Power Factor. For a DC circuit the power is P=VI, and this relationship also holds for the where φ is the phase angle between the voltage and current. This geometric relationship between resistance, reactance and impedance can be . Power factor defines the phase angle between the current and voltage. Power Factor is a measure of an electrical systems efficiency The apparent or The apparent or total electrical power (Kilo Volt Amperes or kVA) used in an in DC Circuits, there is no concept of phase angle between current and voltage.
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.
The filter consists of capacitors or inductors, and makes a non-linear device look more like a linear load. An example of passive PFC is a valley-fill circuit.
A disadvantage of passive PFC is that it requires larger inductors or capacitors than an equivalent power active PFC circuit. Active power factor correction 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 switched-mode 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 a three-phase SMPS, the Vienna rectifier configuration may be used to substantially improve the power factor. That feature is particularly welcome in power supplies for laptops.
Dynamic PFC[ edit ] Dynamic power factor correction DPFCsometimes referred to as "real-time power factor correction," is used for electrical stabilization in cases of rapid load changes e. DPFC is useful when standard power factor correction would cause over or under correction. Importance of power factor in distribution systems[ edit ] 75 Mvar capacitor bank in a kV substation Power factors below 1.
Calculating Power Factor | Power Factor | Electronics Textbook
This increases generation and transmission costs. For example, if the load power factor were as low as 0. Line current in the circuit would also be 1.
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. When the power factor is close to unity, for the same KVA rating of the transformer more load can be connected .
Utilities typically charge additional costs to commercial customers who have a power factor below some limit, which is typically 0. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission.
With the rising cost of energy and concerns over the efficient delivery of power, active PFC has become more common in consumer electronics.
- Calculating Power Factor
- Power Factor
According to a white paper authored by Intel and the U. Small customers, such as households, are not usually charged for reactive power and so power factor metering equipment for such customers will not be installed. The same could be said for a purely capacitive circuit. If there are no dissipative resistive components in the circuit, then the true power must be equal to zero, making any power in the circuit purely reactive. The power triangle for a purely capacitive circuit would again be a vertical line pointing down instead of up as it was for the purely inductive circuit.
If our last example circuit had been purely resistive, we would have been able to deliver a full The poor power factor makes for an inefficient power delivery system.Understanding the Power Triangle and Power Factor
Inductive reactance can only be canceled by capacitive reactanceso we have to add a capacitor in parallel to our example circuit as the additional load. Since we know that the uncorrected reactive power is Figure below Parallel capacitor corrects lagging power factor of inductive load. V2 and node numbers: The power factor for the circuit, overall, has been substantially improved.
The main current has been decreased from 1. The power factor is much closer to being 1: Since the impedance angle is still a positive number, we know that the circuit, overall, is still more inductive than it is capacitive. If our power factor correction efforts had been perfectly on-target, we would have arrived at an impedance angle of exactly zero, or purely resistive. If we had added too large of a capacitor in parallel, we would have ended up with an impedance angle that was negative, indicating that the circuit was more capacitive than inductive.
Power factor - Wikipedia
The SPICE circuit file has a zero volt voltage-source V2 in series with the capacitor so that the capacitor current may be measured. The start time of msec instead of 0 in the transient analysis statement allows the DC conditions to stabilize before collecting data. The reference is Vtotal, to which all other measurements are compared. This is because the applied voltage, Vtotal, appears across the parallel branches of the circuit.
There is no single current common to all components. We can compare those currents to Vtotal. Zero phase angle due to in-phase Vtotal and Itotal. Note that the total current Itotal is in phase with the applied voltage Vtotalindicating a phase angle of near zero. This is no coincidence.