In recent years, Beijing's rapid economic development and the rapid improvement of people's living standards have put forward new requirements for power supply. In order to promote urban development and improve the quality of power supply, the power supply department will continue to build high-voltage substations in bustling commercial areas or residential areas.
High-voltage substation will produce certain intensity of electromagnetic radiation, including high-frequency radiation and power frequency radiation. Radiation pollution may affect human health and the reception of useful signals. In order to determine whether the establishment of high-voltage substations in densely populated areas may affect the quality of life of residents, and to what extent, the design institute of Beijing Power Supply Bureau cooperated with Tsinghua University Electric Machinery Department to measure and analyze the electromagnetic radiation in and around several typical types of high-voltage substations, obtained the characteristics of electromagnetic radiation, understood the location, causes and reduction measures of interference, and judged whether the radiation intensity of each frequency band met the national safety standards. It provides a basis for the design of urban substations and the selection of power equipment in the future, and can also provide a reference for improving environmental conditions, and at the same time, it can alleviate the unnecessary fear of electromagnetic radiation of some residents around high-voltage substations.
2. National safety standards and safety reference standards for electromagnetic radiation.
2. 1 National Safety Standard for High Frequency Electromagnetic Radiation
China's Hygienic Standard for Environmental Electromagnetic Waves (GB9 175-88) stipulates the standard limits of electromagnetic field pollution and protection in normal natural environment, as shown in Table 1.
In order to prevent and reduce the harm of electromagnetic radiation to human health, China's electromagnetic radiation protection standard (GB8702-88) stipulates the limits of environmental electromagnetic radiation for occupational exposure and public exposure.
At the same time, China stipulates that in sunny weather, the transverse distance of 20m outside the RF radiation equipment should be measured according to the specified measurement method, and the interference level of each frequency band should not be greater than 50 dB (the value is lower than that specified in GB8702-88).
2.2 power frequency electric field radiation safety reference standard
Operating high-voltage equipment, especially near transmission lines, will produce power frequency electric fields, and the main effects on human body are electric shock and long-term ecological effects. When a human body at ground potential touches an object insulated from the ground, it may cause a painful electric shock. In recent decades, a great deal of scientific evidence published at CIGRE shows that electric fields below 20 kV/m have no harmful effects on health. However, it cannot be concluded that there is absolutely no danger in long-term exposure to electric fields. Therefore, many countries put forward the safety limit standard of electric field intensity, as shown in Table 2.
At present, there is no safety limit standard for power frequency electric field strength in China. This paper will take the most stringent standard (2.5 kV/m) of developed countries (Japan and the United States) as a reference. The safety reference standard of power frequency electric field mentioned later in this paper refers to this standard.
Compared with the local magnetic field of household appliances, the power frequency magnetic field generated by general high-voltage equipment in operation is very weak, so it can be considered that the power frequency magnetic field has much less influence on human body in electric shock and long-term ecological effect.
Table 1 Hygienic standard limits of environmental electromagnetic waves Table 2 Safety limits of electric field intensity in various countries
Frequency range (Hz) allowable limit (dB)(μV/m)
Level 1 (safety zone) Level 2 (middle zone)
30k~300M < 140 < 145
30M~300M < 130 < 140
300 meters to 300 grams < 135 < 150.
National restrictions and regulations
5 kV/m in the former Soviet Union? An area that is not residential but may be close to residential areas.
10 kV/m? An area with unlimited residence time.
15kV/m? Crossing roads and generally accepted areas
Japan 3 kV/m? An area accessible to the public.
2.5 kV/m in the United States? Commercial and residential areas
3.5 kV/m？ The parking lot opposite the shopping center.
3. Work function
The main research contents of this paper include: according to the requirements of cooperation between Beijing Power Supply Design Institute and Tsinghua University Electric Machinery Department, typical 220/ 10/ 10kV substations (Beitucheng Substation, Zhichunli Substation and Fucheng Substation) with different arrangements for outdoor, indoor and semi-indoor open electrical equipment, closed combined electrical appliances, bare wire connection and cable connection, and closed pipelines. The buildings in different positions under 220 kV bus (Zhichunli Substation) and their nearby buildings were tested to study their electromagnetic radiation characteristics (including radiation intensity and its variation law, frequency range, waveform characteristics and influencing factors, etc.). ), understand the location, causes and reduction measures of interference, and judge whether the radiation field intensity of each frequency band meets the national safety standards.
In this paper, in the frequency band of 150 kHz ~30 MHz, the RR2B field strength jammer produced by Beijing Radio No.2 Factory is selected to measure the electric field strength with a rod antenna. In the frequency band of 30 kHz ~500 MHz, RR3A field strength interferometer produced by Beijing Radio No.2 Factory is selected to measure the electric field strength with dipole antenna, which requires that radiation waves in all polarization directions can be measured. In the power frequency range, the electric field intensity is measured by using the self-developed PFE 1 power frequency electric field measuring instrument and plane measuring electrode.
4. Field measurement of electromagnetic radiation in high voltage substation and its surroundings
4. 1 Beitucheng Substation
Beitucheng Substation adopts indoor 1 10/ 10 kV oil-immersed main transformer, indoor 1 10 kV fully enclosed combined electrical appliance and10 kV open bus. See Figure 1 for the plane layout and measuring point distribution of Beitucheng Power Station.
The analysis of the field measurement data of Beitucheng substation shows that:
(1) The power frequency field strength is very low, mostly in the range of 200V/m, due to the shielding effect of the combined electrical apparatus, the shell of the main transformer and the surrounding walls. At the height of 1.7m, the electric field intensity closest to the main transformer is not the maximum in this direction. On the contrary, it forms a depression with the amplitude of radiation field intensity and reaches the maximum at the horizontal distance of 0.6m from the shell of 1# main transformer.
(2) The maximum power frequency electric field intensity in the substation (referring to the height from the ground 1.7m) is located at the distance 1# horizontal distance of the main transformer shell 1.7m (southwest direction) (point E), just below the bare conductor10kV.
(3) The power frequency radiation under the 10 kV hard bus inside and outside the substation is very small.
(4) In the measuring frequency range, the high-frequency interference radiation with intensity exceeding 20 dB can hardly be measured inside and outside the substation; However, in comparison, the closer to the substation, the greater the background noise of the radio signal, and the worse the reception effect. Outside the range of 10m, the reception is basically unaffected.
(5) The outdoor power frequency radiation and high frequency interference radiation of the substation are within the safe range of residential areas stipulated by national standards and reference standards.
Figure 1 Layout of Beitucheng Substation and Distribution of Measuring Points? Note: A, B and C are 1#, 2# and 3# main transformers respectively; F, G are 10kV arc suppression coil, and E is capacitor; D is a metal mesh door with a height of 2m; ①, ②, ③ and ④ are 6m, 10m, 15m, 20m away from the metal gate respectively. The first floor of the office building of Beijing Power Supply Design Institute is 10kV switch room and10kv switch room. Fig. 2 Layout of Fuchengmen Substation and Distribution of Measuring Points
4.2 Electromagnetic Radiation Measurement of Fuchengmen Substation
Fuchengmen Substation adopts outdoor 1 10/ 10 kV oil-immersed main transformer, indoor 1 10 kV fully enclosed combined electrical appliance, 1 10 kV bus cable closed connection, open arc suppression coil and metal mesh shielding. The layout of the substation and the distribution of measuring points are shown in Figure 2.
The field measurement data analysis of Fuchengmen substation shows that:
(1) Fuchengmen Substation 1 10 kV electrical equipment is fully enclosed, and even the equipment joints are sealed with oil-immersed pipes, which effectively reduces the electromagnetic radiation (including power frequency and high frequency) of substation equipment. It can be seen that the power frequency radiation field strength of Fuchengmen substation (generally less than 20V/m, the maximum 145V/m) is obviously less than that of Beitucheng substation (generally about 200V/m, the maximum is 2 100V/m).
(2) High-frequency interference radiation has regularity, which is influenced by two factors, one is the distance between measuring points, and the other is the shielding of metal mesh. It can be seen that the radiation intensity of the interference radiation wave gradually increases after bypassing the dead angle formed by the metal mesh shielding, and the dead angle range is about 10m outside the metal mesh. Therefore, the interference radiation reaches the maximum at 15m outside the metal mesh. Then the distance of the measuring point plays a leading role, and the interference radiation gradually decreases with the increase of the distance, as shown in Figure 3.
(3) Affected by the refraction and reflection of surrounding buildings, the interference radiation intensity of Fuchengmen substation in each high frequency band is generally higher than that of Zhichunli substation, which is relatively empty and has relatively little influence of refraction and reflection.
(4) The power frequency radiation and high frequency interference radiation inside and outside the substation are within the safe range of residential areas stipulated by national standards and reference standards.
Fig. 3 High frequency interference radiation in Fuchengmen substation? Figure 4 Layout of Zhichunli Substation and Distribution of Measuring Points
4.3 Power Frequency Field Intensity Measurement of Zhichunli Substation
Zhichunli Substation adopts outdoor 220/110/0kV oil-immersed main transformer, indoor 1 10kV open power distribution device and outdoor 220 kV open power distribution device. The layout and measuring point distribution of Zhichunli substation are shown in Figure 4.
The measurement results of power frequency radiation field strength of substation are as follows:
(1) The maximum field strength at the height of 1.3m from the ground is 1)220kV/m, and the maximum field strength at the height of 1.7m from the ground is1.7m. The maximum field strength at the height of 1.3m from the ground is1220kV/m, and the maximum field strength at the height of 1.7m from the ground is 26 15V/m (see point B in Figure 4).
(2) The power frequency electric field of the south window of the dormitory building on the north side of 2)220kV bus shows strong regularity. As can be seen from Figure 5, the power frequency electric field intensity gradually increases from 1 floor, reaches the maximum when the fifth floor is as high as the transmission line, and then decreases, which is basically consistent with the analysis.
(3) The power frequency radiation of the south window is obviously higher than that of Nanyang Station, because there are about 2m cement walls on the east and west sides of Nanyang Station, which have a significant shielding effect on power frequency radiation; In the south window, the field intensity at 0. 1m outside the window is more than 1 times higher than that in the window plane, the field intensity at 0. 1m inside the window is less than 5%, and the field intensity at 1m inside the window is less than 50%. In the North House, the power frequency radiation has been reduced to an almost unmeasurable level due to the shielding of multi-layer walls.
(4) The power frequency intensity inside and outside the residential building next to the bus is within the safe range of residential areas stipulated by national standards and reference standards, and will not have any adverse impact on human health and the normal life of residents; However, in some places, the maximum field strength is close to the safety reference standard of 2.5 kV/m. If there are ungrounded metal objects (metal clothes hangers, metal window bars, etc.). ) from the building, because of the strong power frequency field strength, people may get an electric shock (spark discharge) at the moment of contact with them. In order to avoid this phenomenon, metal objects should be grounded reliably.
The radiation intensity of high frequency interference in substation is lower than 50dB, which meets the national radio interference control index.
4.4 Influence of Humidity on High Frequency Radiation
4.4. 1 High-frequency radiation measurement of Zhichunli substation under different humidity conditions
The layout and measuring point distribution of Zhichunli substation are shown in Figure 4. The results are shown in Table 3.
In the same measuring position, under different humidity conditions, it may also be because high-frequency radiation is affected by other factors (such as equipment operation, etc.). ), and the radiation intensity is not regular.
4.4.2 Measurement of high-frequency electromagnetic radiation under different humidity in laboratory environment
In the shielding room of high-voltage laboratory, high voltage is applied to the new thin copper bare wire to produce corona discharge.
The measurement results of high-frequency radiation in laboratory environment under different humidity and shielding conditions are shown in Table 4.
The interference field strength of other frequencies is lower than 10dB in the range of 30MHz ~500MHz.
The experimental results show that the influence of humidity on high frequency radiation is irregular.
Table 3 Field strength (DB) at measuring frequency (MHz) 1 # main transformer 10m and field strength (dB) at 30m of 2 # main transformer under different humidity.
Humidity 92% Humidity 46% Humidity 92% Humidity 46%
5.3 47