4.178
SEL-700G Relay
Instruction Manual
Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
information on the CGSR report, refer to Section 9: Analyzing Events,
Generator Autosynchronism Report (CGSR Command).
The SEL-700G Relay also triggers and saves synchronism-check reports on
the X-side each time the relay initiates a synchronism-check supervised
generator breaker close. The report contains information about the system and
generator at the time the close is performed and can be viewed using the SYN
command. Refer to Section 9: Analyzing Events, Synchronism-Check Report
for more information on the SYN report.
Figure 4.119
Graphical Display of Generator Autosynchronism Report
Loss-of-Potential
(LOP) Protection
The SEL-700G sets Relay Word bit LOPX or LOPY (loss-of-potential) when
it detects a loss of either the X or Y-side relay ac voltage input, such as that
caused by blown potential fuses or by the operation of molded-case circuit
breakers. Because accurate relaying potentials are necessary for certain
protection elements (undervoltage 27 elements, for example), you can use the
LOP function to supervise these protection elements.
Refer to Figure 4.120 for the generic LOP logic. The logic is applicable to
both X and Y sides. The Relay Word bit LOPX is determined using the
measurements and settings from the X side, and Relay Word bit LOPY is
determined using the measurements and settings from the Y side. The relay
declares an LOP and seals it when there is more than a 25 percent drop in the
measured positive-sequence voltage (V1) and the additional conditions shown
in Figure 4.120 are satisfied. If the seal is not broken for one second, then the
relay latches the LOP Relay Word bit at logical 1. The relay resets LOP when
the positive-sequence voltage (V1) returns to a level greater than
0.75 • Nominal Voltage while negative-sequence voltage (V2) and zero-
sequence voltage (V0) are both less than 5 V secondary (VNOM is a relay
setting).
The LOP element is disabled when the positive-sequence voltage, V1, is
below 10.5 V. This threshold is to coordinate with the frequency tracking
threshold of 10.0 V. For example, the LOP will be disabled before the
frequency tracking on a decreasing voltage condition typically seen during a
generator shutdown.
NOTE:
(Applies to X Side Only)
. When
the global setting EXT3V0_X := VS or
VN, the ground-directional elements
that rely on external zero-sequence
voltage quantities (ORDERX settings
V and U) are not affected by a loss-of-
potential condition on relay voltage
inputs VA, VB, and VC. For more
information on the impact of LOP on
different ground-directional elements
refer to Loss-of-Potential on
page 4.106.
Summary of Contents for SEL-700G Series
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