Motors & starting

One study drives this page: study.motorstart (POST /api/design/study with study = motorstart). It takes the largest motor on the canvas, or the motor you name, and inserts the starting impedance - starting current multiple times rated current at a starting power factor of about 0.35 - into the real load flow that already contains the grid internal impedance and the cable impedances, then reports the starting current, the resulting bus voltage dip, the running voltage, the starting reactive power, the starting torque estimate and the voltage waveform over the start. Equipment practice follows IEC 60034 (direct-on-line starting, default 6 x rated current when nothing is given) and the dip is judged against the usual 15-20 % limit.

Motor starting is the classic reason a correct steady-state design still trips on site: everything is within limits at full load, but the compressor blocks the voltage, the contactor drops out and the drive stalls. Customers and commissioning engineers ask for the starting dip, the starting current and the resulting torque - this page answers with the real load flow instead of a rule of thumb.

Input = topology (motor or load nodes, transformer, cables) plus the study input (motor tag, kW, efficiency, power factor, locked-rotor multiple, start time, dip limit; defaults 6 x rated current and 5 s). Chain: the starting impedance is built from the starting multiple and the starting power factor, added as a load, and the load-flow solver is called once for the running state and once per waveform sample (seven samples, from the full multiple down to 1), so the curve is a sequence of real solutions, not a formula. Output = study.motorstart.motor (rated kW, efficiency, power factor, starting multiple, starting current, start time, torque) + .voltage (dip %, limit, running pu) + .waveform[] + violations. Linkage: a bigger transformer or cable raises the minimum voltage and the short-circuit level, which moves the protection settings and the losses; a smaller starting multiple (soft start, VFD) cuts the dip, the starting kvar and the transformer loading, and therefore the transformer rating you have to buy.