GE D30 Instruction Manual page 375

5 SETTINGS
e) THERMAL OVERLOAD PROTECTION (ANSI 49)

PATH: SETTINGS CONTROL ELEMENTS
PROTECTION 1(2)
 THERMAL
 PROTECTION 1
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
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MESSAGE
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 dif-
ferent elements of the power system. The cold curve characteristic is applied when the estimated I
10% of the base current. If I
p
applied. I current is estimated with a fixed time constant for both cooling and heating that reaches to the final value in two
p
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:
In the above equations,
• 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
GE Multilin

MONITORING ELEMENTS
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 is

τ
× 
t ln
=
op op


τ
× 
t ln
=
op op

, defining maximum permissible current above nominal current
B
D30 Line Distance Protection System

THERMAL OVERLOAD PROTECTION
Range: Disabled, Enabled
Range: SRC 1, SRC 2
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
2 
I
------------------------- - 
2 2

( )
I kI
–
B
2 2

I I
–
p
------------------------- - 
2 2

( )
I kI
–
B
5.7 CONTROL ELEMENTS

THERMAL
current is less than
p
(EQ 5.22)
(EQ 5.23)
5-239
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