Analysis and solution of hospital power quality problemsSolutions Analysis and solution of hospital power quality problemsSolutions
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Analysis and solution of hospital power quality problems

With all kinds of high-precision medical electronic devices entering the hospital, such as electronic scalpels, medical imaging detection instruments, robotic arm endoscopes, respiratory circulation instruments, etc., doctors and patients can grasp the patient's diagnostic data, images and medical records in the first time through electronic and network technology, laying a firm foundation for the next step of treatment! While these medical instruments provide excellent medical quality for the people, they also cause a large number of harmonic pollution due to the high load characteristics of the instruments, thus affecting the quality of the power grid and power supply.

Due to the voltage and current fluctuations generated by harmonics, the electronic components in the medical instrument are interfered with, resulting in equipment damage or malfunction, which may lead to monitoring data errors, tomographic errors, radiation dose inaccuracy, excessive discharge of the instrument, and even electronic scalpel fire. Hospital power distribution systems can also be mandatory for industries equipped with active filters for the state.

Ⅰ.Hospital load analysis

The electrical devices in the medical industry can be divided into three categories: medical equipment, information equipment and ordinary electrical devices. In medical equipment, there are a large number of power electronic components, which generate a large number of harmonics when working, causing pollution. The more common equipment is MRI (magnetic resonance machine), CT machine, X-ray machine, DSA (cardiovascular imaging machine) and so on. Among them, MRI will generate radio frequency pulses and alternating magnetic fields to generate nuclear magnetic resonance, and radio frequency pulses and alternating magnetic fields will bring harmonic pollution; The rectifier bridge of the high-voltage rectifier in the X-ray machine will produce a large harmonic when working, and the X-ray machine is an instantaneous load, the voltage can reach tens of kilovolts during operation, and the primary side of the transformer will increase the instantaneous load of 60~70kW, which will also increase the harmonics of the power grid.

CategoryHarmonic SourceNumber of harmonic currentsHarmonic current distortion rate
Medical equipmentElectronic testing equipment, operating room, gamma knife, etc3, 5, 7, 9, etc. (2n+1) times(10~15)%
Electronic testing equipment, operating room, gamma knife, CT, magnetic resonance imaging, DSA, etc3, 5, 7, 9, etc. (2n+1) times(30~40)%
Accelerator, X-ray machine, gastrointestinal, etc3, 5, 7, 9, etc. (2n+1) times(50~60)%
Information devicesData center (computer)3, 5, 7, 9, etc. (2n+1) times(7~10)%
Ordinary electrical equipmentLighting fixtures, air conditioning, etc3, 5, 7, 9, etc. (2n+1) times(7~10)%
UPS, variable frequency ventilation equipment, elevators, etc5, 7, 9, 11, 13, etc. (6n+1) times(25~35)%

The main harmonic sources can be divided into the following types:

1. Medical equipment: large-scale electronic medical equipment in large hospitals is generally powered by switching power supply, and switching power supply equipment will produce 3, 5, 7 harmonics and other harmonics injected into the power grid.

2. Computer and UPS: At present, hospitals are computer network management, the number of computers is very large, in addition, the server and other data storage systems must be equipped with UPS and other backup power supply. The switching power supply and UPS of personal computers are harmonic sources, which will produce a large number of harmonics of the 3rd, 5th, and 7th degrees. In addition, the use of high-frequency UPS in most of the new data rooms will also cause capacitive reactive power problems.

3. Lighting equipment: Due to the use of a large number of fluorescent lamps in the hospital, it will produce serious harmonic current, mainly for the third harmonic, when multiple fluorescent lamps are connected into a three-phase four-wire load, a large third harmonic current will flow on the middle line.

4. Air conditioning and ventilation equipment: In order to save energy, most hospitals use frequency conversion fans and air conditioners. The frequency converter is a very important harmonic source, and its total harmonic current distortion rate is more than 33%, which will produce a large number of harmonics of the 5th and 7th degree to pollute the power grid.

Ⅱ.Harmonic characteristics

1. The spectrum of harmonic currents generated by harmonic sources is very wide;

2. The harmonic current distortion rate is very high, and the power factor of the equipment is also very high;

3. There are many electronic devices and medical equipment in the hospital, and these devices are sensitive to harmonics;

4. A large number of harmonic currents and harmonic voltages will affect the normal operation of the relay protection equipment in the distribution system, and affect the continuity and stability of the power supply of the distribution system;

5.Hospital harmonic sources are numerous and scattered, and centralized governance is recommended.

Ⅲ. Hazards of harmonics

1. The frequent start of large-scale medical equipment in the hospital causes the current fluctuation to be very fast, the impact on the system is great, and the consequent change of harmonic current is easy to lead to an increase in the failure rate, shortening of life and even damage to precision treatment and diagnostic instruments and equipment;

2. There is a certain 3rd harmonic current in the system, which will cause the center line to overheat and bring fire hazards;

3. Harmonics can cause synchronization offset and data errors in new medical devices that rely on microprocessors;

4. Common-mode interference and overcurrent caused by harmonic resonance will directly endanger the safety of the internal electronic circuits of the equipment, resulting in breakdown or discharge.

Ⅳ. Solution

The existence of harmonics has brought serious harm to the electrical safety of the hospital and the normal operation of the hospital's medical and laboratory equipment, and has become an important factor endangering the hospital's surgical environment. To this end, Bowo provides a complete set of solutions, as follows:

No.Power Quality ProblemSolution
1Large medical equipment (CT machine, B-ultrasound, X-ray machine, nuclear magnetic resonance) produces a large number of harmonics according to inverter air conditioners, elevators, and most medical equipment




2There is a need for reactive power compensation





3CT machine, B-ultrasound, X-ray machine, nuclear magnetic resonance and other high-precision instruments are sensitive to voltage sag and have high requirements for power supply quality



Application case

1. Application of BW-APF in Jilin Medical University Hospital

2. Application of BW-APF in Guangdong Shantou People's Hospital

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