Abstract: This article mainly describes the application of IT isolated power system in ICU and operating room of the Third People's Hospital of Shenzhen city, as well as the importance, advantages and matters needing attention of IT isolated power system. 

Key words: IT isolated power supply, system, ground

1、Project overview

   The project of Shenzhen Third People's Hospital is located in the southwest side of Lilang overpass in Buji Town, Longgang District. The construction area is 10,0005 ㎡, and the total construction area is 81,737 ㎡, including 14 buildings such as outpatient building, medical technology research building, inpatient building, administrative building and academic lecture hall, and supporting roads, squares and greening, etc..As a major construction project of Shenzhen city, it is a modern infectious disease hospital which is compatible with the construction of the central city and ADAPTS to the planned development of Shenzhen city.It is a three-level infectious disease hospital integrating medical treatment, scientific research, prevention and protection, teaching and rehabilitation. 

2、Specification requirements for setting up IT isolated power system

    With the continuous development of society and economy, large comprehensive modern hospitals are constantly put into construction, so the electrical safety and reliability of hospitals have also attracted the attention of the industry.The safety and reliability of power distribution in important occasions such as ICU and operating room have attracted more and more attention from the industry. Especially with regard to IT isolation power Settings.According to gb16895.24-2005 /IEC60364-7-710:2002, the power supply circuit for life-sustaining, surgical, and other medical electrical equipment and systems located in the "patient area" in class 2 medical facilities in the medical field shall be powered by medical IT systems with insulation and monitoring.12.8.6 In the Civil Building Electrical Design Code officially implemented on August 1, 2008, the corresponding requirements and regulations are made for the POWER supply of IT system used in medical places. 

（1）In class 2 medical facilities, the medical IT system shall be used for the power supply circuits for life-sustaining, surgical and other medical electrogas equipment and systems located in the "patient area". 

（2）Separate medical IT systems should be installed at least once in adjacent rooms for the same purpose.And it is equipped with insulation monitor. 

（3）Each health IT system should be located where medical personnel can monitor IT regularly and should be equipped with an audible and visual alarm system. 

（4）Medical IT transformers should be equipped with monitoring devices for overload and overheating. 

In 12.8.10, relevant provisions are made for auxiliary equipotential connection.At the same time, 12.8.1-12.8.6 are stipulated in the provisions of 12.8.10 in accordance with the national standard "Medical Places required by Special Devices or Places" GB16895.24.The two types of places include: emergency room (outpatient operating room), operating room, CU room, catheter intervention room and angiography room.

3、Introduction of IT isolated power system and importance of hospital adoption 

1）IT isolates the power system, and I indicates that the power side is not working grounded, or is grounded through high impedance.T represents the grounding protection of the electrical and gas equipment at the load side.IT system in the power supply distance is not very long, the reliability of power supply is high, good security.Generally used in places where blackouts are not allowed, or where strict continuous power supply is required, IT systems must be used in hospital operating rooms, emergency rooms, ICU rooms, and other type ii places.The use of IT mode power supply system, that is, the neutral point of the power supply is not grounded, once the equipment leakage, single-phase leakage current to the ground is very small, will not destroy the balance of the power supply voltage, so IT can avoid electric shock and other electrical accidents, at the same time is not enough to make the circuit protection electrical equipment action cut off the power supply, to ensure the uninterrupted power supply.So than the power neutral grounding system is safe and reliable. 

2）The importance and necessity of using isolated power systems in hospitals. 

It is well known that when the direct leakage of electrical equipment to the human heart is greater than 10uA, it will cause a micro-shock accident to the patient. 

However, the action response value of the earth leakage protection switch used in general general buildings is mA level (such as: 30 mA), which is far from meeting the needs of the medical field.In the special environment of hospital, leakage current poses a potential danger to patients, so special requirements are put forward for electrical safety design.In particular, those vital places, such as surgical operating rooms, intensive care units, cardiac operating rooms, etc., need to install medical IT isolation power system, the purpose of which is to ensure a safe and reliable power supply to medical appliances in the site, so as to ensure the safety of patients.When the conductor touches the heart (for example, during open-heart surgery or embedding a pacemaker), the tiny currents flowing between normally safely grounded conductors can cause micro-shocks and the possibility of death.The isolation transformer acts as a door separating the non-protected area of the medical area from the electrical wiring in the protected area. All live conductors in the protected area are isolated from the ground to prevent the dangerous current on the line insulation from causing a micro-shock.Insulation monitors must be used together with the isolation transformer, used for continuous monitoring isolation transformer secondary side of charged conductor and earth between the resistance and current, for example, in the process of the operation flow of blood and in vitro metal table may make the patient and to form a path, so there are dangerous currents, once the conductor in the medical electronic equipment form of pathways (such as leakage), will cause the macro electric shock (not all current flows through the heart) or micro electric shock (all electric current flows through the heart).Generally, the power supply network takes the ground as the reference potential, and the current in the phase line can pass through any uninsulated channel to form a circuit to the ground, which is the root cause of electric shock.Isolated power supply is the use of isolated transformer power supply, power through the isolated transformer, the original grid is no longer a reference potential.None of the output lines of the isolating transformer can form a circuit with the ground, but can only form a circuit between two output lines, which improves the reliability of power supply.The isolating transformer is used to separate the unprotected area from the protected area, and the power of the IT system is extracted at the secondary of the isolating transformer to prevent the generation of ground fault current.The IT system will be introduced into the operating room or emergency room, and a distribution box will be set in the room, and insulation monitors will be placed in the box. The use of insulation monitors can show the insulation status of the secondary load part of the isolation transformer as early as possible, and alarm signals will be provided before the insulation failure poses a threat to the person.At this time, the power will not be cut off, to ensure the continuity of power supply.Medical staff can then monitor the leakage current and the actual operation, so that the risk of personal shock is minimized. 

4、Configuration of IT isolated power supply system in a hospital in Shenzhen city

A hospital in Shenzhen has installed a medical IT isolated power system in all operating rooms and ICUs.Specific composition including isolation transformer, insulation monitors, external alarm and display, current transformer, etc., the system sets the continuity of insulation monitoring, monitoring, and improve the fire load transformer temperature monitoring at an organic whole, reduces the contact voltage and the floor drain current, make person get an electric shock hazard to minimize, greatly improve the ability of accident prevention, to keep the power supply security.A hospital in Shenzhen city chose Bendell IT isolated power supply system from Germany. The system diagram is as follows:

1）The IT isolated power system in the ICU is as follows:

Each ICU is equipped with a set of 6.3KVA IT system (including 6.3KVA isolation transformer ES710, insulation monitor 107TD47, current transformer STW2, external alarm display and tester MK2007CBM-CN, special instrument power supply AN450). 

2）Diagram of IT isolated power supply system in operating room

Each operating room is equipped with a set of 8KVAIT isolated power supply system (including isolation transformer 8KVA, insulation monitor, special power supply, external alarm display and tester MK2007CBM-CN).

3）System and equipment functions:

a)Insulation monitor

- Insulation monitoring and alarm system conforms to IEC61557-8 and IEC60364-7-710 standards. 

- Special insulation monitors for medical IT systems

- Insulation monitoring, load monitoring and isolation transformer temperature monitoring functions

- LCD with backlit display

- insulation monitoring response value adjusting range 50kΩ-500Ω

- Adjustment range of overload monitoring response value 5A-50A

- Output alarm relay

- RS485 interface

-Measured value analog current signal output

- Built-in or external self-check button

- Wiring monitoring

- Guide rail installation

- ac impedance should be at least 100kΩ; 

- The test voltage shall not be greater than dc 25V; 

- Even in the case of fault, the peak value of its injected current is not greater than 1Ma; 

- the latest in insulation resistance to the 50 kΩ, should be a signal.And the apparatus for testing this function is configured. 

b)Isolating transformer

- Meeting electrical installations in buildings - Part 7-710: Requirements for special installations or places - Medical places

It is stipulated in GB16895.24-2005/IEC60364-7-710:2002 710.512.1.6 that medical isolating transformers shall meet the requirements of IEC61558-2-15. 

- 3.15-10 kva capacity

- Temperature sensor is installed inside the winding

- Noise below 35 decibels

- The transformer is installed close to the medical site, in the cabinet or in the outer sheath to avoid inadvertent contact with live parts. 

- the rated voltage on the secondary side of the transformer shall not exceed 250V. Medical IT systems for mobile and stationary equipment shall adopt single-phase transformers with rated output capacity of not less than 0.5Kva and not more than 10Kva. 

- The metal housing of the isolating transformer is connected with the local equipotential connection terminal plate. 

c)- External alarm and display devices for insulation monitors

- Digital tube displays insulation resistance and load status

- Buzzer sound alarm and mute button

- RS485 interface

- Chinese panel

- The waterproof panel is easy to clean

- Real-time monitoring of isolating transformer load condition and transformer winding temperature. 

- A green light indicates normal operation; 

- A yellow light lights up when the insulation resistance drops to the minimum setting value.This light indicator should not be eliminated or disconnected; 

- When the insulation resistance drops to the minimum setting value, the sound alarm action.The audible alarm can be cancelled; 

- When the fault is cleared and restored to normal, the yellow signal should go out.Can monitor overload overheating of medical IT transformers

5、IT isolated power system has the following advantages:

1) The shock voltage and leakage current are too small to cause electric shock or other electrical accidents; 

2) In case of ground fault of the power supply system, the circuit protection device will not cut off the power supply, which ensures the uninterrupted power supply. 

6、Precautions for using IT to isolate power systems. 

1) The IT system cannot lead out the neutral wire, because the insulation monitor cannot give an alarm when the neutral wire has ground fault, and the system will

If TT or TN system is changed, the power supply of the system will be cut off if the phase-to-ground fault occurs again, which may have serious consequences. 

2) The other two relatively low voltages will increase when the IT system is connected to the ground, so the electrical circuits and electrical equipment are insulated, the level is high. 

3) The insulation monitor of the IT system needs to be grounded through the PE wire, so its connection with the PE wire must be reliable.

7、An introduction to the Acrel Medical IT Isolation power system

7.1 Overview 

With the wide application of electronic medical equipment in the field of hospitals, leakage current poses more and more threats to patients, especially in those places where life is crucial. During surgery or under anesthesia, a variety of electrodes and sensors are directly inserted into the body of patients, and tiny leakage current may lead to death by electrocution.In addition, some medical equipment is used to maintain the life of seriously ill patients, once the equipment power failure, it will also pose a threat to the lives of patients.Therefore, the electrical design of this special place for medical treatment should be carried out in strict accordance with national standards and norms.

Ankore medical IT system insulation monitoring fault location device and system are suitable for the hospital operating room, ICU(CCU) ward and other important places, can provide safe, continuous, reliable power supply solutions for such places.

7.2 Medical isolation power system

The medical Isolated power monitoring system is used to centrally monitor the health of the medical IT system in all medical 2 locations in the medical building.The centralized monitoring system can be set up in the hospital electrical operation and maintenance personnel on duty room, also can be integrated in other power monitoring system, monitoring by professional electrical personnel, once a set of IT systems fail, electrical maintenance personnel can in time to make a judgment, and according to the site condition for processing.

System topology

7.3 Software functions

Acrel medical isolated power monitoring system is based on the touch screen software design, the software has a variety of functions such as remote measurement, remote parameter setting and remote self-inspection, which provides a powerful system integration tool for the centralized monitoring of the isolated power system in 2 types of hospitals.The main functions of the software are as follows:

■  Primary diagram and field distribution display

The system has the function of one-time diagram and field distribution diagram display, can intuitively understand and timely find the alarm location or area of IT power supply system, so as to facilitate professionals to timely arrive at the scene for fault troubleshooting;

■ Real-time data acquisition and display

The parameters of each isolated power system are collected by means of insulation monitoring instrument and insulation fault location instrument installed in each isolated power system.The collected data will be displayed on the interface of the monitoring system in real time. These monitoring parameters include insulation resistance of IT system to ground, transformer load current, transformer winding temperature and insulation fault circuit, etc.

■ Fault alarm

All kinds of faults in the medical isolated power system, such as insulation fault, overload fault, overtemperature fault and connection break fault, are uniformly processed and recorded, and information such as fault type, monitoring value, fault location and fault occurrence time can be displayed directly on the display interface.At the same time start the monitoring system sound and light alarm system, timely remind the relevant personnel, fault treatment.Among them, the sound alarm signal can be manually eliminated.

■ Remote parameter Settings and queries

Through the system, all kinds of alarm parameter thresholds of insulation monitors in medical isolated power supply systems can be adjusted and set remotely according to requirements, and these alarm parameter values can also be checked at will.The parameters include insulation alarm value, load current alarm value and isolation transformer temperature alarm value

■ Graphic display function:

The system can be in the form of a curve, showing the insulation status of each set of isolated power supply system, load status, as well as the isolation transformer temperature rise status, as well as their change trend, in order to facilitate the sub-managers to understand and analyze the operating changes of each power supply system, targeted maintenance and maintenance of some systems.

Insulation monitoring products of medical IT system (a four-piece set) include AITR S series medical isolation transformer, AIM-M10 medical intelligent insulation monitor, abakh 0.66P26 current transformer and AID series (AID10, AID150) external alarm and display instrument, etc., as shown in Figure 5.

Table 1 Insulation monitoring products of medical IT system (four-piece set)