Isolated Power Supply (IPS)
Earthing systems are classified as IT, TT, TN systems. TN systems are predominately used in most establishments.
IT systems are distribution systems, which are preferably less compared to grounded systems at industrial institutions. The main reason for this is to maintain the installation integrity. But due to the electrical security it provides, IT systems are preferred for the supply of the critical divisions like OT and ICUs in a hospital environment. The main difference that discriminates IT systems from TN or TT systems is the non-presence of the grounding. In an IT system, an isolation transformer is used to isolate live and neutral conductor from earth. Each socket that is connected to this distribution system has its own individual grounding.
Classification of Medical Locations
Medical locations are classified by IEC 60634-7-710 according to the use of “applied parts”. An applied part is a piece of electrical equipment that is brought into physical contact with the patient, or might come into contact with the patient or needs to be touched by the patient.
The classification is as follows:
1. Group 0: Medical locations without applied parts
2. Group 1: Medical locations where applied parts are used externally or invasively to any part of
the body except for the locations described in group 2
3. Group 2: Medical locations where applied parts are used in applications such as intracardiac procedures, operating theatres and vital treatments where discontinuity of the supply can cause danger to life
(Class refers to the maximum break-in time with in which an emergency power supply must be
operational after a power failure.)
Example for allocation of group number and classification for safety services of medical locations
Interpretation of Standard
710.413.1.5 Medical IT System
– In group 2 medical locations, the medical IT system shall be used for circuits supplying medical electrical equipment and systems intended for life support, surgical applications and other electrical equipment located in the “patient environment” excluding equipment listed in 713.413.1.3.
– For each group of rooms serving the same function, at least one separate medical IT system is necessary.
– The medical IT system shall be equipped with an insulation monitoring device in accordance with IEC 61557-8 with the following specific requirements
– the a.c. internal impedance shall be at least 100 kΩ;
– the test voltage shall not be greater than 25 V d.c.; – the injected current, even under fault conditions, shall not be greater than 1 mA peak; –
– indication shall take place at the latest when the insulation resistance has decreased to 50 kΩ.
– For each medical IT system, an acoustic and visual alarm system incorporating the following components shall be arranged at a suitable place so that it can be permanently monitored
(audible and visual signals) by the medical staff: –
– a green signal lamp, to indicate normal operation;
– a yellow signal lamp, which lights when the minimum value set for the insulation resistance is reached.
It shall not be possible for this light to be cancelled or disconnected;
– an audible alarm which sounds when the minimum value set for the insulation resistance is reached. This audible alarm may be silenced,
– the yellow signal shall go out on removal of the fault and when the normal condition is restored. 710.512.1.1 Transformers for medical IT Systems
– Transformers shall be installed in close proximity to, inside or outside, the medical location and placed in cabinets or enclosures to prevent unintentional contact with live parts.
– The rated voltage (Un) on the secondary side of transformers shall not exceed 250 V a.c 710.512.1.6 Medical IT Systems for group 2 medical locations
Transformers shall be in accordance with IEC 61558-2-15, with the following additional requirements:
– The leakage current of the output winding to earth and the leakage current of the enclosure, when measured in no-load condition and the transformer supplied at rated voltage and rated frequency shall not exceed 0.5 mA.
– Single phase transformers shall be used to form the medical IT systems for portable and fixed equipment and the rated output shall not be less than 0.5 KVA and shall not exceed 10 KVA.
– Monitoring of overload and high temperature for the medical IT transformer is required.
Typical Installation In compliance with IEC 60634-7-710
Isolated Power Supply (IPS)
The Isolated Power Supply (IPS) typically consists of four main leading elements
a) Medical Isolation Transformer
b) IT Distribution system with multiple MCB’s (typically 12 nos)
c) Insulation Monitoring device
d) Remote Alarm System
Medical Isolation Transformer
Isolation Transformers are the main devices of Isolated Power Supply Systems. With the help of isolation transformer, the supplied room is isolated from the grounded System. Consequently, the leakage current within the room is reduced from mA levels to µA levels. Besides in case of initial Phase-Ground short circuit, there shall be no blackout.
Complies with IEC 61558-2, safety of power transformers, power supply units
Part 2-15: Particular requirements for isolating transformers for the supply of medical locations:
- Short circuit voltage ≤ 3%
- No-load input current ≤ 3%
- Inrush current ≤ 12 x rated input current
Insulation Monitoring Device
Designed to continuously monitor the insulation resistance of the unearthed connected electrical network and automatically detect if there is any fault between neutral & ground. In the event of an earth fault, the controller will automatically detect which circuit of the isolated power supply system contains the fault, and then indicate to the user via an alarm, which of the sockets within the hospital critical area, such as the operating room, is in fault. This maybe due to a faulty cable, socket outlet or piece of equipment plugged into the socket outlet.
Injection of a low-frequency AC voltage between the network and the earth. Insulation measurement through the earth leakage current in the IMD.
– Response time <1s
– Internal Impedance 110Khz
– Satisfactory insulation resistance
– Drop in insulation resistance below the
fault threshold (Orange Light).
– Transformer management:
– Display Transformer Secondary
– Overload Alarm
– Overtemperature Alarm
- IPS systems range from 4-6-8-10 KVA.
- Single Phase for medical locations
- Outgoing double pole MCB load typically #12 nos.
- Improved process of isolation fault detection and correction, saving time and cost.
- Minimising patient disruption saving time and cost, as well as, enhancing safety