kaushal boghnai
TRANSCRIPT
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SLIP POWER RECOVERY SYSTEM
Prepared By:-• Kaushal Boghani(130760109002).• Kishan Patel(130760109013).Guided By:-• Prof. Keyur Denpiya.
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Slip power recovery
• Instead of wasting the slip power in the rotor circuit resistance, a better approach is to convert it to ac line power and return it back to the line. Two types of converter provide this approach:
1) Static Kramer Drive - only allows operation at sub-synchronous speed. 2) Static Scherbius Drive - allows operation above and below synchronous speed
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Conventional kramer system
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Conventional kramer system• In this method, the speed of an induction motor is controlled
by injecting a voltage in the rotor circuit • The injected voltage to have same frequency as the slip
frequency• When we insert a voltage which is in phase opposition to
induced rotor emf,it amounts to increasing the rotor resistance
• When we insert a voltage which is in phase to induced rotor emf, its equivalent to decreasing the rotor resistance
• Hence by changing of injected emf and the rotor resistance, the speed can be controlled
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ADVANTAGES 1.Any speed within the working range can be obtained,
instead of only two or three as with other methods2.If the rotor converter is over excited, it will take a lead
current which compensates the lagging current drawn by the main motor hence improves the pf of the system
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Static kramer system
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• At zero speed (s=1) the motor acts as a transformer and all the real power is transferred back to the line (neglecting losses). The motor and inverter only consume reactive power.
• At synchronous speed (s=0) the power factor is the lowest and increases as slip increases. The PF can be improved close to synchronous speed by using a step-down transformer. The inverter line current is reduced by the transformer turns ratio -> reduced PF.
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AC Equivalent Circuit of Static Kramer Drive
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Modified kramer system
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Static Scherbius Drive
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Static Scherbius Drive Equation
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• Static scherbius drives are capable of bi-directional power flow, with both positive and negative injected voltages possible, in phase with or opposing the rotor current. As a result, a wider set of operating conditions is possible. Considering the torque equation for slip energy recovery: when motoring, torque is positive, when generating torque is negative.
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Closed loop control of scherbius system
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References:-
•www.nptel.ac.in/courses/108108078/pdf/chap6/student_slides06.pdf•www.electrical4u.com/speed-control-of-three-phase-induction-motor/•Power electronics by muhammad
rashid 4th edition pearson publication.
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THANK YOU