Method for correcting V-shaped characteristic curve of large generator

Abstract

The invention discloses a method for correcting a V-shaped characteristic curve of a large generator, and belongs to the technical field of large generators. The problem that in the prior art, a V-shaped characteristic curve generated in a traditional testing experiment has a large offset error is solved. The method comprises the following steps: acquiring original data obtained in a V-shaped characteristic test process; carrying out a no-load characteristic test on the generator to obtain a test result of stator voltage and exciting current, and drawing a no-load characteristic curve; according to the deviation value of the rated stator voltage, the deviation value of the excitation current is obtained through auxiliary solving of the no-load characteristic curve; and correcting the stator current and the exciting current by taking the rated stator voltage as a reference to obtain the corrected stator current and the corrected exciting current, and drawing a corrected V-shaped characteristic curve under each load. The method effectively solves the problem of deviation of an original test V-shaped characteristic curve, and can be applied to calibration of a reference curve for generator operation.

Description

Technical Field

[0001] The present invention relates to a method for correcting the V-shaped characteristic curve of a large generator, and belongs to the technical field of large generators. Background Art

[0002] The characteristic curve of a large generator reflects the operating characteristics of the generator, the mutual relationship and change trend among electrical parameters; among them, the relationship curve between the stator current and the excitation current is shaped like the letter "V" and is called the V-shaped characteristic curve. The V-shaped characteristic curve reflects the normal excitation, over-excitation, and under-excitation operating states of the generator; the lowest point of the V-shaped characteristic curve corresponds to normal excitation, the right side of the curve is over-excitation, that is, reactive power is generated, and the left side of the curve is under-excitation, that is, reactive power is absorbed. The V-shaped characteristic curve of a large generator is not a single curve, but a curve family composed of several curves.

[0003] At present, the actual V-shaped characteristic curve of a large generator is determined by experimental methods, that is, when the generator is connected to the grid and running, the active power is kept constant, the excitation current is increased or decreased to adjust the reactive power, and at the same time, the stator current and the excitation current are measured, and the V-shaped characteristic curve is plotted according to the stator current and the excitation current; due to grid connection operation, the stator voltage of the generator is the same as the grid voltage, and affected by the grid voltage, the stator voltage of the generator is usually not equal to the rated stator voltage; the rated stator voltage is a standard voltage value determined according to factors such as the insulation class and temperature rise limit of the motor stator during the design of the motor stator, and it is unique; while the stator voltage is the voltage value during the actual operation of the generator, and it fluctuates within a certain range with the rated voltage as the base value, and it is not fixed, and is often higher or lower than the rated stator voltage value; due to the influence of the stator voltage fluctuation with the grid voltage, the stator current and the excitation current during the operation of the generator also change, causing the shape of the V-shaped characteristic curve measured by the experiment to shift, and the shifted V-shaped characteristic curve loses the reference and comparison benchmark function.

[0004] In summary, a method for correcting the V-shaped characteristic curve of a large generator is needed to obtain a reference V-shaped characteristic curve. Summary of the Invention

[0005] A brief overview of the present invention is given below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify the key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is only to present certain concepts in a simplified form as a prelude to a more detailed description to follow.

[0006] In view of this, to solve the problem that the V-shaped characteristic curve generated in the traditional test in the prior art has a large offset error, the present invention provides a method for correcting the V-shaped characteristic curve of a large generator.

[0007] The technical solution is as follows: A method for correcting the V-shaped characteristic curve of a large generator, comprising the following steps:

[0008] S1. Obtain the original data obtained during the test V-shaped characteristic test, including active power, stator voltage, stator current, and excitation current;

[0009] S2. Conduct an open-circuit characteristic test of the generator to obtain the test results of the stator voltage and the excitation current, and plot the open-circuit characteristic curve;

[0010] S3. Based on the deviation value between the test result of the stator voltage and the rated stator voltage, and through the auxiliary solution of the open-circuit characteristic curve, obtain the deviation value of the excitation current;

[0011] S4. Taking the rated stator voltage as a reference, according to the stator current and the stator voltage, correct the stator current to obtain the corrected stator current;

[0012] S5. Based on the test result of the excitation current and the deviation value of the excitation current, correct the excitation current to obtain the corrected excitation current;

[0013] S6. According to the corrected stator current and the corrected excitation current, plot the corrected V-shaped characteristic curve under each load.

[0014] Further, in the above S1, when the active power of the generator is 0, 50%P N , 75%P N , 100%P N respectively, where P N is the rated active power of the generator, increase or decrease the excitation current, adjust the reactive power, conduct the V-shaped characteristic test, and obtain the original data.

[0015] Further, in the above S4, the corrected stator current I a ' is expressed as:

[0016] I a ' = I a * U a / U N

[0017] Wherein, the unit of the corrected stator current I a ' is A, I a is the stator current, the unit is A, U a is the stator voltage, the unit is V, and U N is the rated stator voltage, the unit is V.

[0018] Further, in the above S5, the corrected excitation current I f ' is expressed as:

[0019] I f ' = I f + ΔI f

[0020] Among them, I f is the exciting current, with the unit of A, and ΔI f is the deviation value of the exciting current, with the unit of A.

[0021] The beneficial effects of the present invention are as follows: The present invention corrects the V-shaped characteristic curve drawn based on the original test data. The corrected V-shaped characteristic curve is unique and can be used as the reference curve for the operation of the generator, playing a reference role in the safe operation, reactive power regulation, and fault analysis of large generators; since the stator voltage fluctuates up and down within a certain range with the grid voltage, the change of the stator voltage causes the stator current and the exciting current to change, and the shape of the V-shaped characteristic curve drawn from the original data shifts. However, the correction of the V-shaped characteristic curve of the large generator is carried out based on the rated stator voltage, and it can unify the fluctuating stator voltage to the rated stator voltage of a fixed value; the V-shaped characteristic curve drawn using the original data has a shift, the underexcited part on the left side of the curve is too high, and the overexcited part on the right side of the curve is too low, which is inconsistent with the shape of the V-shaped characteristic design curve. However, the V-shaped characteristic curve drawn according to the corrected data in the present invention has the left and right parts of each curve symmetric, which is consistent with the shape of the design curve and truly reflects the mutual relationship and operating characteristics between the stator current and the exciting current. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the present invention and form a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0023] Figure 1 is a schematic flow chart of the method for correcting the V-shaped characteristic curve of a large generator;

[0024] Figure 2 is a schematic diagram of the V-shaped characteristic curve of the original data;

[0025] Figure 3 is a schematic diagram of the no-load characteristic curve;

[0026] Figure 4 is a schematic diagram of the corrected V-shaped characteristic curve.

[0027] Reference numerals in the drawings:

[0028] 1. V-shaped characteristic curve of the original data when P = 0, where P is the active power; 2. V-shaped characteristic curve of the original data when P = 50%P N ; 3. is the V-shaped characteristic curve of the original data when P = 75%PN V-shaped characteristic curve of the original data at; 4. P = 100%P N V-shaped characteristic curve of the original data at; 5. No-load characteristic curve; 6. Corrected V-shaped characteristic curve at P = 0; 7. P = 50%P N Corrected V-shaped characteristic curve at; 8. P = 75%P N Corrected V-shaped characteristic curve at; 9. P = 100%P N Corrected V-shaped characteristic curve at. Detailed implementation manner

[0029] In order to make the technical solutions and advantages in the embodiments of the present invention clearer and more understandable, the following further details the exemplary embodiments of the present invention with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than an exhaustive list of all embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0030] Refer to Figures 1-4 This embodiment is described in detail. The method for correcting the V-shaped characteristic curve of a large generator specifically includes the following steps:

[0031] S1. Obtain the original data obtained during the test V-shaped characteristic test, which includes active power, stator voltage, stator current, excitation current, etc.;

[0032] S2. Conduct a no-load characteristic test of the generator to obtain the test results of the stator voltage and the excitation current, and draw a no-load characteristic curve;

[0033] S3. According to the deviation value between the test result of the stator voltage and the rated stator voltage, and with the assistance of the no-load characteristic curve, obtain the deviation value of the excitation current;

[0034] S4. Based on the rated stator voltage as a reference, according to the stator current and the stator voltage, correct the stator current to obtain the corrected stator current;

[0035] S5. According to the test result of the excitation current and the excitation current deviation value, correct the excitation current to obtain the corrected excitation current;

[0036] S6. According to the corrected stator current and the corrected excitation current, draw the corrected V-shaped characteristic curves under each load.

[0037] Furthermore, in S1, when the active power of the generator is 0, 50%P N , 75%P N , 100%P N respectively, P N$P_{N}$ is the rated active power of the generator. By increasing or decreasing the excitation current, the reactive power is adjusted, and the V - characteristic test is carried out to obtain the original data.

[0038] Further, in the step S4, the corrected stator current $I$ a ' is expressed as:

[0039] $I$ a ' = $I$ a *$U$ a / $U_{N}$ N

[0040] wherein, the unit of the corrected stator current $I$ a ' is A, $I$ a is the stator current with the unit of A, $U$ a is the stator voltage with the unit of V, and $U_{N}$ N is the rated stator voltage with the unit of V;

[0041] Specifically, when the active power of the generator is constant, the product of the current and the voltage is a constant value, and the corrected stator current $I$ a ' is obtained. When $U$ a >$U_{N}$ N the corrected stator current $I$ a '>$I$ a ; when $U$ a <$U_{N}$ N the corrected stator current $I$ a '<$I$ a ;

[0042] Further, in the step S5, the corrected excitation current $I$ f ' is expressed as:

[0043] $I$ f ' = $I$ f + $\Delta I$ f

[0044] wherein, $I$ f is the excitation current with the unit of A, and $\Delta I$ f is the deviation value of the excitation current with the unit of A;

[0045] Specifically, since the no - load characteristic curve is non - linear, the ratio of the deviation value of the excitation current $\Delta I$ f , the stator voltage, and the deviation value of the rated stator voltage $\vert U$ a - $U_{N}$ N $\vert$ is also non - linear. Therefore, it is more convenient to determine $\Delta I$ f by using the graphical method. Since the deviation value of the excitation current $\Delta I$ f has positive and negative signs, when $U$ a >$U_{N}$ N the corrected stator current $I$f '<I f ; When U a <U N is the case, the corrected stator current I f '>I f ;

[0046] Reference Figure 2 , the V - shape characteristic test is carried out under four typical active power conditions. During the test, the active power needs to be kept constant. At least five test points are collected under each condition, two test points under underexcitation, one test point under normal excitation, and two test points under overexcitation. The three - phase stator voltage and three - phase stator current measured are averaged. The V - shape characteristic curve drawn based on the original data shows that the left and right parts of each curve are significantly asymmetric. It is higher on the left side under underexcitation and lower on the right side under overexcitation; in the rectangular coordinate system where the V - shape characteristic curve of the original data is located, the horizontal axis is the excitation current I f (A), and the vertical axis is the stator current I a (A);

[0047] Reference Figure 3 , during the no - load test of the generator, the stator winding is no - load, the excitation is separately excited, and the excitation current is adjusted unidirectionally to synchronously change the stator voltage. At the same time, the stator voltage and the excitation current are recorded. In the rectangular coordinate system where the no - load characteristic curve is located, the stator voltage U a is set as point A, and the rated stator voltage U N is set as point B. Then, auxiliary lines parallel to the horizontal axis are drawn through point A and point B respectively, intersecting the no - load characteristic curve at point C and point D. Finally, auxiliary lines parallel to the vertical axis are drawn through point C and point D respectively, intersecting the horizontal axis at point E and point F. The distance between point E and point F is the deviation value ΔI f of the excitation current. When U a >U N , the sign of the deviation value ΔI f of the excitation current is negative; when the measured stator voltage U a <U N , the sign of the deviation value ΔI f of the excitation current is positive. Among them, the horizontal axis is the excitation current I f (A), the vertical axis is the no - load stator voltage U0(V), point A is the stator voltage U a , point B is the rated stator voltage U N , point C is the point on the no - load characteristic curve corresponding to the stator voltage U a , point D is the point on the no - load characteristic curve corresponding to the rated stator voltage U N , point E is the excitation current corresponding to the stator voltage U a of the original data, point F is the excitation current corresponding to the rated stator voltage, and the distance between point E and point F is the obtained deviation value ΔI of the excitation currentf ;

[0048] Reference Figure 4 , in the rectangular coordinate system where the corrected V-shaped characteristic curve is located, the horizontal axis is the excitation current I f (A), and the vertical axis is the stator current I a (A). The corrected V-shaped characteristic curve is unique, and the left and right parts of each curve are symmetric. The corrected V-shaped characteristic curve can be used as a reference characteristic curve, which has a role of reference and comparison for the safe operation, reactive power regulation, and fault analysis of large generators.

[0049] Although the present invention has been described based on a limited number of embodiments, those skilled in the art in this technical field will understand, based on the above description, that other embodiments can be envisioned within the scope of the present invention thus described. In addition, it should be noted that the language used in this specification is mainly selected for readability and teaching purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Therefore, many modifications and changes are obvious to those of ordinary skill in this technical field without departing from the scope and spirit of the appended claims. For the scope of the present invention, the disclosure of the present invention is illustrative rather than restrictive, and the scope of the present invention is defined by the appended claims.

Claims

1. Method for correcting V-shaped characteristic curve of large generator, characterized in that, It includes the following steps: S1. Obtain the original data obtained during the test V-shaped characteristic test, which includes active power, stator voltage, stator current, and exciting current; S2. Conduct the no-load characteristic test of the generator, obtain the test results of the stator voltage and the exciting current, and draw the no-load characteristic curve; S3. Based on the deviation value between the test result of the stator voltage and the rated stator voltage, and through the auxiliary solution of the no-load characteristic curve, obtain the deviation value of the exciting current; S4. Taking the rated stator voltage as the reference, based on the stator current and the stator voltage, correct the stator current to obtain the corrected stator current; S5. Based on the test result of the exciting current and the deviation value of the exciting current, correct the exciting current to obtain the corrected exciting current; S6. According to the corrected stator current and the corrected exciting current, draw the corrected V-shaped characteristic curve under each load.

2. The method for correcting the V-shaped characteristic curve of a large generator according to claim 1, wherein, In S1, when the active power of the generator is 0, 50%P N , 75%P N , 100%P N respectively, where P N is the rated active power of the generator, increase or decrease the excitation current, adjust the reactive power, conduct the V-curve test, and obtain the original data.

3. The method for correcting the V-shaped characteristic curve of a large generator according to claim 2, characterized in that, In S4, the corrected stator current I a ' is expressed as: I a ' = I a * U a / U N Among them, the corrected stator current I a ' has the unit of A, and I a is the stator current with the unit of A, U a is the stator voltage with the unit of V, and U N is the rated stator voltage with the unit of V.

4. The method for correcting the V-shaped characteristic curve of a large generator according to claim 3, characterized in that, In S5, the corrected exciting current I f is expressed as: I f ' = I f + ΔI f Among them, I f is the exciting current, with the unit of A, and ΔI f is the deviation value of the exciting current, with the unit of A.

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