GE M60 UR Series

5-146 M60 Motor Protection System GE Multilin
5.6 GROUPED ELEMENTS 5 SETTINGS
5
– I
b
= Motor rated current specified by the MOTOR FULL LOAD AMPS setting.
• THERMAL MODEL CURVE EFFECT: This setting affects the time-to-trip thermal curves when the
THERMAL MODEL
CURVE is selected as “Motor”. This setting takes into account the design of the machine with respect to overload capa-
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:
(EQ 5.10)
In the above equation, the motor stator current (I
motor
) and motor rated current (FLA) are expressed in per units of
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:
(EQ 5.11)
In the above equation, the motor stator current (I
motor
) and motor rated current (FLA) are expressed in per units of
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.
Figure 5–55: 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 THERMAL
MODEL CURVE
setting description. Refer to the IEC 255-8 standard for additional details on its application.
trip time
TD 2.2116623
0.02530337
I
motor
FLA
--------------
1–


2
 0.05054758
I
motor
FLA
--------------
1–


+
------------------------------------------------------------------------------------------------------------------------------------------------
=
trip time
TD 2.2116623
0.02530337
I
motor
OF FLA
-------------------------
1–


2
 0.05054758
I
motor
OF FLA
-------------------------
1–


+
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
=
1
10
100
1000
10000
058
Stator current (multiples of FLA)
SF = 1.15, EFFECT = shift
Trip time (seconds)
SF = 1.15, EFFECT = cutoff