CN110797887A - Low-voltage transformer area three-phase unbalance management self-decision control method - Google Patents
Low-voltage transformer area three-phase unbalance management self-decision control method Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses a self-decision control method for three-phase unbalance treatment of a low-voltage transformer area, which is characterized in that a commutation switch locally decides whether commutation operation is needed or not without depending on communication; firstly, calculating three-phase voltage unbalance and unbalanced voltage according to three-phase voltage data acquired by a phase change switch, and triggering a phase change strategy when the continuous out-of-limit times of the three-phase voltage unbalance exceed a limit value and the accumulated unbalanced voltage is out of limit; and then, calculating the three-phase voltage value and the three-phase voltage unbalance after the phase change according to the three-phase voltage, the load current, the line equivalent impedance and the current phase of the switch, and if the three-phase voltage unbalance is obviously improved after the phase change, performing the phase change operation. The method not only can effectively reduce the three-phase unbalance degree of the head end of the platform area, but also can reduce the three-phase unbalance degree of each branch line.
Description
Technical Field
The invention relates to a low-voltage transformer area three-phase unbalance management self-decision control method, and belongs to the technical field of low-voltage power grids of power systems.
Background
The problem of unbalanced three-phase load of the low-voltage distribution network exists for a long time in the power grid construction process of China. The low-voltage distribution network usually adopts a three-phase four-wire system power supply mode, and most users are single-phase loads or single-phase and three-phase mixed loads, so that the single-phase loads in the distribution network are distributed among three phases seriously and are unbalanced, particularly in the distribution system of residents and commercial buildings. The problems of overlarge zero line current, overhigh power grid loss, unbalanced three-phase voltage, low power grid voltage, low utilization rate of three-phase power equipment, personal safety endangering due to the fact that neutral line positions are increased and the like can be caused by unbalanced three-phase load.
In rural areas of China, the phenomenon of three-phase load imbalance in a power distribution network generally exists. Research shows that only about 10% of 100 distribution transformers in rural power grids in a certain area operate in a state that three-phase loads are basically balanced, 35% of transformers which operate in a state that the three-phase loads are unbalanced but not exceed the regulated loads and 55% of transformers which operate in a state that the three-phase loads are seriously unbalanced. In cities, the problem of unbalanced three phases of loads still exists, and the unbalanced three-phase loads have certain influence on the normal operation of a low-voltage distribution network, for example, the loss of a transformer and a line is increased, so that the working temperature of the transformer in normal operation is increased, the actual available capacity of the transformer is reduced, the three-phase voltage output by the transformer is unbalanced, the neutral point voltage is deviated, and the electric equipment of a user may be burnt in severe conditions. Therefore, the problem of low-voltage three-phase load imbalance should be sufficiently considered.
In order to reduce the power loss of the distribution area and improve the power quality of the distribution network, effective measures are necessary to treat or eliminate the low-voltage three-phase load imbalance. Besides improving planning and management level, the conventional treatment measures for solving the low-voltage three-phase imbalance problem at home and abroad mainly comprise: manual commutation, a reactive power compensation device, an automatic switching device and the like.
(1) Manual phase change: the load is divided equally by adopting manual adjustment, under the condition that the condition allows, the load is divided equally as much as possible by combining historical records and according to real-time online monitoring data in a manual adjustment wiring mode, and the three-phase load distribution control is enhanced. The problem of unbalanced three phase that brings to distribution transformer, through the statistical analysis to load volume data, then carry out the phase modulation to the load and the light phase sequence of load, make it as far as near three-phase balance, but the single-phase consumer coincidence of user side is lower, user's power consumption condition receives season factor influence simultaneously greatly, there is great difference in the power consumption customer every month or the power consumption in every season usually, this will further lead to distribution transformer's three-phase load more unbalanced, simultaneously because the frequent discontinuity of single-phase load, the adjustment effect is unsatisfactory.
(2) Reactive power compensation device: reactive compensation is carried out aiming at the unbalanced problem, the method is a measure mainly adopted by countries in the world for treating the three-phase unbalanced problem at present, and the reactive compensation device is adopted for carrying out reactive compensation, so that the power factor of the system can be greatly improved, the loss of a line and a transformer can be reduced, and the stability of the system can be improved. At present, static reactive compensators, active filters and the like are generally adopted internationally as important devices for reactive compensation. In an actual power system, three-phase imbalance and reactive power often occur simultaneously, so that the three-phase imbalance control system can have the functions of reactive power compensation and three-phase imbalance suppression simultaneously by improving a control algorithm on the basis of the traditional power electronic SVC or SVG reactive power compensation function. However, such devices are often installed on the low-voltage side of a distribution transformer for centralized compensation, and although the power quality of the voltage and current at the outlet of the transformer can be well adjusted to improve the running state of the transformer, the problem of unbalanced three-phase load of a low-voltage line is not fundamentally solved, and the problems of large line loss and voltage quality of a terminal load still exist.
(3) An automatic switching device: the scheme for adjusting the three-phase unbalanced current by the phase change switching device has the advantages that the intelligent logic judgment is adopted to automatically select the power supply phase, the unbalance of the three-phase load is automatically adjusted, the loss of electric energy in the transmission process is reduced, the problem of low voltage at the tail end of a line is effectively solved, the electric energy utilization rate is maximally improved, and the reliability of power supply of a power grid is enhanced; the power supply circuit has the disadvantages of limited power factor improvement, high overall investment cost of equipment and difficult overall reconstruction of facilities.
The existing three-phase unbalanced load change-over switch needs a control terminal to give a remote control command to complete the switching work of phase change. Generally, a master control terminal is installed at the head end of the low-voltage side of a transformer area, a plurality of phase change switches are installed on branch lines, the master control terminal controls the phase change switches to adjust three-phase imbalance, and the mode has higher requirements on communication conditions. The communication modes of the cell are mainly two types: micropower wireless and carrier communication. Both of these communication modes face engineering implementation difficulties. The micro-power wireless communication can cause communication failure or instability when being blocked. Carrier communication is interfered by power electronic equipment such as SVG (scalable vector graphics) or APF (active power filter), and communication interference is also caused by complex load distribution in an economically developed area.
The invention researches a three-phase unbalance management mode independent of communication, adopts a self-decision built-in control strategy, carries out strategy optimization and processing on the basis of the existing load change-over switch, upgrades the load change-over switch into intelligent load change-over switch equipment, and can complete the three-phase unbalance management in a local area range even if the communication is interrupted.
Disclosure of Invention
Aiming at the limitation of the load regulation mode of the existing phase change switch, the invention provides a method for forming a localized self-decision control strategy by collecting and calculating the voltage of each branch line, relying on phase change switch equipment and not depending on communication, thereby adjusting the phase-to-phase load unbalance state.
The technical solution of the invention is as follows: a low-voltage transformer area three-phase unbalance treatment self-decision control method comprises the following steps:
s1: collecting three-phase voltage and load current at a phase change switch, and checking data reasonability;
s2: calculating the voltage unbalance and the accumulated unbalanced voltage, and judging whether a phase change strategy is triggered or not according to the calculated voltage unbalance and the accumulated unbalanced voltage;
s3: if the current phase is the maximum voltage phase, the phase change operation is not carried out, the operation returns to S1, and otherwise, the operation enters S4;
s4: estimating the voltage change value and the three-phase unbalance treatment effect after phase change;
s5: according to the unbalance degree of three-phase voltage before phase changeAnd improved value of voltage unbalance after phase changeCalculating the execution delay time of the commutation command;
s6: and after the phase change is executed, updating the load to be transferred out of the phase and the load to be transferred into the phase line equivalent impedance table.
The invention has the advantages that:
1) the self-decision control strategy algorithm is embedded in the commutation switch, so that the problems of information loss and the like caused by difficult construction of platform area communication or unstable communication can be avoided, and the bottleneck of three-phase imbalance management by relying on data communication between distribution terminal equipment or a centralized control switch and branch commutation equipment is fundamentally broken through;
2) according to data acquisition and analysis of three-phase voltage at the user side, low-voltage three-phase unbalance self-decision control can be realized, the unbalance degree of three-phase current at the head end of the transformer area is reduced, and the unbalance degree of three-phase current of a branch line is effectively reduced.
Drawings
FIG. 1 is a schematic structural diagram of a low-voltage transformer area three-phase unbalance treatment self-decision control system.
FIG. 2 is an algorithm flow chart of a low-voltage transformer area three-phase unbalance treatment self-decision control method.
Detailed Description
A self-decision control method for three-phase unbalance management in a low-voltage transformer area specifically comprises the following steps:
s1: collecting three-phase voltage and load current at a phase change switch, and checking data reasonability, wherein the measured electric quantity is checked whether to be in a reasonable range, and whether the data is 'dead data' is checked;
s2: calculating the voltage unbalance and the accumulated unbalanced voltage, and judging whether a phase change strategy is triggered or not according to the calculated voltage unbalance and the accumulated unbalanced voltage; step S2 includes steps S21, S22 and S23:
In the formula (I), the compound is shown in the specification,is the maximum value of the three-phase voltage,is the minimum value of the three-phase voltage.
S22: calculating the average voltage of three phasesUnbalanced voltage of phase AUnbalanced voltage of phase BUnbalanced voltage of C phase:
In the formula (I), the compound is shown in the specification,is the voltage of the A-phase,is the phase voltage of the B phase,is C phase voltage;
the unbalanced voltages of the phases are accumulated respectively to obtain the accumulated unbalanced voltages of the phases、And:
s23: entering a phase change strategy when the out-of-limit times of the voltage unbalance degree reach a limit value and the accumulated unbalance voltage value reaches the limit value;
s3: if the current phase is the maximum voltage phase, the phase change operation is not carried out, the operation returns to S1, and otherwise, the operation enters S4;
s4: estimating the voltage change value and the phase change treatment effect after phase change, wherein the method comprises two steps of S41 and S42:
s41: calculating the phase voltage converted from the load after phase changeSum load into phase voltage:
In the formula (I), the compound is shown in the specification,for phase-change preload roll-offThe phase voltages are set to be equal to each other,the load is switched into the phase voltage before phase change, i is the load current,the load is transferred out of the equivalent impedance of the phase line,transferring the load into equivalent impedance of a phase line;
s42: calculated according to S41Andand calculating the unbalance degree of the three-phase voltage after the phase change according to the voltage value of the other phaseIf the degree of unbalance improves by a valueThen, the phase-changing operation is carried out,the threshold is improved for the voltage unbalance.
S5: according to the unbalance degree of three-phase voltage before phase changeAnd improved value of voltage unbalance after phase changeCalculating the execution delay time of the commutation command:
In the formula, T1And T2Respectively corresponding reference delay time to the unbalance degree and corresponding reference delay time to the unbalance degree improvement;
s6: judging whether a phase change condition is met, locking the equipment for a period of time after a phase change command is executed, updating the equivalent impedance table of the load phase-out line and the load phase-in line, and storing the voltage and the equivalent impedance before phase change:
in the formula (I), the compound is shown in the specification,to switch the load out of the phase measurement voltage after the phase change,and switching to a phase measurement voltage after phase change.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (5)
1. A low-voltage transformer area three-phase unbalance management self-decision control method is characterized by comprising the following steps:
s1: collecting three-phase voltage and load current at a phase change switch, and checking data reasonability;
s2: calculating the voltage unbalance and the accumulated unbalanced voltage, and judging whether a phase change strategy is triggered or not according to the calculated voltage unbalance and the accumulated unbalanced voltage;
s3: if the current phase is the maximum voltage phase, the phase change operation is not carried out, the operation returns to S1, and otherwise, the operation enters S4;
s4: estimating the voltage change value and the three-phase unbalance treatment effect after phase change;
s5: according to the unbalance degree of three-phase voltage before phase changeAnd improved value of voltage unbalance after phase changeCalculating the execution delay time of the commutation command;
s6: and after the phase change is executed, updating the load to be transferred out of the phase and the load to be transferred into the phase line equivalent impedance table.
2. The self-decision control method for three-phase imbalance management in a low-voltage transformer area as claimed in claim 1, wherein the step S2 specifically comprises the following steps:
In the formula (I), the compound is shown in the specification,is the maximum value of the three-phase voltage,is the minimum value of the three-phase voltage.
S22: calculating the average voltage of three phasesUnbalanced voltage of phase AUnbalanced voltage of phase B and unbalanced voltage of phase C:
In the formula (I), the compound is shown in the specification,is the voltage of the A-phase,is the phase voltage of the B phase,is C phase voltage;
the unbalanced voltages of the phases are accumulated respectively to obtain the accumulated unbalanced voltages of the phases、And:
s23: and entering a phase change strategy when the out-of-limit times of the voltage unbalance degree reach a limit value and the accumulated unbalance voltage value reaches the limit value.
3. The self-decision control method for three-phase imbalance management in a low-voltage transformer area as claimed in claim 1, wherein the step S4 specifically comprises the following steps:
s41: calculating the phase voltage converted from the load after phase changeSum load into phase voltage:
In the formula (I), the compound is shown in the specification,the load is switched out of the phase voltage before the phase change,the load is switched into phase voltage before phase change, and is the load current,to turn to loadThe equivalent impedance of the outgoing line is obtained,transferring the load into equivalent impedance of a phase line;
s42: calculated according to S41Andand calculating the unbalance degree of the three-phase voltage after the phase change according to the voltage value of the other phaseIf the degree of unbalance improves by a valueThen, a phase change operation is performed to improve the threshold for the voltage imbalance.
4. The self-decision control method for three-phase imbalance management in a low-voltage transformer area as claimed in claim 1, wherein the step S5 specifically comprises the following steps: according to the unbalance degree of three-phase voltage before phase changeAnd improved value of voltage unbalance after phase changeCalculating the execution delay time of the commutation command:
In the formula, T1And T2Are respectively provided withThe reference delay time corresponding to the degree of unbalance and the reference delay time corresponding to the degree of unbalance improvement are set.
5. The self-decision control method for three-phase imbalance management of a low-voltage transformer area according to claim 1, wherein the equivalent impedance of the low-voltage line of the transformer area in the step S6 is the line impedance from the low-voltage side of the distribution transformer to the installation position of each phase-change switch, and the step S6 specifically comprises the following steps:
s61: commutation operation execution conditions: when the command execution time is reached and the switch is not locked;
s62: updating line impedance information:
in the formula (I), the compound is shown in the specification,to switch the load out of the phase measurement voltage after the phase change,to convert the measured voltage of the phase from the load before the phase change,to switch to the phase measurement voltage after the phase change,to switch in the phase measurement voltage before the phase change,is the load current; and writing the equivalent impedance value and the voltage before phase commutation into a database for the next estimated voltage after phase commutation.
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