I need to sense 3 phase 240 volts
- Thread starter Trainelectric
- Start date
mendonsy
Member
It will take a bigger gun to get that groundhog!
Trainelectric
Member
OP
um, we're a railroad, remember?
https://tse1.mm.bing.net/th?id=OIP.Ef8izu0q4J8GKXLQVbojTAE3DI
I think I will be making two changes to my existing circuit. I will be using your idea of the relays, and making the two major inputs on a reversing contactor so there's a mechanical interlock on them as well as the software interlock.
That was easy.
https://tse1.mm.bing.net/th?id=OIP.Ef8izu0q4J8GKXLQVbojTAE3DI
I think I will be making two changes to my existing circuit. I will be using your idea of the relays, and making the two major inputs on a reversing contactor so there's a mechanical interlock on them as well as the software interlock.
That was easy.
Isn't experience a wonderful thing?
So, if you aren't concerned about phase rotation, and just power present, use four 120VAC coil 2PDT relays (I'm assuming that your system has a neutral as well as the three phase lines. And I'm assuming a Wye system. Be sure to correct me if I'm wrong).
Wire three of the relays to a different phase and the neutral. This way the individual 120VAC lines will turn on its own relay.
Use three of the N.O. contacts in series to indicate "Power Ready". Use these three contacts to turn on the fourth relay.
Tie the other three N.O. contacts on the first three relays in parallel. Connect one side of this network in series with a N.C. contact on the fourth relay to indicate "Power Fault".
Trainelectric
Member
OP
Another fun thing of this installation is that the ground power is 240 delta, while the generators are 240 y.
Each of the generator cars has a 120/208 transformer bank, while the cars downstream each has it's own 240/120 transformer. Makes load balance easier.
Anyway, is there any reason I can't use 240 volt relays across the phases? There's this wild phase that needs dealt with.
I have a son who is an EE, plus his boss, looking at this. Things were getting complicated.......
Each of the generator cars has a 120/208 transformer bank, while the cars downstream each has it's own 240/120 transformer. Makes load balance easier.
Anyway, is there any reason I can't use 240 volt relays across the phases? There's this wild phase that needs dealt with.
I have a son who is an EE, plus his boss, looking at this. Things were getting complicated.......
Tom Jenkins
Lifetime Supporting Member
For a couple hundred bucks I'd go with a regular phase monitoring relay. Most have time delays etc. built in.
For example:
http://www.alliedelec.com/search/results.aspx?term=phase+monitoring+relay
For example:
http://www.alliedelec.com/search/results.aspx?term=phase+monitoring+relay
As long as you are just trying to monitor the 3 phase "hot" wires you don't need to worry about the wild leg. That only comes into effect if you are using single-phase loads/circuits.
From casually reading your posts here it sounds like you are only doing 3 phase.
Okay so use 240VAC coils. Wire A&B phases to the first relay, B&C to the second relay, and C&A to the third relay. The fourth relay will need to have a 240VAC coil as well.
The recommendations for a phase loss monitor will only show if you have proper 3 phase or not. It won't indicate that you have power across two of your phases. If you hadn't specified the need for the detection of power being present (but not all 3 phases) I would go with one of those.
The recommendations for a phase loss monitor will only show if you have proper 3 phase or not. It won't indicate that you have power across two of your phases. If you hadn't specified the need for the detection of power being present (but not all 3 phases) I would go with one of those.
Just something that I would like to chime in here since it has been mentioned:
I would not trust a check for voltage across any of the three phases to a grounding or grounded conductor (aka neutral or ground). Your voltage can back-feed through the transformers and motor windings under certain circumstances and it would be easier to avoid that during design than deal with that state in your system. However you are choosing to verify voltage, it needs to be leg-to-leg. A to B, A to C, B to C.
As far as more specific power monitoring (other than having voltage on all three phases), would being able to show a fault with a power source not be enough? Once a fault with the power source is made known someone will be there to troubleshoot it.
I would not trust a check for voltage across any of the three phases to a grounding or grounded conductor (aka neutral or ground). Your voltage can back-feed through the transformers and motor windings under certain circumstances and it would be easier to avoid that during design than deal with that state in your system. However you are choosing to verify voltage, it needs to be leg-to-leg. A to B, A to C, B to C.
As far as more specific power monitoring (other than having voltage on all three phases), would being able to show a fault with a power source not be enough? Once a fault with the power source is made known someone will be there to troubleshoot it.
Last edited:
tragically1969
Member
Is that a joke ?
Use the right tools for the right job:
https://www.tele-online.com/resources/data-sheets/en_e1pf400vsy01.pdf
Just make sure that when you are switching the power that everything is electrically and if required mechanically interlocked so you cant crash the two supplies should the PLC or the relays fail
Last edited:
GaryS
Member
This thread takes me way back to when I first started in the industry
Go into a mill and see 3 light bulbs hanging from the ceiling in the middle of the room
All glowing at about ½ bright.
That’s the phase monitor, 1 for each phase to ground
If one is out the other 2 would glow at full bright. Dark light phase is grounded
In those days the system was ungrounded by design. That way if a single motor faulted to ground, wouldn’t take the plant down, you would see it in the lights. Keep running until the next shift change and fix it between shifts Keep production up.
Of course if a second motor faulted to ground on different phase then the whole plant went down theni became an all hands on deck emergency.
In those days they used knob and tube wiring in the mills.
Go into a mill and see 3 light bulbs hanging from the ceiling in the middle of the room
All glowing at about ½ bright.
That’s the phase monitor, 1 for each phase to ground
If one is out the other 2 would glow at full bright. Dark light phase is grounded
In those days the system was ungrounded by design. That way if a single motor faulted to ground, wouldn’t take the plant down, you would see it in the lights. Keep running until the next shift change and fix it between shifts Keep production up.
Of course if a second motor faulted to ground on different phase then the whole plant went down theni became an all hands on deck emergency.
In those days they used knob and tube wiring in the mills.
I was at a safety update class yesterday and they showed us the Safe Side products.
http://www.graceport.com/safeside
http://www.graceport.com/safeside
janner_10
Lifetime Supporting Member
Is that a joke ?
Use the right tools for the right job:
https://www.tele-online.com/resources/data-sheets/en_e1pf400vsy01.pdf
Just make sure that when you are switching the power that everything is electrically and if required mechanically interlocked so you cant crash the two supplies should the PLC or the relays fail
Not it is not. If you took the time to read the original post, you would have seen he has ruled out a phase relay.
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