GF indicator lights for delta xfmr secondary

Status
Not open for further replies.
bbaumer said:
You wire them A-light-Ground, B-light-Ground, and C-light-Ground

As explained in the corner grounded delta thread you have no reference to ground so your phase to ground reading will be unpredictable under normal conditions but likely lower than 480V. You are "capacitively coupled" to the earth only. You could read anywhere from probably less than 100V to close to 480V or maybe even higher.
Click to expand...

Not capacitively coupled; there is a resistive path from "ground" through the lamps, so unless you have a fault then a phase to ground voltage will be the same for each phase, assuming you have equal wattage lamps.
 
dbuckley said:
Not capacitively coupled; there is a resistive path from "ground" through the lamps, so unless you have a fault then a phase to ground voltage will be the same for each phase, assuming you have equal wattage lamps.
Click to expand...

Hmmmmm.

I'll have to give this some thought. On the surface what you say makes sense with the fault indicator lights in place BUT I know for certain I have actually measured L-G on multiple ungrounded 240V delta services (5 or 6 different buildings on the university campus I used to work at) and found the readings to be wild in each case. At one of the buildings I recall reading remarkably close to 120V on 2 of the phases but don't remember the 3rd reading. I thought sure this was a high-leg service and not ungrounded but that proved to be not the case, just a coincidence.

Voltage readings would vary with humidity as well.
 
You do have a couple of additional options.

One is of course to replace the transformer with a proper delta-wye transformer :)

The other is something known as a 'zig-zag' or 'grounding' transformer. This is an autotransformer (a transformer with a single set of coils rather than a separate primary and secondary) that will create a proper neutral from a delta secondary. You can ground this neutral, which effectively gives you a normal grounded wye system.

The grounding transformer needs to be sized to carry fault current for the duration of the fault, which can be quite a bit smaller than the delta being protected.

http://www.electrical-contractor.ne.../ubb/showflat/Number/148726/page/2#Post148726
http://ecmweb.com/mag/electric_basics_zigzag_transformers/

Unfortunately, I don't know anything more than what I've posted above. If you choose this sort of approach, you will need to find a manufacturer who can specify the correct component.

-Jon
 
Now that I think of it, wouldn't the Y-connected bulbs (or PT's) effectively balance the floating-Delta's phase voltages to ground somewhat, and better than capacitance alone? And, the larger the bulbs, the greater the effect?
 
Larry.,,

If my memory serve me right the last time i work on simuair industrail control centre with undgrounded delta one set is on 480 volts and the lightbulbs we used was 100 watters [ normally i use 240 volts bulbs if you can find them unless you can run in PT format ] that will useally hold the line in balance and also you can able tell if the system start have light ground fault you will able spot it in time.

i am sure someone else chime in say something about 200 or 300 watters do the same thing as well.

Merci,Marc
 
LarryFine said:
Now that I think of it, wouldn't the Y-connected bulbs (or PT's) effectively balance the floating-Delta's phase voltages to ground somewhat, and better than capacitance alone? And, the larger the bulbs, the greater the effect?
Click to expand...

This is why some people use resistors connected in a wye, with "indicators" in parallel with the resistors (or portions of them for voltage division if needed).

Square D sells one of these schemes for their Bus Duct. They call a ground detector and neutralizer.
 
by Jove, I think ive got it, run it by you

by Jove, I think ive got it, run it by you

Thanks everyone for chiming in.
Heres what ive gathered tell me if you agree.
option 1: i have a 480v delta secondary. so i need 3- 480 volt indicator lamps of the incandescent sort. i then hook one of them up phase A to my GEC bond strap in the XFMR. the second 480v lamp goes phase B to GEC and phase C gets the same treatment.
under normal conditions all three lamps will burn about 1/2 their brightness since the lamp is only seeing 277v or there bouts.
if a phase goes to ground lets say its C. then lamp C will go out altogether because of the lack of potential. lamps A and B will burn at full brightness. everythings beautiful.
PROBLEM: CANT FIND 480V INDICATOR LAMPS!
SO, option 2: install 277v lamps.
durning normal operation the lamps will again burn maybe up to its full brightness.
during a fault say on phase c. lamp C will again go out altogether while lamps A and B will burn out like a fuse.
would you say this is an acceptable alternative? 277v lamps are easy to get.
Thanks again
Kevin
 
my supply house is having difficulty getting them as well, they are at least availible but at around $100 each. if i can series connect 2-277v lamps @ $100 ea. X 6 or $600, then can I series connect 4-120v indicator lamps that cost $5 ea. or $60? this whole thing is rediculous. Short of replacing an $1100 transformer there has got to be a affordable solution? this thing is required by code since 05 is it not? and they've been installed on systems since before i was born. I talked to SQD teck line today, they dont have a solution either?

Kevin Simpson
Simpson Electrical Construction Co.
 
I have used (2) lamps in series instead of (1) 277V, while they don't ever reach full brightness they do glow at an equal rate. I have also used a "pushbutton syle" transformer pilot lights.
 
One other possibility: use three small 480-120 transformers and three 120v lamps, as mentioned earlier.

For that matter, you could use any secondary voltage you have lamps for.
 
The DS-R3w looks like a good and likely way to go. thanks for the lead.
I am unsure that a transformered pilot light would work the square D tech guy i talked to told me it wouldnt. but after drawing it out i dont see why not.
anyway after looking at the Voltage vision, it appears to be very cost effective. it lists for $104 and is availible from Northcoast.

Also about the A21 lamps. it sounds like a A19 which is your everyday household variety incandescent accept that its 2/8ths of an inch bigger in diameter? I do see a 277v version in the Philips cat.? seems though that the final product would be a monstrosity.

Thanks again for the help, this forum has been a huge help.
Kevin Simpson
Simpson Electrical Construction Co.
 
wasabivan said:
Thanks everyone for chiming in.
Heres what ive gathered tell me if you agree.
option 1: i have a 480v delta secondary. so i need 3- 480 volt indicator lamps of the incandescent sort. i then hook one of them up phase A to my GEC bond strap in the XFMR. the second 480v lamp goes phase B to GEC and phase C gets the same treatment.
under normal conditions all three lamps will burn about 1/2 their brightness since the lamp is only seeing 277v or there bouts.
if a phase goes to ground lets say its C. then lamp C will go out altogether because of the lack of potential. lamps A and B will burn at full brightness. everythings beautiful.
PROBLEM: CANT FIND 480V INDICATOR LAMPS!
SO, option 2: install 277v lamps.
durning normal operation the lamps will again burn maybe up to its full brightness.
during a fault say on phase c. lamp C will again go out altogether while lamps A and B will burn out like a fuse.
would you say this is an acceptable alternative? 277v lamps are easy to get.
Thanks again
Kevin
Click to expand...

Not sure why this is so confusing to everyone. These dround detectors are very common in large industrial plants.

You use PT's, as I said earlier. Why is everyone trying to reinvent the wheel here?

See attachment for schematic
 
zog said:
Not sure why this is so confusing to everyone. These dround detectors are very common in large industrial plants.

You use PT's, as I said earlier. Why is everyone trying to reinvent the wheel here?

See attachment for schematic
Click to expand...

Can you please post or repost the attachment.
 
wasabivan said:
the tech guy from the phase converter company said my AHJ was nuts. that ungrounded deltas are all over the place without this ground fault indicator thing.
.
Click to expand...

That tech is mistaken, he just might be working on an ungrounded system and isnt aware of the ground detector lights in the substations or possibly on the bus runs in the celing.
 
iwire said:
Yeah, I am trying to find an on line diagram, I think the American Electricians Handbook has it but I can't find that right now.

You have 3 lamps with one side of each connected to ground, the other side of each lamp goes to each of the phases.

When you get a ground fault on a phase that lamp goes out.

Often two lamps are used in series on each phase, that may be the only way to do it with 480 volt.


Personally I would just make it a corner grounded delta system and forget the lights.
Click to expand...

The lamps connected in such fashion make this a resistance grounded system.

Use the corner ground if you still work with a stone ax to gather your food....right after you filled out your Geico form.:D
 
Status
Not open for further replies.
Top