Question 1: What is the difference between AC and DC Drive to control motor speed ? Answer: AC Drive works on Ac frequency Hz. The speed of Ac motor can be increased or decreased by increasing or decreasing the Hz. frequency of Ac Drive. DC Drive works on DC motor armeture voltage or field current. The speed of DC motor can be increased or decreased by giving the command in DC Drive by either increasing or decreasing armeture voltage or field current. Question 2: Is DC motor cooling required, if yes, what is the provision ? Answer: Yes, DC motor cooling must required. AC motor with air filter is provided upper mounting of DC motor body for cooling armeture and field coil. Question 3: What is the provision in DC Drive for motor speed feedback ? Answer: Among any of one incremental , absolute encoder or techometer can be installed at DC motor to take speed feedback voltage to DC Drive. Question 4: How can be the speed of slipring motor increased or decreased ? Answer: In Case of small motor, a set of resistance box is provided in motor winding to increase or decrease the resistance value to regulate motor speed. In case of big slipring motor i.e. 1500 hp., LRS is used. ( Liquid Resistance Starter).