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5 +1 things driving IIoT and 4.0: Smart Power

Volker de Haas started electronics and computing with a KIM1 and machine language in the 70s. Then FORTRAN, PASCAL, BASIC, C, MUMPS. Developed complex digital circuits and analogue electronics for neuroscience labs (and his MD grade). Later: database engineering, C++, C#, industrial hard- and software developer (transport, automotive, automation). Designed and constructed the open-source PLC / IPC "Revolution Pi". Now offering advanced development and exceptional exhibits.


February 22, 2021 14:43

Re "5 +1 things driving IIoT and 4.0: Smart Power".
There is one aspect of AC over DC that you don't mention. Safety - though at high voltages it won't make much difference. But at mains and lower voltages (>50V) AC is safer than DC. I believe that was an important consideration (as well as engineering practicalities) in using AC for mains supply. AC you can escape from, but DC will freeze the muscles and "hold" you.

That said, I have recently wondered if domestic electrical installations would not nowadays be better with an ELV DC aspect to them and mains (240 Vac) only for power items (ovens, washing machines, etc.). Lights (LED), consumer gadgets (phones, computers, etc.) all tend to run on ELV DC (5, 12, 24, etc. Volts) and it's so wasteful and frustrating to need so many mains plug PSUs around the house! Also local power generation (solar panels, wind, etc.) tends to generate ELV DC power and storage (batteries) are all ELV DC. UPS provision would be so much simpler - especially if part of the local generation storage backup system. And local EM radiation could be cut too.

0 Votes

February 23, 2021 08:36

@IanBJones Hi Ian Thanks for pointing to the fact that most arguments for DC in the industry could also well be applied for home electrics. You may know that with home electricity, we still have lots of legacy devices which need AC to run, like synchronous motor clocks in all kind of kitchen devices. The transition from Ac to DC will be much more critical as you would (like in industry) need two systems in parallel for quite a long time. In industry, you would decide to run one complete hall on DC, will older halls could stay with AC. At home, such a concept would be more critical but would also be a huge step to green energy. Let me say something about safety: It is a common misconception that DC would be more dangerous than AC. While AC gets dangerous for life up from 50 V, the value for DC is above 120 V. AC generates a higher current through the body because your skin works like a capacitor. With DC, you get a short high current when touching the voltage source and a short high current when letting go. Therefore AC does cause a much less controllable muscle contraction than DC at the same voltage. The danger for the life of low voltages (like 230 V) is not caused by the muscle contractions but by the fact of triggering cardiac ventricular fibrillation. DC can hardly trigger fibrillation. AC on the other hand, is able to trigger cardiac fibrillation. It is a mere accident that 50 Hz frequency is the worst frequency to be used in this aspect of safety: The fibrillation can only be triggered with current flowing through the heart at a certain time of the heart cycle (called vulnerable phase). 50 Hz gives the highest chance to strike just in this time slot. This is the reason why high-frequency AC is used in operations for sealing small vessels by electro-cautery (using much higher voltages and very small contact surfaces for a high current density which generates much heat). But there is indeed a safety risk in DC: It is the electric arc when mechanically switching off a load. The higher the voltage, the longer is the arc distance. AC has a self-extinction effect caused by the zero crossings of the voltage. Very high voltages (several 100 mV) can no longer be switched because there is no other way than mechanical switching. In DC Industry, the switching of loads is always done electronically and thus does not generate electric arcs. You do have other safety aspects with high voltages as there is also a high current through the body, which does immediately coagulate all proteins (it burns body tissue).

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