Schweitzer Engineering Laboratories SEL-311A, Instruction Manual

Page: 53 / 476

Date Code 20011205 Distance and Overcurrent Elements 3-13
SEL-311A Instruction Manual
Phase and ground distance elements are supervised with Fault Identification Selection (FIDS)
logic. This logic identifies the faulted phase(s) for all faults involving ground by comparing the
angle between I0 and I2. For example, when FIDS selects A-phase, FSA asserts and enables
A-phase ground distance elements and CB-phase distance elements. Distance elements BG, CG,
AB, and CA are blocked.
Zone Time Delay Elements
The SEL-311A Relay supports two philosophies of zone timing: independent or common timing
(see Figure 3.9). For the independent timing mode, the phase and ground distance elements drive
separate timers for each zone. For the common mode, the phase and ground distance elements
both drive a common timer.
Common Timer Settings: Z1D and Z2D
Independent Phase Timer Settings: Z1PD and Z2PD
Independent Ground Timer Settings: Z1GD and Z2GD
Pickup Ranges: OFF, 0.00–16,000.00 cycles, 0.25-cycle steps
Pickup and dropout accuracy for all timers: ±0.25 cycle and ±0.1% of setting
Select independent zone timing by using relay words M n PT and Z n GT (where n is the protection
zone number) in the appropriate SEL
OGIC
trip equation.
TR = M1P + Z1G + M2PT + Z2GT + 51GT
Select common zone timing by using relay words Z n T (where n is the protection zone number) in
the appropriate SEL
OGIC
trip equation.
TR = M1P + Z1G + Z2T + 51GT
The timing of the common zone timer is frozen or suspended if the timer is timing and the timer
input drops out. The duration of the suspension is one cycle. This feature prevents the timer
resetting when a fault evolves (e.g.,
ff
to 3
f
, SLG to
ff
G). If the timer expires, the suspension
logic is blocked.