The magnetic couplings uses the magnetic field as the medium, adopts non-contact transmission, and is a purely mechanical structure, without oil, water and other media, with high transmission efficiency, low requirements for the alignment of the motor and the load during installation, convenient and quick installation, and basically free The maintenance, use cost and maintenance cost are low, and the operation is very reliable, which can ensure the safe and stable operation of the transmission equipment, and has broad application prospects. What are the structural characteristics of magnetic coupling and how does it play a role in the application of FPSO?

Structural characteristics of magnetic couplings

Magnetic couplings can be divided into two types in terms of structure: one is the cylinder structure; the other is the disc structure (as shown in Figure 1). When both the inner and outer magnets are radially magnetized, the permanent magnet coupler with the coupling poles arranged radially is a cylindrical permanent magnet coupler; while the inner and outer magnets are both axially magnetized, the couplings poles are arranged axially the configured permanent magnetic coupling is a disc permanent magnetic couplings.

  Magnetic couplings can be divided into two types in principle: one is synchronous type; the other is asynchronous type (as shown in Figure 2). Both the driving disk and the passive disk of the synchronous magnetic couplings are permanent magnet disks. The magnetic fields of the two permanent magnets are coupled in the air gap to convert magnetic energy into mechanical energy and realize torque transmission. The active disk of the asynchronous magnetic coupling is a permanent magnet, and the passive disk is a copper disk. The interaction between the permanent magnet magnetic field and the induced magnetic field is used to transmit torque.

Magnetic couplings for an FPSO

1. Problems in a certain FPSO transmission system

The FPSO is a non-powered flat-bottomed offshore floating production and storage device with an oil storage capacity of 150,000 tons. With years of use, the through-wall pumps on the platform have encountered problems such as poor alignment and high-level vibration to varying degrees. , greatly affecting the stable operation of offshore production.


In the transmission system of the FPSO through-the-wall pump, the installation method adopts the through-the-wall shaft to connect with the motor end and the pump end through the diaphragm coupling. Diaphragm couplings have very high requirements for installation and centering accuracy (0.05-0.08mm), while the wall-through shaft is fixed on the steel plate isolation wall, the position accuracy is difficult to control, and the on-site alignment is very difficult. The most serious part has a difference of 1mm and cannot be adjusted. Therefore, when the equipment is in operation, the vibration is large, which affects the life of the bearing box and the coupling, and the FPSO is at sea, and the wind and waves are strong, and the hull will be deformed accordingly, and this situation will aggravate the problem of misalignment of the coupling Impact. Fatigue damage of some diaphragm couplings has occurred, and there is a lack of replacement spare parts at sea, making maintenance very difficult.


2. The structural characteristics of the FPSO magnetic couplings

In order to solve the problems encountered in the operation of the FPSO transmission system, the disk-type asynchronous magnetic coupling was used to replace the diaphragm coupling on the pump with a high failure rate on site, and the permanent magnet transformation was carried out, which can solve the problems caused by misalignment and deformation of the equipment. , resonance, maintenance difficulties and a series of problems to improve the stability of the entire transmission system.


The magnetic couplings are mainly composed of a copper rotor (conductor rotor) and a permanent magnet rotor. The copper rotor is connected to the motor shaft, and the permanent magnet rotor is connected to the load. There is an air gap between the copper rotor and the permanent magnet rotor, and there is no mechanical connection for torque transmission. A soft (magnetic) connection is formed between the motor and the load. Due to the existence of the air gap, the starting of the motor in the transmission system is a gradual process from no-load to actual load. The specific structure is shown in the figure below:


 1. The comparative advantages of magnetic couplings and diaphragm coupling

(1) The magnetic couplings realize the motor buffer start and stop function, reduces the start peak value, reduces the start time, can realize frequent start, and prolongs the electrical service life of the motor.


(2) The magnetic couplings can isolate the vibration of the motor side and the load side and reduce the vibration of the whole system.


(3) The magnetic couplings allow a large centering error, including the angle, horizontal offset and axial offset between the motor and the permanent magnetic couplings.


(4) Magnetic couplings adopt non-physical connection, transmit torque through the air gap, and reduce equipment vibration and operating noise.


(5) The magnetic couplings themselves do not consume power, do not generate harmonics and electromagnetic interference, and are highly efficient and energy-saving.


Field application of magnetic couplings

The magnetic couplings described in this article have been installed on the above-mentioned FPSO and started to operate (as shown in Figure 4). It is currently in good operation and no abnormalities have occurred. When the magnetic couplings are installed, the overall size is consistent with the original diaphragm coupling, and each interface matches the motor and load. The original diaphragm coupling at the motor end and the load end can be directly replaced with a magnetic coupling without changing the motor, The base of the through-wall shaft and the pump, and can increase the service life of the bearing housing, the motor and the through-wall shaft. The magnetic couplings have a wide range of applications, and the installation and operation process are simple, with low centering requirements and can tolerate large installation errors during installation. Because it is a non-contact transmission, it effectively isolates the transmission of vibration, making the transmission system stable. The frequency of failures is reduced. At the same time, the equipment is basically maintenance-free, reducing the labor intensity of workers and saving maintenance costs.


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