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EHNANCEMENT OFVOLTAGE QUALITY IN

ISOLATED POWERSYSTEMS

By

Rishabh Chadha

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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.

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NEED FOR ENHANCEMENT INVOLTAGEQUALITY

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

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NON-LINEARLOADS

fluorescent lamp .

electric welding machine .

Diode rectifier. Motor drives.

Power discharging devices.

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METHODSTOIMPROVEVOLTAGEQUALITY

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 parellelloads.

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EXTERNAL VOLTAGE CONTROL DEVICES

Also called as compensating devices.

These devices are mainly reactive power

compensators

COMPENSATING DEVICES SHUNT CAPACITOR

SHUNT INDUCTOR

SERIES CAPACITOR

SERIES INDUCTOR

SYNCHRONOUS CAPACITOR

SYNCHRONOUS COIL

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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.

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TYPICAL ISOLATED POWER SYSTEMINSTALLED WITH SERIES COMPENSATOR

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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.

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VOLTAGE RESTORATION

ROLE OF SERIES COMPENSATOR WHEN THE

LOAD VOLTAGE IS HIGH OR LOW THAN THE

SUPPLY VOLTAGE

VOLTAGE SWELL

VOLTAGE SAG

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CONCLUSION

A method to control the injection voltage of the SC sothat it can mitigate the effects of the harmonics has beenproposed.

The SC is also designed to maintain the fundamental

frequency component of the terminal voltage of protectedsensitive load.

In the process of harmonic voltage compensation, it isshown that power exchange exists between the SC andthe external network.

A new SC control strategy is then proposed whichinvolves the phase adjustment of the fundamentalfrequency component of the sensitive load terminalvoltage.

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THANK YOU