GE M60 Instruction Manual page 254

5.6 GROUPED ELEMENTS
– I = the value of
b
• THERMAL MODEL CURVE EFFECT: This setting affects the time-to-trip thermal curves when the
is selected as "Motor". This setting takes into account the design of the machine with respect to overload capa-
CURVE
bility as determined by the overload (service) factor. For motor designs where temperature rise above ambient is
based on full load current, this setting should be selected as "Cutoff". The time to trip is then calculated using the fol-
lowing equation:
In the above equation, the motor stator current (I
relay current.
For specialized motor designs where temperature rise above ambient is based on the product of the service factor and
full load current (OF × FLA), this setting should be selected as "Shifted". The time to trip is then calculated using the
following equation:
trip time
In the above equation, the motor stator current (I
relay current.
In case of uncertainty, the more conservative "Cutoff" value should be used.
The following figure illustrates the impact of this setting on the time to trip thermal curves.
5
Figure 5–48: IMPACT OF THE THERMAL MODEL CURVE EFFECT SETTING
• IEC CURVE k FACTOR: This setting applies only to the IEC motor curve and is applied as described in the
setting description. Refer to the IEC 255-8 standard for additional details on its application.
MODEL CURVE
5-116
x
MOTOR FULL LOAD AMPS MOTOR OVERLOAD FACTOR
------------------------------------------------------------------------------------------------------------------------------------------------
trip time
=
I

motor
× -------------- 1
0.02530337

FLA
--------------------------------------------------------------------------------------------------------------------------------------------------------------------- -
=
I

motor
------------------------ - 1
0.02530337 ×

OF FLA ×
10000
1000
100
10
1
0
Stator current (multiples of FLA)
M60 Motor Protection System
.
×
TD 2.2116623
2
I
 
motor
× -------------- 1
0.05054758
– +
 
FLA
) and motor rated current (FLA) are expressed in per units of
motor
TD 2.2116623 ×
2 I
 
motor
------------------------ - 1
0.05054758 ×
– +
 
OF FLA ×
) and motor rated current (FLA) are expressed in per units of
motor
SF = 1.15, EFFECT = shift
SF = 1.15, EFFECT = cutoff
5 8
5 SETTINGS
THERMAL MODEL
(EQ 5.10)

–

(EQ 5.11)

–

THERMAL
GE Multilin