Schweitzer Engineering SEL-387-0, Instruction Manual

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3.40
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)
Transformer Construction (XTYPE)
Range: 1, 3
A three-phase transformer can consist of one three-phase core and coil
assembly in one physical enclosure or three physically separate single-phase
transformers connected externally. Set XTYPE to either 3 (three-phase core
and coil assembly in one physical enclosure) or 1 (three physically separate
single-phase transformers connected externally).
Transformer Type (TRTYPE)
Range: D, Y
If the power transformer winding associated with the thermal element (see
TMWDG setting) is delta connected OR if the current transformers associated
with this winding are delta connected, set TRTYPE = D (delta). Set TRTYPE
= Y (wye) only if both the power transformer winding AND current
transformers are wye connected.
With TRTYPE = Y, the relay uses the measured currents for each phase in the
thermal element calculations. This means that for a three-phase bank
comprised of single-phase power transformers, the thermal element outputs
may vary between phases because the phase currents may be different. With
TRTYPE = D, the relay selects the highest magnitude phase current and sets
the other two phase currents to that value to force a balanced condition. In this
case the thermal element outputs for three single-phase transformers will be
the same, assuming that each is operating at the same cooling stage and the
thermal constants are set identically.
Winding Temp/Ambient Temp (THwr)
Range: 65, 55
Rated winding rise over ambient temperature is the difference in degrees
Celsius of the winding temperature of a transformer above the ambient
temperature. The actual winding temperature will be between the top-oil and
hot-spot temperature.
Most power transformers manufactured in 1977 and later are rated for a 65°C
rise over ambient. Power transformers manufactured prior to 1977 can be
rated for a 55°C rise over ambient. Set THwr for either 55 or 65, based on the
rating of the power transformer.
This setting determines which set of default transformer constants from
Table 3.3 the relay will use if EDFTC = Y.
Number of Cooling Stages (NCS)
Range: 1–3
Power transformers generally have a self-cooled rating and one or two stages
of forced cooling. Set NCS to the maximum number of cooling stages
associated with the monitored power transformer.