Siemens SIMPRO-100 - Figure 4.3 3000 HP Example Motor Cold Thermal Limit Curve

SIMPRO-100
Settings Calculation
4
PRIM-2400C 51
If you wish to emulate a manufacturer’s specified
thermal limit curve, you may enter additional time
points along the curve. If you do not wish to enter
a time for a point, enter NP. The relay
automatically creates a smooth thermal limit
curve between the entered time points.
Normally, you would use this method only if the
motor thermal limit curve includes a discontinuity
between the stator limit curve and the locked
rotor limit curve, as shown in Figure 4.3.
Example: Thermal Element User Method
Setting
A 4000 V, 3000 HP motor is to be protected
using the SIMPRO-100 Relay Thermal
Element User Method. The motor data
sheet includes the following information:
Rated Horsepower (HP) = 3000 HP
Rated Voltage (V) = 4000 V
Rated Full Load Current (A) = 366 A
Rated Locked Rotor Amps (A) = 2380 A
Safe Stall Time at 100% Volts
Cold = 16 seconds
Hot = 12 seconds
Service Factor = 1.25
The data sheet also includes the Thermal
Limit Curve shown in Figure 4.3.
Figure 4.3 3000 HP Example Motor Cold Thermal
Limit Curve
The discontinuities in the thermal limit curve
between the Overload, Acceleration, and Locked
Rotor curve sections make this motor ideal for
protection using a purpose-built thermal limit
curve. The User setting method provides the
facility to protect this motor.