Multiple steady states of exhaust airflow in a multi-branch tunnel with the combined effects of buoyancy and fan power

The multi-branch tunnel has multiple routes for smoke extraction and air supply, consequently its ventilation and smoke control modes could have multiple solutions owing to the competitive effects of buoyancy and fan power. For the smoke control of a multi-branch tunnel, the mass and energy balance equations for every possible flow pattern were established, and the corresponding multiple solutions were obtained using mathematical methods. The results demonstrate that, even though the exhaust ventilation mode and fan type have been determined in accordance with the anticipation, multiple states of exhausted flow remain and the operation point of the fans will drift away from the design accordingly. This could cause a totally different direction of smoke route from the anticipated one. It is also shown that the type of fan has significant effects on the existence of multiple solutions.     

Dynamic behavior of 500 kV metal oxide arresters with a new type of lead dampers

In order to find out dynamic behaviors of the 500 kV zinc oxide arresters with and without a new type of lead damper, the dynamic behavior experiment and finite element analysis are carried out by means of single point input and single point output(SISO）measurement. The results of dynamic behavior experiment show that the primary frequencies of these two structures are between 1 Hz and 10 Hz and the difference between these two primary frequencies is not obvious, indicating that the overall stiffness of the two structures is low. The frequency of these two structures has hardly changed by the lead dampers, but the damping ratio of the arresters with the dampers is increased nearly 3 times, thus the fashion of vibration-reduction control of the dampers is to provide additional damping to the equipments. Owning to increment of damping device with the new type of lead dampers, there is an above reduction of 46% in the maximum stress of bottom porcelain pipe and the new type lead dampers can also decrease the relative displacement at the top of bushing. The results of finite element analysis show that the level modes of the 500 kV zinc oxide arresters with and without the new type of lead dampers are main modes and the vertical modes and torsional modes are not obvious.