The minimum number of wattmeter(s) required to measure 3 $$-$$ phase, 3 $$-$$ wire balanced or unbalanced power is

In case of an armature controlled separately excited dc motor drive with closed loop speed control, an inner current loop is useful because it

An electric motor with 'constant output power' will have a torque speed characteristic in the form of a

A single-phase transformer is to be switched to the supply to have minimum inrush current. The switch should be closed at