A three-phase unbalanced treatment device for transformer area

Abstract

The present invention relates to a three-phase imbalance control device for a substation. The control device includes a plurality of monitoring devices, a control device and a controller. The monitoring device is used to collect the current and voltage of the three-phase main line and each branch line. The control device is used to adjust the load current of the three-phase main line when the three phases are unbalanced. The controller is used to: 1. calculate the three-phase imbalance according to the three-phase current; 2. average the three-phase current, and use the difference between the current of each phase and the average as the corresponding compensation current; 3. calculate the apparent total power at the load end of the substation according to the three-phase current and the total voltage at the load end; 4. control the control device to adjust the three-phase current according to the threshold range of the apparent total power and the three-phase imbalance so that the three-phase current tends to be balanced. The present invention combines dynamic compensation with automatic phase change method to achieve accurate and efficient control of the three-phase imbalance at the load end of the substation, while reducing equipment costs and reducing power losses.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power systems, and in particular to a device for treating three-phase imbalance in a transformer area. Background Art

[0002] Three-phase imbalance refers to the inconsistency of the amplitude of the three-phase current (or voltage) in the power system, and the amplitude difference exceeds the specified range. The three-phase imbalance of the power system is caused by unbalanced three-phase loads, different power consumption of single-phase loads, and asymmetric three-phase parameters of system components. The three-phase imbalance of the power system is one of the main indicators of power quality.

[0003] The three-phase imbalance in the substation 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. The distribution transformer generates zero-sequence current. 5. Affect the safe operation of electrical equipment.

[0004] Among the existing methods for dealing with three-phase imbalance, the following methods are generally used: uniformly distributed load, increased short-circuit capacity, static compensation, dynamic compensation, etc. However, due to wiring errors by construction personnel and irregular electricity consumption by users, it is difficult to adjust the uniformly distributed charge in time. When high-power electrical appliances are connected, the three-phase imbalance may be aggravated. Increasing the short-circuit capacity does not fundamentally solve the problem of three-phase imbalance. Although it improves the system's bearing capacity, it aggravates the loss of electricity. Although static compensation and dynamic compensation can be precisely controlled, for power systems with large loads such as substations, the required equipment quality requirements are high, which increases the cost of three-phase imbalance management. Summary of the invention

[0005] Based on this, it is necessary to provide a three-phase imbalance management device for the substation to address the problem that the existing three-phase imbalance management is difficult to reduce the management cost while ensuring accurate and efficient management. The present invention is implemented through the following technical solutions: a three-phase imbalance management device for the substation, which includes multiple monitoring devices, a management device and a controller.

[0006] The monitoring device is divided into three main detection devices and multiple sub-monitoring devices. Among them, the main detection device is connected to the three-phase main line at the load end of the substation area, and is used to collect the current and voltage of the three-phase main line in real time. The sub-monitoring device is used to detect the real-time power consumption current and voltage at the user end.

[0007] The control device is used to adjust the load current of the three-phase main line through corresponding technical means when the three-phase is unbalanced, so that the current in the three-phase main line tends to be balanced. The control device includes a current dynamic compensation device and a plurality of phase-changing switches. Among them, the current dynamic compensation device is used to directly adjust the current of the three-phase main line so that the total current of each phase tends to be equal. Each phase-changing switch is connected to a user end, such as the input end of the electric energy meter and the output end of the three-phase main circuit. The phase-changing switch is used to switch the phase line connected to the user end.

[0008] A controller for:

[0009] 1. Calculate the three-phase imbalance based on the three-phase current:

[0010] ε=(I MAX -I MIN ) / I MAX

[0011] Among them, ε is the three-phase unbalance, I MAX For I A ,I B and I C The maximum value in I MIN For I A ,I B and I C The minimum value in I A ,I B and I C They are respectively the currents of phase A, phase B and phase C in the main line at the load end of the substation.

[0012] 2. Take the average of the three-phase currents. The difference between each phase current and the average is used as the corresponding compensation current. The calculation method of the compensation current is as follows:

[0013] I RA =I A -I AVG ;I AVG =(I A +I B +I C ) / 3

[0014] I RB =I B -I AVG

[0015] I RC =I C -I AVG

[0016] Among them, I RA ,I RB ,I RC are the compensation currents of phase A, phase B and phase C respectively, I AVGis the mean value of the three-phase current.

[0017] 3: Calculate the apparent total power P at the load end of the substation based on the three-phase current and the total voltage at the load end:

[0018]

[0019] Wherein, U is the total voltage at the load end.

[0020] 4. Make the following decisions based on the threshold range of apparent total power and three-phase imbalance:

[0021] a: If the three-phase unbalance is lower than a preset threshold value, no adjustment is made to the three-phase current.

[0022] b: If the three-phase imbalance is between threshold 1 and a preset threshold 2, 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 imbalance is lower than the threshold range.

[0023] c: If the three-phase unbalance is between threshold 1 and a preset threshold 2 and the apparent total power is not lower than a preset power threshold or the three-phase unbalance is higher than a preset threshold 2, the three-phase current is adjusted by automatic phase change method to make the three-phase unbalance lower than the threshold range.

[0024] The above-mentioned three-phase imbalance control equipment in the substation adopts a combination of dynamic compensation and automatic phase-changing methods. When the apparent total power is low, dynamic compensation is used to control the three-phase imbalance within the preset range, and automatic phase-changing methods are used to control other three-phase imbalances that are not lower than the preset range, thereby achieving the purpose of accurate and efficient control of the three-phase imbalance at the load end of the substation, while reducing equipment costs and reducing energy losses.

[0025] In one embodiment, the working process of the dynamic compensation device is as follows:

[0026] b1: Calculate the total power of each phase based on the total voltage and the total current of each phase. Calculate the corresponding partial power based on each partial current and its corresponding partial voltage.

[0027] b2: The ratio of the sum of the partial power of each phase to the total power of each phase is used as the compensation ratio. ALL The calculation method is as follows:

[0028] P ALL =P A +P B +P C

[0029]

[0030]

[0031]

[0032] Among them, P A , P B , P C are the power distribution of phase A, phase B and phase C in the total line at the load end of the substation, U A , U B and U C are the divided voltages of phase A, phase B and phase C respectively, and i, j, k are the divided current quantities of phase A, phase B and phase C in the total line at the load end of the substation respectively.

[0033] b3: The product of the compensation ratio and the compensation current of each phase is taken as the actual compensation current of each phase. The calculation method of the actual compensation current is as follows:

[0034] I A0 =KI RA K=P ALL / P

[0035] I B0 =KI RB

[0036] I C0 =KI RC

[0037] Among them, K is the compensation coefficient, I RA ,I RB ,I RC They are the compensation currents of phase A, phase B and phase C respectively.

[0038] b4: Adjust the current of each phase according to the actual compensation current of each phase so that the three-phase imbalance after adjustment is lower than the threshold range.

[0039] In one embodiment, the operation process of the phase-changing switch is as follows:

[0040] Multiple partial currents in each phase are combined into one partial current set.

[0041] Each sub-current in all sub-current sets is redistributed so that the sum of the sub-currents in each sub-current set tends to be equal. 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 average the actual total current of the three phases. c2: Calculate the difference between the actual total current of each phase and the average of the total current, and record it as the ideal switching current of each phase. c3: Swap the sub-current of each phase so that the ideal switching current of each phase tends to zero. There are multiple switching methods that meet the conditions, and the one with the least switching amount is selected as the actual switching method to reduce the number of phase changes.

[0042] The current of the replacement group is commuted according to the reorganized divided current of each phase.

[0043] In one embodiment, the main monitoring device includes a current transformer and an ammeter. The current transformer is respectively mounted on the outside of one of the phase main lines, and is used to collect the current value of the three-phase main line in real time. The ammeter is connected in series to the outside of the current transformer, and is used to monitor the current value passing through the current transformer in real time.

[0044] In one embodiment, the sub-monitoring device includes a smart energy meter, the input end of which is connected to any one-phase main line and the neutral line. The output end of the smart energy meter is used to supply power to the user end. A voltmeter is connected in parallel in the smart energy meter, and the smart energy meter is used to collect the user's power consumption and voltage value in real time.

[0045] In one embodiment, 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, SVG is connected to three-phase main lines respectively. Three parallel current conversion circuits are arranged inside SVG. The current conversion circuit has the function of converting direct current into alternating current and converting alternating current into direct current. A composite transistor IGBT is connected in series in each current conversion circuit to control the on-off state of the corresponding current conversion circuit. The capacitor is connected in series in SVG and is connected to the three current conversion circuits respectively.

[0046] In one 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 to control the current direction. The rectifier is used to convert the AC current higher than the average current in each phase circuit into DC power. The inverter is used to convert DC power into AC power.

[0047] In one embodiment, 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 an electrical accident, and is also used to prevent potential risks caused by manual phase change by users or construction personnel.

[0048] In one embodiment, two electromagnetic relays and a plurality of wires are used 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 contact 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.

[0049] In one embodiment, the working process of the control circuit is as follows:

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] 1. The present invention combines a current dynamic compensation device with a phase-changing switch. When the apparent total power is low, dynamic compensation is used to control the three-phase imbalance within a preset range, and automatic phase-changing is used to control other three-phase imbalances that are not lower than the preset range, thereby achieving the purpose of accurately and efficiently controlling the three-phase imbalance at the load end of the substation, while reducing equipment costs and reducing power losses.

[0055] 2. The phase-changing switch adopted in the present invention achieves the purpose of controlling three-phase imbalance by combining the current of each phase separately and then redistributing it, while switching the least current, thereby reducing the impact of the phase-changing process on the overall power consumption of the substation, reducing the phase-changing frequency, and having lower requirements for the phase-changing equipment, thereby reducing the cost of the three-phase imbalance control equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a structural schematic diagram of a three-phase unbalance treatment device in a transformer area according to Embodiment 1 of the present invention;

[0057] Figure 2 for Figure 1 Schematic diagram of the circuit structure of the three-phase unbalanced treatment equipment in the middle station area;

[0058] Figure 3 This is a flow chart of the method for treating three-phase imbalance in a transformer area according to Embodiment 1 of the invention;

[0059] Figure 4 Based on Figure 1 The structural diagram of the intelligent terminal designed for three-phase unbalanced control equipment in the substation. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] It should be noted that when a component is referred to as being "mounted on" another component, it may be directly on the other component or there may be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may be a central component at the same time. When a component is considered to be "fixed to" another component, it may be directly fixed on the other component or there may be a central component at the same time.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein 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.

[0063] See also Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the structure of the three-phase unbalance treatment equipment in the substation of this embodiment; Figure 2 for Figure 1 Schematic diagram of the circuit structure of the three-phase unbalanced treatment device in the middle transformer area. This embodiment provides a three-phase unbalanced treatment device in the transformer area, which includes: a treatment device, a plurality of monitoring devices and a controller.

[0064] The monitoring device is divided into three main detection devices and multiple sub-monitoring devices. Among them, the main detection device is connected to the three-phase main line at the load end of the substation, and is used to collect the current and voltage of the three-phase main line in real time. The main monitoring device can be a detection circuit composed of sensitive elements, including Hall current sensors, voltage sensors, etc. This embodiment uses a detection circuit composed of a current transformer and an ammeter to collect the current value of the three-phase main line. The three current transformers are respectively arranged on the outside of the three-phase main line to sense the current passing through each main line and measure the corresponding current value according to the current ratio of the transformer. Each ammeter is connected in series on the outside of a transformer to monitor the current value passing through the corresponding transformer in real time. Since the total output voltage at the load end of the substation is generally rated 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 substation can be directly measured by a voltmeter or a multimeter, and no real-time monitoring is required.

[0065] The sub-monitoring device is used to detect the real-time power consumption current and voltage at the user end. Since the user end often installs an electric energy meter at the input end, the sub-current or sub-voltage at the user end can be directly measured and calculated by the electric energy meter. For example, the power voltage in the 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:

[0066] I n =W t / 220t

[0067] Among them, I n is the current distribution of any user end, t is the detection time, W t is the power consumption of the user within the duration t.

[0068] Of course, in actual electricity consumption, the partial voltage at each user end will be affected by line loss and load changes. Therefore, in order to improve the accuracy of current monitoring, a voltmeter can be connected in parallel to the electric energy meter to monitor the partial voltage values ​​passing through the electric energy meter in real time, and then calculate the corresponding partial current.

[0069] The control device is used to adjust the load current of the three-phase main line through corresponding technical means when the three-phase is unbalanced, so that the current in the three-phase main line tends to be balanced. The control device includes a current dynamic compensation device and multiple phase-changing switches. Among them, the current dynamic compensation device is used to directly adjust the current of the three-phase main line so that the total current of each phase tends to be equal. The adjustment method is to convert the part of the AC current that exceeds the average current in the three-phase main line into DC current and store it in the power storage device, and then invert the DC current into AC current and distribute it to the circuit with lower current than the average current.

[0070] 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, SVG is connected to three-phase main lines respectively. Three parallel current conversion circuits are arranged inside SVG. The current conversion circuit has the function of converting direct current into alternating current and converting alternating current into direct current. A composite transistor IGBT is connected in series in each current conversion circuit to control the on-off state of the corresponding current conversion circuit. The capacitor is connected in series in SVG and is connected to the three current conversion circuits respectively. After the three-phase imbalance of the three-phase main circuit exceeds the preset range, SVG receives the 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 other phase main circuits below the average value. In this process, IGBT is used to control the on-off state of the current conversion circuit to control the conversion of current. For example, when the C-phase current is higher than the average current, and the A-phase and B-phase currents are lower than the average current, the IGBT controls the current conversion circuit connected to the C-phase line to convert part of the AC current into a DC current, while the current conversion circuits connected to the other two-phase lines convert the DC current in the capacitor into an AC current according to the compensation current value, and distribute it to the corresponding main phase line. 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 to control the current direction. The rectifier is used to convert the AC current higher than the average current in each phase circuit into a DC current. The inverter is used to convert the DC current into an AC current. Of course, in other embodiments, other methods can also be used for circuit conversion, such as using transistors, chips, etc.

[0071] Each phase-changing switch is connected to a user end, such as the input end of the electric energy meter and the output end of the three-phase main circuit. The phase-changing switch is used to switch the phase line connected to the user end. The phase lines connected to the user end are different. Generally speaking, residential areas and commercial areas are mostly single-phase power supply. Industrial areas include single-phase power supply and three-phase power supply, and the specific power supply ratio is related to the load electrical appliances. For the user end using single-phase power supply, the electric energy meter used is often connected to only 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 area needs to be evenly distributed from the three-phase main line. However, due to the different power consumption of each user at the same time and the different power consumption, it is difficult for the three-phase main circuit to achieve the basic balance of current. The phase line connected to the user end can be switched by the phase-changing switch, thereby changing the load state in the three-phase main line, so that the current of the three-phase main circuit is basically balanced.

[0072] 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.

[0073] 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:

[0074] 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 to supply power to the client.

[0075] 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 a 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.

[0076] 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.

[0077] 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:

[0078] 1. Calculate the three-phase imbalance according to the three-phase current:

[0079] ε=(I MAX -I MIN ) / I MAX

[0080] Among them, ε is the three-phase unbalance, I MAX For I A ,I B and I C The maximum value in I MIN For I A ,I B and I C The minimum value in I A ,I B and I C They are respectively the currents of phase A, phase B and phase C in the main line at the load end of the substation.

[0081] 2. Take the average of the three-phase currents. The difference between each phase current and the average is used as the corresponding compensation current. The calculation method of the compensation current is as follows:

[0082] I RA =I A -I AVG ;I AVG =(I A +I B +I C ) / 3

[0083] I RB =IB-I AVG

[0084] I RC =I C -I AVG

[0085] Among them, I RA ,I RB ,I RC are the compensation currents of phase A, phase B and phase C respectively, I AVG is the mean value of the three-phase current.

[0086] 3: Calculate the apparent total power P at the load end of the substation based on the three-phase current and the total voltage at the load end:

[0087]

[0088] Wherein, U is the total voltage at the load end.

[0089] 4. Make the following decisions based on the threshold range of apparent total power and three-phase imbalance:

[0090] a: If the three-phase unbalance is lower than a preset threshold value 1, no adjustment is made to the three-phase current. In this embodiment, the threshold value 1 is set to 10%.

[0091] b: If the three-phase imbalance is between threshold 1 and a preset threshold 2, 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 imbalance is lower than the threshold range. In this embodiment, threshold 2 is set to 15%.

[0092] The working process of the dynamic compensation device is as follows:

[0093] b1: Calculate the total power of each phase based on the total voltage and the total current of each phase. Calculate the corresponding partial power based on each partial current and its corresponding partial voltage.

[0094] b2: The ratio of the sum of the partial power of each phase to the total power of each phase is used as the compensation ratio. ALL The calculation method is as follows:

[0095] P ALL =P A +P B +P C

[0096]

[0097]

[0098]

[0099] Among them, P A , P B , P C are the power distribution of phase A, phase B and phase C in the total line at the load end of the substation, UA , U B and U C are the divided voltages of phase A, phase B and phase C respectively, and i, j, k are the divided current quantities of phase A, phase B and phase C in the total line at the load end of the substation respectively.

[0100] b3: The product of the compensation ratio and the compensation current of each phase is taken as the actual compensation current of each phase. The calculation method of the actual compensation current is as follows:

[0101] I A0 =KI RA K=P ALL / P

[0102] I B0 =KI RB

[0103] I C0 =KI RC

[0104] Among them, K is the compensation coefficient, I RA ,I RB ,I RC They are the compensation currents of phase A, phase B and phase C respectively.

[0105] b4: Adjust the current of each phase according to the actual compensation current of each phase so that the three-phase imbalance after adjustment is lower than the threshold range.

[0106] c: If the three-phase imbalance is between threshold 1 and a preset threshold 2 and the apparent total power is not lower than a preset power threshold or the three-phase imbalance is higher than a preset threshold 2, the automatic phase change method is used to adjust the three-phase current so that the three-phase imbalance is lower than the threshold range.

[0107] The working process of the phase-changing switch is as follows:

[0108] Combine 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 Cl , I C2 , ..., I Ck}.

[0109] Each sub-current in all sub-current sets is redistributed so that the sum of the sub-currents in each sub-current set tends to be equal. The method for distributing sub-currents includes the following steps:

[0110] c1: Calculate the sum of the partial currents of each phase as the actual total current, and take the average of the actual total currents of the three phases. The actual total current of each phase is expressed as:

[0111]

[0112]

[0113]

[0114] Among them, I SA ,I SB and I SC They are the actual total currents of phase A, phase B and phase C respectively.

[0115] The total current mean value I SAVG Denoted as:

[0116] I SAVG =(I SA +I SB +I SC ) / 3.

[0117] c2: Calculate the difference between the actual total current of each phase and the average total current, and record it as the ideal commutation current of each phase.

[0118] I RA ′=I SA -I SAVG

[0119] I RB ′=I SB -I SAVG

[0120] I RC ′=I SC -I SAVG

[0121] Among them, I RA ′、I RB ′ and I RC ′ are the ideal commutation currents of phase A, phase B and phase C respectively.

[0122] c3: The partial current of each phase is exchanged so that the ideal commutation current of each phase tends to zero. There are multiple exchange methods that meet the conditions. The one with the least exchange amount is selected as the actual exchange method to reduce the number of commutations.

[0123] The current of the replacement group is commuted according to the reorganized divided current of each phase.

[0124] In this embodiment, it is assumed that A ,I B and IC If the currents are 21A, 21A and 24A respectively, the three-phase imbalance is about 8.3%, so there is no need to adjust the three-phase current.

[0125] Hypothesis I A ,I B and I C They are 18A, 21A and 24A respectively, and the three-phase imbalance is 12.5%. If the apparent total power is 8kW and the preset power threshold is 10KW, the dynamic compensation method is used to adjust the three-phase current.

[0126] Hypothesis I A ,I B and I C The three-phase current is 30A, 45A and 24A respectively, and the three-phase imbalance is about 36.4%. The automatic commutation method is used to adjust the three-phase current. If at this time, the number of branch currents of each phase is five, recorded as A = {5, 7, 5, 6, 7}, B = {6, 10, 12, 8, 9}, C = {3, 7, 5, 4, 5}, then the ideal commutation current I of each phase is RA ′、I RB ′ and I RC ' are 3A, -12A and 9A respectively. It can be seen that by exchanging 12A in set B to set C, and exchanging 3A in set C to set A, the sum of the sub-currents in the three sets is adjusted to 33A. Of course, in practical applications, the number of sub-currents in each phase is far more than five. Similarly, the adjustment of the sub-currents may not just balance the three-phase currents, as long as the three-phase imbalance is less than 10%. In addition, when the current compensation method is switched from dynamic compensation to automatic commutation, the switching of the sub-currents is performed in order from small to large. During the switching process, the compensation current of the dynamic compensation changes accordingly.

[0127] Please combine Figure 3 , which is a flow chart of the three-phase unbalanced control method of the transformer area of ​​this embodiment. According to the working process of the above-mentioned three-phase unbalanced control equipment of the transformer area, this embodiment also provides a three-phase unbalanced control method of the transformer area. The control method includes the following process:

[0128] 1: Collect the three-phase current and three-phase voltage at the load end of the substation. The three-phase current includes the total current of phase A, the total current of phase B, the total current of phase C, and multiple sub-currents of each phase. The three-phase voltage includes the total voltage at the load end and the sub-voltage corresponding to each sub-current.

[0129] The load end of the substation is used to supply power to a certain area, such as a residential area, an industrial area, or a commercial area. In actual power consumption, the load end first uses the power meter to count the power consumption in real time, and then supplies power to the electrical appliances. The current passes through the three-phase circuit of the total load end of the substation and connects to each power meter. When collecting the current or voltage at the load end of the substation, it is necessary to collect the total current or total voltage of the three phases of the substation, as well as the sub-current and sub-voltage connected to both ends of each power meter.

[0130] The method of collecting current or voltage may include connecting a detection circuit on the outside of the three-phase circuit respectively. The detection circuit may include any one or more of a voltmeter, an ammeter, a multimeter, and a mutual inductor. At the total output end of the three-phase circuit, the corresponding rated current and voltage need to be detected respectively. The total three-phase current at the total output end of the substation is recorded as I A ,I B and I C , the total voltage is recorded as U. At both ends of the energy meter, only one of the current or voltage needs to be detected. According to the real-time power changes of the energy meter, the corresponding current and voltage are calculated. According to the phase line connected to each energy meter, each sub-current is recorded as the A phase sub-current I A1 ,I A2 ,……,I Ai , B phase current I B1 ,I B2 ,……,I Bj , and the C phase current I C1 ,I C2 ,……,I Ck .

[0131] 2. Calculate the apparent total power P at the load end of the substation based on the three-phase current and the total voltage at the load end:

[0132]

[0133] Among them, I A ,I B and I C They are the currents of phase A, phase B and phase C in the total line at the load end of the substation, and U is the total voltage at the load end.

[0134] 3: Take the average of the three-phase currents. The difference between each phase current and the average is used as the corresponding compensation current. The calculation method of the compensation current is as follows:

[0135] I RA =I A -I AVc ;I AVG =(I A +I B +I C ) / 3

[0136] IRB =I B -I AVG

[0137] I RC =I C -I AVG

[0138] Among them, I RA ,I RB ,I RC are the compensation currents of phase A, phase B and phase C respectively, I AVG is the mean value of the three-phase current.

[0139] 4: The ratio of the maximum compensation current in each phase compensation current to the maximum current in the three-phase current is taken as the three-phase imbalance. The calculation method of the three-phase imbalance is as follows:

[0140] ε=I RMAX / I MAX

[0141] Among them, ε is the three-phase unbalance, I MAX For I A ,I B and I C The maximum value in I RMAx For I RA ,I RB ,I RC The maximum value in .

[0142] There are generally two methods for calculating the existing three-phase unbalance, including:

[0143] ε=(I MAX -I MIN ) / I MAX

[0144] ε=(I MAX -I AVG ) / I AVG

[0145] 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.

[0146] Five: Make the following decisions based on the threshold range of apparent total power and three-phase imbalance:

[0147] a: If the three-phase unbalance is lower than a preset threshold value 1, no adjustment is made to the three-phase current. In this embodiment, the threshold value 1 is set to 10%.

[0148] b: If the three-phase imbalance is between threshold 1 and a preset threshold 2, 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 imbalance is lower than the threshold range. In this embodiment, threshold 2 is set to 15%. The dynamic compensation method includes the following steps:

[0149] b1: Calculate the total power of each phase based on the total voltage and the total current of each phase. Calculate the corresponding partial power based on each partial current and its corresponding partial voltage. The total power of phase A, phase B and phase C are recorded as P A0 =UI A , P B0 =UI B and P C0 =UI C .

[0150] b2: The ratio of the sum of the partial power of each phase to the total power of each phase is used as the compensation ratio. ALL The calculation method is as follows:

[0151] P ALL =P A +P B +P C

[0152] P A =U A1 I A1 +U A2 I A2 +…+U Ai I Ai

[0153] P B =U B1 I B1 +U B2 I B2 +…+U Bj I Bj

[0154] P C =U C1 I C1 +U C2 I C2 +…+U Ck I Ck

[0155] Among them, P A , P B , P Care the sum of the partial powers of phase A, phase B and phase C in the total line at the load end of the substation, and i, j, k are the number of partial currents of phase A, phase B and phase C in the total line at the load end of the substation.

[0156] b3: The product of the compensation ratio and the compensation current of each phase is taken as the actual compensation current of each phase. The calculation method of the actual compensation current is as follows:

[0157] I A0 =KI RA K=P ALL / P

[0158] I B0 =KI RB

[0159] I C0 =KI RC

[0160] Wherein, K is the compensation coefficient.

[0161] 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.

[0162] The dynamic compensation of each phase current can be achieved through an active filter APF or a static var generator SVG. Taking SVG as an example, assuming that in a three-phase unbalanced circuit, I A <I B <I AVG <I C , then at a certain moment, the AC power of phase C is rectified into DC power and stored in the SVG. At another moment, the DC power stored in the SVG is released to 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 real-time, fast, accurate compensation, and ready for use.

[0163] c: If the three-phase imbalance is between threshold 1 and a preset threshold 2 and the apparent total power is not lower than a preset power threshold or the three-phase imbalance is higher than a preset threshold 2, the automatic phase change method is used to adjust the three-phase current so that the three-phase imbalance is lower than the threshold range. The automatic phase change method is as follows:

[0164] Combine 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 , IC2 , ..., I Ck}.

[0165] Each sub-current in all sub-current sets is redistributed so that the sum of the sub-currents in each sub-current set tends to be equal. The method for distributing sub-currents includes the following steps:

[0166] c1: Calculate the sum of the partial currents of each phase as the actual total current, and take the average of the actual total currents of the three phases. The actual total current of each phase is expressed as:

[0167]

[0168]

[0169]

[0170] Among them, I SA ,I SB and I SC They are the actual total currents of phase A, phase B and phase C respectively.

[0171] The total current mean value I SAVG Denoted as:

[0172] I SAVG =(I SA +I SB +I SC ) / 3.

[0173] c2: Calculate the difference between the actual total current of each phase and the average total current, and record it as the ideal commutation current of each phase.

[0174] I RA ′=I SA -I SAVG

[0175] I RB ′=I SB -I SAVG

[0176] I RC ′=I SC -I SAVG

[0177] Among them, I RA ′、I RB ′ and I RC ′ are the ideal commutation currents of phase A, phase B and phase C respectively.

[0178] c3: The partial current of each phase is exchanged so that the ideal commutation current of each phase tends to zero. There are multiple exchange methods that meet the conditions. The one with the least exchange amount is selected as the actual exchange method to reduce the number of commutations.

[0179] The current of the replacement group is commuted according to the reorganized divided current of each phase.

[0180] When the apparent total power is high, the current of each phase is also relatively high. When the three-phase imbalance is high, the compensation current is also relatively large. If the dynamic compensation method is adopted, the equipment specifications for dynamic compensation are also relatively high, which not only increases the equipment cost, but also increases the loss in the current inversion process, resulting in a waste of electric energy. When the apparent total power is low, the current of each phase is also relatively low, which means that the number of sub-currents used for power supply is also relatively low, and the number of users using 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 a balanced state when switching a small number of sub-currents. Therefore, the combination of dynamic compensation and automatic phase-changing methods can achieve accurate and efficient management of the three-phase imbalance at the load end of the substation, while reducing equipment costs and reducing power losses.

[0181] Please combine Figure 4 , which is based on Figure 1 The structure diagram of the intelligent terminal designed for the three-phase imbalance control equipment in the substation area. In order to facilitate the real-time observation of the changes in the three-phase imbalance, this embodiment also designs an intelligent terminal to grasp the changes in the three-phase current in real time. The intelligent terminal is equipped with multiple HPLCs for monitoring voltage and current and AUC devices for controlling three-phase imbalance, and the three-phase current data and control status can be observed in real time.

[0182] When the smart terminal is in use, it first collects multiple current data connected to the three-phase circuit through HPLC, and transmits the current data to the smart terminal. At the same time, the cross-collection data automatically analyzed by the smart terminal is also uploaded synchronously. The smart terminal calculates the three-phase imbalance results of the total output end of the substation and each branch based on the current data and cross-collection data, and manages the three-phase imbalance of the substation through the AUC device. The smart terminal can be a mobile phone, computer, tablet computer, electronic watch, etc. Taking a mobile phone as an example, an APP for managing three-phase imbalance can be installed on the mobile phone. All data collected by HPLC can be uploaded to the APP server, thereby establishing a remote connection between the three-phase imbalance management APP and HPLC, and monitoring the three-phase current data in real time.

[0183] In order to maintain the three-phase balance of the substation area and avoid any one phase or multiple phase current overload during the peak power consumption period, this embodiment also provides a method for calculating the open capacity of the substation area based on the three-phase balance, including the following steps:

[0184] S1: Collect the maximum allowable current and rated output voltage at the load end of the substation, and calculate the rated capacity D0 of the line. The calculation method of the rated capacity is as follows:

[0185] D0=U0I0

[0186] Among them, U0 is the rated voltage and I0 is the maximum allowable current.

[0187] The maximum allowable current at the load end is related to the material and environmental factors of the transmission line in the three-phase circuit. Among them, the transmission material includes copper wire, aluminum wire or aluminum-steel composite wire. The cross-sectional area and erection structure of the transmission line are direct factors affecting the passage of current. The larger the cross-sectional area of ​​the transmission line, the greater the maximum current allowed to pass. Similarly, the temperature, humidity and air pressure in the environment also have an impact on the transmission of current.

[0188] S2: Count the maximum historical load D1 at the load end. For any substation, the load in the past five years or ten years, or other time ranges, can be counted, and the maximum load of each phase and the total maximum load can be found.

[0189] S3: Calculate the maximum line loss D based on the maximum historical load at the load end and the corresponding output capacity loss The maximum loss is calculated as:

[0190] D loss =(D l0 -D l )D0 / D l0

[0191] Among them, D l0 It is the output capacity of the substation when the load end reaches the maximum historical load.

[0192] 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.

[0193] S4: Count the pre-connected capacity D pThe 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.

[0194] S4: Calculate the open capacity D as:

[0195] D=D0-D l -D loss -D p .

[0196] 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, and can be used as reference data for the future three-phase circuit planning in the substation.

[0197] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0198] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A three-phase imbalance control device for a transformer substation, which is used to adjust the three-phase current at the load end of the transformer substation to make the three-phase current tend to be balanced, thereby reducing the power loss and potential risks caused by the three-phase imbalance; characterized in that: It includes: A plurality of monitoring devices, including three main monitoring devices and a plurality of sub-monitoring devices; the three main monitoring devices are respectively connected to the three-phase main line of the load end of the substation area, and are used to collect the total current of each phase of the load end of the substation area in real time; the plurality of sub-monitoring devices are respectively connected to the user end, and are used to collect the sub-current of each user end in real time; A treatment device, comprising a current dynamic compensation device and a plurality of phase-changing switches; the current dynamic compensation device is connected to the three-phase main line at the load end of the substation area, and is used to convert the part of the alternating current in the three-phase current that exceeds the average current into a direct current and store it in a power storage device, and then invert the direct current into an alternating current and distribute it to the circuit with a current lower than the average current; the phase-changing switch is connected to the user end, and is used to switch the phase line connected to the user end; and A controller for:

1. Calculate the three-phase unbalance according to the three-phase current: ε=(I MAX -I MIN ) / I MAX Among them, ε is the three-phase unbalance, I MAX For I A ,I B and I C The maximum value in I MIN For I A ,I B and I C The minimum value in I A ,I B and I C They are the currents of phase A, phase B and phase C in the main line at the load end of the substation respectively; 2. Take the average of the three-phase currents; take the difference between each phase current and the average as the corresponding compensation current; 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 RA ,I RB ,I RC are the compensation currents of phase A, phase B and phase C respectively, I AVG is the mean value of the three-phase current; 3. Calculate the apparent total power P at the load end of the substation based on the three-phase current and the total voltage at the load end as follows: Wherein, U is the total voltage at the load end; 4. Make the following decision based on the threshold range of the apparent total power and the three-phase imbalance: a: If the three-phase unbalance is lower than a preset threshold value 1, no adjustment is made to the three-phase current; b: If the three-phase unbalance is between the threshold 1 and a preset threshold 2, 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 is lower than the threshold range; c: If the three-phase unbalance is between the threshold 1 and a preset threshold 2 and the apparent total power is not lower than a preset power threshold or the three-phase unbalance is higher than a preset threshold 2, the three-phase current is adjusted by an automatic phase change method so that the three-phase unbalance is lower than the threshold range; The working process of the dynamic compensation device is as follows: b1: Calculate the total power of each phase according to the total voltage and the total current of each phase; calculate the corresponding partial power according to each partial current and its corresponding partial voltage; b2: The ratio of the sum of the partial power of each phase to the total power of each phase is used as the compensation ratio; wherein the sum of the partial power P ALL The calculation method is as follows: P ALL =P A +P B +P C Among them, P A , P B , P C are the power distribution of phase A, phase B and phase C in the total line at the load end of the substation, U A , U B and U C are the divided voltages of phase A, phase B and phase C respectively, and i, j and k are the divided current quantities of phase A, phase B and phase C in the total line at the load end of the substation respectively; b3: The product of the compensation ratio and the compensation current of each phase is taken as the actual compensation current of each phase; wherein the actual compensation current is calculated as follows: I A0 =TO RA ;K=P ALL / P I B0 =TO RB I C0 =TO RC Where K is the compensation coefficient, I RA ,I RB ,I RC They are the compensation currents of phase A, phase B and phase C respectively; b4: adjusting the current of each phase according to the actual compensation current of each phase so that the three-phase imbalance degree after adjustment is lower than the threshold range.

2. The three-phase unbalanced treatment equipment for the transformer area according to claim 1 is characterized in that: The working process of the phase-changing switch is as follows: Combining multiple sub-currents in each phase into a sub-current set; Redistribute 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; wherein the method for distributing sub-currents comprises the following steps: c1: calculate the sum of the sub-currents of each phase as the actual total current, and average the actual total currents of the three phases; c2: calculate the difference between the actual total current of each phase and the average of the total current, and record it as the ideal switching current of each phase; c3: swap the sub-currents of each phase so that the ideal switching current of each phase tends 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 phase swaps; The current of the replacement group is commuted according to the reorganized divided current of each phase.

3. The three-phase unbalanced treatment equipment for the substation according to claim 1 is characterized in that: The main monitoring device includes a current transformer and an ammeter; the current transformers are respectively mounted on the outside of one of the phase main lines, and are used to collect the current value of the three-phase main line in real time; the ammeter is connected in series to the outside of the current transformer, and is used to monitor the current value passing through the current transformer in real time.

4. The three-phase unbalanced treatment equipment for the transformer area according to claim 1 is characterized in that: The sub-monitoring device includes a smart electric energy meter, the input end of which is connected to any one-phase main line and the neutral line; the output end of the smart electric energy meter is used to supply power to the user end; a voltmeter is connected in parallel in the smart electric energy meter, and the smart electric energy meter is used to collect the user's power consumption and voltage value in real time.

5. The three-phase unbalanced treatment equipment for the transformer area according to claim 1 is characterized in that: The current dynamic compensation device includes an SVG, an IGBT and a capacitor; the SVG is connected in parallel with the three-phase main lines respectively; three parallel current conversion circuits are arranged inside the SVG, and the current conversion circuits are used to convert alternating current into direct current, and then convert direct current into alternating current; the IGBT is connected in series with the three current conversion circuits respectively, and is used to control the on-off state of each current conversion circuit; the capacitor is connected in series with the SVG, and is used to store the direct current generated during the current conversion process.

6. The three-phase unbalance treatment equipment for the transformer area according to claim 5 is characterized in that: The current conversion circuit includes a rectifier and an inverter connected in series; the rectifier is used to convert the AC current higher than the average current in each phase circuit into DC power; the inverter is used to convert the DC power into AC power.

7. The three-phase unbalance treatment equipment for the transformer area according to claim 1 is characterized in that: The phase-changing switch includes a shell and a control circuit; the input end of the control circuit is connected to the three-phase circuit respectively, and the output end is connected to the user end, and the control circuit is used to control the conduction state of the three-phase circuit; when the control circuit is not started, the user end is only connected to any one phase circuit, and the other phase circuits are not connected; the control circuit is accommodated in the shell to prevent the control circuit from being accidentally touched or manually changed.

8. The three-phase unbalance treatment equipment for the transformer area according to claim 7 is characterized in that: The control circuit includes a first electromagnetic relay, a second electromagnetic relay and a plurality of wires; when the control circuit is not started and the user end is connected to the A-phase circuit, the magnetic contacts of the first electromagnetic relay and the magnetic contacts of the second electromagnetic relay are respectively connected to the controller; 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.

9. The three-phase unbalance treatment equipment for the transformer area according to claim 7 is characterized in that: The working process of the control circuit is as follows: 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 to supply power to the client; Ⅱ. When the controller sends a signal to switch the B-phase circuit, the magnetic contact of the first electromagnetic relay is energized, the normally open contact and the normally closed contact of the first electromagnetic relay are switched 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; 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.

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