An AC system is made up of a lot of components and based on their load consuming nature they can be classified as capacitive, resistive and inductive. In case of purely resistive load the current and voltage are in phase but most of the loads connected in any facility is inductive in nature and in case of inductive loads the current lags the voltage and is therefore out of phase whereas, in case of capacitive load the current leads the voltage (Stokes, 2008). The current which is leading or lagging the voltage is called wattles current because it supplies reactive power and this power is essential for turning motors attached to the AC system (Stokes, 2008). So this type of load cannot be avoided and if this type of load increases then the accounting power requirement increases which in-turn increases the kVA demand for the same kW load (Stokes, 2008). Most of the high tension tariff charge a separate kVA charge along with the kW charges which increases the electricity bill of the consumer (Stokes, 2008). Thus consumers having low power factor have to pay more for the useful power they use making power factor improvement a necessity.
Some of the methods applied to improve power factor in a system are as follows:
Capacitive power factor improvement could be easily implemented as they are capable of supplying the reactive power required by the load by connecting the capacitor bank in parallel to the inductive load (Turchi et al., 2014). The capacitor bank acts like a source of reactive power and thus the inductive load absorbs lower reactive power from the AC system thus reducing the phase difference between the current and voltage.
Power factor improvement using Synchronous Condenser is another method where a three phase overexcited synchronous motor working under no load is connected to the load side of the inductive load (Turchi et al, 2014). Synchronous condenser financial like a capacitor by either supplying reactive power or by drawing lagging current from the AC supply.
Phase advancer is an AC exciter which could improve the power factor of induction motor (Turchi et al., 2014). It is connected to the rotor circuit of the induction motor and is mounted on the shaft of the induction motor (Turchi et al., 2014). The flux required a slip frequency needs exciting ampere turns and the phase advancer supplies this ampere turn and thus improves the power factor.
As seen above most of the methods stated above work similar to a capacitor so as to improve the power factor and therefore capacitor banks are mostly used in power factor improvement. Another advantage of using capacitors in power factor improvement is that they are readily available in different sizes and shapes and are cheaper than other methods used to improve power factor. Therefore, capacitor banks are widely used in the application of power factor improvement. This papers briefly reviews the work carried out in improving the power factor using capacitor banks.
Improvement in power factor has certain advantages as follows (Natarajan, 2005):
- As energy efficiency improves the power consumption reduces which results in reduced fossil fuel usage and greenhouse gas emissions form the power stations.
- Electricity bills are reduced.
- The existing supply can deliver more kVA.
- Losses in distribution equipment and transformers are reduced.
- The voltage drops in long cables are reduced.
- The electrical burden on electrical components are also reduced.
An assembly of number of capacitors is a capacitor bank and are used to generate kVAr in-order to improve power factor (Ramzan et al, 2016). Arrangements of series/paralleled connected units are called Shunt capacitors banks. Some of the types of capacitor banks used in power factor improvement are discussed below.
Grounded Wye - Connected Capacitor Banks (Natarajan, 2005):
They are made out of parallel and series arrangement of capacitors in each stage, providing a low impedance path to ground. They make a low-impedance way to ground giving innate self-insurance to lightning surge streams and some security from surge voltages consequently, working without surge arresters. They offer a low impedance way for high recurrence streams thus they can be utilized as channels in frameworks. In any case, the dissemination of inrush streams and music may cause fizzling and over operation on defensive transfers and wires.
Ungrounded Wye - Connected Capacitor Banks (Natarajan, 2005):
They don't allow substantial capacitor release streams, third consonant ebbs and flows or zero succession ebbs and flows amid framework ground deficiencies to stream. Other favourable position is that over voltages showing up at the present transformer optional may not be as high as on account of grounded banks if the nonpartisan is protected for full line voltage. Be that as it may, it is costly for banks over 15 kV.
There are two classes of associating capacitor bank. They are shunt and arrangement associating. Among these two classifications, shunt capacitors are all the more generally utilized as a part of the power arrangement of all voltage levels (Chandra and Agarwal, 2014). There are some particular points of interest of utilizing shunt capacitors, for example,
- Reduced line current of the framework.
- Improved voltage level of the heap.
- Reduced framework misfortunes.
- Improved power factor of the source current.
- Reduced heap of the alternator.
- Reduced capital speculation per megawatt of the heap.
All the previously mentioned benefits originate from the way that the impact of capacitor lessens responsive current moving through the entire framework. Shunt capacitor draws practically settled measure of driving current which is superimposed on the heap current and therefore diminishes responsive segments of the heap and consequently enhances the power factor of the framework (Miller, 1976). Arrangement capacitor then again has no influence over stream of current (Miller, 1976). As these are associated in arrangement with stack, the heap current dependably went through arrangement capacitor bank. The capacitive reactance of arrangement capacitor kills the inductive reactance of the line henceforth, lessens, viable reactance of the line.
Power factor correction is accomplished by supplementing a capacitive or inductive circuit with a reactance of inverse stage (Andrews et al, 1996). For a normal stage slacking power factor stack, for example, a vast enlistment engine, this would comprise of a capacitor bank as a few parallel capacitors at the power contribution to the gadget. Low power factor is not that quite a bit of issue in private homes it does however turn into an issue in industry where numerous expansive engines are utilized. So there is prerequisite of remedying the power factor in industry.
Low power factor is not acknowledged according to standard since poor or low power factors influence the expenses of both the buyers and the electrical power industry. In-spite of the increased cost of working, reactive power requires the utilization of transmission lines, transformers, circuit breakers, switches and wiring of higher current limits. By utilizing a PLC based capacitor bank framework we can enhance slacking power factor consequently framework will be protected from various burden of slacking power factor by utilization of this framework the power factor control turns out to be quick and exact than different techniques and likewise the electric charges are additionally diminished (Desai et al., 2015). The info waveform of voltage and current with stage distinction are bolstered to zero intersection finders, which give square waves in advanced organization. These advanced waveforms are utilized by microcontroller to compute power factor. Microcontroller takes choice to switch suitable capacitor bank to make up for power factor.
In the wake of identifying poor power factor, automatic power factor control framework switches one capacitor at any given moment out of a gathering of eight capacitors (Tiwari and Sharma, 2014). On the off chance that expected objective to accomplish power factor is met, at that point next cycle rehashed else exchanging of capacitor proceed till pay is not under control. Before the genuine execution of the automatic framework in genuine physical world, we can confirm the evidence of idea utilizing Proteus VSM (Sarkar and Hiwase, 2015).
The power factor correction an additionally be done utilizing solid state switched capacitors Measuring the power factor from the heap by utilizing LM358 zero intersection circuit and CD4070BC stage move indicator, and afterward computing the power factor have been finished by the program and LCD will be utilized for show. On the off chance that the power is not in the range, the switches are on/off modelled by the controller unit and capacitors are initiate/deactivate and enhance the power factor (Popa et al, 2013). This framework gives usage done on Arduino UNO microcontroller utilizing C language software to program the microcontroller, Arduino program to decide time slack amongst current and voltage and Proteus 7.7 to mimic the power factor as indicated by the heap.
Solid state switches are electronic exchanging gadgets that can work on or off positions when a little outer voltage is connected from the microcontroller (Than, 2016). In AC circuits, solid state transfers switch on at zero load current. The circuit cannot be stopped by a sine wave crest, holding the expansive transient voltages that would cause a sudden fall of the attractive field around the inductance and is known as zero-hybrid exchanging. Many focal points show up by utilizing the solid state switches in this framework. There is thinner profile, allowing quieter operation and switching which is quicker than electromechanical transfers; the exchanging time of an ordinary optically coupled SSR is in the range of microseconds to milliseconds depending on the time required to power the LED on and off. It has no moving parts to wear and no contacts to pit or develop carbon. Yield resistance stays steady in any case measure of utilization. It is significantly less delicate to working and capacitance conditions like, mugginess, vibration, mechanical stun and outer attractive fields.
Power Factor Control System with solid state switched capacitor when actualized totally, will accommodate power factor change in low voltage framework. Arduino UNO controller is exceptionally prominent at this occasion, in like manner effectively to compose the program by utilizing the abnormal state language. By the utilizing of solid state switches, it can contrast and the mechanical transfers, such a significant number of dependable and productive results show up. This is the extremely effective framework for different burdens, by utilizing the distinctive sizes of capacitors and setting off the switches which were controlled by the program.
In automatic power factor correction framework, we utilize potential divider circuits rather than customary zero intersection locator which gives a steadier power factor and the cost additionally get chop down in light of the fact that we don't have to utilize ICs (Utpal et al, 2016). Microcontroller usage reduces the expenses. Because of utilization of microcontroller numerous parameters can be controlled and the utilization of additional hard products, for example, clock, RAM, ROM and information yield ports lessens. Overcorrection should be avoided as current and voltage are usually more because of which the power framework or machine winds up plainly precarious and the life of capacitor banks diminishes.
A PLC is a solid state modern PC that controls framework by persistently checking the state of info gadgets and settling on choices in view of foreordained program so as to control the state of yield gadgets (Vukojevic et al, 2015). The essential monotonous strides in the operation of all PLCs, incorporate, filtering the contribution, amid which the state of the considerable number of sources of info associated with the PLC is examined (Jain et al, 2016). Using Program Scan, PLC checks and executes the program rationale in a successive way, producing the yield states. Amid the Output Scan the created yield states are refreshed in the yield status registers to invigorate or de stimulate the yields gadgets that are associated with the PLC yield module. Housekeeping incorporates inward diagnostics, correspondence with programming terminals, and so forth.
There are various routes in which a capacitor bank might be associated, with the decision being reliant on the coveted hand-off security, the framework establishing, the kVAr limit of the bank and the voltage level of the framework. At first the individual capacitor units are chosen to meet the voltage necessities of the framework, at that point the quantities of parallel units are chosen to meet the kVAr requirements of the capacitor bank (Chen et al, 2010). The number of paralleled capacitor units in each stage depends on two criterions as follows:
- If one capacitor unit in a stage fails then it should not create a voltage drop of more than 110 percent of the evaluated voltage.
- If a unit fails, then adequate fault current should flow through the individual circuit to clear the fault within 300s or less. Attention should be provided to this 300s time traverse as it is most extreme, and it should be toned down to 30s of traverse time.
The highest number of parallel connected capacitor units for each arrangement bunch is represented by an alternate thought. At the point when a capacitor unit comes up short, different capacitors in a similar parallel gathering would contain some charge, which would then deplete off as a high-recurrence transient current moves through the damaged unit and its breaker. This transient current has to be withstood by the breaker holder and the fizzled capacitor unit.
The over-voltage induced when a capacitor unit is separated increases the quantity of capacitor units per arrangement. Failure of extra capacitors is well on the way to happen in a similar arrangement bunch as the primary failure, as they have the most elevated voltage push. Every capacitor unit is normally secured by a breaker, remotely mounted between the capacitor bank intertwine transport and the capacitor unit (Locke, 2000). With inside melded capacitors, when a capacitor pack or component falls flat, the present, through its separate fusible connection, will be extensively higher than the ordinary current and may blow the fusible connection, in this way confining the fizzled pack or component.
If a wire blows in a capacitor bank, it would expand the central recurrence voltage happens on the rest of the units in that arrangement gathering. An unbalance location conspire is utilized to screen such conditions and to make a move as required (Shwedhi and Sultan, 2000). This plan more often than excludes three levels of activity.
Over-voltage should be less than 110% which should be indicated using an alarm. The postponement is normally 4s or more prominent.
Over-voltage greater than 110% requires Trip capacitor bank exchanging gadget as the unbalance is increased. The deferral is typically 4s or more noteworthy.
Trip for extreme bank unbalance should provide fast wire clearing time with lower postponement frequency of 0.3 to 0.5s.
Unbalance insurance regularly gives the essential security to arcing flaws inside a capacitor bank and different variations from the norm that may harm capacitor units as well as breakers. Arcing issues may cause generous harm in a little division of a moment. The unbalance security ought to have least purposeful deferral so as to limit the measure of harm to the bank in case of outside arcing.
As Switching of capacitors are done automatically consequently we get more precise outcome, Power factor correction strategies influences framework to steady and because of change in power factor its productivity likewise increments (Than, 2016).. Power factor correction plan can be connected to enterprises, power frameworks and in addition in house hold reason. The utilization of microcontroller decreases the expenses. By utilizing microcontroller different parameters can be controlled and the utilization of additional hard products, for example, clock, RAM, ROM and info yield ports decreases. Before automatic power factor correction circuit inclusion capacitors are associated in parallel to the heap circuit, so they are outlined, for example, to be associated in parallel to stack (Khan and Owais, 2016). Capacitance of capacitors include when associated in parallel, they are associated in parallel with the hand-off switch board. Underneath figure demonstrates the association of capacitor bank. Capacitors are associated in parallel to the heap circuit, so they are composed, for example, to be associated in parallel to stack. Capacitance of capacitors include when associated in parallel, they are associated in parallel with the transfer switch board.
A PLC based power factor change plot is actualized to enhance the power factor under various working conditions. The power factor controller utilizes a query table made in light of the deliberate estimation of power factor as per the look table, the PLC switches the capacitor in each stage using hand-off worked switches (Jain et al, 2016). By introducing appropriately measured power capacitors into the circuit the Power Factor is enhanced and the esteem turns out to be closer to 0.9 to 0.95, therefore, capacitor banks utilized for power factor correction decrease misfortunes and expands the proficiency of the power framework and furthermore builds security (Chen et al, 2010). By utilizing an automatic power recurrence control framework, the productivity of the framework is profoundly expanded.
Utilization of PLC as a power factor controller has turned out to be an adaptable, proficient and savvy instrument for a modern application. This improves the power quality, cost and protection in the system.
By utilizing power factor correction controller, we can accomplish:
higher estimations of capacitors progressively the disfiguring administration, operation with little load or sit out of gear of the engine due the increase of misshaping administration, a major contrast between the power factor in distorting administration and power factor of essentials show a higher twisting administration, if the capacitors banks are associated with arrangement curls, the disfiguring is decreased on the off chance that it utilizes channel with bring down recurrence (< 2 KHz).
The Mechanically Switched Capacitors (MSCs) are the most prudent responsive power remuneration gadgets. They are a basic and minimal effort, other than being low-speed answer for voltage control and system adjustment under substantial load conditions (Oliveira et al, 2010). Their usage has no impact on the short out power yet it underpins the voltage at the purpose of association. The MSCs establishments have other advantageous impacts on the framework, for example, change of the voltage profile, better voltage direction, diminishment of misfortunes and decrease or delay of interests in the transmission and era limit.
Reasonably outlined capacitor banks when associated with acceptance engines can enhance the power factor among different changes in general execution. Any glitch of the capacitor bank can, notwithstanding, cause undesirable corruption of framework execution. Power supply mutilation regularly can be measured by Power Factor and Total Harmonic distortion (Das et al, 2009)
The low power factor is exceptionally undesirable as it causes an expansion in current, bringing about extra misfortunes of dynamic power in every one of the components of power framework from power station generator down to usage gadgets. With a specific end goal to guarantee most great conditions for a supply framework from building and monetary point of view, it is essential to have power factor as near solidarity as would be prudent. Change of power factor influences the service organizations to dispose of the power misfortunes and the buyers are free from low power factor punishment charges.
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