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Mobile WebSiteWith the national policy of continuous tilt to the distributed photovoltaic, photovoltaic innovation technology to improve, reduce the cost of electricity, state subsidies remain unchanged, investment in distributed photovoltaic power plants, is now very cost-effective. However, many people still have some trouble: the roof installed so many PV modules, inverter output so much current, there is no electromagnetic radiation, the human body and home appliances have no effect?
1, what is electromagnetic radiation
What is radiation? It refers to the object in the form of waves or particles to the surrounding space to launch energy process. All the objects in nature as long as the temperature above absolute zero, will be in the form of electromagnetic waves or particles kept to the outside world to send energy, in other words, the world has radiation, including the body itself, all the time in the outward radiation , Such as the sun, in fact, is to accept the sun's radiation. However, not all of the radiation is harmful, and some even inseparable from it, such as the sun's radiation - the sun, the earth's growth needs all the sun.
Although the electromagnetic radiation does not change the molecular nature of the organism, causing direct damage, but if the energy is large, will also have a certain impact on the organism, reflected in two aspects: thermal effects and induced current. Household equipment can also cause interference, such as cell phones, radios and televisions.
"Regulations on the protection of electromagnetic radiation" (GB8702-88) and "environmental electromagnetic health standards" (GB9175-88). The limit of electromagnetic radiation imposed by the provisions of: 50Hz frequency according to the size of the magnetic field strength as the standard calculation, the specific unit is μT, if the radiation is more than 0.4μT is a strong radiation, the human body has a certain harm. If the radiation is below 0.4μT, it is relatively safe. The radio frequency field is calculated as the standard of power density or field strength. The specific unit is μW / c m2 or V / m, 30-3000 MHz. The most sensitive range of the public is 40μW / c m2. In this standard, is safe.
2, the generation of electromagnetic radiation
According to the basic theory of electromagnetism, there will be a corresponding electric field distribution around the charged particles. The charged particles will change with time. If there is a potential difference between the two points with different potentials around the charged particles, Voltage; when a large number of charged particles move when the formation of the current, the current around the magnetic field, with time changes in the current will produce a change in the magnetic field. Similarly, the time-varying magnetic field can produce electric field, so that changes in the electric field and the magnetic field alternately produce, perpendicular to each other and continue to spread to the space, resulting in electromagnetic radiation. Electromagnetic radiation carried by the size of the energy depends on the frequency of the high and low frequency, the greater the energy.
3, the electromagnetic radiation of photovoltaic systems
PV system is composed of PV modules, brackets, DC cables, inverters, AC cables, power distribution cabinets, transformers and other components, which stent is not charged, naturally does not produce electromagnetic interference. PV modules and DC cables, which are DC current, the direction does not change, can only produce electric field, can not produce magnetic field. Although the output transformer is AC, but the frequency is very low, only 50Hz, the resulting magnetic field is very low. Inverter is the DC power into the AC equipment, there are power electronic transformation, the frequency is generally 5-20KHz, it will produce alternating electric field, it will also produce electromagnetic radiation. The state has strict standards for electromagnetic compatibility of photovoltaic inverters.
Radiation emission: Inverters used in low-voltage power supply facilities for domestic or direct connection to residential buildings shall meet the Class 1 class B limits for GB 4824-2004, as shown in the table below.
PV inverter electromagnetic radiation, compared with household appliances, and notebook computers about the same, lower than the induction cooker, hair dryer, refrigerator. So do not worry.
4, photovoltaic inverter EMC electromagnetic interference solution
PV inverter as a power electronic equipment, switching frequency is higher, the group of string inverter is usually about 20K, the current is relatively large, if not take measures, there will be a lot of electromagnetic interference. The usual methods are shielding, filtering and grounding three methods. Shield can effectively suppress electromagnetic interference through space propagation. The purpose of shielding is two, one is to limit the internal radiation electromagnetic energy outside the control area, the other is to prevent the external radiation electromagnetic energy into the internal control area, the inverter using aluminum or iron conductor all-metal package. Filtering is to control EMI conduction interference, usually using three devices to achieve: decoupling capacitors, EMI filters and magnetic components. Inverter input and output are X capacitors and Y capacitors, common mode inductors, magnetic beads, magnetic rings and other magnetic components. Regardless of the method used to suppress EMI interference, eventually through the ground to the electrostatic discharge, so the grounding of the inverter is very important. In addition to suppressing EMI interference, the ground also provides zero potential reference points and safety protection and so on.
Conducted emissions: Inverters used in home or direct connection to residential low voltage power supply facilities shall meet Class 1 Class B limits in GB 4824-2004.
Summary: PV system of electromagnetic radiation, relatively weak, the use of qualified equipment, will not cause harm to the human body, it will not cause interference to household appliances. PV modules are DC, do not produce radiation, the inverter radiation is strictly controlled within the safe range. Installation should pay attention to the following points: the inverter should not be installed in the bedroom and living room, try to install outdoors, ground (PE) must be connected, the corresponding grounding system device must be complete and in line with specifications.
