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.
A Three Dimensional CFD Analysis to Investigate the Effect of Ablative Materials and Venting Arrangement on Arc Characteristics in Low Voltage Circuit Breakers
When a low voltage circuit breaker interrupts a fault current, arc plasma is established between the contacts of the breaker. This paper focuses on influence of various polymer vapors like PA66, POM, PTFE, PMMA etc on the arc behavior and effect of venting on pressure distribution. The ablated polymer vapor, which is generated by strong arc radiation, changes the thermodynamic and transport properties of arc plasma. CFD Simulation showed the cooling of the arc plasma and improvement in gas flow. Three different generations (baffled grills, perforated plates, meshed wires) of vents were studied to obtain their pressure drop characteristics. Three dimensional CFD analysis of these vents were carried out by evaluating the porous jump coefficients and vent parameters. The study of the venting arrangement helped in better design of the vents with optimal pressure drop characteristics and deionization of the gases. The commercial computational fluid dynamics package FLUENT is customized to build electromagnetic capabilities for MCB arc extinction chamber. These two factors, ablative polymers and venting, affect and modify the arcing environment improving the overall quenching efficiency of a low-voltage circuit breaker.
Thermodynamic and mechanical analysis of short circuit events in an underground vault
The occurrence of an electric arc in an underground vault can be a very catastrophic event. The sudden release of a large amount of electric energy associated with the arc can cause the air pressure in the vault to reach levels that can damage the vault and the event can result in personal injury. This paper describes a computer model that is capable of calculating the internal pressure and temperature in the vault throughout an arcing event. The pressure is then used to predict the forces on the manhole cover and ultimately the motion of the cover if it experiences a pressure sufficient to dislodge it from its seat. With the forces known, the program can be used to evaluate modifications to the vault design in an attempt to improve system safety. The program results are compared with experimental measurements conducted for arcing events that were carried out inside rigid test chambers. Results are generated for a series of arc strengths and vault geometries that can be expected to exist in an actual underground vault that contains distribution cables. The generated results are then used to suggest mitigation schemes that would lessen the dangers of this event.