I need to sense 3 phase 240 volts

There has to be something out there, I just don't know what terms to use to search for it.

I need to sense whether or not 240 volt 3 phase power is present.

Does anyone have recommendations, schematics, suggestions, old threads on how to sense whether or not voltage is present?

The situation is this: Passenger train. Three of the cars each have their own generator. Train gets plugged in at night . Each car with a generator can be powered by: the land line, it's own generator, or the generator of the car next to it. I would like to use a plc to sort out which source of power is the priority, whether or not to send power out to the rest of the train, whether it's own generator is running.

I was thinking about using a phase relays, but there are situations where it will not activate,which would result in the plc trying to put two sources together.

There is just voltage, not current, so I don't think a current sensor would work in this application.

The actual control is easy. I just need some suggestions on how to sense whether or not potential exists on the power inputs.

I currently use relay logic, but there are some drawbacks to this.

Thanks
Steve

You could just use 240V coil ice cube relay. If you don't need to sense all three phases, just one relay between L1-L2 would suffice.

good idea, can't be that simple, right?

Trainelectric said:

good idea, can't be that simple, right?

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Sure it could -- and you could use two relays to cover all 3 phases. Otherwise, try searching for a phase loss detector.

thought of that. the problem is that I could have two of the three phases (the plug between the cars loses one), the detector would not turn on, which would trick the plc into thinking there's no power there, so it would then try to hook two sources together, which results in a rather spectacular light show. Don't ask me how I know that.

If it could be possible that one or more phases are off, then you have to monitor each phase to neutral. A simple relay for each phase should be OK.

Relays would do the trick. If you need something more, you could look at something like this:

https://www.janitza.com/energy-and-power-quality-measurement-products.html

There you could see how many phases you are missing etc. But I think that might be overkill.

We've been known to use an elephant gun to shoot a groundhog around here.....

If its that critical - double them up per phase, so 6 relays in total and read all 6 inputs.

The chances of 2 relays sticking closed is almost impossible.

We do something similar, not to detect phase presence, but phase loss. We do this with a current relay in each phase. Thus we get confirmation of the entire path, but then only when current is supposed to flow of course. The 3 relay outputs are connected in series and then to a single PLC input.
In your case you should connect the 3 relay outputs in parallel and then to a PLC input. It is enough to generate an alarm.

Trainelectric said:

We've been known to use an elephant gun to shoot a groundhog around here.....

Click to expand...

Whatever works!! How far is Strasburg from Punxsutawney??

mendonsy said:

Whatever works!! How far is Strasburg from Punxsutawney??

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4 hours ish.

Another take.

If the various power sources are connected via plugs and there are lids on said plugs, then you can monitor the lids. Only one lid may be opened at a time.

I think that any system that is designed so that a PLC fault can cause fireworks probably needs rethinking. I would look at using changeover contactors so that two supplies can never be connected at the same time. Or at the very least mechanically interlocked contactors.

We use phase monitor relays to give a signal to PLC's & SCADA systems. These should give you status contacts:

http://ab.rockwellautomation.com/Ci...r-Protectors/Monitoring-Relays/Phase-Monitors

http://time-mark.com/product-category/3-phase-monitors/