Schweitzer Engineering Laboratories SEL-701 - Figure 4.3 3000 HP Example Motor Cold Thermal Limit Curve

Date Code 20010719 701 Motor Protection Relay
Settings Calculation
Basic Motor Protection
4.19
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.
By examining the curve, we can find the thermal limit times at
various multiples of Full Load Current, as listed in
Table 4.10 on
page 4.20
. These times map directly to the relay settings shown
below the table.
100
200
300
400
500
600
700
800
900
1000
10
20
30
40
50
60
70
80
90
10 20123456789
Time in Seconds
Multiples of Full Load Amps
Acceleration
Overload
Locked Rotor