I don't think that there is any difference in the machines used as generators and those used as motors. The control equipment is different because the power flow is reversed and slip ring motors are rarely operated above synchronous speed. However, wound rotor synchronous motors and squirrel cage induction motors are used for almost all motor applications. With the electronic motor controls available today, slip-ring motors are usually not competitive.

In the DFIG (induction generator double-fed), stator directly connected to the grid and rotor also connected to grid via AC-DC-AC. At below synchronous speed, the converter operated as "inverter", current flow from grid---> converter---> rotor while stator directly connected to the grid.





and at other hand A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring can be used in any electromechanical system that requires unrestrained, intermittent or continuous rotation while transmitting power and / or data. It can improve mechanical performance, simplify system operation and eliminate damage-prone wires dangling from movable joints.

A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring can be used in any electromechanical system that requires unrestrained, intermittent or continuous rotation while transmitting power and / or data. It can improve mechanical performance, simplify system operation and eliminate damage-prone wires dangling from movable joints.

Also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels, or electrical rotary joints, these rings are commonly found in slip ring motors, electrical generators for alternating current (AC) systems and alternators and in packaging machinery, cable reels, and wind turbines. They can be used on any rotating object to transfer power, control circuits, or analog or digital signals including data such as those found on aerodrome beacons, rotating tanks, power shovels, radio telescopes or heliostats.

A slip ring (in electrical engineering terms) is a method of making an electrical connection through a rotating assembly. Formally, it is an electric transmission device that allows energy flow between two electrical rotating parts, such as in a motor.

Try the site below.

In DFIG and slip ring Induction motor, slip-rings are used on rotor . Both cases in rotor winding is connected through power electronics converters for control the power. can anyone clarify that what is the basic different between DFIG and slip-ring Induction generator used in wind farms....