GE B30 Instruction Manual page 294

5.7 CONTROL ELEMENTS
d) THERMAL OVERLOAD PROTECTION

PATH: SETTINGS CONTROL ELEMENTS
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 dif-
ferent elements of the power system. The cold curve characteristic is applied when the previous averaged load current over
the last 5 cycles is less than 10% of the base current. If this current is greater or equal than 10% than the base current, then
the hot curve characteristic is applied.
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
• I = protected element base (nominal) current.
B
5-170

MONITORING ELEMENTS
THERMAL PROTECTION 1
FUNCTION: Disabled
THERMAL PROTECTION 1
MESSAGE
SOURCE: SRC1
THERMAL PROTECTION 1
MESSAGE
BASE CURR: 0.80 pu
THERMAL PROTECTION 1
MESSAGE
k FACTOR: 1.10
THERM PROT 1 TRIP
MESSAGE
TIME CONST: 45 min.
THERM PROT 1 RESET
MESSAGE
TIME CONST: 45 min.
THERM PROT 1 MINIM
MESSAGE
RESET TIME: 20 min.
THERM PROT 1 RESET:
MESSAGE
Off
THERM PROT 1 BLOCK:
MESSAGE
Off
THERMAL PROTECTION 1
MESSAGE
TARGET: Self-reset
THERMAL PROTECTION 1
MESSAGE
EVENTS: Disabled

t
op op

t
op op
, defining maximum permissible current above nominal current.
B
B30 Bus Differential System

THERMAL OVERLOAD PROTECTION
Range: Disabled, Enabled
Range: SRC 1, SRC 2, SRC 3, SRC 4, SRC 5, SRC 6
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

 ------------------------- - 
ln
2 2
 
 
I kI
B
2 2
 
I I
p

 ------------------------- - 
ln
2 2
 
 
I kI
B
5 SETTINGS

THERMAL
(EQ 5.14)
(EQ 5.15)
GE Multilin