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45-tonne slipring motor gets moving

25 February, 2010

MAN Turbo has installed a 14MW, 10kV slipring motor weighing 45 tonnes at its Oberhausen plant in Germany where it is being used to test huge radial, axial, and geared compressors. Usually, motors of this size are fixed and operate continuously. But the MAN motor has to be able to be moved around the test area using cranes and lifting tools, while continuing to operate reliably under severe test conditions.

The motor (shown on the left in the photo above) has two conical shaft ends, allowing it to be used for tests above its normal capacity. The second shaft can be attached to a turbine or an extra motor to deliver the additional power, raising the motor’s mechanical transfer rating 20MW.

The force-cooled motor’s speed is controlled by a liquid rheostat with two tanks for part- or full-load testing. The speed range is 0–1,500 rpm, with normal operations taking place in the 50–100% range, or 750–1,500 rpm. In this range, the motor operates with constant torque. The option of a variable speed drive was considered, but rejected because it would have been much more expensive, and posed a higher risk of torque problems, which can wreck compressor blades.

MAN specified a slipring motor because it has experience of this type of motor, albeit in lower power ranges. Slipring motors are ideal for this type of application because they do not suffer from torque pulsations in their drive train.

The motor was supplied by the Brazilian motor-maker WEG and is based on its M-Line range of modular high-voltage machines.

Initially, MAN Turbo was reluctant to place such a strategically important order with a company it knew little about. However, WEG is one of only three companies worldwide that could design and build a machine that would meet MAN’s specifications. WEG was also able to demonstrate its global credentials, and key personnel from MAN visited Sulzer Pumps’ test bed site in Leeds, UK, where WEG had supplied a similar, but smaller, slipring motor.

After WEG had delivered the motor, MAN conducted a year-long test programme which led to further purchases of WEG motors and generators. In November 2008, MAN signed a framework agreement with WEG Germany making it a key electrical supplier for MAN Turbo production sites at Oberhausen, Berlin, Hamburg, Zürich and Schio.

The largest motor ever built by WEG was a slipring machine used to test aircraft at high Mach numbers in a wind tunnel. This 27MW, 12-pole, 11kV machine, is 7m long and 5m wide and weighs more than 93 tonnes. The high power needed to operate the motor meant that it had to have its own 132kV grid connection. To achieve this, WEG supplied a 35MVA 11kV/132kV transformer with auto-tap changer, which cut the total installation costs.

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