The power supply system of the hospital belongs to the public system, which is the power supply guarantee unit of all localities. The hospital building design mostly adopts semi-centralized type, and the electricity load belongs to a class of load. Its main types of electricity include: lighting system, air conditioning system, medical power system, emergency lighting system.
Lighting and air conditioning system are the main power loads in various types of hospital electricity consumption, which will produce large harmonic feedback to the hospital power grid during use. Due to the use of new types of electricity such as X-ray machine, magnetic resonance machine MRI, CT machine, etc., the use of switching power supply, uninterruptible UPS and other a large number of nonlinear loads, also produce harmonic feedback to the power grid.
The hospital has a high level of electricity consumption, and the system equipment is safe and reliable as the primary factor. Due to the large use of nonlinear load, the characteristic harmonics of 3rd, 5th and 7th order are mainly produced in hospital power network. Harmonics directly affect the stable operation of precision medical equipment, and the accumulation of 3 harmonics on the neutral line causes heat in the middle line, which endangers the safe operation of the hospital power grid.
2. Definition and generation of harmonics
The definition of harmonics: the Fourier series decomposition of the periodic nonlinear sinusoidal quantity, in addition to obtaining the same component as the basic frequency of the power grid, but also a series of components greater than the integral multiple of the fundamental frequency of the power grid, this part of the electricity is called harmonics.
Generation of harmonics: When the current flows through the load, there is a nonlinear relationship with the load voltage, which forms a non-sinusoidal current, resulting in harmonics.
3. Harm of harmonics
1) Harmonics lead to improper power failure and equipment interruption accidents caused by misoperation or refusal of protection and automatic devices, resulting in significant additional losses.
2) The increase in the frequency of harmonic current causes obvious skin effect, which increases the resistance of the wires of power cables and distribution lines, increases the line loss, increases the heat, prematurely aging the insulation, shortens the life, causes damage, and is prone to ground short circuit fault, forming a fire hazard.
3) Induce power grid resonance, lead to harmonic voltage and overcurrent, cause serious accidents, damage capacitor compensation and other electrical equipment.
4) Harmonics affect the normal operation of various electrical equipment. It leads to additional losses and overheating of asynchronous motors and transformers, followed by mechanical vibration, noise and overvoltage, reducing efficiency and utilization, and shortening service life.
5) Interference with adjacent communication, electronic or automatic control equipment, or even make it unable to work normally.
4. Filtering scheme
Shaanxi Central Hospital is a national second-class A hospital with advanced medical equipment and excellent hospital environment. Our professional and technical personnel were entrusted by the hospital in the early stage to measure the power quality of the low-voltage power grid of the hospital. The total distortion rate of the current in the hospital power grid is 10%, mainly distributed in the characteristic harmonics of 3rd, 5th and 7th order. According to the test results, our company configured a set of capacity of 400A active filter device for the hospital, installed in the transformer low voltage outlet side, the use of centralized treatment for harmonic control.
5 Active Filter(/690v-active-power-filter-product/)
5.1 Product Introduction
Active Power filter(/noker-3-phase-34-wire-active-power-filter-apf-ahf-for-dynamic-harmonics-compensation-product/) is a new type of power electronic device used to dynamically suppress harmonics and compensate reactive power, which can compensate for harmonics and reactive power changes in size and frequency.
5.2 Working Principle
The load current is detected in real time by the external CT, and the harmonic value is calculated by the internal DSP. Through the PWM signal is sent to the IGBT, the inverter generates a harmonic current equal to the load harmonic and in the opposite direction into the power grid to offset the harmonic and achieve the purpose of purifying the power grid.
6 .Monitoring and analysis of harmonics control data in hospitals
APF cabinet
The data of APF(/harmonics-compensation-200400v-active-harmonic-filter-ahf-module-triple-phase-product/)harmonic compensation in the hospital was monitored by the power quality analyzer CA8336 of France, and the power quality data were respectively tested under the two conditions of APF operation (after compensation) and shutdown (without compensation), and the data were summarized and analyzed.
6.1 Measurement and analysis of APFs(/3-phase-3-wire-active-power-filter-400v-75a-apf-panel-product/) input and removal data
1：Effective value of current running
2：THDi before Active filter connected
3：THDi after Active filter connected
4：THDi from 1st to 5th before Active filter connected
5：THDi from 1st to 5th after Active filter connected
6：THDi from 1st to 7th before Active filter connected
7：THDi from 1st to 7th after Active filter connected
Result：
| APF | THDi（total） | THDi（5th） | THDi（7th） |
| Before APF connect | 10% | 9% | 3.3% |
| After APF connect | 3% | 3% | 0.5% |
As shown in the figure above, the harmonic control of the hospital by AHF(/low-voltage-active-power-filter-reduce-the-harmonic-current-active-harmonic-filter-ahf-product/) was measured with the professional power quality analyzer CA8336 of France. The comparison of data before and after APF was respectively tested. After using our APF for harmonic control, the total current distortion rate (THDi) of the hospital power network is reduced from 10% to 3%, and the effect is more significant.
7. Summary
The hospital's power supply system is crucial. The introduction of new electrical equipment has greatly improved the medical efficiency and quality of the hospital, and also provided a good treatment environment for the majority of patients. But the new power load also brings harmonic pollution. The existence of harmonics harms the normal operation of hospital power grid and affects the stability of precision treatment equipment. As a part of the public power grid system, harmonics increase the consumption of electricity in hospitals, which is contrary to the national slogan of promoting energy conservation.
After our active filter is put into operation, it greatly improves the quality of the hospital's power grid, eliminates safety hazards, improves safe and clean electric energy for medical equipment, and simultaneously takes into account energy saving and consumption reduction.
Post time: Oct-16-2023