Power Factor Correction actual.ppt

Power Power Factor Factor

CorrectionCorrection

Power Factor CorrectionPower Factor Correction

Power Factor:Power Factor:

Power Factor is a measure of how Power Factor is a measure of how efficiently electrical power is efficiently electrical power is consumedconsumed


The The power factorpower factor of an AC electric power of an AC electric power system is defined as the ratio of the real power system is defined as the ratio of the real power to the apparent power, and is a number to the apparent power, and is a number between 0 and 1.between 0 and 1.


Real Power and Apparent Power:Real Power and Apparent Power:

Real power is the capacity of the circuit for Real power is the capacity of the circuit for performing work in a particular time. Apparent performing work in a particular time. Apparent power is the product of the current and voltage power is the product of the current and voltage of the circuit.of the circuit.



In alternating current circuits, voltage and In alternating current circuits, voltage and current only remain in phase if the load is current only remain in phase if the load is purely resistive. When this happens the power purely resistive. When this happens the power is said to be 'real power'.is said to be 'real power'.



If instead the load is purely reactive (either If instead the load is purely reactive (either Capacitive or Inductive), all of the power is reflected Capacitive or Inductive), all of the power is reflected back to the generator. The load is said to draw zero back to the generator. The load is said to draw zero real power, instead it draws only 'reactive power'. If a real power, instead it draws only 'reactive power'. If a load is both resistive and reactive, its will have both load is both resistive and reactive, its will have both real and reactive power, resulting in total amount of real and reactive power, resulting in total amount of power called the 'apparent power'. power called the 'apparent power'.



In AC power systems, attached loads that In AC power systems, attached loads that store energy behave like combinations of coils store energy behave like combinations of coils (inductors) and capacitors. Coils store power (inductors) and capacitors. Coils store power as magnetic fields and cause delay changes in as magnetic fields and cause delay changes in the current (current lags). Capacitors store the current (current lags). Capacitors store power as electric charge, and therefore cause power as electric charge, and therefore cause advance changes in currents (current leads).advance changes in currents (current leads).



The portion of power flow averaged over a The portion of power flow averaged over a complete cycle of the AC waveform that complete cycle of the AC waveform that results in net transfer of energy in results in net transfer of energy in one one directiondirection is known as real power. The portion is known as real power. The portion of power flow due to stored energy which of power flow due to stored energy which returns to the sourcereturns to the source in each cycle is known as in each cycle is known as reactive power.reactive power.



In reality there are losses along AC power In reality there are losses along AC power transmission lines, due to a purely reactive transmission lines, due to a purely reactive load, which draws no real power itself, and load, which draws no real power itself, and consumes power because the supplied and consumes power because the supplied and reflected power dissipate away on the reflected power dissipate away on the transmission line, and energy is wasted. transmission line, and energy is wasted.


For this reason an AC For this reason an AC load should be load should be

designed to have as designed to have as little reactive power little reactive power

as possible.as possible.



The following terms are used to describe energy The following terms are used to describe energy flow in a System. Each of them is assigned with a flow in a System. Each of them is assigned with a different unit to differentiate between them):different unit to differentiate between them):


Real power (P) [Unit: W] Reactive power (Q) [Unit: VAR] Apparent power (S)[Unit: VA]


Real Power and Apparent Power:Real Power and Apparent Power:The unit for all forms of power is the watt (symbol: The unit for all forms of power is the watt (symbol: W). However, this unit is generally reserved for the W). However, this unit is generally reserved for the real power component. Apparent power is real power component. Apparent power is conventionally expressed in conventionally expressed in volt-amperesvolt-amperes (VA) since (VA) since it is the simple product of rms voltage and rms it is the simple product of rms voltage and rms current. The unit for reactive power is given the current. The unit for reactive power is given the special name "VAR", which stands for volt-amperes special name "VAR", which stands for volt-amperes reactive (since reactive power flow transfers no net reactive (since reactive power flow transfers no net energy to the load, it is sometimes called "wattless" energy to the load, it is sometimes called "wattless" power). power).


Significance of the Power FactorSignificance of the Power FactorConsider an ideal alternating current (AC) circuit Consider an ideal alternating current (AC) circuit consisting of a source and a generalized load, where consisting of a source and a generalized load, where both the current and voltage are sinusoidal. If the load both the current and voltage are sinusoidal. If the load is purely resistive, the two quantities reverse their is purely resistive, the two quantities reverse their polarity at the same time, the direction of energy flow polarity at the same time, the direction of energy flow does not reverse, and only real power flows. If the does not reverse, and only real power flows. If the load is purely reactive, then the voltage and current load is purely reactive, then the voltage and current are 90 degrees out of phase and there is no net power are 90 degrees out of phase and there is no net power flow. This energy flowing backwards and forwards is flow. This energy flowing backwards and forwards is known as reactive power.known as reactive power.


If a capacitor and an inductor are placed in If a capacitor and an inductor are placed in parallel, then the currents flowing through the parallel, then the currents flowing through the inductor and the capacitor oppose and tend to inductor and the capacitor oppose and tend to cancel out rather than adding. Conventionally, cancel out rather than adding. Conventionally, capacitors are considered to generate reactive capacitors are considered to generate reactive power and inductors to consume it. power and inductors to consume it.


In a purely resistive AC circuit, voltage and current In a purely resistive AC circuit, voltage and current waveforms are in phase, changing polarity at the waveforms are in phase, changing polarity at the same instant in each cycle. Where reactive loads are same instant in each cycle. Where reactive loads are present, such as with capacitors or inductors, energy present, such as with capacitors or inductors, energy storage in the loads result in a time difference storage in the loads result in a time difference between the current and voltage waveforms. This between the current and voltage waveforms. This stored energy returns to the source and is not stored energy returns to the source and is not available to do work at the load. Thus, a circuit with a available to do work at the load. Thus, a circuit with a low power factor will have higher currents to transfer low power factor will have higher currents to transfer a given quantity of real power than a circuit with a a given quantity of real power than a circuit with a high power factor.high power factor.


Circuits containing purely resistive heating Circuits containing purely resistive heating elements (filament lamps, heaters, cooking elements (filament lamps, heaters, cooking stoves, etc.) have a power factor of 1.0. stoves, etc.) have a power factor of 1.0. Circuits containing inductive or capacitive Circuits containing inductive or capacitive elements (lamp , motors, etc.) often have a elements (lamp , motors, etc.) often have a power factor below 1.0. power factor below 1.0.


The significance of power factor lies in the The significance of power factor lies in the fact that utility companies supply customers fact that utility companies supply customers with volt-amperes, but bill them for watts. with volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to Power factors below 1.0 require a utility to generate more than the minimum volt-amperes generate more than the minimum volt-amperes necessary to supply the real power (watts). necessary to supply the real power (watts). This increases generation and transmission This increases generation and transmission costs.costs.

An Example to understand the An Example to understand the Power FactorPower Factor

Consider a canal boat being pulled by a horse. If the Consider a canal boat being pulled by a horse. If the horse could walk on water then the angle (Phi) Ø would horse could walk on water then the angle (Phi) Ø would be zero and COSINE Ø=1. Meaning all the horse power be zero and COSINE Ø=1. Meaning all the horse power is being used to pull the load. is being used to pull the load. However the relative position of the horse influences However the relative position of the horse influences the power. As the horse gets closer to the barge, angle the power. As the horse gets closer to the barge, angle Ø1 increases and power is wasted, but, as the horse is Ø1 increases and power is wasted, but, as the horse is positioned further away, then angle Ø2 gets closer to positioned further away, then angle Ø2 gets closer to zero and less power is wasted zero and less power is wasted


Much of the discussion is Much of the discussion is made about Power Factor. made about Power Factor. Now we switch towards the Now we switch towards the means and ways to solve means and ways to solve

the problem low power the problem low power factor.factor.


Power factor correctionPower factor correction (PFC) is the process (PFC) is the process of adjusting the characteristics of electric loads of adjusting the characteristics of electric loads that create a power factor that is less than 1.that create a power factor that is less than 1.


Power factor correction may be applied either by an Power factor correction may be applied either by an electrical power transmission utility to improve the electrical power transmission utility to improve the stability and efficiency of the transmission network; stability and efficiency of the transmission network; or, correction may be installed by individual electrical or, correction may be installed by individual electrical customers to reduce the costs charged to them by customers to reduce the costs charged to them by their electricity supplier. A high power factor is their electricity supplier. A high power factor is generally desirable in a transmission system to reduce generally desirable in a transmission system to reduce transmission losses and improve voltage regulation at transmission losses and improve voltage regulation at the load. the load.


Why Power Factor Correction?Why Power Factor Correction?The current through the reactive component (IThe current through the reactive component (I reactivereactive) ) dissipates no power, and neither does it register on dissipates no power, and neither does it register on the watt hour meter. However, the reactive current the watt hour meter. However, the reactive current does dissipate power when flowing through other does dissipate power when flowing through other resistive components in the system, like the wires, the resistive components in the system, like the wires, the switches, and the lossy part of a transformer (Rswitches, and the lossy part of a transformer (R lineline). ). Switches have to interrupt the total current, not just Switches have to interrupt the total current, not just the active component. Wires have to be big enough to the active component. Wires have to be big enough to carry the entire current, etc. Therefore Correcting the carry the entire current, etc. Therefore Correcting the power factor reduces the amount of oversizing power factor reduces the amount of oversizing necessary. necessary.


The introduction of Power Factor The introduction of Power Factor Correction Correction capacitorscapacitors is a widely is a widely recognized method of reducing an recognized method of reducing an electrical load, thus minimizing electrical load, thus minimizing wasted energy and hence improving wasted energy and hence improving the efficiency of a plant and reducing the efficiency of a plant and reducing the electricity bill.the electricity bill.


Active Power

Reactive Power

Available Active Power


The inductive components, draw Reactive The inductive components, draw Reactive Power (VAr) from the mains. It lags behind Power (VAr) from the mains. It lags behind the Active Power (W) by 90the Active Power (W) by 90oo (Figure 1). A (Figure 1). A capacitor, if connected across the mains, will capacitor, if connected across the mains, will also draw Reactive Power [VAr(c)], but it also draw Reactive Power [VAr(c)], but it leadsleads the Active Power (W) by 90 the Active Power (W) by 90oo. The . The direction of the direction of the capacitivecapacitive Reactive Power Reactive Power [VAr(c)] is opposite to the direction of the [VAr(c)] is opposite to the direction of the inductive Reactive Power (VAr) (Figure 2). inductive Reactive Power (VAr) (Figure 2).


Figure-1


Figure-1


The power factor can also be improved by The power factor can also be improved by synchronous Motors.synchronous Motors. These machines draw leading These machines draw leading kVAR when they are over-excited and, especially kVAR when they are over-excited and, especially when they are running idle. They are employed for when they are running idle. They are employed for correcting the power factor in bulk and have the correcting the power factor in bulk and have the special advantage that the amount of correction can special advantage that the amount of correction can be varied by changing their excitation.be varied by changing their excitation.


The reactive power drawn by the synchronous The reactive power drawn by the synchronous motor is a function of its field excitation. It is motor is a function of its field excitation. It is started and connected to the electrical network. started and connected to the electrical network. It operates at full leading power factor and It operates at full leading power factor and puts VARs onto the network . Its principal puts VARs onto the network . Its principal advantage is the ease with which the amount advantage is the ease with which the amount of correction can be adjusted; it behaves like of correction can be adjusted; it behaves like an electrically variable capacitor.an electrically variable capacitor.Phase advancerPhase advancer can also be used. They are can also be used. They are fitted with individual machines.fitted with individual machines.


Most loads on an electrical distribution system fall into one of Most loads on an electrical distribution system fall into one of three categories; resistive, inductive or Capacitive.The most three categories; resistive, inductive or Capacitive.The most common is inductive load. Typical examples of this include common is inductive load. Typical examples of this include transformers, fluorescent lighting and AC induction motors. transformers, fluorescent lighting and AC induction motors. Most inductive loads use a conductive coil winding to produce Most inductive loads use a conductive coil winding to produce an electromagnetic field, allowing the motor to function. All an electromagnetic field, allowing the motor to function. All inductive loads require two kinds of power to operate:inductive loads require two kinds of power to operate:Active power Active power (kwatts) - to produce the motive force (kwatts) - to produce the motive force Reactive powerReactive power (kvar) - to energise the magnetic field (kvar) - to energise the magnetic field The operating power from the distribution system is composed The operating power from the distribution system is composed of both active (working) and reactive (non-working) elements. of both active (working) and reactive (non-working) elements. The active power does useful work in driving the motor The active power does useful work in driving the motor whereas the reactive power only provides the magnetic field.whereas the reactive power only provides the magnetic field.

Disadvantages of Poor Power Disadvantages of Poor Power factorfactor

As the power factor drops the system becomes less efficient. A As the power factor drops the system becomes less efficient. A drop from 1.0 to 0.9 results in 15% more current being drop from 1.0 to 0.9 results in 15% more current being required for the same load.A power factor of 0.7 requires required for the same load.A power factor of 0.7 requires approximately 43% more current; and a power factor of 0.5 approximately 43% more current; and a power factor of 0.5 requires approximately 100% (twice as much) to handle the requires approximately 100% (twice as much) to handle the same load.same load.

The objective, therefore, should be to reduce the The objective, therefore, should be to reduce the reactive power drawn from the supply by improving the power reactive power drawn from the supply by improving the power factor. If an AC motor were 100% efficient it would consume factor. If an AC motor were 100% efficient it would consume only active power but, since most motors are only 75% to 80% only active power but, since most motors are only 75% to 80% efficient, they operate at a low power factor. This means poor efficient, they operate at a low power factor. This means poor energy and cost efficiency because the Regional Electricity energy and cost efficiency because the Regional Electricity Companies charge you at penalty rates for a poor power Companies charge you at penalty rates for a poor power factor.factor.

Disadvantages of Poor Power Disadvantages of Poor Power factorfactor

Advantages of Power Factor Advantages of Power Factor CorrectionCorrection

The main advantages of the Power Factor The main advantages of the Power Factor Correction are:Correction are:1.1. The electrical load on the Utility is reduced, The electrical load on the Utility is reduced, thereby thereby allowing the Utility to supply the allowing the Utility to supply the surplus power to surplus power to other consumers, without other consumers, without increasing its generation increasing its generation capacity.capacity.2.2. Most of the Utilities impose low power Most of the Utilities impose low power factor factor penalties. By correcting the power penalties. By correcting the power factor, this factor, this penalty can be avoided.penalty can be avoided.3.3. High power factor reduces the load High power factor reduces the load currents. currents. Therefore, a considerable saving is Therefore, a considerable saving is made in the made in the hardware cost, such as cables, hardware cost, such as cables, switchgear, switchgear, substation transformers, etc.substation transformers, etc.4. 4. Voltage regulation is improvedVoltage regulation is improved

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