Internal arc fault simulation using CFD to predict thermal behavior in switchgear
During an event of internal arc fault in LV/MV switchgears an electrical energy of the order of several Mega-joules is released which should be dissipated in the span of few milliseconds. Major portion of this energy is utilized in the heating of the enclosure gases resulting in the significant pressure rise inside the chamber. Objective of the simulation model developed is to improve design efficiency, increased safety, and especially to minimise real-world testing. Internal arc parameters such as pressure rise in various compartment, exhaust gas temperature, indicator temperature and pressure on panel walls are investigated with CFD simulation methodology. A 3-D CFD simulation of high temperature gases in LV/MV panel is carried out with coupled interactions between flow, temperature, turbulence and radiation fields taken into account. The internal temperature and pressure rise due to internal arc at different locations in breaker, cable and busbar compartment were compared. The same is used further to analyse structural forces and stresses on the panel members. Temperature rise at different locations on indicator walls which are modelled at a distance of 300 mm from panel were estimated from simulation. Visualization of the temperature, pressure and flow field is possible with CFD model.
Internal Arc Fault Simulation in Medium Voltage Panel for Thermal and Structural Withstand
During an event of internal arc fault in MV switchgears electrical energy of the order of several MJ is released, major portion of which is utilized in heating the enclosure gases resulting in significant temperature and pressure rise inside the chamber. An internal arc simulation model is developed to investigate various arc parameters such as pressure rise in compartments, exhaust gas temperature, temperature at indicator plane, pressure on panel walls and structural withstand. This simulation model has been developed to improve design efficiency, safety and specially to minimize the need for physical testing. A 3Dimensional CFD simulation of high temperature gases in switchgear panel is carried out taking into account the coupled interactions between flow, temperature, turbulence and radiation fields. Temperature and pressure rise due to internal arc at different locations in breaker, cable and busbar compartments are compared. Temperature rise at different locations on indicator walls are obtained from CFD.Panel enclosure structure should be able to withstand high pressure and temperature caused by arc fault. Overpressure due to arc fault can create significant mechanical stresses on the enclosure structure causing deformation of walls, doors getting blown out, failure at fastener location, etc. Pressure data obtained from CFD is used as an input to carry out stress analysis of the enclosure structure using FEA. Transient structural simulation is performed considering geometric and material non-linearity to obtain deformation and mechanical stresses on all walls. Results from FEA can be used for design qualification as well as for the optimal designing of structure and its components. Simulation model of a typical MV panel arrangement is discussed here.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.