Date Code 20010625
Inputs, Outputs, Timers, and Other Control Logic
7-39
SEL-311L Instruction Manual
Protection: 87L protection still available if hot standby channel is operable, or if
three-terminal protection mode 3R is available. Backup protection is still
available via contacts OUT201, OUT202, OUT101 and OUT102 regardless of
channel problems, and regardless of the result of the channel problem.
Problem:
Problem with dedicated line current differential hardware.
Action:
Assert Relay Word 87HWAL (87L Hardware Alarm), deassert Relay Word bit
87LPE, illuminate 87CH FAIL front-panel target.
Protection: Backup protection still available via contacts OUT101 and OUT102.
Problem:
Problem with backup protection hardware.
Action:
Close ALARM contact, extinguish ENABLE front-panel target.
Protection: 87L and backup protection disabled.
dc2 (+)
dc1 (+)
(—)
(—)
OUT201
Trip Coil 1
52a1
OUT202
Trip Coil 2
52a2
DWG: M311L069
OUT101
OUT102
Figure 7.29: High-Speed Trip Contact Connections—Example 3
87L Tripping Coordinated with Tapped Load Protection—Example 4
The SEL-311L Relay contains instantaneous and inverse time overcurrent elements that operate
on total line current (the vector sum of the currents measured at all line terminals). Use these
T50 and T51 (see Figure 3.20 through Figure 3.25) elements and the integral four-shot reclosing
relay to coordinate line current differential protection with tapped-load protection. For example,
the system in Figure 7.30 contains a load tapped from the protected line. The tapped load is
protected by a fuse. Assume a fault downstream of the tapped load fuse. It may be desirable to
trip the transmission line circuit breakers rapidly, then auto-reclose. If the fault is still present,
then delay line current differential trips to give the tapped load fuse a chance to isolate the fault.
This scheme is commonly referred to as fuse-saving. The SEL-311L Relay can accomplish this.
Make setting
EHST = 0
Summary of Contents for SEL-311L
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