Bus Differential Protection

Voltage Balance
http://www.abb.com/product/db0003db004281/C12573E700330419C1256ECB004F7855.aspx

Low Impedance
Time Overcurrent Differential

Partial Differential

Basics
The general concept behind bus differential protection is that current that enters the zone or bus should equal the current leaving the bus. During in zone faults, the current entering the bus or zone won't equal the leaving. Current going in should at all times equal current going out. There are two

SEL "Bus Protection Considerations for Various Bus Types" by Caitlin Martin,Steven Chase, Thanh-Xuan Nguyen, Dereje Jada Hawaz, Jeff Pope, and Casper Labuschagne

SEL "Consideration for Using High-Impedance or Low Impedance Relay for Bus Differential Protection" by Ken Behrendt, David Costello, and Stanley E. Zocholl

SEL Presentation - Applying the SEL-587Z

SEL Application Note - Applying the SEL-587Z in Switchgear

ABB Presentation - "Bus Protection Fundamentals" by Jack Chang

GE "Bus Differential Protection" by J.G. Andrichak and Jorge Cardenas

Hydro Tasmania Consulting Presentation - "Principles of Differential Relaying" by Patrick Arendse