Investigation on Impact of Motor Dynamics on Operation of Current Limiting Protectors

Prospective short circuit level for MV switchgears of an industrial network is supposed to increase in time, due to inevitable expansion of utility network, probable installation of local generators and increasing the production capacities resulting in more motor contribution. If this short circuit current exceeds the level for which the switchgear was designed, the plant owner shall take some measures to prevent from possible damage. To solve the problem without replacing existing equipment, current limiting protectors have been utilized. These devices could reduce prospective short circuit current coming from upstream and could be an economical solution to this problem. Meanwhile, as these devices are triggered by instantaneous current, events especially relating to sudden increase in current may cause them to operate. This `False Tripping' is troublesome since these devices usually install on main incoming feeders of the network. This paper investigates the issue for a project aiming the reduction of short-circuit level from motor dynamics perspective including contribution to upstream fault and response to voltage dip using PSCAD/EMTDC software.