction of the substation.

[0009] Figure 2 is a graph of the grid voltage when a distributed power source such as a synchronous generator is connected to the secondary side of the SVR. As shown by the dotted line in Figure 2, the grid voltage gradually rises as it moves closer to the distributed power source from the substation (S / S) due to the power supplied to the grid from the distributed power source.

[0010] The SVR performs tap control to maintain the grid voltage at an appropriate voltage (operating voltage). The solid line in Figure 2 shows the state immediately after the SVR controls the grid voltage. In order to maintain the grid voltage, which has risen due to distributed power sources, at an appropriate voltage, the SVR performs tap control to lower the voltage at the SVR installation point.

[0011] In this case, if a distributed power source such as a synchronous generator is connected to the secondary side of the SVR, an event will occur in which the change ΔV2 in the secondary side voltage V2 is small and the change ΔV1 in the primary side voltage V1 is large, as shown by the solid line in Figure 2.

[0012] In this state, if the substation connection direction described above is determined, and the substation is connected to the primary side as seen from the SVR, then the primary side impedance Z1 (= ΔV1 / ΔI1) should be less than the secondary side impedance Z2 (= ΔV2 / ΔI2), as shown in Figure 2. However, because the change ΔV2 in the secondary side voltage V2 is small and the change ΔV1 in the primary side voltage V1 is large, the primary side impedance Z1 (= ΔV1 / ΔI1) is greater than the secondary side impedance Z2 (= ΔV2 / ΔI2), and the substation connection direction is erroneously determined to be opposite to the actual direction.

[0013] Incorrect determination of the substation connection direction can cause the tap to stick to the upper or lower limit position when the SVR subsequently controls the system voltage to be optimized.

[0014] The system voltage immediately after the SVR tap change, shown by the solid line in Figure 2, changes over time as shown in Figure 3 due to constant power factor control using distributed power sources such as synchronous generators, so that the primary side voltage seen from the SVR approaches the value immediately before the tap change, and the secondary side voltage seen from the SVR is adjusted to the appropriate voltage.

[0015] However, even if the system voltage is changed so as to be maintained at the appropriate voltage, the SVR tap will remain stuck at the upper or lower limit position, which will hinder subsequent tap control by the SVR.

[0016] Therefore, the present invention provides a method for determining the connection direction of a substation that can suppress erroneous determination of the connection direction of the substation even when a distributed power source such as a synchronous generator is connected to the secondary side of a voltage regulator installed for regulating the system voltage. [Means for solving the problem]

[0017] The invention described in claim 1 is an automatic voltage regulator installed on a distribution line. When a distributed power source is connected to the secondary side, the automatic voltage regulator Before tap switching Measurement of the primary voltage, secondary voltage and secondary current of m 1 The primary voltage, secondary voltage and secondary current were measured after tap changing. 2 calculating a primary side current before and after the tap changing from a ratio of a secondary current to a primary side voltage and a secondary side voltage before and after the tap changing, calculating a primary side impedance from the primary side voltage and secondary side voltage and the primary side current and secondary side current before the tap changing, and calculating a secondary side impedance from the primary side voltage and secondary side voltage and the primary side current and secondary side current after the tap changing,By comparing the magnitude of both impedances, it is possible to determine whether the substation is connected to the primary or secondary side of the automatic voltage regulator. A method for determining the substation connection direction, comprising: 1 The measurement is performed within the calculation range before the number of excluded cycles before the tap change completion point, and 2 The measurement is performed within the calculation range after the number of excluded cycles after the tap change completion point, which is set taking into account the time constant of the power factor constant control by the distributed power source, and the magnitude comparison of both impedances is performed. 3 (m 1 ×m 2 ) times A method for determining a substation connection direction, comprising:

[0018] The invention described in claim 2 is m3 described in claim 1. If the same judgment result is obtained n times (predetermined number of times) out of the judgments, A method for determining a substation connection direction, characterized in that the result is used as the final determination result.

[0019] The invention of claim 3 is the same as that of claim 1 or claim 2. The first cycle when the amount of change in the differential voltage between the primary and secondary voltages of the automatic voltage regulator before and after tap changing exceeds a predetermined voltage for a certain cycle is detected as the tap changing completion point of the automatic voltage regulator. A method for determining a substation connection direction, comprising: [Effects of the Invention]

[0022] According to the invention of claim 1, even when a distributed power source such as a synchronous generator is connected to a distribution line, it is possible to minimize erroneous determination of the substation connection method.

[0023] Claim 1 According to the described invention, it is possible to improve the accuracy of determining the connection method of the substation.

[0024] Claim 1 According to the described invention, the calculation range used for judgment can be increased, and settings can be made to suit the system state of the distribution line.

[0025] Claim 3 According to the described invention, the tap change completion point can be detected accurately, and therefore the judgment data ranges for the primary and secondary impedances can be set appropriately.

[0026] Claim 1 According to the described invention, It is possible to determine the substation connection direction using constant power factor control by a distributed power source connected to the secondary side of an automatic voltage regulator. [Brief explanation of the drawings]

[0027] [Figure 1]This is a simplified equivalent circuit of a power distribution system. [Figure 2] 10 is a graph showing the system voltage immediately before and after tap switching. [Figure 3] 1 is a graph showing a system voltage several seconds after a tap change. [Figure 4] 10 is a time chart showing the relationship between the tap switching completion point and the data range for impedance determination. [Figure 5] 3 is a flowchart showing a method for determining a substation connection direction according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 5. In the equivalent circuit shown in Fig. 1, when determining whether a substation is connected to the primary side or secondary side of an SVR, the primary side voltage V1, secondary side voltage V2, and secondary side current I2 of the SVR before tap changing, and the primary side voltage V1', secondary side voltage V2', and secondary side current I2' after tap changing are measured. In the present invention, the measurement is performed m1 times before tap changing and m2 times after tap changing. In this embodiment, m1 = 3 times and m2 = 2 times are exemplified, and the primary side voltage V of the SVR before tap changing is measured. 1a ~V 1c , secondary voltage V 2a ~V 2c , secondary current I 2a ~I 2c , primary voltage V after tap change 1a ´~V 1b ´, Secondary voltage V 2a ´~V 2b ´, Secondary current I 2a ´~I 2b It is written as ´.

[0029] Primary current I before and after tap changing 1a ~I 1c ,I 1a ´, I 1b ´ is the secondary current I before and after tap changing 2a ~I 2c ,I 2a ´~I 2b ´ and primary voltage V1a ~V 1c ,V 1a ´~V 1b ´ and secondary voltage V 2a ~V 2c ,V 2a ´~V 2b In this embodiment, the primary current I before tap switching is 1a ~I 1c , the primary current after tap changing I 1a ´~I 1b ´ are calculated respectively.

[0030] The above data was measured using the primary voltage V before tap switching. 1a ~V 1c and secondary voltage V 2a ~V 2c and secondary current I 2a ~I 2c As shown in FIG. 4(a), sampling is performed within the calculation range before the number of excluded cycles before the tap changing before the tap changing completion point.

[0031] Primary voltage V after tap change 1a ´~V 1b ´ and secondary voltage V 2a ´~V 2b ´ and secondary current I 2a ´~I 2b ' is sampled within the calculation range after the number of excluded cycles after tap switching after the tap switching completion point.

[0032] Primary current I before and after tap changing 1a ~I 1c ,I 1a ´~I 1b ´ is the secondary current I before and after tap switching at each sampling 2a ~I 2c ,I 2a ´~I 2b ´ and primary voltage V 1a ~V 1c ,V 1a ´~V 1b ´, Secondary voltage V 2a ~V 2c ,V 2a ´~V 2b Calculated from the ratio of ´.

[0033] The calculation range (synonymous with m calculation cycles) for data measurement before and after the tap change shown in Figure 4(a) is set to minimize the interval time before and after the tap change (the period between the calculation range before the tap change and the calculation range after the tap change) and to improve the accuracy of determining the connection direction of the substation, as described below, because the standard deviation σ of the voltage fluctuations in the distribution line is minimized at this number of cycles. The number of excluded cycles after the tap change is set to minimize the interval time and taking into account the transient phenomenon after the tap change and the time constant of constant power factor control by distributed power sources such as synchronous generators connected to the distribution line.

[0034] In addition, the above-mentioned tap change completion point is the primary side voltage V before the tap change. 1a ~V 1c and secondary voltage V 2a ~V 2c The difference voltage V 12a ~V 12c and the primary voltage V after tap changing 1a ´~V 1b ´ and secondary voltage V 2a ´~V 2b ´ differential voltage V 12a ´~V 12b Difference ΔV between 12a ~V 12b The tap change completion point is detected as the first cycle when a certain number of consecutive cycles (for example, 10 cycles) have been reached in which the voltage change (for example, 50 V) for one tap has exceeded the threshold. The detection condition for this tap change completion point is set with the aim of making the tap change interval as short as possible and enabling accurate calculation of the tap change point.

[0035] The data V sampled in this way before and after tap switching 1a ~V 1c ,V 1a ´~V 1b ´,V 2a ~V 2c ,V 2a ´~V 2b ´,I 2a ~I 2c ,I 2a ´~I2b ´ and I calculated from these data 1a ~I 1c ,I 1a ´~I 1b ´ is the magnitude of the primary impedance of the SVR |Z 1A |~|Z 1F Used to calculate |

[0036] where |Z 1A |=ΔV 1A / ΔI 1A and ΔV 1A =|V 1a -V 1a ´|, ΔI 1A =|I 1a -I 1a ´|. Similarly, |Z 1B |=ΔV 1B / ΔI 1B and ΔV 1B =|V 1a -V 1b ´|, ΔI 1B =|I 1a -I 1b ´|. Also, |Z 1C |=ΔV 1C / ΔI 1C and ΔV 1C =|V 1b -V 1a ´|, ΔI 1C =|I 1b -I 1a ´|、|Z 1D |=ΔV 1D / ΔI 1D and ΔV 1D =|V 1b -V 1b ´|, ΔI 1D =|I 1b -I 1b ´|、|Z 1E |=ΔV 1E / ΔI 1E and ΔV 1E =|V 1c -V 1a ´|, ΔI 1E =|I 1c -I 1a ´|、|Z 1F |=ΔV 1F / ΔI1F and ΔV 1F =|V 1c -V 1b ´|, ΔI 1F =|I 1c -I 1b ´| is.

[0037] In addition, each sampled data before and after tap switching V 2a ~V 2c ,V 2a ´~V 2b ´,I 2a ~I 2c ,I 2a ´~I 2b ´ is the magnitude of the secondary impedance of the SVR |Z 2A |~|Z 2F Used to calculate |

[0038] |Z 2A |=ΔV 2A / ΔI 2A and ΔV 2A =|V 2a -V 2a ´|, ΔI 2A =|I 2a -I 2a ´|. Similarly, |Z 2B |=ΔV 2B / ΔI 2B and ΔV 2B =|V 2a -V 2b ´|, ΔI 2B =|I 2a -I 2b ´|. Also, |Z 2C |=ΔV 2C / ΔI 2C and ΔV 2C =|V 1b -V 1a ´|, ΔI 2C =|I 2b -I 2a ´|、|Z 2D |=ΔV 2D / ΔI 2D and ΔV 2D =|V 2b -V 2b ´|, ΔI 2D =|I 2b-I 2b ´|、|Z 2E |=ΔV 2E / ΔI 2E and ΔV 2E =|V 1c -V 1a ´|, ΔI 2E =|I 2c -I 2a ´|、|Z 2F |=ΔV 2F / ΔI 2F and ΔV 2F =|V 2c -V 2b ´|, ΔI 2F =|I 2c -I 2b ´| is.

[0039] The magnitude of the primary impedance calculated in this way |Z 1A |~|Z 1F | and the magnitude of secondary impedance |Z 2A |~|Z 2F By comparing the size of |, |Z 1A~F |≦|Z 2A~F In the case of |, it is judged as forward transmission and that the substation is connected to the primary side of the SVR, and |Z 1A~F |>|Z 2A~F If |, it is determined that the substation is connected to the secondary side of the SVR as a reverse feed.

[0040] As mentioned above, the primary impedance |Z 1A~F | and secondary impedance |Z 2A~F By comparing the magnitude of |, it is possible to determine with a certain degree of accuracy which SVR a substation is connected to, but the feature of this invention is that if n of these m3 determinations result in the same value, the determination result based on that same value is used as the final determination result. In this case, m3 and n must satisfy the condition (n / m3) > (1 / 2).

[0041] Another feature is that by sampling m1 and m2 times within the calculation range in Figure 4(b), the number of exclusion cycles after tap changing can be set, which can eliminate erroneous determination of the substation connection direction caused by a situation in which constant power factor control by a distributed power source such as a synchronous generator connected to the distribution line is not in time.

[0042] The number of excluded cycles after tap changing that can eliminate erroneous determination of the substation connection direction when the constant power factor control is not completed in time can be, for example, when the completion point of the constant power factor control by the distributed power source is within the calculation range of Figure 4(b), or when it is just before or just after the calculation range.

[0043] The range immediately before or after the calculation range can be determined by setting an appropriate number of samplings and performing calculations in an automatic voltage regulator that implements the determination method, so that when the same value is obtained n times, the determination result based on the same value will match the actual substation connection direction.

[0044] Fig. 5 is a flowchart for explaining the determination method of the present invention. First, in the forward feed state in step S1, when the SVR performs tap switching in step S2 to maintain the load side voltage at an appropriate voltage, the number of backward feed determinations n is set to 0 in step S3.

[0045] Next, in step S4, the impedance |Z 1A~F |,|Z 2A~F A comparison of the magnitudes of | is started, and in step S5 it is determined whether it is forward or backward. If the determination result in step S5 is forward, there is no change in the current state in step S1, so it is determined that the substation is connected in the direction determined to be the power source side in step S1.

[0046] Conversely, if the determination result in step S5 is reverse transmission, it is considered that a change in the connection direction of the substation has occurred due to a system switching or the like. In this case, the number of times reverse transmission determination has been made in step S7 is set to n=n+1. The determination of whether forward transmission or reverse transmission in step S5 is repeated m3 times (six times in this embodiment) between step S5 and step S6.

[0047] Of the m3 determinations, the number of times reverse transmission determinations were made is set to L1 = n. After repeating this determination m3 times, the process proceeds to step S8. If the condition (L1 / m3) ≦ (1 / 2) is met in step S8, the process returns to step S1 and continues control to maintain the SVR load side voltage at an appropriate level, assuming that there is no change in the substation connection direction. For example, if L1 = 3, then (L1 / m3) = (3 / 6) = 0.5 ≦ (1 / 2), so the process returns to step S1 and continues control to maintain the SVR load side voltage at an appropriate level, assuming that there is no change in the substation connection direction.

[0048] If the result of the determination in step S8 is (L1 / m3)>(1 / 2), the process proceeds to step S9, where it is determined that there has been a change in the substation connection direction (forward transmission → reverse transmission), and step S 10 In this case, control is performed to maintain the load side voltage of the SVR on the opposite side at an appropriate level. For example, when L1 = 4, (L1 / m3) = (4 / 6) ≒ 0.7 > (1 / 2), so the process moves to step S9, where it is determined that there has been a change in the substation connection direction (forward → reverse transmission), and step S 10 In this case, control is performed to maintain the load side voltage of the SVR, which is on the opposite side, at an appropriate level.

[0049] Next, step S 11 In step S, the number of times the forward transfer determination is made is set to 0. 12 So, the impedance |Z 1A~F |,|Z 2A~F Start comparing the magnitude of |. Then, step S 13 In step S, it is determined whether the paper is fed forward or backward. 13 If the determination result of step S9 is reverse transmission, there is no change in the current state in step S9, so it is determined that the substation is connected in the direction determined to be the power source side in step S9.

[0050] Conversely, step S 13 If the result of the judgment is forward, it is considered that a change in the connection direction of the substation has occurred due to a system switching or the like. In this case, step S 15 In step S, the number of times the forward judgment is made is set to n=n+1. 13The decision of whether to send forward or backward is made in step S 15 This is repeated m3 times (six times in this embodiment) between the above.

[0051] Of the m3 determinations, the number of times the forward determination is made is L2=n. After the determination is repeated m3 times, step S 16 Move to Step S 16 If the condition (L2 / m3)≦(1 / 2) is met, the process returns to step S9 and continues control to maintain the SVR load side voltage at an appropriate level, assuming that there is no change in the substation connection direction. For example, if L2=2, then (L2 / m3)=(3 / 6)=0.5≦(1 / 2), so the process returns to step S9 and continues control to maintain the SVR load side voltage at an appropriate level, assuming that there is no change in the substation connection direction.

[0052] Also, step S 16 If the result of the determination is (L2 / m3) > (1 / 2), the process proceeds to step S1, where it is determined that there has been a change in the substation connection direction (reverse transmission → forward transmission), and in step S2, control is executed to maintain the load side voltage of the SVR on the opposite side at an appropriate level. For example, if L2 = 4, then (L2 / m3) = (4 / 6) ≒ 0.7 > (1 / 2), so the process proceeds to step S1, where it is determined that there has been a change in the substation connection direction (reverse transmission → forward transmission), and in step S2, control is executed to maintain the load side voltage of the SVR on the opposite side at an appropriate level.

[0053] In the method of determining the substation connection direction shown in FIG. 5 described above, if a distributed power source such as a synchronous generator is connected to the secondary side of the SVR, steps S2 and S 10 As a result of the execution of tap switching of the SVR in the above, an event occurs in which the change ΔV2 in the secondary side voltage V2 becomes smaller and the change ΔV1 in the primary side voltage V1 becomes larger, as shown in FIG.

[0054] This phenomenon occurs when distributed power sources such as synchronous generators operate to maintain a constant power factor, resulting in the power factor of the system being the same as the power factor before tap control by the SVR (constant power factor).As shown in Figure 3, a few seconds after the SVR tap is changed, the primary side voltage seen from the SVR changes to match the state before the tap was changed, and the secondary side voltage seen from the SVR changes to maintain an appropriate voltage.

[0055] Therefore, the present invention provides an exclusion cycle after tap changing shown in FIG. 5 to eliminate the influence of transient phenomena after tap changing, and also to prevent the influence of transient phenomena after tap changing from step S5 to step S6 during the period from FIG. 2 to FIG. 3 until the constant power factor control is completed. 13 The forward and reverse determination in step S1 is performed m3 times, and if the number of determinations (n ​​times = L1) that are different from the forward determination in step S1 satisfies the condition (L1 / m3) > (1 / 2) (step S8), or if the number of determinations (n ​​times = L2) that are different from the reverse determination in step S9 satisfies the condition (L2 / m3) > (1 / 2) (step S 16 ) determines the result of the test that is the same n (L1 or L2) times as the final result.

[0056] This reduces the possibility of erroneous determination compared to when the connection direction of the substation is determined only by the determination immediately after the tap switching, as shown in FIG.

[0057] In the above embodiment, the calculation range, the number of excluded cycles before and after tap switching, and the length of the horizontal axis of the tap switching time shown in Figure 4 are shown as examples, and naturally have no relation to the ratio of the lengths of each time.

[0058] Furthermore, the number of samplings before tap switching is three and the number of samplings after tap switching is two are merely examples, and it goes without saying that any number of m1 and m2 can be set. Note that the number of determinations m3 is determined as m1 × m2.

[0059] As described above, the method of determining the substation connection direction of the present invention determines that the forward / reverse state has changed from the current state n times out of m3 forward / reverse determinations, and if the condition (n / m3) > (1 / 2) is satisfied, the result of the n determinations is used as the final determination result, thereby minimizing erroneous determination of the substation connection direction.

[0060] In addition, the number of AC voltage and AC current cycles used to calculate the optimal interval time before and after tap changing and the amount of voltage and current change have been determined, which eliminates the effects of transient phenomena after tap changing and makes it possible to determine the substation connection direction using constant power factor control with a synchronous generator.

[0061] Furthermore, since the tap switching completion point can be accurately detected, it becomes possible to appropriately set the determination data ranges for the primary side impedance and the secondary side impedance. [Industrial Applicability]

[0062] The present invention is used in an automatic voltage regulator for power distribution.

Claims

1. A method for determining a substation connection direction, in a state where a distributed power source is connected to the secondary side of an automatic voltage regulator installed on a distribution line, measuring the primary side voltage, secondary side voltage, and secondary side current before a tap of the automatic voltage regulator m1 times, measuring the primary side voltage, secondary side voltage, and secondary side current after the tap changing m2 times, calculating the primary side current before and after the tap changing from a ratio of the secondary current, primary side voltage, and secondary side voltage before and after the tap changing, calculating a primary side impedance from the primary side voltage, secondary side voltage, and primary side current, and secondary side current before the tap changing, calculating a secondary side impedance from the primary side voltage, secondary side voltage, and primary side current, and secondary side current after the tap changing, and comparing the magnitudes of both impedances to determine whether the substation is connected to the primary side or the secondary side of the automatic voltage regulator, wherein the m1 measurements are performed within a calculation range prior to the number of exclusion cycles before the tap changing completion point, and The method for determining the connection direction of a substation is characterized in that the measurements are performed within a calculation range after the number of exclusion cycles after the tap changing completion point, which is set taking into account the time constant of the constant power factor control by the distributed power source, and the comparison of the magnitudes of the two impedances is performed m3 (m1 × m2) times.

2. Said m 3 2. The method for determining a substation connection direction according to claim 1, wherein the final determination result is determined when the same determination result is obtained n times (predetermined number of times) among the determinations.

3. 3. The method for determining a substation connection direction according to claim 1, wherein the first cycle in which a difference voltage change amount between the primary side voltage and the secondary side voltage of the automatic voltage regulator before and after tap changing exceeds a predetermined voltage for a certain number of cycles is detected as the tap changing completion point of the automatic voltage regulator.

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