Schweitzer Engineering Laboratories SEL-701-1, Instruction Manual

Page: 75 / 452

Date Code 20011009
SEL-701-1 Monitor
Settings Calculation
Basic Motor Protection
3.17
When the thermal element setting method is set to USER, the monitor allows you
to construct a custom motor protection curve using as few as 5 or as many as 25
thermal limit points. The monitor requires:
The Full Load Amps and Service Factor ratings for the motor.
Time to Trip settings at 2.00 and 2.50 times Full Load Amps for
overload protection.
Time to Trip settings at 5.50, 6.00, and 6.50 times Full Load Amps
for locked rotor protection.
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 monitor 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 3.3 on page 3.18 .
EXAMPLE 3.6 Thermal Element User Method Setting
A 4000 V, 3000 HP motor is to be protected using the SEL-701-1
Monitor 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 3.3 .
Time to trip at 9.00 o FLA 1.0–300.0 s, NP TTT900 = NP
Time to trip at 10.00 o FLA 1.0–225.0 s, NP TTT1000 = NP
Table 3.9 Thermal Element Configuration
Settings, Setting Method = USER
Setting Prompt Setting Range
Setting Name =
Example Setting