Schweitzer Engineering Laboratories SEL-311C, Instruction Manual

Page: 88 / 748

3.20
SEL-311C Relay Instruction Manual
Date Code 20060320
Distance, Out-of-Step, Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Distance Element Operating Time Curves at Nominal Frequency
Zone Time Delay
Elements
The SEL-311C supports two philosophies of zone timing: independent or
common timing (see
Figure 3.16 ). 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.
Select independent zone timing by using Relay Word bits 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 + 51QT
Select common zone timing by using Relay Words bits Z n T (where n is the
protection zone number) in the appropriate SEL
OGIC
trip equation.
TR =
M1P + Z1G + Z2T + 51GT + 51QT
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.,
phase-phase to three-phase, phase-ground to phase-phase-ground). If the timer
expires, the suspension logic is blocked.
If E21P, E21MG, and/or E21XG are set to anything but N, the common timers
are enabled according to the lower of the two enables. For example, if
E21P = 3 and E21MG = 2, enable Z1D and Z2D (two Zones as defined by the
E21MG setting). If an enable is set to OFF, common timing is disabled.
Table 3.5 Zone Timing Settings
Settings
Common Timer:
Independent Phase Timer:
Independent Ground Timer:
Z1D–Z4D
Z1PD–Z4PD
Z1GD–Z4GD
Ranges
Pickup: OFF, 0.00–16,000.00 cycles,
0.25-cycle steps
Accuracy Pickup and dropout
accuracy for all timers: ± 0.25 cycle and ± 0.1% of setting