The low power factor of a single-phase circuit will lead to a decrease in equipment efficiency and an increase in line loss. To control the power factor, we need to analyze the causes and take targeted measures. The following are common control methods:
I. Common causes of low power factor
1. Mainly inductive loads
Equipment such as fluorescent lamps, motors, transformers, etc., need to consume reactive power during operation, resulting in a low power factor (usually less than 0.8).
2. Light load or no load
When the actual load of the equipment is far lower than the rated power (such as "a big horse pulling a small cart"), the proportion of reactive power increases and the power factor decreases.
3. Harmonic influence
Non-linear loads (such as inverters, switching power supplies, LED lights) generate harmonics, resulting in voltage and current waveform distortion and deterioration of the power factor.
II. Power factor control measures
1. Reactive compensation (the most direct and effective)
Through parallel capacitors or dynamic reactive compensation devices, capacitive reactive power is provided to offset the reactive demand of the inductive load and improve the power factor.
a. Fixed capacitor compensation
Applicable scenarios: occasions with stable load and small changes in reactive power demand (such as household single-phase motors and small office equipment).
Advantages: low cost, simple structure, and easy maintenance.
Disadvantages: unable to track load changes, may over-compensate (causing power factor to advance).
Installation method: connect the capacitor in parallel at both ends of the inductive load or in the distribution box, and pay attention to the matching of the capacitor rated voltage with the circuit (such as 220V single-phase system).
b. Dynamic reactive power compensation (such as thyristor switching capacitor)
Applicable scenarios: occasions with frequent load changes (such as welding machines, frequency conversion equipment).
Advantages: capacitors can be automatically switched according to real-time reactive power demand to avoid over-compensation.
Disadvantages: high cost and need to be equipped with a controller.
2. Choose high power factor equipment
a. Replace inefficient equipment: replace traditional equipment with energy-saving inductive loads (such as high power factor fluorescent lamps and permanent magnet synchronous motors).
For example: the power factor of ordinary fluorescent lamps is about 0.5, while energy-saving fluorescent lamps with electronic ballasts can reach more than 0.95.
b. Give priority to resistive or capacitive loads: such as electric heating equipment and LED lamps (high power factor models need to be selected to avoid harmonic products).
3. Reasonably match the load to avoid light load operation
a. Adjust the capacity of the equipment: select equipment with appropriate power according to the actual load to avoid "a big horse pulling a small cart".
Example: If the actual power of a single-phase motor is 0.5kW, select a model with a rated power of 0.75kW instead of 1.5kW.
b. Parallel operation or time-sharing use: For light-load equipment, multiple low-power devices can be connected in parallel to replace a single high-power device, or no-load operation can be avoided (such as turning off idle electrical appliances in time).
4. Harmonic control (for non-linear loads)
a. Install harmonic filters: Install LC filters or active power filters (APF) at the front end of non-linear loads (such as inverters and switching power supplies) to suppress harmonic currents and improve power factors.
b. Isolate non-linear loads: Power non-linear loads and inductive loads separately to avoid mutual influence of harmonics.
c. Select low-harmonic equipment: Give priority to electrical appliances that meet harmonic limit standards (such as IEC 61000-3-2), such as switching power supplies with PFC (power factor correction) circuits.
5. Optimize line layout and maintenance
a. Shorten power supply distance: Reduce line impedance and reduce reactive power loss in the line.
b. Regularly maintain equipment: Clean dust from motors, transformers and other equipment to ensure their operating efficiency and reduce reactive power loss caused by equipment aging.
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Single-phase power factor control needs to be combined with load characteristics, with reactive compensation as the core, supplemented by equipment upgrades, harmonic control and load optimization. For ordinary users, priority is given to simple and easy capacitor compensation and replacement of high-efficiency equipment; for industrial or complex scenarios, professionally designed dynamic compensation and harmonic suppression solutions are required to achieve safe and economical governance effects.