Factor de potencia
Abajo - Una carga inductiva con un factor de potencia menor que 1. La corriente está retrasada (detrás) de la fase de la tensión. El área sombreada en amarillo representa la energía no consumida que se envía de regreso a la fuente.
Hay varios tipos de carga de corriente alterna (CA), algunos de los cuales requieren tensión y corriente al mismo tiempo (cargas resistivas) y otros que requieren tensión y corriente en diferentes momentos (inductivo y capacitivo). El factor de potencia (PF) es un número entre -1 y 1 que se puede aplicar a cargas de CA para describir hasta qué punto su tensión y demanda de corriente (fases) están sincronizados. Una carga con un factor de potencia de 1 (gráfico superior a la derecha) tiene un pico de tensión y corriente simultáneamente en cada ciclo. Una carga con un factor de potencia de menos de 1 (gráfico inferior a la derecha) tiene un pico de tensión y corriente en diferentes momentos de cada ciclo.
El factor de potencia de las cargas se vuelve importante al dimensionar y seleccionar un inversor autónomo. Una carga con un factor de potencia de menos de 1 requerirá que el inversor suministre una corriente que exceda la potencia nominal del aparato para que funcione correctamente. Esta corriente no se incluye en la potencia nominal del aparato, ya que no es consumida por la carga y se devuelve a la fuente. Por lo tanto, el factor de potencia solo se tiene en cuenta para dimensionar el inversor, pero no es relevante al dimensionar el fuente FV o el sistema de almacenamiento de energía.
Contents
Calculando el factor de potencia
Existen diferentes tipos de potencia que se utilizan para determinar el factor de potencia de una carga.
Power factor (PF) = Real power ÷ Apparent power
- Real power is power that is used to perform work. This power is consumed and is measured in watts (W).
- Reactive power is power that is power that does not perform work but is still present in a circuit. This power returns to the source and is measured in volt-amperes or volt-amps (VA).
- Apparent power is the total power present in a circuit. Apparent power is the sum of real power and reactive power. Measured in volt-amperes or volt-amps (VA).
If the current and voltage of a circuit are measured for a circuit with a multimeter and multiplied this will be a measurement of apparent power. Devices specifically designed to measure power consumption, like a Kill-A-Watt meter, can measure real power.
Examples of different load types
Common resistive loads are incandescent light bulbs or an electric heater. These loads will have a power factor of 1, which is also referred to as unity power factor.
- Example 1: A 40 W incandescent bulb is operating on a 120V AC circuit. You measure the current and get .3 A. What is the power factor for this light bulb?
- Power factor = 40 W ÷ (120 V × .3 A) = 1
- All power is consumed by the load.
Common inductive and capacitive loads are fans, televisions, radios, laptops, blenders, refrigerators, and LED lighting. These loads will have a power factor less than 1.
- Example 2: A 20 W laptop is operating on a 120 V AC circuit. You measure the current and get .3 A. What is the power factor for this laptop?
- Power factor = 20 W ÷ (120 V × .3 A) = .5
- 20 W is consumed by the load the rest is reactive power that returns to the source.
Power factor estimates
Power factor values vary significantly between makes and models of appliances and it can be quite difficult to find specific values. The values in the chart below are conservative estimates.
| Load | Estimated power factor |
|---|---|
| LED bulb | .45 |
| Radio | .9 |
| Cell phone charger | .45 |
| LED TV | .55 |
| Laptop charger | .5 |
| Refrigerator | .5 |
| Blender | .8 |
| Printer - idle | .4 |
| Printer - printing | .65 |
| Electric water heater | .97 |
| Fan | .87 |
| Microwave | .9 |
| Projector | .9 |
Notes/references
- Power Studies: Power Factor — The Basics https://www.powerstudies.com/sites/www.powerstudies.com/files/Power%20Factor%20Basics%20Article.pdf
- American Council for an Energy Efficient Economy - Power Factor Requirements for Electronic Loads in California https://www.aceee.org/files/proceedings/2014/data/papers/9-959.pdf
- Ali Ahmadab, Syed Abdul Rahman Kashif, Muhammad Asghar Saqibb, Arslan Ashrafa, Umar Tabrez Shamib. Tariff for reactive energy consumption in household appliances from Energy Volume 186, 1 November 2019, 115818
