CN115078820A - Saturation processing method for protection current transformer of low-voltage intelligent circuit breaker - Google Patents
Saturation processing method for protection current transformer of low-voltage intelligent circuit breaker Download PDFInfo
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Abstract
A saturation processing method for a protection current transformer of a low-voltage intelligent circuit breaker belongs to the field of power supply or power distribution circuit systems and comprises the following steps: the protection current transformer with the determined specification and model is arranged in a sampling circuit, different currents are input to the primary side, sampling, filtering and effective value calculation are carried out on the protection current transformer, the obtained effective value is fitted to obtain a relation function, the relation function is written into the low-voltage intelligent circuit breaker, and the current value of the primary side is obtained according to sampling data and the relation function. The mutual inductor does not need to be changed, so that the material is saved; only the program needs to be upgraded for the commissioned equipment, and any hardware change does not need to be made, so that the transformation cost and the transformation time are saved; meanwhile, the device is higher in integration degree, smaller in size and more convenient to install, transport and use.
Description
Technical Field
The invention belongs to the field of power supply or power distribution circuit systems, particularly relates to a low-voltage intelligent circuit breaker, and particularly relates to a saturation processing method of a protection current transformer suitable for the low-voltage intelligent circuit breaker.
Background
The low-voltage circuit breaker is an important component of the electrical appliance industry, and more than 80% of the electric energy generated by the power generation equipment is distributed and used by the low-voltage circuit breaker. About 2 thousands of low-voltage circuit breakers are matched with each 1 ten thousand kW of power generation equipment.
With the development of intelligent power systems, the development of low-voltage intelligent circuit breakers enters a high-speed development stage. The low-voltage intelligent circuit breaker integrates multiple functions of a traditional circuit breaker, an ammeter, leakage protection, surge protection, a timer, over/under voltage protection, three-section over-current protection and multifunctional instrument power distribution equipment, and further ensures the electricity utilization safety.
The low-voltage intelligent circuit breaker has the characteristics of compact structure, small size and the like. In the low-voltage intelligent circuit breaker, a protection current transformer is one of key components, is used for current protection sampling, provides action basis for three-stage overcurrent protection, and generally requires a measurement range of 0.4 In-15 In (In: rated current) and overload precision of 10% (the measurement precision is less than 10% when the current exceeds the rated current).
The rated current (In) is a current when the electric equipment operates at a rated power under a rated voltage. It can also be defined as the current at which the electrical equipment can operate continuously for a long period of time under rated environmental conditions (ambient temperature, sunlight, altitude, installation conditions, etc.). The current of the electrical appliance during normal operation should not exceed its rated current.
The low-voltage intelligent circuit breaker is required to be compact in structure and small in size, the overcurrent protection range is not reduced, but the protection current transformer meeting the size requirement of the low-voltage intelligent circuit breaker generally has a transformer saturation phenomenon when the current reaches 4-6 times of rated current, so that the low-voltage intelligent circuit breaker refuses to operate under high-power rated overcurrent; the size of the low-voltage intelligent circuit breaker of the protection current transformer, which meets the current protection range and can effectively detect the rated current of 15 times or more and carry out accurate protection, can not meet the standard requirements.
The reason for this phenomenon is mainly due to the saturation problem of the protection current transformer, and the solution in the prior art is as follows: the directional silicon steel sheet with good magnetic conductivity is adopted, the seamless annular iron core is adopted, the length of a magnetic circuit is shortened, the area of the iron core is increased to reduce the magnetic flux density of the iron core, the number of turns of a secondary winding is increased, and the like, so that the requirement for high-power rated current detection is met, the size of the transformer is increased, and a large amount of cost is increased.
Disclosure of Invention
The invention aims to provide a method for solving the problem of protection failure caused by saturation of a protection current transformer under the condition of using a transformer with a smaller size and not changing the body of the protection current transformer.
In order to realize the purpose of the invention, the invention adopts the following technical scheme: the saturation processing method of the protection current transformer of the low-voltage intelligent circuit breaker comprises the following steps:
step 1, determining the specification and model of a protection current transformer, arranging the protection current transformer with the determined specification and model in a sampling circuit,
step 2, applying current to the primary side of the protection current transformer, wherein the current is increased from m In to N In by taking m In as a step length, and In is rated current;
after the current is applied stably every time, AD sampling is carried out on the output of the protection current transformer by taking R as frequency in T time, and the applied current and a corresponding original sampling value are recorded;
step 3, carrying out software filtering on the obtained original sampling value, filtering out an interference value, and keeping a true value;
step 4, carrying out integral processing on the data filtered in the step 3, and solving an effective value;
step 5, substituting the effective value obtained in the step 4 into a fitting algorithm to obtain a relation function of a primary side input value and the effective value of the mutual inductor of the protection circuit;
and 6, writing the relation function obtained in the step 5 into an MCU (microprogrammed control Unit), connecting the MCU with the protection current transformer, carrying out AD sampling on the output of the protection current transformer, and obtaining the current value of the primary side according to the sampling data and the relation function.
Has the beneficial effects that: compared with the existing processing method, the invention does not need to change the mutual inductor, thereby saving materials; only the program needs to be upgraded for the commissioned equipment, and any hardware change does not need to be made, so that the transformation cost and the transformation time are saved; meanwhile, the device is higher in integration degree, smaller in size and more convenient to install, transport and use. The invention is not only suitable for a low-voltage intelligent circuit breaker, but also can be used in other application scenes using the protection current transformer, and can improve the protection range and the action precision while reducing the cost and the occupied space of the protection current transformer and realize the purpose of ensuring the reliable operation of a power system.
The invention will be further explained with reference to the drawings.
Drawings
FIG. 1 is a schematic diagram of a sampling circuit;
FIG. 2 shows waveforms at both ends of a sampling resistor with a primary side applied with 1 time of rated current;
FIG. 3 is a graph showing waveforms at both ends of a sampling resistor with 3 times of rated current applied to the primary side;
FIG. 4 is a diagram showing waveforms at both ends of a sampling resistor with 4 times of rated current applied to the primary side;
FIG. 5 is a graph showing waveforms across a sampling resistor with 5 times of rated current applied to the primary side;
FIG. 6 shows waveforms across a sampling resistor with 11 times of rated current applied to the primary side;
FIG. 7 is a flow chart of the present invention.
Detailed Description
The invention has two key premises: 1. whether identifiable differences exist in waveforms output by the current transformer within a required measuring range or not is protected; 2. and whether the waveforms output by the protection current transformers of the same type in the required measuring range are consistent or not.
Before saturation, the device must meet the above requirements, the key being the output after saturation.
A conventional 250A/50mA protection current transformer is selected, and the parallel sampling resistance is 1 omega. When different current values are applied to the primary side, an oscilloscope is used for capturing the sampling resistor, and it can be seen that:
the waveforms in fig. 2 and 3 are basically normal, and it can be seen from fig. 3 that when 4 times of rated current is applied, the secondary side output waveform is already obviously distorted, and the accuracy of algorithms such as FFT and the like commonly used is affected; when 5 times of rated current is applied, the distortion is more obvious, as shown in figure 5; as can be seen from fig. 6, the transformer has approached saturation when the applied value is increased to 11 times the rated current, and the sampling error is more than 50%, which would result in protection rejection if the existing comprehensive protection technology is used.
Theoretically, the characteristics of the transformer depend on the iron core material, the number of turns of the coil, the air gap and the like, and the dependent variable is not changed under the condition of a certain independent variable, namely, the consistency is good.
To verify the above guess, the inventor selects a protection current transformer for a 250A (rated current: 250A) intelligent circuit breaker in north Hu, applies a corresponding rated multiple current value on the primary side, performs AD sampling on the output of the protection current transformer, and solves effective values for comparison, and table 1 shows the effective values of the protection current transformer output under different primary side currents.
Table 1: protecting the effective value of the current transformer output under different primary side currents
The above table clearly shows that: the error between the primary side current value and the calculated effective value is gradually increased along with the increase of the primary side current, and the accurate current value cannot be obtained by adopting the traditional method, but the waveforms output within the range (15 In) required by the specification have identifiable differences.
A plurality of protection current transformers with the same model are selected to carry out the same test, and the result shows that the calculated effective values are very good in consistency under the condition of different primary side current input.
Therefore, the two key preconditions of the invention can be satisfied, and the input and output matching can be carried out again through further processing.
On the basis of the above verification, the present embodiment gives the following steps, see fig. 7:
step 1, determining specification models of protection current transformers, and arranging the protection current transformers with the determined specification models in a sampling circuit, wherein primary side current flows on a bus and passes through the protection current transformers as shown in fig. 1.
When the protection current transformer is determined to be selected, factors to be considered include the materials, the transformation ratio, the forming process and the like of the transformer, the fact that the same specification and model have better consistency parameters is guaranteed, and verification is preferably carried out through the experiment.
Step 2, applying current to the primary side of the protection current transformer, wherein the current is increased from m In to N In by taking m In as a step length, and In is rated current; and after the current is applied stably every time, sampling AD sampling is carried out on the output of the protection current transformer by taking R as frequency in T time, and the applied current and a corresponding AD original sampling value are recorded.
The following are the AD raw sampling values in the monolithic memory when the primary side current is 4 times rated:
:020000042000DA
:0C76F40008000000010000000000000081
:107700000000020007000E0016001E002A003600CE
:1077100044005400630076008900A100BB00D7003C
:10772000FA001F0148017301A001CD01FB012A02EB
:1077300056028502B202DD020A0335036403910397
:10774000BD03E6030E043404530471048A04A00448
:10775000AF04BA04BC04B804AC04960470043A0440
:10776000EF0394032D03C8025F02F5018B0123018F
:10777000BD005E00080000000000010000000000E5
:107780000100030007000E0015001F002A0036004C
:1077900043005300630076008A00A100BB00D800BC
:1077A000F9001F01480172019F01CD01FB0129026F
:1077B00057028502B202DE020903340363038F031A
:1077C000BD03E7030E043204530470048B049E04CB
:1077D000AE04B804BC04B704AC04960470043A04C4
:1077E000EF0395032D03C7025F02F5018A01210112
:0577F000BC005D00007B
:00000001FF
the stepping multiple m and the upper limit multiple N of the current are set according to the requirements of precision and measuring range, and the smaller m is, the higher precision is; the larger N, the larger the range. In the present embodiment, m =0.1 and N = 20. If more accurate data is needed, m can be reduced appropriately; only 15 times of rated value is defined in the specification, and N =20 can meet the general requirement.
After the primary side applied value is stabilized, taking continuous T =20ms AD original sampling values, and the AD sampling frequency R =6400 Hz.
And 3, carrying out software filtering on the obtained original sampling value, filtering out an interference value, and keeping a true value.
And (3) performing software filtering on the obtained AD original sampling value by taking the group as a unit and adopting composite three-point median filtering, filtering out an interference value and keeping a true value.
The sampled values at each current are a set, such as: the first set of 20ms original samples of 0.1In, the third set of 20ms original samples of 0.2In, and so on.
The composite three-point median filtering is an algorithm for filtering and preventing interference through three continuous sampling points, and has multiple implementation modes, wherein the simplest common one is as follows: and comparing the current sampling point by using the average value of the previous sampling point, the next sampling point and the current sampling point, if the average value accords with the fluctuation value of the sine wave, the current sampling point is a real sampling point, if the average value does not accord with the fluctuation value of the sine wave, the current sampling point is interfered, the average value is used for replacing the current sampling point, and if the current abrupt change occurs, additional processing is needed.
And 4, carrying out integral processing on the data filtered in the step 3, and solving an effective value.
When the secondary side output waveform of the protection current transformer begins to be distorted, through test tests, the distorted waveform has larger solving errors by algorithms such as FFT (fast Fourier transform) and the like, and through tests, the effective value is solved by an integral method, so that the solving scheme has the highest precision and is simple in calculation, and the method is suitable for popularization and use.
And 5, executing step 5, substituting the effective value obtained in step 4 into a proper fitting algorithm, and solving a relation function between the primary side input value and the effective value of the mutual inductor of the protection circuit.
In order to obtain a more accurate result, the steps 2 to 4 can be repeated for more than five times, the effective values obtained in the step 4 are averaged, and the average value is used for algorithm fitting.
When fitting, the form of f (x) can be equation of one time, different polynomial (f (x) = a) 1 x m +a 2 x m-1 +... ... +a m x+a m+1 M =2, 3.), hyperbolic equation (f (x) = a) 1 /x+a 2 ) And the protection current transformers with different specifications and models need to determine which form is used specifically according to actual requirements and final fitting precision requirements. When the polynomial is selected, the calculated amount is increased sharply along with the increase of the value of m, so that m is not suitable to be too large.
Fitting was performed with a linear equation.
And (3) setting a plane rectangular coordinate system, wherein y is the value of the applied current on the primary side, x is the effective value obtained in the step (4), and if a straight line is arranged between two adjacent current points, the equation of the straight line between the two points is as follows: y = ax + b, a = (y1-y2)/(x1-x2), b = y1-ax 1.
Wherein, (x1, y1), (x2, y2) respectively correspond to the coordinates of two adjacent points in the rectangular coordinate system.
Thus, the entire fitting curve is composed of multiple straight lines, and when the sampling points are sufficiently dense (i.e., m is sufficiently small), the fitting curve can be well fitted.
Taking the data in table 1 as an example:
the equation of a straight line corresponding to the two points (522.9,612) and (593.3,714) is: y =1.35x-146.21,
the equation of a straight line corresponding to the two points (593.3,714) and (662.0,816) is: y =1.48x-166.88,
… …
the equation for the straight line corresponding to the two points (1499.5,2856) and (1525.9,2958) is: y =3.32x-2121.34,
… …
the equation of a straight line corresponding to the two points (1738.9,3978) and (1761.1,4080) is: y =4.95 x-4011.54.
In practical application, writing the effective value of each section and the corresponding one-dimensional linear equation into the MCU; and taking the obtained effective values as reference, and when the effective values fall between certain effective values, calculating the current value by using a corresponding linear equation of a unary. For example: if the obtained effective value x is equal to or greater than 1499.5 and less than 1525.9, the primary-side current value is calculated with y =3.32 x-2121.34.
Fitting was performed with a polynomial.
In this embodiment, y is the primary-side applied current value, and x is the effective value obtained in step 4, so that y is i And x i One-to-one correspondence, i =1,2,3.. n, then y = f' (x) can be obtained.
i =1, y 1 =0.1In, x1 is the valid value for y1, and N = N/m is the number of samples. In the present embodiment, m =0.1, N =20, and N = 200.
Observed data (x) i ，y i ) The distribution trend In the interval of 0-20 In on the plane is close to the trend of the unitary cubic function, therefore, let f (x) = a 1 x 3 +a 2 x 2 +a 3 x+a 4 When the sum of squares of the distances of f '(x) and f (x) is infinitely close to 0, then f' (x) = f (x) can be considered.
At this time, only a needs to be solved 1 、a 2 、a 3 、a 4 The desired f' (x) can be obtained.
“
"here means" approach ", that is, the former result is made approximately equal to 0, and the smaller the absolute error of the calculated result from 0 is, the better, the optimum result is" =0 ".
When J is
At the time of 0, the number of the first,
k =1,2,3,4, and r is set to make the formula look simple and clear and non-bloated j (x)=x(3-j) J =0,1,2,3, then relates to a 1 、a 2 、a 3 、a 4 The system of linear equations of (1) is:
x is due to 3 、x 2 、x、x 0 The Haar condition is satisfied so the above system of equations has a unique solution.
Order to
Then equation
Can be expressed as:
in this embodiment, according to the input current value and the effective value obtained by processing the AD original sample value, the following solutions are obtained:
a 1 =1.0329e-06，
a 2 =-0.0019918，
a 3 =2.9363，
a 4= -544.99，
the following steps are carried out: y =1.0329e-06 x 3 -0.0019918*x 2 +2.9363*x-544.99。
For the same data, the result obtained by fitting the fourth-order polynomial is basically completely coincided with the data curve, but the calculation amount is large.
And 6, writing the relation function obtained in the step 5 into a low-voltage intelligent circuit breaker program, compiling and burning the relation function into an MCU (microprogrammed control Unit), connecting the MCU with the protection current transformer, carrying out AD sampling on the output of the protection current transformer, and obtaining the current value of the primary side according to the sampling data and the relation function.
Randomly selecting a plurality of current values to be applied to the primary side of the low-voltage intelligent circuit breaker, observing whether the action value of the circuit breaker meets the precision requirement, and if so, indicating that the fitting function obtained in the step 5 is correct and can be used; if not, the obtained fitting function has problems. And repeating the steps 2 to 6 until a fitting function meeting the requirement is obtained.
Because of the performance difference of the protection current transformers with the same specification and model is not great, the protection current transformers can be popularized and used in batches only by fitting once or several times, but because the individuals have certain difference, the correction coefficient operation is required to be carried out: burning the same program on a newly produced low-voltage intelligent circuit breaker using the protection current transformer with the same specification and model, applying rated current on the primary side of the low-voltage intelligent circuit breaker, performing coefficient correction operation, and applying 1In, 10In, 15In and the like on the primary side for verification after the coefficient correction is finished, so as to ensure that each device meets the requirements.
In this example, step 6, the product obtained in step 5 was subjected to
y=1.0329e-06*x 3 -0.0019918*x 2 +2.9363 × x-544.99, writing into the MCU, putting into three-stage overcurrent protection of the low-voltage intelligent circuit breaker, randomly applying current on its primary side, and recording the protection action values as follows:
table 2: application specific data
It can be seen from the above table that the maximum error is less than 3%, which meets the requirements of the relevant specifications.
And writing the effective value of each section obtained by the equation-of-one fitting and the corresponding unitary equation-of-one into the MCU, and putting the MCU into three-section overcurrent protection of low-voltage intelligent short circuit to obtain basically the same result.
In practical application, the fitted curve may be used to calculate the primary side current value under all conditions, or the original function may be used when the primary side current is less than 1In, and the fitted curve may be used to calculate the primary side current value when the primary side current is greater than 1In, and the determination is specifically performed according to the obtained effective value.
And (3) product test results:
the KE-6609-250-series low-voltage intelligent circuit breakers produced by using the protection current transformers are used, and each low-voltage intelligent circuit breaker is provided with 3 protection current transformers; the test mode is as follows: applying a corresponding rated multiple current value on the primary side, and recording a protection current value during the protection action of the circuit breaker, namely a processed 'true value' (effective value); the number of tested low-voltage intelligent circuit breakers is as follows: a batch of 200 protected current transformers under test: 600 protection current transformer devices are randomly extracted, and test results are recorded in the following table.
TABLE 3 test results
TABLE 3 test results
TABLE 3 test results
TABLE 3 test results
TABLE 3 test results
Since only 15 times the rating is defined in the specification, only 20 times the rating is measured.
The consistency for different rated times of current values is shown in the following table.
TABLE 4 consistency
In the above two tables, "multiple" indicates the magnitude of the current applied at the primary side, and is expressed as a multiple of the rated current, and "2" indicates 2In =2 × 250A = 500A.
The consistency calculation method comprises the following steps: the average is first averaged laterally and then divided by the applied current value and then subtracted by 1. The smaller the consistency, the higher the consistency.
As can be seen from Table 2, the maximum error of the low-voltage intelligent circuit breaker adopting the method provided by the invention is less than 3%, and the related standard requirements are met; as can be seen from tables 3 and 4, the low-voltage intelligent circuit breaker manufactured by adopting the protection current transformers of the same type has very good consistency, the results are all less than two thousandths, the judgment consistency standard is that the results are less than one hundredth, and the standard requirements are also met.
Claims (5)
1. The saturation processing method of the protection current transformer of the low-voltage intelligent circuit breaker is characterized by comprising the following steps of:
step 1, determining the specification and model of a protection current transformer, arranging the protection current transformer with the determined specification and model in a sampling circuit,
step 2, applying current to the primary side of the protection current transformer, wherein the current is increased from m In to N In by taking m In as a step length, and In is rated current;
after the current is applied stably every time, AD sampling is carried out on the output of the protection current transformer by taking R as frequency in T time, and the applied current and a corresponding original sampling value are recorded;
step 3, performing software filtering on the obtained original sampling value, filtering out an interference value, and keeping a true value;
step 4, performing integral processing on the data filtered in the step 3, and solving an effective value;
step 5, substituting the effective value obtained in the step 4 into a fitting algorithm to obtain a relation function of a primary side input value and the effective value of the mutual inductor of the protection circuit;
and 6, writing the relation function obtained in the step 5 into an MCU (microprogrammed control Unit), connecting the MCU with the protection current transformer, carrying out AD sampling on the output of the protection current transformer, and obtaining the current value of the primary side according to the sampling data and the relation function.
2. The saturation processing method of the protection current transformer of the low-voltage intelligent circuit breaker according to claim 1, characterized in that: in step 3, the original sampling values are subjected to software filtering by using a composite three-point median filter in a group unit, and the sampling values under each current are in a group.
3. The saturation processing method of the protection current transformer of the low-voltage intelligent circuit breaker according to claim 1, characterized in that:
in step 2, m =0.1 and N = 20; t =20ms, R =6400 Hz.
4. The saturation processing method of the protection current transformer of the low-voltage intelligent circuit breaker according to claim 1, characterized in that: the fitting algorithm in the step 5 specifically comprises:
setting a plane rectangular coordinate system, wherein y is a primary side applied current value, x is an effective value obtained in the step 4, and a relation function of a primary side input value and the effective value of the protection circuit transformer is as follows: y = f' (x),
y i and x i One for each, i =1,2,3,... N, N = N/m,
let f (x) = a 1 x 3 +a 2 x 2 +a 3 x+a 4 ，
When J
At the time of 0, the number of the first,
，k=1,2,3,4；
let r be j (x)=x (3-j) ，j=0,1,2,3；
Then
Solving the system of equations to obtain a 1 、a 2 、a 3 、a 4 ，
Let y = f' (x) = f (x), the relationship function is obtained.
5. The saturation processing method of the protection current transformer of the low-voltage intelligent circuit breaker according to claim 1, characterized in that: in the step 1, m is more than or equal to 0.05, and N is more than or equal to 20.
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