4.29
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Remember that the O87P setting must yield an operating
current value of at least a minimum of 0.1 • INOMn/TAPn,
where n = X, Y. In this case, O87P = minimum
((0.1 • INOMn)/TAPn) = 0.5/3.14 = 0.159. 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 which we discuss at the end of this
section.
Example of Setting the SEL-700G Relay (Generator Differential):
This example describes the generator differential element, which does not
include a step-up transformer in its protection zone.
Figure 2.23 illustrates an application that uses a 13.8 kV generator with a
rating of 30 MVA and current transformer ratios of 2000/5 A.
Step 1. Select/calculate the configuration settings for the current
transformer connections, ratios, and generator nominal current.
The ratios are equal to primary current divided by secondary
current. The configuration settings are as follows:
CTRX and CTRY := 2000/5 = 400
INOM = (30 • 1000)/(1.732 • 13.8 • 400) = 3.1
CTCONY = WYE
Step 2. Enable the differential settings: E87 = GEN.
Step 3. The relay will automatically calculate and set settings TAPX
and TAPY based on the INOM. You cannot change the TAP
settings:
TAPX = INOM = 3.10
TAPY = (INOM • CTRX)/CTRY = 3.10
Step 4. Set the differential element characteristic.
When E87 = GEN the SEL-700G uses the dual-slope
percentage- restraint differential characteristic without
harmonic restraint or blocking. Also, the relay automatically
sets SLP2 = 70 percent and IRS1 = 6, and hides these settings.
In some installations where uneven CT saturation during
external events, such as faults or transformer energization, can
lead to differential operation, consider programming the
SEL
OGIC
high security mode equation, HSM. Set HSMDOT
longer than the duration of expected inrush. Similarly, set
O87P2 to avoid an undesired operation when under severe CT
U87P = 10 (unrestrained differential Operate current
level, multiple of tap)
PCT4 = 15 (block operation if fourth harmonic is
above 15 percent)
PCT5 = 35 (block operation if fifth harmonic is
above 35 percent)
TH5P = OFF (no fifth-harmonic alarm)
HRSTR = Y (harmonic restraint enabled)
HBLK = Y (harmonic blocking enabled)
HSM = 0 (high security mode disabled)
O87P2 = 1.25
HSMDOT = 10.00
Summary of Contents for SEL-700G Series
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