Current Differential Relay
GARD 8000 SYS RFL Electronics
June 20, 2014 13-1 973.334.3100
SECTION 13. CURRENT DIFFERENTIAL RELAY
13.1 OVERVIEW
The GARD 8000 Current Differential Module provides a comprehensive set of primary protection
algorithms. An additional set of backup protection algorithms are available when inter-relay
communications are lost for any reason.
The GARD 8000 Current Differential Module can be configured for optional single-pole tripping. The
standard ordering version is for three-pole tripping only. Three terminal configuration is also available
as an option.
Other GARD 8000 Current Differential Module features include sequence of events recorder (SOE)
and oscillography.
13.1.1 PROTECTION FUNCTIONS
The primary protection functions included in the GARD 8000 Current Differential Module include:
Current Differential
Close Into Fault
High Set Trip
Open Conductor
Dual Breaker
The current differential protection is the heart of the relay. The algorithm includes a secure
communications protocol and a robust current measurement that reduces the impact of momentary
measurement transients. For protection values the measurement has a maximum of 16A, at which
point the routines saturate and do not know how much greater the actual current was.
The communications channel delay is removed as part of the normal data processing. The design of
the algorithm will tolerate fairly modest errors in the channel delay measurement or changes in the
delay due to network conditions.
The current differential protection can easily be configured to accommodate any specific installation.
Line charging currents and system resonances create particular concerns immediately following a
breaker closing. Proper system configuration allows the relay to ride-through these normal transient
events while allowing a trip if the system closes into a faulted line.
The high set trip routines provide an extremely fast response for high fault currents.
The open conductor routines allow the system to respond to system imbalances when the fault
condition results in a phase open circuiting rather than shorting to another phase or ground.
Dual breaker operation allows a second CT input to be used for breaker and half or ring bus schemes.
To Next Page