GE F60 Instruction Manual page 540
Feeder protection system
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MONITORING ELEMENTS
5.9.0.9 Thermal overload protection (ANSI 49)
SETTINGS CONTROL ELEMENTS MONITORING ELEMENTS THERMAL OVERLOAD PROTECTION
THERMAL PROTECTION 1(2)
THERMAL
PROTECTION 1
5
The thermal overload protection element corresponds to the IEC 255-8 standard and is used to detect thermal overload
conditions in protected power system elements. Choosing an appropriate time constant element can be used to protect
different elements of the power system. The cold curve characteristic is applied when the estimated I
10% of the base current. If I
is applied. I
current is estimated with a fixed time constant for both cooling and heating that reaches to the final value in
p
two seconds on a step change (either step up or step down) signal.
The IEC255-8 cold curve is defined as follows:
The IEC255-8 hot curve is defined as follows:
where
t
= time to operate
op
τ
= thermal protection trip time constant
op
I = measured overload RMS current
I
= measured load RMS current before overload occurs
p
k = IEC 255-8 k-factor applied to I
I
= protected element base (nominal) current
B
5-326
THERMAL PROTECTION 1
FUNCTION: Disabled
THERMAL PROTECTION 1
SOURCE: SRC1
THERMAL PROTECTION 1
BASE CURR: 0.80 pu
THERMAL PROTECTION 1
k FACTOR: 1.10
THERM PROT 1 TRIP
TIME CONST: 45 min
THERM PROT 1 RESET
TIME CONST: 45 min
THERM PROT 1 MINIM
RESET TIME: 20 min
THERM PROT 1 RESET:
Off
THERM PROT 1 BLOCK:
Off
THERMAL PROTECTION 1
TARGET: Self-reset
THERMAL PROTECTION 1
EVENTS: Disabled
current is greater or equal than 10% than the base current, then the hot curve characteristic
p
, defining maximum permissible current above nominal current
B
Range: Disabled, Enabled
Range: SRC 1, SRC 2, SRC 3, SRC 4
Range: 0.20 to 3.00 pu in steps of 0.01
Range: 1.00 to 1.20 in steps of 0.05
Range: 0 to 1000 min. in steps of 1
Range: 0 to 1000 min. in steps of 1
Range: 0 to 1000 min. in steps of 1
Range: FlexLogic operand
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
F60 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
current is less than
p
Eq. 5-32
Eq. 5-33
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