POWER QUALITY• Power Quality is a term used to broadly encompass the entire scope of interaction among electrical suppliers, the environment, the systems and products energized, and the users of those systems and products. It is more than the delivery of "clean" electric power that complies with industry standards. It involves the maintainability of that power, the design, selection, and the installation of every piece of hardware and software in the electrical energy system. Stretching from the generation plant to the utility customer, power quality is a measure of how the elements affect the system as a whole.
POWER QUALITY PROBLEMS• ‘Any power problem that results in failure or misoperation of customer equipment, manifests itself as an economic burden to the user, or produces negative impacts on the environment.
TYPES OF PROBLEMS• Harmonic Distortion• Voltage Transients• Voltage Sags or Dips• Voltage Surges
Power Quality Problems:• VOLTAGE SAGS : Voltage sags are under-voltages on the power system and commonly caused by power failures, downed lines, utility recloser operations, and storms. They can be corrected by using backup power sources such as UPSs, generators or similiar voltage restoration technologies
VOLTAGE SWELLS:• Steady state voltage rise for several seconds• Caused by line to ground fault in a three phase system
VOLTAGE TRANSIENTS:• Classified into two categories, namely, Impulsive Transient Oscillatory Transient• These terms reflect the wave shape of a current or voltage transient.
• HARMONICS DISTORTION: Harmonics result from distortions to the voltage and/or current sine waves. Harmonics are commonly caused by ASDs, industrial processes, certain electronic loads, and wiring connections. Harmonic problems often can be corrected by filtering or resizing power system components.
• Power Quality Solutions: The need for solutions to power quality problems grows with every passing second. Currently many projects are under way and they are loooking at how to collect data to find and analyze power quality problems. Presently, the analysis ;of power quality problems is often difficult due to the fact that the source of a problem can be a few feet away in the form of a loose connection, or a hundred miles away in the form of a power system fault. If we look back at the stated power quality problems of sags, surges, harmonics, and wiring and grounding, one can see that each one has possible solutions to correcting these problems.
METHODS OF SOLUTIONSThe solutions for power quality may be obtained by the following methods:• Using HYBRID FILTERS• Using TRANSFORMER METHODS• Using COIL CLOCKS• Using POWER FACTOR CORRECTION• Using UNIFIED SWITCHED CAPACITOR COMPENSATOR
1.HYBRID FILTERS• Hybrid filters constructed of active and passive filters• with different structures are used for removing the• disadvantages of passive filters such as probability of• resonances and non dynamic responses and also high• costs of active filters, while using both the advantages of• both of them with lower costs. Different structures of• hybrid filters can be utilized in power systems such as• shunt passive filter and series active power filter with• nonlinear loads, shunt active and passive filter with• nonlinear load, series active and passive filter parallel• with nonlinear load, etc. shown in Fig. 1.
2. TRANSFORMER METHODSIn this method we can control varous power quality problems such as• Large inrush currents• Reduction of electromagnetic field emission• Reduction of electromagnetic noise
a)LARGE INRUSH CURRENTS• Currently virtually all power transformers are built with high permeability GOSS cores. An unwanted• feature of using high permeability core materials is that the inrush currents are largely increased. This is• even more problematic when the transformers are toroidal shaped made of tape wound GOSS. To solve• the inrush problems, transformer manufacturers resort to gaps in the core. Gapping is an expensive• production methodology and is difficult to control and test. In addition, gapped transformers become• acoustically noisy.• With our proprietary technology (gapless) we can produce toroidal transformers that have reduced inrush• currents without resorting to gaps or external components. The magnitude of the inrush currents has• become another specification to meet rather than a problem.
b).REDUCTION OF ELECTROMAGNETIC FIELD EMISSION• We have been able to further reduce• the amount of stray fields emitted by a toroidal transformer by a factor of 2 to 5 when compared to the• standard practice. The following design parameters play important roles in reducing the stray fields:• a) The design flux density.• b) The permeability of the material.• c) The core geometry (flat, tall, squared cross sectional area, etc.)• d) Winding sequence.• e) Winding style (precision, random, casual, bank, sector, etc.)• f) Single, bifilar, or multi-filar windings.• g) Use shielding core bands.
c).REDUCTION OF ELECTROMAGNETIC NOISE• The• secondary winding (or the primary winding) is extended with an extra winding with• equal number of turns, connected in reverse phase to the existing secondary winding through a capacitor• At low frequencies, the impedance of the capacitor Cfp is high, the capacitor acts as an open switch,• only one secondary winding functions and thus the 50/60 Hz is free to cross the transformer. At higher• frequencies (above 1 kHz), the capacitor begins to act as a closed switch. Both secondary windings are• now at 180 degrees phase difference. Therefore the voltage induced in the two windings cancel one• another and no transfer of high frequency signals occurs. The transformer acts as an effective low pass• filter with adjustable bandwidth.
3.COIL CLOCKS• The Coil-Lock protects ac relay, contactor and solenoid hold-in-devices by keeping motors and other critical process control elements engaged during those annoying momentary voltage sags or dips. Literally, any device that is controlled by energizing an ac coil, when powered through a Coil-Lock unit will remain latched through these power disturbances.
4.POWER FACTOR CORRECTION• Increased source efficiency - lower losses on source impedance - lower voltage distortion (cross-coupling) - higher power available from a given source• Reduced low-frequency harmonic pollution• Compliance with limiting standards (IEC 555- 2, IEEE 519 etc.)
POWER FACTOR CORRECTION TECHNIQUES• PASSIVE METHODS: LC filters• ACTIVE METHODS: High-frequency converters
5.UNIFIED SWITCHED CAPACITOR COMPENSATOR• These loads are usually nonlinear and temporal in nature.• The proposed low cost (USCS) capacitor scheme ensures• both power quality (PQ) enhancement, RMS/power• current level reduction, efficient power Energy utilization• and effective demand side management. The reduction in THD of source• current translates into improved power factor
BENEFITS OF POWER QUALITY• Power quality in the container terminal environment• impacts the economics of the terminal operation, affects• reliability of the terminal equipment, and affects other• consumers served by the same utility service. Each of• these concerns is explored in the following paragraphs
TYPES OF BENEFITS1. Economic Impact a. Power Factor Penalties b. System Losses c. Power Service Initial Capital Investments2. Equipment Reliability3. Power System Adequacy4. Environment
POWER QUALITY CRITERIA• As mentioned earlier, one can be aware of the power quality issues, however, appropriate criteria must be defined to insure the system delivered properly addresses the needs of the application.
TYPES OF CRITERIA1. Harmonic Mitigation Criteria2. Power Factor Criteria
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