Ungrounded 480x240 delta to delta 3ph 3w voltage to ground reading

[killer76]

Need clarification / conformation on the voltage readings to ground, and suggestions / solutions.

Knowing the secondary 240 line to line should be 240v and line to ground should be 0v.
Found a voltage reading to ground on a disconnect and was able to determine the circuit that was causing the fault.
Removed the wiring from both the disconnect and wiring to the circuit breaker at the panel board and locked out both. Have not been able to troubleshoot further at this time.

Now another disconnect is reading to ground. I am not able to secure this circuit, and know this needs to be addressed before another fault may occur. Can someone explain what may occur if this is not repaired or resolved.

The location has an old CH V48M24T12F is a Delta to Delta transformer. Eaton’s tech support sent me this “Since this transformer does not create a neutral there is nothing to ground and the 240 VAC does not have a reference to ground and you should not see voltage to ground, only line to line.”

I am suggesting the ungrounded transformer be replaced with a grounded system.

Thank you,
Robert

 

[iceworm]

Just to clarify:
The secondary is 240D, ungrounded?

If it is, then this is not right:

“Since this transformer does not create a neutral there is nothing to ground and the 240 VAC does not have a reference to ground and you should not see voltage to ground, only line to line.”

 

[killer76]

yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings

 

[iceworm]

yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings

Since the 240D is ungrounded, then the phase to ground voltage is undefined. It can be about anything (between 240V and 0V). One can usually measure something because of capacitive coupling. If the coupling is perfect balanced, the phase to ground voltage would be 139V = 240/(sqrt(3)

If you are reading phase to ground of:
240V
240V
0V
that is telling you that you one phase has an unintentional ground.

Before I suggested changing to a grounded system, suggest checking why the existing is ungrounded, and the requirement of the existing loads. Some loads may not be happy with some types of grounded systems.

 

[iceworm]

yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings

There should be ground detectors - Could be as little as three incandescing light bulbs.

 

[killer76]

the only loads are to single phase and three phase receptacles for welding machines and a couple plasma cutters, fused disconnects feed the receptacles.

going to get the measurements from the disconnects when no load in present.

 

[killer76]

was told that using digital volt meter will give different readings compared to the wiggy type meter, i have an Ideal Vol-Con tester and digital UEI and will use both.
I was asked to see if you can you give a little more on the ground detectors - Could be as little as three incandescence light bulbs. How would they be connected
any advice or suggestions are greatly appreciated

 

[augie47]

Ive seen systems as simple as lights connected in series between phases and ground or you can get more "professional"
http://www.directindustry.com/prod/elektro-mechanik/product-112693-1690990.html

 

[electrofelon]

was told that using digital volt meter will give different readings compared to the wiggy type meter, i have an Ideal Vol-Con tester and digital UEI and will use both.
I was asked to see if you can you give a little more on the ground detectors - Could be as little as three incandescence light bulbs. How would they be connected
any advice or suggestions are greatly appreciated

The vol con will be more likely to give you "0" volts (if there is not a fault) and more useful information.

 

[iceworm]

... I was asked to see if you can you give a little more on the ground detectors - ...

Code section is 2017 NEC 250.21.B Also suggest reading 250.21.A and 250.21.C.

This is not a design. It is missing minor things like fuses.

If 240V incandescent bulbs are not available, 240V transformered pilots also work.

the worm

 

[Jraef]

Just to clarify, in a 240V 3 phase delta system, you must have ground fault monitoring, OR you must have a grounded phase, a.k.a. "corner grounded", in which case one of the phases will measure zero V to ground, the other two will measure 240V to ground and all 3 will measure 240V phase to phase. A 3 phase delta system without one or the other is a code violation.

 

[killer76]

that is correct. no corner ground, and no monitors.
additional issues, in this application

400A MAIN City Supply to 600A 480V 3Ph MLO panelboard, 150A, 480V 3P [should be 175A]
to 112.5kva 480v 3ph D x 240v 3ph D 3W to (no secondary OCP 240.4 (F) indicates delta-delta 3-wire shall not be considered)
42CKT 225A 240V MLO load center w/
6) 50A 3p left side (third cb removed first leg on 3p failed)
5) 50A 3p & (1) 30A 3p right side
load center is over loaded, the phases are not balanced due to the usage of single-phase welders. one other has failed on one leg have not confirmed what phase
both are locked out,
all breakers are feeding 60A fused disconnects w/ 60A fuses all for welding machines, some of the disconnect have (3) twist lock receptacles (1) 50A 3ph & (2) 30A 1ph.
the twist locks are showing sign of burning at the prong opening

suggest replace the Delta xfmr with wye or add detectors to code, increase size to support load
suggest add individual fused disconnect w/ correct fusing & receptacles for each welder. client does not want hard wire they will use extension cords of various lengths, another concern.
any additional suggestions would be great.

Thanks

 

[__dan]

I would look at the load again first and then try to figure out the best way to feed it..You can corner ground the delta secondary of the existing transformer and this should give you functionality for OCPD operation, for other leg faults to ground. That is necessary imo, compared to monitoring the existing floating system for faults and then expecting to have someone available to manually clear faults when the detector gives abnormal reading. Not likely and not a scenario I would lean into. Guys today will just keep running it until the breaker or fuse trips, then try resetting the breaker or replacing fuses to get it running again.

Converting to all solidly grounded system I would look for. But that is load dependent. You have to look at the load including maybe consulting with the welding machines manufacturer to see what they prefer as a source.

Possibly the supply was a much older existing installation and the new loads were simply added on to what was available. You want to know if 240 delta, floating or grounded, is necessary for the machines that are there now. Really an unknown at this point. I would guess the 112kVA floating 240 delta secondary dates from an earlier era than the present load. Is it necessary or can it run on the utility 480 V supply.

The welding machines are possibly dual voltage at the input, 480 or 240 with adjustable taps would be common. If so, I would have an eye on moving the load to the utility transformer. But first I would check that transformer to see what it is, grounded and probably Y, but I would check it and recheck it.

The welding machine manufacturer may have a preference for an isolating transformer, or not. Only they know this answer. If the machines can run on the 480 V supply, I would probably be interested in moving the load there.

Make sure you have good EGC grounding attachment to everything.

Replace the twistlok devices that show signs of burning and maybe wring it out for faults. If they are continuous production machines, running big welders on cords and twistloks is going to take a beating.

I would not consider monitoring over solid grounding, if I felt there was no one who really understood the system and could troubleshoot it safely, a ghostbuster.

 

[killer76]

I have been told replacing fuses and resetting the breaker is normal, the new issue is one leg at the disconnect has no voltage, and the breakers are starting to fail.

I believe the breakers are failing due to (3) receptacles from one disconnect(s) and unbalanced phase's

I need a better understanding of 630.11 to be safe I go with the 100%, for (B) group welders even more confused. I found an old section from NEC2005 the show a diagram of several welders fed by one disconnect, would think if it’s not in 2017 then something is different
630.12 OCP shall be provided in 630.12 (A) & (B) not more than 200%, If anyone can provide further explanation maybe a sketch that would be great, then 630.13 indicates a switch or circuit breaker for each welder.

only one of the welders has integral cb other than this one shouldn't all of the others comply with 630.13 or is the method described in 630.11 and 630.12 permit multiple welders to one disconnect.

I have gone with manufactures installation in the manual. It states each welder has disconnect, conductor size, fuse requirements, along with max. distance from panelboard.

Most of the welders are 230 / 460 single & three phase, only about three are 230 single phase.

the 600A 480V 3Ph panelboard has 200A fused disconnect w/ 125A fuses hard wired to the buss to a another 200A fused disconnect w/ 125A fuses to the other end of the facility. this is supplying a 125A 480V 3Ph (6) ckt panelboard for (6) welders (2) 15A 3p, (2) 25A 2p, (1) 35A 3p, (1) 20A 3p.

In the 600A panel some breakers are spare, and several 2p are to lighting some 3p only using 2 legs, would rather use the 150A 480V 3p and run to another small panel closer to the welding location.

Thank you for your feedback

 

[__dan]

I have been told replacing fuses and resetting the breaker is normal, the new issue is one leg at the disconnect has no voltage, and the breakers are starting to fail.

I believe the breakers are failing due to (3) receptacles from one disconnect(s) and unbalanced phase's



Most of the welders are 230 / 460 single & three phase, only about three are 230 single phase.



Thank you for your feedback

If you are blowing fuses and breakers anywhere on the ungrounded 240 V delta, it means you normally operate every day with faults to ground on the floating delta and the fuses only blow for the second ground fault (so it's actually a line to line fault through two shorts in series). It burns in two places and has line to line fault current available.

You are not a candidate to safely retain and operate the ungrounded system. You should blow no fuses on a floating system, but clear the first fault quickly and permanently, before the second fault happens.. That is the design intent of the industrial floating secondary.

Breakers are failing from repeated resetting, or they may actually be doing their job. Change the burned out breakers.

What type of welders, what duty cycle. Are the welders used in the production process or are they just there to repair the plant.

If the welders are just there to repair the plant, you probably don't use more than one at the same time in the same spot. Load calc is for the actual load. I would say you can have as many welder outlets on a circuit as you want if you are only going to plug in and operate one welder at a time. Load is added to the circuit by the use of the welders (since it is manual only).

If you use the welders in the production process, that load calc is completely different and I probably would not want to derate too much.

I am thinking the portable plant repair welders, design wise, I would want to see it on 480 as much as possible. Even then the cords and outlets are going to be heavy to lug around.

If most of the heavy load and special use industrial equipment can be moved to the utility 480, dual voltage rated equipment, I would consider that as a path forward, with an eye on reducing the load on the 112 kVA 240 delta secondary so much, that that dog can be retired. If I could get the remaining load under 30 kVA, I would like that, and plan on eliminating the 240 delta transformer, refeeding the load with a grounded Y secondary.

So survey it first to see if the 240 delta can be retired and most of it's load moved to the utility 480. Check that service to make sure it does not have the same problems. Refeed the rest if it's under 30 kVA remaining.

If you still have a lot of load for the 240 delta. Most likely I would try to retain it with a corner grounded secondary and new panels and breakers for it.

They need to spend some money sounds like. Put the plan together first.

Key issue seems to be how much load do you really need to put on the existing 240 delta. There may be nothing wrong with the transformer if you actually have the right or necessary load for it. If you don't really have more than 30 kW of load, it's a dog, especially if you can (benefit from) a move the welders to 480.

 

[killer76]

I agree the ungrounded system is not for this application.

As for faults, at first discovery the system was ungrounded. One breaker continued tripping. Measuring one leg to ground with voltage on several disconnects. (using wiggy type meter)
Turned off all the disconnects isolated the disconnect to that breaker, as soon as it was turned on the breaker would trip, removed the wiring from the breaker and disconnect and the voltage to ground was gone.

All welders are dual voltage and are all production use, it is common to see 2 or 3 welders running on one disconnect. Figure the breaker trips when all are simultaneously in use, this also could be causing the receptacles to begin melting.

Fuses were blowing some time ago, only the breakers have been tripping. Checked disconnects, fuses have been replaced with 60A FRN-R-60 time delay fuses. Some are wired with #8 and some #6.

So, the breaker is doing as it should, just going bad from constant over-current usage. Using dedicated fused disconnects, correctly sized breakers and install new receptacles, should correct this.

Load for the welders needing 230v is very low going to a smaller KVA would work, nothing needs the 240v.

480 service is fine, three of the larger welders are hard wired to dedicated disconnects running fine.
Moving to 480 from the 600A panel may be best.

Cost compared moving to 480 or to use the ungrounded system, both require additional induvial disconnects. Cost for a detection system or corner grounding.

To use the 240 system, you indicate new panel and breakers; can you explain further. The 3-phase panel has straight voltage 240v breakers.

I may need further advice on the plan for 480 600A panel, with the 200A disconnect bussed, probably should post under electrical calculations.

Thank you for all your support.

 

[__dan]

Niiice.

To refeed from the utility 480, most likely I would be considering 1 1/4" or 2" conduit run to a new 480 panel board close to the load. There is also the consideration of reusing as much of the existing distribution wiring in an economical manner.

So you would already have a 480 V feed at the 240 delta transformer location. You may be able to reuse that feed, even if the neutral was not carried to it. That may be one location for a new 480 V panel board and breakers, refeed the existing load out from there with some reuse of the existing branch circuits tied on after the old transformer, but now refed out at 480, which will give you a lot more current and kVA per existing circuit.

Most likely the existing load had no neutral and the reconfig to 480 will not take a neutral either, but care and following the manufacturer's instruction are necessary for this. It's may be possible to refeed most of the dual voltage load without a neutral, from where the 112 kVA tranny is now.

So one new 480 panel at the old tranny location and one new 480 feeder and panel board close to the load.

I mentioned new panel board and breakers earlier because it is a lot cheaper to buy a new panel board fully loaded with breakers as a package, than it is to buy or have the panel already but add breakers one by one.

Still lot of money to spend. You can put together plan A, plan B and looks at each costs. I would see only plan A at this point with plan B possibly retaining the 240 delta. Some money needs to be spent to get from B to A. But it sounds like they got all they could out of the existing system and it is going to cost them money one way or the other.

You could try to justify some costs savings in efficiency gains eliminating the dog 240 delta idling losses and shifting them to the utility side.

For me, the new protective devices and updated outlets and connectors is where I would tell them they are saving money. They can do it right the first time or pay for it ten times over in downtime, injuries, rework, and repeated fixing of the same things like clockwork going forward. Improvements considered here should be extremely reliable, safer, and lower cost over time.

Would only take one OHSA complaint to make the entire upgrade bid look cheap.

Retaining the existing 240 delta with corners grounding, the new panel board would be loaded with 1 and 2 pole breakers for single and three phase, but a very substantial type of properly rated breaker.

 

[__dan]

I am thinking you may be able to tap the existing transformer feeder to power the new 480 panel. New panel location likely adjacent to the existing tranny load side panel board.

With both systems powered at the same time you would be able to make the load side changes one at a time, each equipment reconfig to 480 V will take skill and time.

Having both systems powered and running gives the schedule a huge competitive advantage, makes the job doable within some civilized and necessary time frame,

Still I know how hard it is to pry money out of the customer's (accountant's) pocket. They all want to run their men and equipment as hard as they can (costing more over time).

 

[synchro]

I've not followed all the details of this thread, but could a grounding transformer such as a zig-zag be an option instead of corner grounding the delta? It would offer some advantages but the costs would have to be considered.

 

[__dan]

I've not followed all the details of this thread, but could a grounding transformer such as a zig-zag be an option instead of corner grounding the delta? It would offer some advantages but the costs would have to be considered.

My concern would be, most of the people encountering the system would have no understanding of it exactly as its parts. They would only have some guess that it is like all the others and at some level, has the engineering controls like breakers that trip when they have to.

Consider the environment. The workforce probably does not have their own electrician or EE on staff. But they run 100kW of production welders. They are guys who like to make sparks with electricity. They have hand held guns that can pop studs into the I beam webbing for poured concrete applications.

They have no idea how it works but the guys who do that job like that gun. They need just a copy of some standard (extremely reliable) system that their equipment manufacturer specifies. If you try anything non standard, no one will understand its operation and it will be the first thing chopped out when they have trouble.

They make their living melting stuff with that 112 kVA 240 floating delta.