Discussion on electric deepening design of large medical equipment

- Sep 22, 2017-

Electrical design requirements of large medical equipment manufacturers, because of the difference, the key still in design and equipment manufacturers of professional engineers to communicate, understand English materials, installation process and working principle of the real understanding of the equipment.

The equipment host must be equipped with a dedicated field distribution box, the distribution box and its connection switch (EAT) and emergency switch (AT) must be installed in place before the installation. Auxiliary equipment and other electric facilities (such as lighting, air conditioning etc.) power supply should be the hospital public power grid, control switch and circuit protection they can be installed in the field distribution box, but absolutely not allowed to supply the site distribution box.

The following is the circuit principle of the central power supply circuit of the DSA equipment in the tumor center:

System power supply conforms to the national standard, voltage 380V, maximum deviation shall not exceed 10%. Frequency 50Hz, maximum deviation shall not exceed 0.5Hz. The maximum deviation between the phases voltage shall not exceed 2% of the minimum phase voltage. Maximum power is 171KVA, continuous power 20KVA, power factor 0.9; maximum instantaneous peak current of 289A, the continuous current of 31A, the circuit breaker rated current 160A circuit breaker protection. Equipment requirements, dedicated line power supply. The three-phase line indicates the phase sequence and then is introduced into the power distribution cabinet with the PE line. The incoming cable must adopt a plurality of copper core wires and be connected to a circuit breaker with a rated current of 160A in the cabinet, and the cable color and circuit breaker specifications must comply with the provisions of the standard electrical installation manual. The distribution cabinet must have an open cover locking function to ensure electrical safety operation. The emergency power off button of the distribution cabinet shall be installed on the wall beside the operating table in the operating room, so that the operator can cut off the power supply in case of emergency.

System power cable

From the transformer to the field distribution box, it is best to configure a dedicated power cable, and must be copper core cable. In this power cable, do not access high-power inductive load, such as air conditioning, elevators, refrigerators, etc., in order to avoid interference caused by equipment start and stop. In order to ensure the power line with internal resistance on the table in the requirements, must be according to the actual length of cable laying resistance, transformer output value and field distribution box within its own resistance, calculated the minimum cross-sectional area of the cable laying, laying resistance length is longer, the output end of the transformer and the field distribution box higher values cable section requires greater.

At the beginning of the design, the equipment manufacturers will request separate ground, we should understand that the equipment to the ground steel plate on the ground wire should not be connected to other equipment, so as not to disturb.

It is difficult to set up separate grounding for the electronic equipment in the building with common earthing system. Because of the equipment shell, the metal component of the whole building, the steel bar and the electrical protective earthing system are all connected to the common earthing system. It is difficult to avoid the counter voltage from the electronic equipment to separate the ground wire to the outdoor single grounding electrode separately and completely isolate it from the common earthing system.

A single dedicated ground wire has high impedance in the case of high frequency (frequency of operation of the information equipment), so it is pointless to require a small resistance. Because the impedance of the dedicated ground wire is infinite under self resonance, it is equivalent to disconnecting and becoming an antenna, which allows the device to accept interference signals.

Individual grounding is not conducive to over-voltage protection.

In the case of TN - S systems, there is no need to worry about power frequency current, noise, or electronic equipment. In the case of electronic equipment, the steel pipe and the enclosed steel wire slot should be applied to avoid the single phase grounding short-circuit current to flow through the common grounding system, which will cause interference to the electronic equipment.

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