1 Introduction
With the increasingly stringent requirements for global energy conservation, China has strongly supported energy-saving technological innovation and industrialization of energy-saving products. Light Emitting Diodes (LEDs) have emerged. At present, the use of LED lights can really save a lot of energy, but whether harmonics will be generated during use, affecting the quality of electrical energy is worth thinking about. This paper analyzes the actual measurement of urban LED street lamps and puts forward effective suggestions.
2 LED lighting characteristics and application range
It has been more than 30 years since the first LEDs entered the market in 1968. With the development of new materials and processes, LEDs tend to be brighter and full-color. The emergence of blue LEDs based on gallium nitride has expanded the field of application of LEDs. LEDs are all-solid cold light sources with small size, light weight, rugged construction, low operating voltage and long life. The power of a single LED is generally 0.05 to 1 W, but the clustering method can meet different needs.
In the field of lighting, the application of LED lighting products is attracting the attention of the world. As a new type of green light source, the 21st century will enter the era of new lighting sources represented by LED.
2.1 Advantages of LED light source
LED light sources have the following advantages:
(1) New green environmental protection light source: LED uses cold light source and does not produce harmful substances during use. LEDs have better environmental benefits, no ultraviolet and infrared rays in the spectrum, and waste can be recycled, no pollution, no mercury, safe to touch, and are typical green lighting sources.
(2) Long life: LED is solid cold light source, epoxy resin package, anti-vibration, no loose part in the lamp body, no shortcomings such as filament light-emitting, heat deposition and light decay, the service life can reach 60,000~10 Ten thousand hours, more than 10 times that of traditional light sources. Good LED products have stable performance and can work normally from -30 °C to 50 °C.
(3) Multi-variation: LED light source can use the three primary colors of red, green and blue. Under the control of computer technology, using 3 colors with 256 levels of gray and mixing them arbitrarily, 16 777 216 colors can be produced. The color combination of the LED combination is varied, enabling a variety of dynamic changes and various images.
(4) High-tech: LED light source is a low-voltage microelectronic product, which successfully combines computer technology, network communication technology, image processing technology and embedded control technology.
2.2 LED application
In recent years, the LED market has rapidly increased in scale, and the application fields have also expanded to various industries, including the following applications.
(1) Application in the display. At present, LED displays have been widely used in stations, banks, various types of exchanges and hospitals. In terms of LED demand, the LED display ranks second only to the LED indicator, accounting for 23.1% of the total LED sales. In addition, the full-color LED display is widely used in sports venues, municipal squares, stations and airports due to its unique advantages.
(2) Application in car lights. From the perspective of the entire LED application market, the market for applications in automobiles is still in its infancy and small in scale. LED as a car headlight mainly benefits from good orientation, low power consumption, long life and fast speed. Although LEDs currently face low power and related policy restrictions, it will take some time to enter the taillights and headlights market, but with the advancement of technology, LED lights will eventually open the market for automotive lights.
(3) Application in interior decorative lights. The interior decorative lighting market is another emerging market for LEDs. By controlling the current, LEDs can be varied in thousands of colors. The diversified characteristics of LED colors are very conducive to the development of the LED decorative light market. LEDs have begun to be used as small decorative lights and decorative curtain walls in hotels and living rooms.
(4) Application in landscape lighting. Due to the low power consumption of LED lamps, they are highly competitive in the landscape lighting market with large power consumption. LEDs are now increasingly used in landscape lighting.
3 Harmonic hazards
With the development of China's power grid, various non-linear transmission and distribution and power equipment have entered the power grid. These devices, even if the applied voltage waveform is purely sinusoidal, will be distorted in its current waveform. The main harmonic sources in the power system are various commutation devices, electronic voltage regulating devices, electric arc furnaces, induction furnaces, and various industrial power equipment for energy conservation and control.
Sub-equipment, as well as a variety of household appliances and lighting equipment.
Harmonic pollution of the electromagnetic environment of the power system will endanger the system itself and the vast number of power users. The hazard is very extensive. The main aspects are as follows:
(1) Generate additional losses and increase the temperature rise of the equipment. Compared with the fundamental current, although the proportion of harmonic current is not large, the effective resistance of the device will increase due to the skin effect. In the electrical equipment with iron core, the hysteresis loss and eddy current loss of the core will also Increase. In addition to increasing the loss of the power system, these additional losses also increase the temperature rise of the equipment, especially the temperature rise of the local heating point may increase more, and the insulation aging of the equipment is accelerated.
(2) Deteriorating insulation conditions and shortening the service life of equipment. In addition to the additional heating effect on the insulation life, it is also because the partial discharge of the insulation is intensified under the action of the electric field of higher frequency, and the loss is significantly increased, so that the temperature rise is increased. When the voltage distortion waveform has a cusp wave, the partial discharge intensity is also increased, thereby reducing the insulation life.
(3) May cause mechanical vibration of the motor. The pulsating torque generated by the interaction between the harmonic current and the rotating magnetic field of the motor may cause the motor to vibrate, but the natural frequency of the mechanical system of the motor may be damaged by the above-mentioned torque and may cause resonance, which may damage the motor equipment and cause a crisis. Safety.
(4) Interference and malfunction caused by relay protection, automatic control devices and computers. These protection and control devices are usually designed with power frequency and sinusoidal waveforms of voltage or current applied in the work. The presence of harmonics causes their normal working conditions to be disturbed, and in severe cases, it will cause malfunction.
(5) Affect the accuracy of the measuring instrument and cause errors in the energy metering.
(6) Interfering with the normal operation of adjacent communication lines and railway signal lines.
Of course, the degree of harmonic hazard will vary depending on the amount of harmonics and other various conditions of the device. However, the hazard is objective and should be given sufficient attention and effective monitoring and management. At the same time, it is also necessary to perform harmonic analysis and evaluation on the newly introduced power supply equipment and transmission and distribution equipment, especially the equipment to be widely used (such as the LED street lamp studied in this paper) before use.
As a substitute for traditional light sources, LED has received extensive attention for its energy saving, environmental protection, long life and high reliability. Especially in recent years, due to the sharp decline in the cost of developing high-power LED lamps, in the near future, The large-scale application of LEDs will be realized. However, while seeing the many advantages of LEDs, there is not enough relevant data for the study of power quality problems caused by large-scale applications, especially the impact of harmonics generated on the grid.
In this paper, for the large-scale application of LED street lamps, according to the latest national standard of power quality, advanced power quality measuring instruments are used to measure and analyze the harmonics generated by many different types of street lamps and compare them with LED street lamps. At the same time, combined with the requirements of power quality of urban power grid, a large amount of data was collected. On the basis of data analysis, the degree of influence of harmonics generated by large-scale application of LED street lamps on the power grid was given.