Black-start system path selection method

Abstract

The invention belongs to the field of power system black start, and particularly relates to a black start system path selection method. The method comprises the following steps: acquiring path equipment parameters of a to-be-tested black-start system; calculating line capacitive reactance, generator reactance and transformer leakage reactance according to the acquired equipment parameters; comparing the circuit capacitive reactance with the sum of the reactance of the generator and the leakage reactance of the transformer to obtain a comparison result; judging whether the black-start system path to be detected can generate self-excitation or not according to the obtained comparison result; according to the method, a proper path can be selected for the black-start system, and the self-excitation phenomenon in the black-start system is avoided, that is, the parameter resonance phenomenon caused by positive feedback of a no-load long power transmission line capacitance current magnetic aiding effect is avoided; according to the method, the self-excitation condition of the black-start system is analyzed, the formulation of a black-start path and the self-excitation phenomenon are researched, and the determination of a black-start control strategy scheme can be guided.

Description

Technical Field

[0001] This application belongs to the field of black start of power systems, and particularly relates to a method for selecting a path of a black start system. Background Art

[0002] With the continuous expansion of the scope and scale of the power grid, people's dependence on electricity is increasing. This requires the power grid to have high power supply reliability and fast accident recovery ability. When a large-scale power outage or even a complete power outage occurs in the power grid, it is required that the power grid can quickly restore as many electrical loads as possible in the power outage area, so that the power grid can return to a safe and economic operation state after taking recovery actions. How to quickly formulate a power grid black start plan after a large-scale power outage is of great significance to the safe and economic operation of the power grid.

[0003] In a black start plan, units with self-starting ability, such as hydro turbine units and gas turbine units, are generally selected. After the black start unit starts, power is supplied to units without self-starting ability. During the black start process, self-excitation phenomenon is very likely to occur because at the initial stage of system startup, the unit serving as the startup power source drives a long no-load line, which is equivalent to driving a capacitive load. The capacitive charging power of the line is very large, and the system is easy to meet the conditions for self-excitation to occur. Therefore, the self-excitation phenomenon must be considered when formulating a black start plan.

[0004] In the prior art, a hydropower plant (including pumped storage power plant) is generally selected as a reliable black start power source. Hydro turbine units have advantages such as fast startup speed, but hydro turbine units generally use salient pole generators with large synchronous reactance and small moment of inertia, and are prone to self-excitation phenomenon. Summary of the Invention

[0005] To solve the problem that the self-excitation phenomenon easily occurs in the black start plan of the prior art and affects the stability of the power system, a method for selecting a path of a black start system is proposed;

[0006] A method for selecting a path of a black start system includes:

[0007] Step 1: Obtain the equipment parameters of the path of the black start system to be measured;

[0008] Step 2: Calculate the line capacitive reactance, generator reactance, and transformer leakage reactance according to the obtained equipment parameters;

[0009] Step 3: Compare the magnitude of the line capacitive reactance with the sum of the generator reactance and the transformer leakage reactance to obtain a comparison result;

[0010] Step 4: Determine whether the path of the black start system to be measured can generate self-excitation according to the obtained comparison result.

[0011] Advantages of the present application: A black start system path selection method of the present application can effectively calculate the line capacitance, generator reactance and transformer leakage reactance according to the black start system path equipment parameters, and then compare the line capacitance with the sum of the generator reactance and the transformer leakage reactance, and judge whether the black start system path to be tested can generate self-excitation according to the comparison result; if the black start system path to be tested will not generate self-excitation, the path is selected as the black start system path; the method can select a suitable path for the black start system to avoid the occurrence of self-excitation in the black start system, that is, to avoid the parameter resonance phenomenon caused by the positive feedback of the magnetic assist effect of the capacitive current of the unloaded long transmission line; the method analyzes the self-excitation situation of the black start system, studies the formulation of the black start path and the self-excitation phenomenon, which is conducive to guiding the determination of the black start control strategy scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A flow chart of a black start system path selection method according to a specific implementation method of the present application;

[0013] Figure 2 A simplified self-excitation circuit diagram of a specific implementation method of the present application;

[0014] Figure 3 A schematic diagram of a black start path according to a specific implementation method of the present application;

[0015] Figure 4 This is a schematic diagram of a second black start path of a specific implementation method of the present application. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0017] Specific implementation method 1: The following will be combined with the attached embodiment of the present invention Figure 1 To Attachment Figure 4 , illustrate this implementation mode, and clearly and completely describe the technical solutions in the embodiments of the present invention:

[0018] A black start system path selection method, comprising:

[0019] Step 1: Obtain the path equipment parameters of the black start system to be tested;

[0020] Step 2: Calculate the line capacitance, generator reactance and transformer leakage reactance based on the acquired equipment parameters;

[0021] Step 3: Compare the line capacitive reactance with the sum of the generator reactance and the transformer leakage reactance to obtain a comparison result;

[0022] Step 4: Determine whether the path of the black start system under test can generate self-excitation according to the obtained comparison result.

[0023] Specifically, the fundamental cause of the self-excitation phenomenon is that when the current in the excitation winding is zero, the voltage spontaneously rises due to excessive capacitive load. Therefore, the essence of the self-excitation problem in black start can be approximately analyzed by combining the physical process and occurrence phenomenon of the self-excitation phenomenon. In the black start scheme, the water turbine unit is generally selected as the starting power source. The damping winding effect of the water turbine unit can be considered negligible. Assuming that the angular frequency ω = 1 and remains constant, the simplified equivalent circuit obtained is as shown in the appendix Figure 2 shown in the appendix Figure 2 where E Q is the equivalent electromotive force of the water turbine generator; X q is the quadrature-axis synchronous reactance; X c is the line capacitive reactance; r is the line resistance.

[0024] It can be known through the impedance comparison method that the condition for the generator to generate self-excitation is: X q <X c <X d , where X d is the generator reactance;

[0025] Excitation can be divided into two categories: synchronous self-excitation and asynchronous self-excitation. The water turbine generator is a salient-pole generator, and generally for a salient-pole synchronous generator, X d ≠X q , and usually synchronous self-excitation is generated. The steam turbine generator is a non-salient-pole generator, and usually asynchronous self-excitation is generated. Therefore, when X c <X q , the case of asynchronous self-excitation is not considered. Considering the influence of the transformer parameters on the generation of self-excitation, the leakage reactance of the transformer should be incorporated into the generator reactance, that is: X c <X d +X T ;

[0026] In this application, this condition is selected as the judgment basis for self-excitation generation in black start. It requires few parameters, is easy to obtain, is intuitive and simple, and is derived from the self-excitation generation mechanism, which can meet the requirements for the self-excitation criterion in black start. This type of impedance comparison method has certain engineering practicability; it is judged whether it falls into this interval according to X c to determine whether the system has a self-excitation phenomenon.

[0027] Furthermore, the equipment parameters of the path of the black start system under test include: line length, line capacitance, transformer frequency, transformer rated capacity, line base voltage, generator terminal voltage, transformer rated voltage, generator base voltage, transformer base voltage, generator rated power, transformer rated capacity, and short-circuit voltage percentage.

[0028] Further, the method for calculating the line capacitive reactance according to the obtained device parameters includes:

[0029]

[0030] where X c is the line capacitive reactance, S N is the rated capacity of the transformer, f is the transformer frequency, c is the line capacitance, l is the line length, U cN is the line reference voltage, U T is the rated voltage of the transformer.

[0031] Further, the method for calculating the generator reactance according to the obtained device parameters includes:

[0032]

[0033] where X d is the generator reactance, S N is the rated capacity of the transformer, U d is the generator terminal voltage, P d is the rated power of the generator, U dN is the generator reference voltage.

[0034] Further, the method for calculating the transformer leakage reactance according to the obtained device parameters includes:

[0035]

[0036] where X T is the transformer leakage reactance, S N is the rated capacity of the transformer, U k % is the percentage of the short-circuit voltage, P T is the rated capacity of the transformer, U TN is the transformer reference voltage.

[0037] Further, the comparison results include that the line capacitive reactance is greater than the sum of the generator reactance and the transformer leakage reactance, and the line capacitive reactance is not greater than the sum of the generator reactance and the transformer leakage reactance;

[0038] The method for judging whether the path of the to-be-tested black start system can generate self-excitation according to the obtained comparison result includes:

[0039] If the line capacitive reactance is greater than the sum of the generator reactance and the transformer leakage reactance, the path of the to-be-tested black start system does not generate self-excitation; if the line capacitive reactance is not greater than the sum of the generator reactance and the transformer leakage reactance, the path of the to-be-tested black start system generates self-excitation. Specific Example 1:

[0041] Set the black-start power source point of black-start path 1 as Unit 2 of Plant A, and the power source point to be started as the 200MW generator set No. 7 of Plant E;

[0042] As Figure 3 shown, black-start path 1 is: Unit 2 of Plant A - 220kV A plant bus - 220kV l1 line - 220kV B plant bus - 220kV l2 line - 220kV C plant bus - 220kV l3 line - 220kV D plant bus - 220kV l4 line - 220kV E plant bus - 10.5kV 200MW generator set No. 7 of Plant E;

[0043] Known conditions: The model of Unit 2 of Plant A is TSK460 / 100 - 32, rated voltage 11.00kV; rated output 18.00MW; rated power factor 0.90, generator reactance X d = 5.2030; The model of the main transformer of Plant A is SFPSB - 50000 / 220, rated voltage and transformation ratio are 242(+1 / -3)×2.5% / 121 / 11kV, capacity S N = 50 / 50 / 50×1MVA, connection group Y0 / Y0 / Δ - 12 - 11; Short-circuit voltage U KI—II 21.50%, UK I—III 13.60%, UK II—III 7.12%; Short-circuit loss P KI— II 246.40kW, P KI—III 242.60kW, P KII—III 180.50kW; No-load loss P0 = 75.50kW; No-load current I0 = 0.65%;

[0044] The model of the No. 7 main transformer of Plant E is SFP7 - 240000 / 220, rated voltage and transformation ratio 242±2×2.5% / 15.75kV; Capacity S N = 240×1MVA; Connection group Yn / d11; Short-circuit voltage U KI—III 13.5%; Short-circuit loss P KI— III 594.1 kW; No-load loss P0 = 160kW; No-load current I0 = 0.264%;

[0045] Calculate according to the known conditions: X T (main transformer of Plant A) = 0.3291, X d (Unit 2 of Plant A) = 5.2030, X T (Plant C) = 0.02028, X T (No. 7 main transformer of Plant E) = 0.0681;

[0046] The length of the 220 kV l1 line is 4.25 km, and its reactance is 179.83 p.u.; the length of the 220 kV l2 line is 77.55 km, and its reactance is 10.2603 p.u.; the length of the 220 kV l3 line is 24.8 km, and its reactance is 21.2122 p.u.; the length of the 220 kV l4 line is 5.779 km, and its reactance is 98.3555 p.u.;

[0047] When starting the l1 line, X c = 179.83, X c > X d (Unit 2 of Factory A) + X T (Main transformer of Factory A), and no self-excitation phenomenon occurs in the system;

[0048] When starting the l2 line, X c = 179.83 / / 10.2603 = 9.7065, X c > X d (Unit 2 of Factory A) + X T (Main transformer of Factory A), and no self-excitation phenomenon occurs in the system;

[0049] When starting the l3 line, X c = 179.83 / / 10.2603 / / 21.2122 = 6.6593,

[0050] X c > X d (Unit 2 of Factory A) + X T (Main transformer of Factory A), and no self-excitation phenomenon occurs in the system;

[0051] When starting the l4 line, X c = 179.83 / / 10.2603 / / 21.2122 / / 98.3555 = 6.6237,

[0052] X c > X d (Unit 2 of Factory A) + X T (Main transformer of Factory A), and no self-excitation phenomenon occurs in the system;

[0053] It can be seen from the above calculations that the starting power source point of the black start path 1 is Unit 2 of Factory A, and the power source point to be started is Unit 7 of Factory E, and no self-excitation phenomenon occurs in the system. For the black start path 1, although the line put into operation by Factory A is no-load, it is not long, and the capacitive charging power is small. After calculation, it is about 4.3363×10-2 MVar, while the reactive power generated by Factory A is about 3.3 MVar, which is much larger than the line charging power. Therefore, generator self-excitation does not occur. During the black start process, when the generator is initially stable and reaches the bus of Factory E, some loads are timely put into operation, destroying the long transmission line no-load capacitive reactive power injection required for self-excitation and avoiding generator self-excitation. Specific Embodiment 2:

[0055] Set the black start power source point of the black start path 2 as the Unit 2 of Factory A, and the power source point to be started as the 600MW generator set of Factory H;

[0056] As Figure 4 shown, the black start path 2 is: Unit 2 of Factory A - 220kV A Factory Bus - 220kV l1 Line - 220kV B Factory Bus - 220kV l2 Line - 220kV C Factory Bus - 500kV C Factory Bus - 500kV l5 Line - 500kV F Factory Bus - 500kV l6 Line - 500kV G Factory Bus - 500kV l7 Line - 500kV H Factory Bus - 24kV Unit 4 of Factory H;

[0057] The length of the 500kV l5 line is 184.04km, and the reactance is 0.4195 p.u.; the length of the 500kV l6 line is 133.51km, and the reactance is 0.6933 p.u.; the length of the 500kV l7 line is 47.493km, and the reactance is 1.931 p.u.;

[0058] When starting the l5 line, X c = 179.83 / / 10.2603 / / 0.4195 = 0.40212,

[0059] X c <X d (Unit 2 of Factory A) + X T (Main transformer of Factory A) + X T (Linhai Substation), and self-excitation phenomenon occurs in the system;

[0060] It can be seen from the calculation results that when the black start path 2 has the starting power source point as the Unit 2 of Factory A and the power source point to be started as the generator set of Factory H, self-excitation phenomenon occurs in the system when the l5 line is charged without load. For the black start path 2, when starting the l5 line, the line length is 184.04km, the line length is long, and the capacitive charging power is large, so generator self-excitation occurs.

[0061] Specific Embodiment 2: A computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that when the processor executes the computer program, it implements the steps of the method described in any one of the Specific Embodiments 1.

[0062] Specific Embodiment 3: A computer-readable storage medium, on which a computer program is stored, characterized in that when the computer program is executed by a processor, it implements the steps of the method described in any one of the Specific Embodiments 1.

[0063] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Accordingly, it should be understood that numerous modifications may be made to the exemplary embodiments, and other arrangements may be devised, without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a separate embodiment may be used in other described embodiments.

Claims

1. A method for selecting a black start system path, characterized in that Including: Step 1: Obtain the device parameters of the path of the black start system to be tested; Step 2: Calculate the line capacitive reactance, generator reactance, and transformer leakage reactance based on the obtained device parameters; Step 3: Compare the magnitude of the line capacitive reactance with the sum of the generator reactance and the transformer leakage reactance to obtain a comparison result; Step 4: Determine whether the path of the black start system to be tested can generate self-excitation based on the obtained comparison result.

2. A method for selecting a path of a black start system according to claim 1, characterized in that: The device parameters of the path of the black start system to be tested include: line length, line capacitance, transformer frequency, transformer rated capacity, line base voltage, generator terminal voltage, transformer rated voltage, generator base voltage, transformer base voltage, generator rated power, transformer rated capacity, and short-circuit voltage percentage.

3. A method for selecting a black start system path according to claim 2, characterized in that: The method for calculating the line capacitive reactance based on the obtained device parameters includes: Among them, X c is the line capacitive reactance, S N is the rated capacity of the transformer, f is the transformer frequency, and c is the line capacitance. l is the line length, U cN is the line reference voltage, U T is the rated voltage of the transformer.

4. A method for selecting a black start system path according to claim 2, characterized in that: The method for calculating the generator reactance based on the obtained device parameters includes: Among them, X d is the generator reactance, S N is the rated capacity of the transformer, U d is the terminal voltage of the generator, P d is the rated power of the generator, U dN is the base voltage of the generator.

5. A method for selecting a black start system path according to claim 2, characterized in that: The method for calculating the transformer leakage reactance based on the obtained device parameters includes: Among them, X T is the leakage reactance of the transformer, S N is the rated capacity of the transformer, U k % is the percentage of short-circuit voltage, P T is the rated capacity of the transformer, U TN is the base voltage of the transformer.

6. A method for selecting a black start system path according to claim 1, characterized in that: The comparison results include that the line capacitive reactance is greater than the sum of the generator reactance and the transformer leakage reactance, and the line capacitive reactance is not greater than the sum of the generator reactance and the transformer leakage reactance; The method for determining whether the path of the black start system to be tested can generate self-excitation based on the obtained comparison result includes: If the line capacitive reactance is greater than the sum of the generator reactance and the transformer leakage reactance, the path of the black start system to be tested does not generate self-excitation; if the line capacitive reactance is not greater than the sum of the generator reactance and the transformer leakage reactance, the path of the black start system to be tested generates self-excitation.

7. A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method according to any one of claims 1 to 6.

Images