Power Factor is defined as the ratio of the real power flowing to the load versus the apparent power in the circuit. Basically, it is the percentage of Amps supplied (by an electric utility or other source) that actually performs work in your electrical system.
Real Power, Reactive Power, and Apparent Power
Real Power has a common unit measurement of kilo-watts (kWs). Real Power does real work. It’s that portion of power that results in a net transfer of energy in a single direction, also known as active power.
This is as opposed to Reactive Power which is measured in kilo-volt-ampere-reactives (kVAr), and which is produced when the current wave form is out of phase with the voltage waveform due to inductive or capacitive loads.A motor needs a strong magnetic field to turn the rotor. When amps flow in, the magnetic field expands to store electrical energy, when it collapses it forces amps back into the source. These are reactive amps.
Apparent Power has a common unit of the kilo-volt-amp (kVA), and is the vector sum of Real Power and Reactive Power. It’s the total burden placed on the grid by the combination of both Real Power and Reactive Power elements.
Understanding Power Factor
A power factor of 1 means that 100% of the amps flowing through the electrical wires are used. The best example of a system with a power factor of 1 might be the filament of a light bulb or the coils of a toaster, which transfer 100% of the Amps into energy in the form of heat and light. But more complicated electrical systems have inefficiencies. A device has low power factor when it draws more current than it uses. A motor that has a .6 power factor means that 60% of the amps flowing in the system are real while 40% are not—an inefficiency that costs money.
Minimum Power Factor Standards
Utilities have long specified power factor performance regulations for large inductive motors, and they can generally charge industrial customers for reactive power consumption because they’re the ones that have to provide extra current to meet the demand of less efficient systems. Although utilities currently charge residential customers only for real power consumption, they have to add power to the system to support the out-of-phase losses, and losses due to poor power factor can quickly add up.
While there is no single standard established in the US for power factor of commercial or industrial facilities that are connected to the grid, certain utilities do establish minimum power factor as an operational requirement. Utilities want to exercise some manner of control over disturbances on the grid that might cause outages and they will penalize or credit larger commercial and industrial customers. Thankfully, there are power factor correction devices that can help.
What is Power Factor Correction?
Power factor correction (PFC) devices are introduced at the main power input to maintain the power factor within the desired range. At the most basic level, a PFC device is a stepped capacitor bank and will switch on the capacitors depending on the power factor at any given time to try and maintain a desired power factor during operation and minimize inefficiencies by redirecting reactive amps in resonance with the capacitor and the motor, thereby keeping them from flowing in the electrical wires and bringing current and voltage phases back into alignment. The entire idea of power factor correction is to eliminate reactive amps and harmonic amps.
Why Power Factor Correction is Necessary?
Modern PFC solutions offer much more than simple capacitors. There are bridgeless PFC solutions which account for power losses that arise from the diode bridge at the front-end. Other PFCs apply interleaving operation, where one converter is replaced by two or more paralleled converters each operating out of phase. This has a cancelling effect on the ripple current that results in lower filtering requirements.
PFC components are not complex—basically an inductor, power switch, diode and capacitor—but the market for these parts is competitive and there are many types of components within this design that can help maximize power efficiencies for specific applications. Paying special attention to inductor materials, keeping in mind the proper winding size for a given inductor, can make a difference in your PFC. The PFC diode is crucial because it carries significant current in operation. Ultrafast diodes can mitigate this problem, as well as diodes with soft-recovery characteristics. Recent advances in MOSFET technology have changed the options in choices of switch components. MOSFETs with low capacitance will reduce switching losses.
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As more systems hook into the power grid, power factor will increasingly become a concern for designs, both industrial and commercial. Thankfully, as the demands on power have grown, so have the engineering options in designing customized and effective PFC solutions.