This paper describes the application of active filter device Yang Junjun
Ankerui Electric Co., Ltd.
Abstract: Nowadays, the development of science and technology is changing with each passing day, and the medical level is constantly improving. At the same time, with the introduction of various large-scale advanced medical equipments, a large number of harmonics are generated in these medical facilities, which brings serious harm to the electrical safety of medical equipment and the normal operation of equipment. Active filtering devices are a key device to solve this problem.
Keywords: active filter device, harmonic control, medical institution
0 Preface
This paper analyzes which devices in the hospital are harmonic sources, analyzes their hazards, proposes control measures, and analyzes how to select active filter devices based on actual cases.
1. Harmonic source of hospital power supply and distribution system
1.1 medical equipment
There are a large number of power electronic components in medical equipment, which generate a lot of harmonics and cause pollution when working. More common devices include MRI (nuclear magnetic resonance), CT, X-ray, DSA (cardiovascular). Among them, MRI will generate RF pulse and alternating magnetic field to generate nuclear magnetic resonance, and RF pulse and alternating magnetic field will bring harmonic pollution; the rectifier bridge of X-ray machine will produce larger harmonics when working. Moreover, the X-ray machine is a transient load, and the working voltage can reach several tens of kilovolts. The primary side of the transformer will increase the instantaneous load of 60~70kw, which will also increase the harmonics of the power grid.
1.2 Electrical equipment
Ventilation equipment in hospitals such as air conditioners, fans, etc., as well as lighting equipment such as fluorescent lamps, generate a large amount of harmonics. In order to save energy, most of the hospitals use inverter fans and air conditioners. The frequency converter is a very important harmonic source, and its total harmonic current distortion rate THD-i reaches 33% or more, which will generate a large number of 5th and 7th harmonic currents to pollute the power grid. Among the lighting equipment inside the hospital, there are a large number of fluorescent lamps, which also generate a large amount of harmonic current. When multiple fluorescent lamps are connected to a three-phase four-wire load, a large third harmonic current flows through the neutral line.
1.3 communication equipment
At present, the hospitals are all computerized network management, which means that the number of computers, video surveillance and audio equipment are numerous, and these are typical harmonic sources. In addition, the computer network management system has a server for storing data, and must be equipped with a backup power source such as a UPS. The UPS first rectifies the mains into a direct current, one part is stored in the battery, and the other part is converted into a regulated alternating current by the inverter to supply power to the load; when the mains terminal is supplied, the battery is supplied to the inverter to continue working. The normal operation of the load. And we know that rectification and inverter will use IGBT and PWM technology, so the UPS will generate a large number of 3, 5, and 7 harmonic currents during operation.
2. Harmonics harm to medical equipment
From the above description, we can find that there are many harmonic sources in the hospital's power distribution system, which will generate a large number of harmonics (mostly the 3rd, 5th, and 7th harmonics), which will seriously pollute the power grid, causing harmonics to exceed the standard and neutrality. Power quality problems such as line harmonic overload. These problems can affect the use of medical equipment.
2.1 Harm of Harmonics on Image Acquisition Equipment
Due to the influence of harmonics, medical workers often encounter equipment failures. These faults can cause problems such as data errors, image blur, and information loss. The damage to the board components can cause the medical equipment to continue to work normally. Especially in some imaging equipment, the internal electronic components may record fluctuations when affected by harmonics. And changing the output will cause the waveform image to be overlaid or blurred, which may cause misdiagnosis.
2.2 Harmonic harm to therapeutic nursing equipment
There are many electronic devices for treatment, and surgical instruments are the most harmful to harmonics. Surgical treatment refers to treatment with laser, high-frequency electromagnetic wave, radiation, microwave, ultrasound, etc. alone or in combination with traditional surgery. The related equipment is subject to harmonic interference, and the output signal will contain clutter or directly amplify the harmonic signal, causing strong electrical stimulation to the patient. When treating certain important parts, there are major safety hazards. Nursing instruments such as ventilators, pacemakers, and ECG monitors are closely related to the life of the ward. Some instruments have very weak signals. When subjected to harmonic interference, the information may be incorrect or even inoperable. And the hospital caused significant losses.
3. Harmonic measures
According to the causes of harmonics, the control measures can be roughly divided into the following three types: reducing system impedance, limiting harmonic sources, and installing filter devices.
3.1 reduce system impedance
To achieve the goal of reducing system impedance, it is necessary to reduce the electrical distance between the non-linear electrical equipment and the power supply, in other words to increase the supply voltage level. For example, the main equipment of a steel plant is an electric arc furnace. It was originally powered by 35KV. The two 110KV substations were respectively set up with a 35KV dedicated line. The harmonic components were measured on the 35KV bus. The distance was changed to a distance. Only 4 km of 220KV substation is equipped with 5 35KV dedicated lines, and the harmonics on the busbar are obviously improved. In addition, the plant also uses a large-capacity synchronous generator to greatly reduce the electrical distance of these non-linear loads. The amount of harmonics produced by the plant is reduced. This method has the largest investment and needs to be coordinated with the development plan of the power grid. It is suitable for large-scale industrial projects, and the hospital requires continuous power supply without interruption. It is generally powered by two or more substations, so this method is not given priority.
3.2 Limiting Harmonic Sources
This method needs to change the configuration of the harmonic source, limit the working mode of generating a large number of harmonics, concentrate the devices with harmonic complementarity to make the harmonics of the devices cancel each other, increase the number of phases of the converter device, and increase the number of characteristic harmonics. Thereby greatly reducing the effective value of the harmonic current. This method requires re-arranging the equipment lines and coordinating the use of the instrument, which has high limitations. The hospital can make minor adjustments according to its own situation, which can reduce the amount of harmonics to a certain extent.
3.3 installation filter device
At present, commonly used AC filter devices are: passive filter device and active filter device (APF). Passive filter device, also known as LC filter device, uses the principle of LC resonance to artificially create a series resonant branch, which provides a channel with extremely low impedance for a certain number of harmonics to be filtered out, so that it is not injected into the grid. The passive filter device has a simple structure and the harmonic absorption effect is obvious, but it is limited to the harmonic of the natural frequency, and the compensation characteristic has a great influence on the impedance of the power grid. (At a certain frequency, the impedance between the grid and the LC filter device may occur. Parallel resonance or series resonance). Active Filtering Device (APF) is a new type of power electronic device for dynamically suppressing harmonics and compensating for reactive power. It can collect and analyze the current signal of the load in real time, separate the harmonics and reactive power, control the converter output and harmonic and reactive current equal amplitude and reverse compensation current through the controller to cancel the harmonics in the load. Current, thus achieving the purpose of harmonic control. The active filter device has significant advantages such as real-time tracking, fast response, and comprehensive compensation (which can compensate for both reactive power and 2~31 harmonics).
4 ANAPF active filter device in medical institutions
With the continuous improvement of people's living standards and the aging of the population, the demand for medical services is steadily increasing, and the medical service industry is about to enter a period of rapid growth. The most significant and most important representative of the medical industry is the hospital. Due to the special social value and importance of the hospital, the solution to the problem of power quality cannot be delayed.
4.1 Selection of ANAPF
The benefits of harmonic control are first of all to ensure the safety of patients and medical personnel, that is, to reduce the adverse effects of the harmonics by eliminating harmonics or eliminating the adverse effects on the distribution system, and to ensure the normal operation of the transformers and medical instruments. Benefit, that is, to ensure the normal operation of the low-voltage capacitor compensation system, play its due role, reduce the harmonic content in the power grid, and improve the power factor, reduce the reactive power loss, and extend the service life of the equipment.
The distribution system of the People's Hospital of a high-tech zone in a city, the main load is electronic medical precision equipment, lighting and variable frequency ventilation equipment, computer and UPS, etc., the main load harmonic current distortion rate can be roughly referred to the following table.
Load harmonic current empirical value | ||
Harmonic source load type | Harmonic current frequency | Harmonic current distortion rate |
Lighting fixtures, computers, etc. | 3,5,7,9, etc. (2n+1) times | (7~10)% |
Electronic testing equipment, operating room, gamma knife, etc. | 3,5,7,9, etc. (2n+1) times | (10~15)% |
CT, magnetic resonance, DSA, etc. | 3,5,7,9, etc. (2n+1) times | (30~40)% |
Accelerator, X-ray machine, gastrointestinal machine, etc. | 3,5,7,9, etc. (2n+1) times | (50~60)% |
UPS, variable frequency ventilation equipment, elevators, etc. | 5,7,9,11, etc. (6n+1) times | (25~35)% |
Through the on-site personnel, the load that needs to control harmonics is concentrated under four transformers. The capacity of these four transformers are: two 1600KVA, the specific parameters are shown in Figure 1.
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Figure 1 Suzhou High-tech Zone People's Hospital 3# Transformer
Two 2000KVA, the specific parameters are shown in Figure 2.
.png)
Figure 2 Suzhou High-tech Zone People's Hospital 5# Transformer
According to the transformer capacity and the specific equipment usage, we can find that most of the systems are non-linear devices, which generate a lot of harmonics, which will affect the reactive power cabinet and other power equipment. In order to avoid this kind of harm, considering the effect and cost of governance, and combining customer governance requirements, according to formula (1), our plan is to use two 200A active filter devices and two 250A active filters. The device separately compensates the secondary sides of the four transformers. Two of the 1600KVA transformers use 200A APF supporting 3000/5 sampling current transformers, and two 2000KVA transformers use 250A APF supporting 4000/5 sampling current transformers.
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....................................... Formula 1) .png)
........ transformer load ratio, that is, the ratio of load to the rated capacity of the transformer, usually taken from 0.6 to 0.8; .png)
........ current total harmonic distortion rate; .png)
........ transformer rated capacity, unit KVA; .png)
........ Low voltage system voltage, generally takes 0.38~0.4. 4.2 ANAPF installation method
.png)
The cabinet of the project adopts modular modular installation, as shown in Figure 1, which has the following advantages in this project:
(1) The capacity of the APF device can be increased or decreased at any time according to changes in load usage;
(2) Each module is separately installed with a heat dissipation unit, and a cooling fan can be installed on the cabinet body, and the heat dissipation effect is good;
(3) Although there are communication connections between multiple modules, the failure of each station does not affect the other modules to continue working;
(4) It is convenient to maintain in the later stage, and the faulty module can be repaired and replaced separately; the ANAPF active filter device can work continuously during maintenance.
Figure 1 Schematic diagram of modular modular installation
The installation scheme in this project is centralized compensation on the load side. It is easy to install. It only needs to put the cabinet to the designated position and connect to the main circuit wiring and the current transformer wiring to debug. The wiring schematic is shown in Figure 3.
.png)
Figure 3 Main circuit wiring and transformer wiring schematic
One end of the main circuit wiring is connected to the main busbar and the line point, and the other end is connected to the ANAPF cabinet rear inlet bus copper bus A/B/C/N; the current transformer is placed between the ANAPF grid point and the load to be compensated. Sampling is performed and the signal is connected to the transformer terminals in the cabinet.
5 Conclusion
From this article, we can understand that harmonics are very harmful to the medical industry. A large number of harmonics will affect the performance and use of precision instruments. In severe cases, it may endanger personal safety; it will also increase line power loss and conductor heat generation. The importance of harnessing harmonics is self-evident, reducing the efficiency and longevity of equipment. By installing an active filter device, the purpose of harmonic control can be well achieved, thereby ensuring personal and equipment safety. In the short-term, the harmonic control requires a certain amount of up-front capital investment; but in terms of long-term development, the ANAPF active filter device is easy to maintain in the later stage and can be used in real time. It can control the economic benefits brought by harmonics and clean the grid. The social benefits are also obvious.
[References]
[1] Ankerui Power Quality Monitoring and Governance Selection Manual. 2015.08 version
[2] Ankerui Electric Co., Ltd. Product Manual.2013.01.
About the Author
Yang Junjun, female, undergraduate. Position: Now working at Ankelui Electric Co., Ltd. Tel, mobile, QQ
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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