SIMULATION AND MITIGATION OF POWER QUALITY DISTURBANCES ON A DISTRIBUTION SYSTEM USING DVR

Voltage sag is the most important power quality problem faced by many industrial
customers. Equipment such as process controllers, programmable logic controllers,
adjustable speed drives, robotics, etc used in modern industrial plants are actually
becoming more sensitive to voltage sags. Voltage sags are normally described by the
magnitude variation and duration, and also characterized by unbalance, non-sinusoidal
wave shape and phase angle shift.
One of the most common mitigation solution is installing uninterrupted power supply
(UPS). To meet the demand for more efficient mitigation solution, the Dynamic Voltage
Restorer (DVR) will be deployed. When a fault occurs, either at the high voltage source
end or at the consumer end, the DVR injects active and reactive power for the restoration
of the voltage sags in the network.
This thesis presents the power quality problems faced by the power distribution systems
in general and then concentrates on analyzing an important and specific distribution
system in particular. A dynamic voltage restorer (DVR) is connected on the 11KV of an
utility feeder to Ipoh hospital, in reducing the voltage sags, that affect the operation of
sensitive loads to the hospital.
Case studies were conducted at four industrial sites (Hitachi plant and Nihoncanpack at
Bemban, Filrex at Bercham and Ipoh Hospital) by monitoring and taking physical sag
measurements for a period of one month. The real time measurements were carried out to identify the types power quality disturbances that exits in the various plants before
providing the custom power device as a mitigation tool.
The Ipoh Hospital is taken for a special case study since the hospital has to maintain high
quality power supply to the medical equipments such as CT Scan, Magnetic Resonance
Imaging (MRI), Magnetic Scanner, X-ray unit, and other life savingequipment.
For simulation study, PSS/ADEPT and PSCAD/EMTDC software packages were used in
modeling of the power distribution system. With the PSS/ADEPT simulation tool, the
voltage severity is studied by introducing different types of faults. The PSCAD/EMTDC
is a graphical user interface simulation tool to simulate sag waveforms for various types
of faults. A DVR was modeled using the PSCAD/EMTDC software and simulated for
voltage sag mitigation. The recorded waveform shows the DVR as a potential custom
power solution provider. The DVR can improve the overall voltage regulation. The
results obtained from the DVR show that the voltage sags are reduced by bringing the
supply voltage level to 100%. The simulated results were verified for selected faults
theoretically.
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