8pole

An eight-pole machine, often called an eight-pole motor or generator, is an electrical machine in which the magnetic field has eight poles, forming four pole pairs. The pole count (p) determines the synchronous speed with Ns = 120 f / p, where f is supply frequency. With a 50 Hz supply, an eight-pole machine runs at 750 rpm in synchronous operation; with 60 Hz, 900 rpm. This lower speed compared with fewer-pole designs makes eight-pole machines well suited to applications requiring higher torque at reduced speeds.

In operation, induction eight-pole motors develop torque through slip between the rotating magnetic field and the rotor, so actual running speed is somewhat below Ns. Synchronous eight-pole machines lock the rotor to the rotating field, yielding constant speed.

The increased number of poles increases the torque capability at a given stator current and enables direct coupling to slower loads. However, higher pole counts typically reduce power density and may increase copper and iron losses, affecting efficiency and cost. Design choices include the rotor type (squirrel-cage for induction, wound rotor or permanent magnet for synchronous) and winding arrangements to achieve eight poles.

Common applications include low- to intermediate-speed drives such as conveyors, rolling mills, hoists, cranes, pumps, fans, and winders, where direct or near-direct drive at modest speeds is advantageous. Eight-pole machines are one option among a family of pole-count designs (e.g., 4-pole, 6-pole, 8-pole) used to balance speed, torque, and efficiency with application needs.