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Khagendra Thapa,Gihwan Yoon,Sang Ho Lee,Yongsug Suh,Yong Cheol Kang 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.3
Cutback control in a grid code is one of the functions of a wind power plant (WPP) that is required to support the system protection and frequency stability. When a cutback control command signal is delivered to the WPP from the system operator, the output of a WPP should be decreased to 20% of the rated power within 5 s. In this paper, we propose a dedicated cutback control algorithm of a WPP based on the ratio of the command power to the available power. If a cutback control signal is delivered, the algorithm determines the pitch angle for the cutback control and starts the pitch angle control. The proposed algorithm keeps the rotor speed at the speed before the start of the cutback control to quickly recover the previous output prior to the cutback control. The performance of the algorithm was validated for a 100 MW aggregated WPP based on a permanent magnet synchronous generator under various wind conditions using an EMTP-RV simulator. The results clearly shows that the proposed algorithm not only successfully reduces the output to the command power within 5 s by minimizing the fluctuation of the pitch angle, but also rapidly recovers to the output level before the cutback control.
Thapa, Khagendra,Yoon, Gihwan,Lee, Sang Ho,Suh, Yongsug,Kang, Yong Cheol The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.3
Cutback control in a grid code is one of the functions of a wind power plant (WPP) that is required to support the system protection and frequency stability. When a cutback control command signal is delivered to the WPP from the system operator, the output of a WPP should be decreased to 20% of the rated power within 5 s. In this paper, we propose a dedicated cutback control algorithm of a WPP based on the ratio of the command power to the available power. If a cutback control signal is delivered, the algorithm determines the pitch angle for the cutback control and starts the pitch angle control. The proposed algorithm keeps the rotor speed at the speed before the start of the cutback control to quickly recover the previous output prior to the cutback control. The performance of the algorithm was validated for a 100 MW aggregated WPP based on a permanent magnet synchronous generator under various wind conditions using an EMTP-RV simulator. The results clearly shows that the proposed algorithm not only successfully reduces the output to the command power within 5 s by minimizing the fluctuation of the pitch angle, but also rapidly recovers to the output level before the cutback control.
Tripathi, Khagendra,Gyawali, Gobinda,Lee, Soo Wohn American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.37
<P>This study reports the influence of CVD-graphene on the tribological performance of gray cast iron (GCI) from the internal combustion engine (ICE) cylinder liners by performing a ball-on-disk friction tests. The graphene-coated specimen exhibited a significant reduction (similar to 53%) of friction as compared to that of the uncoated specimen, whereas wear resistance increased by 2- and 5-fold regarding the wear of specimen and ball, respectively. Extremely low shear strength and highly lubricating nature of graphene contribute to the formation of a lubricative film between the sliding surfaces and decreases the interaction between surfaces in the dry environment. Under the applied load, a uniform film of iron oxides such as Fe2O3, Fe3O4, and FeOOH is found to be formed between the surfaces. It is proposed that the graphene encapsulation with the metal debris and oxides formed between the specimens increases the lubricity and decreases the shear force. The transformation of graphene/graphite into nanocrystalline graphites across the contact interfaces following the amorphization trajectory further increases the lubricity of the film that ultimately reduces friction and wear of the material.</P>
Bhandari, Khagendra P.,Roland, Paul J.,Kinner, Tyler,Cao, Yifang,Choi, Hyekyoung,Jeong, Sohee,Ellingson, Randy J. The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.13
<▼1><P>We use a solution-based bromide anion hot injection method to synthesize stable, phase pure and highly crystalline cubic iron pyrite (FeS2) nanocrystals, with size varying from ∼70 to ∼150 nm.</P></▼1><▼2><P>We use a solution-based hot injection method to synthesize stable, phase pure and highly crystalline cubic iron pyrite (FeS2) nanocrystals, with size varying from ∼70 to 150 nm. We use iron(ii) bromide as an iron precursor, elemental sulfur as the sulfur source, trioctylphosphine oxide (TOPO) and 1,2-hexanediol as capping ligands, and oleylamine (OLA) as a non-coordinating solvent during the synthesis. We report on the influence of hydrazine treatment, and of thermal sintering, on the morphological, electronic, optical, and surface chemical properties of FeS2 films. Four point probe and Hall measurements indicate that these iron pyrite films are highly conductive. Although they are unsuitable as an effective photovoltaic light-absorbing layer, they offer clear potential as a conducting contact layer in photovoltaic and other optoelectronic devices.</P></▼2>
Cooperatizing Cooperative Federalism of Nepal
Prasai, Khagendra 한국외국어대학교 인도연구소 2020 남아시아연구 Vol.26 No.3
The Constitution of Nepal has institutionalized Nepal as a cooperative federalism and has laid down cooperation, coordination and coexistence as principles of federal governance. It is too early to pass a judgement on how the Nepalese federalism will fare in actual practice. However, we should not lose sight of problems built into the constitution of Nepalese federalism. Closer examination shows that there are conceptual-theoretical inconsistencies and contradictions inherent in the conception of cooperative federalism evident in the idea of autonomy, federation and concurrence of power. Nepalese federalism is no exception to this. In the absence of clarity and concretization of autonomy, federalism and concurrence of power, cooperative federalism will be inoperative by inviting insurmountable conflicts. To me, the most effective way to overcome this situation, is that cooperation as normative ideal and as enshrined in the Constitution of Nepal can and ought to be consolidated by instituting constitutional and legal provisions which require higher federal units to have consultation and discussion with the lower units before legislating and implementing programs and policies having a bearing on and to be implemented by the latter. These provisions can contribute to cooperatizing cooperative federalism by requiring higher body to behave as a coordinator or a leader in cooperative relations. Furthermore, there are practical problems that are largely attributable, among others, to elitist and undemocratic political culture rampant in political parties manifested in inter-party as well as intra-party relations; and lack of constitutional provisions necessary for maintaining a balance between federalism and autonomy. In addition, absence of national programs in Nepal, which, otherwise, would have decidedly compelled, induced and driven all units to work together in the true spirit of cooperation, constitutes a barrier to the effective practice of cooperative federalism.
Enhanced transmission due to antireflection coating layer at surface plasmon resonance wavelengths
Park, Myung-Soo,Bhattarai, Khagendra,Kim, Deok-Kee,Kang, Sang-Woo,Kim, Jun Oh,Zhou, Jiangfeng,Jang, Woo-Yong,Noyola, Michael,Urbas, Augustine,Ku, Zahyun,Lee, Sang Jun The Optical Society 2014 Optics express Vol.22 No.24