Refiner Synchronous Motor


Our customer is a forest industry group that manufactures paperboard, paper and wood products. They are approximately 60 per cent self-sufficient in wood and 50 per cent in electricity.
The group has six production plants in Sweden with one located in the UK, and they employ approximately 3000 people.. The forests and hydro power facilities are located in Sweden.

Reason for project

Our customer’s goal was to increase the production of their refiner synchronous motors from 10 MW to 11.5 MW, without altering the current foundation and installation. This meant, a complete retrofit was needed.

Motor rated specification is as follows:

Frame size – BSM95.127/4W
Standard – IEC60034, IEEE115
Poles – 4
Output – 11500 kW, 0.95 PF, 10500 V , 683 A, 50 Hz , 1500 RPM
Efficiency – 98.1 %
Insulation Class – Stator F and Rotor H
Excitation – Brushless
Enclosure – IP54
Starting – Direct on line with aid of rotating excitation control units. 2.81 per unit starting current with a maximum voltage drop of 10 %.
Cooling – IC8W1
Mounting – IM1005
Duty – S1

Where did PPI come in

Various OEM’s found it too challenging to achieve the desired 11.5 MW output on the existing foundations while adhering to the vibration and electrical starting specification desired by the customer. We at PPI Engineering were confident that we could meet the vibration and electrical starting specification and therefore proceeded with the project. Our engineering team designed the motor with the objective to minimise starting current, hence voltage drop, meet the efficiency requirement, and to provide sufficient motor stiffness at the correct areas of the motor frame in order to accurately predict motor vibration. These objectives were the focus points while keeping in mind the associated manufacture-ability and cost.


We designed and oversaw the manufacturing of the motor. During the FAT the efficiency measured 98.1% which is in excess of the requirement. On site the motor starting current was 2.8 per unit and the maximum voltage drop was 9.91 %. The axial vibration level on the NDE was 2.5 mm/s rms which was within the customers specification. The customer was very satisfied and it again proved the quality and experience of PPI Engineering’s design team. The project posed numerous difficulties such as keeping the cost down and ensuring ease of manufacturing, while designing the motor for highest efficiency, lowest starting current and vibration levels.

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