Schweitzer Engineering Laboratories SEL-311L, Instruction Manual

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Date Code 20011112 Line Current Differential, Distance, Out-of-Step, Overcurrent, 3-17
Voltage, Synchronism Check, and Frequency Elements
SEL-311L Instruction Manual
EHSC (Y, N)
If the relay is equipped with two 87L channels and is set for two-terminal protection (E87L = 2),
setting EHSC = Y enables the channel not selected by PCHAN as a hot-standby 87L protection
channel. The relay executes all 87L protection algorithms continuously, using aligned data from
both the primary and hot-standby channel. When the primary channel is healthy, the relay uses
trip decisions based on the 87L elements processed with currents from that channel. If the
primary channel fails, the relay uses trip decisions based on 87L elements processed with currents
from the hot-standby channel.
There is no delay encountered when switching from primary
to hot-standby channels.
The primary and hot-standby channels need not be the same type of interface, and it is not
necessary to match the delays from primary to hot-standby channels. This enables diverse
routing of primary and hot-standby 87L channels. The two channels can even be of different data
rates (64 kbps for one, 56 kbps for the other).
If the primary channel is restored, protection resumes using the primary channel. If both primary
and hot-standby channels fail, 87L protection is safely disabled.
CTR_X and CTR_Y (1–6000)
Set CTR_X to match setting CTR in the remote SEL-311L Relay connected to Channel X. Set
CTR_Y to match setting CTR in the remote SEL-311L Relay connected to Channel Y. Settings
CTR_X and CTR_Y may be different from each other and different from the local CTR setting.
This accommodates different CT ratios at all line terminals. All 87L line current differential
settings are in secondary Amps, referenced to the highest CTR setting (the maximum of CTR,
CTR_X, and CTR_Y).
87LPP (OFF, 1–10 A Secondary)
The phase line current differential elements 87LA, 87LB, and 87LC restrain when the phase
difference current is less than 87LPP. Set 87LPP to detect three-phase faults as described above.
The setting is in secondary Amps, referenced to the relay with the highest CTR setting. For
example, assume E87L = 2, PCHAN = X, CTR = 200, and CTR_X = 400. If setting 87LPP = 6
A in both relays, the phase 87L elements assert for all internal faults that produce more than 6 •
400 = 2400 A of phase difference current.
87L2P (OFF, 0.5–5 A Secondary)
The negative-sequence differential element 87L2 restrains when |3I2| is less than 87L2P. As
mentioned above, set 87L2P above expected line charging current unbalance. As with setting
87LPP, setting 87L2 is in Amps secondary referenced to the relay with the highest CTR setting.
87LGP (OFF, 0.5–5 A Secondary)
The zero-sequence differential element 87L2 restrains when the |3I0| is less than 87LGP. Set
87LGP above expected line charging current unbalance. As with setting 87LPP, setting 87LG is
in Amps secondary referenced to the relay with the highest CTR setting.