18.5 kW at 380-480 V — HVAC drive for asynchronous motors
The ATV21WD18N4 is a Schneider Electric Altivar 21 variable-frequency drive rated for 18.5 kW motor power on a 380-480 V three-phase supply, drawing 27.8 A line current at 480 V or 34.9 A at 380 V. This is the HVAC-dedicated branch of the Altivar family — the PI regulator, BACnet/LonWorks/Metasy N2 option cards, and the 1:10 speed range all point to pump, fan, and compressor duty in building services.
Panel fit and feeder sizing
Footprint is 12.4 in deep by 12.2 in wide by 26.2 in tall (315 x 310 x 665 mm) — a substantial enclosure that needs a backplate cutout and clearance for the heat sink fins. The line current at 480 V (27.8 A) sets the branch-circuit conductor and overcurrent device rating; at 380 V the draw climbs to 34.9 A, so the feeder must be sized for the higher figure if the site runs at the lower voltage.
Switching frequency and derating — motor noise vs thermal budget
Default carrier frequency is 6 kHz, adjustable up to 16 kHz — raising it quiets the motor whine but requires derating above 8 kHz. The drive's transient overtorque capability is 120 % of nominal motor torque for 60 seconds, which covers fan inertia starts and pump breakaway torque. Speed accuracy is ±10 % of nominal slip across the 0.2 Tn to Tn range — open-loop vector control is adequate for HVAC loads that don't need closed-loop encoder feedback.