4.96
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
The cooling thermal time constant (TCONCn) setting defines the cooling ther-
mal time constant of thermal element n in state x of the equipment when the
equipment is de-energized (i.e., when the current is below the IEQPU value).
The thermal level alarm limit (THLAn) setting specifies the percentage ther-
mal level when the relay asserts the thermal alarm Relay Word bit.
The thermal level trip limit (THLTn) setting specifies the percentage thermal
level when the relay asserts the thermal trip Relay Word bit.
The maximum temperature of the equipment (TMAXn) setting specifies the
maximum operating temperature of the protected equipment. This setting is
used to calculate FAMBn (see Equation 4.9). When TAMB := OFF, the
TMAXn setting is ineffective, i.e., the relay does not use TMAXn in the
FAMBn calculation and FAMBn is forced to 1.
The thermal element reset (RSTTHn) setting specifies the conditions that reset
the thermal element n calculation to 0.
The equivalent heating current pickup value in per unit (IEQPUn) is used by
the relay to switch between the hot and cold time constant thermal equations.
This setting defines what the equipment considers to be insignificant operating
current that results in negligible heating effects. Typically this value is very
close to zero, corresponding to when the protected equipment is de-energized.
The thermal level trip dropout ratio (THLTDRn) setting defines the dropout
ratio of thermal level trip. If the thermal level drops below THLTDRn •
THLTn, Relay Word bit THRLT resets.
The thermal level trip dropout ratio (THLADRn) setting defines the dropout
ratio of thermal level alarm. If the thermal level drops below THLADRn •
THLAn, Relay Word bit THRLA resets.
Table 4.33 IEC Thermal Element Settings (Sheet 1 of 2)
Setting Prompt Setting Range
Setting Name :=
Fac to ry De fault
a
ENABLE IEC THML ELEM N, 1–3 E49IEC := N
AMB TMP SRC OFF, RTD, RA TAMB := OFF
AMB TMP SRC LOC 1–12, if TAMB := RTD
1–128, if TAMB := RA
TAMBLOC := 1
TMP HLTH DO TIME 0.1–900.0 sec THAMBDO := 1.0
OPERATING QTY IARMS, IBRMS,
ICRMS, IMAX
THRO1 := IARMS
THRO2 := IBRMS
THRO3 := ICRMS
BASIC CURR VALUE 0.1–3.0 PU IBASn := 1.0
CURRENT CORR FAC 1.00–2.00 KCONSn := 1.00
CURRENT PU 0.05–1.0 PU IEQPUn := 0.05
TIME CONS SWI SEL
OGIC THSTn := 0
HEAT TIME CONS 1–500 min TCONHnx := 60
COOL TIME CONS 1–500 min TCONCnx := 60
TRIP PU 1–150% THLTn := 100
ALARM PU 1–100% THLAn := 50
TRIP DO RATIO 0.01–0.99 PU THLTDRn := 0.98
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