Line Design
In order to design the line there are few important elements to define: voltage drop, the load, sizing the cable, ampacity, and cable temperature. The load is based on the motor. Ampacity is that which is adequate for the rms value of the motor current profile plus the fast transient spike.
Choosing cable temperature includes the choice of ambient temperature for the line design.
The Load
The load is the current profile summarized in the motor electrical analysis. It is repeated here. The peak current is 1062 A, which lasts for 6 min. This is followed by 24 min with a current of 220 A. This cycle is repeated for 10 h/day.
The rms value of this current profile is:
(1,062)2 × (6 min) = 6,767,064
(220)2 × (24 min) = 1,161,600 / 7,928,664
Dividing this sum by 30 min yields the mean square, or 264,289 A2. The rms value is the square root, or 514 A. This is an rms load of:
(480) × (514) × (1.732) × 10-3 = 427kVA
