Implementation of Over Current Relays with Non-Cascade Scheme on Medium Voltage Switchgear as Busbar Protection Study Case in PT PLN (Persero) UIT JBB

摘要

Busbar is the main terminal in switchgear that connecting all feeders. The highest short circuit current occurs on the busbar. Thus, it needs to be considered to provide a busbar protection system to reduce the effect by detecting and shutting down the busbar immediately whenever bus fault occurs. Mostly, this protection system doesn't installed at MV switchgear due to efficiency reason. The absence of busbar protection system on MV busbar, impact to 60 MVA 150/20 kV transformer condition. Conventional protection scheme only using delay time cascading of overcurrent relay on incoming and outgoing feeder to clearing the fault. Time delay on incoming feeder should be slower than outgoing feeder. The problem is that whenever busbar fault occurs, it would be delayed for fault clearing. Trough fault current (TFC) would flow in transformer for particular delay time and decrease health index and accelerate transformer aging. This paper deals about implementations of overcurrent relays with a non-cascade scheme on MV switchgear as busbar protection. This scheme doesn't use Kirchhoff current law principle for busbar protection. It only uses simple coordination between each relay in MV switchgear. Natural conditions are used to determine whether external or internal busbar fault. When it occurs internal fault, it can provide instantaneous clearing time. However, for external fault would be clear with delay time. By using this scheme, busbar fault can be detected and trip immediately.