256 Adirect-on-line start
85 Ain star
104 Nmstar torque vs 117 Nm needed
The motor
EM3-160L-4-15: 15 kW 4-pole, 400 / 690 V winding (delta at 400 V), MN 97.2 Nm, MA 3.2 × MN, IA 9.1 × 28.1 A.
Direct on line Star (1/3)
Starting current 256 A 85 A
Starting torque 311 Nm 104 Nm
Case 1 · Centrifugal pump
A pump started against a closed valve needs little torque at low speed: its load rises with the square of speed. 104 Nm accelerates it easily, and the switch to delta happens near full speed. Star-delta works, and the supply sees a third of the current.
Case 2 · Loaded belt conveyor
A conveyor stopped with material on it needs breakaway torque of about 120 % of motor torque, 117 Nm, from standstill. In star the motor gives 104 Nm: it will not start, will sit stalled in star, and trip or overheat.
Choosing
- Square-law loads (pumps, fans with low inertia): star-delta is fine.
- Constant-torque loads starting under load (conveyors, crushers, compressors): direct on line, or a soft starter or inverter that can deliver the breakaway torque.
- The transition from star to delta should happen at 85–90 % of speed, or the current peak at changeover approaches the direct-on-line value.
Application study: an engineering example worked by EMPD with catalogue data. Your application is confirmed by our engineers before quotation. Send us your duty.
