Contact behavior of electrical vehicle-battery junction box under high shorting and breaking current

The motor of an electric vehicle and its equipment are connected to the battery via a junction box that contains power relays that ensure current flow when closed but can break the current in abnormal situations. The contacts of such relays have to ensure and maintain a low contact resistance and support a shorting current of a few kA and an acceptable breaking capacity under a normal load of a few hundred amps. We have developed a test involving a shorting current of 4000A passing during 50ms through closed contacts in which we study welding and arcing phenomena. The origin of arcing has been attributed to the shorted contact produced by the electromagnetic repulsion force that is able to counterbalance the contact force and separate the contact. The power arcing burns during the short circuit and a irreversible damage is observed when the accumulated arc energy exceeds a certain critical value. In this paper, the main cause of the repulsion phenomena and minimum arc energy criteria inducing substantial damage and capsule breaking is studied. By varying conditions of current for two relays equipped with different materials, filled with a specific gas and employing a magnetic field we found that shorting damage was not avoided below 2KJ. Fortunately breaking capacity is achieved without damage and relay function is ensured.