Posted tagged ‘magnetic field’

Magnetic Levitation Train

September 29, 2011

Love to turn a 45 minute car ride to an 8 minute blur?

China was the first to country to have an up and running Maglev you could buy tickets to. Back in 1979 the Germans developed the 1st Magnetic levitation (Maglev) train.  The first to overcome the limitation of wheel and rail, because the rail moves entirely without contact!

This is a wonderful topic for your mechanical engineering seminar as well as project if you dare to make a working model.

The functions of the wheel and rail on a normal rail road including support guidance propulsion and braking are accomplished through an electro magnetic levitation and propulsion system. The mechanics have been replaced by electronics. Support Magnets draw the vehicle towards the guide way from below. While, guidance magnets hold’s the vehicle laterally on track. These support and guidance magnets are mounted on both sides of the vehicle along its entire length. An electronic control system ensures that it levitates at a constant height above the guide way. The Maglev train is propelled and braked by a synchronous long stator linear motor. This motor is not located in the vehicle itself but rather in the guide way. It functions on the same principle as a traditional rotating electrical motor, whose stator has been cut open, unrolled and stretched length wise along both sides of the guide way. But, instead of a rotating magnetic field a traveling magnetic field is generated in the windings, one that pulls the vehicle along the guide way without contact.

The guide way can be elevated where it makes ecological sense. in this way it won’t divide the landscape or developed areas and the area beneath the guide way can continue to be used as before. The guide way can be built at ground level to allow easier co location with existing transportation systems. Therefore, the guide way can be adapted to the landscape instead of being the other way round.

Maglev Train

The operation control system controls and safe guards the vehicle’s switches, guide ways and stations along the maglev route. The vehicle communicates with the control system by means of directional radio data transmission. The vehicle’s location is monitored by means of a location reference system integrated into the guide way. The only motor section in operation along the guide way, is the one in which the vehicle is currently traveling. When the vehicle passes from one section to the next, the new motor section is automatically switched on. More power is supplied on gradients and acceleration segments along the route than on flat segments this way the propulsion power is distributed very economically. It is always available exactly where it is needed.

The technology’s success in India could ultimately hinge on a combination public funding and private investments.

 

References:

MAGNETIC BEARING TECHNOLOGY

August 22, 2011

01-Magnetic_Bearing-magnetic bearing technology-active non contact position sensors

Magnetic bearings have been utilized by a variety of industries for over a decade with benefits that include non-contact rotor support, no lubrication and no friction.

Conventional mechanical bearings, the kind that physically interface with the shaft and require some form of lubrication, can be replaced by a technology that suspends a rotor in a magnetic field, which eliminates friction losses.

01-floating rotors-magnetic bearing technologies-SKF compressor drive-advanced drive system

There are two types of magnetic bearing technologies in use today – passive and active.  Passive bearings are similar to mechanical bearings in that no active control is necessary for operation. In active systems, non-contact position sensors continually monitor shaft position and feed this information to a control system.  This in turn, based on the response commanded by the system, flows to the actuator via current amplifiers.  These currents are converted to magnetic forces by the actuator and act on the rotor to adjust position and provide damping.

Additional benefits of magnetic bearings include:

  • No friction
  • No lubrication
  • No oil contamination
  • Low energy consumption
  • Capacity to operate within a wide temperature range
  • No need for pumps, seals, filters, piping, coolers or tanks
  • Environmentally friendly workplace
  • Impressive cost savings

In practice, these attractions are balanced in order to maintain a gap between the shaft (rotor) and static parts (stator). The function of the magnetic bearing is to locate the shaft’s rotation axis in the center, reacting to any load variation (external disturbance forces),


01-typical examples for Floating rotors to run a heavy machineries-magnetic bearing systems to run shaft without friction

Floating rotors could boost compressor efficiencies

Traditional centrifugal compressors are based on low-speed drives, mechanical gears and oil-film bearings, resulting in high running costs because of their high losses, wear, and need for maintenance.

This new compressor drive (above) uses a permanent magnet motor, operating at an efficiency of around 97%, to drive a rotor “floating” on magnetic bearings, which spins the compressor impeller at speeds of around 60,000 rpm. These drives experience almost no friction or wear, and need little maintenance. They also minimize the risk of oil contamination, and result in compressors that are about half the size of traditional designs.


How they work

 

01-general-magnetic-principles-monitoring the air gap of shaft and bearings contact and position-position sensor-closed loop system-controlling of shafts in center position-position controller
Magnetic bearings are basically a system of bearings which provide non-contact operation, virtually eliminating friction from rotating mechanical systems. Magnetic bearing systems have several components. The mechanical components consist of the electromagnets, position sensors and the rotor. The electronics consist of a set of power amplifiers that supply current to electromagnets. A controller works with the position sensors which provide feedback to control the position of the rotor within the gap.

01-magnetic-5 axis shaft control-radial bearings-air gap- advanced bearing technologies

The position sensor registers a change in position of the shaft (rotor). This change in position is communicated back to the processor where the signal is processed and the controller decides what the necessary response should be, then initiates a response to the amplifier. This response should then increase the magnetic force in the corresponding electromagnet in order to bring the shaft back to center. In a typical system, the radial clearance can range from 0.5 to 1 mm.

This process repeats itself over and over again. For most applications, the sample rate is 10,000 times per second, or 10 kHz. The sample rate is high because the loop is inherently unstable. As the rotor gets closer to the magnet, the force increases. The system needs to continuously adjust the magnetic strength coming from the electromagnets in order to hold the rotor in the desired position.