Neutral loss detection in 3phase 4 wire systems

[bhagyashri41294]

Neutral loss detetion in 3phase 4 wire system

I want to detect neutral loss ,in 3phase 4 wire system but, In my circuit Resistor chain is connected between all phases and neutral ,so it always creates virtual neutral point ,so can i detect neutral failure even if the virtual neutral point is present.

 

[KlausST]

Re: Neutral loss detetion in 3phase 4 wire system

Hi,

Maybe just two lines are not enough to describe the complete situation.
A drawing may be useful.

****
Without more information we can guess only.
My idea. If usual voltage measurement or current measurement gives no reliable results, then maybe you should consider to "introduce" a measurement signal.
Maybe DC is suitable, because your system is AC only.
Mesure the DC current flow to detect of neutral is connected or not.

In any case you neet to specify a threshold level ... at which value you consider it to be connected.

Klaus

 

[bhagyashri41294]

Re: Neutral loss detetion in 3phase 4 wire system

i dont understand about the measurement signal,can you please explain with help of schematic.

 

[KlausST]

Re: Neutral loss detetion in 3phase 4 wire system

Hi,

Please provide the schematic about your situation.

I like to help, but I don´t like to do your job.

Klaus

 

[bhagyashri41294]

Re: Neutral loss detetion in 3phase 4 wire system

Refer schematic as below

 

[KlausST]

Re: Neutral loss detetion in 3phase 4 wire system

Hi,

This schematic seems to be a measurement circuit.

But first we need a circuit about your current 3 phase 4 wire situation. Source, load, earth, wiring, connectors, voltages, currents, where do you expect the loss of neutral ...

Klaus

 

[andre_luis]

Re: Neutral loss detetion in 3phase 4 wire system

The above circuit lacks a diode in reverse polarization in parallel with the optocoupler input, so as to prevent a reverse voltage above the allowed, which usually lies in the range of a few volts (besides of course the opto input pins are reversed). Another problem is that considering typical values for most optocouplers, the 330K resistor in series with Neutral seems to provide a somewhat small current that is specified for most optocouplers, assuming line voltage of 220Vrms at each phase.

 

[FvM]

Re: Neutral loss detetion in 3phase 4 wire system

First point to consider is that you can't clearly distinguish neutral interruption and phase loss respectively large voltage asymmetry. Respectively you need to specify which voltage difference between virtual star point and actual neutral terminal should be considered as failure.

 

[schmitt trigger]

Re: Neutral loss detetion in 3phase 4 wire system

Elaborating what FvM has mentiond;
You require 3 independent voltage-value monitoring circuits, one for each phase vs. neutral.
Your simplistic circuit is neither.

When the neutral connection is lost, there will be a voltage imbalance. You will have to check all relationships: R-N vs S-N, S-N vs T-N, and finally T-N vs R-N.
When a voltage delta, which you have established previously, is exceeded, you trigger an alarm.

 

[bhagyashri41294]

Re: Neutral loss detetion in 3phase 4 wire system

schematic is about neutral detection circuit where 3 phase voltage input is given and currents are not measured.i expect neutral loss detection for voltage measurement.

 

[KlausST]

Re: Neutral loss detetion in 3phase 4 wire system

Hi,

schematic is about neutral detection circuit where 3 phase voltage input is given and currents are not measured.i expect neutral loss detection for voltage measurement.

I am unable to help, as long as you don´t give the requested informations.

again:
I don´t need to see your meausrement circuit.
--> I need to see how your 3 phase 4 wire system looks like (again: wihthout your measurement circuit).

Klaus