Application of IT system in medical places and expansion of insulation detection function
Keywords: IT system insulation monitoring overload detection isolation transformer temperature detection fault location
1 Introduction With the rapid development of the national economy and the improvement of people's living standards year by year, people's demand for electricity has suddenly increased. At the same time, electric shocks and electrical fire accidents caused by power outages, leakage, and line insulation failures have also increased dramatically, posing a serious threat to people's lives and property safety. In order to strengthen the safety and reliability of the system power supply, "Code for Electrical Design of Civil Buildings" (JGJ 16-2008) Article 12.8.6 stipulates that: in category 2 medical premises, it is used to maintain life, surgery and other areas located in the "patient area" The medical electrical equipment and power supply circuits in the system shall all use medical IT systems. IT systems have the advantages of low leakage current and faulty operation. Therefore, IT systems have been widely used in medical places, underground mines, chemical enterprises, ships, telecommunications, metallurgy, petrochemicals, and transportation engineering.
2 IT system and its characteristics
2. 1 IT system definition and composition
The power terminal of the IT system is not grounded or grounded through high impedance. The exposed conductive parts of its electrical devices are connected to the grounding electrode individually or collectively through the protective wire (PE). In practical applications, IT systems are generally isolated from TN or TT systems by isolation transformers.
Under normal circumstances, only a small leakage current of the line-to-ground capacitance exists in the system. Figure 1 shows the schematic diagram of the first ground fault in the IT system. When the first single-phase ground fault occurs in the system, the fault current is the phasor and Id of the two non-fault relative ground capacitance currents. It will not cause personal electric shock or other accidents, nor will it cut off the power supply, ensuring the continuity of the system power supply. However, if the fault is not eliminated in time, when the second ground fault occurs in the other phase, it is equivalent to forming a phase-to-phase short circuit, causing the overcurrent protection device to operate, causing a power interruption, which is not allowed for important power supply sites .
Figure 1 Schematic diagram of IT system ground fault
Fig. 1 IT system grounding fault diagram
In order to prevent the occurrence of the above short-circuit fault, the T system should be equipped with an insulation monitor. In this way, when the first ground fault occurs in the system, the insulation monitor can detect the ground fault in time and send out an alarm signal (usually an audible and visual alarm signal) through the alarm device to remind the staff to rush out of phase in the second Before the ground fault, eliminate the fault in time and eliminate hidden dangers, so as to effectively ensure the continuity of the system power supply.
A special fault detector can be installed in the system. When the insulation monitoring detects an insulation fault, a start signal is given to the fault detector, and the fault detector starts to be detected one by one, or a hand-held fault locating device can be used to detect possible faults The circuit is checked point by point, and finally the fault point is found and the location of the fault point is displayed, which greatly facilitates the staff to troubleshoot.
In order to ensure the continuity of power supply of the system, the national "Electrical Installations of Buildings Part 7-710: Requirements for Special Devices or Places-Medical Places" GB16895.24-2005 / IEC60364-7-710: 2002 710.53.1 states: " ...... Overload protection is not allowed for the transformer inlet and outlet circuit of the medical IT system ... "to prevent the protection switch from cutting off the power when the system is overloaded. This requires that the insulation monitor in the system must also have load detection and overload alarm functions. In some important places, due to the continuous operation of the isolation transformer, the temperature may be too high and cause the isolation transformer to work abnormally. Therefore, the insulation monitor also needs to detect the temperature of the transformer in real time. When the temperature is too high, there should be a corresponding over-temperature alarm signal to remind relevant personnel to deal with it in time.
From the above analysis, we can see that a typical single-phase IT system, its components mainly include: isolation transformer, insulation monitor, current transformer, and external alarm and display, see Figure 2.
Figure 2 Block diagram of single-phase IT system
Fig. 2 Schematic diagram of the composition of single-phase IT system
In the system, the insulation monitor has the functions of system insulation detection, system overload detection and transformer temperature detection, as well as the alarm and display functions of the corresponding faults, and is generally installed in the terminal power distribution cabinet on site. The external alarm and display instrument is used to centrally display the corresponding detection value, and has an over-limit alarm function. It is generally installed in a place with obvious location, which is convenient for personnel to view. On the intelligence panel of the room.
2. 2 Characteristics of IT system
a. Since the live conductor at the power supply end of the system is not grounded, even if a single-phase ground fault occurs in the system, the system can only form a loop through the system's ground capacitance. The fault loop impedance is extremely large, the fault current is extremely small, and the risk of electric shock is very small, so it is not necessary Cut off the power supply to prevent electric shock, so as to maintain the uninterrupted power supply, only when the second ground fault occurs, it is required to cut off the power supply [1]. At the same time, the insulation monitor installed in the system can timely detect and give the system insulation fault alarm signal to remind the staff to eliminate the fault in time. Therefore, the IT system is a continuous and reliable power supply system.
b. The insulation monitor in the IT system, on the one hand, monitors the insulation status of the system in real time, on the other hand, it also detects the overload of the system and the temperature rise status of the transformer, and immediately alarms if an abnormality occurs. Therefore, the IT system can reduce electrical fire accidents caused by system heat and leakage, and greatly improve the fire safety of the system.
c. In the IT system, improving the insulation resistance of the loop and reducing the capacitance of the loop to ground are the keys to improving the safety and reliability of the system. Therefore, in the system design, the length of the power distribution line of the system should be shortened, the system capacity, the number of branch circuits of the system should be reduced, and the insulation protection measures of the line should be done. This restricts the IT system to be used only in important local power supply places, such as some program control production lines in chemical and pharmaceutical companies, operating rooms in medical places, and intensive care units.
3 Application of IT system in medical places Medical IT system is a typical example of IT system application. Because of the special nature of their functions, hospitals have special requirements for their power distribution methods. Such as surgical operating room, intensive care unit, etc., need to use IT systems to provide a safe, reliable, and continuous power distribution system.
3.1 Application of medical IT system According to the national standard "Electrical Installations of Buildings Part 7-710: Requirements for Special Devices or Places in Medical Places" (GB 16895.24–2005 / IEC 60364–7-710: 2002), the medical places are divided into 0 Class places, Class 1 places and Class 2 places. Because Class 0 and Class 1 locations do not use medical devices that are in direct contact with patients, or the equipment used will not cause harm to patients after power off, you can use the TN-S system, but it must be equipped with a residual current action protector, When a ground fault occurs, the fault circuit can be disconnected in time. At the same time, the residual current monitoring equipment can be configured to monitor the leakage current value of each loop of the system in real time, and an alarm signal is issued before the protection equipment acts, to avoid causing loop power failure and causing serious consequences [2]. For Class 2 medical sites, the power failure or ground fault of medical equipment will endanger the lives of patients. According to relevant standards and specifications, such places must use medical IT systems to ensure the continuity and safety of system power supply.
The 2 types of medical places that use IT systems include operating rooms, emergency rescue rooms, various intensive care units (ICU), cardiac catheters and contrast rooms. Each room should be equipped with an independent isolated power system. For multiple such locations, the power distribution scheme shown in Figure 3 can be used.
Figure 3 Power distribution plan for category 2 medical sites
Fig. 3 Power distribution scheme in Class II medical site
In the picture, each operating room and intensive care unit respectively use independent IT power supply systems. All IT systems are distributed by the operation department and the ICU main distribution cabinet through the TN-S system. The insulation monitors of each IT system and the residual current monitoring equipment in the main power distribution cabinet feed back each monitoring signal to the central monitoring room of the operation department through the RS485 bus based on the Modbus protocol, and the central control room's upper computer passes the central control System software for centralized monitoring. The operation status of each IT system and TN-S system can be displayed on the upper computer of the central monitoring room, which is convenient for the staff to monitor and manage the system.
Various operating rooms and intensive care rooms are equipped with separate IT systems according to the capacity of each system. The main medical equipment, shadowless lamps, multi-functional pendant and other electrical equipment must be powered from the IT system. Illumination lights, film viewing lights, and power doors do not require electricity from the IT system. Figure 4 is a diagram of an operating room or ICU power distribution system using a medical isolation power system. The insulation monitor monitors the insulation status of the IT system at all times, and gives an alarm signal when the system fails. The external alarm and display instrument communicates with the insulation monitor in real time through the RS485 interface to display the detection results of the insulation monitor, and A sound and light alarm signal is issued during the alarm. In addition to insulation monitoring equipment, the system is also equipped with an insulation fault tester and an insulation fault assessor. The insulation fault tester can find the circuit where the fault occurs online. It works with the insulation monitor. When the insulation monitor detects the insulation fault of the system, the insulation fault tester immediately starts fault location, and the insulation fault assessor periodically sends a Special test current, the test current flows through the fault location, is detected by the current transformer, and the fault circuit is evaluated by the electronic evaluator, and the evaluation result is sent to the alarm and display instrument for display.
Figure 4 Operating room or ICU power distribution system diagram
Fig. 4 Powr distribution system diagram for operating room or ICU
The medical IT system is also equipped with insulation fault location equipment, which can locate the faulty circuit in time while discovering the system insulation fault, which greatly facilitates the staff to understand the system status and troubleshoot the fault in time, thus effectively ensuring medical IT The safety and reliability of the system.
3.2 Precautions for the application of IT systems in medical places Due to the special nature of medical places, special attention should be paid to the following points when designing medical IT systems:
a. Medical IT systems must use isolation transformers for power supply in medical places, and should meet the requirements of the national standard "Safety of Power Transformers, Power Supply Units and Similar Products Part 16: Special Requirements for Isolation Transformers for Power Supply in Medical Places".
b. In order to reduce the capacitance of the medical system to the ground and improve the insulation strength, the distribution box of the IT system should be installed as close as possible to the use place, and the system capacity and the number of system branches should be reduced as much as possible, and the length of the system distribution line should be shortened as much as possible.
c. In the operating room where the surgical equipment such as heart surgery is in direct contact with the human heart, anti-shock measures must be taken. Sometimes an IT system with insulation monitoring alone is not enough. Local equipotential bonding should also be done so that all conductive parts in the protection zone are at the same potential level.
4 Conclusion The IT system with insulation monitoring can provide a safe, reliable and continuous power supply for local places, which is unmatched by other systems. Therefore, in some important production and processing places, medical places, and important equipment operation places, you can give priority to using IT systems. At present, China has not issued regulations and standards on insulation monitoring products for IT systems, and there are few domestic products for insulation monitoring and fault location of IT systems. Therefore, while looking forward to the introduction of national standards as soon as possible, we still need to work hard to develop various types of insulation monitoring equipment and fault location equipment for IT systems. I believe that in the near future, with people's full understanding of IT systems, IT systems will also be more and more widely used.
The article comes from: "Building Electric" 2010, Issue 4.
references
[1] Wang Houyu. Design, installation and inspection of low-voltage electrical installations. Second edition. Beijing: China Electric Power Press, 2007: 48-52.
[2] Shao Jianxun. Application of medical IT system in medical places. Information Management, 2008 (6): 32-39.
About the Author:
Yu Jing, female, undergraduate, engineer of Wuhan Ankerui Electric Co., Ltd., the main research direction is intelligent power monitoring and power management system
Notonthehighstree Notonthehighstree
Bossgoo(China)Tecgnology.(Bossgoo(China)Tecgnology) , https://www.cn-gangdao.com