1 Harm of harmonics Due to the use of a large number of non-linear load devices (inverter air conditioners, elevators, X-ray machines, CT machines, nuclear magnetic resonance machines, energy-saving lamps, EPS rectification equipment) in the hospital, the harmonic pollution of hospital power supply systems is generally compared. serious. Harmonic pollution can cause serious hazards and hidden dangers to electrical equipment and power supply systems. The major ones are: 2 National standards for the regulation of power quality The requirements of national standards for harmonics are also stipulated in detail. “JGJ16-2008 Electrical Design Code for Civil Buildings†22.3.2 “Government office buildings at or above the provincial level, office buildings at bank branches, branches and financial institutions, medical technology buildings at Grade III A hospitals, large computer centers and other buildings, It is advisable to install active filtering devices on dedicated distribution lines such as sensitive medical equipment and important computer network equipment; and to specify the parameters of harmonics: "22.3.1 The power quality of the public power grid should meet the following requirements:" 3 Solution The harmonic source of the hospital is more, and the distribution is more decentralized. The harmonic distortion generated by different devices is different, the number of harmonics is also different, the harmonic current and the harmonic voltage component are also relatively large, so it is necessary to harmonics of the hospital. Effective management requires proper design of the primary and secondary power supply systems. APF active power filter devices are connected in parallel to the power grid. By detecting the harmonic and reactive components of the load in real time, PWM inverter technology is used to generate an inverse current harmonic component and reactive component from the converter. The component is injected into the power supply system in real time to achieve harmonic rejection and reactive power compensation. 5.2 Partial Compensation for Specific Branches When non-linear equipment is concentrated on certain branches, an APF active filter device can be installed on the branch to perform local compensation. 5.3 The specific equipment on-site compensates a single non-linear medical device with stable operation with a large capacity, a non-linear load with obvious spectral characteristics, a low natural power factor, and harmonics generated by a harmonic source are relatively concentrated in three consecutive or The following (eg, 3, 5, 7) harmonics can be compensated on-site for harmonic sources such as MRI, X-ray machines, ECT, central air conditioning, etc. This method can achieve very good Compensation and energy-saving effects do not affect the branch and the entire system. When designing a harmonic control solution, the above three harmonic control methods can be flexibly adopted according to the harmonic monitoring data of the distribution network, and the harmonic pollution of the hospital can be better managed, and the hidden troubles of the power supply system can be eliminated and the harmonics can be eliminated. Wave pollution minimizes the impact on the hospital's entire system and equipment, avoids affecting the normal operation of important medical equipment, and ensures the safety of power supply in the 2 types of places. The essence of the required compensation current estimate is to calculate what the actual harmonic current is when the load is operating. 6.1.1 Centralized compensation capacity calculation Centralized compensation method The harmonic current that needs to be compensated can be estimated by the transformer capacity. The load factor of the transformer needs to be taken into account. The specific formula can be estimated according to the following formula: K1 is the load ratio: that is, the ratio of the load to the rated capacity of the transformer, which is usually taken as 0.6 to 0.8, where 0.6 is taken; The above figure shows the measured data waveforms. Before the APF active power filter was used, the harmonic pollution of the circuit was serious, the waveform was seriously distorted, and the three-phase current was also seriously unbalanced. After the APF device is used to compensate the harmonic source device in situ, the measured waveform data is better compensated. Special Grease,Anti Seize Grease,Non Soap Grease,Non Melt Grease Hangzhou Xingang Lubrication Technology Co., Ltd. , https://www.newlubes.com
Interfere with the normal operation of electronic equipment;
Influencing the performance of equipment such as nuclear magnetic resonance, causing noise interference and image disturbances;
Caused malfunction of electrical automatic devices, resulting in blackouts;
Make the precision test equipment vibration and noise increase, shorten the service life;
As a result, the power loss of the power supply system increases, causing grid resonance, accelerating the insulation aging, lowering the power factor of the system, and increasing system risks. 
3.1 The rational design of a system must first be a reasonable design of the system, such as the use of D, yn11 K-transformer transformers, harmonic source equipment using special transformer power supply, improve three-phase load balancing.
3.2 Harmonic Measurements and Harmonic Waves Harmonic monitoring of system harmonics is performed in real time. Harmonic measurement and analysis are prerequisites for the secondary treatment of harmonics.
Transformer low-voltage side switches are equipped with harmonic monitoring and analysis instruments, real-time monitoring of the power system current and voltage harmonic distortion data, and can set the harmonic distortion limit alarm, can be configured APF active filter device for centralized compensation;
The harmonic distortion rate of power supply loops with more harmonic sources such as medical technology buildings is monitored and APF active power filter devices are configured to perform partial or on-site compensation;
Harmonics monitoring is performed on electrical circuits in Class 2 locations such as operating rooms and ICU wards. If the harmonics exceed the standard, a small-capacity APF active power filter device is used for local control to ensure power safety.
4 APF active power filter device principle APF active power filter device can dynamically filter the harmonic current generated by the non-linear load in the power supply system, reduce the voltage harmonic distortion rate, and effectively eliminate harmonics on transformers, capacitors and precision equipment. influences. The principle of APF active filter device is shown in Figure 3-1: 
5 Compensation Methods In the hospital power supply system, APF active power filter devices can use three kinds of filter compensation methods.
5.1 Concentrated compensation on the outgoing side of the transformer When the number of non-linear loads is large and the distribution is relatively decentralized and the harmonic distortion is not too high, an APF active power filter device can be centrally installed on the low voltage distribution bus of the transformer. Compensation, such as lighting load transformers with more energy-saving lamps. This compensation method can effectively improve the operating performance of the transformer and improve the overall power quality of the system. 
6 Harmonic control equipment selection calculation
6.1 Selection of active filter equipment When calculating the active filter selection, according to the location of the installation and the object to be compensated, estimation and calculation of the required compensation current can be performed. The calculation is mainly based on the type of customer load, which is calculated from the typical data of this type of load and the user load current calculation.
Due to different equipment used in various industries, there are differences in harmonic loads. Based on empirical values, the recommended values ​​of current harmonic distortion in various industries are as follows: 
K2 is the harmonic coefficient, and the centralized compensation field is suitable for occasions where the overall harmonic pollution is not high but scattered, taking 12%;
ST is the rated capacity of the transformer in kVA;
US is the low voltage system voltage, which generally takes 0.4.
According to the above formula, a transformer with a capacity of 2000 kVA has an output side harmonic current of ITHD=206 A. An active power filter cabinet with a harmonic compensation capacity of 200 A can be selected for compensation.
6.1.2 Computation of Local Compensated Capacity of Branches Local compensation is performed for specific branches with relatively concentrated harmonic source loads. The calculation formula can be calculated based on the calculation formula of concentrated compensation. For example, the branch line with capacity of 250 kVA for medical technology buildings, most of the equipment For medical equipment, the current harmonic distortion ratio is selected according to 20%, the load ratio is 0.8, and the ITTD is 56A. A 75A active power filter cabinet can be selected for local compensation.
6.1.3 Calculation of local equipment compensation capacity The single unit of large-capacity harmonic source can achieve the best compensation effect by performing on-site compensation. Harmonic contents of various typical harmonic source equipment are shown in the following table: 
According to experience, the compensation capacity can be calculated as ITTH=SL*K2. SL is the equipment load, and the unit kW and K2 are the harmonic coefficients. See the above table for the values. The formula above involves only the calculation of numbers, not units.
6.2 APF Active Power Filter Compensation Effect 