Arcing Simulation for Automatic Transfer Switches using In-House UDF

Automatic transfer switches (ATS) play an important role in the providing uninterrupted power to various applications like data Centre, hospitals etc. They can be connected between two utility sources, two gensets or a combination of them. It operates when one of the sources to which the load is connected is not available or the preferred source is up. While they do their job smoothly, they internally see harsh conditions. When an active source disconnects, an arc is generated between the contacts. The arc forms when the current jumps through the small air gap breaking it into ions and electrons at very high temperatures, typically above 10000K. This arc needs to be quenched quickly to avoid damage to the contacts and current carrying conductors. This paper throws light on an in-house methodology that is developed using the commercial tool Ansys Fluent. The physics of arc consisting of flow, thermal and electromagnetic fields are modelled. This paper includes the simulation of arc propagation along with the moving arm and effect of arc roots formed at the arc chute plates that help in quenching the arc. When the arc gets in contact with the splitter plates the plasma sheath layer gets formed. This results in a voltage drop across both sides of plates. A mechanism is devised in house to model this effect of arc roots and validate using the available literature. When the current is flowing through the air it generates a magnetic field which causes the movement of the arc. For introducing this effect User defined scalars are used to incorporate the governing equation for magnetic field and User Defined Function (UDF) is used to calculate the magnetic field. The simulation results are validated with test.