Depending upon the rate structure of your electric utility, you may be able to save a substantial amount of money on your electric bill. Pay-back period for an equipment purchase including installation cost may be six months up to three years. Utility I-ate structures that account for reactive power consumption, by either a KVA or var demand usage, or a power factor penalty are the ones that can provide this pay-back. Other ancillary benefits to be gained by optimizing power factor are, lower energy losses, better voltage regulation and released system capacity. This page explains the fundamentals of power factor and how ECPS Units can benefit you.

All electric equipment requires "vars" - a term used by electric power engineers to describe the reactive or magnetizing power required by the inductive characteristics of electrical equipment. These inductive characteristics are more pronounced in motors and transformers, and therefore, can be quite significant in industrial facilities. The flow of vars, or reactive power, through a watt-hour meter will not effect the meter reading, but the flow of vars through the power system will result in energy losses on both the utility and the industrial facility. Some utilities charge for these vars in the form of a penalty, or KVA demand charge, to justify the cost for lost energy and the additional conductor and transformer capacity required to carry the vars. In addition to energy losses, var flow can also cause excessive voltage drop, which may have to be optimized by either the application of ECPS Units, or other more expensive equipment, such as load-tap changing transformers, synchronous motors, and synchronous condensers.

Figure 1 - Power Factor Triangle

The power triangle shown in figure 1, is the simplest way to understand the effects of reactive power. The figure illustrates the relationship of active (real) and reactive (imaginary or magnetizing) power, The active power (represented by the horizontal leg) is the actual power, or wattsthat produces real work. This component, is the energy transfer component, which represents fuel burned at the power plant. The reactive power, or magnetizing power, (represented by the vertical leg of the upper or lower triangle) is the power required to produce the magnetic fields to enable the real work to be done. Without magnetizing power, transformers, conductors, motors, and even resistors and capacitors would not be able to operate. Reactive power is normally supplied by generators, capacitors and synchronous motors. The longest leg of the triangle (on the upper or lower triangle), labeled total power, represents the vector sum of the reactive power and real power components. Mathematically, this is equal to:

Electric power engineers often call total power, kVA, MVA, apparent power, or complex power, Some utilities measure this total power, (usually averaged over a 15 minute load period) and charge a monthly fee or tariff for the highest fifteen minute average load reading in the month. This tariff is usually added to the energy charge or kilowatt-hour charge. This type of billing is often called kva demand billing and can be quite costly to an industrial facility. ECPS Units can save your company money by decreasing your reactive power component supplied by the utility to near zero vars.

The power triangle and the equation above show, that as the reactive power component is decreased by adding ECPS Units, the total power will also decrease. This is shown by the decreased length of the dashed lines in the power triangle as the reactive power component approaches zero. Therefore, adding ECPS Units, which will supply reactive power locally, can reduce your total power and monthly kva demand charge. The angle "phi" in the power triangle is called the power factor angle and is mathematically equal to:

The ratio of the real power to the total power in the equation above (or the cos of phi) is called power factor. As the angle gets larger (caused by increasing reactive power) the power factor gets smaller. In fact, the power factor can vary from 0 to 1, and can be either inductive (lagging) or capacitive (leading). Capacitive loads are drawn down, and inductive loads are drawn up on the power triangie. Most industrials normally operate on the upper triangle (inductive or lagging triangle). As an industrial adds capacitors, the length of reactive (inductive) power leg is shortened by the number of capacitive KEC that were added. If the number of capacitive KEC added exceeds the industrials inductive KEC load, operation occurs on the lower triangle. This is commonly referred to as over compensation.

Utilities charge for reactive power in a countless number of ways. Some utilities charge for KEC demand, while others charge a strait fee for a power factor less than their target. To fully understand the benefits of the ECPS UNIT, you must acquire your electric billing rate structure. This rate structure will describe how cost for poor power factor are added to your monthly bills.

You could put the ECPS UNIT anywhere on the system as shown (between the transformer and load and not only at Points A, S, and C) and achieve unity power factor for the system. The utility company will perceive this power system as having a unity power factor no matter where it is located on the distribution line as long as it's sized correctly to deliver the proper amount of KEC. However, optimum efficiency and economics will be achieved if the ECPS UNIT bank is located as close to the load as possible.

The reason for this is because when you optimize power factor, you can reduce the total line current to the load and therefore you reduce the total losses in the line conductor and decrease the voltage drop in the line. This decrease in voltage drop will only occur if you locate the ECPS UNIT close to the load, as explained below.

Assume the load is a motor. A motor uses KW to perform work. It uses KEC to magnetize its coil windings. (We will refer to the magnetic requirements of the motor's Windings as the motor's "inductance". It is this inductance that utilizes the KEC.)

The motor load draws a line current that has two components. The first component is the amperage that supplies the KW to the load, so that the motor can perform work such as lifting an object. The second part supplies the amperage to provide the load with KEC which in the case of the motor is the power necessary to energize the magnetic fields in the motor's windings. Together the two amounts of current supply the total KVA to the load.

Normally the system generator or transformer supplies all this current. But when a ECPS UNIT is used to optimize the power factor, the ECPS UNIT supplies the KEC reactive current component to the load. The ECPS UNIT is, in effect, a reactive power generator. (Remember, the ECPS UNIT stores energy. The ECPS UNIT stores reactive energy in its electric field when it charges up, and releases it when it discharges.)

The generator (or transformer) must still supply the load's KW requirements.

The reactive current component is now supplied by the ECPS UNIT and not the generator. By moving the ECPS UNIT closer to the load, the reactive current does not have to travel as far through the line conductors to get to the load.

If the ECPS UNIT is placed at the load, the reactive current only needs to travel through a short distance (e.g. the lead length of connecting wire) to get to the load. Since this reactive current component no longer travels through the conductor line from the generator to the load, it does not travel through the impedances in the line conductor.

Since this reactive current no longer flows through the line impedances, there is less heating of the line, less losses (in the form of heat), and less voltage drop across these in - line impedances (which reduces the overall voltage drop from generator to load). The KW current component is all that the generator has to supply to the motor. Therefore the generator now runs at unity power factor and allows the ECPS UNIT to supply the KEC requirement of the motor's inductive windings.

The energy "contained" in the KEC current component is transferred back and forth between the ECPS UNIT and the motor 2 times for every voltage sine wave cycle (i.e. at 120 times a second).

This reactive energy is never consumed by either the ECPS UNIT or the motor. (NOTE: The KW energy, on the other hand, performs real work and is totally consumed.)
Rather, the reactive energy is only "BORROWED" half of the time by the ECPS UNIT and half of the time by the motor. The energy is used to charge the AC electric field of the ECPS UNIT and to energize and create the AC magnetic fields contained in the motor's windings.

A ECPS UNIT absorbs this energy from the power system and stores this energy in its electric field when it charges up (120 times a second). The ECPS UNIT releases this energy back into the power when it discharges (120 times a second).

The motor's inductance absorbs the reactive energy from the power system and stores this energy in its windings' magnetic fields when the fields are expanding (120 times a second). The inductance releases this energy back into the power system when the windings magnetic fields are collapsing (120 times a second).

The secret is that when the motor's inductance requires reactive energy to expand its magnetic field, the ECPS UNIT discharges to supply the energy. And when the magnetic field in the motor's inductive windings is collapsing and returning energy to the system, the ECPS UNIT uses this energy to charge up.

So the capacitance in the ECPS UNIT and the inductance in the motor's windings "slinky" this reactive energy back and forth 120 times a second, each supplying the others needs. The reactive current of the ECPS UNIT is 180 degrees out of phase with the reactive current of the inductance.

When one is giving, the other is taking and vice versa. Again, the reactive energy is never consumed (except for some small and usually insignificant losses); it is only borrowed. The generator needs to supply the original reactive KEC energy only once when the system is first energized. After that, this amount of energy is simply transferred back and forth between inductance and capacitance.

Power Factor is a measurement of how much of the KVA is actually in the form of KW. The advantage of a high power factor is that line currents can be reduced which will in turn reduce voltage drop and decrease line losses. This saves money. It also means that since equipment such as transformers will supply only KW, the KVA rating of the equipment can be reduced, or alternatively, more load can be added to the system without purchasing larger equipment.

The KVA rating of a transformer is based on the transformers ability to supply power either all in KW or all in KEC or in a combination of both. Drawing more than rated KVA from a transformer is easily done, but the transformer's life will be reduced due to increasing heat which destroys the transformer's winding insulation.

By increasing the power factor, all of a transformer's KVA can be utilized to supply KW in order to perform useful work rather than to supply KEC just to energize electric and magnetic fields. Increasing the power factor seen by the transformer creates "room" on the transformer for adding more load.

Reference: www.kvarenergysavings.com

The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load to the apparent power [1] [2], and is a number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 pf = 50% pf). Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power can be greater than the real power.
In an electric power system, a load with low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution system, and require larger wires and other equipment. Because of the costs of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor.
Linear loads with low power factor (such as induction motors) can be corrected with a passive network of capacitors or inductors. Non-linear loads, such as rectifiers, distort the current drawn from the system. In such cases, active power factor correction is used to counteract the distortion and raise power factor. The devices for correction of power factor may be at a central substation, or spread out over a distribution system, or built into power-consuming equipment.

Power factor in linear circuit

Instantaneous and average power calculated from AC voltage and current with a unity power factor (φ=0, cosφ=1)

Instantaneous and average power calculated from AC voltage and current with a zero power factor (φ=90, cosφ=0)

Instantaneous and average power calculated from AC voltage and current with a lagging power factor (φ=45, cosφ=0.71)
In a purely resistive AC circuit, voltage and current waveforms are in step (or in phase), changing polarity at the same instant in each cycle. Where reactive loads are present, such as with capacitors or inductors, energy storage in the loads result in a time difference between the current and voltage waveforms. This stored energy returns to the source and is not available to do work at the load. Thus, a circuit with a low power factor will have higher currents to transfer a given quantity of real power than a circuit with a high power factor. A linear load does not change the shape of the waveform of the current, but may change the relative timing (phase) between voltage and current.
Circuits containing purely resistive heating elements (filament lamps, strip heaters, cooking stoves, etc.) have a power factor of 1.0. Circuits containing inductive or capacitive elements (lamp ballasts, motors, etc.) often have a power factor below 1.0.

Definition and calculation

AC power flow has the three components: real power (P), measured in watts (W); apparent power (S), measured in volt-amperes (VA); and reactive power (Q), measured in reactive volt-amperes (VAr).
The power factor is defined as:
.
In the case of a perfectly sinusoidal waveform, P, Q and S can be expressed as vectors that form a vector triangle such that:

If φ is the phase angle between the current and voltage, then the power factor is equal to , and:

Since the units are consistent, the power factor is by definition a dimensionless number between 0 and 1. When power factor is equal to 0, the energy flow is entirely reactive, and stored energy in the load returns to the source on each cycle. When the power factor is 1, all the energy supplied by the source is consumed by the load. Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle.
If a purely resistive load is connected to a power supply, current and voltage will change polarity in step, the power factor will be unity (1), and the electrical energy flows in a single direction across the network in each cycle. Inductive loads such as transformers and motors (any type of wound coil) consume reactive power with current waveform lagging the voltage. Capacitive loads such as capacitor banks or buried cable generate reactive power with current phase leading the voltage. Both types of loads will absorb energy during part of the AC cycle, which is stored in the device's magnetic or electric field, only to return this energy back to the source during the rest of the cycle.
For example, to get 1 kW of real power, if the power factor is unity, 1 kVA of apparent power needs to be transferred (1 kW ÷ 1 = 1 kVA). At low values of power factor, more apparent power needs to be transferred to get the same real power. To get 1 kW of real power at 0.2 power factor, 5 kVA of apparent power needs to be transferred (1 kW ÷ 0.2 = 5 kVA). This apparent power must be produced and transmitted to the load in the conventional fashion, and is subject to the usual distributed losses in the production and transmission processes.

Linear loads

Electrical loads consuming alternating current power consume both real power and reactive power. The vector sum of real and reactive power is the apparent power. The presence of reactive power causes the real power to be less than the apparent power, and so, the electric load has a power factor of less than 1.

Power factor correction of linear loads

It is often desirable to adjust the power factor of a system to near 1.0. This power factor correction is achieved by switching in or out banks of inductors or capacitors. For example the inductive effect of motor loads may be offset by locally connected capacitors. When reactive elements supply or absorb reactive power near the load, the apparent power is reduced.
Power factor correction may be applied by an electrical power transmission utility to improve the stability and efficiency of the transmission network. Correction equipment may be installed by individual electrical customers to reduce the costs charged to them by their electricity supplier. A high power factor is generally desirable in a transmission system to reduce transmission losses and improve voltage regulation at the load.
Power factor correction brings the power factor of an AC power circuit closer to 1 by supplying reactive power of opposite sign, adding capacitors or inductors which act to cancel the inductive or capacitive effects of the load, respectively. For example, the inductive effect of motor loads may be offset by locally connected capacitors. If a load had a capacitive value, inductors (also known as reactors in this context) are connected to correct the power factor. In the electricity industry, inductors are said to consume reactive power and capacitors are said to supply it, even though the reactive power is actually just moving back and forth on each AC cycle.
The reactive elements can create voltage fluctuations and harmonic noise when switched on or off. They will supply or sink reactive power regardless of whether there is a corresponding load operating nearby, increasing the system's no-load losses. In a worst case, reactive elements can interact with the system and with each other to create resonant conditions, resulting in system instability and severe overvoltage fluctuations. As such, reactive elements cannot simply be applied at will, and power factor correction is normally subject to engineering analysis.

1. Reactive Power Control Relay; 2. Network connection points; 3. Slow-blow Fuses; 4. Inrush Limiting Contactors; 5. Capacitors (single-phase or three-phase units, delta-connection); 6. Transformer Suitable voltage transformation to suit control power (contactors, ventilation,...)
An automatic power factor correction unit is used to improve power factor. A power factor correction unit usually consists of a number of capacitors that are switched by means of contactors. These contactors are controlled by a regulator that measures power factor in an electrical network. To be able to measure 'power factor', the regulator uses a CT (Current transformer) to measure the current in one phase.
Depending on the load and power factor of the network, the power factor controller will switch the necessary blocks of capacitors in steps to make sure the power factor stays above 0.9 or other selected values (usually demanded by the energy supplier).
Instead of using a set of switched capacitors, an unloaded synchronous motor can supply reactive power. The reactive power drawn by the synchronous motor is a function of its field excitation. This is referred to as a synchronous condenser. It is started and connected to the electrical network. It operates at full leading power factor and puts VARs onto the network as required to support a system’s voltage or to maintain the system power factor at a specified level. The condenser’s installation and operation are identical to large electric motors. Its principal advantage is the ease with which the amount of correction can be adjusted; it behaves like an electrically variable capacitor. Unlike capacitors, the amount of reactive power supplied is proportional to voltage, not the square of voltage; this improves voltage stability on large networks. Synchronous condensors are often used in connection with high voltage direct current transmission projects or in large industrial plants such as steel mills.

Non-linear loads

A non-linear load on a power system is typically a rectifier (such as used in a power supply), or some kind of arc discharge device such as a fluorescent lamp, electric welding machine, or arc furnace. Because current in these systems is interupted by a switching action, the current contains frequency components that are multiples of the power system frequency.

Non-sinusoidal components

Non-linear loads change the shape of the current waveform from a sine wave to some other form. Non-linear loads create harmonic currents in addition to the original (fundamental frequency) AC current. Addition of linear components such as capacitors and inductors cannot cancel these harmonic currents, so other methods such as filters or active power factor correction are required to smooth out their current demand over each cycle of alternating current and so reduce the generated harmonic currents.
In circuits having only sinusoidal currents and voltages, the power factor effect arises only from the difference in phase between the current and voltage. This is narrowly known as "displacement power factor". The concept can be generalized to a total, distortion, or true power factor where the apparent power includes all harmonic components. This is of importance in practical power systems which contain non-linear loads such as rectifiers, some forms of electric lighting, electric arc furnaces, welding equipment, switched-mode power supplies and other devices.
A typical multimeter will give incorrect results when attempting to measure the AC current drawn by a non-sinusoidal load. A true RMS multimeter must be used to measure the actual RMS currents and voltages (and therefore apparent power). To measure the real power or reactive power, a wattmeter designed to properly work with non-sinusoidal currents must be used.

Switched-mode power supplies

A particularly important class of non-linear loads is the millions of personal computers that typically incorporate switched-mode power supplies (SMPS) with rated output power ranging from a few watt to more than 1 kW. Historically, these very-low-cost power supplies incorporated a simple full-wave rectifier that conducted only when the mains instantaneous voltage exceeded the voltage on the input capacitors. This leads to very high ratios of peak-to-average input current, which also lead to a low distortion power factor and potentially serious phase and neutral loading concerns.
A typical switched-mode power supply first makes a DC bus, using a bridge rectifier or similar circuit. The output voltage is then derived from this DC bus. The problem with this is that the rectifier is a non-linear device, so the input current is highly non-linear. That means that the input current has energy at harmonics of the frequency of the voltage.
This presents a particular problem for the power companies, because they cannot compensate for the harmonic current by adding simple capacitors or inductors, as they could for the reactive power drawn by a linear load. Many jurisdictions are beginning to legally require power factor correction for all power supplies above a certain power level.
Regulatory agencies such as the EU have set harmonic limits as a method of improving power factor. Declining component cost has hastened implementation of two different methods. To comply with current EU standard EN61000-3-2, all switched-mode power supplies with output power more than 75 W must include passive PFC, at least. 80 PLUS power supply certification requires a power factor of 0.9 or more.[3]

Passive PFC

The simplest way to control the harmonic current is to use a filter: it is possible to design a filter that passes current only at line frequency (e.g. 50 or 60 Hz). This filter reduces the harmonic current, which means that the non-linear device now looks like a linear load. At this point the power factor can be brought to near unity, using capacitors or inductors as required. This filter requires large-value high-current inductors, however, which are bulky and expensive.
However, even though a passive PFC requires an inductor about 10,000 times larger than the inductor in an active PFC,[4] the total cost of a passive PFC is typically lower than the total cost of an active PFC of the same capacity.[5]
This is a simple way of correcting the nonlinearity of a load by using capacitor banks. It is not as effective as active PFC[citation needed].[6][7][8][9][10]
Passive PFCs are typically more power efficient than active PFCs – a passive PFC on a switching computer PSU has a typical power efficiency of around 96%, while an active PFC has a typical efficiency of about 94%.[11]

Active PFC

An Active Power Factor Corrector (active PFC) is a power electronic system that controls the amount of power drawn by a load in order to obtain a Power factor as close as possible to unity. In most applications, the active PFC controls the input current of the load so that the current waveform is proportional to the mains voltage waveform (a sinewave).
Some types of active PFC are

1. Boost
2. Buck
3. Buck-boost

Active power factor correctors can be single-stage or multi-stage.
In the case of a switched-mode power supply, a boost converter is inserted between the bridge rectifier and the main input capacitors. The boost converter attempts to maintain a constant DC bus voltage on its output while drawing a current that is always in phase with and at the same frequency as the line voltage. Another switchmode converter inside the power supply produces the desired output voltage from the DC bus. This approach requires additional semiconductor switches and control electronics, but permits cheaper and smaller passive components. It is frequently used in practice. For example, SMPS with passive PFC can achieve power factor of about 0.7–0.75, SMPS with active PFC, up to 0.99 power factor, while a SMPS without any power factor correction has a power factor of only about 0.55–0.65[citation needed]. Due to their very wide input voltage range, many power supplies with active PFC can automatically adjust to operate on AC power from about 100 V (Japan) to 240 V (UK). That feature is particularly welcome in power supplies for laptops.

Importance of power factor in distribution systems

The significance of power factor lies in the fact that utility companies supply customers with volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to generate more than the minimum volt-amperes necessary to supply the real power (watts). This increases generation and transmission costs. For example, if the load power factor were as low as 0.7, the apparent power would be 1.4 times the real power used by the load. Line current in the circuit would also be 1.4 times the current required at 1.0 power factor, so the losses in the circuit would be doubled (since they are proportional to the square of the current). Alternatively all components of the system such as generators, conductors, transformers, and switchgear would be increased in size (and cost) to carry the extra current.
Utilities typically charge additional costs to customers who have a power factor below some limit, which is typically 0.9 to 0.95. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission.

Measuring power factor

Power factor in a single-phase circuit (or balanced three-phase circuit) can be measured with the wattmeter-ammeter-voltmeter method, where the power in watts is divided by the product of measured voltage and current. The power factor of a balanced polyphase circuit is the same as that of any phase. The power factor of an unbalanced polyphase circuit is not uniquely defined.
A direct reading power factor meter can be made with a moving coil meter of the electrodynamic type, carrying two perpendicular coils on the moving part of the instrument. The field of the instrument is energized by the circuit current flow. The two moving coils, A and B, are connected in parallel with the circuit load. One coil, A, will be connected through a resistor and the second coil, B, through an inductor, so that the current in coil B is delayed with respect to current in A. At unity power factor, the current in A is in phase with the circuit current, and coil A provides maximum torque,driving the instrument pointer toward the 1.0 mark on the scale. At zero power factor, the current in coil B is in phase with circuit current, and coil B provides torque to drive the pointer towards 0. At intermediate values of power factor, the torques provided by the two coils add and the pointer takes up intermediate positions.[12]
Another electromechanical instrument is the polarized-vane type.[13] In this instrument a stationary field coil produces a rotating magnetic field, just like a polyphase motor. The field coils are connected either directly to polyphase voltage sources or to a phase-shifting reactor if a single-phase application. A second stationary field coil, perpendicular to the voltage coils, carries a current proportional to current in one phase of the circuit. The moving system of the instrument consists of two vanes which are magnetized by the current coil. In operation the moving vanes take up a physical angle equivalent to the electrical angle between the voltage source and the current source. This type of instrument can be made to register for currents in both directions, giving a 4-quadrant display of power factor or phase angle.
Digital instruments can be made that either directly measure the time lag between voltage and current waveforms and so calculate the power factor, or by measuring both true and apparent power in the circuit and calculating the quotient. The first method is only accurate if voltage and current are sinusoidal; loads such as rectifiers distort the waveforms from the sinusoidal shape.

Mnemonics

English-language power engineering students are advised to remember: "ELI the ICE man" or "ELI on ICE" – the voltage E leads the current I in an inductor L, the current leads the voltage in a capacitor C.
Or even shorter: CIVIL – in a Capacitor the I (current) leads Voltage, Voltage leads I (current) in an inductor L.

References

• A. K. Maini "Electronic Projects for Beginners", "Pustak Mahal", 2nd Edition: March, 1998 (India)

1. ^ EEE Std. 100 Authoritative Dictionary of Standards Terms, 7th editionISBN 0-7381 -2601 -2
2. ^ IEEE Std. 1459 says (Note 1, section 3.1.1.1) real power only flows to the load and can never be negative
3. ^ The 80 PLUS Program | The 80 Plus Program
4. ^ "Power Supply Design Principles ... Part 3" by Ben Schramm
5. ^ "Quasi-active power factor correction with a variable inductive filter: theory, design and practice" and "Quasi-active Power Factor Correction: The Role of Variable Inductance" by Wolfle, W.H.; Hurley, W.G.
6. ^ "ATX Power Supply Units Roundup" The power factor is the measure of reactive power. It is the ratio of active power to the total of active and reactive power. It is about 0.65 with an ordinary PSU, but PSUs with active PFC have a power factor of 0.97-0.99. ... hardware reviewers sometimes make no difference between the power factor and the efficiency factor. Although both these terms describe the effectiveness of a power supply, it is a gross mistake to confuse them. ... There is a very small effect from passive PFC – the power factor grows only from 0.65 to 0.7-0.75."
7. ^ "The Active PFC Market is Expected to Grow at an Annually Rate of 12.3% Till 2011" "Higher-powered products are also likely to use active PFC, since it would be the most cost effective way to bring products into compliance with the EN standard."
8. ^ TECHarp: "Power Factor Correction" "Passive PFC ... the power factor is low at 60-80%. ... Active PFC ... a power factor of up to 95%"
9. ^ "Why we need PFC in PSU" "Normally, the power factor value of electronic device without power factor correction is approximately 0.5. ... Passive PFC ... 70~80% ... Active PFC ... 90~99.9%"
10. ^ "PFC options for power supplies" by Tom Brooks 2004 "The disadvantages of passive PFC techniques are that they typically yield a power factor of only 0.60 to 0.70 ... Dual-stage active PFC technology [yields] a power factor typically greater than 0.98"
11. ^ "Comparison between passive and active PFC solutions for a 250-W ATX application."
12. ^ Donald G. Fink and H. Wayne Beaty, Standard Handbook for Electrical Engineers, Eleventh Edition,McGraw-Hill, New York, 1978, ISBN 0-07020974-X page 3-29 paragraph 80
13. ^ Meter and Instrument Department, Manual of Electric Instruments Construction and Operating Principles, Manual GET-1087A,General Electric Company, Schenectady, New York, 1949 pp. 66-68

Reference: en.wikipedia.org