TWI610508B - Method for adjusting three-phase balance for distribution transformer wiring - Google Patents

Abstract

The invention relates to a three-phase balanced phase adjustment method for a distribution transformer connection, which is mainly connected with an automatic commutation switching switch on the high voltage side of the distribution transformer, and then the automatic commutation switching switch is connected to the three-phase high-voltage distribution feeder. The automatic commutation switch is connected with a microelectronic controller. Under normal power supply conditions, the high voltage side of the distribution transformer is only connected to the single phase of the three-phase high voltage distribution feeder, and the microelectronic controller is used to control the automatic conversion. According to this, the micro-electronic controller is used to control the automatic commutation switch to control the connection of the distribution transformers, effectively improve the three-phase unbalance of the three-phase high-voltage distribution feeder, and reduce the three-phase voltage. Balance rate to reduce power transmission losses.

Description

Three-phase balanced phase adjustment method for distribution transformer wiring

The invention relates to a three-phase balanced phase adjustment method for distribution transformer wiring, in particular to a micro-electronic controller for controlling an automatic commutation switch to control the connection of distribution transformers, and effectively improving the three-phase high-voltage distribution feeder In the case of phase imbalance, the three-phase voltage unbalance rate is reduced, so that the power transmission loss can be reduced, and the three-phase balanced phase adjustment method of the distribution transformer wiring with more practical and practical characteristics is used.

According to the power system, in the process of power supply, there will be many problems that cause the power quality to drop. Among them, the three-phase imbalance is a big problem.

The power system theoretically balances the three-phase voltage supply. The three-phase voltage balance is defined as the equalization of the three-phase voltage and the phase of any two phases needs to be 120 degrees apart. If the three-phase power supply does not meet any of the two conditions, Called three-phase unbalance, and the actual power The system is often affected by different types of power load types, power consumption time changes and power supply types, resulting in three-phase unbalance problems. When three-phase unbalance occurs, the line transmission loss may occur, and the power supply of the power grid may be generated. In addition, when the three-phase unbalance is severe, the motor equipment such as the motor will be overheated, noise will be generated, the output torque will be reduced, and even the equipment will be burnt, which will greatly affect the running performance and life of the motor, resulting in false alarms for the protection of the power grid. Power supply stability has decreased. The reason for the three-phase imbalance can be roughly divided into the following factors:

1. Impedance imbalance factor: Since the line planning of the power distribution system is affected by the environment and the location of the user, the structure of the power distribution system needs to consider the surrounding terrain and user demand constraints, and it needs to cooperate with the client to design, and the line architecture is in addition to the general three-phase. Outside the line, there are also single-phase and two-phase lines for the user's power supply structure, which makes the transmission and distribution lines easy to generate three-phase unbalance; in addition, the distance between the feeder lines of each phase is not equal, which will produce different sizes of mutual inductance, so that the impedance of the feeder is non- Symmetry, even if the three-phase current is balanced, the voltage drop generated by each phase is also different, resulting in unbalanced three-phase voltage at the power receiving end. In addition, the distribution transformer has many wiring methods, which may be used with electrical load requirements or protection system reliability. The requirements vary, or with the different feeder structure, and the adaptive wiring mode, the three-phase impedance will be uneven when the power supply, and the three-phase impedance is asymmetrical, which leads to the three-phase voltage imbalance problem.

2. Load imbalance factor: Due to the user load characteristics, it is necessary to consider the power consumption time and load type. When the three-phase system needs to supply single-phase power, it is easy to cause unbalance situation; although the load can be evenly distributed during planning Assigned to each phase feeder for power supply, but It is impossible to ensure that all loads are used at the same time. When the usage time of various loads is different, it will easily lead to different supply loads of different phases, thus causing three-phase unbalance.

3. Fault imbalance factor: Adding a capacitor or static virtual power compensator on the line can effectively compensate the imaginary part current and reduce the three-phase current value of the feeder. The capacitors available for grid connection have single-phase capacitors and Δ wiring three-phase. Capacitor (5) [please refer to the schematic diagram of the conventional Δ wiring power capacitor shown in Figure 7] and the Y-connected three-phase capacitor (6) (please refer to the schematic diagram of the existing Y wiring power capacitor shown in Figure 8). The Δ wiring capacitor can lock the harmonic current in the Δ loop and has the function of filtering. The Y wiring is the main form adopted by the current domestic power distribution system; when the capacitor is affected by external force, such as lightning strike or current surge, it may cause Capacitor damage failure, resulting in unbalanced three-phase virtual power compensation of the line, causing high neutral current and voltage changes, etc., not only cause transmission loss, but also increase the possibility of power system failure.

4. Maintenance imbalance factor: When the distribution line performs maintenance, reconstruction or fault isolation, the load on the original feeder must be transferred to the other feeders for power supply. When the load is transferred, the line switching is mostly carried out for each phase. Therefore, a considerable neutral current will be generated during the switching. This neutral current is generated due to the switching process, so the duration is short, but it may cause the power to judge abnormally and cause jump, which affects the power quality and reliability. .

At present, the literature has proposed installing compensation equipment and adopting appropriate control strategies to improve the voltage problem of unbalanced power distribution systems to improve the quality of power supply; The challenges are as follows:

1. Adding distribution transformers: Power supply is provided by the main domestically-developed Y-open Δ wiring method. The wiring method is composed of two distribution transformers, which are composed of three-phase wiring, which will cause a large three-phase voltage unbalance rate. A distribution transformer can be added to form a complete three-phase wiring. By adding a transformer and powering the single-phase load and three-phase load separately from different transformer groups, the three-phase voltage imbalance can be effectively improved. The problem is that the improvement strategy still needs to consider the investment in expansion equipment such as poles, wires and cross-arms, and it is necessary to consider the difficulties faced by the practical execution surfaces such as setting space and public perception.

2. Adjusting the connection phase of the distribution transformer: For a single node in the power distribution system, because it needs to supply three-phase and single-phase load power at the same time, it may cause uneven power consumption of each phase, which leads to three-phase unbalance. The situation occurs, and when the currents of the high-voltage feeders are uneven, the three-phase unbalance will be more serious, so the connection of the open Y-open D distribution transformers used in the domestic system can be adjusted to effectively reduce the situation. The degree of unbalanced load of each phase feeder reaches the goal of mitigating the three-phase imbalance problem; however, during the improvement strategy, the power supply must be cut off to ensure the safety of the construction personnel, and the user may have a long power outage and pay a high power outage. Cost, in addition, manual execution of the commutation operation requires not only a high labor cost implementation, but also an adaptive adjustment with changes in load usage time.

3. Installation of energy storage system: The energy storage system is applied when the load of the feeder in the system is at a peak, releasing the stored energy supply load to share the load on the feeder, which can promote the load of each phase feeder supply. Balance, you can also reduce each feeder The power supply at the peak time reduces the line current and voltage drop, thus effectively improving the three-phase unbalance of the system; however, the energy storage system and its related control technology are not yet mature, and the energy storage system is still high in price, belonging to the advanced power grid. Equipment, its practical application benefits are open to question.

4. Install static virtual power compensator: The improvement of three-phase unbalance can be achieved by adding static virtual compensator (S) to the appropriate position of the power distribution system (please refer to the ninth figure). The schematic diagram of the existing static virtual power compensator is mainly composed of power electronic components (71), capacitors (72) and reactors (73), and the static virtual power compensator (7) can compensate the virtual power of the feeder. The line current value is reduced, the transmission power factor is increased, the line loss is reduced, and the feeder voltage can be adjusted by the static virtual power compensator (7) to achieve an improvement of the three-phase imbalance; however, the static virtual power compensator is expensive. The investment cost will be greatly increased. In addition, the static virtual power compensator has the disadvantage of injecting harmonic current into the power system.

After the domestic power industry is operating in the power distribution system, it is used to improve the three-phase unbalance. The main method is to manually perform the connection of the distribution transformers to balance the feeder load to reduce the three-phase voltage imbalance. However, this approach will likely cost a large blackout and labor costs and will not be able to achieve immediate adjustments.

In view of this, the inventor has provided the experience of rich design, development and actual production of the relevant industry for many years, and has made research and improvement on the existing technical methods and defects, and provided a three-phase balanced phase adjustment method for distribution transformer wiring, in order to achieve effective change Good three-phase imbalance problem.

The main object of the present invention is to provide a three-phase balanced phase adjustment method for distribution transformer wiring, which mainly uses a microelectronic controller to control an automatic commutation switch to regulate the connection of distribution transformers, and effectively improve the three-phase high-voltage distribution feeder. The three-phase unbalance condition reduces the three-phase voltage unbalance rate, so as to reduce the power transmission loss, and the utility model has more practical utility characteristics in its overall implementation.

The main purpose and effect of the three-phase balanced phase adjustment method for the distribution transformer of the present invention are achieved by the following specific technical means: the automatic switching switch is connected to the high voltage side of the distribution transformer, so that the automatic commutation switching The switch is connected to the three-phase high-voltage distribution feeder, and the automatic commutation switch is connected with a micro-electronic controller, and the micro-electronic controller is used to control the switching of the automatic commutation switch, and the control of the micro-electronic controller is Including: a. Reduce the maximum voltage unbalance rate evaluation index of the controlled power system: The calculation method of the voltage unbalance rate is based on the line voltage of the three-phase power supply, as shown in the following formula:

Where |V _ab |, |V _bc |, |V _ca | is the line voltage value of the three-phase system, V _avg is the average value of the three-phase line voltage; the improvement of the voltage imbalance rate can be equivalent to the risk assessment index And can represent the following formula:

Where f ₁ is the first evaluation indicator, N _B is the total number of nodes installing the automatic phase change switch, and V _i ^avg is the average value of the three-phase line voltage of the i-th node, V _i ^ab , V _i ^bc , V _i ^Ca is the line voltage value of the three-phase of the i-th node; b. reducing the maximum neutral current value of the controlled power system: the improvement of the neutral current can be equivalent to the safety evaluation index, and The evaluation indicator is expressed as follows:

Wherein f ₂ is a second evaluation index, I _i ^N for the line current of the i-th among the nodes, I _i ^a, I _i ^b I _i ^c of the three-phase currents i-th nodes, which second The evaluation index is also calculated after obtaining the neutral current value of each node, taking the maximum neutral current value of the system as the basis for regulation; c. The evaluation of the power supply loss of the controlled power system: evaluating the power supply of the controlled power system The loss of electrical energy can be equivalent to an economic evaluation indicator, and the evaluation indicator can be expressed as follows:

. d Analysis of a decision result obtained by evaluation index: The analysis of these three evaluation index, so that the controller may have a microelectronic follow decision-making, the decision result is obtained appropriately, so that the objective function as shown in the following equation: Min F ( X _c , X _d )= w ₁ f ₁ + w ₂ f ₂ + w ₃ f ₃

Where X _c is the vector consisting of the control variables to be solved, the control variable is a set of all the distribution transformers in the distribution network that need to be adjusted, and X _d is the vector composed of the dependent variables to be solved. The control variable is substituted into the system for power flow calculation, and the dependent variable is the three-phase line voltage and the three-phase phase current of each node obtained after the power flow calculation, and w ₁ , w ₂ and w ₃ are the target component weights of the consideration.

The three-phase balanced phase adjustment method for the distribution transformer of the invention, wherein the reduced voltage unbalance rate evaluation index of the controlled power system is further considered, the power flow of the distribution network is in accordance with the principle of balance of power supply and demand, and the supply and demand of the power flow network power flow The balance constraints are expressed as follows:

Wherein, P _i+1 and Q _i+1 respectively represent real power and virtual power flowing out of the i+1th node; P _L,i+1 and Q _L,i+1 respectively represent the supply of the i+1th node Real power and virtual power; V _i is the voltage of the i-th node; R _i,i+1 and X _i,i+1 are the resistance and reactance of the line connecting the i-th node and the i+1th node.

The three-phase balanced phase adjustment method for the distribution transformer of the present invention, wherein the maximum voltage unbalance rate evaluation index of the controlled power system is reduced, when the voltage unbalance rate is too high, the voltage unbalance rate is limited, and the voltage imbalance is The rate limit is expressed as follows:

Among them, (VU%) _i is the voltage imbalance rate of the i-th node. From this formula, the voltage unbalance rate of each node needs to be less than the upper limit of (VU%) _max , and the voltage imbalance rate is limited. Set to 2%.

The three-phase balanced phase adjustment method for the distribution transformer of the present invention, wherein the maximum neutral current value evaluation index of the controlled power system is reduced, and the upper limit value of the neutral current is taken into account when performing the power flow calculation of the commutation control In order to ensure the safe operation of the system, the limit of the neutral current can be expressed as follows:

Where I _i ^N represents the neutral current of the i-th node, and the neutral current value of each node needs to be lower than the upper limit of the neutral current specified by the domestic electric industry. The specification is that the neutral current is not available. More than 120 amps.

The three-phase balanced phase adjustment method for the distribution transformer of the present invention, wherein, in order to ensure the stability of the power supply voltage of the power system and avoid damage caused by the use of an inappropriate voltage of the electrical equipment, it is necessary to limit the three-phase phase voltage to be maintained within a feasible range, and to three-phase The phase voltage limit expression is expressed as follows:

Wherein, V _i ^a , V _i ^b and V _i ^c are the three-phase voltages of the i-th node, and V _i ^min and V _i ^max are the minimum and maximum values of the safe operation voltage, and the voltage operation limit value is set to The value of 0.95 is between 1.05 and the value of the standard.

The three-phase balanced phase adjustment method for the distribution transformer of the present invention, wherein in the power system, each feeder has its upper limit of the transmission capacity, and the corresponding limit is as follows:

Wherein, I _l ^a , I _l ^b and I _l ^c are the three-phase line currents of the first feeder, and I _l ^max is the rated capacity of the first feeder, and each line current needs to be smaller than the rated value that the feeder can transmit.

(1)‧‧‧Distribution transformer

(2) ‧‧‧Automatic commutation switch

(3)‧‧‧Three-phase high-voltage distribution feeder

(4) ‧‧‧Microelectronic Controller

(5) ‧‧‧Δ wiring three-phase capacitor

(6)‧‧‧Y wiring three-phase capacitor

(7)‧‧‧Static virtual power compensator

(71)‧‧‧Power electronic components

(72)‧‧‧ Capacitors

(73)‧‧‧Reactor

First: Schematic diagram of the architecture of the present invention

Second: Schematic diagram of the zero crossing point of the detected voltage waveform of the present invention

Third figure: schematic diagram of the test system of the present invention

The fourth figure: the unbalanced rate of each busbar voltage of the modified 13-node system of the present invention Improve comparison chart

Fig. 5: Comparison of voltage imbalance ratio results of each node of the optimal control strategy under the three objectives of the present invention

Figure 6: Comparison of the results of the neutral currents of the optimal control strategy improved by the three objectives of the present invention

Figure 7: Schematic diagram of the existing Δ wiring power capacitor

Figure 8: Schematic diagram of existing Y-connected power capacitors

Figure IX: Schematic diagram of the existing static virtual power compensator

For a more complete and clear disclosure of the technical content, the purpose of the invention and the effects thereof achieved by the present invention, the following is a detailed description, and please refer to the illustrated drawings and drawings: first, due to domestic The distribution transformer installed in the distribution network mainly adopts the Y-open Δ wiring to supply the power consumption required by the three-phase and single-phase load users. Please refer to the first diagram, which is shown in the schematic diagram of the present invention. The automatic commutation switch (2) is connected to the high voltage side of the distribution transformer (1), and the automatic commutation switch (2) is connected to the three-phase high voltage distribution feeder (3), the automatic commutation switch (2) It can be composed of a high-power thyristor or a power transistor, and the automatic commutation switch (2) is connected with a micro-electronic controller (4). Under normal power supply conditions, the distribution transformer (1) The high voltage side is only connected to the three-phase high voltage distribution feeder (3) Single phase.

Among them, because the power transistor switch is turned on or off, the power transistor switch still has voltage and current at the same time, which causes the switch to continuously generate power consumption and easily cause the switch to be damaged. Therefore, zero voltage switching (ZVS) can be applied. The power transistor switch is controlled by a soft cutting method such as zero current switching (ZCS), that is, when the switch cross voltage is zero or no current flows through the switch, switching is performed, which can effectively reduce the generation during switching. Switching losses. In addition, since the voltage waveform and the current waveform of the alternating current have zero crossing characteristics, that is, when the voltage or current waveform changes from a positive half cycle to a negative half cycle (positive value becomes a negative value), or the waveform changes from a negative half cycle During the transition period of positive half cycle (negative value becomes positive value), the voltage or current value will become zero. Therefore, if the switchover is performed at the zero crossing point, it can help reduce the load required during switching. Voltage stress.

For the switching of the automatic commutation switch (2), please refer to the second diagram of the detection voltage waveform zero-crossing point diagram of the present invention, which assumes that the three-phase high-voltage distribution feeder (3) and the automation The phase change switch (2) is in a state in which the A phase switch is turned on, and the B and C phase switches are turned off. At this time, the load power supplied by the distribution transformer (1) is supplied from the A phase feed line on the high voltage side, and when A The amount of current transmitted by the phase-feeding line is large. When the C-phase feeder is small, when the distribution transformer (1) is to be transferred from the A-phase power supply to the C-phase power supply, the A-phase and C-phase voltage waveforms need to be detected separately. Zero crossing point, and then let the automatic commutation switch (2) switch the switch, that is, Before the voltage zero of the phase A, the power transistor or thyristor signal of the automatic phase-switching switch (2) of the phase A is given, and after cutting off and cutting off, the voltage of the phase C is zero. The power transistor or thyristor signal of the C-phase automatic switching switch (2) turns on the automatic commutation switch (2) to supply the load power to the C phase to complete the phase adjustment procedure.

The control of the microelectronic controller (4) first considers the calculation of the voltage unbalance rate. The present invention adopts the calculation method defined by the domestic electric power company mainly adopting the National Electrical Manufactures Association (NEMA) standard specification. The calculation method of the voltage unbalance rate is based on the line voltage of the three-phase power supply, as shown in the following equation:

Where |V _ab |, |V _bc |, |V _ca | is the line voltage value of the three-phase system, and V _avg is the average value of the three-phase line voltage. This calculation method is the voltage value between the lines and the voltage average between the three lines. The difference between the values is taken as the ratio of the maximum value to the average value of the three-phase voltage.

Then reduce the maximum voltage unbalance rate of the controlled power system as one of the evaluation indicators of the plan, and improve the voltage imbalance, which can reduce the operation risk of the power grid equipment, avoid the user load being affected and fail, so the voltage imbalance rate Improvement can be equivalent to a risk assessment indicator and can be expressed as follows:

Where f ₁ is the first evaluation indicator, N _B is the total number of nodes installing the automatic phase change switch, and V _i ^avg is the average value of the three-phase line voltage of the i-th node, V _i ^ab , V _i ^bc , V _i ^Ca is the line voltage value of the three-phase node of the i-th node. The operation mode of the decision target is to calculate the voltage imbalance rate of each node, and take the maximum voltage imbalance rate in the system as the objective function value, and then use wisdom. The calculation technology selects each distribution transformer to control and reduce the value, which can effectively reduce the overall voltage imbalance rate of the system and reduce the operation risk of the transmission and distribution system.

The second evaluation index of the control consideration of the microelectronic controller (4) is to reduce the maximum neutral current value of the controlled system. When the neutral current is from the three-phase system Y wiring, each phase will be One end is connected to form a neutral contact. Generally, the neutral contact is connected to the earth loop to derive harmonic current and three-phase unbalanced current to avoid power supply problem and power equipment fault damage. When the three-phase voltage is not When balancing, it will also cause the neutral current to rise, which will increase the power transmission loss of the system. The domestic electricity industry is easy to supply three-phase load and single-phase load power by adopting the Y-open Δ architecture wiring mode. due to load imbalance among the respective phases of the line currents higher, the formula is calculated as _{follows: I N = I a + I} b + I c (4)

Where I _a , I _b and I _c are the three-phase phase currents on the high voltage side of the distribution transformer, respectively, and I _{N is} the neutral current. When the three phases are balanced, the phases of the phases are equal to each other due to the equal magnitude of the three phases. Degree, so the current flowing through the neutral line is equal to zero.

If the neutral current is too large, it may cause damage to the equipment operation, or it may cause the protection system to trip, which may affect the safety of the system operation. Therefore, the improvement of the neutral current can be equivalent to the safety evaluation index and can be The evaluation indicator is expressed as follows:

Where f ₂ is the second evaluation index, I _i ^N is the i-th node neutral current, I _i ^a , I _i ^b and I _i ^c are the three-phase current of the i-th node, the second term The evaluation index is also used to calculate the neutral current value of each node, and take the maximum neutral current value of the system as the basis for regulation.

The third evaluation indicator of the control consideration of the microelectronic controller (4) is to evaluate the power loss of the system, and by reducing the power loss of the power supply, the power supply operation efficiency of the system can be increased, and the power required for power generation in the electric industry can be increased. Reducing, and thus reducing the cost of power generation, with economic benefits, can be equivalent to economic evaluation indicators, and can be expressed as follows:

Through the analysis of the above three evaluation objectives, it can be judged whether the system operation reliability and the operation efficiency are effectively achieved, and the microelectronic controller (4) can have decision-making compliance and exhibit efficient improvement benefits, and the microelectronics The decision of controller (4) is to consider the evaluation of each evaluation index separately, and also consider the coordination between the three evaluation index functions to obtain the appropriate decision result, so the objective function can be as follows: Min F ( X _c , X _d )= w _l f ₁ + w ₂ f ₂ + w ₃ f ₃ (7)

Where X _c is the vector composed of the control variables to be solved, and the control variable is a set consisting of all the distribution transformers (1) to be adjusted in the distribution network, and X _d is the dependent variable to be solved. The composed vector is obtained by substituting control variables into the system for power flow calculation. The dependent variable is the three-phase line voltage and three-phase phase current of each node obtained after the power flow calculation, and w ₁ , w ₂ and w ₃ are the target component weights of the consideration. This is the importance of each evaluation goal in the overall decision making process.

In addition, the power flow of the distribution network needs to meet the principle of balance of power supply and demand. The supply and demand balance constraints of the distribution network power flow are as follows:

Wherein, P _i+1 and Q _i+1 respectively represent real power and virtual power flowing out of the i+1th node; P _L,i+1 and Q _L,i+1 respectively represent the supply of the i+1th node real power and reactive power; V _i is the voltage of the i-th nodes; R _{i, i + 1} and X _{i, i + 1} is connected to node i and i + 1-th line nodes of resistance and reactance.

When the voltage unbalance rate is too high, not only the power supply efficiency and stability are lowered, but also the user equipment may be damaged. Therefore, it is necessary to limit the voltage unbalance rate to ensure the power supply quality. The limit of the voltage imbalance rate is expressed as follows:

Among them, (VU%) _i is the voltage imbalance rate of the i-th node. From this formula, the voltage unbalance rate of each node needs to be less than the upper limit of (VU%) _max , and the voltage imbalance is analyzed by foreign countries. The standard specification of the rate also knows that the current norm of the voltage imbalance rate is mostly limited to 2%. Therefore, in the discussion of the subsequent simulation analysis, the limit specification of the voltage unbalance rate is also set to 2%.

When planning the power distribution network, the power company's designers need to carefully consider the neutral current upper limit value to avoid system misjudgment, resulting in protection power failure. Therefore, when the power flow calculation of the commutation control is performed by the present invention, the upper limit of the neutral current is considered to ensure the safety of the system operation, and the neutral current limit can be expressed as follows:

Where I _i ^N represents the neutral current of the i-th node, and the neutral current value of each node needs to be lower than the upper limit of the neutral current specified by the domestic electric industry. The specification is that the neutral current is not available. More than 120 amps.

In order to ensure the stability of the power supply voltage of the power system and to avoid damage caused by the use of improper voltages in the electrical equipment, it is necessary to limit the three-phase phase voltage to be maintained within a feasible range, and the present invention expresses the three-phase phase voltage limit type as follows:

Wherein, V _i ^a, V _i ^b and V _i ^c is the three-phase voltage of node i, V _i ^min and the voltage V _i ^max is a consideration of the minimum and maximum safe operation. For the operating voltage specification value of the domestic electricity industry, the voltage operation limit value is set to be between 0.95 standard value and 1.05 standard value.

In the power system, each feeder has its upper limit of transmission capacity, so the three-phase line current must be smaller than the upper limit that the feeder can withstand to avoid feeder burnout. The corresponding limit is as follows:

Where I _l ^a , I _l ^b and I _l ^c are the three-phase line current of the first feeder, and I _l ^max is the rated capacity of the first feeder, and each line current needs to be smaller than the rated value that the feeder can transmit, so The invention will be based on the rated transmission capacity of the actual feeder as a limiting basis.

In addition, in order to facilitate the relevant personnel to evaluate the improvement performance before and after the control of the automatic commutation switch (2), a numerical evaluation method suitable for the phase adjustment decision of the distribution transformer (1) of the present invention is proposed as a correlation. The personnel judged the improvement of the grid operation efficiency before and after the regulation. The evaluation of this numerical value is as follows:

Among them, F is the objective function value obtained through the algorithm control, F _b is the benchmark objective function value in the system, and three evaluation indicators such as economy, safety and risk have been established in the above, and (7) In the formula, the objective function of the comprehensive evaluation between the three indicators is established. The present invention mainly reduces the voltage imbalance rate, so the three weight values of w ₁ , w ₂ and w _{3 in the} equation (7) are respectively set to 0.4, 0.3 and 0.3, after establishing the completion of the objective function, continue to integrate the comprehensive evaluation function of the formula into (14) for score evaluation, and multiply the percentage by (14) to obtain the system. According to the evaluation of the comprehensive operation efficiency, the present invention provides relevant information on the current operation status according to the evaluation index. When the evaluation score is about 80 points or more, the system is in a better state after the system is adjusted, and 60 points to 80 points. In the general state, 60 points or less is a poor state.

The invention is used in operation, which assumes that the automatic commutation switching switch (2) turns on the A phase and the B phase to supply power, and at this time, the total load of the A phase feeder supply on the high voltage side of the distribution transformer (1) is higher. The B-phase feeder is high, and the load of the C-phase feeder is lighter than that of the A-phase and B-phase feeders. Therefore, in order to distribute the load of each phase feeder evenly, the power supply phase of the distribution transformer (1) is required. Do not adjust phase A and phase B to phase B and phase C. As for adjusting the phase difference between the two power distribution transformers (1), the microelectronic controller (4) needs to judge according to the above-mentioned evaluation target mode, and after the evaluation is completed, the automatic commutation switching is performed. The B-phase switch in the switch (2) is interlocked, that is, it can only control the power phase of the A-phase and the C-phase during the commutation operation. Body switch to avoid connecting the two phases connected to the distribution transformer (1) to phase B. After confirming the two controllable phases of the distribution transformer (1), it is necessary to separately detect the zero crossing point of the phase A and phase C voltage waveforms, and then perform the switching operation, that is, first After the power transistor switch of phase A is cut off from the mains, the phase transistor of the phase C is closed, and the procedure of phase change adjustment can be completed.

While the present invention is to verify the feasibility of the application, please refer to the following tests:

Test one:

Firstly, the improvement performance before and after the control is evaluated only by the evaluation index for reducing the voltage imbalance rate, and the verification is performed by the modified IEEE 13-node test system. Please refer to the third diagram of the circuit diagram of the test system of the present invention. The number of control variables that can be controlled by commutation reaches eight, so that all possible combinations of regulation come to 3 ⁸ =6561 possible cases. Firstly, the exhaustive search method is used for verification analysis, which is most suitable for the system. The optimal voltage unbalance rate value is shown in Table 1. The original phase-by-connection situation of the system can be compared with the optimal phase-connected situation obtained by the exhaustive search method, in which the 645 node is unchanged, and the second is known from Table 2. The load of each phase of power supply at the 670 node where the power station is located shows that the load of each phase is balanced after the regulation, the objective function value is effectively reduced, and the maximum voltage imbalance rate of the system is reduced from 2.31% to 0.31%.

Then, the solution method adopted is used for performance verification analysis. The voltage imbalance ratio of each bus bar of the modified 13-node system of the present invention is shown in the fourth figure. has improved.

Test 2:

In order to evaluate whether multiple operating targets can help improve the overall efficiency of the system, the three objective functions of voltage imbalance, total line loss and neutral current are taken into account. Table 3 shows that some nodes change the connected phases via the control, and Table 4 shows the improvement of each target. The maximum voltage imbalance rate of the system, the maximum neutral current of the system, and the system power loss are effectively reduced. Referring to the fifth figure, the comparison result of the voltage unbalance rate of each node of the optimal control strategy under the three-objective consideration of the present invention shows that the voltage imbalance rate of each node of the system can be controlled to obtain the overall improvement effect. In addition, please refer to the sixth figure. The comparison diagram of the neutral line current results of the improvement of the optimal control strategy under the three-objective consideration of the present invention also shows that the source node near the substation is in the case of load imbalance. The line current has a higher situation, and an effective improvement can be achieved after the commutation control.

It can be seen from the above description of the implementation of the present invention that the present invention mainly uses a microelectronic controller to control an automatic commutation switch to control the phase difference of the distribution transformers. Improve the three-phase unbalance of the three-phase high-voltage distribution feeder, reduce its three-phase voltage unbalance rate, so as to reduce the power transmission loss, and increase the utility performance characteristics in its overall implementation.

While the invention has been described in connection with the preferred embodiments described above, it is not intended to limit the scope of the invention. The technical scope protected by the invention.

In summary, the embodiments of the present invention can achieve the expected use efficiency, and the specific methods disclosed therein have not been seen in similar products, and the same technology has not been found in the pre-application literature. Cheng has fully complied with the requirements and requirements of the Patent Law. He has filed an application for an invention patent in accordance with the law, and he is pleased to review it and grant a patent.

(1)‧‧‧Distribution transformer

(2) ‧‧‧Automatic commutation switch

(3)‧‧‧Three-phase high-voltage distribution feeder

(4) ‧‧‧Microelectronic Controller

Claims (6)

A three-phase balanced phase adjustment method for distribution transformer wiring, which is mainly connected with an automatic commutation switching switch on a high voltage side of a distribution transformer, so that the automatic commutation switching switch is connected to a three-phase high-voltage distribution feeder, and the automatic commutation is performed The switch is connected with a microelectronic controller, and the microelectronic controller is used to control the switching of the automatic commutation switch. The control of the microelectronic controller includes: a. reducing the maximum voltage imbalance rate of the controlled power system. Evaluation index: The calculation method of voltage unbalance rate is based on the line voltage of three-phase power supply, as shown in the following formula: Where |V _ab |, |V _bc |, |V _ca | is the line voltage value of the three-phase system, V _avg is the average value of the three-phase line voltage; the improvement of the voltage imbalance rate can be equivalent to the risk assessment index And can represent the following formula: Where f ₁ is the first evaluation indicator, N _B is the total number of nodes installing the automatic phase change switch, and V _i ^avg is the average value of the three-phase line voltage of the i-th node, V _i ^ab , V _i ^bc , V _i ^Ca is the line voltage value of the three-phase of the i-th node; b. reducing the maximum neutral current value of the controlled power system: the improvement of the neutral current can be equivalent to the safety evaluation index, and The evaluation indicator is expressed as follows: Where f ₂ is the second evaluation index, I _i ^N is the i-th node neutral current, I _i ^a , I _i ^b and I _i ^c are the three-phase current of the i-th node, the second term The evaluation index is also calculated after obtaining the neutral current value of each node, taking the maximum neutral current value of the system as the basis for regulation; c. The evaluation of the power supply loss of the controlled power system: evaluating the power supply of the controlled power system The loss of electrical energy can be equivalent to an economic evaluation indicator, and the evaluation indicator can be expressed as follows: d. Analysis and evaluation indicators to obtain decision-making results: The analysis of the above three evaluation indicators enables the microelectronic controller to have decision-making compliance and obtain appropriate decision results, so the objective function can be expressed as follows: Min F ( X _c , X _d )= w ₁ f ₁ + w ₂ f ₂ + w ₃ f ₃ where X _c is the vector of the control variables to be solved, and the control variables are all adjusted phases in the distribution network. The set of other distribution transformers, X _d is the vector composed of the dependent variables to be solved, and the control variables are substituted into the system for power flow calculation. The dependent variables are the three-phase line voltage and three-phase of each node obtained after the power flow calculation. phase current, w _1, w ₂ and w ³ is the weight of the target component weight considerations. For example, the method for adjusting the three-phase balanced phase of the distribution transformer according to the first aspect of the patent application scope, wherein the reduction of the maximum voltage imbalance rate evaluation index of the controlled power system further considers that the power flow of the distribution network conforms to the principle of balance of power supply and demand, The supply and demand balance constraints for power distribution network power flows are expressed as follows: Wherein, P _i+1 and Q _i+1 respectively represent real power and virtual power flowing out of the i+1th node; P _L,i+1 and Q _L,i+1 respectively represent the supply of the i+1th node real power and reactive power; V _i is the voltage of the i-th nodes; R _{i, i + 1} and X _{i, i + 1} is connected to node i and i + 1-th line nodes of resistance and reactance. The method for adjusting a three-phase balanced phase of a distribution transformer according to the first aspect of the patent application, wherein the maximum voltage imbalance rate evaluation index of the controlled power system is reduced, and when the voltage imbalance rate is too high, the voltage imbalance is rate limit, limit the rate of voltage imbalance represented by the formula shown in the following formula :( VU%) _I ( VU %) _max where (VU%) _i is the voltage imbalance ratio of the i-th node. From this equation, the voltage imbalance ratio of each node needs to be less than the upper limit of (VU%) _max , and the voltage is not The limit specification for the balance rate is set to 2%. For example, the method for adjusting the three-phase balanced phase of the distribution transformer according to the first application of the patent scope, wherein the maximum neutral current value evaluation index of the controlled power system is reduced, and the neutralization is performed when the power flow calculation of the commutation control is performed. The upper limit of the line current is taken to ensure the safe operation of the system. The limit of the neutral current can be expressed as follows: Where I _i ^N represents the neutral current of the i-th node, and the neutral current value of each node needs to be lower than the upper limit of the neutral current specified by the domestic electric industry. The specification is that the neutral current is not available. More than 120 amps. For example, the three-phase balanced phase adjustment method for the distribution transformer wiring according to the scope of claim 1 is to ensure that the power supply voltage of the power system is stable and the electrical equipment is prevented from being damaged by using an inappropriate voltage, and the three-phase phase voltage is required to be maintained. In the interval, the three-phase phase voltage limit expression is expressed as follows: Wherein, V _i ^a , V _i ^b and V _i ^c are the three-phase voltages of the i-th node, and V _i ^min and V _i ^max are the minimum and maximum values of the safe operation voltage, and the voltage operation limit value is set to The value of 0.95 is between 1.05 and the value of the standard. For example, in the power system, each feeder has its upper limit of the transmission capacity, and the corresponding limit is as follows: Wherein, I _l ^a, I _l ^b I _l ^c and the three-phase line currents of the article feeder 1, I _l ^max Article 1 of the rated capacity of the feeder, each feeder line current is less than the required rating can be transmitted.