Based on earlier work that led to development of a generator product for producing high voltage for direct transmission to the grid, ABB Inc. has introduced a novel "very high voltage" (VHV) ac synchronous motor product able to operate with inputs in the 20-70 kV range. VHV "Motorformer," an ABB-trademarked name, combines motor and transformer functions, eliminating the need for an intermediate transformer. The design applies to 4- and 6-pole machines. When not speed regulated, the four-pole motor has synchronous speed of 1,500/1,800 rpm at 50/60 Hz operation.

ABB's VHV motor appears to be a unique development, with no other comparable product on the market when it was introduced. Motorformer's development favored the synchronous rather than induction motor type because of higher power levels available (>100 MW versus up to 20 MW); higher inherent efficiency; wider air gap that eases design; and ability to control reactive power.

Motorformer's design is based on conventional synchronous motor technology, including many proven parts, such as an identical salient-pole rotor and conventional bearings. However, the main differentiator is the stator, in which ABB incorporated uniquely designed stator windings and stator core slots. Motorformer's cables are cylindrically shaped, which produces a homogenous electrical field strength, and makes it possible to increase voltage levels compared to the conventional rectangular-shaped windings. The cylindrical cable incorporates a solid dielectric layer of cross-linked polyethylene (XLPE) insulation, but uses no metallic shielding. Presently, the stator can handle voltage supply as high as 70 kV. However, the cable design can work up to a 150-kV limit. www.abb.com

• Very high voltage synchronous motor up to 70 kV
• New cable technology eliminates power transformer system
• Higher efficiency for lower operating costs
• System simplicity reduces maintenance and footprint