A method for identifying the position state of the bus coupler switch of a three-winding transformer operating in parallel

Abstract

The present invention discloses a method for identifying the position state of a busbar switch of three-winding transformers running in parallel. By obtaining basic data of the substation, including the primary wiring mode of the substation, the parameters of the three-winding transformer, and the historical and real-time measured values of the active power on the high-voltage side of the transformer, the active power distribution relationship on the high-voltage side of the transformer when the high and medium voltage sides of two and three three-winding transformers are running in parallel is derived. The derived power distribution relationship is used as the judgment standard to realize the identification of the position state of the busbar switch. In order to verify the correctness and effectiveness of the present invention, not only a simulation example is established to demonstrate it through power flow simulation, but also it is verified based on the measured data of a 500 kV substation.

Description

Technical Field

[0001] The present invention relates to the technical field of power system state estimation, and more particularly to a method for identifying the position state of a busbar switch of a three-winding transformer operating in parallel. Background Art

[0002] Power system state estimation is one of the important functions of modern power dispatching systems. Identifying topological errors has always been a difficult and key point in state estimation. Existing research has developed a variety of topological error identification methods based on the full network data of the dispatching center. Traditional static state estimation methods identify topological errors by converting circuit breakers into zero-impedance branches for power flow iteration, but the state estimation speed is slow and the position state of the bus tie breaker cannot be identified. The existing innovation vector neural network method uses a fast state recognition speed to identify the circuit breaker, but it has high requirements for measurement redundancy, low efficiency, and cannot identify the position state of the bus tie breaker. Combining the zero-impedance branch model with the innovation graph method can identify the erroneous state of the bus tie breaker, but it requires the physical model of the suspicious bus to be known in advance, which is not flexible and convenient. To this end, we propose a bus tie breaker position state identification method for parallel-operated three-winding transformers. Summary of the Invention

[0003] The object of the present invention is to provide a method for identifying the position state of a busbar switch of a three-winding transformer running in parallel, so as to solve the problems raised in the above background technology.

[0004] To achieve the above purpose, the technical solution adopted includes the following steps:

[0005] 1. Obtain basic data of the power grid, including the primary connection mode of the substation, parameters of the three-winding transformer, and historical and real-time measurements of the active power on the high-voltage side of the transformer;

[0006] 2. Preprocess the basic data of the power grid and establish an equivalent circuit model for two three-winding transformers operating in parallel based on the primary wiring method of the substation. Use the ring network power flow distribution calculation method to derive the active power distribution relationship on the high-voltage side of the transformers when the high and medium voltage sides of the two three-winding transformers operate in parallel.

[0007] 3. Preprocess the basic data of the power grid and establish an equivalent circuit model for three three-winding transformers operating in parallel based on the primary wiring method of the substation. Combined with the ring network power flow distribution calculation method and the Ward equivalent method, the active power distribution relationship on the high-voltage side of the transformers when the high and medium voltage sides of the three three-winding transformers operate in parallel is derived.

[0008] 4. According to the derived distribution relationship, obtain the calculation results of the historical measured values of the active power on the high-voltage side of the three-winding transformer, and obtain the distribution interval of the calculation results according to the 3σ principle. At the same time, obtain the calculation results of the real-time measured values;

[0009] 5. Judge whether the calculation result of the real-time measured value is within the distribution interval of the calculation results of the historical measured values. If the calculation result is within the distribution interval, the three-winding transformer operates in parallel, and the position of the bus-coupling switch should be the closed position; otherwise, the three-winding transformer operates separately, and the position of the bus-coupling switch should be the open position.

[0010] Preferably, the specific steps in step 2 are as follows: A. When two three-winding transformers operate in parallel, without considering the excitation branch of the transformer, its equivalent circuit diagram is a single loop network. Moreover, by splitting node 1, an equivalent circuit diagram of an equivalent two-terminal power supply network can be obtained, as shown in Figure 1 shown. B. According to Let where, Derive C. Since R << X for the transformer, let R = R 2H = R 1M = R 2M = 0, then G ∑ = 0, B ∑ = 1 / X ∑ , derive D. According to the primary wiring mode of the existing 500 kV substations in Chongqing area, there are only capacitor or reactor circuits on the low-voltage side except for the station service transformer. Therefore, the active power load on the low-voltage side is approximately 0. In this case, let P2 = P4 = 0, and derive In the formula: X 1H , X 1M respectively represent the reactances of the high- and medium-voltage sides of the No. 1 main transformer; X 2H , X 2M respectively represent the reactances of the high- and medium-voltage sides of the No. 2 main transformer.

[0011] Preferably, the specific steps in step 3 are as follows: A. When three three-winding transformers operate in parallel, without considering the excitation branch of the transformer, its equivalent circuit is a double loop network. Take the equivalent circuit of the No. 1 transformer as the internal network, and the parallel circuit of the No. 2 and No. 3 transformers as the external network. With the high- and medium-voltage side buses of the three-winding transformer as the boundary conditions, use the Ward equivalent method to convert the equivalent circuit into a single loop network, as shown in Figure 2 shown, and calculate the transfer admittance B. According to Let where, Derive C. Since the R of the transformer << X, let R 1H = R 2H = R 1M = R 2M = 0, then G ∑ = 0, B ∑ = 1X ∑ , it is deduced that D. According to the primary wiring mode of the existing 500 kV substations in Chongqing area, it can be seen that there are only capacitor or reactor circuits on the low-voltage side except for the station service transformer, so the active load on the low-voltage side is approximately 0. In this case, let P7 = 0, and it is deduced that[[ID=X]] Similarly, In the formula: X 1H , X 1M respectively represent the reactances of the high- and medium-voltage sides of the No. 1 main transformer; X 2H , X 2M respectively represent the reactances of the high- and medium-voltage sides of the No. 2 main transformer; X 3H , X 3M respectively represent the reactances of the high- and medium-voltage sides of the No. 3 main transformer.

[0012] Preferably, the specific steps in step 4 are as follows: A. Calculate the power ratio of the historical measurement values according to the deduced power distribution relationship. A1. When two three-winding transformers in the substation are operating in parallel, according to calculate the ratio samples of the historical measurement values of the active power on the high-voltage sides of the No. 1 main transformer and the No. 2 main transformer; A2. When three three-winding transformers in the substation are operating in parallel, according to calculate the ratio samples of the historical measurement values of the active power on the high-voltage sides of the three transformers. B. Calculate the mean and variance of each sample, and obtain the ratio interval according to (μ - 3σ, μ + 3σ). C. Calculate the power ratio of the real-time measurement values according to the deduced power distribution relationship.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] The present invention combines the equivalent circuit model of three-winding transformers running in parallel with the ring network power flow distribution calculation method and the Ward equivalent method, and for the first time derives the active power distribution law of two or three three-winding transformers running in parallel, which is innovative. At the same time, the invention has a certain degree of versatility. For all two or three three-winding transformers running in parallel on the high and medium voltage sides, when the resistance is very small and approximately 0 and the active load on the low voltage side is 0, the active power on the high-voltage side of the transformers running in parallel is inversely proportional to the sum of the reactances on the high and medium voltage sides of the transformers. Moreover, the invention is simple and convenient, and requires a small amount of data. After calculating the value range of the active power ratio on the high-voltage side of the transformer by combining historical measurement data with the derived power distribution relationship, it is only necessary to judge in real time whether the transformers are running in parallel based on the power measurement value on the high-voltage side of the transformer and the transformer impedance value, thereby realizing the identification of the position state of the busbar switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the equivalent circuit diagram of two three-winding transformers running in parallel;

[0016] Figure 2 This is the equivalent circuit diagram of three three-winding transformers running in parallel;

[0017] Figure 3 This is a simulation diagram of two three-winding transformers running in parallel;

[0018] Figure 4 This is a simulation diagram of three three-winding transformers running in parallel;

[0019] Figure 5 This is the sample distribution histogram of CJQ substation K1;

[0020] Figure 6 This is the K2 sample distribution histogram of CJQ substation;

[0021] Figure 7 This is the sample distribution histogram of K3 of CJQ substation;

[0022] Figure 8 The present invention is a flow chart of the method for identifying the position state of the bus tie switch of a three-winding transformer running in parallel. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0024] To verify the correctness of the present invention, on the one hand, simulation models were established using the PSASP simulation system. The active power on the high-voltage side of the transformer under different load conditions was calculated through power flow calculations, and the active power ratio was calculated for data comparison and analysis. On the other hand, actual measurement data from the substation was collected to determine the position status of the bus tie switch according to the present invention. The specific steps are as follows:

[0025] 1. Simulation analysis of two three-winding transformers running in parallel

[0026] A simulation model of two three-winding transformers operating in parallel on the high and low voltage sides is established. All transformer parameters in the model are set to the same, and the active load on the low voltage side is set to 0. Various simulation schemes are shown in Table 1, where the load size is set according to the percentage of its rated capacity.

[0027] Table 1 Various simulation schemes for parallel operation of two three-winding transformers

[0028]

[0029] As shown in Table 2, when the total active load on the medium-voltage side of the main transformer and the reactive load on the low-voltage side are both constant, and regardless of whether the reactive loads on the low-voltage sides of the main transformers are equal, as the power factor on the medium-voltage side of the main transformer varies between 0.9 and 1, the high-voltage side active power ratio is approximately 1, regardless of whether the medium-voltage side load is capacitive, inductive, or purely resistive. Therefore, the influence of the medium-voltage side power factor and load characteristics on the high-voltage side active power ratio of two three-winding transformers operating in parallel on the high and high voltage sides can be ignored.

[0030] Table 2 Active power ratio of high voltage side of M1 and M2 simulation schemes

[0031]

[0032] As shown in Tables 3 and 4, when the total active and reactive loads on the MV side are constant, the high-voltage side active power ratio is approximately 1 as the reactive load on the LV side changes. Furthermore, a comparison of simulation schemes M3 and M4 shows that the high-voltage side active power ratio is also approximately 1 as the total MV side load changes. Therefore, the effects of changes in MV and LV side loads on the high-voltage side active power ratio of the two three-winding transformers operating in parallel on the MV and LV sides can be ignored.

[0033] Table 3 Active power ratio on the high-voltage side of the M3 simulation scheme

[0034]

[0035] Table 4 Active power ratio on the high-voltage side of the M4 simulation scheme

[0036]

[0037] 2. Simulation analysis of three three-winding transformers running in parallel

[0038] A simulation model of three three-winding transformers running in parallel on the high and low voltage sides was established. All transformer parameters in the model were set to the same, and the active load on the low voltage side was set to 0. Various simulation schemes are shown in Table 5, where the load size is set according to the percentage of its rated capacity.

[0039] Table 5 Various simulation schemes for parallel operation of three three-winding transformers

[0040]

[0041] Table 6 Active power ratio of high voltage side of M5 and M6 simulation schemes

[0042]

[0043] As shown in Table 6, when the total active load on the medium-voltage side of the main transformer and the reactive load on the low-voltage side are both constant, and regardless of whether the reactive loads on the low-voltage sides of the main transformers are equal, as the medium-voltage power factor of the main transformer varies between 0.9 and 1, the ratio of the high-voltage side active power of any one main transformer to the sum of the high-voltage side active powers of the other two main transformers is approximately 0.5, regardless of whether the medium-voltage load is capacitive, inductive, or purely resistive. Therefore, the influence of the medium-voltage side power factor and load characteristics on the high-voltage side active power ratio of three three-winding transformers operating in parallel on the high and low voltage sides can be ignored.

[0044] The simulation results obtained according to the M7 simulation scheme are as follows: the ratio of the active power on the high-voltage side of the #1 main transformer to the sum of the active power on the high-voltage sides of the other two main transformers is shown in Table 7, the ratio of the active power on the high-voltage side of the #2 main transformer to the sum of the active power on the high-voltage sides of the other two main transformers is shown in Table 8, and the ratio of the active power on the high-voltage side of the #3 main transformer to the sum of the active power on the high-voltage sides of the other two main transformers is shown in Table 9.

[0045] Table 7 Active power ratio of the high-voltage side of the #1 main transformer and the other two parallel main transformers in the M7 simulation scheme

[0046]

[0047] Table 8 Active power ratio of the high-voltage side of the #2 main transformer and the other two parallel main transformers in the M7 simulation scheme

[0048]

[0049] Table 9 Active power ratio of the high-voltage side of the #3 main transformer and the other two parallel main transformers in the M7 simulation scheme

[0050]

[0051] According to the M8 simulation scheme, the ratio of the active power on the high-voltage side of the #3 main transformer to the sum of the active power on the high-voltage sides of the other two main transformers is shown in Table 10.

[0052] Table 10 Active power ratio of the high-voltage side of the #3 main transformer and the other two parallel main transformers in the M8 simulation scheme

[0053]

[0054] Comparing the simulation results of M7 and M8 shows that when the total active and reactive loads on the medium voltage side are constant, as the reactive load on the low voltage side changes, the ratio of the active power on the high voltage side of any main transformer to the sum of the active powers on the high voltage sides of the other two main transformers is approximately 0.5. Therefore, the effect of changes in the low voltage side load on the high voltage side active power ratio of the three three-winding transformers operating in parallel on the high and medium voltage sides can be ignored.

[0055] Table 11 shows the ratio of the active power on the high-voltage side of the #3 main transformer to the sum of the active power on the high-voltage sides of the other two main transformers, obtained using simulation scheme M9. A comparison of the simulation results for schemes M7 and M8 shows that when the medium-voltage side load changes, the ratio of the active power on the high-voltage side of any main transformer to the sum of the active power on the high-voltage sides of the other two main transformers is approximately 0.5. Therefore, the effect of medium-voltage side load changes on the high-voltage side active power ratio of the three three-winding transformers operating in parallel on the high and medium voltage sides can be ignored.

[0056] Table 11 Active power ratio of the high-voltage side of the #3 main transformer and the other two parallel main transformers in the M9 simulation scheme

[0057]

[0058] 3. Simulation Conclusion

[0059] In summary, when the active load on the low-voltage side is 0, for the three-winding transformers running in parallel on the high- and medium-voltage sides, if the parameters of the transformers running in parallel are consistent, the following conclusions can be drawn:

[0060] (1) When two main transformers are operated in parallel, as the load on the medium and low voltage sides changes, the ratio of the active power measurement values on the high voltage sides of the two main transformers is approximately 1.

[0061] (2) When the three main transformers are operated in parallel, as the load on the medium and low voltage sides changes, the ratio of the active power measurement value on the high voltage side of any main transformer to the sum of the active power measurements on the high voltage sides of the other two main transformers is approximately 0.5.

[0062] 4. Practical Application

[0063] (1) Analysis of active power ratio of substation equipped with two three-winding transformers

[0064] Measurements were collected from six 500 kV substations equipped with two three-winding transformers, and the high-voltage side active power ratio of each transformer was calculated. Simultaneously, impedance values were calculated based on the transformer parameters, revealing that the reactance ratio of transformers within the same substation was approximately 1. Therefore, based on the relationship between the high-voltage side active power distribution and the main transformer reactance derived in this paper, it is clear that when two three-winding transformers in each substation operate in parallel, their high-voltage side active power ratio should be approximately 1.

[0065] As shown in Table 12, except for the SY substation, the high-voltage side active power ratios of the transformers in the other five substations are all approximately 1. Therefore, according to the present invention, it can be directly determined that the medium-voltage bus tie breaker connecting the two main transformers in the SY substation should be in the open position. At the other substations, at least one of the medium-voltage bus tie breaker connecting the two main transformers is in the closed position. This determination is consistent with the actual position of the bus tie breaker in each substation.

[0066] Table 12 Actual high-voltage side active power ratio of two three-winding transformers

[0067]

[0068] (2) Analysis of active power ratio of substation equipped with three three-winding transformers

[0069] We sampled measurements from five 500 kV substations equipped with three three-winding transformers and calculated the ratio of the active power measured on the high-voltage side of any one main transformer to the sum of the active power measurements on the high-voltage sides of the other two main transformers. We also calculated impedance values based on the parameters of each transformer and found that, with the exception of the CJQ substation, the transformer reactance ratio within each substation was approximately 1.

[0070] As shown in Table 13, with the exception of the CJQ and BN substations, the ratio of the measured high-voltage active power value of any main transformer to the sum of the high-voltage active power values of the other two main transformers in the remaining three substations is approximately 0.5. Therefore, according to the present invention, it can be directly determined that at least one of the medium-voltage bus tie switches in the BN substation is in the open position. The medium-voltage bus tie switches connecting the three main transformers in the BQ, SQ, and SP substations should be in the closed position. This determination is consistent with the actual position of the bus tie switches in each substation.

[0071] Table 13 Actual high-voltage side active power ratio of three three-winding transformers

[0072]

[0073] For the CJQ substation, since the impedance of the newly added No. 3 main transformer is similar to that of the previous two transformers but differs significantly, it is impossible to directly determine the position of the bus tie breaker based on the active power ratio. Therefore, a large amount of historical active power measurement data from the high-voltage side of the CJQ substation main transformers was collected, and the ratio of the active power on the high-voltage side of any main transformer in each data set was calculated according to formula (1.3), thereby obtaining three ratio samples. Then, the value range of each ratio was calculated according to the 3σ principle. Finally, as shown in Table 14, the real-time active power ratio of the high-voltage side of the CJQ substation transformers is within the range, so the three main transformers are operating in parallel, thereby identifying that the medium-voltage side bus tie breaker connecting the three main transformers of the CJQ substation should be in the closed position.

[0074] Table 14 Comparison of real-time measurement ratios and value ranges

[0075]

[0076] Although the embodiments of the present invention have been shown and described, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

Claims

1. A method for identifying the position state of a bus tie switch of a three-winding transformer operating in parallel, characterized by: The following steps are involved: ① Obtain basic data of the power grid, including the primary wiring method of the substation and the measurement information of the substation, including the historical and real-time measurement values of the active power on the high-voltage side of the three-winding transformer; ②Preprocess the basic data of the power grid, establish an equivalent circuit model for the parallel operation of two three-winding transformers based on the primary wiring mode of the substation, and use the loop network power flow distribution calculation method to deduce the relationship between the active power distribution of the high-voltage side of the transformer when the high- and medium-voltage sides of the two three-winding transformers are operating in parallel; the specific steps in step ② are as follows: A. When two three-winding transformers are operating in parallel, without considering the excitation branch of the transformer, its equivalent circuit diagram is a single loop network, and by splitting node 1, an equivalent circuit diagram of an equivalent two-end power supply network can be obtained, B. According to Let where, Deduce C. Since R << X for the transformer, let R 1H = R 2H = R 1M = R 2M = 0, then G ∑ = 0, B ∑ = 1 / X ∑ Deduce D. According to the primary wiring mode of the existing 500 kV substations in Chongqing area, there are only capacitor or reactor circuits on the low-voltage side except for the station service transformer, so the active power load on the low-voltage side is approximately 0; in this case, let P2 = P4 = 0, and deduce In the formula: X 1H , X 1M respectively represent the reactances of the high- and medium-voltage sides of the No. 1 main transformer; X 2H , X 2M respectively represent the reactances of the high- and medium-voltage sides of the No. 2 main transformer; ③Preprocess the basic data of the power grid, establish an equivalent circuit model for the parallel operation of three three-winding transformers based on the primary wiring mode of the substation, and derive the active power distribution relationship of the high-voltage side of the transformer when the high- and medium-voltage sides of the three three-winding transformers are operating in parallel by combining the power flow distribution calculation method of the loop network and the Ward equivalent method; The specific steps in step ③ are as follows: A. When the three three-winding transformers are operating in parallel, without considering the excitation branch of the transformer, its equivalent circuit is a double-loop network. Regard the equivalent circuit of the No. 1 transformer as the internal network, and the parallel circuit of the No. 2 and No. 3 transformers as the external network. With the high- and medium-voltage side buses of the three-winding transformer as the boundary conditions, use the Ward equivalent method to transform the equivalent circuit into a single-loop network and calculate the transfer admittance B. According to Let where, Derive C. Since R << X for the transformer, let R 1H = R 2H = R 1M = R 2M = 0, then G ∑ = 0, B Σ = 1 / X ∑ Derive D. According to the primary wiring mode of the existing 500 kV substations in Chongqing area, there are only capacitor or reactor circuits on the low-voltage side except for the station service transformer, so the active load on the low-voltage side is approximately 0; In this case, let P7 = 0 and derive Similarly, Where: X 1H 、X 1M Respectively represent the reactance of the high and medium voltage sides of No. 1 main transformer; X 2H 、X 2M Respectively represent the reactance of the high and medium voltage sides of No. 2 main transformer; X 3H 、X 3M Respectively represent the reactance of the high and medium voltage sides of No. 3 main transformer; ④ Based on the derived distribution relationship, the calculation results of each historical measurement value of the active power on the high-voltage side of the three-winding transformer are obtained, and the distribution interval of the calculation results is obtained according to the 3σ principle, and the calculation results of the real-time measurement value are obtained at the same time; ⑤ Determine whether the calculation result of the real-time measurement value is within the distribution range of the calculation result of the historical measurement value. If the calculation result is within the distribution range, the three-winding transformer operates in parallel and the bus tie switch position should be the closed position; otherwise, the three-winding transformer operates in separate columns and the bus tie switch position should be the open position.

2. The method for identifying the position state of a bus tie switch of a three-winding transformer in parallel operation according to claim 1, characterized in that: The specific steps in step ④ are: A. Calculate the power ratio of the historical measurement value based on the derived power distribution relationship; A1. When the substation is equipped with two three-winding transformers running in parallel, according to Calculate the ratio samples of each historical measured value of active power on the high voltage side of No. 1 main transformer and No. 2 main transformer; A2. When the substation is equipped with three three-winding transformers running in parallel, according to A. Calculate the ratio samples of the historical measured values of the active power on the high-voltage side of the three transformers; B. Calculate the mean and variance of each sample, and obtain the ratio interval based on (μ-3σ, μ+3σ); C. Calculate the power ratio of the real-time measured values based on the derived power distribution relationship.

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