Power factor improvement in a weakdistribution grid is a challenging problem, particularly when it may not be aneconomical to simply upgrade the network. Therefore to cope with an outdatedand overstressed distribution power network of Pakistan, the electricityconsumers have mostly employed voltage regulators or capacitor banks toregulate the voltage on AC power distribution lines.
The consumers need tocorrect the power factor for the following reasons:• Largequantity of induction motors are used to drive their pumps, conveyors, andother machinery in the plant causes power factor to be inherently. For lowerpower factor, usually below 0.80 or 0.
85, electric utility companies placepower factor penalty on the industry.• Manyelectric utility companies charge for maximum metered demand based on eitherthe highest registered demand in kilowatts (KW meter), or a percentage of thehighest registered demand in KVA (KVA meter), whichever is greater. If thepower factor is low, the percentage of the measured KVA will be significantlygreater than the KW demand. • Loadsdrawing reactive power also demand reactive current causing excessive loss indistribution system• A lowerpower factor causes a higher current flow for a given load. As the line currentincreases, the voltage drop in the conductor increases, which may result in alower voltage at the equipment due to which they do not operate effectively • Uncorrectedpower factor causes excessive loss in distribution system• Excessivevoltage drops causes overheating and premature failure of other equipment• Energysaving is achievedThe voltage regulators tries to maintainconstant output voltage for loads (air conditioners, refrigerators, inductionmotors etc.
). The voltage stabilizers are equipped with VARIAC(autotransformer) where a servomechanism is used to select an appropriate tapon multiple taps autotransformer. If the output voltage is not in acceptablerange, the servomechanism switches the tap, changing the turn’s ratio of thetransformer in order to move the secondary voltage close to acceptable level.The controls also provide a dead band preventing it from constantly adjustingthe voltage as it varies by an acceptably small amount.In summers, the air conditioning andrefrigerating heavily loads the distributions grid.
As these loads demand highreactive power and if not provided with an adequate supply results in lowvoltage. The voltage stabilizers, if installed, help in maintaining the voltageclose to its nominal level. However, each tap changing operation will alsoresult in an increase in the line current and thus the reactive losses.
If theweak distribution grid is predominantly equipped with voltage stabilizers, thenthe cumulative voltage stabilizing actions will result in high currents andthus high losses, and may result in short term voltage stability. On the otherhand, switched capacitors relieve the power grid by providing the reactivepower support; however, the control is manual and only helpful in constant lowvoltage. The voltage level varies on weak grid as the load demand changes andtherefore requires a control device that can automatically regulate reactivepower.1.1 State ofthe ArtIn Pakistan, the substantial part ofelectrical power distribution system is outdated and overstressed 1 2. This weak gridinfrastructure is hampering the provision of available electricity in itsproper form, i.e. the electricity is provided to the end consumer in poor powerquality, that not only increases the rate of losses but also reduces the powersystem efficiency 3.
Also the loadsconnected to the poor power quality electrical network are less efficient andhave a reduced lifetime 4. The maincontributor to the poor power factor is an inadequate supply of reactive powerwhere low voltages loads up the supply system unnecessary.It has been identified that majority of theindustrial load and certain domestic loads are highly inductive in nature suchas induction motors, air conditioners, AC/DC drives, welding machines, arcfurnaces, fluorescent Lightings, electronic controls and computers 5.The heavy inductiveloads results in very poor lagging power factor and if left uncorrected, theconsumers will heavily load the grid. The weak distribution grid generallyunable to compensate the reactive power demand and therefore results in reducedelectrical network efficiency. In order to cope, the consumers haveinstalled either voltage regulators or switched capacitors 5 however the formerheavily loads the grid and reduces power factor while later is unable tocompensate frequent load variations resulting in high voltages that mightdamage the consumer’s equipment.
A possible solution to these problems isStatic Synchronous Compensator (STATCOM). The basic idea behind STATCOM is todetect the load current and calculate the reactive current demand of load andinject the required reactive current to compensate for the poor power factor.The most important factor to be considered in designing STATCOM is how toobtain the compensating current. The compensating current can be obtained bymeans of Instantaneous Power Theory or Filtration methods. Traditionallyreactive power in single-phase or three- phase circuits for steady state is calculatedusing average value concept for sinusoidal voltage and current waveforms. 6 Proposes a novelinstantaneous reactive power compensator which requires practically no energystorage components. The instantaneous reactive power in three-phase circuitsincluding transients is calculated on the basis of the instantaneous valueconcept for arbitrary voltage and current.
However .VSC based system can control active andreactive power independently. It could also lower down harmonic contents of ACcurrent and improves power factor of the connected AC system. 7 Proposes a dynamicmodel of VSC and method for respective power control has been derived accordingto the switching function model and predictive current control theory, such acontrol system give a good response than the one designed on steady state modelwith no overshoot in the power adjustments. __This research project willinvestigate the latest technology of voltage regulation that will providereal-time control of reactive power employing the power electronic devices andthe pulse width modulated (PWM) switching technique, i.e. Flexible AlternatingCurrent Transmission Systems (FACTS).
The project will develop a power qualityimprovement device for small industrial consumer that will be able to maintainvoltage at its nominal level and thus improves efficiency of distribution gridand electrical loads. The device will be more robust and will work well underdifferent system conditions.1.2 ResearchobjectiveThis research aims to develop power factorcorrection device that can provide real time control of reactive power withsolid state devices (power electronic) and eliminating the electromechanicalrelays. The desired device will have a potentialto provide both steady state and transient reactive power compensation underdifferent loading conditions for the domestic and small industrial loadsconnected to the weak distribution grid. The purpose of this project is toimprove consumers load efficiency and relieves the distribution grid fromoverloading.