701 Motor Protection Relay Date Code 20010719
Settings Calculation
Basic Motor Protection
4.20
Table 4.10 3000 HP Motor Th ermal Limit Times
Phase current transformers having 500:5 ratios are selected for the
application. The SEL-701 Relay settings for the application are
calculated as shown below.
Current Transformer Ratio (CTR) = 500/5 = 100
CT Secondary Rating (ITAP) = 5
Full Load Amps (FLA) = 366/100 = 3.66 A secondary
Service Factor (SF) = 1.25
Time to Trip at 1.30 x FLA (TTT130) = NP
Time to Trip at 1.40 x FLA (TTT140) = NP
Time to Trip at 1.50 x FLA (TTT150) = NP
Time to Trip at 1.75 x FLA (TTT175) = 625.0 seconds
Time to Trip at 2.00 x FLA (TTT200) = 400.0 seconds
Time to Trip at 2.25 x FLA (TTT225) = NP
Time to Trip at 2.50 x FLA (TTT250) = 225.0 seconds
Time to Trip at 2.75 x FLA (TTT275) = NP
Time to Trip at 3.00 x FLA (TTT300) = NP
Time to Trip at 3.50 x FLA (TTT350) = NP
Time to Trip at 4.00 x FLA (TTT400) = 72.0 seconds
Time to Trip at 4.50 x FLA (TTT450) = 58.0 seconds
Time to Trip at 5.00 x FLA (TTT500) = 30.0 seconds
Time to Trip at 5.50 x FLA (TTT550) = 25.0 seconds
Time to Trip at 6.00 x FLA (TTT600) = 18.1 seconds
Time to Trip at 6.50 x FLA (TTT650) = 15.2 seconds
Time to Trip at 7.00 x FLA (TTT700) = 13.2 seconds
Time to Trip at 7.50 x FLA (TTT750) = NP
Time to Trip at 8.00 x FLA (TTT800) = NP
Time to Trip at 8.50 x FLA (TTT850) = NP
Time to Trip at 9.00 x FLA (TTT900) = NP
Time to Trip at 10.00 x FLA (TTT1000) = NP
The relay neither requests settings for thermal limit times less
than the service factor nor does it require that all settings have a
time entered. You can enter NP for some points and the relay auto-
matically builds the thermal limit curve between the nearest two
Table 4.10 3000 HP Motor Thermal Limit Times
Multiples of Full Load Current Thermal Limit Time (Sec)
1.75 625
2.00 400
2.50 225
4.00 72
4.50 58
5.00 30
5.50 25
6.00 18.1
6.50 15.2
7.00 13.2
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