उच्च गति वाले अल्टरनेटरों (टर्बो-अल्टरनेटर) में किस प्रकार के रोटर का उपयोग किया जाता है?

What is the coupling field commonly used between electrical and mechanical systems in electromechanical energy conversion devices?

In a DC shunt motor operating at rated voltage, if the field flux is reduced to 70% of its nominal value while keeping the armature current constant, the percentage increase in speed (assuming negligible armature reaction) is approximately __________.