CN115085225A - Transformer area three-phase imbalance management and open capacity calculation method - Google Patents
Transformer area three-phase imbalance management and open capacity calculation method Download PDFInfo
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Abstract
The invention relates to a three-phase unbalance treatment and open capacity calculation method for a transformer area. The treatment method comprises the following steps: firstly, the method comprises the following steps: collecting three-phase current and three-phase voltage of a platform area load end; II, secondly, the method comprises the following steps: calculating the apparent total power of the load end of the transformer area according to the three-phase current and the total voltage of the load end; thirdly, the method comprises the following steps: taking the average value of the three-phase current; taking the difference value of each phase current and the average value as corresponding compensation current; fourthly, the method comprises the following steps: taking the ratio of the maximum compensation current in each phase of compensation current to the maximum current in the three-phase current as the three-phase unbalance; fifthly: and (4) according to the apparent total power and the threshold range of the three-phase unbalance degree, treating the three-phase unbalance of the transformer area by adopting a dynamic compensation or automatic phase commutation method. The three-phase imbalance treatment method for the transformer area combines dynamic compensation and an automatic phase commutation method, achieves accurate and efficient treatment on the three-phase imbalance of the load end of the transformer area, and simultaneously reduces equipment cost and electric energy loss.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a three-phase unbalance treatment method for a transformer area and a transformer area openability capacity calculation method based on three-phase balance.
Background
The three-phase imbalance means that the amplitudes of three-phase currents (or voltages) are inconsistent in a power system, and the amplitude difference exceeds a specified range. The three-phase imbalance of the power system is caused by three-phase load imbalance, different power consumption of single-phase loads, asymmetric three-phase parameters of system elements and the like. The three-phase unbalance of the power system is one of the main indicators of the quality of the electric energy.
Three-phase imbalances in the platform area circuit have the following hazards: 1. increasing the power loss of the line. 2. Increasing the power loss of the distribution transformer. 3. The distribution output decreases. 4. The distribution transformer generates zero sequence current. 5. Affecting the safe operation of the electric equipment.
The existing three-phase unbalance processing method generally adopts the following methods: evenly distributing load, increasing short circuit capacity, static compensation, dynamic compensation, etc. However, due to wiring errors of constructors and untimely power utilization of users, the uniformly distributed charges are difficult to adjust in time, and under the condition that high-power electrical appliances are connected, the three-phase unbalance degree may be increased. Increasing the short-circuit capacity does not fundamentally solve the problem of three-phase imbalance, and although the bearing capacity of the system is improved, the loss of electric quantity is aggravated. Although the static compensation and the dynamic compensation can be accurately regulated, the required equipment quality requirement is higher for power systems with large load capacity such as a platform area, and the treatment cost of three-phase unbalance is increased.
Disclosure of Invention
Therefore, the method for three-phase imbalance management and calculation of the open capacity of the transformer area is needed to solve the problem that the existing three-phase imbalance management is difficult to reduce the management cost under the condition of ensuring accurate and efficient management. The invention is realized by the following technical scheme: a three-phase unbalance treatment method for a transformer area comprises the following steps:
firstly, the method comprises the following steps: collecting three-phase current and three-phase voltage of a platform area load end; the three-phase current comprises an A-phase total current, a B-phase total current, a C-phase total current and a plurality of fractional currents of each phase of current; the three-phase voltage comprises a total voltage of a load end and a partial voltage corresponding to each partial current;
II, secondly: calculating the apparent total power P of the load end of the transformer area according to the three-phase current and the total voltage of the load end as follows:
wherein, I A 、I B And I C The current of the A phase, the B phase and the C phase in a platform load end bus line are respectively, and U is the total voltage of a load end;
thirdly, the steps of: taking an average value of three-phase currents; taking the difference value of each phase current and the average value as corresponding compensation current;
fourthly, the method comprises the following steps: taking the ratio of the maximum compensation current in each phase of compensation current to the maximum current in the three-phase current as the three-phase unbalance;
fifthly: making the following decision according to the apparent total power and the threshold range of the three-phase imbalance degree:
a: if the three-phase unbalance is lower than a preset threshold value I, the three-phase current is not adjusted;
b: if the three-phase unbalance degree is between the first threshold and a second preset threshold and the apparent total power is lower than a preset power threshold, the three-phase current is adjusted by adopting a dynamic compensation method so as to enable the three-phase current to be in a state of being equal to the first threshold
The degree of unbalance is below the threshold range;
c: and if the three-phase unbalance is between the first threshold and a second preset threshold and the apparent total power is not lower than a preset power threshold or the three-phase unbalance is higher than the second preset threshold, adjusting the three-phase current by adopting an automatic phase change method so as to enable the three-phase unbalance to be lower than the threshold range.
The three-phase imbalance treatment method for the transformer area combines dynamic compensation and an automatic phase commutation method, achieves accurate and efficient treatment on the three-phase imbalance of the load end of the transformer area, and simultaneously reduces equipment cost and electric energy loss.
In one embodiment, the compensation current is calculated 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
wherein, I RA 、I RB 、I RC Compensation currents of phase A, phase B and phase C, I AVG Is the average value of the three-phase current.
In one embodiment, the three-phase imbalance is calculated as follows:
ε＝I RMAX /I MAX
wherein ε is the degree of three-phase imbalance, I MAX Is I A 、I B And I C Maximum value of (1); i is RMAX Is I RA 、I RB 、I RC Maximum value of (2).
In one embodiment, the dynamic compensation method comprises the following steps:
b 1: respectively calculating the total power of each phase according to the total voltage and the total current of each phase; calculating corresponding partial power according to each partial current and the corresponding partial voltage;
b 2: taking the ratio of the sum of the fractional powers of all the phases to the total power of all the phases as a compensation proportion;
b 3: taking the product of the compensation proportion and the compensation current of each phase as the actual compensation current of each phase;
b 4: and adjusting the current of each phase according to the actual compensation current of each phase so that the unbalance degree of the three phases after adjustment is lower than the threshold range.
In one embodiment, the sum of the partial powers P ALL The calculation method of (2) is as follows:
P ALL ＝P A +P B +P C
P A ＝U A1 I A1 +U A2 I A2 +…+U Ai I Ai
P B ＝U B1 I B1 +U B2 I B2 +…+U Bj I Bj
P C ＝U C1 I C1 +U C2 I C2 +…+U Ck I Ck
wherein, P A 、P B 、P C The branch power of the A phase, the B phase and the C phase in the load end bus line of the transformer area are respectively, and i, j and k are the branch current quantity of the A phase, the B phase and the C phase in the load end bus line of the transformer area respectively.
In one embodiment, the actual compensation current is calculated as follows:
I A0 ＝KI RA ；K＝P ALL /P
I B0 ＝KI RB
I C0 ＝KI RC
wherein K is a compensation coefficient.
In one embodiment, the auto commutation method is as follows:
combining the plurality of partial currents in each phase into a set of partial currents;
redistributing each partial current in all the partial current sets so that the sum of the partial currents in each partial current set tends to be equal;
and carrying out phase change on the current of the replacement group according to the partial current after each phase is recombined.
In one embodiment, the method for distributing the current comprises the following steps:
c 1: calculating the sum of the partial currents of each phase as the actual total current, and averaging the actual total currents of the three phases;
c 2: calculating the difference value between the actual total current of each phase and the average value of the total current, and recording the difference value as the ideal commutation current of each phase;
c 3: the divided currents of each phase are transposed to make the ideal commutation current of each phase tend to zero; there are various kinds of commutation methods satisfying the conditions, and one having the smallest commutation amount is selected as an actual commutation method to reduce the number of commutation.
The invention also provides a platform area openness capacity calculation method based on three-phase balance, which comprises the following steps:
s1: collecting the maximum allowable current and rated output voltage of the load end of the transformer area, and calculating the rated capacity D of the line 0 ；
S2: counting the maximum historical load D of the load end l ；
S3: calculating the maximum loss D of the line according to the maximum historical load quantity of the load end and the corresponding output capacity loss ；
S4: statistical preconnecting capacitance D p (ii) a The pre-connection capacity represents the total power consumption of the electric appliance communicated with the load end of the transformer area in a future period of time;
s4: the calculated openability capacity D is:
D＝D 0 -D l -D loss -D p 。
in one embodiment, the rated capacity is calculated as follows:
D 0 ＝U 0 I 0
wherein, U 0 To rated voltage, I 0 Is the maximum allowable current;
correspondingly, the calculation method of the maximum loss amount comprises the following steps:
D loss ＝(D l0 -D l )D 0 /D l0
wherein D is l0 The output capacity of the transformer area when the load end reaches the maximum historical load amount.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention combines dynamic compensation and automatic commutation method, under the condition of lower apparent total power, the three-phase unbalance in the preset range is treated by dynamic compensation, and other three-phase unbalance not lower than the preset range is treated by automatic commutation method, thereby achieving the purpose of accurately and efficiently treating the three-phase unbalance at the platform load end, reducing equipment cost and reducing electric energy loss.
2. The automatic commutation method adopted by the invention achieves the purpose of governing the three-phase unbalance by respectively combining the split currents of each phase and then redistributing the split currents under the condition of commutation of the minimum split current, reduces the influence of the commutation process on the electricity consumption of the whole transformer area, reduces the commutation frequency, has lower requirements on commutation equipment, and reduces the cost of the three-phase unbalance governing equipment.
Drawings
Fig. 1 is a flowchart of a method for treating three-phase imbalance in a distribution room in embodiment 1 of the present invention;
fig. 2 is a structural diagram of an intelligent terminal designed according to the platform area three-phase imbalance management method of fig. 1;
FIG. 3 is a schematic structural diagram of a three-phase imbalance treatment apparatus of a platform area designed according to the three-phase imbalance treatment method of the platform area in FIG. 1;
fig. 4 is a schematic circuit structure diagram of the three-phase imbalance treatment equipment in the platform area in fig. 3.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
It will be understood that when an element is referred to as being "mounted on" another element, it can be directly on the other element or intervening elements may also be present. When a component is referred to as being "disposed on" another component, it can be directly on the other component or intervening components may also be present. When an element is referred to as being "secured to" another element, it can be directly secured to the other element or intervening elements may also be present.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "or/and" includes any and all combinations of one or more of the associated listed items.
Referring to fig. 1, fig. 1 is a flowchart of a method for treating three-phase imbalance in a distribution room according to the present embodiment. The embodiment provides a three-phase unbalance treatment method for a transformer area. The treatment method comprises the following steps:
firstly, the method comprises the following steps: and collecting three-phase current and three-phase voltage of a load end of the transformer area. The three-phase current includes a total phase current, and a plurality of fractional currents of each phase current. The three-phase voltage comprises the total voltage of the load end and the partial voltage corresponding to each partial current.
The load side of the distribution room is used for supplying power to a certain area, such as a residential area, an industrial area or a commercial area. In actual electricity utilization, the load end firstly counts electricity consumption in real time through the electric energy meter and then supplies power to the electricity utilization electric appliance. And the current is respectively communicated with each electric energy meter through a three-phase circuit at the total load end of the transformer area. When the current or voltage of the load end of the transformer area is collected, the total current or the total voltage of three phases of the transformer area, and the divided current and the divided voltage communicated to the two ends of each electric energy meter need to be collected respectively.
The method for collecting the current or the voltage can comprise the step of connecting a detection circuit on the outer side of the three-phase circuit respectively, wherein the detection circuit can comprise any one or more of a voltmeter, an ammeter, a multimeter and a mutual inductor. Corresponding rated current and voltage are respectively detected at the total output end of the three-phase circuit, and the total three-phase current at the total output end of the transformer area is respectively marked as I A 、I B And I C The total voltage is denoted as U. And only one of the current or the voltage needs to be detected at two ends of the electric energy meter, and the corresponding current and voltage are calculated according to the real-time electric quantity change of the electric energy meter. According to the phase line communicated with each electric energy meter, each divided current is respectively marked as A-phase divided current I A1 、I A2 、……、I Ai Phase B fractional current I B1 、I B2 、……、I Bj And a C-phase component current I C1 、I C2 、……、I Ck 。
II, secondly: calculating the apparent total power P of the load end of the transformer area according to the three-phase current and the total voltage of the load end as follows:
wherein, I A 、I B And I C The current of the A phase, the B phase and the C phase in a load end bus line of the transformer area are respectively, and U is the total voltage of the load end.
Thirdly, the method comprises the following steps: and averaging the three-phase currents. And taking the difference value of each phase current and the average value as corresponding compensation current. The compensation current is calculated 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
wherein, I RA 、I RB 、I RC Compensation currents of phase A, phase B and phase C, I AVG Is the average value of the three-phase current.
Fourthly, the method comprises the following steps: and taking the ratio of the maximum compensation current in the compensation currents of all phases to the maximum current in the three-phase current as the three-phase unbalance. The method for calculating the three-phase unbalance comprises the following steps:
ε＝I RMAX /I MAX
wherein ε is the degree of three-phase imbalance, I MAX Is I A 、I B And I C Maximum value of (2). I is RMAX Is I RA 、I BB 、I RC Maximum value of (2).
The existing three-phase unbalance degree generally has two calculation methods, including:
ε＝(I MAX -I MIN )/I MAX
ε＝(I MAX -I AVG )/I AVG
wherein, I MIN Is I A 、I B And I C Minimum value of (1).
In this example, I RMAX ＝|I MAX -I AVG I or I MIN -I AVG Compared with the two calculation methods, the three-phase unbalance degree provided by the embodiment can describe the unbalance state of the three-phase current more clearly.
Fifthly: the following decision is made based on the apparent total power and the threshold range of three-phase imbalance:
a: if the three-phase unbalance is lower than a preset threshold value one, the three-phase current is not adjusted. In this embodiment, the threshold one is set to 10%.
b: and if the three-phase unbalance is between the first threshold and a second preset threshold and the apparent total power is lower than a preset power threshold, adjusting the three-phase current by adopting a dynamic compensation method so as to enable the three-phase unbalance to be lower than the threshold range. In this embodiment, the threshold two is set to 15%. The dynamic compensation method comprises the following steps:
b 1: and respectively calculating the total power of each phase according to the total voltage and the total current of each phase. And calculating corresponding power division according to each partial current and the corresponding partial voltage. The total power of the A phase, the B phase and the C phase is respectively marked as P A0 ＝UI A 、P B0 ＝UI B And P C0 ＝UI C 。
b 2: and taking the ratio of the sum of the divided power of each phase to the total power of each phase as a compensation proportion. Sum of partial powers P ALL The calculation method of (2) is as follows:
P ALL ＝P A +P B +P C
P A ＝U A1 I A1 +U A2 I A2 +…+U Ai I Ai
P B ＝U B1 I B1 +U B2 I B2 +…+U Bj I Bj
P C ＝U C1 I C1 +U C2 I C2 +…+U Ck I Ck
wherein, P A 、P B 、P C The sum of the sub-powers of the A phase, the B phase and the C phase in a load end bus line of a transformer area is U A 、U B And U C The voltage distribution is divided into a phase A, a phase B and a phase C, and i, j and k are the number of the divided currents of the phase A, the phase B and the phase C in the load end bus circuit of the transformer area respectively.
b 3: and taking the product of the compensation proportion and the compensation current of each phase as the actual compensation current of each phase. The actual compensation current is calculated as follows:
I A0 ＝KI RA ；K＝P All /P
I B0 ＝KI RB
I C0 ＝KI RC
wherein K is a compensation coefficient.
b 4: and adjusting the current of each phase according to the actual compensation current of each phase so that the adjusted compensation current of each phase is lower than the threshold range.
The dynamic compensation of the currents of the phases can be done by means of an active filter APF or a static var generator SVG. Taking SVG as an example, suppose that in a three-phase unbalanced circuit, I A ＜I B ＜I AVG ＜I C Then, at a certain moment, the alternating current of the C phase is rectified into direct current and stored in the SVG, and at another moment, the direct current stored in the SVG is inverted and then released to the A phase and the B phase, so that the three-phase current reaches a balanced state. Compared with other dynamic compensation methods, the SVG dynamic compensation method has the advantages of being real-time, fast, accurate in compensation and capable of being used at any time.
c: and if the three-phase unbalance is between the first threshold and a second preset threshold and the apparent total power is not lower than a preset power threshold or the three-phase unbalance is higher than the second preset threshold, adjusting the three-phase current by adopting an automatic phase change method so as to enable the three-phase unbalance to be lower than the threshold range. The automatic phase-changing method comprises the following steps:
in each phaseThe plurality of partial currents are combined into one partial current set. The partial currents in the phase a, the phase B and the phase C are respectively combined into a set, and the set is marked as a { I ═ I A1 ，I A2 ，……，I Ai }，B＝{I B1 ，I B2 ，……，I Bj }，C＝{I C1 ，I C2 ，……，I Ck }。
And redistributing each partial current in all the partial current sets so that the sum of the partial currents in each partial current set tends to be equal. The method for distributing the branch current comprises the following steps:
c 1: the sum of the partial currents of each phase is calculated as the actual total current, and the actual total currents of the three phases are averaged. The actual total current for each phase is expressed as:
wherein, I SA 、I SB And I SC Actual total currents of the A phase, the B phase and the C phase are respectively.
Then the average value of the total current I SAVG Is recorded as:
I SAVG ＝(I SA +I SB +I SC )/3。
c 2: and calculating the difference value of the actual total current of each phase and the average value of the total current, and recording the difference value as the ideal phase change current of each phase.
I RA ′＝I SA -I SAVG
I RB ′＝I SB -I SAVG
I RC ′＝I SC -I SAVG
Wherein, I RA ′、I RB ' and I RC ' ideal commutation currents for phases A, B and C, respectively.
c 3: the fractional currents of each phase are transposed so that the ideal commutation current of each phase tends towards zero. There are various kinds of commutation methods satisfying the conditions, and one having the smallest commutation amount is selected as an actual commutation method to reduce the number of commutation.
And carrying out phase change on the current of the replacement group according to the partial current after each phase is recombined.
In this example, assume I A 、I B And I C 21A, 21A and 24A, respectively, the three-phase imbalance is about 8.3%, and the three-phase current does not need to be adjusted.
Let I A 、I B And I C Respectively 18A, 21A and 24A, the unbalance degree of the three phases is 12.5%, and if the apparent total power is 8kW and the preset power threshold is 10KW, the three-phase current is adjusted by adopting a dynamic compensation method.
Let I A 、I B And I C 30A, 45A and 24A respectively, the three-phase unbalance is about 36.4%, and the three-phase current is adjusted by adopting an automatic phase change method. If the number of partial currents in each phase is five, and is denoted by a being {5,7,5,6,7}, B being {6,10,12,8,9}, and C being {3,7,5,4,5}, the ideal commutation current I in each phase is obtained RA ′、I RB ' and I RC ' are 3A, -12A and 9A, respectively. It can be seen that 12A in set B is swapped into set C and 3A in set C is swapped into set a, so that the sum of the partial currents in the three sets is adjusted to 33A. In practical applications, the number of the divided currents of each phase is far more than five, and similarly, the adjustment of the divided currents does not necessarily enable the three-phase currents to be just balanced, as long as the degree of unbalance of the three phases is less than 10%. In addition, when the current compensation method is switched from dynamic compensation to automatic phase commutation, the switching of the branch current is switched from small to large, and the compensation current of the dynamic compensation is changed along with the switching process.
The current per phase is relatively high at high apparent total power, and the compensation current is relatively high at high unbalance of the three phases. If the dynamic compensation method is adopted, the requirement on the specification of the dynamic compensation equipment is correspondingly higher, so that the equipment cost is increased, the loss in the current inversion process is increased, and the waste of electric energy is caused. In the case of a low apparent total power, the current per phase is also relatively low, which means that the number of partial currents for supplying power is also relatively low and the number of users who are using power is small. If the three-phase current is adjusted by adopting the automatic phase-changing method, the adjustment precision is relatively low, and the three-phase current is difficult to be adjusted to a state of tending to balance under the condition of switching a small number of distributed currents. Therefore, the dynamic compensation and the automatic phase change method are combined, the three-phase imbalance of the load end of the transformer area is accurately and efficiently treated, the equipment cost is reduced, and the electric energy loss is reduced.
Please refer to fig. 2, which is a structural diagram of an intelligent terminal designed according to the method for treating three-phase imbalance in a distribution room of fig. 1. In order to facilitate the observation of the change of the three-phase unbalance degree in real time, the embodiment also designs an intelligent terminal to master the change condition of the three-phase current in real time. The intelligent terminal is matched with a plurality of HPLC (high performance liquid chromatography) devices for monitoring voltage and current and AUC (automatic control) devices for treating three-phase unbalance, so that three-phase current data and treatment conditions can be observed in real time.
When the intelligent terminal is used, a plurality of current data communicated with the three-phase circuit are collected through HPLC respectively, the current data are transmitted to the intelligent terminal, and meanwhile, the alternate collection data automatically analyzed by the intelligent terminal are also uploaded synchronously. And the intelligent terminal calculates the three-phase unbalance results of the total output end and each branch of the transformer area according to the current data and the alternating current data, and governs the three-phase unbalance of the transformer area through AUC equipment. The intelligent terminal can be a mobile phone, a computer, a tablet computer, an electronic watch and the like. Taking a mobile phone as an example, an APP for governing three-phase imbalance can be installed on the mobile phone. All data collected by the HPLC can be uploaded to the APP server, so that remote connection between the APP and the HPLC is established for three-phase imbalance management, and three-phase current data are monitored in real time.
In order to maintain three-phase balance of the platform area and avoid overload of any one or more phases of current during peak power utilization, the embodiment further provides a platform area openness capacity calculation method based on three-phase balance, which comprises the following steps:
s1: collecting the maximum allowable current and rated output voltage of the load end of the transformer area, and calculating the rated capacity D of the line 0 . The rated capacity is calculated as follows:
D 0 ＝U 0 I 0
wherein, U 0 To rated voltage, I 0 Is the maximum allowable current.
The maximum allowable current at the load side is related to the material and environmental factors of the transmission line in the three-phase circuit. Wherein, the power transmission material comprises a copper wire, an aluminum wire or an aluminum steel composite wire and the like. The cross-sectional area of the transmission line, the erection structure and the like are direct factors influencing the passing of current. The larger the cross-sectional area of the transmission line, the greater the maximum current allowed to pass. Similarly, the temperature, humidity, air pressure, etc. in the environment also have an effect on the transmission of the current.
S2: counting the maximum historical load D of the load end l . For any region, the load capacity of the region in the last five or last ten years or other time ranges can be counted, and the maximum load capacity of each phase and the total maximum load capacity can be found.
S3: calculating the maximum loss D of the line according to the maximum historical load quantity of the load end and the corresponding output capacity loss . The calculation method of the maximum loss amount comprises the following steps:
D loss ＝(D l0 -D l )D 0 /D l0
wherein D is l0 The output capacity of the transformer area when the load end reaches the maximum historical load amount.
Because the influence of the environmental factors is difficult to obtain through direct measurement, analysis can be performed according to historical data, a difference value between the total output current of the transformer area load end and the actual current consumed by an actual user is used as an influence value, a ratio of the influence value to the total output current in the historical data is fitted, the influence value corresponding to the situation that the total output current reaches the ideal maximum current is calculated, and the influence value is used as the maximum loss.
S4: statistical preconnecting capacitance D p . The pre-connection capacity represents the total electricity consumption of the electric appliance communicated with the load end of the transformer area in a future period of time. When circuit equipment is modified or built in the range of the transformer area, the total power consumption in the transformer area is also modified. And (4) counting planned construction circuits in a future period of time, such as one month, half year or other periods of time, and determining the final required pre-connection capacity, so that the open capacity in the transformer area is sufficient, and power utilization accidents caused by current overload are avoided.
S4: the calculated openability capacity D is:
D＝D 0 -D l -D loss -D p 。
the analysis and calculation results of the open capacity are used for predicting the electricity utilization condition in a period of time in the future, so that the sufficient electricity utilization and the electricity utilization safety in the transformer area are ensured, and the open capacity can be used as reference data for planning a three-phase circuit in the transformer area in the future.
Referring to fig. 3 and 4, fig. 3 is a schematic structural diagram of a three-phase imbalance treatment apparatus of a transformer area designed according to the three-phase imbalance treatment method of the transformer area in fig. 1; fig. 4 is a schematic circuit structure diagram of the three-phase imbalance treatment equipment in the platform area in fig. 3. According to the above three-phase unbalance management method for the transformer area, this embodiment provides a three-phase unbalance management device for the transformer area, which includes: administer device, a plurality of monitoring devices and controller.
The monitoring device is divided into three main detection devices and a plurality of sub-monitoring devices. The main detection device is communicated with a three-phase main line at a platform load end and is used for collecting current and voltage of the three-phase main line in real time. The main monitoring device can be a detection circuit formed by sensitive elements, and comprises a Hall current sensor, a voltage sensor and the like. In the embodiment, a detection circuit formed by a current transformer and an ammeter is used for collecting the current value of the three-phase main line. The three current transformers are respectively sleeved on the outer sides of the three-phase main lines and used for sensing the current amount passing through each main line and measuring the corresponding current value according to the current ratio of the transformers. Each ammeter is connected in series to the outer side of one transformer and used for monitoring the current value passing through the corresponding transformer in real time. Since the total output voltage of the platform load end is generally rated unchanged, the preset output voltage can be used as the actual voltage, or the output voltage can be directly measured to be used as the constant total voltage value. The terminal voltage of the platform area load can be directly measured through a voltmeter or a multimeter, and real-time monitoring is not needed.
The branch monitoring device is used for detecting the real-time electricity utilization current and voltage of the user terminal. Because the user side is often provided with an electric energy meter at the input end, the divided current or the divided voltage of the user side can be directly obtained by measuring and calculating the electric energy meter. If the power consumption voltage of residential area can be regarded as 220V, according to power consumption and power consumption time that the electric energy meter measured, can derive real-time power consumption electric current and be:
I n ＝W t /220t
wherein, I n Is the divided current of any user terminal, t is the detection duration, W t The power consumption of the user terminal in the time length t.
Certainly, in actual power utilization, the partial voltage of each user terminal is affected by line loss and load change, so that in order to improve the accuracy of current monitoring, a voltmeter can be connected in parallel in the electric energy meter for monitoring the partial voltage value of the electric energy meter in real time, and further calculating the corresponding partial current.
The treatment device is used for adjusting the load current of the three-phase main line through corresponding technical means when the three phases are unbalanced so as to enable the current in the three-phase main line to tend to be balanced. The treatment device comprises a current dynamic compensation device and a plurality of phase change switches. The current dynamic compensation device is used for directly adjusting the current of the three-phase main line so as to enable the total current of each phase to tend to be equal. The regulating method comprises the steps of converting part of alternating current exceeding the average current in the three-phase main line into direct current to be stored in the power storage device, and then inverting the direct current into the alternating current to be distributed to a circuit lower than the average current.
The current dynamic compensation device may include a capacitor, and one or both of an active filter (APF) and a Static Var Generator (SVG). Taking SVG as an example, SVG is respectively communicated with a three-phase main line. And three parallel current conversion circuits are arranged in the SVG. The current conversion circuit has a function of converting direct current into alternating current and converting alternating current into direct current. Each current switching circuit is respectively connected with a composite transistor IGBT in series and used for controlling the on-off state of the corresponding current switching circuit. The capacitors are connected in series in the SVG and are respectively communicated with the three current conversion circuits. After the three-phase unbalance degree of the three-phase main circuit exceeds a preset range, the SVG receives a compensation current signal, converts alternating current exceeding the average current value in the three-phase circuit into direct current and stores the direct current in a capacitor, and then converts the direct current in the capacitor into alternating current which is distributed to other-phase main circuits lower than the average value respectively. In this process, the IGBT is used to control the on-off state of the current switching circuit to control the switching of the current. For example, when the phase C current is higher than the average current and the phase a and the phase B currents are lower than the average current, the IGBT controls the current converting circuit connected to the phase C circuit to convert part of the alternating current into direct current, and the current converting circuits connected to the other two phase circuits convert the direct current in the capacitor into alternating current according to the compensation current value and distribute the alternating current to the corresponding main phase lines. In this embodiment, each current converting circuit includes a rectifier and an inverter connected in series, and an IGBT is connected between the rectifier and the inverter to control the direction of current flow. The rectifier is used for converting alternating current higher than average current in each phase circuit into direct current. The inverter is used for converting direct current into alternating current. Of course, in other embodiments, other ways of circuit switching may be used, such as transistors, chips, etc.
Each phase-change switch is communicated with a user terminal, such as the input end of the electric energy meter and the output end of the three-phase main circuit. The phase change switch is used for switching the phase line communicated with the user side. The phase lines communicated with the user side are different, and generally speaking, most residential areas and business areas supply power in a single phase. The industrial area comprises single-phase power supply and three-phase power supply, and the specific power supply proportion is related to the electric appliances of the load. The electric energy meter used by the user side adopting single-phase power supply is usually only communicated with one main phase line. In order to maintain a substantial balance of three-phase currents, a uniform distribution from the three-phase main line is required for single-phase power supply in the same area. However, the power consumption of each user in the same time is different, and the power consumption is different, so that the three-phase main circuit is difficult to achieve the basic balance of the current. The phase-change switch can switch the phase line communicated with the user terminal, thereby changing the load state in the three-phase main circuit and enabling the current of the three-phase main circuit to basically reach a balance state.
The commutation switch comprises a shell and a control circuit. The input end of the control circuit is respectively communicated with the three-phase circuit, and the output end of the control circuit is communicated with the user side. When the phase change switch is not in operation, the user side is conducted with one phase main line through the phase change switch and is not conducted with other phase main lines. The control circuit is used for switching the phase line communicated with the user side according to the phase change signal sent by the controller. The control circuit is accommodated in the shell and used for preventing the control circuit from being touched by mistake to cause power utilization accidents and simultaneously preventing potential risks caused by manual phase change of users or constructors.
The control circuit can be a circuit composed of a plurality of switches and used for controlling the on-off of each phase line, a miniature circuit composed of transistors, or a chip with the function of controlling the on-off of the circuit. In the embodiment, two electromagnetic relays and a plurality of wires are adopted to form a control circuit in consideration of cost and actual installation conditions. The magnetic contacts of the two electromagnetic relays are respectively communicated with the controller and used for receiving the output signals of the controller. In order to distinguish the circuit structure of the electromagnetic relay, a first relay and a second relay are named. In actual installation, when the control circuit is in a non-starting state, the user side is only communicated with any one phase of main line. Taking the phase a circuit as an example, the two normally closed contacts of the first electromagnetic relay are respectively communicated with the user side and the phase a circuit, and the two normally open contacts are respectively communicated with the user side and the phase B circuit. Two normally closed contacts of the second electromagnetic relay are respectively communicated 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 communicated between the user side and the C-phase circuit. And when the three-phase unbalance exceeds a preset threshold range, the controller sends out 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:
and I, when the controller does not send out a phase change signal, the B-phase circuit and the C-phase circuit are not conducted. And the A-phase circuit is communicated with the client and used for supplying power to the client.
And II, when the controller sends a signal for switching the B-phase circuit, the magnetic contact of the first electromagnetic relay is electrified, the normally open contact and the normally closed contact of the first electromagnetic relay are switched to be in a conducting state, the A-phase circuit and the C-phase circuit are not conducted, and the B-phase circuit is conducted with the client and used for supplying power to the client.
And III, when the controller sends a signal for switching the C-phase circuit, the magnetic contact of the first electromagnetic relay and the magnetic contact of the second electromagnetic relay are simultaneously electrified, all normally open contacts and normally closed contacts are switched to be in a conducting state, the A-phase circuit and the B-phase circuit are not conducted, and the C-phase circuit is conducted with the client and used for supplying power to the client.
The controller can calculate the three-phase unbalance and the corresponding compensation current according to the collected data of current, voltage and the like. And then the treatment device is controlled to adjust each phase of current so as to lead the three-phase current to tend to be balanced. Specifically, the controller is configured to:
firstly, calculating the three-phase unbalance according to the three-phase current as follows:
ε＝(I MAX -I MIN )/I MAX
wherein ε is the degree of three-phase imbalance, I MAX Is I A 、I B And I C Maximum value of (1), I MIN Is I A 、I B And I C Minimum value of (1), I A 、I B And I C The current of the A phase, the B phase and the C phase in the main circuit of the load end of the transformer area are respectively.
And secondly, averaging the three-phase currents. And taking the difference value of each phase current and the average value as a corresponding compensation current. The compensation current is calculated 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
wherein, I RA 、I RB 、I RC Compensation currents of phase A, phase B and phase C, I AVG Is the average value of the three-phase current.
Thirdly, the method comprises the following steps: calculating the apparent total power P of the load end of the transformer area according to the three-phase current and the total voltage of the load end as follows:
wherein, U is the total voltage of the load end.
Fourthly, making the following decision according to the apparent total power and the threshold range of the three-phase unbalance:
a: if the three-phase unbalance is lower than a preset threshold value one, the three-phase current is not adjusted. In this embodiment, the threshold one is set to 10%.
b: and if the three-phase unbalance is between the first threshold and a second preset threshold and the apparent total power is lower than a preset power threshold, adjusting the three-phase current by adopting a dynamic compensation method so as to enable the three-phase unbalance to be lower than the threshold range. In this embodiment, the threshold two is set to 15%.
The dynamic compensation device works as follows:
b 1: and respectively calculating the total power of each phase according to the total voltage and the total current of each phase. And calculating corresponding power division according to each partial current and the corresponding partial voltage.
b 2: and taking the ratio of the sum of the divided power of each phase to the total power of each phase as a compensation proportion. Wherein the sum of the partial powers P ALL The calculation method of (2) is as follows:
P ALL ＝P A +P B +P C
wherein, P A 、P B 、P C The sub-powers, U, of A, B and C phases in a load end bus line of a transformer area A 、U B And U C The voltage distribution is divided into a phase A, a phase B and a phase C, and i, j and k are the number of the divided currents of the phase A, the phase B and the phase C in the load end bus circuit of the transformer area respectively.
b 3: and taking the product of the compensation proportion and the compensation current of each phase as the actual compensation current of each phase. The calculation method of the actual compensation current comprises the following steps:
I A0 ＝KI RA 。K＝P ALL /P
I B0 ＝KI RB
I C0 ＝KI RC
wherein K is a compensation coefficient, I RA 、I RB 、I RC The compensation currents of the A phase, the B phase and the C phase are respectively.
b 4: and adjusting each phase current according to the actual compensation current of each phase so that the unbalanced degree of the three phases after adjustment is lower than the threshold range.
c: and if the three-phase unbalance is between the first threshold and the second preset threshold and the apparent total power is not lower than the first preset power threshold or the three-phase unbalance is higher than the second preset threshold, adjusting the three-phase current by adopting an automatic phase change method so as to enable the three-phase unbalance to be lower than the threshold range.
The working process of the phase change switch is as follows:
the multiple partial currents in each phase are combined into one set of partial currents. The partial currents in the phase a, the phase B and the phase C are respectively combined into a set, and the set is marked as a { I ═ I A1 ，I A2 ，……，I Ai }，B＝{I B1 ，I B2 ，……，I Bj }，C＝{I C1 ，I C2 ，……，I Ck }。
And redistributing each partial current in all the partial current sets so that the sum of the partial currents in each partial current set tends to be equal. The method for distributing the branch current comprises the following steps:
c 1: the sum of the partial currents of each phase is calculated as the actual total current, and the actual total currents of the three phases are averaged. The actual total current for each phase is expressed as:
wherein, I SA 、I SB And I SC Actual total currents of the A phase, the B phase and the C phase are respectively.
Then the average value of the total current I SAVG Is recorded as:
I SAVG ＝(I SA +I SB +I SC )/3。
c 2: and calculating the difference value of the actual total current of each phase and the average value of the total current, and recording the difference value as the ideal phase change current of each phase.
I RA ′＝I SA -I SAVG
I RB ′＝I SB -I SAVG
I RC ′＝I SC -I SAVG
Wherein, I RA ′、I RB ' and I RC ' ideal commutation currents for phases A, B and C, respectively.
c 3: the fractional currents of each phase are transposed so that the ideal commutation current of each phase tends towards zero. There are various kinds of commutation methods satisfying the conditions, and one having the smallest commutation amount is selected as an actual commutation method to reduce the number of commutation.
And carrying out phase change on the current of the replacement group according to the partial current after each phase is recombined.
In this example, assume I A 、I B And I C 21A, 21A and 24A, respectively, the three-phase imbalance is about 8.3%, and the three-phase current does not need to be adjusted.
Let I A 、I B And I C Respectively 18A, 21A and 24A, the three-phase unbalance degree is 12.5%, and if the apparent total power at this time is 8kW and the preset power threshold is 10kW, the three-phase current is adjusted by adopting a dynamic compensation method.
Let I A 、I B And I C 30A, 45A and 24A respectively, the three-phase unbalance is about 36.4%, and the three-phase current is adjusted by adopting an automatic phase change method. If the number of the partial currents in each phase is five, and is denoted as a ═ 5,7,5,6,7, B ═ 6,10,12,8,9, and C ═ 3,7,5,4,5, then the ideal commutation current I in each phase is obtained RA ′、I RB ' and I RC ' are 3A, -12A and 9A, respectively. It can be seen that 12A in set B is swapped into set C and 3A in set C is swapped into set a, so that the sum of the partial currents in the three sets is adjusted to 33A. In practical applications, the number of the divided currents of each phase is far more than five, and similarly, the adjustment of the divided currents does not necessarily enable the three-phase currents to be just balanced, as long as the degree of unbalance of the three phases is less than 10%. In addition, when the current compensation method is switched from dynamic compensation to automatic phase commutation, the switching of the branch current is switched from small to large, and the compensation current of the dynamic compensation is changed along with the switching process.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A three-phase unbalance treatment method for a transformer area is used for adjusting three-phase current at a load end of the transformer area so as to enable the three-phase current to tend to be balanced and reduce power consumption loss caused by three-phase unbalance; it is characterized by comprising the following processes:
firstly, the method comprises the following steps: collecting three-phase current and three-phase voltage of a platform area load end; the three-phase current comprises an A-phase total current, a B-phase total current, a C-phase total current and a plurality of fractional currents of each phase of current; the three-phase voltage comprises a total voltage of a load end and a partial voltage corresponding to each partial current;
II, secondly, the method comprises the following steps: calculating the apparent total power P of the load end of the transformer area according to the three-phase current and the total voltage of the load end as follows:
wherein, I A 、I B And I C The current of the A phase, the B phase and the C phase in a platform load end bus line are respectively, and U is the total voltage of a load end;
thirdly, the method comprises the following steps: taking an average value of three-phase currents; taking the difference value of each phase current and the average value as corresponding compensation current;
fourthly, the method comprises the following steps: taking the ratio of the maximum compensation current in each phase of compensation current to the maximum current in the three-phase current as the three-phase unbalance;
fifthly: making the following decision according to the apparent total power and the threshold range of the three-phase imbalance degree:
a: if the three-phase unbalance is lower than a preset threshold value I, the three-phase current is not adjusted;
b: if the three-phase unbalance is between the first threshold and a second preset threshold and the apparent total power is lower than a preset power threshold, adjusting three-phase currents by adopting a dynamic compensation method so as to enable the three-phase unbalance to be lower than the threshold range;
c: and if the three-phase unbalance is between the first threshold and a second preset threshold and the apparent total power is not lower than a preset power threshold or the three-phase unbalance is higher than the second preset threshold, adjusting the three-phase current by adopting an automatic phase change method so as to enable the three-phase unbalance to be lower than the threshold range.
2. The three-phase unbalance management method for the transformer area according to claim 1, wherein the compensation current is calculated by the following method:
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
wherein, I RA 、I RB 、I RC Compensation currents of phase A, phase B and phase C, I AVG Is the average value of the three-phase current.
3. The three-phase unbalance management method in the transformer area according to claim 2, wherein the three-phase unbalance degree is calculated by the following method:
ε＝I RMAX /I MAX
wherein ε is the degree of three-phase imbalance, I MAX Is I A 、I B And I C Maximum value of (1); i is RMAX Is I RA 、I RB 、I RC Of (2) is calculated.
4. The three-phase unbalance management method for the transformer district of claim 3, wherein the dynamic compensation method comprises the following steps:
b 1: respectively calculating the total power of each phase according to the total voltage and the total current of each phase; calculating corresponding partial power according to each partial current and the corresponding partial voltage;
b 2: taking the ratio of the sum of the fractional powers of all the phases to the total power of all the phases as a compensation proportion;
b 3: taking the product of the compensation proportion and the compensation current of each phase as the actual compensation current of each phase;
b 4: and adjusting the current of each phase according to the actual compensation current of each phase so that the unbalance degree of the three phases after adjustment is lower than the threshold range.
5. The method of claim 4, wherein the sum P of the sub-powers is equal to or less than the sum P of the sub-powers ALL The calculation method of (2) is as follows:
P ALL ＝P A +P B +P C
P A ＝U A1 I A1 +U A2 I A2 +…+U Ai I Ai
P B ＝U B1 I B1 +U B2 I B2 +…+U Bj I Bj
P C ＝U C1 I C1 +U C2 I C2 +…+U Ck I Ck
wherein, P A 、P B 、P C The branch power of the A phase, the B phase and the C phase in the load end bus line of the transformer area are respectively, and i, j and k are the branch current quantity of the A phase, the B phase and the C phase in the load end bus line of the transformer area respectively.
6. The three-phase unbalance management method for the transformer area according to claim 5, wherein the actual compensation current is calculated by the following method:
I r0 ＝KI RA ；K＝P ALL /P
I B0 ＝KI RB
I C0 ＝KI RC
wherein K is a compensation coefficient.
7. The three-phase unbalance management method for the transformer area according to claim 3, wherein the automatic phase-changing method comprises the following steps:
combining the plurality of partial currents in each phase into a set of partial currents;
redistributing each partial current in all the partial current sets so that the sum of the partial currents in each partial current set tends to be equal;
and carrying out phase change on the current of the replacement group according to the partial current after each phase is recombined.
8. The three-phase imbalance management method for the transformer district of claim 7, wherein the current distribution method comprises the following steps:
c 1: calculating the sum of the partial currents of each phase as the actual total current, and averaging the actual total currents of the three phases;
c 2: calculating the difference value of the actual total current and the average value of the total current of each phase, and recording as the ideal phase-change current of each phase;
c 3: the divided currents of each phase are transposed to make the ideal commutation current of each phase tend to zero; there are various kinds of commutation methods satisfying the conditions, and one having the smallest commutation amount is selected as an actual commutation method to reduce the number of commutation.
9. A platform area openability capacity calculation method based on three-phase balance adjusts three-phase currents of a platform area through the three-phase unbalance treatment method according to any one of claims 1 to 8, and then openability capacity is calculated in a platform area circuit with the three-phase balance; the method is characterized by comprising the following steps:
s1: collecting the maximum allowable current and rated output voltage of the load end of the transformer area, and calculating the rated capacity D of the line 0 ；
S2: counting the maximum historical load D of the load end l ；
S3: according to the loadCalculating the maximum loss D of the line by the maximum historical load of the terminal and the corresponding output capacity loss ；
S4: statistical preconnecting capacitance D p (ii) a The pre-connection capacity represents the total power consumption of the electric appliance communicated with the load end of the transformer area in a future period of time;
s4: the calculated openability capacity D is:
D＝D 0 -D l -D loss -D p 。
10. the three-phase balance-based bay openness capacity calculation method of claim 9, wherein the rated capacity is calculated as follows:
D 0 ＝U 0 I 0
wherein, U 0 To rated voltage, I 0 Is the maximum allowable current;
correspondingly, the calculation method of the maximum loss amount comprises the following steps:
D loss ＝(D l0 -D l )D 0 /D l0
wherein D is l0 The output capacity of the transformer area when the load end reaches the maximum historical load amount.
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