3 phase monitoring system neutral fail problem

Hi all

I am building a 3 phase protection system, the 3 phases voltages are read as shown in the attached diagram, 3 transformers are used to measure voltage and one transformer is used to power the circuit on, the system works well except when the neutral fails, in this case the board does not turn off, and the voltages at the inputs of the transformers increases to a harmful value. How can I protect my board from this issue? How can I turn of the board when neutral cuts? And is there a way to sense the neutral (mean that is there a way to find out if neutral is present or not)?


Robert Wall's picture

Re: 3 phase monitoring system neutral fail problem

What sort of power supply system do you have? Can you describe it in terms of this Wikipedia article? Essentially, there are two ways of going about it, which of these will be effective or practical I cannot say from the information you give. One way will be to measure the neutral-earth voltage, the other to measure the imbalance between phases. You cannot sense the presence of the neutral directly (because if the system is totally balanced, you don't need the neutral anyway!).


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