A Method for Governing Three-Phase Imbalance in a Substation Area and Calculating Open Capacity

Abstract

The present invention relates to a method for governing three-phase imbalance in a transformer substation area and calculating the openable capacity. The governing method includes the following steps: First, collect the three-phase current and three-phase voltage at the load end of the transformer substation area; Second, calculate the apparent total power at the load end of the transformer substation area according to the three-phase current and the total voltage at the load end; Third, take the average value of the three-phase current; use the difference between each phase current and the average value as the corresponding compensation current; Fourth, take the ratio of the maximum compensation current in each phase compensation current to the maximum current in the three-phase current as the three-phase imbalance degree; Fifth, according to the apparent total power and the threshold range of the three-phase imbalance degree, adopt the dynamic compensation or automatic phase conversion method to govern the three-phase imbalance in the transformer substation area. The above-mentioned method for governing three-phase imbalance in the transformer substation area combines the dynamic compensation and automatic phase conversion methods, achieving precise and efficient governance of the three-phase imbalance at the load end of the transformer substation area, while reducing equipment costs and minimizing power losses.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and particularly to a method for managing three-phase imbalance in a distribution area and a method for calculating the openable capacity of a distribution area based on three-phase balance. Background Art

[0002] Three-phase imbalance refers to the situation where the amplitudes of three-phase currents (or voltages) in a power system are inconsistent, and the amplitude difference exceeds the specified range. The three-phase imbalance in a power system is caused by factors such as unbalanced three-phase loads, asynchronous power consumption of single-phase loads, and asymmetry of the three-phase parameters of system components. The three-phase imbalance degree of a power system is one of the main indicators of power quality.

[0003] The three-phase imbalance in the distribution area circuit has the following hazards: 1. Increase the power loss of the line. 2. Increase the power loss of the distribution transformer. 3. Reduce the output of the distribution transformer. 4. Generate zero-sequence current in the distribution transformer. 5. Affect the safe operation of electrical equipment.

[0004] In the existing methods for dealing with three-phase imbalance, generally the following methods are adopted: evenly distributing the load, increasing the short-circuit capacity, static compensation, dynamic compensation, etc. However, due to the wiring mistakes of construction personnel and the unpredictability of user power consumption, it is difficult to adjust the evenly distributed charge in a timely manner. In the case of the access of high-power electrical appliances, the three-phase imbalance degree may be aggravated. Increasing the short-circuit capacity does not fundamentally solve the three-phase imbalance problem. Although it improves the system's tolerance, it exacerbates the power loss. Although static compensation and dynamic compensation can perform precise regulation, for power systems with a large load such as distribution areas, the quality requirements for the required equipment are relatively high, increasing the cost of managing three-phase imbalance. Summary of the Invention

[0005] Based on this, in view of the problem that it is difficult to reduce the management cost while ensuring precise and efficient management of the existing three-phase imbalance management, it is necessary to provide a method for managing three-phase imbalance and calculating the openable capacity in a distribution area. The present invention is realized through the following technical solutions: A method for managing three-phase imbalance in a distribution area includes the following processes:

[0006] One: Collect the three-phase currents and three-phase voltages at the load end of the distribution area; the three-phase currents include the total current of phase A, the total current of phase B, and the total current of phase C, as well as multiple sub-currents of each phase current; the three-phase voltages include the total voltage at the load end and the sub-voltages corresponding to each sub-current.

[0007] Two: Calculate the apparent total power P at the load end of the distribution area according to the three-phase currents and the total voltage at the load end as:

[0008]

[0009] Where, I A 、IB and I C are the currents of phase A, phase B, and phase C in the total line at the load end of the transformer substation area respectively, and U is the total voltage at the load end;

[0010] Third: Take the average value of the three-phase currents; Take the difference between each phase current and the average value as the corresponding compensation current;

[0011] Fourth: Take the ratio of the maximum compensation current in each phase compensation current to the maximum current in the three-phase currents as the three-phase unbalance degree;

[0012] Fifth: Make the following decisions according to the threshold range of the apparent total power and the three-phase unbalance degree:

[0013] a: If the three-phase unbalance degree is lower than a preset threshold one, no adjustment is made to the three-phase currents;

[0014] b: If the three-phase unbalance degree is between the threshold one and a preset threshold two, and the apparent total power is lower than a preset power threshold, the dynamic compensation method is used to adjust the three-phase currents so that the three-phase

[0015] unbalance degree is lower than the threshold range;

[0016] c: If the three-phase unbalance degree is between the threshold one and a preset threshold two and the apparent total power is not lower than a preset power threshold or the three-phase unbalance degree is higher than a preset threshold two, the automatic phase change method is used to adjust the three-phase currents so that the three-phase unbalance degree is lower than the threshold range.

[0017] The above method for governing three-phase unbalance in the transformer substation area combines the dynamic compensation and automatic phase change methods, achieving precise and efficient governance of three-phase unbalance at the load end of the transformer substation area, while reducing equipment costs and minimizing power losses.

[0018] In one of the embodiments, the calculation method of the compensation current is as follows:

[0019] I RA = I A - I AVG ; I AVG = (I A + I B + I C ) / 3

[0020] I RB = I B - I AVG

[0021] I RC = I C - I AVG

[0022] Among them, I RA , I RB , I RC are the compensation currents of phase A, phase B, and phase C respectively, and I AVG is the average value of the three-phase current.

[0023] In one embodiment, the calculation method of the three-phase unbalance degree is as follows:

[0024] ε = I RMAX / I MAX

[0025] Among them, ε is the three-phase unbalance degree, and I MAX is the maximum value among I A , I B and I C ; I RMAX is the maximum value among I RA , I RB , I RC .

[0026] In one embodiment, the dynamic compensation method includes the following steps:

[0027] b1: Calculate the total power of each phase according to the total voltage and the total current of each phase respectively; calculate the branch power according to each branch current and its corresponding branch voltage;

[0028] b2: Take the ratio of the sum of the branch powers of each phase to the total power of each phase as the compensation ratio;

[0029] b3: Take the product of the compensation ratio and the compensation current of each phase as the actual compensation current of each phase;

[0030] b4: Adjust the current of each phase according to the actual compensation current of each phase so that the three-phase unbalance degree after adjustment is lower than the threshold range.

[0031] In one embodiment, the calculation method of the sum of the branch powers P ALL is as follows:

[0032] P ALL = P A + P B + P C

[0033] P A = U A1 I A1 + U A2 I A2 +…+ U Ai I Ai

[0034] P B=U B1 I B1 +U B2 I B2 +…+U Bj I Bj

[0035] P C =U C1 I C1 +U C2 I C2 +…+U Ck I Ck

[0036] Wherein, P A , P B , P C are the sub - powers of phase A, phase B and phase C in the total line at the load end of the transformer substation area respectively, and i, j, k are the numbers of sub - currents of phase A, phase B and phase C in the total line at the load end of the transformer substation area respectively.

[0037] In one embodiment, the calculation method of the actual compensation current is as follows:

[0038] I A0 =KI RA ; K = P ALL / P

[0039] I B0 =KI RB

[0040] I C0 =KI RC

[0041] Wherein, K is the compensation coefficient.

[0042] In one embodiment, the automatic phase - change method is as follows:

[0043] Combine the multiple sub - currents in each phase into a sub - current set;

[0044] Re - distribute each sub - current in all sub - current sets so that the sum of the sub - currents in each sub - current set tends to be equal;

[0045] Perform phase - change on the current of the replacement group according to the re - combined sub - currents of each phase.

[0046] In one embodiment, the method of sub - current distribution includes the following steps:

[0047] c1: Calculate the sum of the sub - currents of each phase as the actual total current, and take the average value of the actual total currents of the three phases;

[0048] c2: Calculate the difference between the actual total current of each phase and the average value of the total current, and record it as the ideal commutation current of each phase;

[0049] c3: Swap the branch currents of each phase to make the ideal commutation current of each phase tend to zero; there are multiple swapping methods that meet the conditions, and select the one with the least swapping amount as the actual swapping method to reduce the number of commutations.

[0050] The present invention also provides a method for calculating the openable capacity of a power distribution area based on three-phase balance, which includes the following steps:

[0051] S1: Collect the maximum allowable current and the rated output voltage at the load end of the power distribution area, and calculate the rated line capacity D0;

[0052] S2: Statistically record the maximum historical load D at the load end l ;

[0053] S3: Calculate the maximum power loss D of the line according to the maximum historical load at the load end and the corresponding output capacity loss ;

[0054] S4: Statistically record the pre-connected power capacity D p ; The pre-connected power capacity represents the total power consumption of electrical appliances connected to the load end of the power distribution area within a future period of time;

[0055] S4: Calculate the openable capacity D as:

[0056] D = D0 - D l -D loss -D p .

[0057] In one embodiment, the calculation method of the rated capacity is as follows:

[0058] D0 = U0I0

[0059] where U0 is the rated voltage and I0 is the maximum allowable current;

[0060] Correspondingly, the calculation method of the maximum power loss is:

[0061] D loss = (D l0 -D l )D0 / D l0

[0062] where D l0 is the output capacity of the power distribution area when the load end reaches the maximum historical load.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] 1. By combining the dynamic compensation method with the automatic phase conversion method, the present invention conducts governance on the three-phase unbalance within a preset range through dynamic compensation under the condition of a relatively low apparent total power, and conducts governance on the three-phase unbalance not lower than the preset range through the automatic phase conversion method, so as to achieve the purpose of accurately and efficiently governing the three-phase unbalance at the load end of the substation area, while reducing the equipment cost and power loss.

[0065] 2. The automatic phase conversion method adopted by the present invention combines the sub-currents of each phase respectively and then redistributes them. Under the condition of performing phase conversion on the sub-current with the least amount, the purpose of governing the three-phase unbalance is achieved, the impact of the phase conversion process on the overall power consumption of the substation area is reduced, the phase conversion frequency is decreased, the requirements for the phase conversion equipment are relatively low, and the cost of the three-phase unbalance governance equipment is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 is a flowchart of the method for governing the three-phase unbalance in the substation area according to Embodiment 1 of the present invention;

[0067] Figure 2 is according to Figure 1 The structural diagram of the intelligent terminal designed by the method for governing the three-phase unbalance in the substation area;

[0068] Figure 3 is according to Figure 1 The structural schematic diagram of the three-phase unbalance governance equipment in the substation area designed by the method for governing the three-phase unbalance in the substation area;

[0069] Figure 4 is Figure 3 The circuit structural schematic diagram of the three-phase unbalance governance equipment in the substation area; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0070] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0071] It should be noted that when a component is referred to as being "installed on" another component, it can be directly on the other component or there may also be an intermediate component. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time. When a component is considered to be "fixed to" another component, it can be directly fixed to the other component or there may be an intermediate component at the same time.

[0072] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0073] Please refer to Figure 1 , Figure 1 which is a flowchart of the method for managing three-phase imbalance in the power distribution area of this embodiment. This embodiment provides a method for managing three-phase imbalance in the power distribution area. The management method includes the following processes:

[0074] First: Collect the three-phase current and three-phase voltage at the load end of the power distribution area. The three-phase current includes the total current of phase A, the total current of phase B, and the total current of phase C, as well as multiple sub-currents of each phase current. The three-phase voltage includes the total voltage at the load end and the sub-voltages corresponding to each sub-current.

[0075] The load end of the power distribution area is used to supply power to a certain area, such as a residential area, an industrial area, or a commercial area, etc. In actual power consumption, the load end first statistically calculates the power consumption in real time through an electric energy meter and then supplies power to electrical appliances. The current passes through the three-phase circuits of the total load end of the power distribution area to connect each electric energy meter respectively. When collecting the current or voltage at the load end of the power distribution area, it is necessary to collect the total current or total voltage of the three phases of the power distribution area respectively, as well as the sub-currents and sub-voltages connected to both ends of each electric energy meter.

[0076] The method for collecting current or voltage may include connecting a detection circuit respectively outside the three-phase circuit. The detection circuit may include any one or more of a voltmeter, an ammeter, a multimeter, and a transformer. At the total output end of the three-phase circuit, it is necessary to detect the corresponding current and voltage respectively. The three-phase total currents at the total output end of the power distribution area are respectively denoted as I A , I B and I C , and the total voltage is denoted as U. While only one of the current or voltage needs to be detected at both ends of the electric energy meter, and the corresponding current and voltage are calculated according to the real-time power change of the electric energy meter. According to the phase wires connected to each electric energy meter, each sub-current is respectively denoted as the sub-current of phase A I A1 , I A2 , ……, I Ai , the sub-current of phase B I B1 , I B2 , ……, I Bj , and the sub-current of phase C I C1 , I C2 , ……, I Ck .

[0077] Second: Calculate the apparent total power P at the load end of the power distribution area according to the three-phase current and the total voltage at the load end as:

[0078]

[0079] Among them, I A 、I B and I C are the currents of phase A, phase B, and phase C in the total line at the load end of the transformer substation area respectively, and U is the total voltage at the load end.

[0080] III. Take the average value of the three-phase currents. Take the difference between each phase current and the average value as the corresponding compensation current. The calculation method of the compensation current is as follows:

[0081] I RA =I A -I AVG ; I AVG =(I A +I B +I C ) / 3

[0082] I RB =I B -I AVG

[0083] I RC =I C -I AVG

[0084] Among them, I RA 、I RB 、I RC are the compensation currents of phase A, phase B, and phase C respectively, and I AVG is the average value of the three-phase currents.

[0085] IV. Take the ratio of the maximum compensation current in each phase compensation current to the maximum current in the three-phase currents as the three-phase unbalance degree. The calculation method of the three-phase unbalance degree is as follows:

[0086] ε = I RMAX / I MAX

[0087] Among them, ε is the three-phase unbalance degree, I MAX is the maximum value among I A 、I B and I C . I RMAX is the maximum value among I RA 、I BB 、I RC .

[0088] There are generally two calculation methods for the existing three-phase unbalance degree, including:

[0089] ε=(I MAX -IMIN ) / I MAX

[0090] ε = (I MAX -I AVG ) / I AVG

[0091] where I MIN is the minimum value among I A , I B and I C .

[0092] In this embodiment, I RMAX = |I MAX -I AVG | or |I MIN -I AVG |. Compared with the above two calculation methods, the three-phase unbalance degree provided in this embodiment can more clearly describe the unbalanced state of the three-phase current.

[0093] V: Make the following decisions according to the apparent total power and the threshold range of the three-phase unbalance degree:

[0094] a: If the three-phase unbalance degree is lower than a preset threshold one, no adjustment is made to the three-phase current. In this embodiment, the threshold one is set to 10%.

[0095] b: If the three-phase unbalance degree is between the threshold one and a preset threshold two, and the apparent total power is lower than a preset power threshold, a dynamic compensation method is used to adjust the three-phase current so that the three-phase unbalance degree is lower than the threshold range. In this embodiment, the threshold two is set to 15%. The dynamic compensation method includes the following steps:

[0096] b1: Calculate the total power of each phase according to the total voltage and the total current of each phase respectively. Calculate the sub-power according to each sub-current and its corresponding sub-voltage. The total powers of phase A, phase B and phase C are denoted as P A0 = UI A , P B0 = UI B and P C0 = UI C .

[0097] b2: Take the ratio of the sum of the sub-powers of each phase to the total power of each phase as the compensation ratio. The calculation method of the sum of the sub-powers P ALL is as follows:

[0098] P ALL = P A +P B +P C

[0099] P A= U A1 I A1 + U A2 I A2 + … + U Ai I Ai

[0100] P B = U B1 I B1 + U B2 I B2 + … + U Bj I Bj

[0101] P C = U C1 I C1 + U C2 I C2 + … + U Ck I Ck

[0102] Among them, P A , P B , P C are respectively the sum of the sub - powers of phase A, phase B and phase C in the total line at the load end of the transformer substation area. U A , U B and U C are respectively the sub - voltages of phase A, phase B and phase C, and i, j, k are respectively the quantities of sub - currents of phase A, phase B and phase C in the total line at the load end of the transformer substation area.

[0103] b3: Multiply the compensation ratio by the compensation current of each phase as the actual compensation current of each phase. The calculation method of the actual compensation current is as follows:

[0104] I A0 = KI RA ; K = P All / P

[0105] I B0 = KI RB

[0106] I C0 = KI RC

[0107] Among them, K is the compensation coefficient.

[0108] b4: Adjust the current of each phase according to the actual compensation current of each phase so that the compensation current of each phase after adjustment is lower than the threshold range.

[0109] The dynamic compensation of the current of each phase can be completed by the active power filter APF or the static var generator SVG. Taking SVG as an example, assume that in a three - phase unbalanced circuit, I A <IB <I AVG <I C , at a certain instant, the alternating current of phase C is rectified into direct current and stored in the SVG. At another instant, the direct current stored in the SVG is released into phases A and B after inversion, so that the three-phase current reaches a balanced state. Compared with other dynamic compensation methods, SVG dynamic compensation has the advantages of being real-time fast, compensating accurately, and being ready to use immediately.

[0110] c: If the three-phase unbalance degree is between the first threshold and a preset second threshold and the apparent total power is not lower than a preset power threshold, or the three-phase unbalance degree is higher than a preset second threshold, then an automatic phase change method is used to adjust the three-phase current so that the three-phase unbalance degree is lower than the threshold range. The automatic phase change method is as follows:

[0111] Combine the multiple sub-currents in each phase into a sub-current set. The sub-currents in phases A, B, and C are respectively combined into a set, denoted as set A = {I A1 , I A2 , ……, I Ai}, B = {I B1 , I B2 , ……, I Bj}, C = {I C1 , I C2 , ……, I Ck}.

[0112] Reallocate each sub-current in all sub-current sets so that the sum of the sub-currents in each sub-current set tends to be equal. The method of sub-current allocation includes the following steps:

[0113] c1: Calculate the sum of the sub-currents in each phase as the actual total current, and take the average value of the actual total currents of the three phases. The actual total current of each phase is expressed as:

[0114]

[0115]

[0116]

[0117] Among them, I SA , I SB , and I SC are the actual total currents of phases A, B, and C respectively.

[0118] Then the average total current I SAVG is denoted as:

[0119] I SAVG =(I SA +ISB +I SC ) / 3。

[0120] c2: Calculate the difference between the actual total current of each phase and the average value of the total current, and denote it as the ideal commutation current of each phase.

[0121] I RA ′ = I SA -I SAVG

[0122] I RB ′ = I SB -I SAVG

[0123] I RC ′ = I SC -I SAVG

[0124] Among them, I RA ′, I RB ′ and I RC ′ are the ideal commutation currents of phase A, phase B and phase C respectively.

[0125] c3: Swap the branch currents of each phase to make the ideal commutation current of each phase tend to zero. There are multiple swapping methods that meet the conditions. Select the one with the least swapping amount as the actual swapping method to reduce the number of commutations.

[0126] Commutate the current of the replacement group according to the recombined branch currents of each phase.

[0127] In this embodiment, assume that I A , I B and I C are 21A, 21A and 24A respectively, then the three-phase unbalance degree is about 8.3%, and the three-phase current does not need to be adjusted.

[0128] Assume that I A , I B and I C are 18A, 21A and 24A respectively, then the three-phase unbalance degree is 12.5%. If the apparent total power is 8kW and the preset power threshold is 10KW at this time, the dynamic compensation method is used to adjust the three-phase current.

[0129] Assume that I A , I B and I CThey are 30A, 45A, and 24A respectively. Then the three-phase unbalance degree is approximately 36.4%. The automatic phase-changing method is used to adjust the three-phase current. If at this time, the number of branch currents in each phase is five, denoted as A = {5, 7, 5, 6, 7}, B = {6, 10, 12, 8, 9}, C = {3, 7, 5, 4, 5}, then the ideal phase-changing current I RA ′, I RB ′, and I RC ′ are 3A, -12A, and 9A respectively. It can be seen that by swapping the 12A in set B to set C and swapping the 3A in set C to set A, the sum of the branch currents in the three sets is adjusted to 33A. Of course, in practical applications, the number of branch currents in each phase is far more than five. Similarly, the adjustment of the branch currents may not necessarily make the three-phase current exactly balanced, as long as the three-phase unbalance degree is less than 10%. In addition, when the current compensation method switches from dynamic compensation to automatic phase change, the switching of the branch currents is carried out in ascending order. During the switching process, the compensation current of the dynamic compensation changes accordingly.

[0130] In the case of a relatively high apparent total power, the current in each phase is also relatively high. In the case of a relatively high three-phase unbalance degree, the compensation current is also relatively large. If the dynamic compensation method is used, the requirements for the equipment specifications of the dynamic compensation are correspondingly high, which not only increases the equipment cost but also increases the loss during the current inversion process, resulting in a waste of electric energy. In the case of a relatively low apparent total power, the current in each phase is also relatively low, which means that the number of branch currents for power supply is relatively low, and the number of users consuming electricity is small. If the automatic phase-changing method is used to adjust the three-phase current, the adjustment accuracy is relatively low, and it is difficult to adjust the three-phase current to an approximately balanced state by switching a small number of branch currents. Therefore, by combining the dynamic compensation and the automatic phase-changing method, it is possible to achieve precise and efficient management of the three-phase unbalance at the load end of the transformer substation area, while reducing the equipment cost and minimizing the electric energy loss.

[0131] Please combine Figure 2 , which is the structural diagram of the intelligent terminal designed according to the three-phase unbalance management method of Figure 1 . In order to facilitate real-time observation of the change of the three-phase unbalance degree, in this embodiment, an intelligent terminal is also designed to keep track of the change of the three-phase current in real time. The intelligent terminal is equipped with multiple HPLCs for monitoring voltage and current and AUC devices for managing the three-phase unbalance, and the three-phase current data and the management status can be observed in real time.

[0132] When in use, the intelligent terminal first collects multiple current data connected to the three-phase circuit through HPLC and transmits the current data to the intelligent terminal. At the same time, the AC sampling data automatically analyzed by the intelligent terminal is also uploaded synchronously. The intelligent terminal calculates the three-phase unbalance results at the total output end of the transformer substation area and each branch according to the current data and the AC sampling data, and controls the three-phase unbalance of the transformer substation area through the AUC device. The intelligent terminal can be a mobile phone, a computer, a tablet computer, an electronic watch, etc. Taking a mobile phone as an example, an APP for controlling three-phase unbalance can be installed on the mobile phone. All data collected by HPLC can be uploaded to the APP server, so as to establish a remote connection between the three-phase unbalance control APP and HPLC and monitor the three-phase current data in real time.

[0133] In order to maintain the three-phase balance of the transformer substation area and avoid overloading of any one or more phases of current during the peak electricity consumption period, this embodiment also provides a method for calculating the openable capacity of the transformer substation area based on three-phase balance, including the following steps:

[0134] S1: Collect the maximum allowable current and rated output voltage at the load end of the transformer substation area, and calculate the rated capacity D0 of the line. The calculation method of the rated capacity is as follows:

[0135] D0 = U0I0

[0136] Wherein, U0 is the rated voltage and I0 is the maximum allowable current.

[0137] The maximum allowable current at the load end is related to the materials of the transmission lines in the three-phase circuit and environmental factors. Among them, the transmission materials include copper wires, aluminum wires, or aluminum-steel composite wires, etc. The cross-sectional area of the transmission line and the erection structure, etc. are all direct factors affecting the passage of current. The larger the cross-sectional area of the transmission line, the larger the maximum current allowed to pass. Similarly, temperature, humidity, and air pressure in the environment also affect the transmission of current.

[0138] S2: Statistically analyze the maximum historical load D at the load end l . For any transformer substation area, the load within the past five years, the past ten years, or other time ranges can be statistically analyzed, and the maximum load of each phase and the total maximum load can be found.

[0139] S3: Calculate the maximum loss D of the line according to the maximum historical load at the load end and the corresponding output capacity loss . The calculation method of the maximum loss is:

[0140] D loss = (D l0 - D l )D0 / D l0

[0141] Wherein, D l0It is the output capacity of the substation when the load end reaches the maximum historical load.

[0142] Since the impact of environmental factors is difficult to obtain through direct measurement, we can analyze it based on historical data, take the difference between the total output current at the load end of the substation and the actual current consumed by the actual user as the impact value, fit the ratio of the impact value to the total output current in the historical data, and calculate the impact value corresponding to when the total output current reaches the ideal maximum current, which is taken as the maximum loss.

[0143] S4: Count the pre-connected capacity D p The pre-connected capacity represents the total power consumption of electrical appliances connected to the load end of the substation in the future. When there is rectification or construction of circuit equipment within the substation, the total power consumption in the substation will also change accordingly. Statistics are collected for the planned construction circuits in the future, such as one month, half a year or other time periods, to determine the final required pre-connected capacity, so as to ensure sufficient open capacity in the substation and avoid power accidents caused by current overload.

[0144] S4: Calculate the open capacity D as:

[0145] D=D0-D l -D loss -D p .

[0146] The analysis and calculation results of the open capacity are used to predict the power consumption in the future to ensure sufficient and safe power consumption in the substation area, and can be used as reference data for the future three-phase circuit planning in the substation area.

[0147] Please combine Figure 3 and Figure 4 , Figure 3 Based on Figure 1 The schematic diagram of the structure of the three-phase unbalanced treatment equipment in the middle station area designed by the three-phase unbalanced treatment method; Figure 4 for Figure 3 Schematic diagram of the circuit structure of the three-phase unbalanced treatment device in the middle transformer area. According to the above-mentioned three-phase unbalanced treatment method in the transformer area, this embodiment provides a three-phase unbalanced treatment device in the transformer area, which includes: a treatment device, multiple monitoring devices and a controller.

[0148] The monitoring device is divided into three main detection devices and multiple sub-monitoring devices. Among them, the main detection devices are connected to the three-phase main lines at the load end of the transformer area and are used to collect the current and voltage of the three-phase main lines in real time. The main monitoring device can be a detection circuit composed of sensitive elements, including Hall current sensors, voltage sensors, etc. In this embodiment, a detection circuit composed of current transformers and ammeters is adopted to collect the current values of the three-phase main lines. The three current transformers are respectively sleeved outside the three-phase main lines and are used to sense the current passing through each main line and measure the corresponding current value according to the current ratio of the transformers. Each ammeter is connected in series outside a transformer and is used to monitor the current value passing through the corresponding transformer in real time. Since the total output voltage at the load end of the transformer area is generally rated and unchanged, the preset output voltage can be used as the actual voltage, or the output voltage can be directly measured as a constant total voltage value. The voltage at the load end of the transformer area can be directly measured by a voltmeter or a multimeter and does not need to be monitored in real time.

[0149] The sub-monitoring devices are used to detect the real-time power consumption current and voltage at the user end. Since an electric energy meter is often installed at the input end of the user end, the sub-current or sub-voltage at the user end can be directly measured and calculated through the electric energy meter. For example, the power consumption voltage in a residential area can be regarded as 220V. According to the power consumption and power consumption time measured by the electric energy meter, the real-time power consumption current can be obtained as:

[0150] I n =W t / 220t

[0151] Wherein, I n is the sub-current of any user end, t is the detection duration, and W t is the power consumption of the user end during the duration t.

[0152] Of course, in actual power consumption, the sub-voltage of each user end will be affected by line loss and load change. Therefore, in order to improve the accuracy of current monitoring, a voltmeter can be connected in parallel in the electric energy meter to monitor the sub-voltage value passing through the electric energy meter in real time, and then calculate the corresponding sub-current.

[0153] The rectification device is used to adjust the load current of the three-phase main lines through corresponding technical means when the three-phase is unbalanced, so that the current in the three-phase main lines tends to be balanced. The rectification device includes a current dynamic compensation device and multiple phase change switches. Among them, the current dynamic compensation device is used to directly adjust the current of the three-phase main lines so that the total current of each phase tends to be equal. The adjustment method is to convert the part of the alternating current exceeding the average current in the three-phase main lines into direct current and store it in the energy storage device, and then invert the direct current into alternating current and distribute it to the circuits with current lower than the average current.

[0154] The current dynamic compensation device may include a capacitor, and one or both of an active power filter (APF) and a static var generator (SVG). Taking SVG as an example, the SVG is respectively connected to the three-phase main line. Three parallel current conversion circuits are provided inside the SVG. The current conversion circuit has the functions of converting direct current into alternating current and converting alternating current into direct current. A composite transistor IGBT is respectively connected in series in each current conversion circuit for controlling the on / off state of the corresponding current conversion circuit. The capacitor is connected in series in the SVG and is respectively connected to the three current conversion circuits. After the three-phase unbalance degree of the three-phase main circuit exceeds the preset range, the SVG receives a compensation current signal, converts the alternating current exceeding the average current value in the three-phase circuit into direct current and stores it in the capacitor, and then converts the direct current of the capacitor into alternating current and distributes it to the other phase main circuits lower than the average value respectively. During this process, the IGBT is used to control the on / off state of the current conversion circuit to control the conversion of current. For example, when the current of phase C is higher than the average current, and the currents of phases A and B are both lower than the average current, the IGBT controls the current conversion circuit connected to the phase C line to convert part of the alternating current into direct current, while the current conversion circuits connected to the other two-phase lines convert the direct current in the capacitor into alternating current according to the compensation current value and distribute it to the corresponding main phase lines. In this embodiment, each current conversion circuit includes a rectifier and an inverter connected in series, and an IGBT is connected between the rectifier and the inverter for controlling the current direction. The rectifier is used to convert the alternating current higher than the average current in each phase circuit into direct current. The inverter is used to convert direct current into alternating current. Of course, in other embodiments, other methods can also be used for circuit conversion, such as using transistors, chips, etc.

[0155] Each phase change switch is connected to a user terminal, such as being connected to the input end of the electric energy meter and the output end of the three-phase main circuit. The phase change switch is used to switch the phase line connected to the user terminal. The phase lines connected to the user terminal are different. Generally speaking, most residential and commercial areas are single-phase power supply. While industrial areas include single-phase power supply and three-phase power supply, and the specific power supply ratio depends on the electrical appliances of the load. For a user terminal with single-phase power supply, the used electric energy meter is often only connected to one of the main phase lines. In order to maintain the basic balance of the three-phase current, the single-phase power supply in the same distribution area needs to be evenly distributed from the three-phase main line. However, due to the different electricity consumption situations and power consumption of each user at the same time, it is difficult for the three-phase main circuit to achieve the basic balance of current. By using the phase change switch, the phase line connected to the user terminal can be switched, thereby changing the load state in the three-phase main line and making the current of the three-phase main circuit basically reach the balanced state.

[0156] The phase-changing switch includes a housing and a control circuit. The input end of the control circuit is connected to the three-phase circuit respectively, and the output end of the control circuit is connected to the user end. When the phase-changing switch is not working, the user end is connected to one of the phase main lines through the phase-changing switch, and is not connected to the other phase main lines. The control circuit is used to switch the phase line connected to the user end according to the phase-changing signal sent by the controller. The control circuit is contained in the housing to prevent the control circuit from being accidentally touched and causing power accidents, and also to prevent potential risks caused by manual phase-changing by users or construction personnel.

[0157] The control circuit can be a circuit composed of multiple switches for controlling the on and off of each phase line, or a microcircuit composed of transistors, or a chip with the on and off function of the control circuit. In consideration of cost and actual installation conditions, this embodiment uses two electromagnetic relays and a number of wires to form a control circuit. The magnetic contacts of the two electromagnetic relays are respectively connected to the controller for receiving the output signal of the controller. In order to distinguish the circuit structure of the electromagnetic relay, the first relay and the second relay are named. In actual installation, when the control circuit is not started, the user end is only connected to any one phase of the main line. Taking the A phase line as an example, the two normally closed contacts of the first electromagnetic relay are respectively connected to the user end and the A phase circuit, and the two normally open contacts are respectively connected to the user end and the B phase circuit. The two normally closed contacts of the second electromagnetic relay are respectively connected between the B phase circuit and the normally open contacts of the first electromagnetic relay, and the two normally open contacts of the second electromagnetic relay are respectively connected between the user end and the C phase circuit. When the three-phase imbalance exceeds the predetermined threshold range, the controller sends a phase change signal to control the phase change switch to switch the connected phase line. The specific working process of the control circuit is as follows:

[0158] Ⅰ. When the controller does not send out a phase change signal, the B-phase and C-phase circuits are not conducting. The A-phase circuit is conducting with the client and is used to supply power to the client.

[0159] Ⅱ. When the controller sends a signal to switch the B-phase circuit, the magnetic contacts of the first electromagnetic relay are energized, the normally open contacts and normally closed contacts of the first electromagnetic relay switch to the conducting state, the A-phase circuit and the C-phase circuit are not conducting, and the B-phase circuit is conducting with the client to supply power to the client.

[0160] III. When the controller sends a signal to switch the C-phase circuit, the magnetic contacts of the first electromagnetic relay and the magnetic contacts of the second electromagnetic relay are energized at the same time, all normally open contacts and normally closed contacts switch to the conducting state, the A-phase circuit and the B-phase circuit are not conducting, and the C-phase circuit is conducting with the client to supply power to the client.

[0161] The controller can calculate the three-phase imbalance and the corresponding compensation current based on the collected current, voltage and other data. Then the control device can adjust the current of each phase to make the three-phase current tend to be balanced. Specifically, the controller is used to:

[0162] 1. Calculate the three-phase unbalance degree based on the three-phase current as follows:

[0163] ε = (I MAX - I MIN ) / I MAX

[0164] where ε is the three-phase unbalance degree, I MAX is the maximum value among I A , I B and I C , I MIN is the minimum value among I A , I B and I C , and I A , I B and I C are the currents of phase A, phase B, and phase C in the main line at the load end of the transformer substation area, respectively.

[0165] 2. Take the average value of the three-phase current. Use the difference between each phase current and the average value as the corresponding compensation current. The calculation method of the compensation current is as follows:

[0166] I RA = I A - I AVG ; I AVG = (I A + I B + I C ) / 3

[0167] I RB = I B - I AVG

[0168] I RC = I C - I AVG

[0169] where I RA , I RB , I RC are the compensation currents of phase A, phase B, and phase C respectively, and I AVG is the average value of the three-phase current.

[0170] 3. Calculate the apparent total power P at the load end of the transformer substation area based on the three-phase current and the total voltage at the load end as follows:

[0171]

[0172] where U is the total voltage at the load end.

[0173] 4. Make the following decisions based on the apparent total power and the threshold range of the three-phase unbalance degree:

[0174] a: If the three-phase unbalance degree is lower than a preset threshold one, no adjustment is made to the three-phase current. In this embodiment, the threshold one is set to 10%.

[0175] b: If the three-phase unbalance degree is between the threshold one and a preset threshold two, and the apparent total power is lower than a preset power threshold, the dynamic compensation method is used to adjust the three-phase current so that the three-phase unbalance degree is lower than the threshold range. In this embodiment, the threshold two is set to 15%.

[0176] The working process of the dynamic compensation device is as follows:

[0177] b1: Calculate the total power of each phase according to the total voltage and the total current of each phase respectively. Calculate the branch power according to each branch current and its corresponding branch voltage.

[0178] b2: Take the ratio of the sum of the branch powers of each phase to the total power of each phase as the compensation ratio. Among them, the calculation method of the sum of the branch powers P ALL is as follows:

[0179] P ALL = P A + P B + P C

[0180]

[0181]

[0182]

[0183] Among them, P A , P B , P C are the branch powers of phase A, phase B, and phase C in the total line at the load end of the transformer substation respectively, U A , U B and U C are the branch voltages of phase A, phase B, and phase C respectively, and i, j, k are the numbers of branch currents of phase A, phase B, and phase C in the total line at the load end of the transformer substation respectively.

[0184] b3: Take the product of the compensation ratio and the compensation current of each phase as the actual compensation current of each phase. Among them, the calculation method of the actual compensation current is as follows:

[0185] I A0 = KI RA . K = P ALL / P

[0186] I B0 = KI RB

[0187] I C0 = KI RC

[0188] where K is a compensation coefficient, and I RA 、I RB 、I RC are the compensation currents of phase A, phase B, and phase C, respectively.

[0189] b4: Adjust the currents of each phase according to the actual compensation current of each phase so that the three-phase unbalance degree after adjustment is lower than the threshold range.

[0190] c: If the three-phase unbalance degree is between a threshold one and a preset threshold two and the apparent total power is not lower than a preset power threshold, or the three-phase unbalance degree is higher than a preset threshold two, then use the automatic phase change method to adjust the three-phase current so that the three-phase unbalance degree is lower than the threshold range.

[0191] The working process of the phase change switch is as follows:

[0192] Combine the multiple sub-currents in each phase into a sub-current set. Combine the sub-currents in phase A, phase B, and phase C into a set, denoted as set A = {I A1 ,I A2 ,……,I Ai}, B = {I B1 ,I B2 ,……,I Bj}, C = {I C1 ,I C2 ,……,I Ck}.

[0193] Reallocate each sub-current in all sub-current sets so that the sum of the sub-currents in each sub-current set tends to be equal. The method of sub-current allocation includes the following steps:

[0194] c1: Calculate the sum of the sub-currents in each phase as the actual total current, and take the average value of the actual total currents of the three phases. The actual total current of each phase is expressed as:

[0195]

[0196]

[0197]

[0198] where I SA 、I SB and I SC are the actual total currents of phase A, phase B, and phase C, respectively.

[0199] Then the average value of the total current I SAVG is denoted as:

[0200] I SAVG = (I SA + I SB + I SC ) / 3.

[0201] c2: Calculate the difference between the actual total current of each phase and the average value of the total current, and denote it as the ideal commutation current of each phase.

[0202] I RA ' = I SA - I SAVG

[0203] I RB ' = I SB - I SAVG

[0204] I RC ' = I SC - I SAVG

[0205] Wherein, I RA ', I RB ' and I RC ' are the ideal commutation currents of phase A, phase B, and phase C respectively.

[0206] c3: Swap the branch currents of each phase to make the ideal commutation current of each phase tend to zero. There are multiple swapping methods that meet the conditions. Select the one with the least swapping amount as the actual swapping method to reduce the number of commutations.

[0207] Commute the current of the replacement group according to the recombined branch currents of each phase.

[0208] In this embodiment, assume that I A , I B and I C are 21A, 21A, and 24A respectively, then the three-phase unbalance degree is about 8.3%, and the three-phase current does not need to be adjusted.

[0209] Assume that I A , I B and I C are 18A, 21A, and 24A respectively, then the three-phase unbalance degree is 12.5%. If the apparent total power is 8kW and the preset power threshold is 10KW at this time, the dynamic compensation method is used to adjust the three-phase current.

[0210] Assume that I A , I B and I CThey are 30A, 45A, and 24A respectively. Then the three-phase unbalance degree is approximately 36.4%. The automatic phase-changing method is used to adjust the three-phase current. If at this time, the number of branch currents in each phase is five, denoted as A = {5, 7, 5, 6, 7}, B = {6, 10, 12, 8, 9}, C = {3, 7, 5, 4, 5}, then the ideal phase-changing current I RA ′, I RB ′, and I RC ′ are 3A, -12A, and 9A respectively. It can be seen that by swapping the 12A in set B to set C and swapping the 3A in set C to set A, the sum of the branch currents in the three sets is adjusted to 33A. Of course, in practical applications, the number of branch currents in each phase is far more than five. Similarly, the adjustment of the branch currents may not necessarily make the three-phase current exactly balanced, as long as the three-phase unbalance degree is less than 10%. In addition, when the current compensation method is switched from dynamic compensation to automatic phase change, the switching of the branch currents is carried out in ascending order. During the switching process, the compensation current of the dynamic compensation changes accordingly.

[0211] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0212] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A method for managing three-phase imbalance in a transformer substation area, which is used to adjust the three-phase current at the load end of the transformer substation area to make the three-phase current tend to be balanced and reduce the power consumption loss caused by three-phase imbalance; characterized in that, It includes the following processes: One: Collect the three-phase current and three-phase voltage at the load end of the substation area; the three-phase current includes the total current of phase A, the total current of phase B, and the total current of phase C, as well as multiple sub-currents of each phase current; the three-phase voltage includes the total voltage at the load end and the sub-voltage corresponding to each sub-current; Two: Calculate the apparent total power P at the load end of the substation area according to the three-phase current and the total voltage at the load end as: Among them, I A , I B and I C are respectively the currents of phase A, phase B and phase C in the total line at the load end of the substation area, and U is the total voltage at the load end; Three: Take the average value of the three-phase current; take the difference between each phase current and the average value as the corresponding compensation current; Four: Take the ratio of the maximum compensation current in each phase compensation current to the maximum current in the three-phase current as the three-phase unbalance degree; Five: Make the following decisions according to the threshold range of the apparent total power and the three-phase unbalance degree: a: If the three-phase unbalance degree is lower than a preset threshold one, no adjustment is made to the three-phase current; b: If the three-phase unbalance degree is between the threshold one and a preset threshold two, and the apparent total power is lower than a preset power threshold, a dynamic compensation method is used to adjust the three-phase current so that the three-phase unbalance degree is lower than the threshold range; c: If the three-phase unbalance degree is between the threshold one and a preset threshold two and the apparent total power is not lower than a preset power threshold or the three-phase unbalance degree is higher than a preset threshold two, an automatic phase change method is used to adjust the three-phase current so that the three-phase unbalance degree is lower than the threshold range; Among them, the dynamic compensation method includes the following steps: b1: Calculate the total power of each phase according to the total voltage and the total current of each phase respectively; calculate the corresponding sub-power according to each sub-current and its corresponding sub-voltage; b2: Take the ratio of the sum of the sub-powers of each phase to the total power of each phase as the compensation ratio; b3: Take the product of the compensation ratio and the compensation current of each phase as the actual compensation current of each phase; b4: Adjust each phase current according to the actual compensation current of each phase so that the three-phase unbalance degree after adjustment is lower than the threshold range; Among them, the sum of the sub - powers P ALL is calculated as follows: P ALL = P A + P B + P C P A = U A1 I A1 + U A2 I A2 + … + U Ai I Ai P B = U B1 I B1 + U B2 I B2 + … + U Bj I Bj P C = U C1 I C1 + U C2 I C2 + … + U Ck I Ck Wherein, P A 、P B 、P C are the sub - powers of phase A, phase B, and phase C in the total line at the load end of the transformer substation area respectively, U A 、U B and U C are the sub - voltages of phase A, phase B, and phase C respectively, and i, j, k are the quantities of sub - currents of phase A, phase B, and phase C in the total line at the load end of the transformer substation area; I A1 、I A2 、……、I Ai are the 1st, 2nd, ……, i - th sub - currents of phase A respectively, I B1 、I B2 、……、I Bj are the 1st, 2nd, ……, j - th sub - currents of phase B respectively, I C1 、I C2 、……、I Ck are the 1st, 2nd, ……, k - th sub - currents of phase C respectively; U A1 、U A2 、……、U Ai are the 1st, 2nd, ……, i - th sub - voltages of phase A respectively, U B1 、U B2 、……、U Bj are the 1st, 2nd, ……, j - th sub - voltages of phase B respectively, U C1 、U C2 、……、U Ck are the 1st, 2nd, ……, k - th sub - voltages of phase C respectively; Among them, the calculation method of the actual compensation current is as follows: I A0 = KI RA ; K = P ALL / P I B0 = KI RB I C0 = KI RC Wherein, I RA , I RB , I RC are the compensation currents of phase A, phase B, and phase C respectively, and K is the compensation coefficient.

2. The method for managing three-phase imbalance in a transformer substation area according to claim 1, wherein The calculation method of the compensation current is as follows: I RA = I A - I AVG ; I AVG = (I A + I B + I C ) / 3 I RB = I B - I AVG I RC = I C - I AVG Among them, I AVG is the average value of the three-phase current.

3. The method for governing three-phase imbalance in a transformer substation area according to claim 1, characterized in that, The automatic phase change method is as follows: Combine the multiple sub-currents in each phase into a sub-current set; Re-distribute each sub-current in all sub-current sets so that the sum of the sub-currents in each sub-current set tends to be equal; Perform phase change on the current of the replacement group according to the reorganized sub-current of each phase.

4. The method for governing three-phase imbalance in a substation area according to claim 3, wherein, The method of sub-current distribution includes the following steps: c1: Calculate the sum of the sub-currents of each phase as the actual total current, and take the average value of the actual total currents of the three phases; c2: Calculate the difference between the actual total current of each phase and the average value of the total current, and record it as the ideal phase change current of each phase; c3: Exchange the sub-currents of each phase so that the ideal phase change current of each phase tends to zero; there are multiple exchange methods that meet the conditions, and select the one with the least exchange amount as the actual exchange method to reduce the number of phase changes.

5. A method for calculating the openable capacity of a power distribution area based on three-phase balance, which adjusts the three-phase current of the power distribution area through the three-phase unbalance control method described in any one of claims 1 to 4, and then calculates the openable capacity in the three-phase balanced power distribution area circuit; characterized in that, It includes the following steps: S1: Collect the maximum allowable current and rated output voltage at the load end of the substation area, and calculate the line rated capacity D0; S2: Statistically analyze the maximum historical load D at the load end l ; S3: Calculate the maximum loss D of the line according to the maximum historical load of the load side and the corresponding output capacity loss ; S4: Statistically calculate the pre-connected capacitance D p ; The pre-connected capacitance characterizes the total electricity consumption of electrical appliances connected to the load end of the transformer substation within a future period of time; S4: Calculate the openable capacity D as: D = D0 - D l -D loss -D p 。 6. The openable capacity calculation method for a transformer substation area based on three-phase balance according to claim 5, characterized in that The calculation method of the rated capacity is as follows: D0 = U0I0 where U0 is the rated voltage and I0 is the maximum allowable current; Correspondingly, the calculation method of the maximum loss is: D loss = (D l0 - D l ) D0 / D l0 Among them, D l0 is the output capacity of the transformer substation area when the load end reaches the maximum historical load capacity.

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