Off-Shore Power Supply For Magnetic Bearings

Magnetic bearing technology is a solution for contact-free rotation. The rotating shaft is held in by the electromagnetic forces generated in radial and axial directions. These electromagnets require continuous power and a control system that keeps the load stable.

Our customer’s installations are located in isolated offshore production sites that are difficult to access. It is therefore necessary, even essential, to have reliable equipment with as little maintenance possible.

The high-speed magnetic bearing rotation renders the motor very sensitive to power loss. In case of outage, it is necessary to reduce the engine speed in order to place the shaft on a bearing. An interruption in the power supply can cause the shaft to suddenly de-levitate, forcing it to land on bearings and resulting in friction-related heating. This can cause the bearing to break or even worse, the motor to break completely. To guarantee the maximum availability of the motor, it is essential to have an energy source with at least the same level of availability.

Our customer was looking for a power backup solution that can be integrated into a cabinet developed to control the magnetic bearing equipment itself. He was looking for a power supply with high reliability and availability and a minimum of maintenance.

Alpha Innovations’ R&D team, together with the customer’s R&D team, has developed a compact, modular and configurable UPS cabinet to secure power supplies and to protect the equipment in case of a power outage.

 

Alpha Innovations’ team designed a fully customized solution based on this customer’s requirements. The solution consists in a compact cabinet with UPS and internal batteries. The UPS delivers 300Vdc and a backup time of 5 to 10 minutes (depending of the configuration). This gives the necessary time (2 minutes) to check the lines and (3 minutes) to slow down the speed of the rotor in case of a power outage and most of all to protect the equipment. Most power outages are less than 2 minutes. When a power outage lasts longer than 2 minutes, this generally means that it may last a few hours.

Alpha’s solution is driven by a controller that is in continuous communication with the bearing controller. Keeping both controllers separate can improve the maintenance practices and reduce safety risks as operators can work in one area without affecting the other.

Reliability

The reliability of the UPS is essential: as the rotor speed is very high, in case of an interruption of the main, a procedure to stop the rotor has to be launched to slow it down  before a complete stop. An immediate stop at full speed could destroy the bearing or even the motor itself.

Collaboration

The intensive collaboration between Alpha Innovations’ R&D and the R&D team of our OEM customer has been the key factor for the success of this project. Both teams confronted the task to design power interaction, both for hardware and firmware.

Tailor-made

The capacity of Alpha Innovations to customize its power converters and its monitoring solutions, coupled to its experience in designing power systems, have been an important factor to deliver a configurable product family, optimally fitted for the final application. In order to provide even more availability, Alpha Innovations is now developing a load analysis and a predictive maintenance system for this customer.