3.47
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)
Oil Thermal Time Constant (OTRxy)
Range: 0.1–20 hours, in 0.1-hour steps
The oil thermal time constant is the time it takes the top-oil temperature rise
over ambient temperature to reach 63.2 percent of the difference between final
rise and initial rise during a load change. If not provided, OTR can be
calculated from the following equation:
Equation 3.33
The default value from Table 3.3 is 0.08 hours. You can select other values
from within a range of 0–2 hours. The default values listed in Table 3.3 are
from IEEE C57.92-1981, Tables 2 and 4.
Oil Exponent (EXPnxy)
Range: 0.1–5, in 0.1 steps
This exponent is a constant that the thermal element uses in calculating
ultimate top-oil rise over ambient temperature (
TO
).
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 5.
Winding Exponent (EXPmxy)
Range: 0.1–5, in 0.1 steps
This exponent is a constant that the thermal unit uses in calculating ultimate
hot-spot conductor rise over top-oil temperature (
H
).
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 5.
Application Guideline,
Using the SEL-2030
to Send Temperature
Data to the SEL-387-6
While the SEL-387-5, SEL-387-6 relays can communicate directly with the
SEL-2600A for gathering temperature readings, some applications may use
the SEL-2030 communications processor for retrieving the temperature data
from the SEL-2600A.
where:
C = transformer thermal capacity (watt-hours/degree)
= 0.06 • (weight of core and coil assembly in pounds)
+ 0.04 • (weight of tank and fitting in pounds)
+ 1.33 • (gallons of oil)
or
C = 0.1323 • (weight of core and coil assembly in kilograms)
+ 0.0882 • (weight of tank and fitting in kilograms)
+ 0.3513 • (liters of oil)
P
r
= total loss at rated load (watts)
THor = top-oil rise over ambient at rated load
where:
1 kg = 2.2046 pounds
1 gallon = 3.785 liters
OTR C
THor
P
r
--------------• =
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