به عنوان یک فناوری جدید پیشرفته پویا هارمونیک پیشرفته, در فیلتر برق فعال دارای پیشرفته مبتنی بر فناوری است, که در بسیاری از زمینه ها به طور گسترده مورد استفاده قرار گرفته است. هنگام راه اندازی فیلتر برق فعال, لازم به ذکر است که سیستم فیلتر فعال فعال باید به قطع کننده مدار و ترانسفورماتور جریان CT وصل شود.
اما نحوه محاسبه اندازه فیلتر برق فعال برای یک پروژه واقعی? Coepower بر اساس تجربه دهه های ما در این زمینه راه حل کیفیت قدرت ، برخی از مرجع ها را برای شما خلاصه کرده است.
1. روش طراحی
در کل, برای پروژه های جدید, Users can configure the APF capacity according to the following reference.
Firstly understand the distribution system of the drawing, estimate the harmonic current value, select the capacity of APF according to the harmonic current value; then select the corresponding APF model according to this capacity; and then determine the installation location and installation method according to the product size; and finally reflect the product model on the drawing to complete the type selection process. Details can be done following the following procedures:
（1）Capacity select
（2）Model Select
（3）Dimension confirm
（4）Drawing on the schematic
1.1 انتخاب ظرفیت
This step is mainly to determine the installation capacity of APF. During the design, طراح الکتریکی ابتدا مقدار مؤثر جریان هارمونیک سیستم توزیع برق را تخمین می زند.
فرآیند دقیق دقیق مرحله طراحی ظرفیت به شرح زیر است:
محاسبه مقدار جریان هارمونیک با عوامل زیادی درگیر است. برای محاسبه مقدار جریان هارمونیک, ما یک ابزار ویژه تجزیه و تحلیل کیفیت قدرت را پیشنهاد می کنیم. هر چند, برای پروژه های جدید, فقط در مرحله طراحی, طراحان الکتریکی نمی توانند به اندازه کافی داده های الکتریکی داده هارمونیک را بدست آورند, این را در نظر بگیرید, ما APF را برای این نوع پروژه جدید بر اساس تست و تجربه خلاصه بسیاری از صنایع پیکربندی می کنیم, فرمول تجربه برای طراحان برقی در انتخاب طراحی به عنوان مرجع. با استفاده از فرمول زیر ، الزامات طراحی را برای انتخاب APF با توجه به جریان هارمونیک محاسبه شده مطابقت می دهد.
1.2 حاکمیت متمرکز
Formula -1:
Noted:This formula is Suitable for centralized treatment on the secondary side of the transformer.
Formula data explanation：
S : Transformer capacity；
U : Transformer secondary side rated voltage；
K : Load Rtaio；
IHR: Harmonic Current；
قصبهمن : Total Harmonic Current Distortion ratio
The taken value range:
1）K Represents the load rate of the transformer，The taken value range of transformer design is 0.6-0.85。
2）THDI Is the only variable value in the formula above formula，Its range of value depends on different industries and industry loads.
1.3 Local governance
The above formula is determined for the centralized treatment of the harmonic on the secondary side of the transformer. Here, it is recommended to treat the harmonic at the secondary side of the transformer, همچنین می توان آن را به صورت محلی در انتهای ورودی بار درمان کرد. محاسبه با استفاده از فرمول قابل انجام است 2 زیر.
در این فرمول, در نشان دهنده جریان امتیاز APF. the فرمول فوق فقط بار در حال اجرا با بار کامل را در نظر می گیرد (k = 1).عملیاتی واقعی k aavalues باید در طراحی در نظر گرفته شود, همانطور که در فرمول 3.
1.4 حکومتی جزئی
اگر ظرفیت دانستن را بدانیم / قدرت, سپس مقدار جریان هارمونیک را می توان محاسبه کرد. به عنوان مثال, ظرفیت بار کل (قدرت) در زیر شاخه A P قرار دارد (و در اینجا می تواند یک دستگاه واحد یا چندین دستگاه باشد), سپس جریان هارمونیک را می توان با فرمول محاسبه کرد 4.
فرمول 4:
کجا, U N نشان دهنده ولتاژ رتبه بندی شده است (ولتاژ خط) از دستگاه. P نشان دهنده کل ظرفیت است (قدرت).K نشان دهنده نرخ بار است.
توضیح فرمول:
(1) THDI را انتخاب کنید
همانطور که از تجزیه و تحلیل بالا می بینیم, that THDi is the main variable value need to be confirmed, and then this value can be determined based on the harmonic analysis in Chapter.
(2) Quick model select
Quickly selected can according to formula _ 1-4 of the industry summary of various industry harmonics ,and then in Table 3.9.
2 .انتخاب محصول:
Refer to the harmonic current value calculated in Section 1.1 to determines the capacity to be installed according to the model of APF.The APF installation capacity can be determined according to Formula 5,The coefficient is to maintain the capacity reductant
Formula-5:
Among these, the IA presents the installation capacity of the APF.The IHR represents the harmonic current value.
See the product selection section in the product introduction in Chapter 4 for detailed product selection.Among these, the IA presents the installation capacity of the APF.The IHR represents the harmonic current value.
2.1 برنامه های ارتفاع زیاد
با توجه به استاندارد صنعت مکانیکی JB/T7573-94, ما نتیجه می گیریم که قوانین تأثیر اصلی زیر شرایط آب و هوایی فلات به شرح زیر است: فلات شرایط آب و هوایی طبیعی سخت دارد, مشخص شده توسط:
بوها,فشار هوای کم یا تراکم هوای کم;
شرح,دمای هوا کم است و درجه حرارت بسیار تغییر می کند;
جف, رطوبت مطلق هوا کم است;
د, روشنایی اشعه خورشیدی زیاد است;
اشمیه, بارش کمتر;
ج, روزهای بادی بیشتر;
جف,دمای خاک کم است, و دوره انجماد طولانی است.
این خصوصیات تأثیرات اصلی زیر در عملکرد محصولات الکتریکی دارد:
1） تأثیر بر استحکام محیط عایق
کاهش فشار هوا یا تراکم هوا باعث کاهش قدرت عایق خارجی می شود. در ارتفاع 5000 متر, هر افزایش 1000 متر,این است, the average air pressure decreases by 7.7 to 10.5kPa,The external insulation strength is reduced by 8%~13%.The impact of the low air pressure on the equipment is mainly manifested in the decline of the external insulation performance to the electrical equipment: when the altitude rises, the air density decreases, the heat dissipation conditions deteriorate, and the temperature rise of the high pressure components increase during operation.The rated current can be maintained the same, but the air insulation strength is weakened, which makes the external insulation strength of the components also weakened, easy to occur such as insulation breakdown or flash collaterals destructive discharge accidents.
2）Effect on medium cooling effect,product temperature rise
کاهش فشار هوا یا تراکم هوا باعث کاهش اثر خنک کننده متوسط هوا می شود. برای محصولات الکتریکی با همرفت طبیعی, تهویه اجباری یا رادیاتور هوا به عنوان حالت اصلی اتلاف گرما, افزایش دما به دلیل کاهش توانایی اتلاف گرما افزایش می یابد. در ارتفاع 5000 متر,هر افزایش 1000 متر,این است, the average air pressure decreases by 7.7 to 10.5kPa,وسوسه افزایش می یابد 3%-10%.
بوها、میزان افزایش دما لوازم الکتریکی استاتیک با افزایش افزایش می یابد, هر افزایش 100 متر به طور کلی در 0.4K است, اما برای لوازم گرمایش زیاد, مانند کوره برقی, مقاومت, دستگاه جوشکاری, میزان افزایش دما با ارتفاع به بیش از 2 k در هر 100 متر.
شرح、 افزایش دما ترانسفورماتور برق به حالت خنک کننده مربوط می شود. نرخ افزایش در هر 100 متر است: غوطه وری, 0.4% از افزایش درجه حرارت درجه; خودکشی خشک, 0.5% از افزایش درجه حرارت درجه; غوطه وری نفتی خنک کننده هوای اجباری, 0.6% از افزایش درجه حرارت درجه; خنک کننده هوای اجباری خشک, 1.0% از افزایش درجه حرارت درجه;
جف、 افزایش دما موتور با ارتفاع افزایش درجه حرارت افزایش یافته است 1% در هر 100 متر.
خلاصه: برای استفاده از فیلتر برق فعال در سطح ارتفاع بالای 1000 متر,هر افزایش 100 متر, ظرفیت APF باید توسط کاهش یابد 1% .
2.2 تأیید بعد
پس از تعیین ظرفیت و انتخاب محصول تأیید شد, مکان نصب و روش نصب را می توان با توجه به APF انتخاب شده برای برآورده کردن نیازهای سایت انتخاب کرد. / روشهای نصب کابینت عمودی برای ظرفیت بزرگ نصب.
2.3 نقاشی
پس از تعیین ظرفیت و اندازه, طراحی APF می تواند نمودار سیستم توزیع را انتخاب کند. نصب APF نصب, لوازم جانبی زیر مورد نیاز است:
ترانسفورماتور فعلی (CT), circuit breaker.The CT and circuit breakers need to be shown on the drawings.See Chapter 4 for product selection for the host size and accessories.
2.4 Design procedure reference
Capacity design and product selection：
Selection type is distribution system of a hospital: rated capacity of transformer is 1000kVA, transformer ratio is 10 / 0.4 kV.The K value is 0.8 and the THDi value is 20% (according to the harmonic analysis in Chapter 3) ,and is available according to Formula 1 (the design method in Chapter 1)：
Harmonic current is 226A，we calculate according to this formula and also give some reductant capacity，hence ,we selected APF 4L/250-0.4（APF Capacity is 250A，rack mounted installation method）
تأیید بعد：Harmonic current is 226A，we calculate according to this formula and also give some reductant capacity，hence ,we selected APF 4L/250-0.4（APF Capacity is 250A，rack mounted installation method）。
APF Adopt a modular design.A total capacity of 250A, is composed of two modules with a parallel capacity of 100A, and a capacity of 50A.The parallel machine system needs to be equipped with an active filter cabinet, the configuration cabinet size is 800（W）×800（D）×2000（H）mm 。
To meet the site requirements, we can also choose the same type of distribution cabinet as the low voltage distribution sets (but must meet the width ≥ 600mm).Unified color standard and appropriate adjust cabinet size according to user requirements to make the overall distribution unified.For example, in this case, select the GCS model power distribution cabinet with 800 (W) × 800 (د) × 2200 (سخنرانی) mm.
Product selection
Instructions:Figure 2.2 APF 3P4L Product
1、 APF can be applied in three phase four wire system（such as model select 2.2），select based on real power distribution system.
2、 For three-phase four wire products, need three units CT, The CTS shall be installed on A, شرح, C three phase, as in this example; we adopt CT with 5A at secondary side,XXXX/5.
3、 CT access point：If there is capacitor banks in presence of the system,the CT access point should be connected between capacitor banks and the load,in other words,the CT should be connected downstream of the capacitor banks.Just like the 2000A/5A CT Access point in this example.
4、 The CT on the APF input side in this case is not the principle of the APF system, it’s only to ensure the consistent cabinet type.
5、 Installation location of CT and APF output cables:
There is no big difference in the the individual signle wall mounted APF module system.However, In the parallel system, the installation point of the CT is closer to the load side relative to the access point of the power cable (من. e., the connection point of the circuit breaker), called the CT load side connection method.It’is recommended to adopt the CT load side connection method for both single and parallel systems.
2.5 دستورالعمل برای انتخاب
1、 The APF, circuit breaker and CT constitute the whole APF system, so these three must be well reflected in the type selection.
2、 For APF/CT/Circuit Breaker selection of the above three, see product selection in Chapter 4.
3、 If have any doubt about selection,please contact us for explanation.
3. Harmonic Analysis
In an ideal clean power system, both voltage and current are pure sinine waves.In fact, a non-sinusoidal current forms when the current flows through the load where the power supply is not linear to the added voltage.This type of nonlinear load is collectively known as harmonic source loads.
Fourier analysis of the periodic nonsinusoidal current yields a superposition of a series of sine wave currents at different frequencies, except for the power of the base wave frequency, whose full multiple of the base wave frequency is called the harmonic.
The order of harmonics is the ratio of harmonic frequency to base frequency (n=fn/f1), such as 150Hz is called 3 harmonics and 250Hz is called 5 harmonics
Harmonic current causes problems both in the power system and in the device.The following problems are mainly caused by harmonic: high voltage distortion; over zero noise; neutral line overload; overheating of transformer and induction motor; circuit breaker error; correct overload damage of power factor capacitor; and skin collection effect.
3.1 ساختمان اداری
3.1.1 Industry introduction
In recent years, modern office buildings are developing rapidly into building automation, the number and proportion of non-linear load power equipment in the electricity equipment are rapidly increasing, and the power quality pollution to the urban power grid is increasingly serious.Among these large number of automation equipment, common nonlinear loads are: video display equipment (CRT and LCD display equipment), computer equipment, air conditioning, all kinds of energy saving lighting equipment (fluorescent lights, various high pressure gas discharge lights, dimlights, و غیره), office electrical equipment (printers, copiers, scanner, projector, و غیره), speed control drive (frequency conversion pump, air conditioning compressor, large elevator).These will all become the harmonic distortion perturbation source of the low-voltage power supply system.
Office Building power distributionsystem has many single-phase equipment and high nonlinear load ratio.The main power quality problems include:
1) A large number of zero sequence third harmonic current injected into the power grid, so that the third harmonic voltage of the low-voltage power supply bus seriously exceeds the national standard limit, and affects the safe and normal operation of the low-voltage electrical equipment, especially the harmonic-sensitive equipment.
2) The current on the neutral line is too high (zero sequence current will be superimposed on the neutral line, mainly third harmonic current), resulting in neutral line heating and increased line damage, while the wire used in the design is thin, so it is prone to cause fire hazard due to high temperature.
APF targets at the characteristics of zero sequence harmonics pooling on the neutral line, and the filtering capacity of the neutral line reaches three times of the phase line, effectively reducing the neutral line current and improving safety reliabilit
3.2 Medical institutions
3.2.1 معرفی صنعت
Medical technology equipment is the key harmonic source: mainly NMR equipment and accelerators.The harmonic spectrum of NMR equipment is very complex. The typical spectrum is concentrated in 3,5,7 and 9 orders, and the harmonic spectrum range is from 3 ~ to 43 orders.The typical spectrum of Accelerator is concentrated in 3,5,7,9,11,13 orders, the spectrum is wide, and the harmonic spectrum range is 3~49 orders.
We conducted an equipment test in a hospital,and fund from the test data analysis that the accelerator, X optical machine, gastrointestinal machine and other equipment produced THDi in about 50%~60%, CT(computed tomography), magnetic resonance, DSA(digital subtraction angiography machine) in about 30%; electronic detection equipment, operating room, gamma knife, OTC. between 10%~15%, frequency conversion equipment in about 35%, OTC.
The harmonic current in the hospital power distribution system has the following characteristics:
1 ) The spectrum of the harmonic current produced by the harmonic sources is very wide.
2 ) The harmonic current distortion rate is high as well as the natural power factor of the device.
3 ) There are many electronic equipment, medical technology and equipment in the hospital, and these equipment are very sensitive to harmonics.
3.3 مرکز داده
3.3.1 معرفی صنعت
UPS is an indispensable part of the equipment used to ensure the high reliability of communication and electricity consumption.In today’s large and medium-sized UPS production, more 6-pulse silicon controllable silicon type rectifier UPS design scheme is used.UPS can provide high quality power supply with high voltage stabilization and high accuracy, stable frequency and small waveform distortion.On the one hand, the use of DC switch power supply in UPS and communication room solves the power quality problems of ordinary users well, such as voltage instability and power supply continuity. هر چند, because the input side of UPS and DC switch power supply adopts rectification circuit, both have become the main nonlinear load in the power grid.
The main power quality problems as follows:
1) Produces a large amount of harmonic current, which not only pollutes the power grid but also transfer the harmonic to the IT equipment, causing serious interference and even harm to the communication system.Harmonics are very sensitive to these systems and may occur such as computer system paralysis or death, stagnation, distortion, and system control distortion, which will cause great losses.And it should be specifically pointed out that the harmonic interference hides the disaster of the entire system collapse that will happen at any time.
2) harmonics will cause power loss of the standby generator, reduce the output power of motor operation at full load, and affect the power supply safety.
3.3.2 Harmonic analysis
The UPS application, usually uses the “N+ 1” redundancy.Then the total harmonic distortion rate of the input side current THDi (leading to UPS is often different, some cases THDi can exceed 50%, pollution is quite serious.The following table shows the harmonic measurement results on the UPS input side of a company.
3.4 Public facilities
3.4.1 معرفی صنعت
Public facilities include large performing arts centers, studios, exhibition centers, stadiums, etc.The above occasions have high requirements for light and shadow and sound. The stage dimming is mainly a silicon controlled light dimming system. The basic principle is to adjust the output voltage range of both ends of the light by changing the control angle size of the silicon controllable light, so as to realize the light brightness adjustment.The basic principle of phase control rectification determines that the current distortion is serious during this load operation, especially with light load operation, which brings harmonic pollution to the power distribution system.In addition, the UPS and the central air conditioning system are also common harmonic sources.After using APF filter for harmonic elimination, it can ensure the normal operation of electric energy quality sensitive equipment such as dimming system and sound system, avoid false action of the switch cabinet, reduce the harmonic crowding out the transformer capacity, and eliminate the serious safety hidden danger of overheating of the neutral line caused by the superposition of 3 harmonic waves in the neutral line.
3.5 Banking Finance
3.5.1 معرفی صنعت
Banking and securities system adopts high quality safe and stable automation management, and adopts huge office automation, equipment automation system and communication automation system.The large amount of UPS and switching power in banking and securities systems rooms produced a large number of harmonics.In addition, the large number of electrical equipment used in the office system and the frequency converter-controlled elevators and air conditioning also produce considerable harmonics.Harmonic is very sensitive to the automatic control of banking and securities system, which may cause paralysis of computer system, system control abnormal, and banking system network operation, such as failure of data processing center, will affect the operation of the whole networked system, which will cause immeasurable losses.
3.6 Manufacturing industry
3.6.1 معرفی صنعت
There are many kinds of large production and manufacturing industries, typical of cigarette factories, automobile manufacturers and so on.There are many kinds of load in cigarette factory, از جمله: 1 production equipment: shreds production line, winding production line, packing production line and other production equipment; 2 power center load: including fan, water pump, etc.Most of these equipment use frequency conversion drive equipment, in addition to some use of DC speed adjustment.Both the former and the latter, the rectifying circuit is adopted in its electrical design, bringing serious harmonic pollution to the system.The influence of harmonic on automatic production equipment cannot be ignored, will affect its safety operation, reduce the efficiency of the motor; and will cause serious waste of electric energy.
The main hazards caused are as follows:
1) harmonics make the components in the public grid produce additional harmonic loss, reduce the use efficiency of power generation, power transmission and electrical equipment, and a large number of three harmonics flow through the middle line to overheat or even fire.
2) harmonics affect the normal operation of various electrical equipment.In addition to additional loss, the influence of harmonic on the motor will also produce mechanical vibration, noise and overvoltage, which makes the transformer seriously overheated.Harmonics make capacitors, cables and other equipment overheating, insulation aging, life shortening and damage; for compensation power capacitors and series resistance, high harmonic current through the capacitor circuit, may cause series resonance or parallel resonance phenomenon, overheating damage, vibration, flicker accidents; according to statistics, the capacitor accounts for about 40% of electrical equipment damaged due to harmonic accounted for about 30%, other electrical equipment damaged by harmonic is also greatly related to the capacitor.
3) harmonics is prone to cause parallel or series resonances between the grid and the compensation capacitors.Make the harmonic current magnified several times or even dozens of times, causing excessive current, causing damage to the capacitor, the connected reactor and resistors, and even causing serious accidents.
4) harmonics cause misactions of relay protection and automatic devices (اشمیه. g. relay protection, fuses, و غیره) and also cause inaccurate measurement of electrical measuring instruments.
در 5) harmonic will interfere with the adjacent communication system through electromagnetic induction and conduction coupling, which induces noise and reduces the communication quality; which causes information loss and the communication system cannot work normally.
3.7 Water treatment plant
3.7.1 معرفی صنعت
The sewage treatment plant adopts a large number of power electronic equipment, such as UPS, frequency converter, soft starter, computer equipment, etc.Power electronic devices are a non-linear load, and they absorb energy from the system by not continuous sine waves, but take current from the system by pulse interruption, resulting in a distortion of the input side current.These power electronic equipment are the harmonic source of sewage treatment plant, the operating conditions of these equipment often change, such as a large number of frequency converter used in the submersible pump and blower group, its harmonic component and proportion change greatly, and have a great impact on power supply and consumption.In the actual process, because the blower room is a non-linear load center, many blowers use the frequency converter centrally, it is likely to produce a large number of harmonics, which can cause abnormal motor heating, unstable state during continuous operation and large motor vibration, so that the blower cannot operate normally and reduce the sewage treatment effect, the sewage treatment process is serious, not only causes direct economic losses, but also leads to water environment pollution.Therefore, sewage treatment plant harmonic treatment to reduce harmonic pollution.
3.8 صنعت دیگر
In addition to the above industries, there are petrochemical, mineral development, steel plants, non-ferrous metal processing, glass factory, port, urban transportation and other occasions will be contaminated by harmonic distortion.Among these industries, the common harmonic sources are hot mill, cold mill, دستگاه جوشکاری, Intermediate Frequency furnace, arc furnace, DC motor, frequency converter, electrolytic tank, etc.The characteristics of this kind of enterprises is that the load current is large, and the current changes rapidly, strong impact, and the voltage level is also different, it is still difficult to carry out general statistics.
از این رو, if the harmonic governance is to be carried out on the above industries, we must understand the specific load of the actual power distribution system, and the power of this kind of load is large, it is recommended to adopt local governance or partial governance.
For designers to conduct harmonic governance on such industries or the unmentioned industries, please contact CoEpower for more explanation.
4 انتخاب محصول
4.1 APF را انتخاب کنید
1,The capacity configuration of the APF is only related to the harmonic current value of the installation location.The APF capacity is only defined by the output current of the APF, not by the power consumed by conventional other electrical equipment, which must be clear.
2,The harmonic current of the installation position can be calculated from the formula contained in Chapter, select by the capacity of APF according to this value,.
3, The APF 380/400V class has a single-machine capacity of 30A,50بوها,75بوها,100بوها,150A.If you want to choose a large capacity, it can be expanded in parallel through the above modules. The maximum number of recommended cabinet configuration is no more than 6 modules. Other capacity levels can be contacted with the Company.
Model explanation
APF Signle module：
Suggest model select
For 380 / 400V voltage rating, three-phase four-wire systems, we recommend APF using the following installation capacity. At present, CoEpower APF adopts three three-phase four-line system, For other line system requirements please contact our company.
Table 4.2 APF technical parameters
4.2 Accessories selection
CT selection
1. The rated working voltage of the CT shall comply with the system-rated voltage.
2. The CT primary current ≥ rated system load current, It’s generally selected by 1.5~2 times of the system. The secondary side current is 5A, and the CT ratio is XXXX / 5بوها.
3. Select the appropriate accurate class CT according to the requirements of electrical measurement and relay protection. Generally, 0.5-accuracy class CT can meet the requirements. If used for accurate measurement, we suggest a 0.2 accuracy class.
4. We suggest split core CT, please check the following table for details.
5. Currently we suggest using CT：150/5一6000/5.
Circuit breaker select:
1. The rated operating voltage of the circuit breaker shall comply with the system-rated voltage.
2. Rated current: Generally selected rated current is 1.25~1.5 times the APF output current, or choose a higher grade.
3. Limit separation ability, choose the same grade as the electrical equipment of the same level.
Cabinet select:
1. Considering that the design selection is mainly for new projects, in order to ensure coordination and beauty with the distribution environment, CoEpower APF recommends the rack installation method and choose to be installed inside the cabinet.
2. When the CoEpower APF is rack-mounted, the APF module is placed in the cabinet.
3. The cabinet adopts bottom incoming and bottom outgoing; front and rear doors, front operation, and rear maintenance.
4. The cabinet is equipped with a perfect and reliable grounding system and protection circuit, which can meet the requirements of the power distribution system, ensure the reliability of the power supply, and also ensure the safety of the equipment and system.
5. The cabinet size is 800（W）×800（D）×2000/2200（H）mm. The appropriate cabinet height can be selected according to the actual number of parallel modules.
6. CoEpower APF cabinet can select the same type of cabinet as the power distribution cabinet(such as GCK, GCS, MNS, GGD) in parallel, or the unified color standard and the cabinet size can be appropriately adjusted according to the requirements of the user, so that the power distribution cabinets can be unified.
7. CoEpower APF also can be placed in the original distribution cabinet, only if the size and heat dissipation requirements are available for APF.
8. It must be clearly noted that If the APF module is installed inside the cabinet, the user must ensure convenient installation and maintenance, especially good ventilation and heat dissipation.
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