Schweitzer Engineering SEL-387-0, Instruction Manual

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3.45
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Thermal Element (SEL-387-6 Relay)
With XTYPE = 1 and cooling system efficiency being calculated for each of
the three single-phase transformers, the CSE bit is set when any of the three
values exceeds the limit. The thermal report will show which transformer was
above the setting.
General Cooling System Constants
Normal Insulation Life (ILIFE)
Range: 1000–999999 hr, in 1-hour steps
IEEE C57.91: 1995 suggests that normal transformer insulation life is 20.55
years or 180000 hours.
Table 3.3 lists this default value. You can select other
values within a range of 1000–999999 hours.
Enable Default Constants (EDFTC)
Range: Y, N
Setting EDFTC enables or disables the default transformer constants in
Table 3.3 .
When EDFTC is set to Y (yes), the transformer constants shown in Table 3.3
are in effect, and the individual settings are not accessible. When EDFTC is
set to N (no), the individual transformer constant settings are accessible.
Hot-Spot Thermal Time Constant (Thsx)
Range: 0.01–2.00 hours, in 0.01-hour steps
IEEE C57.91-1995 section 7.2.6 states that the winding time constant,

H
(Ths), is the time it takes the winding-temperature rise over oil-temperature
rise to reach 63.2 percent of the difference between final rise and initial rise
during a load change. The winding time constant may be estimated from the
resistance cooling curve during thermal tests or calculated by the
manufacturer using the mass of the conductor materials.
NOTE:
In the following settings x
designates a transformer, and y
designates the cooling system that
the transformer uses. If XTYPE = 3,
x = 1. If XTYPE = 1, x = 1, 2, and 3. For
example, if the transformer is self-
cooled, y = 1. For a transformer cooled
by forced air, y = 2. For a transformer
with both forced air and forced oil
cooling, y = 3.
Table 3.3 Default Transformer Constants
THwr
a
= 55°C
a
THwr = average winding rise over ambient at rated load.
THwr
a
= 65°C
IEEE
C57.91: 1995 Setting CS = 1 CS = 2 CS = 3 CS = 1 CS = 2 CS = 3

TO,R
THor (°C) 45° 40° 37° 55° 50° 45°

H,R
THgr (°C) 20° 25° 28° 25° 30° 35°

TO,R
OTR (hours) 3.0 2.0 1.25 3.0 2.0 1.25
R RATL 3.0 3.5 5.0 3.2 4.5 6.5
n EXP n 0.8 0.9 1.0 0.8 0.9 1.0
m EXP m 0.8 0.8 1.0 0.8 0.8 1.0

H
Ths (hours) 0.08
B BFFA 15000
Normal
Insulation Life ILIFE 180000