CN109787254B - Switching strategy for three-phase load unbalance regulation period - Google Patents
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Abstract
A switching strategy for a three-phase load unbalance adjustment period relates to a calculation method of an action period, in particular to a switching strategy for controlling the three-phase load unbalance adjustment period, and relates to an improvement technology of power supply quality of a transformer substation in a transformer area. Mining for three-dimensional dynamic regressionThe method determines a three-phase load imbalance regulation period. The invention balances the factors such as the load rate of the power grid, the three-phase unbalance degree and the like, dynamically switches and adjusts the period of the three-phase unbalance according to the real-time condition of the line on the premise of ensuring the power supply quality, scientifically and reasonably plans the adjusting time, reduces the action times of the relay and prolongs the service life of the relay. The method is realized by the following formula:Z=
*K+T
Description
Technical Field
The invention relates to a calculation method of an action period, in particular to a switching strategy for controlling a three-phase load unbalance regulation period, and relates to a power supply quality improvement technology of a transformer substation in a transformer area.
Background
The low-voltage transmission lines in China are mostly three-phase four-wire power supply networks, and with the improvement of national economic level, the load of the power network is increased rapidly, especially the impact and nonlinear load capacity is increased continuously, so that the power network has the problems of voltage waveform distortion, voltage fluctuation, flicker, three-phase load unbalance and other power quality. The problems of load change, three-phase load unbalance and the like cause negative sequence voltage and negative sequence current of a power grid, the power supply quality is seriously influenced, the line loss is increased, and the power supply reliability is reduced.
At present, the power supply radius of a low-voltage line is long, the power consumption is dispersed, and the conditions that single-phase lighting users and three-phase power users are mixed to use power lead to extreme unbalance of three-phase loads and serious low voltage at the tail end of the line.
In order to improve the power supply quality of a power distribution area, a phase change measure is adopted as a main mode for treating unbalance of three-phase current. With the development of the technology, the load condition is mostly detected at regular intervals, and the phase change switch is controlled to act according to the line condition to complete phase change, so that the three-phase current balance is finally achieved.
In order to ensure the power supply quality, the detection time interval is required to be as short as possible, at present, a fixed time interval is mostly adopted, for example, the detection is carried out once every 15 minutes, and if the three-phase unbalance degree is more than a certain value, the adjustment is completed by adjusting the phase of the load.
The phase change action is completed by a relay, and the mechanical life and the electrical life of the relay are limited. The current technical scheme only considers the power supply quality and does not care about the service life of the relay. If the service life of a relay is 10000 times, in the limit case, a phase change action is executed every 15 minutes, and 10000 times of actions are reached in about 100 days. The damage of the relay not only causes direct economic loss, but also brings about the problem that the three-phase imbalance of the power grid cannot be adjusted in time, and brings about greater hidden danger to the power grid.
Under the condition of light load of a line, generally the load rate is lower than 30%, even if the unbalance degree is large, the transformer cannot be greatly damaged on the premise of meeting the requirement of power utilization of a user; under the condition of heavy load of the line, generally, the load rate is higher than 80%, if three-phase unbalance occurs, the unbalance cannot be greatly improved by adjusting.
When the unbalance degree is higher than a certain degree (the national power grid assessment index is 15%), when the load reaches a certain degree, the three-phase unbalance can bring great harm, such as large loss to the transformer, wide low-voltage problem involvement range of users and the like.
The current technology does not take the above situation as a reference condition.
Disclosure of Invention
The invention aims to adjust and judge the period of three-phase unbalance of a power grid in real time and reduce the action times of a relay on the premise of balancing the factors such as the load rate, the three-phase unbalance and the like of the power grid and guaranteeing the power supply quality.
In order to achieve the purpose, the invention adopts the following technical scheme: the key point of the switching strategy of the three-phase load unbalance regulation period is that,
weight of degree of unbalanceK 1 = a/(a+b)，
Load rate weightK 2 = b/(a+b)，
Wherein a is a three-phase unbalance degree adjusting limit value with a value range of 0-100%, and b is a load rate adjusting lower limit value with a value range of 0-100%;
computingZmin=
，
Wherein x takes the value of 100, y takes the value of c, and c is the upper limit value of load rate adjustment and ranges from 0 to 100 percent;
calculating a correction factorK=(Tmin-Tmax)/Zmin，
Wherein the content of the first and second substances,Tminin order to minimize the time interval between adjustments,Tmaxis the maximum adjustment time interval;
the transformer substation in the transformer area calculates a three-phase unbalance adjustment time interval Z according to the real-time three-phase unbalance x and the line load rate y,
Z(x,y)=
*K+Tmax。
the value of a is 15%, the value of b is 30% and the value of c is 80%.
Tmin(ii) =15 minutes, after the reaction,Tmax=1440 minutes.
If the three-phase unbalance degree of the power supply line exceeds 15%, adjustment is necessary; when the line load rate is less than 30%, even if the unbalance degree is large, the transformer can not be greatly damaged on the premise of meeting the power consumption of a user, in addition, when the line load rate is small, the number of adjustable loads is small, and the adjustment can not work, so that when the line load rate is small, three-phase unbalance adjustment is not carried out or the adjustment period is not prolonged, namely the time interval of two-time adjustment is not carried out.
Under the condition of heavy load of the line, generally, the load rate is higher than 80%, if three-phase unbalance occurs, the unbalance cannot be greatly improved by adjusting.
The invention comprehensively considers the three-phase unbalance degree and the load rate of the line, dynamically switches and adjusts the period of the three-phase unbalance according to the real-time condition of the line on the premise of ensuring the power supply quality of a power grid, scientifically and reasonably plans the adjustment time, reduces the action times of the relay and prolongs the service life of the relay.
Drawings
Fig. 1 is a graph of the calculated three-phase imbalance, line load rate and regulation period of the present invention.
Detailed Description
The method is used for determining the three-phase load unbalance regulation period by adopting a three-dimensional dynamic regression algorithm. The algorithm is implemented by the following formula:
Z=
*K+T
in the formula, the weight of the degree of unbalanceK 1 = a/(a + b), load factor weightK 2 = b/(a+b)。
The method comprises the following steps that a is a three-phase unbalance degree adjusting limit value, the value range is 0-100%, and when the three-phase unbalance degree is larger than a, adjustment is needed; b is a lower limit value of load rate adjustment, the value range is 0-100%, and when the load rate of the line is less than b, adjustment is not performed.
K1The weight representing the degree of unbalance of the three phases of the line,K2and a weight representing a line load rate, the two weights being correlated with each other. The values of a and b can be changed according to different line power supply requirements, so that the two weights are changedThe value is obtained.
In this embodiment, a =15%, b =30%, which can be calculatedK1=0.33，K2=0.67。
When the line load ratio is greater than a certain value, the adjustment of the three-phase imbalance is substantially ineffective, in which case no adjustment is made. The value is the upper limit value c of load factor adjustment, and the value range is 0-100%.
In this example, c = 80%.
When the three-phase unbalance degree of the line is the maximum and the load rate is the maximum, the regulation period of the three-phase unbalance is the minimum.
In this embodiment, when x =100% and y = c =80%, the circuit condition is the worst, and adjustment is required in the shortest time. Calculating according to the parameters:
Zmin=
。
Zmin=-16380。
calculating a correction factorK=(Tmin-Tmax)/Zmin。
Wherein the content of the first and second substances,Tminin order to minimize the time interval between adjustments,Tmaxthe maximum adjustment time interval.
In the embodiment, the minimum adjusting time interval is 15 minutes, namely, the three-phase imbalance is judged and adjusted once every 15 minutes,Tmin=15 minutes; the maximum adjustment time interval is 1 day, i.e.Tmax=1440 minutes.
From this, calculateK=0.087。
And finally, obtaining a calculation formula:
Z(x,y)=
*K+Tmax。
Z(x,y)in the three phases of unbalance ofxLine load ratio ofyIn the case of (2), the time interval of three-phase imbalance is adjusted.
In order to make the result of the algorithm more adaptive to the actual situation, the result can be based on the actual power supply lineHistorical empirical data versus weight parameterK1、K2、KAnd (5) further optimizing.
Historical empirical data can be used for manually determining the optimal adjustment time interval according to actual parameters of the collected lines.
The historical empirical data is a data set, each data item in the set isX，Y，ZTherein ofZIs at a three-phase unbalance ofXLine load ratio ofYIn the case of (2), the optimum adjustment time interval is determined manually.
For each set of data, the following processing is performed:
using the formula of the invention, the unbalance degree of three phases is calculatedxLine load ratio ofyIn the case of (2), adjusting the time interval of three-phase imbalanceZ(Xi,Yi)。
Calculating the mean square error of the result obtained by the formula and the optimal adjustment time:Ei=(Z(Xi,Yi)-Zi)2/2。
wherein the leafXi，Yi，ZiAnd i is the ith item in the data set, i is an integer from 1 to n, and n is the number of data in the data set.
And if the mean square error of 10 continuous times is less than 5 percent, ending.
Otherwise, the following weight and correction coefficient optimization is performed.
K 1=a/(a+b)+Δk 1 ，K 2=b/(a+b)+Δk 2
Regulating rateη=0.25。
According to newly obtainedK1、K2RecalculatingK。
To this end, a calculation function for the three-phase load imbalance regulation period of the line is obtained:
Z(x,y)=
*K+Tmax
the transformer substation calculates the three-phase unbalance adjustment time interval according to the real-time three-phase unbalance x and the line load rate yZ(x,y)And the judgment and adjustment are carried out according to the judgment and adjustment.
As can be seen from figure 1, the adjustment period is shortened along with the increase of the three-phase unbalance degree and the line load rate, and the method accords with the practical application condition.
In actual operation, the transformer substation in the transformer area samples the three-phase unbalance and the line load rate, calculates the three-phase unbalance adjustment time interval according to the sampling result, and adjusts the three-phase unbalance when the time reaches the calculated time.
In this embodiment, the sampling, calculating, and determining the three-phase imbalance adjustment time are performed in two parallel processes.
Sampling and calculating:
6.1, sampling the three-phase unbalance and the line load rate of the transformer substation once per minute, and calculating the average value of the three-phase unbalance and the line load rate when 15 samples are obtained.
6.2, if the three-phase unbalance degree is larger than a and the line load rate is larger than b and smaller than c, 6.3 is executed, and otherwise 6.4 is executed.
6.3, calculating a three-phase imbalance adjustment time interval by taking the average value as a parameter, and storing the acquisition time of the first sample in the calculation plus the calculated time interval as a time point; sample data is cleared and 6.1 is performed.
6.4, clear all sample data or keep the last 10 times sample data, perform 6.1.
Examples are as follows.
For ease of illustration, the start time of the sampling is 00: 00.
Sampling and calculating:
when the time reaches 00:14, 15 samples are collected, data from 0:00 to 0:14 are calculated, the condition of 6.2 is met, the time interval is calculated to be 60 minutes, the collection time of the first sample in the calculation is 00:00, and after 60 minutes is added, 01:00 is stored as a time point. The calculated 15 sample data are cleared and sampling is resumed.
At time 00:29, 15 samples have been collected and the data calculated, not satisfying condition 6.2.
At this time, the calculation may be performed by resampling without considering the data sampled previously. In this embodiment, the correlation of the historical sample data is considered: clearing the samples collected at 00:15, 00:16, 00:17, 00:18 and 00:19, and reserving the latest 10 sampling data; the sampling is started.
When the time reaches 00:34, 15 samples exist, after the data of 00: 20-00: 34 are calculated, the adjustment period is calculated to be 35 minutes, and 00:55 is stored as a time point. The calculated 15 sample data are cleared and sampling is resumed.
When the time reaches 00:49, 15 samples exist, after the data of 00:35 to 00:49 are calculated, the adjustment period is calculated to be 60 minutes, and 01:35 is stored as a time point. The calculated 15 sample data are cleared and sampling is resumed.
Judging the three-phase unbalance adjustment time:
in this example, 3 time points, i.e. 01:00, 00:55, 01:35, have been saved at 00: 50.
When the current time reaches 00:55, 00:55 is one of the saved time points, and the following steps are executed:
carrying out three-phase unbalance adjustment;
all saved time points are cleared, in this embodiment, two time points of 01:00 and 01:35 are cleared.
At this point, there is already sampled data starting at 00:50 during the sampling and calculation process. Since the three-phase imbalance has been adjusted, the original data has no reference, so all sampled data is cleared, 6.1 is executed, and the sampling calculation is restarted.
The practical operation shows that the invention can reduce the action of the relay by more than 40 percent, greatly prolong the service life of the relay and further improve the power supply quality of the circuit.
Claims (7)
1. A switching method of three-phase load unbalance regulation period is characterized in that,
weight of degree of unbalanceK 1 = a/(a+b)，
Load rate weightK 2 = b/(a+b)，
Wherein a is a three-phase unbalance degree adjusting limit value with a value range of 0-100%, and b is a load rate adjusting lower limit value with a value range of 0-100%;
computingZmin=
，
Wherein x takes 100% of value, y takes c which is the upper limit value of load factor adjustment and ranges from 0 to 100%;
calculating a correction factorK=(Tmin-Tmax)/Zmin，
Wherein the content of the first and second substances,Tminin order to minimize the time interval between adjustments,Tmaxis the maximum adjustment time interval;
the transformer substation in the transformer area calculates a three-phase unbalance adjustment time interval Z (x, y) according to the real-time three-phase unbalance x and the line load rate y,
Z(x,y)=
*K+Tmax。
2. the handover method according to claim 1, wherein a takes a value of 15% and b takes a value of 30%.
3. The handover method according to claim 1, wherein c takes a value of 80%.
4. The handover method according to claim 1,Tmin(ii) =15 minutes, after the reaction,Tmax=1440 minutes.
5. The handover method according to claim 1, wherein the handover method is performed based on historical empirical dataK 1 、K 2 AndKthe optimization is carried out, and the optimization is carried out,
history empirical data as data itemX，Y，ZSet of (b) }, in whichZIs at a three-phase unbalance ofXLine load ratio ofYIn the case of (2), the optimum adjustment time interval,
for each data item, the following processing is performed:
Ei=(Z(Xi,Yi)-Zi)2/2，
wherein the leafXi，Yi，ZiIs the ith data item in the set, i is an integer from 1 to n, n is the number of data items in the set,
recording the calculation resultsEiIf the calculation result of 10 times of continuous calculation is less than 5 percent, ending;
if not, then,
K 1=a/(a+b)+Δk 1 ，K 2=b/(a+b)+Δk 2
whereinη=0.25，
RecalculationK。
6. The handover method according to claim 1 or 5,
sampling and calculating:
step 6.1, sampling the three-phase unbalance and the line load rate of the transformer substation once per minute, and calculating the average value of the three-phase unbalance and the line load rate when 15 samples are obtained;
step 6.2, if the three-phase unbalance is larger than a and the line load rate is larger than b and smaller than c, executing step 6.3, otherwise, executing step 6.4;
step 6.3, calculating a three-phase unbalance adjustment time interval by taking the average value as a parameter, and storing the acquisition time of the first sample in the calculation and the calculated three-phase unbalance adjustment time interval as a time point; clearing the sampling data and executing the step 6.1;
6.4, clearing all the sampling data, and executing the step 6.1;
judging the three-phase unbalance adjustment time:
when the current time reaches one of the saved time points, the following steps are executed:
carrying out three-phase unbalance adjustment;
clearing all saved time points;
all sampled data is cleared and step 6.1 is performed.
7. The handover method according to claim 6,
and 6.4, reserving the latest 10 times of sampling data and executing the step 6.1.
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