What this drive is
The ABB ACS550-U1-157A-4+B055 is a member of the ACS550 series general-purpose drive family, configured at the 157 A frame and ordered with the +B055 option suffix that ships from the ASEA BROWN BOVERI line under the ABB Drives catalog. The order code carries the ACS550-U1 series designation within ABB's motor drives line, positioned under the Motors & Motor Controls category as a Motor Drive.
Sizing and what the +B055 suffix implies
The +B055 option is added to the base ACS550-U1-157A-4 code, so a buyer comparing the two is looking at the same power frame with an extra factory-fit option bolted on — wiring, footprint, and current class are unchanged, but option-dependent features (commonly a braking chopper, line filter, or communication card on this platform) will differ between the two variants.
Sourcing posture
ACS550 series drives are specified into the BOM and quoted to order rather than pulled off a stocking shelf for a line-down event — the right move on a replacement order is an RFQ against the full order code including the +B055 option, so the factory ships a drive with the option fitted rather than a base unit that has to be field-modified.