Glossary
Torque motor and high torque motor
A torque motor is an electrical motor that is used for applications at low rotary speed quite often in direct drive without gear.
Moreover, the torque motors are very often used in cyclic machines with acceleration, constant speed, deceleration and return and also in applications of machines with constant operation delivering a power at constant speed. Torque motors are therefore more often qualified in torque and related speed than in power and the maximum torque is equal to 3 to 4 times the rated torque for allowing high dynamics.
Traditionnally the applications of motion control in factory automation and in particular machine-tools used electrical motors with high rotary speed coupled through a gear to the load for reducing the motor speed and increasing the motor torque to the ones needed by the axis of the machine. However, the gears create problems of maintenance, reliability, accuracy, plays and loss of efficiency that penalize technically and economically the servomechanisms. That is the reason why the machine builders have initiated since several years to eliminate the gears by using motors rotating at low speed and consequently with high torque capability for achieving a direct drive of the automated axis.
Currently, the applications of torque motors and high torque motors are not only regarding motion control in processes and cyclic machines of factory automation but also motion control outside factories as stage technologies, amusement parks, electrical ground and subsea vehicles. There are DC and AC multiphase torque motors. Nowadays, the applications of AC three- phase synchronous permanent magnets Torque motors and High Torque motors, as ALXION ST and STK, are increasing more and more.
Motor & alternator for direct drive
A direct drive motor or alternator is a motor which is directly coupled to its load or an alternator to its driving engine or turbine without using a gear. As a matter of fact, the gears create problems of maintenance, reliability, accuracy, mechanical plays and loss of energy efficiency that penalize technically and economically the servomechanisms in motion control ; additionnaly they generally do not allow the presence of through hollow shafts that can be necessary for passing cables, pipes, auxiliary shafts, or other processes needed by the load. That is the reason why the machine builders have initiated since several years to eliminate the gears by using permanent magnets synchronous torque motors rotating at low speed and consequently with high torque capability for achieving a direct drive of the automated axis.The servo motor may operate with various energy sources. In the case of ALXION, we are focused on direct drive electrical motors and more particularly permanent magnet AC 3 phase direct drive motors and alternators with our ranges of ST complete motors, STK frameless motors and STK frameless alternators.
Frameless motor or alternator
A frameless motor or alternator is constituted of 2 parts : one stator and one rotor without frame nor bearings.In the case of a frameless permanent magnet AC motor, the stator is constituted of an assembly of laminations carrying a 3 phase winding inserted inside a housing. The rotor is constituted of a magnetic core carrying permanent magnets.For being operational, the 2 parts need to be integrated by the user inside a mechanics with bearing(s). The interest of frameless torque motors or alternators by comparison with complete housed motors with bearings, shaft, flanges, resides in the capability to achieve a compact mechatronic system in direct drive without gear without redundant parts or components and highest reliability, efficiency and precision. Frameless torque motors are particularly recommended for optimizing technically and economically the direct drive applications in machine-tools, printing, plastics, rubber, electronic components industries and wind turbine or water turbine in the case of permanent magnets alternators for energy generation. ALXION has a range of high performance STK frameless torque motors with highest torque density and diameter between 145 mm and 800 mm for and STK frameless alternators mainly used for wind or water turbines.
Wind turbine
A wind turbine is a machine converting the wind energy in mechanical energy then in electrical energy. The energy conversion is made by a turbine driving an electrical generator (DC or more often multiphase AC ) . Technically, the main figures of merit for classifying a wind turbine are :
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the highest rate of wind energy that is converted to mechanical energy in the limit of physical laws
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the highest efficiency of the conversion from mechanical energy to electrical energy
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the lowest windspeed for initiating energy production
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the most silent operation at a given windspeed
There are 2 mains kinds of wind turbines: Horizontal Axis Wind Turbines or HAWT, Vertical Axis Wind Turbines or VAWT. The HAWT generally rotate at higher speed than VAWT for a given windspeed. For a given power, the HAWT have consequently a lower torque and smaller generator or alternator than VAWT, but they are generally less silent than VAWT. That is the reason why the VAWT are considered more particularly for use in urban environment.
Permanent magnet alternator
A permanent magnet alternator is an electrical generator making the conversion from mechanical energy to AC electrical energy. The permanent magnet alternator is by principle a multiphase AC synchronous machine and more particularly a 3 phase machine delivering a balanced system of AC voltages and currents, in which both statoric and rotoric magnetic fields are rotating synchronously that is to say at the same speed. The excitation of the permanent magnet alternator or inductor is made by permanent magnets bonded to the rotor. There are structures of permanent magnet alternators with internal rotor and external stator on one hand and structures of permanent magnet alternators with internal stator and external rotor on the other hand. However, the permanent magnet alternators with external stator are more performing in terms of power-to-weight and torque-to-weight because the cooling of statoric windings is easier when the stator is in contact with the air. The ALXION STK permanent magnet alternators have external stator and internal rotor and are excited by strong rare earth permanent magnets.
Wind turbine alternator
A wind turbine alternator is an electrical machine making the conversion from mechanical energy to electrical energy in a wind turbine (see that word ). The wind turbine alternator is by principle a multiphase AC synchronous machine and more particularly a 3 phase machine delivering a balanced system of AC voltages and currents, in which both statoric and rotoric magnetic fields are rotating synchronously that is to say at the same speed. Therefore it is an AC electrical generator. The excitation of the alternator or inductor can be made by coils with DC currents implemented on the rotor or much more frequently nowadays by permanent magnets bonded to the rotor. There are structures of wind turbine alternators with internal rotor and external stator on one hand and structures of wind turbine alternators with internal stator and external rotor on the other hand. However, the wind turbine alternators with external stator are more performing in terms of power-to-weight and torque-to-weight because the cooling of statoric windings is easier when the stator is in contact with the air. The ALXION STK alternators have external stator and internal rotor and are excited by strong rare earth permanent magnets at the rotor.
Permanent magnet generator
A permanent magnet generator is a device that converts mechanical energy to electrical energy. In this device the rotor windings have been replaced with permanent magnets. These devices do not require a separate DC supply for the excitation circuit or do they have slip rings and contact brushes. These machines are superior alternatives to traditional induction motors that can be coupled with turbines, diesel generators and used for hybrid vehicles. Another major advantage is that these machines does not require any specific work environment and hence can be used in wind and water machines.
The PMG can be a DC voltage machine with brushes and rotary collector or much more frequently an AC synchronous multiphase machine whereas the stator and rotor magnetic fields are rotating at the same speed. This eliminates the excitation losses in the rotor, which otherwise typically represent 20 to 30 percent of the total generator losses. The reduced losses also give a lower temperature rise in the generator, which means that a smaller and simpler cooling system can be used. If you are considering a permanent magnet DC generator then the inductor will be found at the stator with an array of permanent magnets. But in case of an AC generator the inductor is located at the rotor with an assembly of permanent magnets.
A PMG reduces loses in the rotor by 20 to 30 percent. Thus we get a much cooler system. This temperature reduction also reduces the temperature of the bearings and hence improves the reliability and the lifetime of the bearings. Recent developments in PMG technology have been made possible by a significant improvement of the magnetic materials during the past decade. A little piece of Neodymium Boron Iron (NeFeB) is 10 times stronger than the traditional ones made from ferrite magnate. Thus with further research we can improve the strength and reliability of these devices.
The demand for these devices is increasing day by day. With the increasing cost of electricity people are looking for an alternate source of energy and the permanent magnet generator perfectly fits in that place. These devices do not use any environmental resources to produce energy and thus are environment friendly. Besides no wastage or by products is generated from these device in the process of energy generation. Environment experts recommend the use of permanent magnet generators as these can reduce the impact of pollution by up to 50%.
ALXION manufactures 3 phase permanent magnet alternators, see STK Alternators range.
Windmill generator
A windmill or wind turbine generator is an electrical machine making the conversion from mechanical energy to electrical energy in a windmill or wind turbine (see that word). The windmill generator can be a DC voltage and current machine with brushes and rotary collector or much more frequently an AC multiphase machine. There are 2 families of AC electrical generators : the asynchronous ones whereas the frequencies of the rotor and stator magnetic fields generated by coils are not the same and the synchronous ones in the opposite case. The AC synchronous generators are also called alternators. The asynchronous AC generators are less used nowadays than the AC synchronous generators as windmill generators thanks to the lowest dimensions and higher efficiency allowed today by the use of permanent magnets in replacement of excitation coils of inductors at the rotor of AC synchronous generators. The ALXION STK alternators are AC 3-phase synchronous permanent magnet generators.
small wind turbine
A small wind turbine is a « wind turbine » of low power rate. Typically, the expression « small wind turbine » is used for electrical power ratings up to 100 KW maximum. The segment of small wind turbines includes in particular the machines used for supplying electricity to private houses and farms from 3KW up to 6 KW and also for remote equipments as cell phone antennas, watering installations, illumination of highways areas,… up to 10 KW or even 15 KW. ALXION is only addressing the segment of small wind turbines under 100 KW with its STK alternators. If the applications of high power wind turbines, over 100 KW and up to 4 MW are only composed of Horizontal Axis Wind Turbines, the small wind turbine applications are made by two kinds of machines : Horizontal Axis Wind Turbines and Vertical Axis Wind Turbines, the latter mainly in urban zones. The media evoke quite often the projects or installations of high power wind turbines and consequently the populations are generally aware of those applications. This is not the case of small wind turbines applications and many times, people do not even know that they could use a small wind turbine in their garden for producing their own electricity, if the local wind charts allow it.