Bus fault statistics; Pros and cons of providing bus bar protection;
Different bus bar arrangements (One main and transfer, two main, two main and transfer,
ring main, one & half breaker scheme);
Protection classification – high, medium and low impedance
schemes; High impedance – current based scheme, AC & DC schematics, CT
specification, work out for exciting current, KPV and stabilizing resistor, need for
non-linear resistor, location of CTs to avoid blind spots; High impedance – Voltage
based scheme.
Performance for internal and external faults, voltage setting
calculations; Medium impedance scheme, one cycle protection, relay operation and
characteristics for internal and external fault conditions; Low impedance schemes,
numerical bus bar protection, stabilized differential algorithm & directional current
comparison algorithm; Isolator auxiliary contacts – need for reliability.
