I don't see what AC current magnitude has to do with zero crossing. By nature, an AC current measurement is a kind of averaged quantity.it's not that easy. output currents are AC; how the diagnosis system will discriminate between zero crossing and phase loss?
suppose I do so, How a disconnected phase will be detected?
when a phase get disconnected the current of the other phases will be equal.
in 3-wire system, when a phase get lost, currents of two phases will be equal ( simple KCL). Therefore your recommended circuit cannot detect that.
Sorry if I was not clear enough! What I suggested and wrote that you need to process each phase individually and not together. This is the same principle that is used in the clamp on current meter.
You process each phase independently and get three outputs from three secondary coils.
All the three phases are detected together in case of ground fault interrupter. If for some reason, the sum of the currents in the three phases is not zero, that indicates that somewhere a leak is taking place. But we are not talking about that.
Why "but", everyone agreed to this point as far as I see.But in 3-wire system a phase is lost, still the sum of the currents is zero. A phase that is disconnected =0, and two phases with equal current.
In analog measurement, like galvanometer, AC quantities measured as RMS value. But how about measuring with MCU?
still beats meCan we conclude that the only remaining problem is that you don't know how to implement current imbalance detection?
Generally speaking, don't you think these method are rather slow? however in this application we don't need very fast diagnosis. It seems also expensive a transformer, bridge, ... .I feel that there are about one thousand Edaboard threads discussing AC current measurement by a microcontroller, starting with the classical analog circuits (rectifier+averaging filter+ADC or rectifier+rms-circuit+ADC).
But in 3-wire system a phase is lost, still the sum of the currents is zero.
Thank you,That is precisely the reason you must not sum the currents. You are simply detecting the condition when one of the phase is not having current but the two other phases are having current.
You have the following truth table:
Phase 1 Phase 2 Phase 3 Condition
Active Active Active Good
Inactive Inactive Inactive Good
-----------------------------------------------------------------------
Any other combination Fault
-----------------------------------------------------------------------
we need RMS value of AC values.
We do not need the current values; we just want to know whether a given phase is carrying current or not. We set a threshold and every current value above the threshold is considered 1 (active).
We next do an XOR of the three signals coming from the three phases.
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