GE 469 Instruction Manual page 186

5–44
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If the motor starting current begins to infringe on the thermal damage curves, it may
become necessary to use a custom curve to tailor the motor protection so that successful
starting may occur without compromising protection. Furthermore, the characteristics of
the starting thermal damage curve (locked rotor and acceleration) and the running
thermal damage curves may not fit together very smoothly. In this instance, a custom
curve may be necessary to tailor motor protection to the motor thermal limits so it may be
started successfully and be utilized to its full potential without compromising protection.
The distinct parts of the thermal limit curves now become more critical. For these
conditions, it is recommended that the 469 custom curve thermal model be used. The
custom overload curve feature allows the user to program their own curve by entering trip
times for 30 pre-determined current levels.
As seen in the figure below, if the running overload thermal limit curve were smoothed into
one curve with the locked rotor overload curve, the motor could not start at 80% line
voltage. A custom curve is required.
TIME TO TRIP AT
4.75 x FLA: 16.2
TIME TO TRIP AT
5.00 x FLA: 14.6
TIME TO TRIP AT
5.50 x FLA: 12.0
TIME TO TRIP AT
6.00 x FLA: 10.0
TIME TO TRIP AT
6.50 x FLA: 8.5 s
TIME TO TRIP AT
7.00 x FLA: 7.3 s
TIME TO TRIP AT
7.50 x FLA: 6.3 s
TIME TO TRIP AT
8.00 x FLA: 5.6 s
TIME TO TRIP AT
10.0 x FLA: 5.6 s
TIME TO TRIP AT
15.0 x FLA: 5.6 s
TIME TO TRIP AT
20.0 x FLA: 5.6 s
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1
Range: 0.5 to 99999.9 s in steps of 0.1