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# Machine Riddle No.37 – Voltage rating of motor

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• #738
V.K.Nambiathiri

Which voltage is better for a 1000kW motor? 3.3kV or 6.6kV or 11kV? What is the criteria of selection of voltage based on its kW rating for a motor? Please explain
Which voltage is better for a 1000kW motor? 3.3kV or 6.6kV or 11kV? What is the criteria of selection of voltage based on its kW rating for a motor? Please explain

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• #2548
Hamid

Each rated voltage has an optimum power range, the lower and upper limits of which should not be exceeded if a favourable construction is to be produced. If the voltage is excessively high with respect to the power, the conductors become rather thin, and the number of turns increases drastically. In the opposite case, the winding has to be made of preformed copper, which increases the winding costs. For example 630kW is typically the limit for a 400V machine. The rated current of such a machine is about 1080 A, which is a value that can be considered a practical maximum for the rated current of a direct-on-line (DOL) induction motor. The starting current of such a machine may reach even 10 kA. According to the IEC 60034-1 standard, the minimum rated output is 100kW for a rated voltage UN = 1

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