Hospital complex

Modern medical institutions in order to improve the level of medical services, continue to introduce new and sophisticated various advanced medical equipment such as nuclear magnetic resonance, CT, X-ray machine, hemodialysis machine, etc., while a variety of energy-saving lighting, inverter air conditioner, elevator equipment, Put into use. These devices are non-linear devices, will produce a large number of high-order harmonics during operation, causing some interference to the power distribution system and medical equipment. At the same time, these advanced medical equipment has high-end computer components and a large number of highly sensitive microelectronic devices, which have high requirements on the power quality of the power supply, are very sensitive to voltage fluctuations and power harmonics, and cause serious problems of power harmonics. Equipment damage can even lead to medical accidents. The source of harmonics.

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. Harmonic characteristics

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Harmonic source load type	Harmonic current times	Harmonic current distortion rate
Lighting, computer and so on	3、5、7、9,（2n+1）	（7-40）%
Electronic testing equipment, operating room, gamma knife and so on	3、5、7、9,（2n+1）	（10-15）%
CT, magnetic resonance, DSA and so on	3、5、7、9,（2n+1）	（30-40）%
Accelerator, X-ray machine, gastrointestinal machine	3、5、7、9,（2n+1）	（50-60）%
UPS, variable frequency ventilation equipment, elevators and so on	5、7、9、11,（6n+1）	（25-35）%

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Harmonic Hazard Analysis

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Harmonic hazards to the distribution system so that the additional loss of electrical components increases, easy to cause a fire; affect the normal operation of electrical equipment; cause grid resonance; make relay protection misoperation

For electrical measurement error is too large; make industrial control system collapse.

Harmonic Harm to Medical Equipment Causes Mismatch and Data Errors in Devices Relying on Microprocessor Technology; Directly Harmful to Electronic Circuits in Devices, Causes Breakdown or

Discharge; affect the performance and precision of precision medical equipment.

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Harmonic network requirements of China's national standards

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Currently used power quality (harmonic) assessment standards, mainly for China's national standard "power quality: public power grid harmonics"

(GB / T14549-1993). The standard specifies the distortion rate of current and voltage in the power grid. It is also an important basis for the evaluation and control of harmonics.

Table 1: Grid Harmonic Voltage National Standard: Cited in (GB / T14549-1993)

Grid Nominal Voltage (KV)	Total harmonic distortion rate (%)	Each harmonic voltage content (%)
		Odd times	Even time
0.38	5.0	4.0	2.0
6	4.0	3.2	1.6
10
35	3.0	2.4	1.2
66
110	2.0	1.6	0.8

 

Table 2: Allowable values of harmonic current injected into the grid common connection point: Cited by (GB / T14549-1993)

Nominal voltage (KV)	Reference Short Circuit Capacity (MVA)	Harmonic frequency and harmonic current allowable value (A)
		2	3	4	5	6	7	8	9	10	11	12	13
0.38	10	78	62	39	62	26	44	19	21	16	28	13	24
10	100	26	20	13	20	8.5	15	6.4	6.8	5.1	9.3	4.3	7.9
		14	15	16	17	18	19	20	21	22	23	24	25
0.38	10	11	12	9.7	18	8.6	16	7.8	8.9	7.1	14	6.5	12
10	100	3.7	4.1	3.2	6	2.8	5.4	2.6	2.9	2.3	4.5	2.1	4.1

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Applications

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A large outpatient hospital in a large three-A hospital complex total of four 2000kVA and a 1600kVA transformer and a 800kW diesel generator, according to the hospital of non-linear transformer load capacity of the device size and the corresponding harmonic distortion rate and The simultaneous use of various nonlinear devices to calculate the size of the harmonic current, configured with five different active capacity of the filter specifications.

Below 1 # active filter put into operation before and after the power distribution system power quality test comparison and analysis as an example to describe in detail, including 1 # transformer load lighting lighting, elevators, submersible sewage pumps, computer centers.

Active filter before and after the operation of the data

(1) Before the active filter input, the current waveform distortion is serious. The three-phase current harmonic content is 19.7%, 27.8% and 26.6% respectively. The three-phase currents are 45A, 40A and 64A, respectively, and the neutral current is 37A.

(2) The current waveform distortion of the active filter significantly improves, and the three-phase current harmonic content decreases obviously, which are 2.9%, 2.8% and 3.4% respectively. The three-phase currents are 47A, 48A and 47A respectively. Current is 5A.

(3) The current waveform is obviously improved. The waveform of the current is approximately sinusoidal after using the filter. The work of harmonic control achieves the expected goal and effect.

The Significance of Active Filters in Hospital Buildings

Protect the safety of medical electrical equipment, purify the power, protect the power factor compensation equipment, prevent the malfunction of the protective device, reduce the power loss and expand the power supply capacity of the transformer and generator, so as to control the generated harmonics to a minimum and achieve scientific and reasonable Electricity, inhibit grid pollution, improve power quality, ensure the safety of medical equipment。