The two frequency drives limited the drive system to 2x 1175 A. However, the motor’s nominal rating at full-load is 2120 A, climbing to as much as 2350 A at 10% overload.
To resolve the issue, we equipped the motor with two windings, each drawing 1060 A at nominal rating. This keeps our motor within the frequency drives’ maximum available current.
To create a more compact pump package, the impeller is mounted directly to the motor shaft. In practice, this means all the forces generated by the pump transfer to the motor’s bearings. We made our calculations based on the specifications in the customer’s loading diagram indicating radial loads of up to 140 kN and axial loads of 250 kN. Under certain conditions, however, so-called cavitation can occur in the pump during dredging, briefly generating an opposing axial load of approximately 1250 kN. This, too, we took into consideration. To withstand those forces, we designed a special bearing system with a double-row spherical roller bearing and an axial spherical roller thrust bearing. Both the bearings on the drive and non-drive ends of the motor are oil-filled and hermetically sealed. Using simulation software, we applied the Finite Element Method to the bearing system and motor shaft to calculate the required dimensions for the bearings and shaft. During this stage we again kept a strict eye on the size.
The motor’s shaft seals have to keep the oil in and water out of the bearing system. This is achieved by means of a dual-action mechanical seal (with a shaft size of Ø 340 mm) that creates a seal based on an oil compensator with an over-pressure of 0.5 bar over the water pressure.