GE M60 UR Series, Instruction Manual

Page: 277 / 662

GE Multilin M60 Motor Protection System 5-149
5 SETTINGS 5.6 GROUPED ELEMENTS
5
FlexCurves be used. FlexCurves allows the user to program selected trip times for pre-determined current levels. As
seen below, if the running (2) and the locked rotor thermal limit curves were smoothed into one standard overload
curve, the motor could not start at 80% line voltage. A custom curve (1) is required.
For high inertia load applications (when the
VOLTAGE DEPENDENT FUNCTION
is enabled), the locked rotor thermal limit
section of the programmed motor or the FlexCurve overload curve is modified and becomes dynamically adaptive to
system voltage changes. The detailed explanation of this function is covered later in this section.
Figure 5–57: FLEXCURVE EXAMPLE
The FlexCurve programming is based on per-unit current values. The equivalent primary amperes and
multiplier of full load current are also indicated above.
• UNBALANCE BIAS K FACTOR: Unbalanced phase currents will cause rotor heating that is not shown in the motor
thermal damage curve. When the motor is running, the rotor will rotate in the direction of the positive sequence current
at near synchronous speed. Negative sequence current, which has a phase rotation that is opposite to the positive
sequence current, and hence opposite to the direction of rotor rotation, will generate a rotor voltage that will produce a
833004A2.CDR
6500 hp, 13800 volt induced draft fan motor
Full load current = 280 amps; CT ratio = 500/5
Typical FlexCurve™
1
2
3
4
5
1
Programmed custom curve
2
Running safe time (stator limit)
3
Acceleration safe time (rotor limit)
4
Motor current at 100% voltage
5
Motor current at 80% voltage
10000
1000
100
10
Time
to
trip
(in
seconds)
1.0
0.1
0.56
280
1
Amp
FLA
pu 5.6
2800
10
56
28000
100
NOTE