Project Description

Bus Protection Products

Buses with statically assigned zone currents are well suited for the use of high-impedance bus relaying (if suitable CTs are available) and do not require disconnect status inputs. For substations with terminals capable of switching between different buses, it is necessary to dynamically assign input currents to the bus zones of protection based on the disconnect auxiliary contact status. To avoid misoperations resulting from disconnect auxiliary contact failures, such substation configurations can require the use of a second trip criterion, such as a check zone.

Low-impedance numerical relays are especially well suited for protecting more complex bus configurations with dynamic zone selection because they enable zone reconfiguration without any need for corresponding changes to physical CT wiring.

While bus differential relaying provides protection for all bus arrangements, fast bus tripping and directional elements can provide adequate protection for some arrangements.

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

SEL offers superior protection performance combined with integrated station automation for all your bus protection needs.

Related Products

SEL-487B Bus Differential and Breaker Failure Relay

The SEL-487B provides optimized bus differential fault detection by using high-speed, subcycle protection coupled with high-security operation for external faults. Superior protection performance is combined with integrated station automation features for seamless transition into new and retrofit applications.

SEL-587Z High-Impedance Differential Relay

The SEL-587Z Relay is a flexible high-impedance differential relay that combines time-proven high-impedance analog technology with the advantages of microprocessor technology. Use event reports and Sequential Event Recorder (SER) for quick post-event analysis.


487B 587Z
Breaker Failure Protection f
Bus Differential
High-Impedance Bus Differential
Low-Impedance Bus Differential
Three-Phase Current Inputs 7/10
Three-Phase Voltage Inputs 1
27/59 Under-/Overvoltage
46 Current Unbalance f
50 (N,G) Overcurrent (Neutral, Ground)
50P Phase Overcurrent
50Q Negative-Sequence Overcurrent
51 (N,G) Time-Overcurrent (Neutral, Ground)
51P Phase Time-Overcurrent
51Q Negative-Sequence Time-Overcurrent
87 Current Differential
87Z High-Impedance Differential
Single-Pole Trip/Close
Three-Phase Differential Bus Zones 2/3/6 1
Check Zones 3
79 Automatic Reclosing f
Dynamic Zone Selection
SELogic Control Equations
Nonvolatile Latch Control Switches
SELogic Remote/Local Control Switches
Display Points
Multiple Settings Groups
Substation Battery Monitor
Event Report (Multicycle Data)
Sequential Events Recorder
Instantaneous Meter
Demand Meter
IEC 61850 +
Built-In Web Server
Simple Network Time Protocol (SNTP)
Mirrored Bits Communications
Parallel Redundancy Protocol (PRP)
Connectorized (Quick Disconnect) Available +
Standard Feature
+ Model Option
f This function may be created using settings