What this braking unit delivers — and what it cannot
The VW3A7211 is a network braking unit rated for 250 kW peak braking power at 400 V supply, with a permanent braking power of 135 kW that defines the continuous dissipation ceiling in a deceleration duty cycle. At 97 % efficiency and unity power factor (cos phi = 1), the unit converts nearly all the regenerated energy to heat in the external resistor bank — the 3 % loss is the internal switching and control overhead.
Lifecycle status — obsolete, sourced through surplus channels
Available through independent distribution against an RFQ; quantities and pricing confirmed at quote time. No pin-compatible direct replacement exists in the current Altivar accessory range — a system-level review of the braking resistor bank and control wiring is needed if substituting.
The IP20 enclosure (937 mm high, 380 mm wide, 395 mm deep) is sized for floor-mounting in a drive cabinet — the height demands a tall enclosure section, and the 395 mm depth must clear the backplane wiring duct. Operating altitude derating applies above 1000 m: 5 % current reduction per additional 1000 m, which directly reduces the achievable braking torque at high-altitude installations.
Overload and protection coordination
Overload protection is set at 1.2 times the maximum current — the unit can sustain 120 % of its rated braking current momentarily before the thermal model trips the IGBT gate drive. The associated fuse rating is 500 A at 1000 V — this is the upstream short-circuit protection for the DC bus connection, not the braking resistor branch. The resistor branch requires its own overcurrent device sized to the resistor cold resistance.