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Importance of Requirement of Isolated System in Hospitals Isolated systems were first introduced in Hospitals World wide as to prevent Fire and Explosions in operating areas where inflammable gases were used for Anesthesia. It is general feeling that as of today inflammable gases are not used in hospitals, why still isolation system is recommended or mandatory? Presently so many electrical and electronic gadgets are used for benefit of patient. Hence shock hazards to patient is increased. Today medical and nursing are progressively dependent on electrical apparatus for saving life of a hospitalized patients. Presently more cardiac operations are performed, In some of which patient’s life is dependent on artificial stimulate and regulate heart action. At the same time equipment, Surgeon, Nurse may be standing on prepping solution, blood, urine and other conductive fluids that reduces the passage of unintended electrical current. Isolated system reduces the ignition hazard from arcs and sparks between line conductor and grounded metal and mitigates hazard os shock or burn from electric current flowing through body to ground. Reverence to these facts may be found in the Standards for Health Care Facilities NFPA 99 and USA National electrical code NFPA 70. It is the purpose of this writeup to explain the other advantages that isolated power system offer such as: 1. Reduced shock hazard 2. Continuity of power 3. Noise reduction 4. Advance waning of equipment failure Please note the copy of NFPA NEWS Brief referring to electrical shocks in operating rooms which have installed grounded power. In conclusion Isolated Power Systems supplies special protection against electrical shock in “wet Locations”or any area where the interruption of power cannot be tolerated. 1. Reduced shock hazard A- Grounded system: Transformer Phase = L2 0V Neutra 1000 ohm 230 V L1 Conventional grounded system with typical 1000 ohm person Ground Fig. 1: Grounded System Fig. 1 above shows schematic of conventional grounded system. The neutral of the transformer is bonded to ground, which, if adequately sized will provide equipotential bond between the neutral and ground conductors. As the fig. Shows, normally we would expect 0 volt from ground to neutral and 230 volts fronm the conductor to either neutral or ground. If we assume that the person has a body resistance of 1000 W and comes in contact with line conductor the following result is expected as shown in the equivalent circuit Fig. 2. SWITCHTR TR NICS Medicare Company Page 03 1000 ohm Person 230 =230 mA V = -----I=— R 1000 Fig. 1: Schematic representation of 1000 W person in contact with line conductor The current of 230 mA would flow from the line conductor - via the 1000 W person - and return to neutral via the vary low impedance neutral ground connection. This 230 mA could prove fatal to our 1000 W person. NOTE: should our person have a reduced ohmic resistance, due to excessive moisture or internal body connection, we could expect potentially lethal current to flow. (In this example system capacitance has been neglected as the impedance value is is very high compared to neutral ground bonding) B. The Isolated System (IPS) Transformer Phase = L2 Neutra C1 C2 1000 ohm L1 Isolated Power system with typical 1000 ohm person Ground Fig. 3: Isolated Power Ungrounded System with Typical 1000 ohm person Fig. 3 shows the schematic representation of Isolated Power System (IPS). The IPS is a system in which transformer neutral - ground connection is deliberately omitted. In this we will see how our 1000 ohm person is protected against potentially lethal shock hazards. Consider only Isolation system without any external connected equipments, which will only increases system’s net capacitance and leakage current C1 C2 Schematic Representation of Isolated Power System (IPS) Fig. 4: Repesents Schematic representation of Isolated Power System (IPS) Fig. 4 assumes that a typical equally distributed balanced capacitive system where small leakage current, say 50 µA allowable leakage current for medicinal transformer, flow from L1 via C1,through ground and returns ti L2 via C2. Page 02 SWITCHTR TR NICS Medicare Company7 NOTE: On the proper system there will be negligible leakage current in parallel in net capacitance due to resistance which is not considered in this example. Considering balanced capacitive load, C1 = C2. We can measure the voltage drop across across system capacitance by using high impedance voltmeter. Being balance system voltage drop will be equal and 115 V from each line to ground for 230 V system.( Leakage current can be measured by connecting mA or µA meter from either L1 or L2 to ground.) NOTE: This is not recommended on grounded system. By using Ohm’s Law we will now examine circuit parameters more closely of Fig. 4 above. Z - Impedance V - Voltage across capacitor 115 V = ----------Z=— = 2.3 x 10 -6 Ohms 50 x 10 I i - current flowing (say 50 µA) 6 HENCE impedance value of C! Or C2 is 2.3 Mega ohm (MW) Value of C1 or C2 can be worked out as: -6 1 1 C = ------------------ =-------------------------------- = 0.001386 x10 Farads = 0.00138 mF 2 x p x F x Xc 2 x 3.142 x50 x 2.3 x10 C - capacitance Xc - reactance = Z F - frequency 50 HZ Now let us concider the 1000 ohm person comes in contact with line L2. Let us calculate the voltage C1 L2 L1 C2 1000 ohm Person L1 C1 L2 C2 R 100 ohm Person Fig. 5: 1000 ohm person in contact with one of the line now let us calculate the voltage present across the 1000 ohm person. 6 2300000000 2.3 x 10 x1000 =----------------Total impedance as C2 in parallel with 1000 ohm =------------------------= 999.957 say 1000 W 6 2301000 (2.3 x 10 ) + 1000 The conclusion is 1000 W person shunts C2 completely 230 V = ---------------------Total leakage current from L1 to L2 is current passing through 1000 W person = ---= 100 mA 1000 + 2300000 R Our 1000 W person coming in contact with L2 has approximately double the leakage current to 100 mA which is still extremely low level. 1000 x230 = 0.1 V Voltage across C1 will be 229.9 V. Voltage across the person would be ----------2301000 In Isolation Power System Line Isolation Monitor has 2 adjustable hazard levels. They are 2mA and 5 mA SWITCHTR TR NICS Medicare Company Page 03 Now let us compare Isolated Power System with Grounded Power System and our 1000 ohm person in contact with line conductor in both cases. V Person is the voltage across 1000 ohm person I Person is the current passing through 1000 ohm person Grounded V Person 230 V I Person 230 mA Isolated Power system 0.1 V with 50 mA leakage current 100mA with 50 mA initial leakage current 5 mA and 5 V theoretical maximum values with LIM reading of 5 mA 2 mA and 2 V theoretical maximum values with LIM reading of 2 mA Hence Isolated Power system considerably offers greater protection to operator and patient. C. Line Isolator Monitor (LIM) Line Isolator Monitor is a devise which continuously monitors impedance (capacitance and resistance) from all lines (single phase and three phase) to ground and indicates what current would flow through a patient of body resistance 1000 ohms, should the patient come into contact with live conductor (i. e. defective equipment) A Note on interpretation of LIM reading many variables exists to exactly what current could flow through the patient. 1. The value of 1000 ohms may vary between less than 100 ohms to 20000 ohms depending on the condition of the patient (moisture content, muscle condition, dry skin etc.) 2. Parallel leakage return paths will also bypass a portion of leakage current from the patient. D. Conclusion: We have seen how Isolated Power System (IPS) helps to protects the patient from electrical shock hazards. We have made these calculations of first order, and as simple as possible so that only basic knowledge of Ohm’s Law is sufficient to understand the importance of Isolation System concept. ICU and ICCU areas, where patient may be connected to several pieces of equipment, all which contain their respective leakages, both resistive and capacitive, greatly add to possibility of hazardous leakage currents flowing. We must never neglect the fact that leakage on a grounded system return via a low impedance of parallel path to a ground - for example our 1000 ohm patient. Also patient operated in operation Theater is protected for leakages foe a few hours remains unprotected for several days in ICU or ICCU. The Isolated Power system (IPS) does not have low impedance connection. It has high impedance capacitive / resistance return path. This provides additional layer of safety to protect operator and patient. The principals are not different outside the operating room. Only the difference of “wet location”is present to recommend that IPS is better solution and then only when continuity of supply is is concerned, as per US standards. But in India NEC 1985 recommends department wise of hospitals. It is recommended for 14Anaesthetic Room, 15- Operating Theater, 16- Operating Preparation room, 17- operating Plaster room, 18Operating Recovery Room, 19- Out patient Operating Theater, 20- Heart Catheterization Room, 21- Intensive Care Unit (ICU), Intensive Cardiac Care Unit (ICCU) 22- Intensive Examination Room, 23- Intensive monitoring Room, 24- Angiographic Exmination Room, 25- Hemodialysis Room, 27- Central Monitoring Room. In addition to this list IPS is also recommended as additional safety in NEC 1985 for 4- Delivery Room 7- Examination or Treatment Room, 8- Labor Room, 13- Physiotherapy Room Page 04 SWITCHTR TR NICS Medicare Company7 2- Continuity of Supply: Probably strongest argument for the application of Isolated Power System (IPS) where continuity of power supply is essential. In USA article 517-20(a)of the 1993 National Electrical Code states that single phase receptacles suppling wet locations shall be provided with ground fault circuit interrupters (ELCB), If interruption of power can be tolerated or Isolation Power System (IPS) if If interruption of power can not be tolerated. With Isolated Power System ELCB does not trip maintaining power to the equipment. This gives the hospital personnel choice of what to do since the equipment may be supporting patient’s life. At the same time during such time Line Isolation Monitor would clearly alarm as to the fault condition so that action can be taken. 3- Noise Reduction: The increased use of sanative electronic system in the hospital environment has created growing need to supply these systems with “clean” voltage, free of noise and transients. Many types of data storage and monitoring equipments may be extremely sanative to the transient and line noise which is frequently present on voltage feeders. The Isolated Power System (IPS) contains high quality shielded medicinal Isolation transformer which provides a convenient and effective means of greatly reducing or even eliminating line to line and line to ground noise on voltage feeders. Many manufacturers of voltage sensitive equipment have recognized the problem created by transient and noise on their equipments input line and have provided a measure of protection. The problem, however may not be adequate to frequent or serious disturbances. Although the primary reason for Isolated Power System (IPS) design and installation was not to archive noise reduction but to provide a low leakage secondary power system, we must consider the “built in” advantages of of the system again when comparing Isolated power with conventional grounded power system. 4- Advance warning of Equipment failure: It is required that all hospital biomedical equipment that may come in contact with the patient be periodically tested for leakage currents. Many large hospitals may have well in excess of 10,000 pieces of equipments. This creates a nightmare situation for the hospital electrician or biomedical engineer or whoever is in charge of equipment testing. As with all testing the values of leakage found at the time of test were just that. A few minutes, hours or even few days later, the equipment may have been exposed to environmental conditions which caused further decline in insulation integrity. Liquid spillage, cable damage, equipment misuse, or just plain heat aging through continued usage are all factors which may contribute to the decline of insulation value. Any help that can be given to let the equipment operator know that his/her device is in correct and safe condition, is benefit to both operator and patient alike. Isolation Power System (IPS) contain a Line Isolation Monitor (LIM). This devise continuously monitors all potential parallel leakage paths to ground. The LIM monitors all circuitry from the isolation transformer via circuit breakers and power and ground modules and finally each piece of connected equipment. Should if faulty piece of equipment be plugged into any of the sockets of Isolated Power System (IPS), then this would immediately cause LIM to alarm, a warning that such an event had just occurred. The operator can now choose to remove the equipment or continue to use it by taking extra caution that this this may cause a serious hazard to the patient or operator should either comes in contact with other line conductor. SWITCHTR TR NICS Medicare Company Page 05 If we compare the same occurrence on a grounded system, and use as an example, a line to ground fault, then we are back our colourful situation as described in section 2 A. When initially energized, a piece of equipment may operate correctly and be in a safe condition. However during operation mal function may occur due to spillage of liquid or cable damage (cart running over power cable or equipment being dropped) In any case result would be the same The level of electrical safety has now been reduced. Such occurrences on an Isolated Power System (IPS) would as described above result in the LIM alarming and warning being issued of potential fault hazard. 6- Conclusion: Isolation Power System (IPS) provide many advantages and levels of protection over conventional grounded system. The grounded system is excellent where unskilled operators or electrically unknowledgeable people come into contact with everyday equipment. It’s operation is simple and any failure generally results in equipment or circuit disconnection, very quickly within less than one cycle. However, grounded power systems are potential killer should a grounded person comes in contact with the line conductor. How many of us has never received some form of electric shock ? Isolated Power Systems (IPS) are the best solution for reliable and safe power particularly in the hospital environment, It has been the intent of this paper to try to explain to the decision makers, in layman’s term, some of the main benefits to having Isolated Power System (IPS) in their faculties. Page 06 SWITCHTR TR NICS Medicare Company7