Schweitzer Engineering SEL-387-0, Instruction Manual

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3.46
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Thermal Element (SEL-387-6 Relay)
Constant to Calculate FAA (BFFAx)
Range: 0–100000, in steps of 1
IEEE C57.91-1995 section 5.2 states that B (BFFA) is an empirical constant
equal to 15000.
Table 3.3 lists this value as the default. You can select other
values from within a range of 0 to 100000. The thermal element uses this
constant to calculate the transformer insulation aging acceleration factor
(FAA).
Cooling Stage n Constants
Top-Oil Rise Over Ambient Temperature (THorxy)
Range: 0.1 to 100°C, in 0.1°C steps
Top-oil rise over ambient temperature is the difference in degrees Celsius of
the top-oil temperature of a transformer above the ambient temperature.
The default values listed in Table 3.3 are from IEEE C57.92-1981, Tables 2
and 4. If specific values for a particular transformer are known, you can enter
values from within a range of 0 to 100°C.
Hot-Spot Conductor Rise Over Top-Oil Temperature (THgrxy)
Range: 0.01 to 100°C, in 0.1°C steps
Hot-spot rise over top-oil temperature is the difference in degrees Celsius of
the temperature of the hottest spot on the conductor winding over the top-oil
temperature. If not provided, THgr can be calculated from the following
equation:
Equation 3.32
Table 3.3 lists default values. The setting range for THgr is 0 to 100°C.
Ratio Losses (RATLxy)
Range: 0.1–100, in 0.1 steps
RATL is the ratio of load loss at rated load to no-load loss. The default values
listed in
Table 3.3 are from IEEE C57.92-1981, Tables 2 and 4. If specific
values for a particular transformer are known, you can enter values from
within a range of 0 to 100.
where:
THwr = average winding rise over ambient at rated load (55°C or
65°C)

hswr
= hot-spot winding rise over average winding rise
= (10°C if THwr = 55 or 15°C if THwr = 65)
THgr THwr

hswr
THor
– + =