static scherbius drive

1. Shroff S.R. Rotary Institute of Chemical Technology
Principal Supporter & Sponsor- UPL LTD./ Shroff family
Managed By Ankleshwar Rotary Education Society
Approved by AICTE, New Delhi, Govt. of Gujarat & GTU Affiliated
Guided By:
Mr. Krunal Shah
Assistant Professor, Department of Electrical Engineering,
Shroff S. R. Rotary Institute of Chemical Technology, Vataria, Ankleshwar
Name of Student Chauhan Sachin V.
Enrollment No. 170993109001
Semester 6TH
Name of Topic Static Scherbius Drive
Name of Course Control Of Electrical Drive
Course Code 2160913
Academic Term January-June, 2019
Year of Admission 2017
Department of Electrical Engineering
Active Learning Assignment (ALA)

2. Static Scherbius Drive:
The main limitation of the Kraemer drive discussed is the
operation at sub-synchronous range due to diode rectifier.
Super synchronous speeds can be achieved if the power is
fed to the rotor from the ac mains. This can be made
possible by replacing the converter cascade by a static
scherbius drive system using cycloconverter in rotor circuit.

4. A cycloconvereter allows power flow in either direction
making the drive operate at both sub and super
synchronous speeds. However, the converter becomes
costly and has a complex control. The current in the rotor
circuit is nearly sinusoidal. The torque pulsations and other
reactions are minimal. The performance of the drive
improves with respect to additional losses and torque
pulsation. A smooth transition is possible from sub to super
synchronous speed without any commutation problems.
Speed reversal is not possible. A step up transformer may
be interpossed between the lines and the converter to
reduce the voltage reating of the converter.

6. Static Scherbius Drive, with power flow to and from the
rotor, can also be realized by replacing the diode rectifier
on the rotor side by means of a controlled bridge rectifier
using thyristors, as shown in Fig. 4.18. This provides
speeds below and above synchronous speed. The effects of
non-sinusoidal rotor current are present. In addition the
commutation of the bridge rectifier at very small slips (near
synchronous speed) poses problems.

8. Either forced commutation or artificial commutation of the
thyristors is employed at and about synchronous speed.
These methods are shown in Fig. 4.18. A current source
inverter can be advantageously employed to obtain a Static
Scherbius drive.

9. Operating modes of static sherbius drive :
The following are the operating modes of static scherbius
dives :
Sub-synchronous motoring :
in this mode of operation the slip and torque both are
positive and hence the injected voltage is in phase with
rotor current. The power flows into the stator and
feedback into the rotor circuit.

10. Super-synchronous motoring :
when the speed of the motor is above the
synchronous speed, then the slip is negative. Thus,
the voltage and current are out of phase with each
other. The power feeds into the rotor from the drive
circuit along with input power flowing into the stator.
Sub-synchronous generating :
for sub-synchronous speed, the torque is required to
be positive, although the slip is positive . The power is
fed into the rotor through the slip-ring.

11. Super-synchronous generating :
when the speed of the motor of the above the
synchronous speed, then the slip and torque becomes
negative. Thus, the injecting voltage is in phase with te
rotor. The mechanical power is injected by the shaft and
the output power is obtained from the stator and rotor
circuit.