GE M60 Instruction Manual page 292

GROUPED ELEMENTS
5
During the interval of discontinuity, the longer of the two trip times is used to reduce the chance of nuisance tripping
during motor starts.
In some applications, the shape of the motor thermal damage curve substantially deviates from the standard.
Furthermore, the characteristics of the starting (locked rotor and acceleration) and running thermal damage curves may
not correspond smoothly. In these cases, it can be necessary to use a custom curve so the motor can be started
successfully and used to its full potential without compromising protection. For these conditions, it is recommended that
the FlexCurves be used. FlexCurves allows the user to program selected trip times for pre-determined current levels. As
seen in the following figure, if the running (2) and the locked rotor thermal limit curves were smoothed into one standard
overload curve, the motor cannot start at 80% line voltage. A custom curve (1) is required.
5-164
Figure 5-77: Standard motor curves
OF x FLA
100000
10000
1000
100
10
1.00
0.10 1.00
Multiples of Pickup ( Pickup = OF x FLA)
8 x OF x FLA
x15
x1
10 100
833003A2.CDR
M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS