Nowadays, electrical device, equipment, facility andetc. has become an essential element in our daily life, so to ensure itsoperation and functionality power quality become a very important factor. Accordingto IEEE the definition of power quality is the concept of powering andgrounding electronic equipment in a manner that is suitable to the operation ofthat equipment and compatible with the premise wiring system and otherconnected equipment. 1 Power is the rate of the energy being deliver and isproportional to the product of the voltage and current as the formulaP = VIThe power supply system can only control by thevoltage quality and the current that might draw by a particular load is cannotbe control.
Therefore, power quality is control by maintaining the supplyvoltage within certain limits. So why we concerned about the power factor? Economicvalue is the main reason. Power quality have a direct impact on both the utilityand industry consumer due to the use of modern technology today in theirmanagement and production area so, if any disturbance or problem occur it willcause a huge economy and financial lost. Furthermore, it also causes impact tothe commercial customer indirectly for example they are not able to use theinternet due to the serve is interrupted.2.0 Type of power quality problems 1. Transients2. Interruptions3.
Sag / Undervoltage4. Swell / Overvoltage5. Waveform distortion6. Voltage fluctuations7. Frequency variations 2.5 Waveform distortionWave distortion is defined as a steady-state deviationfrom idea sine wave of power frequency principally characterized by the spectralcontent of the deviation. 3 The primary types of waveform distortion are1.
DC offset2. Harmonics3. Interharmonics4. Notching 5. Noise2.5.1 DC offsetDC offset occur when there is a DC current or voltageexist in an AC power system.
The existence of DC current in an AC distributionsystem is normally due to the failure of rectifiers within several AC to DCconversion technologies that have proliferated modern equipment. DC can passthrough the AC power system and add unnecessary current to the device that hadoperating at its rated level. This will causes additional heating and decreasein transformer life. In addition, these additional heat not only make thetransformer hot but also causes it to be unable to deliver full power to theload and subsequently create more instability in the system due to thedistortion of waveform.
Figure1: DC offset 2.5.2 HarmonicsWhen, the sinusoidal voltage or current have multiplestime higher frequency than the frequency of the supply system that is designedthen harmonic distortion occur. The fundamental frequency of the supply system isnormally 50 Hz or 60 Hz. Waveform that had distorted periodically can be breakdown into a sum of fundamental frequency and the harmonics. Harmonic distortionoriginates in the nonlinear characteristics of device and load of power system.3 Nonlinear loads are the one that producing harmonic current. These harmoniccurrent produce will interact with the power system equipment and can causeinterference with telecommunication lines and result error in the powermetering.
Furthermore, it will also the reason of overheatedtransformers, neutral conductor and other electrical powered equipment, trippingof circuit breaker and loss of synchronization of a timing circuit. 2 Figure2: typical harmonic waveformdistortion 2.5.3 InterharmonicsWhen, the sinusoidal voltage or current have frequencythat are not multiples time higher than the frequency of the supply system thatis designed then interharmonic distortion occur. 3 The main source of thistype of waveform distortion are static frequency converter, cycloconverters,induction furnace, and arcing device.
Signal that carried by the power line canalso be considerate as interharmonics. The most common effect of the harmonicsdistortion is the flickering of the visual display and the light bulb. Figure3: Interharmonics waveform distortion 2.5.4 Notching Notching is a periodic voltage disturbance caused by the powerelectronic device under normal operation when current is commutated from onephase to another. 3 Notching can be characterized through the harmonicspectrum of the affected voltage since it occur continuously.
The problem willface when notching occur in a system usually are system halt, data loss, datatransmission problem and etc. 2 Figure4: Notching 2.5.5 NoiseNoise is the unwanted electrical signal with broadbandspectrum content lesser than 200 kHz superimposed upon the power system voltageor current in phase conductor or found on neutral conductors or signal lies. Thereare three type of noise in the electrical power system, which is the line toneutral, neutral to ground, line to ground.
Noise usually caused by the power electronic device,arcing equipment, control circuit, load with solid-state rectifier, switchingpower supplies and etc. The existence of noise are usually because of theimproper grounding that fails to conduct noise away. 3 Figure5: Noise 2.6 Voltage FluctuationVoltage fluctuation are systematic variation of thevoltage envelop or a series of voltage randomly change.
Loads that showcontinuous and rapid change in the load current magnitude will cause voltagefluctuation that called flicker. The term flicker in this case is actuallyderived from the voltage fluctuation happen on a lamp and cause the lamp to flicker.2 Figure6: Voltage fluctuation Arc flicker is one of the most cause of voltagefluctuation on distribution system and utility transmission. The flicker signalis define by its rms magnitude systems expressed as a percent of thefundamental. Sensitivity of the human eye is used as a standard to measure thevoltage flicker.
For a perceptible lamp to flicker the magnitudes is as low as0.5 percent and if the frequencies are between 6 to 8 Hz. 3 2.
7 Power frequency variation Power frequency variations are defined as the changeof the power system fundamental frequency from it specified nominal value. Therotational speed of the generators supplying system is directly related to thepower system frequency. When the dynamic balance between load and generationchanges there will have a slight variation in frequency. The loadcharacteristics and the response of the generation control system to loadchanges define the size of the frequency shift and its duration.
3Power frequency variation is very rare and unlikely tohappen in a stable utility power system, especially system that isinterconnected through power grid. This variation of frequency are more likelyto happen in load that are supplied by a generator that is isolated from theutility system. 3 Figure7: Power frequency variation Method to solve power quality problem1. Troubleshootingand replacingTo solve this DC offset problem,first is to troubleshoot the device circuit board and find out the faultycomponent that causes DC offset and replace the faulty component with the newone.2.
FiltersAdding filters is one of the methoduse to remove harmonic and noise. Noise filter remove the unwanted noise of thesystem. The type of filters are the low pass filter, high pass filter, bandpass and notch. Different types of filters are used to remove different type ofnoise that the system desire. The most common filter use are the high passfilter and low pass filter to remove the unwanted high or low frequency noise. Harmonics filter reduce the unwantedharmonics in the system. There are 2group of harmonics filter which is the passive filter and ate active filter. Toremove the harmonics of several components amount of passive filter is connectin parallel to the component.
But there’s a problem face by passive filterwhich is when the harmonics component is change, the passive filter will becomeuseless and will even cause resonance to the system. Therefore, active filteris introduced, it calculated the current consumed by the component and thengenerate a current that will cancel the harmonics current produced by thecomponent. The reason why in the passday people choose to use passive filter but not active filter is that activefilter is very expensive compare to the passive filter. 3. UninterruptiblePower Supply (UPS)UPS can solve many power qualitydisturbance such as interharmonics, notching, voltage fluctuation and powerfrequency variation. UPS help to avoid complete power interruption which isalso called black out. During the event of momentary interruption UPS providepower continuously to the loads. There are 3 types of UPS:i.
Offline UPSThistype of UPS is a low cost method for a small, non-critical, independent system.It provide power to the load by electrical utility for example battery, andgive protection during sag, swells and power interruption. It’s low cost andhigh efficiency, but it has a problem which is the capacity of power supplingis limited by the battery and it has regulation at the output voltage andnoticeable transfer time.ii.
Line interactive UPSThistype of UPS are used when the rate of voltage fluctuation high. Unlike theoffline UPS which has poor output regulation line interactive can regulate theoutput voltage well and without depletion the battery. Line interactive UPS hasbetter output regulation and high efficiency, but it has noticeable transfertime.iii. True on-line UPSThistype of UPS has the highest level of power protection among the others. It issuitable to use in the critical power system. It is able to convert from AC toDC for battery charging and inverter powering.
To power the critical loads, DCthat converted will then convert again back to AC. It has no noticeable transfertime and good in eliminate voltage fluctuation, but it has less efficiencycompare to the others and may has more audible noise. 4. VoltageregulatorIt is the most common type method usedto remove or control the voltage fluctuation problem in the input side of thecircuit.
There are three type of voltage regulator:i. Tap chargerItable to adjust the changing input voltage by transferring taps automatically ona power transformer. It is high efficiency, large input range, high capabilityin overload current and less noise, but noise may produce during the changingof taps and waveform that gone wrong won’t have any correction.ii. Buck boostIthas exactly same function as tap charger just the transformer is not isolated.It is high efficiency, suitable to operate with high in-rush current, butfacing the problem as tap charges and also have bad noise isolation. iii.
Constant voltage transformer (CVT)CTVable to maintain nearly constant output voltage during large variation in inputvoltage. It has very good noise isolation and for overload protection it isable to precisely limiting the output voltage and current, but it very large insize and may have audible noise and low efficiency.