Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156656
J. Kumar, P. P. Kumar, Aeidapu Mahesh, Ankit Shrivastava
This paper describes a systematic approach for designing a self-tuning adaptive power system stabilizer (PSS) based on artificial neural network (ANN). An ANN is used for self-tuning the parameters of PSS e.g. stabilizing gain Kstab and time constant (T1) for Lead PSS in realtime. The inputs to the ANN are generator terminal active power (P) and reactive power (Q). Investigations are carried out to assess the dynamic performance of the system with self-tuning PSS based on ANN (ST-ANNPSS) over a wide range of loading conditions. The simulations are performed using Matlab/Simulink's neural network toolbox. The simulation and experimental results demonstrate the effective dynamic performance of the proposed system.
{"title":"Power system stabilizer based on artificial neural network","authors":"J. Kumar, P. P. Kumar, Aeidapu Mahesh, Ankit Shrivastava","doi":"10.1109/ICPES.2011.6156656","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156656","url":null,"abstract":"This paper describes a systematic approach for designing a self-tuning adaptive power system stabilizer (PSS) based on artificial neural network (ANN). An ANN is used for self-tuning the parameters of PSS e.g. stabilizing gain Kstab and time constant (T1) for Lead PSS in realtime. The inputs to the ANN are generator terminal active power (P) and reactive power (Q). Investigations are carried out to assess the dynamic performance of the system with self-tuning PSS based on ANN (ST-ANNPSS) over a wide range of loading conditions. The simulations are performed using Matlab/Simulink's neural network toolbox. The simulation and experimental results demonstrate the effective dynamic performance of the proposed system.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121920589","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156630
K. Ravishankar, D. Thukaram
This paper presents comparative evaluation of the distance relay characteristics for UHV and EHV transmission lines. Distance protection relay characteristics for the EHV and UHV systems are developed using Electromagnetic Transients (EMT) program. The variation of ideal trip boundaries for both the systems are presented. Unlike the conventional distance protection relay which uses a lumped parameter model, this paper uses the distributed parameter model. The effect of larger shunt susceptance on the trip boundaries is highlighted. Performance of distance relay with ideal trip boundaries for EHV and UHV lines have been tested for various fault locations and fault resistances. Electromagnetic Transients (EMT) program has been developed considering distributed parameter line model for simulating the test systems. The voltage and current phasors are computed from the signals using an improved full cycle DFT algorithm taking 20 samples per cycle. Two practical transmission systems of Indian power grid, namely 765 kV UHV transmission line and SREB 24-bus 400kV EHV system are used to test the performance of the proposed approach.
{"title":"Analysis of distance relay trip regions for EHV and UHV transmission lines","authors":"K. Ravishankar, D. Thukaram","doi":"10.1109/ICPES.2011.6156630","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156630","url":null,"abstract":"This paper presents comparative evaluation of the distance relay characteristics for UHV and EHV transmission lines. Distance protection relay characteristics for the EHV and UHV systems are developed using Electromagnetic Transients (EMT) program. The variation of ideal trip boundaries for both the systems are presented. Unlike the conventional distance protection relay which uses a lumped parameter model, this paper uses the distributed parameter model. The effect of larger shunt susceptance on the trip boundaries is highlighted. Performance of distance relay with ideal trip boundaries for EHV and UHV lines have been tested for various fault locations and fault resistances. Electromagnetic Transients (EMT) program has been developed considering distributed parameter line model for simulating the test systems. The voltage and current phasors are computed from the signals using an improved full cycle DFT algorithm taking 20 samples per cycle. Two practical transmission systems of Indian power grid, namely 765 kV UHV transmission line and SREB 24-bus 400kV EHV system are used to test the performance of the proposed approach.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122321343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156695
Toshikatsu Tanaka, Zengbin Wang, T. Iizuka, M. Kozako, Y. Ohki
Various types of epoxy/BN composites were prepared to optimize material conditions for high thermal conductivity and high breakdown strength. The best composite was found to be epoxy/conglomerated h-BN/ nano silica nano micro composite with thermal conductivity 12 W/m•K and BD strength 15 kVpeak/0.2 mm. One of the most important factors to obtain high values of the two performances is to reduce void content. Surface treatment of fillers and nano filler addition are also useful.
{"title":"High thermal conductivity epoxy/BN composites with sufficient dielectric breakdown strength","authors":"Toshikatsu Tanaka, Zengbin Wang, T. Iizuka, M. Kozako, Y. Ohki","doi":"10.1109/ICPES.2011.6156695","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156695","url":null,"abstract":"Various types of epoxy/BN composites were prepared to optimize material conditions for high thermal conductivity and high breakdown strength. The best composite was found to be epoxy/conglomerated h-BN/ nano silica nano micro composite with thermal conductivity 12 W/m•K and BD strength 15 kVpeak/0.2 mm. One of the most important factors to obtain high values of the two performances is to reduce void content. Surface treatment of fillers and nano filler addition are also useful.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133318818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156641
D. Pitsa, M. Danikas
Several polymer nanocomposites have been examined by the research community, aiming to clarify how the incorporation of nanoparticles in a pure polymer affects its dielectric properties. A number of factors can affect the nanocomposites properties, such as the nanoparticles size, the nanoparticles loading, the interfaces which are formed between the nanoparticles and the polymer, the space charge distribution etc. In this paper the influence of nanoparticles size on the electrical properties of the polymer nanocomposites is examined. More specifically, the electrical treeing behavior in epoxy/TiO2 under different nanoparticles size is simulated. The simulations are performed under dc voltage. The results show that the nanoparticles size influences the tree propagation. It is observed that as the nanoparticles size decreases, the growth of the electrical tree is hindered and its length decreases.
{"title":"Electrical treeing behavior in polymer nanocomposites under different nanoparticles size","authors":"D. Pitsa, M. Danikas","doi":"10.1109/ICPES.2011.6156641","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156641","url":null,"abstract":"Several polymer nanocomposites have been examined by the research community, aiming to clarify how the incorporation of nanoparticles in a pure polymer affects its dielectric properties. A number of factors can affect the nanocomposites properties, such as the nanoparticles size, the nanoparticles loading, the interfaces which are formed between the nanoparticles and the polymer, the space charge distribution etc. In this paper the influence of nanoparticles size on the electrical properties of the polymer nanocomposites is examined. More specifically, the electrical treeing behavior in epoxy/TiO2 under different nanoparticles size is simulated. The simulations are performed under dc voltage. The results show that the nanoparticles size influences the tree propagation. It is observed that as the nanoparticles size decreases, the growth of the electrical tree is hindered and its length decreases.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133257009","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156624
P. Chauhan, J. K. Chatterjee
Single control loop based two schemes for regulation of voltage and frequency of Self Excited Induction Generator (SEIG) based stand-alone 3-phase 4-wire renewable energy conversion system (RECS), under perturbations in speed and balanced/unbalanced load are presented. For the regulation, a Generalized Impedance Controller (GIC), a PWM voltage source converter having battery storage at its dc bus, controls reactive and active power flow in each phase of the SEIG using, (i) 3-phase stator voltage feedback only and (ii) 3-phase PCC voltage feedback only. The SEIG is operated with isolated neutral, while load and the GIC neutrals are interconnected. A mathematical model of integrated system having 3-phase 4-wire configuration of SEIG-load in closed-loop with the GIC has been developed and simulated in MATLAB/Simulink, with each control scheme, under variety of source and load perturbations. The novel feature of these schemes is successful regulation of both the amplitude and frequency of SEIG terminal voltage using only voltage feedback loop and no frequency feedback.
{"title":"Single-loop voltage and frequency control schemes for SEIG-battery storage based stand-alone three-phase four-wire RECS","authors":"P. Chauhan, J. K. Chatterjee","doi":"10.1109/ICPES.2011.6156624","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156624","url":null,"abstract":"Single control loop based two schemes for regulation of voltage and frequency of Self Excited Induction Generator (SEIG) based stand-alone 3-phase 4-wire renewable energy conversion system (RECS), under perturbations in speed and balanced/unbalanced load are presented. For the regulation, a Generalized Impedance Controller (GIC), a PWM voltage source converter having battery storage at its dc bus, controls reactive and active power flow in each phase of the SEIG using, (i) 3-phase stator voltage feedback only and (ii) 3-phase PCC voltage feedback only. The SEIG is operated with isolated neutral, while load and the GIC neutrals are interconnected. A mathematical model of integrated system having 3-phase 4-wire configuration of SEIG-load in closed-loop with the GIC has been developed and simulated in MATLAB/Simulink, with each control scheme, under variety of source and load perturbations. The novel feature of these schemes is successful regulation of both the amplitude and frequency of SEIG terminal voltage using only voltage feedback loop and no frequency feedback.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"330 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124656459","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156658
G. Kumar, M. Kalavathi
Voltage stability is of major concern in power systems stability. Main reason for the cause of voltage instability is the sag in reactive power at various locations in an interconnected power system. Improving the systems reactive power handling capacity via FACTS devices during a line outage categorized under large disturbance voltage instability is the idea behind this research paper. Various Series, Shunt and Series-Shunt FACTS devices are used to improve the reactive power profile which is tested on IEEE 14-bus system.
{"title":"CPF, TDS based voltage stability analysis using series, Shunt and Series-Shunt FACTS controllers for line outage contingency","authors":"G. Kumar, M. Kalavathi","doi":"10.1109/ICPES.2011.6156658","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156658","url":null,"abstract":"Voltage stability is of major concern in power systems stability. Main reason for the cause of voltage instability is the sag in reactive power at various locations in an interconnected power system. Improving the systems reactive power handling capacity via FACTS devices during a line outage categorized under large disturbance voltage instability is the idea behind this research paper. Various Series, Shunt and Series-Shunt FACTS devices are used to improve the reactive power profile which is tested on IEEE 14-bus system.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125027010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156644
N. Godha, S. Deshmukh, R. Dagade
Reliability cost/worth is an important aspect of power system planning and operation. One approach used to assess reliability worth is to relate it to the costs or losses incurred by utility, customers due to electric supply interruptions. This paper is concerned with the evaluation of reliability cost/worth indices of Distribution System using Monte Carlo Simulation. These results can be used to make decisions in distribution system planning and design.
{"title":"Application of Monte Carlo Simulation for reliability cost/worth analysis of distribution system","authors":"N. Godha, S. Deshmukh, R. Dagade","doi":"10.1109/ICPES.2011.6156644","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156644","url":null,"abstract":"Reliability cost/worth is an important aspect of power system planning and operation. One approach used to assess reliability worth is to relate it to the costs or losses incurred by utility, customers due to electric supply interruptions. This paper is concerned with the evaluation of reliability cost/worth indices of Distribution System using Monte Carlo Simulation. These results can be used to make decisions in distribution system planning and design.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121580071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156636
P. S. Kumar, J. Amarnath, B. Singh
Development of partial discharge (PD) detection methods by A/D conversion has acquired very important place in diagnosis for healthiness assessment of dielectric insulation of stator windings in turbine generators (TG). Evaluation of acquired digital spectrum for characteristics of PDs of the machine is the critical aspect in PD analysis. This paper describes the method of detecting PDs in (TG) high voltage windings of global vacuum pressure impregnation (GVPI) technology. Apparent PDs are digitally displayed on note book PC and analyzed for voids location. Data analysis for characterizing the PD activity as per IEC60270 standard such as apparent PD, peak discharges, average discharge current and power on phase resolved partial discharge (PRPD) histograms are presented to demonstrate the PD activities for 40MW, 11KV TG. Inception and extinction voltages of PDs are determined. Predominant frequencies of these stochastic process time series signals have been obtained by FFT analysis. Acquired data is stored as authenticated signatures for future reference to assess the condition of the dielectric insulation at customer premises. Experience to obtain very low PD intensities during manufacture of dielectric of TGs is shared. Precautions to be taken during GVPI process are presented. On-going research activities by Wavelet Transform(WT) for de-noising PD interference is highlighted.
{"title":"Partial discharges in stator winding insulation of turbine generators — A case study and remedies","authors":"P. S. Kumar, J. Amarnath, B. Singh","doi":"10.1109/ICPES.2011.6156636","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156636","url":null,"abstract":"Development of partial discharge (PD) detection methods by A/D conversion has acquired very important place in diagnosis for healthiness assessment of dielectric insulation of stator windings in turbine generators (TG). Evaluation of acquired digital spectrum for characteristics of PDs of the machine is the critical aspect in PD analysis. This paper describes the method of detecting PDs in (TG) high voltage windings of global vacuum pressure impregnation (GVPI) technology. Apparent PDs are digitally displayed on note book PC and analyzed for voids location. Data analysis for characterizing the PD activity as per IEC60270 standard such as apparent PD, peak discharges, average discharge current and power on phase resolved partial discharge (PRPD) histograms are presented to demonstrate the PD activities for 40MW, 11KV TG. Inception and extinction voltages of PDs are determined. Predominant frequencies of these stochastic process time series signals have been obtained by FFT analysis. Acquired data is stored as authenticated signatures for future reference to assess the condition of the dielectric insulation at customer premises. Experience to obtain very low PD intensities during manufacture of dielectric of TGs is shared. Precautions to be taken during GVPI process are presented. On-going research activities by Wavelet Transform(WT) for de-noising PD interference is highlighted.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128725107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156692
A. Kumar, C. Kumar, J. S. Rajan, K. Singh
Moisture content influences the dielectric properties of paper oil insulation of power transformers. The Polarization/Depolarization current measurements help to understand the dielectric response and conductivity of paper-oil insulation system. This unique concept facilitates the dissipation factor measurement over a wide frequency range. The results provide information on insulation condition such as moisture content in paper oil insulation in both qualitative and quantitative way. This paper discusses the PDC and FDS characteristics of paper oil insulation containing moisture and copper sulphide which is formed due to sulphur in oil.
{"title":"Characteristics of paper oil insulation by PDC/FDS method","authors":"A. Kumar, C. Kumar, J. S. Rajan, K. Singh","doi":"10.1109/ICPES.2011.6156692","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156692","url":null,"abstract":"Moisture content influences the dielectric properties of paper oil insulation of power transformers. The Polarization/Depolarization current measurements help to understand the dielectric response and conductivity of paper-oil insulation system. This unique concept facilitates the dissipation factor measurement over a wide frequency range. The results provide information on insulation condition such as moisture content in paper oil insulation in both qualitative and quantitative way. This paper discusses the PDC and FDS characteristics of paper oil insulation containing moisture and copper sulphide which is formed due to sulphur in oil.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116845668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-12-01DOI: 10.1109/ICPES.2011.6156627
J. Krishnan, N. S. Kumar, M. A. Khan
This paper presents a systematic method of developing the mathematical model for small signal stability enhancement in multi machine power systems using different types of FACTS devices namely (i) SVC (ii)STATCOM (iii) TCSC (iv) SSSC and (v) UPFC. Two axis model of the synchronous machine is used for investigating the small signal dynamic behavior of the multimachine power system. Local stabilizing signals such as real power perturbations, bus voltage deviations are used as control inputs for the damping controllers in FACTS devices. A nonlinear optimization model is developed which tunes the gains, time constants of the FACTS based damping controllers in the stabilizing loop. Case studies are carried out on the standard WSCC 3 Machine 9 − Bus system and the 10 Machine, 39 bus New England system. All computations are carried out using MATLAB v7.6.
{"title":"On the optimal tuning of FACTS based stabilizers for dynamic stability enhancement in multimachine power systems","authors":"J. Krishnan, N. S. Kumar, M. A. Khan","doi":"10.1109/ICPES.2011.6156627","DOIUrl":"https://doi.org/10.1109/ICPES.2011.6156627","url":null,"abstract":"This paper presents a systematic method of developing the mathematical model for small signal stability enhancement in multi machine power systems using different types of FACTS devices namely (i) SVC (ii)STATCOM (iii) TCSC (iv) SSSC and (v) UPFC. Two axis model of the synchronous machine is used for investigating the small signal dynamic behavior of the multimachine power system. Local stabilizing signals such as real power perturbations, bus voltage deviations are used as control inputs for the damping controllers in FACTS devices. A nonlinear optimization model is developed which tunes the gains, time constants of the FACTS based damping controllers in the stabilizing loop. Case studies are carried out on the standard WSCC 3 Machine 9 − Bus system and the 10 Machine, 39 bus New England system. All computations are carried out using MATLAB v7.6.","PeriodicalId":158903,"journal":{"name":"2011 International Conference on Power and Energy Systems","volume":"97 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114070028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：