
4.30
SEL-700G Relay
Instruction Manual
Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
saturation conditions. You can set and edit the remaining
settings according to the suggestions in the previous setting
descriptions.
Remember that the O87P setting must yield an operating
current value of at least 0.1 • I
NOM
. In this case, O87 must be
greater than or equal to (0.1 • I
NOMn
)/TAPn = 0.5/3.1 = 0.16.
Therefore, the O87P setting of 0.3 is valid.
The differential unit settings are complete for this specific application. At this
point, you can also choose to set backup overcurrent elements. More
discussion of these elements is at the end of this section.
Application Guidelines
It is vital that you select adequate current transformers for the differential
application. Use the following procedure, based on ANSI/IEEE Standard
C37.110: 1996, IEEE Guide for the Application of Current Transformers Used
for Protective Relaying Purposes.
CT Arrangements
Use separate relay restraint circuits for each power source to the relay. In the
SEL-700G1 you may apply two restraint inputs to the relay. You may connect CT
secondary windings in parallel only if both circuits meet the following criteria:
➤
They are connected at the same voltage level.
➤
Both have CTs that are matched in ratio and C voltage ratings.
➤
Both circuits are radial (no fault current contributions).
CT Sizing
Sizing a CT to avoid saturation for the maximum asymmetrical fault current is
ideal but not always possible. Such sizing requires CTs with C voltage ratings
greater than (1 + X/R) times the burden voltage for the maximum symmetrical fault
current, where X/R is the reactance-to-resistance ratio of the primary system.
As a rule of thumb, CT performance will be satisfactory if the CT secondary
maximum symmetrical external fault current multiplied by the total secondary
O87P = 0.3 (Operate current pickup in multiple of
tap)
SLP1 = 25 (25 percent initial slope)
SLP2 = 70 (70 percent second slope, fixed)
IRS1 = 6.0 (limit of slope 1 restraint current in
multiple of tap, fixed)
U87P = 10 (unrestrained differential operate current
level, multiple of tap)
HSM = (DRDOPT OR HRT) AND NOT RHSM
(high security mode enabled)
O87P2 = 1.25 (high security mode operate current
pickup in multiple of TAP)
HSMDOT = 5.00 (high security mode dropout time in
seconds)
Содержание SEL-700G Series
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