Specifically, Hitachi developed the "high cooling rotor structure" (to be explained below) by forming ventilating ditches on the rotor of a generator to efficiently cool the permanent magnet located inside the rotor. The company developed a technology to design a generator that can keep a balance between electrical characteristics and mechanical strength. It used electromagnetical field analysis, stress analysis and thermo-fluid analysis to optimize the location of the magnet and the dimensions of the ventilating ditches for cooling.

As the output power of a permanent magnet-type generator increases, the diameter of its rotor becomes larger, increasing centrifugal force. Therefore, it is necessary to design a generator in a way that keeps a balance between electrical characteristics and mechanical strength. This time, Hitachi reduced the size and weight of a generator by improving cooling capability and enabling to mount components more densely.

Hitachi prototyped a permanent magnet-type generator with an output power of about 2,000kW by using the new technology. And it reduced mass by about 30% while keeping a power generation efficiency of 97% or higher, which is equivalent to the power generation efficiency of the company's wound rotor induction generator with an output power of about 2,000kW for wind power generation. Currently, generators used for wind power generation are normally wound rotor induction generators.

The high cooling rotor structure is made by forming ventilating ditches for cooling between the permanent magnet's north and south poles so that the amount of cooling wind increases. The structure enables to send cooling wind to the inside of the generator in an appropriate way and effectively cools the permanent magnet in the rotor.

In addition, the ditches reduce the magnetic flux that increases the heat generated by the permanent magnet (magnet loss), contributing to reducing the size and weight and improving the efficiency of a generator.

Hitachi permanent magnet innovation with ventilating ditch.