Zhiting Zhou,Hui Li,Yong Yang,Haibo Zhang,Zhennan Fan
1 State Key Laboratory of Power Transmission Equipment&System Security and New Technology(Chongqing University),Shapingba District,Chongqing 400044,China
2 Dongfang Electric Machinery Co.,Ltd Research and Test Center Sichuan Deyang 618000,China
3 The Key Laboratory of Fluid and Power Machinery,Ministry of Education,Xihua University,Chengdu 610039,China
Abstract: In this study, a real-time rotor temperature monitoring system for large turbogenerators using SmartMesh IP wireless network communication technology was designed and tested.The system is capable of providing comprehensive,accurate,continuous,and reliable real-time temperature monitoring for turbogenerators.Additionally, it has demonstrated satisfactory results in a real-time monitoring test of the rotor temperature of various famous large-scale turbogenerators and giant nuclear power half-speed turbogenerators designed and manufactured in China.The development and application of this wireless temperature measurement system would aid in improving the intelligent operation quality, safety, and stability of China’s large turbine generators and even the entire power system.
Keywords:SmartMesh IP;wireless network communication; turbine generator; rotor temperature; realtime monitoring
I.INTRODUCTION
In global industry and academia, continuously monitoring the rotor temperature of large generators online has been a challenge.In recent years, China’s power grid has been connected to a large number of giant turbogenerators and giant nuclear power turbine generators.Due to their huge power capacity, if a rotor overheating fault occurs, it will result in serious consequences.As a result, it is imperative to implement comprehensive,accurate,and continuous online monitoring of rotor temperature.This is not only an important technical guarantee for the intelligent operation of generators and power grids but also a prerequisite for ensuring the operation of generators and power grids.
Unfortunately,the complex distribution of the electromagnetic field within the generator results in a nonuniform state of the loss (i.e., heat source) distribution of each component within the rotor.Meanwhile, the variances in heat dissipation between rotor components result in the complex and nonuniform characteristics of the temperature distribution of the rotor [1].These make the temperature monitoring of turbogenerator rotor a critical problem in the power industry has remained unresolved [1–14].While a series of early technical approaches were employed in the power industry to monitor the temperature of generator rotors, those methods were still insufficient to meet the requirements of intelligent online monitoring [2, 3].For instance, the most traditional resistance method, based on the resistance’s temperature effect, can only determine the average temperature of the rotor excitation winding.It is incapable of accurately showing the temperature of each part of the rotor.The temperature measurement method using test paper and the temperature measurement method using discolored paint do not clearly show the timeliness of temperature monitoring.Although carbon brush slip ring contactor temperature measurement (as shown in Figure 1 and mercury extractor temperature measurement excel in terms of monitoring range and flexibility,there are some problems,such as high workload associated with slip ring processing and installation, a complex process, easy wear, unstable contact resistance, a high risk of overheating, high mercury toxicity, a high environmental risk, and mercury oxidation affecting contact resistance and measurement accuracy[2,3].Additionally,these temperature measurement methods are limited to short-term experiments, making long-term continuous temperature online monitoring difficult to implement.However, although there have been some constructive achievements in monitoring and evaluating the rotor temperature of electric machinery[4–14],most of these advancements have concentrated on local simple measurements and algorithmic indirect estimation of induction motor rotor temperature [4–9],as well as sensors for direct temperature measurement and infrared temperature measurement of the rotor and damper windings of low-speed hydro-generators[10–12], with little emphasis on turbine rotor temperature monitoring[4–12].Furthermore,the infrared temperature measurement method can only measure the temperature of the rotor’s optically visible surface area,ensuring that the temperature measurement range is far from exhaustive.Recently, the combination of sensor and wireless communication technologies enabled wireless temperature measuring devices to be used to monitor the temperature of low-speed hydrogenerators [13, 14].However, due to the strong alternating electromagnetic field generated by a largescale turbogenerator and the long-term operation state of high voltage,high current,high pressure,and highspeed, wireless temperature measurement of the rotor faces some issues, including significant electromagnetic interference,limited signal transmission distance,easy loss of data transmission and communication signals, the instrument’s small “channel volume ratio”,and continuous power supply time of the measuring device very short.Worse still, these problems have resulted in an unpredictably high risk of rotor overheating for a large number of turbogenerators in the power grid.The operational safety of generators and power grids,intelligence monitoring,and reliability all have adverse effects that must be addressed.
Figure 1. Conductive slip ring for temperature measurement of carbon brush slip ring contactor.
SmartMesh IP sensor wireless communication network technology was introduced in recent years as a new low-power wireless mesh network technology that is well suited for harsh industrial process automation applications.Due to the advantages of high signal transmission reliability,strong two-way communication capability,scalability,low-power consumption,and time slot communication to effectively avoid contention, etc., it has been applied in many fields, such as renewable energy development, data center energy management, and building automation.Thousands,if not millions, of SmartMesh systems have been deployed worldwide to date.These systems have securely connected various smart devices to their respective applications to provide solutions that are smarter,environmentally friendly, and efficient.As a result,we believe that developing and designing a large-scale turbogenerator rotor temperature monitoring device based on the SmartMesh IP technology may improve upon the defects of existing large-scale turbogenerator rotor temperature monitoring methods.As a result, it can address the problems of long-term comprehensive real-time monitoring of such generators’rotor temperature.However, until today, research and related results in this area have been rarely mentioned in public reporting.As a result,it is critical to perform in-depth research.
In view of this, this study develops and designs a new type of real-time monitoring system for the rotor temperature of large turbine generators using SmartMesh IP network communication technology.And the real-time monitoring of the rotor temperature of the 350MW air-cooled turbo generator(China’s largest air-cooled generator),the 1200 MW,1550 MW,and 1750 MW giant nuclear power turbine generators(the world’s largest such generators), which were designed and manufactured by Dongfang Electric Co,Ltd, has been effectively applied, achieving satisfactory results, and improving the real-time monitoring of the state of large turbine generators and intelligent operation of the power grid.
II.OVERVIEW OF SMARTMESH IP SENSOR WIRELESS COMMUNICATION NETWORK
SmartMesh IP,the sensor wireless communication network, is a self-managed low-power internet protocol network consisting of a receiving manager and multiple wireless transmitting unit nodes,as shown in Figure 2.The reception manager is primarily responsible for monitoring and managing the network performance and security and serves as a bridge between the host application and the wireless network.The wireless transmitting unit is capable of two-way communication,data collection,and acting as a repeater.SmartMesh IP has the following significant advantages:First,the network reliability of 99.999%,which can better avoid the common communication signal loss of other wireless networks.Second, the AES-128-bit encryption certified by NIST can protect data by means of end-to-end encryption,message integrity checking,and device authentication.Third, it is highly scalable.It uses a time-slotted channel frequency modulation protocol to avoid intranetwork conflicts,thereby maximizing expansion and minimizing the high power consumption and highdelay transmission retry behavior caused by network congestion.
Figure 2. SmartMesh IP internet.
Fourth, using time-slotted communication technology can effectively avoid contention.
Fifth,it has a strong two-way communication capability, which is very suitable for monitoring and controlling the operational status of power equipment.
In terms of data transmission,the SmartMesh IP network uses the following two methods:
First,the gateway direct connection method;that is,the application program is directly connected to the manager,and the manager can use the port to send data packets to any port on the remote server, as shown in Figure 3.
Figure 3. Direct connection to the gateway.
Second, the end-to-IP connection, that is, the edge router connected to the IPv6 network,uses the embedded manager to send the compressed IP address data packet to the network,as shown in Figure 4.
Figure 4. End-to-end IP connection.
III.STRUCTURE DESIGN OF GENERATOR ROTOR TEMPERATURE MONITORING SYSTEM
The structure of the rotor wireless temperature measurement system is shown in Figure 5.It is mainly composed of the platinum thermal resistance installed on the rotor, the temperature signal acquisition transmitter, the wireless relay, the signal receiver, and the upper computer.The system uses the SmartMesh IP wireless communication network to implement temperature signal transmission and real-time temperature data collection and transmission.
Figure 5. Structure of rotor wireless temperature measurement system.
The SmartMesh IP wireless communication network architecture for temperature sampling and transmission is shown in Figure 6.
Figure 6. Wireless communication architecture.
In this network architecture,the front-end temperature acquisition transmitter is directly installed on the generator rotor, which is composed of an acquisition module, a control module, and a power supply module.The system uses a micro programmable control chip to realize the control sampling, signal demodulation,and A/D conversion of temperature sensing signals.The converted digital temperature signals are transmitted to the remote SmartMesh IP network receiver (manager) through the wireless acquisition front-end module, namely the front-end wireless unit transmitter node(mote)of the SmartMesh IP network.The signal receiver exchanges data with the upper machine through USB communication.
In order to improve the stability and propagation distance of the wireless network,multiple SmartMesh IP network relay transmitting nodes (motes) are set outside the generator rotor and even the outer space area of the generator, serving as wireless repeaters for wireless transmission of temperature measurement sampling signals.On this basis, the above wireless communication nodes and the receiving end are automatically linked to a topological structure so that the temperature measurement signal can realize multipath transmission in the wireless communication network to ensure the stability of data transmission.
IV.HARDWARE DESIGN AND INSTALLATION OF GENERATOR ROTOR TEMPERATURE MONITORING SYSTEM
4.1 Design of Wireless Temperature Acquisition Transmitter
A programmable acquisition control chip can be used for the front-end wireless temperature acquisition transmitter directly installed on the rotor, and the acquisition circuit is specially designed according to the measurement channel requirements.
Finally,the following design scheme is adopted:the wireless temperature acquisition transmitter adopts a three-layer circuit encapsulation structure.The bottom two layers are the temperature acquisition module,and the top layer is the power supply and control module.The multi-layer circuits are connected by the plug-and-pull interface.Each circuit board has a separate fixed shell,and each layer of the shell is assembled into an integrated device through the stacking and assembling process(Figure 7).The device has 40 measuring channels,and the channel interface is arranged into two axial layers,with two(20 channels)per layer.
Figure 7. Structure schematic of wireless temperature acquisition transmitter.
Since the temperature acquisition transmitter will be directly installed in the high-speed rotating rotor area,the structure must exhibit excellent centrifugal force resistance.In addition, because the generator’s internal space, particularly the rotor area, is limited, the space volume is particularly small, and the volume of the device should be as small as possible.As a result, the following miniaturization structure design was adopted for the temperature acquisition transmitter: According to the structural characteristics and geometric size design range of the existing large turbo generator rotor in China, the major rotation radius of the temperature acquisition transmitter is about 40 mm, and its shape and mass are symmetrically distributed in the geometric center,allowing it to be easily installed in the narrow space of the rotor shaft end.At the same time, to minimize the weight of the device and ensure its structural strength,the shell is made of the high-strength 7075 aluminum alloy, the structure is optimized to effectively reduce the centrifugal force of the acquisition transmitter during high-speed rotation,and the black oxidation treatment is performed on the shell to ensure the structural safety of its long-term operation.
4.2 Installation of Wireless Temperature Acquisition Transmitter
The wireless temperature acquisition transmitter is installed and fixed in a special flange, which is manufactured from a high-strength aluminum alloy.The 3D structure is centrally symmetric,and its center of gravity is located on the rotating axis.
This design has greatly reduced the influence of the temperature measurement device on the dynamic balance of the rotor, improved the safety of the system,facilitated the installation and debugging of the device,and facilitated the wireless signal transmission of the device,as shown in Figure 8.The mounting flange is then embedded and installed at the end of the excitation end of the measured generator rotor,as shown in Figure 9.
Figure 8. Physical object of the wireless temperature acquisition transmitter(already installed in the flange).
Figure 9. Wireless temperature acquisition transmitter and its fixed flange installed on the generator.
A lead connection scheme,as shown in Figure 10,is designed to ensure that the temperature sampling signal from the temperature measurement point can reliably reach the temperature acquisition transmitter.The lead wires of the measuring point temperature sensor are grouped into 4 L-shaped plug-in plugs(fixed on the mounting flange).The common end of the L-shaped plug is out, and through the D-shaped special plug is connected to the input channel of the signal transmitter.This connecting scheme of the sensor lead can not only ensure the stability of signal transmission but also facilitate the installation and disassembly of the rotor temperature measuring device.
Figure 10.Lead design plan of introducing the temperature measurement signal of the temperature sensor into the temperature acquisition transmitter.
4.3 The Choice of Temperature Sensor
Because of the high-speed rotation state (1500 rpm/3000 rpm, 1800 rpm/3600 rpm) of the large turbogenerator rotor,and the narrow rotor area, the high loss and heat, and the strong alternating magnetic field, in order to ensure the accuracy and rationality of the rotor temperature measurement, it is required that the temperature sensor installed on the rotor body be light weight,small in size,anti-electromagnetic interference,and have a higher insulation level and antipressure ability.In particular,the temperature measuring element installed on the rotor coil, in addition to satisfying the above conditions,also requires the lead wire of the temperature measuring element to be able to adapt to the high temperature, high voltage, and high pressure environment.
In order to meet the above requirements,a thin-film thermal resistance with high sampling accuracy and stable indexing characteristics is used as the rotor temperature sampling sensors.On this basis,through special packaging, multiple test verifications, and structural improvements,the temperature sensors meet the following performance: The temperature tolerance is up to 200°C, the pressure tolerance is greater than 2MPa, and the DC insulation voltage is greater than 500V.The sensors are specially prefabricated by us.The miniaturization process has been adopted in production.The insulation of the end package is strengthened, and the strength and insulation of the lead line are also improved.Some of the temperature sensors and their packages are shown in Figure 11.
Figure 11. Some temperature sensors used in the system.
4.4 Arrangement of Temperature Sensor
Considering that the rotor is rotating at high speed when the turbine generator is running(1500 rpm/3000 rpm, 1800 rpm/3600 rpm), to ensure the long-term safe and stable operation of the rotor temperature monitoring system,the temperature sensors on the surface of the rotor and the coil measuring point must be in a safe and reliable fixed state.
To this end,after repeated tests,the following methods are finally used to install and fix the sensors and their leads: the temperature sensors are installed on the surface of the rotor and the coil, the tail wires of which are collected into the insulated lead pipe fixed on the excitation end of the rotor through their respective slots; then it passes through the pole core block, the conductive screw, and the conductive rod;and lastly, it is introduced to the temperature acquisition transmitter at the end of the excitation end of the rotating shaft.As shown in Figures 12, 13.
Figure 12. Schematic diagram of temperature sensor layout.
Figure 13. Schematic diagram of the temperature sensors signal transmission lead path.
4.5 Power Supply for Wireless Front-End Temperature Measurement Equipment
To ensure the long-term stable operation of the temperature sensor, it is also necessary to design the best sensor fixing and wiring method according to the structural characteristics of different turbine generator rotors to avoid wear or breakage of the sensor probe and its tail wire due to force.For this reason,it is found through experiments that the following four key points should be accomplished in the installation of temperature sensors: First,ensure that the sensor probe is firm and reliable at the measuring point,and avoid damage due to looseness.Second,try to fix the sensor tail wire to a stable member with good insulation.Third,when embedding the sensor tail wire into the rotor movable part,the small radius right-angle turn of the sensor tail wire should be minimized.If it is necessary to turn at the junction of adjacent movable parts, protective measures must be designed to protect the lead at the turning position.Fourth, when the sensor tail wire is embedded in the rotor coil accessory, in order to prevent the insulation damage of the sensor tail wire from affecting the temperature measurement,it is necessary to avoid direct contact between the lead wire and the rotor coil.
For wireless front-end temperature measurement devices such as wireless temperature acquisition transmitters, rechargeable lithium batteries are used for power supply.The power management device has the functions of overvoltage and overcurrent protection, temperature protection, anti-explosion, circulating power supply, switchable power supply, etc., and the charging port is a multiplex charging port.As a result,it can ensure a sustainable long-term power supply for the wireless front-end temperature measurement equipment.The battery picture is shown in Figure 14.
Figure 14.Rechargeable lithium batteries used for power supply of wireless front-end temperature measurement equipment.
4.6 Measures to Avoid the Influence of the Electromagnetic Environment
To avoid the influence of the electromagnetic environment on measurement accuracy, the following measures were adopted.First, high-strength aluminum alloy to manufacture the outer casing of the wireless temperature acquisition transmitter is used to avoid the interference of the alternator’s electromagnetic field on the chip inside the temperature acquisition transmitter.
Second, the shielding layer is used to protect the data leads from the interference of the alternating electromagnetic field of the generator.
Third,when the temperature measurement data signal is wirelessly sent,a transmission frequency different from that of the generator’s alternating magnetic field is used to avoid interference from the latter.
4.7 Wireless Signal Receiver
This study uses the wireless signal receiver to transmit the temperature data to the monitoring software on the PC through the USB interface data cable.As the convergence point of network data and the access point of all relay nodes,the wireless signal receiver realizes the management and configuration of the wireless link network through the receiving management module.The receiver is directly powered by the USB data cable connected to the computer;no other power supply is required,and it is convenient to use,as shown in Figure 15.
Figure 15. Schematic diagram of on-site remote host computer acquisition.
V.SYSTEM SOFTWARE DESIGN
For the rotor temperature monitoring system described in this study,in the design of its control software function, we rely on the programmable data acquisition control chip to carry out software programming development.
Figure 16. Primary interface of temperature statistical analysis.
Figure 17. Software acquisition data and signal display interface.
Specifically, on the basis of the DUST SmartMesh IP embedded intelligent network software, the development of various functional software such as wireless network AP configuration, topological network management, management and configuration of acquisition and control modules,and man-machine interface is implemented.A variety of necessary monitoring functions, such as system network status monitoring,system configuration, temperature data display, and human-machine visual interaction, are realized.On this basis,a series of more comprehensive temperature monitoring and operation and maintenance functions such as temperature alarm threshold setting,real-time temperature alarm,temperature and time data query of each monitoring point,real-time curve output of temperature change at the measuring point,wireless signal communication quality monitoring and display, and historical data export to Excel files have been further realized.Some of the software interfaces are shown in Figures 16,17,18.
Figure 18. Wireless signal communication quality monitoring and display interface.
VI.REAL-TIME TEMPERATURE MONITORING TEST OF ACTUAL TURBINE GENERATOR
To test the accuracy, rationality, and reliability of the real-time monitoring system of the turbine generator rotor temperature designed in this study, we selected some important large-scale turbine generators designed and manufactured in China as the research examples.By installing the system designed in this study, we implemented wireless real-time monitoring of the temperature of these generator rotors.
First, we chose China’s largest air-cooled turbogenerator (350 MW) designed and manufactured by Dongfang Electric Co.,Ltd.as the test example.During the in-plant type test stage, the rotor temperature was monitored in real time for the three key temperature test schemes,such as the rotor full current temperature rise test, the rotor overcurrent temperature rise test and the rotor negative sequence temperature rise test.
6.1 Rotor Winding Connection for Rotor Full Current and Overcurrent Temperature Rise Test
During the test, considering the large capacity of this generator, it is difficult to carry out a load test in the factory.As a result, to ensure the safety of the generator in the test, the method of reversely connecting the partial windings of the rotor is adopted.Some of the rotor’s magnetic potential is offset,thereby weakening the air gap magnetic field.Currently,even when the rotor current reaches its rated value, the no-load test will not cause overvoltage on the stator winding,and it will not cause stator overcurrent during a shortcircuit test.At this time,the loss and heat of the rotor winding are basically the same as those in the rated load operation.
The normal wiring diagram of the rotor winding is shown in Figure 19a.Connect the rotor windings No.2,3,6,and 7 in reverse,as shown in Figure 19b.
Figure 19. Comparison diagram of rotor winding connection.
6.2 Electrical Measures for Rotor Negative Sequence Temperature Rise Test
According to Chinese national standards“JB/T 8445-1996 Test method for Negative Sequence Current Bearing Capacity of Three-Phase Synchronous Generator” the two-phase steady-state short-circuit test method is selected for the steady-state negative sequence capability test;the two-phase short-circuit sudden excitation test method is selected for the transient negative sequence capability test.
6.3 Temperature Monitoring Sensor Layout
Before the start of the test,based on the rotor ventilation heating theory and simulation calculation results of the temperature field, 36 temperature monitoring points were selected in the the slot coil straight area and end region coil (multi-turn coil position) and the surface of the rotor for installation of temperature sensors.On this basis,a sensor system for real-time measurement of the temperature distribution of the rotor as a whole was constructed.
The above-mentioned sensor installation work is implemented in the generator rotor assembly stage and is completed before the installation of the rotor guard ring.Some of the test scenes are shown in Figure 20.
Figure 20. Real-time monitoring test scenario for rotor temperature of large turbogenerator.
6.4 Analysis of Some Test Results
The full current temperature rise test results are shown in Figure 21.In this figure, not only the temperature measured by the system designed in this study but also the data obtained by the traditional temperature measurement test paper method are shown.
Figure 21. Data curve of rotor full current temperature rise test(comparison of temperature measured value and simulated value).
As shown in Figure 21, the sample point, the temperature measurement value obtained by the system designed in this study is close to the calculated value and the value of the temperature measurement test paper.However, its rationality is higher than the temperature measurement value of the test paper.The primary reason is that the test paper measurement results can only read a few fixed temperature discoloration values, such as 65°C, 71°C, and 77°C.As a result, it is difficult to measure more specific and accurate temperature values, such as the system in this study.In addition,the test paper temperature measurement cannot realize the long-term real-time online monitoring of temperature, but the system designed in this study can do it.
Additionally, in Figures 22, 23, 24 the monitoring results of temperature in the rotor overcurrent test and transient negative sequence test are shown,respectively.
Figures 22, 23 show that the system designed in this study is capable of measuring the variation law of rotor temperature with time, which means that it has relatively reliable continuous online monitoring ability.
Figure 22. Measurement data of real-time temperature variation in rotor overcurrent test.
Figure 23. Measurement data of rotor surface temperature variation curve in transient negative sequence test (I2t =10s).
As shown in Figure 24,for the transient negative sequence test condition,the transient maximum temperature measured by the system designed in this study is close to the calculated value and the measured value by the test paper method, which shows the accuracy and rationality of the temperature online monitoring system in this study.
Figure 24. Measured and calculated data of rotor surface maximum temperature in transient negative sequence test(I2t=10s)
Additionally, we chose some well-known giant nuclear half-speed turbogenerators as test examples,including the world’s largest giant nuclear power half-speed turbine generator(1750MW,1500rpm)and the famous “Hualong No.1” giant nuclear power half-speed turbine generator(1200MW),another giant nuclear half-speed turbogenerator (1550 MW,This is designed by China National Major Science and Technology Projects 2010ZX06004-013-04-02 and 2012ZX06002-017-02-01), using this temperature monitoring device designed in this paper, the similar real-time temperature monitoring tests are carried out on these generators,as shown in Figure 25.
Figure 25. Real-time monitoring test scenario for rotor temperature of large turbogenerator.
It is worth noting that the these latest giant turbogenerators and nuclear power turbogenerators incorporate the technology designed in this study during the plant’s design, manufacture, and type testing stages.The long-term continuous online monitoring of the rotor temperature was performed under various operating conditions, and fairly comprehensive and reasonable continuous online monitoring results of the rotor temperature were obtained.The design and production processes have been improved as a result of this test data.It ensures the smooth and safe operation of these massive generators.
We found that the wireless real-time monitoring system for rotor temperature designed in this study reliably achieved the following excellent performance indicators during the temperature measurement test described above.First, it is capable of parallel temperature collection in 40 channels.Second,the temperature acquisition system error satisfies±1°C in a timevarying magnetic field environment,and the temperature measurement range is 0°C–170°C.Third,it is capable of stable operation at a rotor speed of up to 3600 rmp and an indoor wireless transmission distance of up to 50m for temperature measurement signals.Outdoor wireless transmission distances of up to 300 m are possible(line of sight,ideal electromagnetic environment).Fourth,the wireless front-end measurement device can obtain a continuous and stable power supply for an extended period of time.The above performance indicators can better meet the requirements for real-time monitoring of the rotor temperature on large turbine generators.
This system would then be expanded to include online monitoring of the operation status of China’s large turbine generators and hydro-generator and wind generator,as well as smart operation and maintenance.
VII.CONCLUSION
In this study, a real-time monitoring system for the rotor temperature of a large turbine generator using SmartMesh IP wireless network communication technology was designed.The system overcomes a series of inherent shortcomings of conventional rotor temperature monitoring methods, such as resistance temperature measurement, carbon brush slip ring contactor temperature measurement, and mercury extractor temperature measurement.Additionally, satisfactory results have been achieved in the real-time monitoring of the rotor temperature of some well-known turbine generators designed and manufactured in China,including China’s largest air-cooled turbine generator(350 MW),another giant nuclear power half-speed turbine generator(1550 MW),“Hualong No.1”giant nuclear power half-speed turbine generator(1200 MW),and the world’s largest giant nuclear power half-speed turbine generator(1750 MW).
This study is critical for improving the intelligent monitoring, operation, and maintenance of China’s large-scale turbine generators and, indeed, the entire power system.
ACKNOWLEDGEMENT
This work was supported by the National Natura Science Foundation of China (NSFC),No.51607146,China National Major Science and Technology Projects 2010ZX06004-013-04-02 and 2012ZX06002-017-02-01, Sichuan Science and Technology Program,No.2018GZ0391, Sichuan Hydropower Energy and power equipment technology Engineering Research Center, Xihua university,Chengdu 610039,China,No.SDNY2020-001.
APPENDIX:GENERATOR TEMPERATURE CALCULATION MODEL
Physical Models
Flow field and thermal status were analyzed with CFD software package, generating3D models of the generator and the fluid domain respectively, which were stitched together via couple-interfacing.The calculation domain was discretized by polyhedral meshing.
The flow field model comprised domains of the frame, air coolers, end winding, iron core, rotor surface and axial fans,as shown in Figure 26.
Figure 26. Numerical model of the airflow field (cutaway view).
The coupling relation between the stator and rotor was simulated by multi-reference frame(MRF)model,where the mass flow inlet boundaries were set at the upstream side of axial fans while the pressure outlet boundaries were set at the downstream side of the main coolers.For amount of relevant structure details,the calculation domain contains more than 200 million mesh nodes and more than 36 million polyhedral elements.
Mathematical Methods
To calculate the density,velocity,temperature,energy and turbulence in the domain, conservation equations for mass,momentum,and energy were established and numerically discretized.For any variable,the differential form of the conservation equation can be expressed as follows:
The RNG k-εtwo-equation turbulence model [7]was adopted to simulate the flow field.The velocity and pressure coupling equations were calculated using the SIMPLEC algorithm.The conjugate heat transfer model was used to simulate solid-surface convection in the interface domain.The Nusselt numbers of the cells in the first layer near a wall [8] were calculated as follows:
