Schweitzer Engineering Laboratories SEL-701-1, Instruction Manual

Page: 67 / 452

Date Code 20011009
SEL-701-1 Monitor
Settings Calculation
Basic Motor Protection
3.9
Thermal Element RATING Setting Method
When you select the RATING thermal element setting method, the monitor
requests information on the protected motor capabilities. Obtain all of the requested
information except the Locked Rotor Trip Time Dial from the motor specifications.
Occasionally, only one locked rotor time will be specified for a particular motor.
Unless the specification states otherwise, assume the time is the cold locked rotor time.
Multiply the cold locked rotor time by 0.833 to determine a hot locked rotor time that
is acceptable for most motors. If only the hot locked rotor time is specified, multiply
that value by 1.2 to determine a cold locked rotor time that is acceptable for most
motors.
EXAMPLE 3.3 Thermal Element Rating Method Setting
A 4160 V, 600 HP motor is to be protected using the SEL-701-1
Monitor Thermal Element Rating Method. The motor data sheet
includes the following information.
Rated Horsepower (HP) = 600 HP
Rated Voltage (V) = 4160 V
Rated Full Load Current (A) = 76.9 A
Rated Locked Rotor Amps (A) = 462.0 A
Safe Stall Time at 100% Volts
Table 3.5 Thermal Element Configuration Settings,
Setting Method = RATING
Setting Prompt Setting Range
Setting Name =
Factory Default
Setting Method OFF, Rating, Generic,
User
SETMETH =
RATING
Full Load Amps 1.00–8.00 A
ITAP = 5 A FLA = 5.00
0.20–1.60 A A
ITAP = 1 A
A
The range of the Full Load Amps and Locked Rotor Amps settings depends on the ITAP setting as shown.
FLA = 1.00
Service Factor 1.00–1.50 SF = 1.15
Locked Rotor Amps 2.50–80.00 A
ITAP = 5 A LRA = 30.00
0.50–16.00 A
a
ITAP = 1 A
LRA = 6.00
Hot Locked Rotor Time 1.0–200.0 s LRTHOT = 2.1
Cold Locked Rotor Time 1.0–240.0 s LRTCOLD = 2.5
Locked Rotor Trip Time Dial 0.10–1.50 TD = 1.00