Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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Date Code 20170814 Instruction Manual SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Settings
The LOPX and LOPY functions, when available in a given SEL-700G model,
are always active unless blocked by the corresponding SEL
OGIC
control
equations LOPBLKX and LOPBLKY, respectively (see Table 4.50 for the
settings and Figure 4.120 for the logic). You must incorporate the LOP
function into a SEL
OGIC
control equation to supervise relay protection
elements (see Example 4.5).
LOP Impact on Other Protection Elements
Several elements (for example, 64G2, 51C, 51V, 21C, 40Z, 67, 27, 32, etc.)
require accurate relaying potentials for correct operation. It is critical that the
relay detects an LOP condition and prevents operation of these elements. For
example, when dropping a wrench on the phase-voltage input fuse holders, the
relay LOP logic accurately determines that this loss of input voltages is an
LOP condition and does not trip (if the LOP Relay Word bit supervises
selected tripping elements, see Example 4.5). If you are using voltage-
determined relay elements for tripping decisions, then blocking these elements
is crucial when the voltage component is no longer valid.
EXAMPLE 4.5 Supervising Protection Elements by LOP
See Figure 4.75 and Figure 4.77 for examples of Relay Word bit LOPY
automatically supervising elements.
The factory-default settings also supervise protection elements, as in,
for example, the following torque control settings.
51CTC := 27PPX1 AND NOT LOPX
51VTC := NOT LOPX
40ZTC := NOT LOPX
LOP Monitoring and Alarms
You should take steps to immediately correct an LOP problem so that normal
protection is rapidly restored. Include the LOP Relay Word bit in an output
contact alarm to notify operation personnel of abnormal voltage input
conditions and failures that can be detrimental to the protection system
performance if not quickly corrected.
It should be noted that when the relay is first energized with the generator
offline, the relay logic asserts Relay Word bit LOP as it detects no voltage in
the circuits. As soon as the generator starts and the relay detects the voltages,
the LOP Relay Word bit deasserts. Once the relay control power is ON and the
generator is taken offline, the relay does not assert Relay Word bit LOP
because it does not detect the zero voltage condition.
Table 4.50 Loss of Potential (LOP) Settings
Setting Prompt Setting Range
Setting Name :=
Factory Default
LOPX BLOCK SEL
OGIC
LOPBLKX := 0
LOPY BLOCK SEL
OGIC
LOPBLKY := 0