Kramer Drive System
• Kramer drive is a rotor side speed control drive of induction motor.
• Slip is the difference between synchronous speed and rotor speed.
• It is the method for saving slip power loss in rotor by returning power back to the line.
• It convert the slip power into AC power and return back to line.
• Constant power control is obtained by this method.
• This method control the speed of induction motor by injecting the opposite phase voltage in the rotor.
• It consists of wound rotor induction motor, smoothing reactor, 6 pulse bridge, and DC motor.
• By varying the field current of DC motor speed control is obtained.
• The induction motor and DC motor is mechanically coupled the same shaft.
• If less speed range is required then diode bridge can also be use in place of thyristor bridge.
• Thyristor bridge is use for more speed range control.
• Output torque supplied to the load is the sum of torque of induction motor and DC motor.
• The static Kramer drive is costlier because of the cost of DC motor.