True Professional Engineer
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Monday, June 26, 2017

High technology problem after a electrical power shutdown

A recent expansion called for incoming electrical power shutdown for installation of new VCB (Vacuum Circuit Breaker).

It had been a normal practice that engineering team has to standby to rectify issues caused by power shutdown. I always refer to this as the "high technology problem", because this type of problem seldom happen to the traditional equipment with hard wired control circuit.

As the digital technology advanced, a lot of control had been digitized. More and more companies are now promoting the "4th Industrial Revolution". I believe that this is the right direction but sometimes I cannot stop myself doubting on how many of those involved really understand the practical problems behind this development.

Digitizing means more electronic components are used in plant automation. The advantages for electronic components are low power consumption, higher flexibility in equipment production and modification.  Nevertheless, digitizing also means that higher chances of component failure caused by electrical surge.

With a high number of PLCs and VFDs used in the plant automation, it had been a norm that a few VFD fail after power shutdown. This time, five VFDs need to be replaced.

The same happen to earth leakage and over current relays. One unit is replaced this time.

There may be someone thinking that it is caused by unhealthy electrical quality. The fact is we had carried out various electrical quality check and the same problem never end.

One other problem that frequently faced is the Ethernet communication used for production line PLCs and VFDs. The lines are fully auto, with ability to set in recipe which is known as flexibility. But the system tends to lost communication. Sometimes problem is rectified by replacement if Ethernet switches, but quite often the issue is solved by a few restarting of the control system and/or unplugging and plugging of Ethernet cables. We believe this is not a professional method, but it works.


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