27-07-2012, 12:27 PM
EHNANCEMENT OF VOLTAGE QUALITY IN ISOLATED POWER SYSTEMS
EHNANCEMENT OF VOLTAGE QUALITY I.ppt (Size: 49.5 KB / Downloads: 62)
INTRODUCTION :
ISOLATED power systems are commonly found in rural an remote areas of the world. These systems represent the alternative to grid connection, where interconnection to a large grid is not viable due to high cost and/or geographical obstacles
Furthermore, power systems such as those onboard of ships, in oil exploration areas and remote mining districts are characterized by limited generating capacity, supplying loads which can consist of significant amount of motor drives and power converters.
NEED FOR ENHANCEMENT IN VOLTAGE QUALITY
Due to the abnormal conditions which include sudden switching and faults, mainly due to the non-linear loads on the load side of the power system the voltage is reduced or sometimes increased.
Therefore for reliable and uniform supply to the consumers necessary compensating devices are installed at different parellel loads in an isolated power system
METHODS TO IMPROVE VOLTAGE QUALITY
INTERNAL METHOD - Excitation control
EXTERNAL METHOD - Install voltage control device externally
External method is more suitable than Internal method since it is not recommended for parellel loads.
Main functions of compensating devices
Shunt capacitor mainly improves the powerfactor of the load.
Shunt inductor limits the ferranti effect.
Series inductor limits the fault current.
Series capacitor improves the power system stability.
Descriptions of above SC diagram
Shows a typical isolated power system supplying a converter load.
The RL load may be used to represent an aggregate of dc motor drives, supplied via the converter.
The converter is often a controlled six-pulse rectifier through which the motor torque is regulated by adjusting the firing angle of the rectifier.
The motor-drive load is nonlinear and would involve commutation process within the converter.
CONCLUSION
A method to control the injection voltage of the SC so that it can mitigate the effects of the harmonics has been proposed.
The SC is also designed to maintain the fundamental frequency component of the terminal voltage of protected sensitive load.
In the process of harmonic voltage compensation, it is shown that power exchange exists between the SC and the external network.
A new SC control strategy is then proposed which involves the phase adjustment of the fundamental frequency component of the sensitive load terminal voltage.