Active Power Factor Correction
Active Power Factor Correction (PFC)
What is Active Power Factor Correction?
The active power factor correction (APFC) system is a device that corrects the power factor of AC electrical systems. APFC devices are designed to reduce harmonic distortion and increase efficiency. Harmonic distortion occurs when the current waveform contains higher frequency components than the fundamental 60 Hz sine wave. These higher frequencies cause additional losses in the distribution network and result in reduced efficiency. The APFC device reduces these harmonics and increases efficiency.
How does APCF work?
An APFC device consists of two major parts: a rectifier circuit and a capacitor bank. A rectifier converts alternating current (AC) voltage to direct current (DC). The DC output of the rectifier is then connected to the input of the capacitor bank. The capacitor bank filters out high-frequency currents and stores them until they are discharged back to the utility line. When the capacitor bank discharges, the stored energy is converted back to AC voltage. The AC voltage is then sent back to the load.
Listed below are some of the benefits of using an APFC device:
- Reduces harmonic distortion
- Increases efficiency
- Improves reliability
- Eliminates costly transformer replacement
- Minimizes maintenance costs
- Protects equipment from damage due to overloading
- Prevents equipment failure
- Allows for use of smaller transformers
- Provides a cost savings
The Purpose of an Active Power Correction Factor
An active power correction factor (APCF) is a device that helps to reduce voltage fluctuations in electrical systems. They are also known as APC devices or ACF devices.
An APCF is a type of reactive load that is connected between the source and the load. The purpose of an APCF is to provide a constant current flow from the source to the load regardless of changes in the load impedance. This allows the system to operate at its maximum efficiency.
A typical example of an APCF would be a capacitor connected across the output terminals of a transformer. If the transformer has no other loads attached, then the capacitor provides a constant DC current flow from the primary winding to the secondary winding.
Power Factor
Calculating power factor from voltage and current phases is only accurate if both waveforms are sinusoidal. Power Quality Analysers, often referred to as Power Analysers, make a digital recording of the voltage and current waveform (typically either one phase or three phase) and accurately calculate true power (watts), apparent power (VA) power factor, AC voltage, AC current, DC voltage, DC current, frequency, IEC61000-3-2/3-12 Harmonic measurement, IEC61000-3-3/3-11 flicker measurement, individual phase voltages in delta applications where there is no neutral line, total harmonic distortion, phase and amplitude of individual voltage or current harmonics, etc.
Retrieved 6 November 2017. “WT3000E Series Precision Power Analyzers”(PDF).Yokogawa Corporation.
Power Factor and Power Factor Correction
The power factor correction is a technique of increasing the power factor of a power supply.
Power factor correction tries to push the power factor of the electrical system such as the power supply towards 1, and even though it doesn’t reach this it gets to as close as 0.95 which is acceptable for most applications.
Ideal power factor occurs when the current and voltage waveforms are in phase: pf = 1 (i.e. cos 0) When the power factor is not equal to 1.0, power losses, and potentially harmonics that disrupt other devices, occur.
Not only does this shift the effective current peak away from that of the voltage waveform in time, it also introduces high-harmonic-content switching waveforms that potentially worsen the distortion of the current waveform.
That regulator is designed not only to maintain a constant dc voltage to feed the main converter stage of the power supply, but also to draw current from the input in-phase with the incoming ac voltage waveform.
A small number of test & measurement suppliers offer power analyzers; by rapidly sampling current and voltage waveforms and performing a suite of calculations – and applying a Fourier transform to extract harmonic information – every detail of a load’s performance in terms of distortion and power factor are revealed.
Power Factor Correction Devices
A power factor correction device typically includes nothing but a capacitor that is to be connected in parallel as the additional load.
Reactive Loads
Where reactive loads are present, such as with capacitors or inductors, energy storage in the loads results in a phase difference between the current and voltage waveforms.
In the electric power grid, reactive loads cause a continuous “ebb and flow” of non-productive power.
The power factor describes the amount of real power transmitted along a transmission line relative to the total apparent power flowing in the line. The power factor can also be computed as the cosine of the angle θ by which the current waveform lags or leads the voltage waveform, one can relate the various components of AC power by using the power triangle in vector space.
Power factor is described as leading if the current waveform is advanced in phase with respect to voltage, or lagging when the current waveform is behind the voltage waveform.
Real Power
In electrical engineering, the power factor of an AC power system is defined as the ratio of the absorbed by the real power In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred.
The general expression for power factor is given by where is the real power measured by an ideal wattmeter, is the rms current measured by an ideal ammeter, and is the rms voltage measured by an ideal voltmeter.
A circuit with a low power factor will use a greater amount of current to transfer a given quantity of real power than a circuit with a high power factor thus causing increased losses due to resistive heating in power lines, and requiring the use of higher-rated conductors and transformers.
AC power has two components: Real power or active power() (sometimes called average power), expressed in watts(W) Reactive power(), usually expressed in reactive volt-amperes(var), together, they form the complex power () expressed as volt-amperes (VA).
The SI explicitly disallows using units for this purpose or as the only source of information about a physical quantity as used. The power factor is defined as the ratio of real power to apparent power.
As power is transferred along a transmission line, it does not consist purely of real power that can do work once transferred to the load, but rather consists of a combination of real and reactive power, called apparent power.
The power factor describes the amount of real power transmitted along a transmission line relative to the total apparent power flowing in the line. The power factor can also be computed as the cosine of the angle θ by which the current waveform lags or leads the voltage waveform, one can relate the various components of AC power by using the power triangle in vector space.
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).
Electrical loads consuming alternating current power consume both real power and reactive 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.
To measure the real power or reactive power, a wattmeter designed to work properly with non-sinusoidal currents must be used.
DPFC uses semiconductor switches, typically [28] Power factors below 1.0 require a utility to generate more than the minimum volt-amperes necessary to supply the real power (watts).
For example, if the load power factor were as low as 0.7, the apparent power would be 1.4 times the power used by the load.
Note 1, section 3.1.1.1, when defining the quantities for power factor, asserts that real power only flows to the load and can never be negative.
Source: en.wikipedia.org
