Zero Sequence CT

[Ingenieur]

why are you doing this?
personnel protection? if so a really bad method
equipment protection? won't work, but even if it did a ngr on the supply xfmr is better, cheaper
can't trip each circuit but can alarm and operate while you isolate the fault
could put a cheap gf voltage imbalance alm on each ckt to id or trip

 

[junkhound]

real experience in lab work or field work dealing with this subject

But you are not in a lab ?

If in a lab you can build any type CT (or active hall effect circuit) that can detect about anything you want. Years ago for a military program built a hall effect sensor that could control the current draw of a 200A line to 1 micoramp. note; biggest problem was maintaining stability of a system with > 160 dB gain

Only field work on the subject was using CT to detect why PT blew a fuse every time a genset shut down. Had been rewired to leave field current on during slowdown!

 

[buffalonymann]

no one is upset, just amused
you ask, we respond, we are wrong and you stubbornly defend your position
and you toss in passive agressive back handed insults for good measure
do as you like, it will work fine, seriously, let us know how it works out
it is you who do not understand the subject matter, if you did you would not ask
do you know what symmetrical components are? the 0 seq is one of them

I have 30 years experience dealing with sgf (sensitive and nml gnd fault protection)
been required in mining and oil and gas forever
just wrote a federal law on it

these guys are industry leaders in the subject
see if they make a 2 wire passive ct rated for 0.1 A
http://m.littelfuse.com/~/media/fil...es/111-groundfault-ct-selection-flowchart.pdf

I strongly suggest you hire an engineer in this matter
200 ckts
material/install
$250k-$300k or more
the ct needs wired to a relay and the relay to the cb
forget the plc, there is a reason it's never done that way

This is amusing - I posted on the engineering page looking for feedback on my project. You offer some opinions and I attempt to get to the basis for your opinions which then you make snide comments because I asked, and then the snowflake starts high-fiving you for the snide comment. Any real engineer would have explained the basis for their opinions on a matter like this.

Thanks for your input; I'll look for somebody who has some experience and training in this subject matter. Oh, you pointed out it is I who doesn't know the subject matter, what was your first clue to arrive at that idea? The fact that I posted on an engineering website seeking feedback?

 

[buffalonymann]

But you are not in a lab ?

If in a lab you can build any type CT (or active hall effect circuit) that can detect about anything you want. Years ago for a military program built a hall effect sensor that could control the current draw of a 200A line to 1 micoramp. note; biggest problem was maintaining stability of a system with > 160 dB gain

Only field work on the subject was using CT to detect why PT blew a fuse every time a genset shut down. Had been rewired to leave field current on during slowdown!

I understand - From what I read about these zero sequence current transformers it leads me to believe they are well suited for this application. The info came from littlefuse, I guess I could call them and ask their opinion on how their product would work for my app.

Thanks for the input

 

[drktmplr12]

This is amusing - I posted on the engineering page looking for feedback on my project. You offer some opinions and I attempt to get to the basis for your opinions which then you make snide comments because I asked, and then the snowflake starts high-fiving you for the snide comment. Any real engineer would have explained the basis for their opinions on a matter like this.

Thanks for your input; I'll look for somebody who has some experience and training in this subject matter. Oh, you pointed out it is I who doesn't know the subject matter, what was your first clue to arrive at that idea? The fact that I posted on an engineering website seeking feedback?

oh brother. :roll: he has being doing this, in the field, for 30 years and also has a PE license, can perform the calcs, and tell you exactly what to use to achieve what you are asking for. i'm not sure how you gathered from his posts that he doesn't know what he's talking about. he pointed out that your concept would work, in theory, but real world conditions (non-ideal) make your approach impractical due to inaccuracies of the coil operating at the extreme of its range (Ct's are not linear devices, but we operate them in a linear region). the fact that this appears to be is lost on you tells us you are not understanding a key concept of how CT's operate in the real world. there's nothing wrong with that, we are all continuously learning.

you are trying to pick up 100 mA of ground fault on trace heaters (have't provided typical load, important information). a zero sequence CT is not what you want to use to achieve this and there are very good reasons (previously stated) for it. the problem is you are looking (googling) for "ground fault sensing CT". that would be zero sequence. if you read more about applications of zero sequence CT's in ground fault sensing, you will see they are intended for much higher secondary currents that what you specified. ground fault is detected by summing CT secondary currents for each of the three phases. they should equal zero.

there are industrial product offerings, UL listed and warrantied by the manufacturer, that do exactly what you are asking for. if you insist on engineering something else-you may be taking the liability if something happens because it did or didn't trip when it was supposed to. i hope no one gets hurt in the process. :happysad:

lastly, it is this engineer's opinion that relying on a PLC for the safety function described is not advised.

 

[Jraef]

Why not just buy an electronic circuit breaker with a 100mA GF trip unit in it already, dispense of all that external stuff.

And also, my opinion is that the PLC is superfluous here. A dedicated trip unit, whether internal or external, is going to be more reliable if not safer.

 

[buffalonymann]

oh brother. :roll: he has being doing this, in the field, for 30 years and also has a PE license, can perform the calcs, and tell you exactly what to use to achieve what you are asking for. i'm not sure how you gathered from his posts that he doesn't know what he's talking about. he pointed out that your concept would work, in theory, but real world conditions (non-ideal) make your approach impractical due to inaccuracies of the coil operating at the extreme of its range (Ct's are not linear devices, but we operate them in a linear region). the fact that this appears to be is lost on you tells us you are not understanding a key concept of how CT's operate in the real world. there's nothing wrong with that, we are all continuously learning.

you are trying to pick up 100 mA of ground fault on trace heaters (have't provided typical load, important information). a zero sequence CT is not what you want to use to achieve this and there are very good reasons (previously stated) for it. the problem is you are looking (googling) for "ground fault sensing CT". that would be zero sequence. if you read more about applications of zero sequence CT's in ground fault sensing, you will see they are intended for much higher secondary currents that what you specified. ground fault is detected by summing CT secondary currents for each of the three phases. they should equal zero.

there are industrial product offerings, UL listed and warrantied by the manufacturer, that do exactly what you are asking for. if you insist on engineering something else-you may be taking the liability if something happens because it did or didn't trip when it was supposed to. i hope no one gets hurt in the process. :happysad:

lastly, it is this engineer's opinion that relying on a PLC for the safety function described is not advised.

I understand they're typically intended for higher currents; I would like to find a higher end CT that will pick up milliamps. The bottom line is that although I'd like to pickup the 100mA signal, the current will continue to rise and will produce a signal in the secondary. A signal between 2mA to 8mA will turn on the bit in the PLC and that is my goal.

is there any basis for your opinion about the PLC?

 

[buffalonymann]

Why not just buy an electronic circuit breaker with a 100mA GF trip unit in it already, dispense of all that external stuff.

And also, my opinion is that the PLC is superfluous here. A dedicated trip unit, whether internal or external, is going to be more reliable if not safer.

You had some posts from 2015 about this equipment, which lead me to post here in the first place.

I am correcting an oversight from the original machine design, therefore dispensing with other stuff is not an option; the PLC the shunt trip CBs the logic is all in place and necessary. The best adaptation is to use CTs to monitor the circuit for imbalance, capture with a high speed device and trip the breaker

 

[buffalonymann]

oh brother. :roll: he has being doing this, in the field, for 30 years and also has a PE license, can perform the calcs, and tell you exactly what to use to achieve what you are asking for. i'm not sure how you gathered from his posts that he doesn't know what he's talking about. he pointed out that your concept would work, in theory, but real world conditions (non-ideal) make your approach impractical due to inaccuracies of the coil operating at the extreme of its range (Ct's are not linear devices, but we operate them in a linear region). the fact that this appears to be is lost on you tells us you are not understanding a key concept of how CT's operate in the real world. there's nothing wrong with that, we are all continuously learning.

you are trying to pick up 100 mA of ground fault on trace heaters (have't provided typical load, important information). a zero sequence CT is not what you want to use to achieve this and there are very good reasons (previously stated) for it. the problem is you are looking (googling) for "ground fault sensing CT". that would be zero sequence. if you read more about applications of zero sequence CT's in ground fault sensing, you will see they are intended for much higher secondary currents that what you specified. ground fault is detected by summing CT secondary currents for each of the three phases. they should equal zero.

there are industrial product offerings, UL listed and warrantied by the manufacturer, that do exactly what you are asking for. if you insist on engineering something else-you may be taking the liability if something happens because it did or didn't trip when it was supposed to. i hope no one gets hurt in the process. :happysad:

lastly, it is this engineer's opinion that relying on a PLC for the safety function described is not advised.

FYI - Just wrapped up conversation with engineer at GE, he's onboard with what I'm doing.

 

[Ingenieur]

This is amusing - I posted on the engineering page looking for feedback on my project. You offer some opinions and I attempt to get to the basis for your opinions which then you make snide comments because I asked, and then the snowflake starts high-fiving you for the snide comment. Any real engineer would have explained the basis for their opinions on a matter like this.

Thanks for your input; I'll look for somebody who has some experience and training in this subject matter. Oh, you pointed out it is I who doesn't know the subject matter, what was your first clue to arrive at that idea? The fact that I posted on an engineering website seeking feedback?

the only thin skinned snowflake is you
what is amusing is you dismiss all opinions but your own
hire an engineer, you are in over your head

I have explained my opinion
won't work
ct will not produce a v
the equip is not rated for epd
poor practice to use the plc, the cb would trip before the plc woud shunt it

I have been working with gf protection for 30 years
in the lab and field
wrote laws
MSEE, PE, engr manager for a gov bureau that inspects/tests gf protection

go ahead, install it, all is good

 

[Ingenieur]

You had some posts from 2015 about this equipment, which lead me to post here in the first place.

I am correcting an oversight from the original machine design, therefore dispensing with other stuff is not an option; the PLC the shunt trip CBs the logic is all in place and necessary. The best adaptation is to use CTs to monitor the circuit for imbalance, capture with a high speed device and trip the breaker

it will NOT work
there is a reason no one does it

 

[Ingenieur]

I understand - From what I read about these zero sequence current transformers it leads me to believe they are well suited for this application. The info came from littlefuse, I guess I could call them and ask their opinion on how their product would work for my app.

Thanks for the input

read more
a 50:5 will NOT produce a v output at 0.1 A primary
read the link I posted
will only start to work >2 A, and very inaccurate at that level

 

[Ingenieur]

Why not just buy an electronic circuit breaker with a 100mA GF trip unit in it already, dispense of all that external stuff.

And also, my opinion is that the PLC is superfluous here. A dedicated trip unit, whether internal or external, is going to be more reliable if not safer.

yep, first choice is an lsig cb
but he already has the cb's
next, a listed gf relay rated for <0.5 A
the plc is a bad idea

 

[Ingenieur]

epd?

According to the literature the Modicon module turns on at 2 to 8 mA within 30uS

fs?

am I mistaken to understand that a 100mA primary will produce a 10mA secondary current?

solid grounded wye

tell me why the ZCT is not well suited for solid grounded system

electrical protection device

plus processing loop time
the input Z or burden is too high, the ct will not drive it

at 100 mA primary the sec will be 0, losses, flux, charging, etc
the link I posted shows the curves

zero seq is not recommended for mA gf on a solid gnd wye (suited for a Z gnded wye)
it should be on the egc for solid
an explanation is in the links posted

 

[kingpb]

I am correcting an oversight from the original machine design, therefore dispensing with other stuff is not an option; the PLC the shunt trip CBs the logic is all in place and necessary. The best adaptation is to use CTs to monitor the circuit for imbalance, capture with a high speed device and trip the breaker

In the OP you said ground fault, now you changed it to circuit imbalance. So, which is it?

 

[buffalonymann]

the only thin skinned snowflake is youwhat is amusing is you dismiss all opinions but your ownhire an engineer, you are in over your headI have explained my opinionwon't workct will not produce a vthe equip is not rated for epdpoor practice to use the plc, the cb would trip before the plc woud shunt itI have been working with gf protection for 30 yearsin the lab and fieldwrote lawsMSEE, PE, engr manager for a gov bureau that inspects/tests gf protectiongo ahead, install it, all is good

Look, I appreciate that you responded and I'm sure you have the skills to run wires in a mine, but this subject is simply not your forte.

 

[buffalonymann]

In the OP you said ground fault, now you changed it to circuit imbalance. So, which is it?

Well, the circuit imbalance is the method to detect a ground fault.

 

[buffalonymann]

it will NOT work
there is a reason no one does it

I'm working with an engineer from GE; they design and build this equipment, he knows what I'm looking for and has a CT in mind for me to use. The guy was a real pleasure to speak with.

A guy claiming to be an EE once told me that a center tapped transformer ( like those serving homes ) is 2 phase power. Is that your belief?

 

[ron]

Guys, stand down.

Do what you want.

There is a lot of good information shared.

 

[kingpb]

Well, the circuit imbalance is the method to detect a ground fault.

Well, technically not correct. An imbalance can still vectorally sum to zero, whereas a GF will not. So you are looking for current leaving the system, not looking for an imbalance.

Let us know how this works out. Always open to learning something new.