24-03-2011, 04:47 PM
PRESENTED BY
THUSHARA.K.P
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POWER QUALITY ENHANCEMENT BY COMPENSATING CUSTOM POWER DEVICES
INTRODUCTION
The term power quality refers to maintaining a sinusoidal waveform of bus voltage at rated voltage and frequency.
Over the last 20 years the number of PQ problems are experienced in industrial and commercial sites are increased dramatically.
The waveform of electric power at generation stage is purely sinusoidal and free from any distortions. There are many devices the distort the waveform that propagate all over the electrical network.
TYPES OF DISTURBANCES
SHORT DURATION
VOLTAGE VARIATIONS
LONG DURATION VOLTAGE
TRANSIENTS
VOLTAGE IMBALANCE
WAVEFORM DISTORTIONS
VOLTAGE FLUCTUATIONS
POWER FREQUENCY
VARIATIONS
PASSIVE FILTER
Passive filters are used to provide a low impedance path for harmonic currents so
that they flow in the filter and not the supply
The filter may be designed for a single harmonic or for a broad band depending on requirements.
DRAW BACKS
Passive filter is designed only to particular harmonic frequencies. That is for fixed compensation.
In some installation harmonic content is less predictable.
They are prone to resonances.
custom power specification
No power interruption.
Tight Voltage regulation including short duration sags or swells .
Low harmonic Voltages .
Acceptance of fluctuating and non linear loads without effect on terminal voltage.
custom power devices
These are power electronics controllers that are used for power quality improvement.
2 types
Network reconfiguration type.
Compensating type.
Network reconfiguration type
These devices changes the configuration of power system network for power quality enhancement.
3 Types
SSCL (Solid State Current Limiter)
SSCB (Solid State Circuit Breaker)
SSTS (Solid State Transfer Switch)
Compensating type cpd
Main functions
Active filtering
Load balancing
Power factor correction
Voltage regulation
Classification
DSTATCOM (Distribution Static compensator)
DVR (Dynamic voltage restorer)
UPQC( Unified power quality conditioner )
DSTATCOM
VSC
Dc energy storage device
Coupling transformer
PRINCIPLE OF OPERATION
The D-STATCOM is a shunt connected power electronics based reactive power compensation equipment.
The D-STATCOM provides operating Characteristics similar to a rotating Synchronous compensator without the mechanical inertia.
The D-STATCOM employs solid state power switching devices and provides rapid controllability of the three phase voltages, both in magnitude and phase angle.
The D-STATCOM employs an inverter to convert the DC page link voltage Vdc on the capacitor to a voltage source of adjustable magnitude and phase. Therefore the D-STATCOM can be treated as a voltage controlled source.