Method for Round Setting of Static Stability Impedance for Loss of Excitation Protection of Hydro Generator

Abstract

A method for setting the static stable impedance circle for loss-of-excitation protection of a hydro-generator is disclosed. The method involves deriving a true model of the static stable impedance circle for loss-of-excitation protection of the hydro-generator, based on the different reactances of the direct-axis and quadrature-axis of the generator, which lead to different power expressions for salient-pole and non-salient-pole generators. Ignoring the physical meaning of the direct and quadrature axes, a mathematical simulation is performed, approximating the salient-pole generator as a non-salient-pole generator. This model is then compared with several existing setting methods based on the characteristics of the hydro-generator. This invention overcomes the difficulty of setting the protection value for loss-of-excitation protection based on engineering experience using a new and simple method.

Description

Technical Field

[0001] This invention belongs to the field of relay protection for hydro-generators, and specifically relates to a method for setting the static stability impedance of hydro-generator loss of excitation protection. Background Technology

[0002] Loss-of-excitation protection is a primary protection mechanism for generators, especially large and medium-sized hydroelectric generators, which are closely integrated with the power system. It typically requires a statically stable circle as the impedance criterion. However, since xq and xd are not equal, the actual statically stable circle is a teardrop-shaped circle, not a circle. According to the "Guideline for Setting and Calculation of Relay Protection for Large Generators and Transformers" (DL / T 684-2012), setting a teardrop-shaped statically stable circle is simple; for the protection device, only the upper and lower boundaries of the statically stable circle need to be given, and the internal logic of the protection device automatically calculates the boundary of the impedance circle. However, in practical applications, different manufacturers use different protection principles. Furthermore, due to the development of microcomputer protection, the calculation capabilities of relay protection devices have increased, and their functions have been continuously improved. Currently, some protection relay protection devices can achieve teardrop-shaped statically stable circle settings. However, the actual logical calculation methods for the statically stable circle in other protection devices are inconsistent, with some devices directly simulating a circle. If the static stability circle of the turbine is set according to DL / T684-2012 "Guidelines for Setting and Calculating Relay Protection of Large Generators and Transformers", the operating range will be set too small. The generator will enter a demagnetization state, but the protection device will not operate correctly. This is especially true for generators that are not closely connected to the system, i.e., small and medium-sized hydro generators, particularly generators connected through 10kV or 35kV grid lines. This may cause the generator to go directly from the demagnetization state to the out-of-synchronization state. Summary of the Invention

[0003] In view of the technical problems existing in the background art, the static stable impedance circle setting method for hydro-generator loss of excitation protection provided by the present invention overcomes the difficulty of setting the protection value based on engineering experience for hydro-generator loss of excitation protection based on the static stable circle impedance principle through a new and simple setting method.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for circularly setting the static stability impedance for loss-of-excitation protection of a hydro-generator, comprising the following steps: Step 1: When the turbine is connected to the infinitely large system via the system's interconnection impedance, according to the salient-pole generator power equation, the formula for the active power input to the system is: (1) The formula for reactive power is: (2) In the formula , ; For the direct-axis synchronous reactance of the generator; For quadrature axis synchronous reactance, The system connection impedance; Step 2, from formulas (1) and (2), we derive that: because the direct-axis and quadrature-axis reactances of the generator are different, the power expressions of the salient-pole generator and the non-salient-pole generator are different; ignoring the physical meaning of the direct-axis and quadrature-axis, we perform a mathematical simulation, approximating the salient-pole generator as a non-salient-pole generator, and derive: (3) The upper boundary of the static steady impedance circle of the salient-pole generator is still chosen as Xs, and the lower boundary is taken as... The statically stable impedance circle is directly tuned using formula (3).

[0005] Preferably, the derivation process of the upper and lower boundaries is as follows: For the statically stable limit of the terminal measurement impedance, there exists Therefore, for the active power, we can take the partial derivative with respect to δ: (4) In the formula,

[0006] For the statically stable limiting power angle, the electromotive force of a salient-pole generator at its statically stable limit is related to the power angle. Corresponding to a certain ; Substituting equation (4) into equations (1) and (2), we can see that the generator's output power is... (5) (6) From formulas (5) and (6), the measurement admittance at the infinite busbar in the statically stable limit can be derived: (7) The terminal measurement impedance for the statically stable limit is: (8) (9) (10) In the formula, Z zd To measure the impedance at the generator terminals, R This section measures the impedance resistance at the generator terminals. For measuring the impedance and reactance at the generator terminals, The measurement admittance at the infinite busbar in the statically stable limit; Draw the static stability limit impedance circle of the salient pole generator according to formulas (9) and (10); take and Two scenarios, representing the upper and lower boundaries of the static stability limiting impedance circle of a salient pole generator on the X-axis.

[0007] This patent can achieve the following beneficial effects: This invention employs a simple setting method to overcome the difficulty of setting protection values ​​based on engineering experience for the loss of magnetization protection of counter-current turbines using the static stable circular impedance principle. Attached Figure Description

[0008] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a system diagram of the large-scale water turbine of the present invention, with the system connection impedance being infinite. Figure 2 To illustrate the static stability limiting impedance circle scatter plot of the salient pole generator according to equation (9) and formula (10) of this invention; Figure 3 The boundary curve diagram of the statically stable circle derived by formula (3) in this invention is shown. Detailed Implementation

[0009] There are two types of impedance circles for loss of excitation protection of salient pole generators: asynchronous impedance circles and statically stable impedance circles.

[0010] Because the synchronous reactances of the direct-axis and quadrature-axis of a hydro-generator are not equal, the static stability boundary circle of a hydro-generator differs significantly from that of a salient-pole generator. For a generator set, after demagnetization, it always reaches the static stability limit first, and then switches to asynchronous operation. For example... Figure 1 As shown, when a large hydro turbine is connected to an infinitely large system via a system connection impedance, according to the salient pole generator power equation, the active power and reactive power input to the system are... [2] They are respectively: (1) (2) In the formula , , , These are the generator direct-axis synchronous reactance and quadrature-axis synchronous reactance, respectively. This is the system connection impedance.

[0011] From formulas (1) and (2), we can deduce that: due to the different magnitudes of the direct-axis and quadrature-axis reactances of the generator, the power expressions of the salient-pole generator and the non-salient-pole generator are different; ignoring the physical meaning of the direct-axis and quadrature-axis, we can simulate the salient-pole generator mathematically, approximating it as a non-salient-pole generator, and derive: (3) The upper boundary of the static steady impedance circle of the salient-pole generator is still chosen as Xs, and the lower boundary is taken as... The statically stable impedance circle is directly tuned using formula (3).

[0012] Example 1: A certain hydroelectric generator , ,

[0013] An actual statically stable circle is a teardrop-shaped circle, such as... Figure 3 The blue line represents the asynchronous circle, the gray circle represents the circle conforming to the standard procedure, and the orange circle represents the circle according to the present invention. As can be seen from the figure, the circle determined by the present invention is closest to the statically stable circle, and its difference from the actual region is not significant.

[0014] The derivation process for the upper and lower boundaries in existing tuning methods is as follows: For the statically stable limit of the terminal measurement impedance, there exists Therefore, for the active power, we can take the partial derivative with respect to δ: (4) In the formula,

[0015] For the statically stable limiting power angle, the electromotive force of a salient-pole generator at its statically stable limit is related to the power angle. Corresponding to a certain ; Substituting equation (4) into equations (1) and (2), we can see that the generator's output power is... (5) (6) From formulas (5) and (6), the measurement admittance at the infinite busbar in the statically stable limit can be derived: (7) The terminal measurement impedance for the statically stable limit is: (8) (9) (10) In the formula, Z zd To measure the impedance at the generator terminals, R This section measures the impedance resistance at the generator terminals. For measuring the impedance and reactance at the generator terminals, The measurement admittance at the infinite busbar in the statically stable limit; Draw the static stability limit impedance circle of the salient pole generator according to formulas (9) and (10); take and Two scenarios, representing the upper and lower boundaries of the static stability limiting impedance circle of a salient pole generator on the X-axis.

[0016] like Figure 2 As shown, the static stability limit impedance circle of the salient pole generator is drawn according to equations (8) and (9). In the variable plane, there exists (0, ),when In the RX plane, there exists (0, ), which are the upper and lower boundaries of the static stability limiting impedance circle of the salient pole generator on the X-axis.

[0017] Example: A certain hydroelectric generator , ,

[0018] For a statically stable impedance circle, since it's a Pascal's spiral, the actual curve can be fitted using the values ​​of R and X. Regarding sensitivity... If the value is between 0 and 2π, divide it into 24 equal points, and use the formula editor to calculate the corresponding values. Find R and X, as shown by the solid points in the figure. A curve can be fitted using a scatter plot. This allows for a simple and quick way to draw the static impedance circle of a salient-pole generator.

[0019] like Figure 2 As shown, the upper boundary is Xs, and the lower boundary is -Xq. This is consistent with the upper and lower boundaries in the setting method of DL / T 684-2012 "Guidelines for Calculation of Relay Protection Settings for Large Generators and Transformers" ( Figure 2 (This is the static stability limit impedance circle in the guide). It can be seen that the curve obtained according to the above formula (3) is consistent with the curve in the setting calculation book, reflecting the static stability boundary impedance of the generator demagnetization.

[0020] Method for determining the static stability of a circular shape: In practical applications, distinguishing between salient-pole and non-salient-pole generators in the statically stable circular part of the protection device requires directly setting the center and radius of the circle, or setting the upper and lower boundaries of the circular impedance circle. If set according to DL / T 684-2012 "Guidelines for Setting Calculation of Relay Protection for Large Generators and Transformers", the upper boundary is Xs, the lower boundary is -Xq, and the center is... radius is It is smaller than the actual impedance circle.

[0021] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be defined as the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for round-setting the static stability impedance for loss-of-excitation protection of a hydro-generator, characterized in that... Includes the following steps: Step 1: When the hydro-generator is connected to an infinitely large system via the system's interconnecting impedance, according to the salient-pole generator power equation, the formula for the active power input to the system is: （1）； The formula for reactive power is: （2）； In the formula , ； For the direct-axis synchronous reactance of the generator; For quadrature axis synchronous reactance, The system connection impedance; Step 2, from formulas (1) and (2), we derive that: due to the different magnitudes of the direct-axis and quadrature-axis reactances of the hydro-generator, the power expressions of the salient-pole generator and the non-salient-pole generator are different; ignoring the physical meaning of the direct-axis and quadrature-axis, we perform a mathematical simulation, approximating the salient-pole generator as a non-salient-pole generator, and derive: （3）； The upper boundary of the static steady impedance circle of the salient-pole generator is still chosen as Xs, and the lower boundary is taken as... The statically stable impedance circle is directly tuned using formula (3).

2. The method for round setting of static stability impedance for loss-of-excitation protection of a hydro-generator according to claim 1, characterized in that: The derivation process of the upper and lower boundaries is as follows: For the statically stable limit of the terminal measurement impedance, there exists Therefore, for the active power, we can take the partial derivative with respect to δ: （4）； In the formula, For the statically stable limiting power angle, the electromotive force of a salient-pole generator at its statically stable limit is related to the power angle. Corresponding to a certain ; Substituting equation (4) into equations (1) and (2), we can see that the output power of the hydro-generator is... （5）； （6）； From formulas (5) and (6), the measurement admittance at the infinite busbar in the statically stable limit can be derived: )（7） The terminal measurement impedance for the statically stable limit is: (8)； (9)； (10)； In the formula, Z zd To measure the impedance at the turbine generator terminals, R For measuring the impedance resistance at the turbine generator terminals, For measuring the impedance and reactance at the turbine generator terminals, The measurement admittance at the infinite busbar in the statically stable limit; Draw the static stability limit impedance circle of the salient pole generator according to formulas (9) and (10); take and Two scenarios, representing the upper and lower boundaries of the static stability limiting impedance circle of a salient pole generator on the X-axis.

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