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263 results on '"Li, H.Q."'

33. High-speed operation of a gas-bearing supported MEMS-air turbine

Author

Teo, C.J., Liu, L.X., Li, H.Q., Ho, L.C., Jacobson, S.A., Ehrich, F.F., Epstein, A.H., and Spakovszky, Z.S.

Subjects
Bearings (Machinery) -- Usage, Bearings (Machinery) -- Mechanical properties, Gas-turbines -- Speed, Gas-turbines -- Electric properties, Gas-turbines -- Mechanical properties, Science and technology
Abstract

Silicon based power micro-electro-mechanical system (MEMS) applications require high-speed microrotating machinery operating stably over a large range of operating conditions. The technical barriers to achieving stable high-speed operation with micro-gas-bearings are governed by (1) stringent fabrication tolerance requirements and manufacturing repeatability, (2) structural integrity of the silicon rotors, (3) rotordynamic coupling effects due to leakage flows, (4) bearing losses and power requirements, and (5) transcritical operation and whirl instability issues. To enable high-power density the micro-turbomachinery must be run at tip speeds comparable to conventional scale turbomachinery. The rotors of the micro-gas turbines are supported by hydrostatic gas journal and hydrostatic gas thrust bearings. Dictated by fabrication constraints the location of the gas journal bearings is at the outer periphery of the rotor The high bearing surface speeds (target nearly 10 x [10.sup.6] mm rpm), the very low bearing aspect ratios (L/D

Published
2009

41. A method of voltage stability evaluation for branch and generator outage contingencies

Author

Yorino, N., Li, H.Q., Harada, S., Ohta, A., and Sasaki, H.

Subjects
Electric power systems -- Research, Business, Electronics, Electronics and electrical industries
Abstract

This paper proposes a fast computation method to evaluate the load power margins with respect to saddle node bifurcations under branch outage as well as generator outage contingencies. The voltage stability evaluation for generator outages is a new topic, while there exist various studies for the branch outage contingencies. The proposed method is based on the conventional linear sensitivity method. The linear estimations are improved by taking into account nonlinearities of the power flow equations and by using a fast line search technique. Compared with existing methods, the accuracy is considerably improved. The effectiveness of the proposed method is demonstrated through IEEE 14-, 30-, and 57-bus systems. The estimation errors in load power margins are not more than 5% for generator outage and 15% for all branch outage (route open outage) contingencies. Index Terms--Contingency, load power margin, saddle node bifurcation, voltage stability.

Published
2004

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