Standby power supply system for high-voltage auxiliary power of power plant and simulation method

Abstract

The invention discloses a power plant high-voltage auxiliary power standby power supply system and a simulation method, and belongs to the technical field of power plants. The power plant high-voltage auxiliary power standby power supply system comprises an interconnecting transformer, a step-down transformer and a 35kV power distribution device; the high-voltage side and the medium-voltage side of the interconnecting transformer are connected with a power grid system, and the rated voltage of the low-voltage side of the interconnecting transformer is 37.5 kV; the high-voltage station standby power supply is led and connected by a low-voltage winding of the interconnecting transformer; the power supply of the step-down transformer is led from the low-voltage side of the interconnecting transformer; the 35kV power distribution device is provided with a lightning arrester, a capacitor voltage transformer, a disconnecting switch (double grounding), a circuit breaker and a current transformer. The device can adapt to and meet the operation requirement of a power system of a power plant, achieves the purpose of stand-by power supply connection with high efficiency and low cost, and improves the operation reliability of the power plant.

Description

Technical Field

[0001] The present invention relates to the technical field of power plants, and in particular to a high-voltage auxiliary power supply system and a simulation method for a power plant. Background Art

[0002] As an important part of the power plant, the plant power system is related to whether the overall power plant can operate safely, reliably and efficiently. According to relevant standards and specifications, a backup power supply should be set for the high-voltage plant power busbar connected to Class I loads.

[0003] There are three options for conventional backup power supply: to draw power from the high-voltage busbar of the booster station and set up a high-voltage starting / standby transformer, or to draw power from the low-voltage side of the interconnection transformer, or to draw power from a dedicated line from an external power grid. When a power plant is equipped with an interconnection transformer, the first option is to draw power from the high-voltage busbar of the booster station and set up a high-voltage starting / standby transformer. The investment is relatively large because a high-voltage distribution device interval needs to be set up, and a high-voltage starting / standby transformer needs to be set up at the same time. Considering the impact on the voltage fluctuation of the high-voltage plant busbar, the transformer usually adopts the on-load voltage regulation type; for option 2, when the voltage on the high and medium voltage sides is adjusted, the voltage on the low-voltage side of the interconnection transformer will also be affected, thereby affecting the stability of the voltage of the high-voltage plant busbar. In addition, in order to limit the short-circuit current of the high-voltage plant busbar on the low-voltage side, a current limiting reactor is usually required on the low-voltage side; since the plant load is generally large, the third option of drawing power from a dedicated line from the external power grid also requires investment in the construction of corresponding transmission lines, so the scope of application of this option is relatively limited.

[0004] The design and equipment selection of the high-voltage power supply system for plant power supply should be based on the calculation of short-circuit current and the voltage drop verification of the high-voltage power supply busbar when the motor starts, so as to ensure that a low-impedance transformer and a switchgear with a low breaking level can be selected. The traditional calculation method is mainly based on the national power industry standard "Technical Specifications for Power Supply Design of Thermal Power Plants" (DL / T5153). The calculation process is relatively complicated and cannot analyze the dynamic process of motor starting. Designers not only have a large workload and low efficiency, but also there is a certain error between the calculation results and the actual situation. China's comprehensive power engineering solution providers and infrastructure contractors are actively promoting international development. Usually, foreign project owners will hire consulting companies in Western countries to check the project design. Traditional calculation methods are not recognized by foreign owners and consultants. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high-voltage backup power supply system and simulation method for a power plant, which can adapt to and meet the operating needs of the power plant power system, achieve the goal of backup power connection with high efficiency and low cost, and improve the reliability of power plant operation.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A high-voltage plant power backup power supply system for a power plant comprises a connecting transformer, a step-down transformer and a 35kV power distribution device; the high and medium voltage sides of the connecting transformer are connected to a power grid system, and the rated voltage of the low voltage side is 37.5kV; the high-voltage plant power backup power supply is connected by the low voltage winding of the connecting transformer; the power supply of the step-down transformer is drawn from the low voltage side of the connecting transformer; and the 35kV power distribution device is provided with a circuit breaker.

[0007] A further improvement of the technical solution of the present invention is that the interconnecting transformer adopts an autotransformer.

[0008] A further improvement of the technical solution of the present invention is that: the low-voltage side of the interconnecting transformer adopts steel-core aluminum stranded wire, which is connected to the high-voltage side of the step-down transformer via a 35kV distribution device; the 35kV distribution device also includes at least a capacitive voltage transformer, a grounding switch, an isolating switch and a current transformer.

[0009] A further improvement of the technical solution of the present invention is that a lightning arrester is also arranged on the low-voltage side of the interconnecting transformer.

[0010] A further improvement of the technical solution of the present invention is that the rated voltage of the low-voltage side of the step-down transformer is determined according to the voltage level of the high-voltage plant power system.

[0011] A further improvement of the technical solution of the present invention is that the step-down transformer adopts on-load voltage regulation, the voltage regulating switch is arranged on the high-voltage side of the step-down transformer, and the impedance selection of the step-down transformer is determined based on the bus voltage drop when the largest motor is started and the short-circuit current of the factory power system verified by ETAP software simulation.

[0012] A further improvement of the technical solution of the present invention is that when the voltage of the high-voltage plant power system is 6 kV, the transformation ratio of the step-down transformer is 35 / 6.3 kV.

[0013] A further improvement of the technical solution of the present invention is that the low-voltage side of the step-down transformer is connected to the backup power supply incoming cabinet of the 6kV power distribution device using a common box enclosed busbar.

[0014] A simulation method for a high-voltage auxiliary power supply system for a power plant uses ETAP software to build an electrical wiring model. By calculating the short-circuit current and analyzing the bus voltage drop when the largest motor is started, the high-voltage auxiliary power supply system is simulated to optimize equipment selection.

[0015] A further improvement of the technical solution of the present invention is that the simulation method specifically includes the following steps: Step 1: Build an electrical wiring model in ETAP software according to the main electrical wiring force; Step 2, assign values ​​to each equipment module in ETAP software; Step 3, preliminarily selecting the impedance of the step-down transformer as the standard sequence to calculate the short-circuit current of the high-voltage plant bus section; Step 4, determine whether the short-circuit current of the high-voltage plant bus section calculated in step 3 meets the requirements, if so, proceed to the next step, if not, increase the impedance of the step-down transformer, and return to step 3 to recalculate; Step 5, analyzing the bus voltage drop when the largest motor is started; Step 6, determine whether the bus drop in step 5 meets the requirements, if so, proceed to the next step, if not, reduce the impedance of the step-down transformer and return to step 3 to recalculate; Step 7, finally obtain the impedance of the step-down transformer and the short-circuit current of each busbar, and guide the selection of conductors and switchgear.

[0016] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is: 1. The present invention can adapt to and meet the operating needs of the power system of a power plant, and realize the goal of connecting the backup power supply with high efficiency and low cost, which not only improves the reliability of the power plant operation, the convenience of construction and installation, and equipment overhaul and maintenance, but also saves the project cost, facilitates engineering application and promotion, and can be widely used in the field of power plants.

[0017] 2. The interconnecting transformer of the present invention adopts an autotransformer, which saves engineering cost, reduces active and reactive power losses, improves transformer efficiency, and is convenient for engineering application and promotion.

[0018] 3. The present invention optimizes the main wiring design to the maximum extent, and has the advantages of simple system design, compact design, and small footprint.

[0019] 4. The present invention draws the backup power supply from the low-voltage side of the interconnection transformer, and there is no need to draw the power supply from the booster station and set up a high-voltage starting / backup transformer, which saves engineering costs and facilitates engineering application and promotion.

[0020] 5. The present invention sets a 35kV on-load voltage-changing step-down transformer on the low-voltage side of the interconnecting transformer to meet the voltage deviation requirement of the 6kV busbar for plant use, improve the quality of plant standby power supply, and facilitate engineering application and promotion.

[0021] 6. The present invention sets a circuit breaker between the low-voltage winding of the interconnecting transformer and the step-down transformer. When a fault occurs in the step-down transformer or the common box enclosed busbar of the step-down transformer to the 6kV distribution device, the circuit breaker and the relay protection cooperate to quickly cut off the fault current to prevent the expansion of the accident scope, effectively improving the safety and reliability of the system and facilitating engineering application and promotion.

[0022] 7. The present invention draws the backup power supply from the low-voltage side of the interconnecting transformer and selects conventional equipment and conductors, including step-down transformers, circuit breakers, common box enclosed busbars, etc. All equipment and conductors have mature operating experience, saving engineering costs, and there is no need to develop new conductor equipment. The overall system is safe and reliable.

[0023] 8. The present invention adopts ETAP software to simulate the high-voltage plant power backup power system. The calculation process is simple and the operability is strong. Compared with the traditional equipment selection calculation method, it can significantly improve the work efficiency and design quality of designers and facilitate the promotion of engineering applications.

[0024] 9. The present invention adopts ETAP software to simulate the high-voltage plant power backup power system. Through this simulation method, the equipment parameters that meet various boundary conditions can be accurately calculated, the equipment selection can be optimized, the project cost can be saved, and the project application promotion can be facilitated. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. Figure 1 It is a wiring schematic diagram of a high-voltage auxiliary power supply system for a power plant provided in an embodiment of the present invention; Figure 2 It is a flow chart of a simulation method of a high-voltage auxiliary power supply system of a power plant provided in an embodiment of the present invention; Figure 3 It is an electrical wiring model diagram of a certain expanded power plant constructed in the ETAP software in an embodiment of the present invention; Figure 4 is a diagram of short-circuit current simulation results based on ETAP software in an embodiment of the present invention; Figure 5 It is a bus voltage drop simulation result (static start-up analysis) diagram of the maximum motor (GBC3) start-up based on ETAP software in an embodiment of the present invention; Figure 6 It is a diagram of bus voltage drop simulation results (dynamic starting analysis) of starting of the largest motor (GBC3) based on ETAP software in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0027] The present invention is further described in detail below with reference to the accompanying drawings and embodiments: like Figure 1 As shown, a high-voltage plant power backup power supply system for a power plant includes a connecting transformer, a step-down transformer and a 35kV distribution device; the high and medium voltage sides of the connecting transformer are connected to the power grid system, and the rated voltage of the low voltage side is 37.5kV; the high-voltage plant backup power supply is connected by the low voltage winding of the connecting transformer; the power supply of the step-down transformer is drawn from the low voltage side of the connecting transformer; and the 35kV distribution device is provided with a circuit breaker.

[0028] Furthermore, the interconnecting transformer adopts an autotransformer, which saves the engineering cost, reduces the active and reactive power losses, improves the transformer efficiency, and facilitates engineering application and promotion.

[0029] Furthermore, the low-voltage side of the interconnection transformer uses steel-core aluminum stranded wire, which is connected to the high-voltage side of the step-down transformer via a 35kV distribution device; the 35kV distribution device at least includes a capacitive voltage transformer, a grounding switch, an isolating switch, and a current transformer. Specifically, a 40.5kV isolating grounding switch (double grounding) is used.

[0030] Furthermore, in order to prevent overvoltage caused by voltage fluctuations on the system side under different operating conditions from damaging the 35kV distribution equipment and step-down transformer-related equipment, a lightning arrester is also installed on the low-voltage side of the interconnecting transformer.

[0031] Furthermore, the rated voltage of the low voltage side of the step-down transformer is determined according to the voltage level of the high voltage auxiliary power system. For the convenience of description, the voltage of the high voltage auxiliary power system in the present invention is considered to be 6kV, that is, the transformation ratio of the step-down transformer is 35 / 6.3kV.

[0032] Furthermore, in order to meet the voltage deviation requirements of the bus, the step-down transformer adopts on-load voltage regulation, and the voltage regulating switch is set on the high-voltage side of the step-down transformer. The bus voltage drop when the largest motor is started and the short-circuit current of the factory power system are verified based on ETAP software simulation to determine the impedance selection of the step-down transformer.

[0033] Furthermore, when the high-voltage plant power system is 6 kV, the transformation ratio of the step-down transformer is 35 / 6.3 kV.

[0034] Furthermore, in order to improve operational reliability and reduce the failure rate, the low-voltage side of the step-down transformer is connected to the backup power supply incoming cabinet of the 6kV distribution device using a common box enclosed bus.

[0035] Specifically, the high and medium voltage sides of the interconnecting transformer are connected to the 220kV and 110kV power grid systems respectively, and the rated voltage of the low voltage side is 37.5kV, from which the backup power supply of the power plant is connected. The step-down transformer adopts an on-load tap-changing transformer with a transformation ratio of 37.5 / 6.3kV. The low voltage side of the step-down transformer adopts a common box enclosed busbar to be connected to the backup power supply incoming cabinet of the 6kV distribution device. A 40.5 kV circuit breaker is set between the low voltage winding of the interconnecting transformer and the step-down transformer. When the step-down transformer or the common box enclosed busbar from the step-down transformer to the 6kV distribution device fails, the circuit breaker cooperates with the relay protection to quickly cut off the fault current to prevent the expansion of the accident scope.

[0036] A simulation method for a high-voltage auxiliary power supply system for a power plant uses ETAP software to build an electrical wiring model. By calculating the short-circuit current and analyzing the bus voltage drop when the largest motor is started, the high-voltage auxiliary power supply system is simulated to optimize equipment selection.

[0037] like Figure 2 As shown, the simulation method specifically includes the following steps: Step 1: Build an electrical wiring model in ETAP software according to the main electrical wiring force; Step 2, assign values ​​to each equipment module in ETAP software; Step 3, preliminarily selecting the impedance of the step-down transformer as the standard sequence to calculate the short-circuit current of the high-voltage plant bus section; Step 4, determine whether the short-circuit current of the high-voltage plant bus section calculated in step 3 meets the requirements, if so, proceed to the next step, if not, increase the impedance of the step-down transformer, and return to step 3 to recalculate; Step 5, analyzing the bus voltage drop when the largest motor is started; Step 6, determine whether the bus drop in step 5 meets the requirements, if so, proceed to the next step, if not, reduce the impedance of the step-down transformer and return to step 3 to recalculate; Step 7, finally obtain the impedance of the step-down transformer and the short-circuit current of each busbar, and guide the selection of conductors and switchgear.

[0038] Example: Relying on a certain project, simulation calculations can be performed through ETAP software. The calculation results provide a basis for the design of the high-voltage plant power backup power supply system and equipment selection. The specific steps are as follows: In this phase of the project, a power plant will build a new set of E-class "one-to-one" gas turbine combined cycle units, two sets of E-class gas turbine simple cycle units, as well as four hot water boilers and three steam boilers. One of the combined cycle gas generators and one steam turbine generator are connected to the 220kV booster station after being stepped up by a double-winding transformer, and the two simple cycle gas generators are connected to the expansion bay of the original 110kV booster station after being stepped up by the corresponding double-winding transformers. According to the electrical wiring diagram of the power plant, select the equipment module in the ETAP software database and assign values ​​to build a simulation model, refer to the attached Figure 3 , which is the electrical wiring model of the power plant built in ETAP software.

[0039] Each generator set is equipped with a 6kV unit section to supply power to the unit's medium-voltage load, the unit's common medium-voltage load and the low-voltage transformer. There are four 6kV unit sections in the whole plant (BA-1, BA-2, BA-3, BA-4). The power supply of each 6kV working bus is drawn from the corresponding high-voltage plant transformer. The whole plant is equipped with two spare 6kV sections (01A, 01B), which serve as the open standby power supply for the 6kV sections of the two units respectively. The power supply of each spare 6kV section is drawn from the 6kV side of the step-down transformer. The gas hot water boiler room is equipped with four 6kV working sections (BB-1, BB-2, BB-3, BB-4) to supply power to the 6kV motor and low-voltage transformer of the hot water boiler system. The working power supply of the 6kV working section of the hot water boiler is drawn from the 6kV unit section, and the standby power supply is drawn from the standby 6kV section. It is required that the short-circuit level of the 35kV system between the interconnecting transformer and the step-down transformer shall not exceed 31.5kA, the short-circuit level of the 6kV distribution device shall be 31.5kA, and the 6kV bus voltage drop shall not be less than 80% when the largest motor is started.

[0040] The impedance of the step-down transformer is initially selected as 10% of the standard sequence. According to the principle of considering the worst working conditions, the power supply of the plant power system is switched to the backup power supply system, that is, step-down transformer #1 (SDT1) carries BA-2 section and BB-2, and step-down transformer #2 (SDT2) carries BA-3 section and BB-3. Figure 4 , which is the short-circuit current simulation result based on ETAP software. The short-circuit currents of the two spare 6kV sections (01A, 01B) are 23kA and 25.6kA respectively, which meets the requirement of 31.5kA short-circuit level of 6kV distribution equipment.

[0041] Analyze the bus voltage drop when the largest motor starts. The largest motor is the GBC3 motor. When the simulation #2 step-down transformer (SDT2) is loaded with BA-3 section and BB-3, start the GBC3 motor connected to the BA-3 section bus. Without considering the input of the interconnecting transformer voltage regulator, set the relevant parameters of its on-load voltage regulator in the ETAP software step-down transformer model according to ±8×1.25%; the rated voltage of the GBC3 motor is 6kV, the rated power is 3300kW, and the motor starting current multiple is 6. Set the electrical and mechanical model parameters of the motor in the GBC3 motor model; after creating a new event and setting boundary conditions such as simulation duration, you can analyze the impact of the static and dynamic starting of the motor on the bus voltage. Refer to the attached Figure 5 , based on the bus voltage drop simulation results (static start analysis) of the largest motor (GBC3) started by ETAP software, the bus voltage drop of the standby 6kV section (01B) is 83.04% when the GBC3 motor is started; refer to the attached Figure 6 Based on the bus voltage drop simulation results (dynamic starting analysis) of the largest motor (GBC3) started by ETAP software, the bus voltage drop of the standby 6kV section (01B) when the GBC3 motor starts is 83.52%, which meets the requirements.

[0042] If the calculation result does not meet the requirements, it is necessary to reset the step-down transformer impedance and calculate the short-circuit current of the spare 6kV section. Once the requirements are met, analyze whether the bus voltage drop when the largest motor starts meets the requirements. Repeat this cycle and eventually the optimal equipment selection can be obtained.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high voltage backup power supply system for power plants, characterized in that: It includes a connecting transformer, a step-down transformer and a 35kV distribution device; the high and medium voltage sides of the connecting transformer are connected to the power grid system, and the rated voltage of the low voltage side is 37.5kV; the high voltage plant standby power supply is connected by the low voltage winding of the connecting transformer; the power supply of the step-down transformer is drawn from the low voltage side of the connecting transformer; the 35kV distribution device is provided with a circuit breaker.

2. A power plant high voltage backup power supply system according to claim 1, characterized in that: The interconnecting transformer is an autotransformer.

3. A power plant high voltage backup power supply system according to claim 1, characterized in that: The low-voltage side of the interconnecting transformer adopts steel-core aluminum stranded wire, which is connected to the high-voltage side of the step-down transformer via a 35kV distribution device; the 35kV distribution device also includes at least a capacitive voltage transformer, a grounding switch, an isolating switch and a current transformer.

4. A power plant high voltage backup power supply system according to claim 3, characterized in that: A lightning arrester is also arranged on the low voltage side of the interconnecting transformer.

5. The high voltage backup power supply system for power plants according to claim 1 is characterized by: The rated voltage of the low-voltage side of the step-down transformer is determined according to the voltage level of the high-voltage auxiliary power system.

6. A power plant high voltage backup power supply system according to claim 1, characterized in that: The step-down transformer adopts on-load voltage regulation, and the voltage regulating switch is set on the high-voltage side of the step-down transformer. The impedance selection of the step-down transformer is determined based on the bus voltage drop when the largest motor is started and the short-circuit current of the factory power system verified by ETAP software simulation.

7. A power plant high voltage backup power supply system according to claim 6, characterized in that: When the voltage of the high-voltage auxiliary power system is 6 kV, the transformation ratio of the step-down transformer is 35 / 6.3 kV.

8. A high voltage backup power supply system for power plants according to claim 7, characterized in that: The low voltage side of the step-down transformer is connected to the backup power supply incoming cabinet of the 6kV power distribution device using a common box enclosed busbar.

9. A method for simulating a high voltage auxiliary power supply system for a power plant according to any one of claims 1 to 8, characterized in that: Using ETAP software, we built an electrical wiring model, calculated the short-circuit current, analyzed the bus voltage drop when the largest motor was started, simulated the high-voltage factory power backup power system, and optimized equipment selection.

10. The simulation method of a high voltage auxiliary power supply system for a power plant according to claim 9, characterized in that: The simulation method specifically comprises the following steps: Step 1: Build an electrical wiring model in ETAP software according to the main electrical wiring force; Step 2, assign values ​​to each equipment module in ETAP software; Step 3, preliminarily selecting the impedance of the step-down transformer as the standard sequence to calculate the short-circuit current of the high-voltage plant bus section; Step 4, determine whether the short-circuit current of the high-voltage plant bus section calculated in step 3 meets the requirements, if so, proceed to the next step, if not, increase the impedance of the step-down transformer, and return to step 3 to recalculate; Step 5, analyzing the bus voltage drop when the largest motor is started; Step 6, determine whether the bus drop in step 5 meets the requirements, if so, proceed to the next step, if not, reduce the impedance of the step-down transformer and return to step 3 to recalculate; Step 7, finally obtain the impedance of the step-down transformer and the short-circuit current of each busbar, and guide the selection of conductors and switchgear.

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