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Al-cage SR motor pairs IE5 efficiency with low costs
The Japanese motor manufacturer Nidec has developed a new design of electric motor which, it claims, combines the high efficiency of a synchronous reluctance (SR) motor with the low cost of a cage-type induction motor. It says that the IE5-efficiency SynRA (synchronous reluctance motor with aluminium cage rotor) machine is the world’s first SR motor with an aluminium cage. It does not need an electronic controller and can be connected directly to a mains power supply.
Traditional cage-type induction motors can operate directly from a mains supply. They do not need to be controlled by an inverter, making them a low-cost method used widely to drive fans, pumps, compressors, cranes, elevators and other loads.
SR (synchronous reluctance) motors rotate like induction motors when they start and rotate in synchronisation with the power supply frequency. They have lower losses and higher efficiencies than cage-type induction motors, but need special controllers making them more expensive.
For variable-speed applications such as air-conditioners, cage-type induction motor can be operated using simple and low-cost v/f (voltage/frequency) converters. But these motors generate a rotation gap (loss) between their rotors and stators, making them less efficient than SR motors.
The rotor of Nidec’s new SynRA motor incorporates a cage structure. It operates direct online, rotating like an induction motor when started, and spins in synchronisation with the mains frequency during operation. This cuts its losses and makes it more efficient than a standard cage-type induction motor.
The new motor can also be used with a simple v/f open-loop controller, unlike a conventional SR motor, which needs vector control or precise control parameters.
Nidec says that the SynRA motor has been certified to have an IE5 efficiency – the highest possible – and can be produced at a low cost, similar to that of a standard cage-type induction motor. The company hopes that it will replace induction motors for applications such as fans, pumps and some compressors. It adds that it will not be able to replace all squirrel-cage induction machines.
Nidec says that for a 7.5kW motor operating 7,000 hours a year, the new design could save 1,500kWh. Another advantage is that it does not need rare-earth magnet materials, cutting costs and reducing environmental concerns.
The new motor has been developed by Nidec’s Western Home Appliance business working with Taiwan’s Motor Basic Technology Research Institute. The motor is being launched initially in the US market under Nidec’s US Motors brand, in IE4 versions from 1-10hp, 1,800 rpm and IE5 versions from 1-15hp, 3,600 rpm. It is available in 230V, 460V and 575V voltage ratings and in IP23, IP44 and IP54 protection ratings.
Nidec says it is “committed to offering revolutionary solutions for energy-efficient motors to suppress electricity consumption, and contribute to curbing environmental burdens”.
