Corner Grounded Delta Transformer Bank
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- Опубліковано 23 лип 2024
- This demonstration video shares the wiring, voltage and history of a corner grounded delta bank. We use our trainer model made by Three Phase Innovations to do the demonstration. Thank you and enjoy
- Наука та технологія
I see open deltas all the time in West Texas. It’s very common in the oil field. Thanks for the video.
Great video. I'm an electrician and an HVAC co-worker approached me this morning with the problem of; two phases had 480 to ground and one phase 0. Never heard of this before. Very good presentation and explanation.
35 years as an electrician, i like the layout and demo man, very well explained , corner grounding can get tricky,.
Thank you for the compliment moe molar. I don't have much field experience with this bank myself but you are correct. Everyone says they are tricky for sure.
I work with so many Corner Grounded 3 W Delta services in the oil fields of East Texas its not even funny. Thank you for explaining!
Thank you for the comment jvck blvck. I can only imagine what goes on in those oil fields. I bet you guys deal with "Phantom or Ghost" voltage in all those straight 240V or 480V DELTA banks all the time. Especially tying them together. Thank goodness meters have a "LoZ" setting now. Stay safe.
@@jasonleary6717 Its bad. We have to really pay attention and watch the younger guys, teach them not to just go through the motions because even though the next bank looks the same, its not. Oh yeah LOZ is a life saver. You should see what the phase angles look like for the pump jacks. Current and voltage are never in unity and PF jumps from .51 to .16 lol you be safe also brother
Just ran into this in a waste water treatment plant. 480v delta. Reading 480v to ground on A, and B phase but on C phase i was reading ~11v. Thought I had lost a phase, called POCO, lineman came out and explained what type of system we have.... this video has a great explanation! Thank you for making videos like this so other people can learn! 💯
Hello Mr. Rodriguez. Thank You for taking the time to check it out. We really appreciate it.
i'm seeing the same thing at a similar location. if i may ask, where are you seeing the conductor being grounded?
@@betta3301 not sure I understand your question. I was reading the ~11v after the transformer
@@pumarodriguez3964 you stated you have a grounded phase conductor and i was just wondering where you see the phase being grounded at, if possible. if its inside a pad mount transformer then its not obvious as compared to up at the pole. or maybe its grounded somewhere else?
Very nice trainer, with 4 bushing secondaries. Great video.
Love you man… thanks for explaining
Did you make the prop or purchase it? I am a planner and have been looking to make one to help explain phase and voltages to planners in training.
Great Video
Thank you for the compliment Echo.Whiskey.
Very well explained. Corner-grounded delta has long intrigued me and have never seen one, although I've read quite a bit about it. I do think the term "grounded phase" seems like an oxymoron, maybe that's one reason it puzzles me some. I also think it's pretty cool just because it can be done.
One a Wye Delta center tap you remove the grounds off of the x2 bushing on the outer cans. What happens if you forget to remove a strap and why?
LUIS LOREDO imagine the one ground center tapped. If a ground is added on either side of the transformer that has been grounded it will result in a ground fault short on that phase.
Dumb question. A ground and a neutral are basically the same thing when adding your corner?
Thank you for the question. A Ground and a neutral have different functions in a electrical circuit but in a 4 wire corner grounded Delta, the neutral is acting as a safety or to prevent the stealing of power. (120 volts) If a 3 wire delta is corner grounded then you can't have a phase get accidental GROUNDED and no one not know there is a phase to ground potential in the circuit. Always remember, a DELTA circuit is a series circuit (one path for current to flow) a neutral can show up and know know there is a potential to ground, if you ground a 3 wire delta now you have protection from accidental grounding.
Here is a great you tube channel for all thing electrical. ua-cam.com/video/JBpQ9Fodz_Q/v-deo.htmlsi=TzDHvtDCX1sRkBXN
So when you have a circuit on the grounded phase and that circuit has a short to ground how will that circuit be grounded if it is already grounded? Im so confused.
Thank you for the question. A Delta circuit can be a 3 wire circuit with no ground or a 4 wire circuit with a corner ground or the neutral can be used to get different voltages for the customer. ONLY ONE NEUTRAL CAN BE USED IN A DELTA CIRCUIT. If the circuit is a 3 wire DELTA then no phase to ground voltage is present, because you have no neutral. The danger with this 3 wire circuit is a neutral could show up accidentally and the DELTA circuit will not show any signs of a problem other than having a phase to ground potential there and no one aware of it. If you chose to ground a 3 wire circuit, then you have a 4 wire CORNER GROUNDED DELTA. Now one phase has a ground potential in the circuit. If there is a problem or a fault in the other two phases now you will blow a fuse and know you have problem because TWO neutrals will be in your DELTA circuit causing a dead short. Just remember a Corner grounded delta is used for two purposes. (1), To prevent the stealing of power by a customer (120) volts. (2) to prevent a 3 wire delta from accidentally being grounded and creating a phase to ground voltage without the customer knowing they have a problem with accidental grounding that could cause a accident for workers working on the equipment.
How would it be possible to change a delta high leg from the meter? I changed a 4wire 120/208 delta high, load center. Upon putting the meter back in the high leg tests 320v to ground and 420v c phase. I grounded&bonded the 4th wire with the ground rod... Just as it was before... I still just can seem to figure out how I could ever change voltage downstream..
Great question, if you are a member of our (lineman transformer discussion page) on Facebook, would you please repost this question their. We have some very smart guys on their. Also this would be a great quest for other members to hear about and discuss. Thanks for the questions.
Can you corner ground a 240 delta system and have an ungrounded 120V center tap? I understand you cannot have a redundant ground, but couldn't you still have a 120VCT with a corner grounded system?
I just found out about corner grounded delta transformers and I'm so confused about how you can take a phase to ground and it not behave like a short?
Hello Adam. Thanks for watching the video. Electromagnetic Induction is the whole reason a transformer is able to not "short out" when grounding ONE side of a transformer's coil. Faraday's and Lenz's Law describe a transformers ability to create a CEMF force that opposes the applied voltage. This keeps a delta or wye circuit in balance. A Delta circuit is tying the transformer coils in series. You can always put ONE neutral in a Delta circuit and you will not destroy a transformers ability to create the CEMF force. Two neutrals in the Delta circuit will create a "dead short" across the transformer coil. If you destroy the transformer's ability to produce a CEMF, Ferroresonance will occur. Another crazy phenomenon dealing with electricity.
ua-cam.com/video/k2RzSs4_Ur0/v-deo.html Video about Lenz's law
ua-cam.com/video/U7dNdQc1NL4/v-deo.html Ferroresonance CEMF
Thanks Jason, they were very helpful!
@@jasonleary6717 hope you can answer but how could we get around this when we connect our 3phase solar inverter on such systems. Will isolation transformers work?
Hi Buddy, you have a nice presentation, We have almost the same system in your video , we have WYE Ungrounded- corner grounded delta (3ph, 3wire grounded delta). What is the difference between the WYE ungrounded primary to Wye grounded Primary? The secondary banking is the same.Thanks
Hello Mr. Padilla, Thank you for the comment and sorry it took awhile to get back to you. If you are referring to a "Floating Neutral" it has several considerations. A WYE-WYE bank must always be tied to ground to stabilize the bank. When you have a DELTA secondary and a WYE primary some utilities will want the Primary neutral not grounded on the WYE high side. One reason is when ground fault happens on the distribution system or at the transformer bank itself the ground fault will not go through the transformer bank or the fault won't go back out on the system. In short, it isolates the transformer bank from the system and the system from the transformer bank so fault current will find a different path. If the transformer bank has a fault, it does not go back on the system and might create damage to other equipment on the system. If the system has a fault, it won't ground out through a customer's transformer bank and go somewhere else to ground out.
Second reason: When you lose a phase on a closed bank and the neutral is floated the customer will realize they have a problem and will call the utility to let them know something is wrong. If the bank is not floated on the WYE side and the bank is grounded, the closed bank will turn into a "OPEN" bank when a phase is lost. Two transformers in the Delta secondary are trying to carry the original 3 Phase load and if they KVA has not been rated for this type of situation, the customer may not know they have a problem until the other two transformer burn up trying to carry a load designed for three transformers. Example: 3 transformers each with a 100 KVA. Closed bank total KVA is 300 KVA (3 X100). If you lose a phase with the WYE grounded, the bank is now "OPEN" 2 transformer are now trying to carry a 300 KVA load. They won't be able to do it. Their capacity is has been reduced to 173.2 KVA. There are two different ways to do the calculation. 300 KVA x 57.7% = 173 KVA or you lose a phase and are left with 200 KVA x 86.6%= 173 KVA. 2 transformers will try but can't produce the same load all 3 were working together. They will burn up if the phase is not put back in over time based on the load and all other factors. Ambient temp for example. One thing to remember. If you are going to "FLOAT" the neutral. You must connect it to energize the bank. Then you can float it. When you de-energize the bank, put the neural connection back on, then you can open the bank. You will have high voltages on the neutral itself until you make the ground connection. Ferroresonance can also occur and can be dangerous. Whole topic explained very well be Dennis Merchant.
ua-cam.com/video/U7dNdQc1NL4/v-deo.html
@@jasonleary6717 Lovely. I am very happy in your answer. It Enlightens me more. That's why when we do V-phase banking, we connect the one lead to the neutral (usually the center one). Our seniors never explain that way. Thanks jason.
@@cristobalpadilla4117 Glad I could help. When we get some time I hope to make a video about a floating neutral sometime soon.
Hello, and thanks for the video. What if I need a neutral on the corner grounded delta??
Thank you for the compliment. A Delta circuit is a Series circuit (one path for current to flow). You can ONLY put ONE neutral in a delta circuit. You can use the neutral as a corner ground or use the neutral to center tap a can for different voltages but you can only do one or another at a time. You can't center tap with a neutral and corner ground at the same time. It would be to many neutrals in a delta circuit at the same time causing a short in the circuit.
@@jasonleary6717 hey thanks for the response, so i got it. so the corner ground acts as a neutral to carry the load unbalance¿? the reason i ask os because i installed a buck amd boost on that corner delta for a three phase stove, and i read in the buckboost that if the load is unbalanced it needs to be tied to a 4 wire system, but i am not sure what is the asumption. their specs are very poor, just a label.
@@celsiusfahrenheit1176 I have never used a buck-boost transformer but I'm guessing that it is a transformer that makes changes to a fixed voltage. As a lineman we have pole mounted transformer with tap changers that do the same thing by adjusting the primary coil's turns ratio to match high or low voltage on a distribution circuit. If you have a 3 wire delta bank, you would have just one voltage to chose from between any two phases; however, when you corner ground a phase you do stabilize the ungrounded phases. An example would be having a 240v 3 wire delta. There would be no phase to ground voltage except for phantom or ghost voltage which can be corrected by using a meter with a LoZ setting on it. We have a phantom or ghost voltage video on a 3 wire delta on here as well. So, lets say you corner ground B phase on a delta circuit. Now your voltages change in the circuit. B to neutral will read zero but A and C phase to neutral will read 240 volts. It stabilizes the other two phases not grounded. I'm guessing like you mentioned the neutral on that type of transformer is needed for the unbalanced load to have a completed circuit to stabilize the ungrounded phases but that is just my best guess on this situation.
@@jasonleary6717 nobody really knows, i wil talk to the engineer from the poco. i never saw a three phase stove before, i told the custumers in writting when they asked me, that their service was a 3 phase corner delta no neutral 240v they still got a 3 phase 208v no neutral required. anyways thanks for your replays.
Cool
In one section of the plant I work in I'm reading 480v between all phases and A: 488v B: 402v and C: 82v to Ground. I was under the assumption it was a corner grounded delta and maybe something isn't bonded properly but I'm not positive. I know you can wind up reading a little bit of voltage on the Grounded phase but I have never seen something as high as 80v. I was hoping you could shed some light on what might be happening in the system.
Hello Bryan, Corner Grounded deltas or 3 wire delta banks can be tricky. One of the phases should be labeled or have some kind of identification to let you know what phase is grounded. If it is a corner ground, the other two phase not grounded should be stable to ground. An example would be having the B phase grounded. It should read 10 volts or less on a meter (B Phase to ground) but if you have a meter with Low "Z" setting you should get a more accurate reading. Phase A and Phase C would still read 480V to ground if it is a corner ground. If it's a 3 wire delta and have have readings like you mentioned then whole new troubleshooting problems occur. You may have a piece of equipment or a ground come into the circuit and now you have to find it. When a 3 wire Delta gets an accidental ground, volt meter reading can become very strange depending on the resistance to ground or the type of meter you are using. The Corner ground Delta bank was created to prevent some real troubleshooting problems for 3 wire delta banks and for safety. Just one ground can exist in a Delta bank and not affect the bank at all. I doubt this helped you much with your situation, but you might want to see if your plant has any old electrical prints, warning lights or maybe check out the transformer bank outside on the pole feeding into the building. Sometimes a corner ground Delta is much easier to spot on the transformer pole itself to see if a phase is grounded. good luck.
This was helpful. So it sounds more likely that we have a 3 wire delta, thus the goofy voltages. I’ll be digging into this a bit more now to verify. Thank you for your quick response and expertise.
@@jasonleary6717 hello. i like your explanation and video demonstration. i have an ungrounded 3 phase 3 wire delta going to a customer's 3ph 480v motor. he has no electrical issues to speak of but i wonder if he's aware that one of the phases is grounded at the meter. there is no identification on the grounded conductor; however, at the meter socket is a bonding jumper on the middle phase wiring lug with a manufacturer's tag that clearly states: 'When service is not grounded, remove bonding strap..."
i think that's dangerous to ground a phase at the meter because what happens if the equipment (in this case the meter enclosure) ground comes loose? so where is the proper place to ground a phase if not at the meter?
@@betta3301 Thank you for taking the time to check out the video. I really can't give you a great answer to your question; however, when it comes to grounding any electrical circuit, the NEC Code book is very detailed to say the least. I suspect that Local or state codes might also have something to do how the circuit is grounded. I also suspect the circuit might be grounded only in one location so the circuit could easily be underground if need be at certain times for whatever reason. The main thing to remember when dealing with any DELTA circuit is always be aware of back-feed and ONE neutral can be in the circuit making it a 4 wire DELTA. Corner grounded or center tapped to obtain different voltages (120/240 etc..) Electricians have always said troubleshooting a DELTA, which is just a series circuit can be tricky. Section 250.1 helps you overcome a common problem that leads to misapplication of Article 250. Most folks are so overwhelmed by Article 250 that they immediately get lost when confronted with it. However, it’s divided into 6 logical groupings of information and Section 250.1 of the NEC codebook tells you what those are. Good Luck and stay safe. :)
how vectors diagram work? can you do a video end explain
We might come up with a video describing the current flow or angular displacement between the primary and secondary coils in a transformer. I will get with our crew and see what we can come up with in the future. Thank you for your reply Mr. Barajas
What voltage fluctuations or surges would there be if one we're to remove the ground while under load ?
Very good question koontreeguy. The only info I have read about losing the ground is a relay should set off an alarm or warning that the ground phase has been lost. Most engineering companies stop with their info right there and don't explain the effects of the bank losing the neutral under load. Schneider Electric only explains the advantages and disadvantages of this old type of system (I copied them below). Sorry about not be able to give you a definite answer to your question.
Corner-grounded delta systems:•Stabilize voltages of the un-grounded phases to ground.•Reduce the generation of transient over-voltages.•Provide a method for protecting electrical distribution systems when used in combination with equipment grounding.
Due to its disadvantages, the corner-grounded delta system has little reason for modern day use:•The system is unable to supply dual-voltage service for lighting and power loads.•It requires a positive identification of the grounded phase throughout the system.•A higher line-to-ground voltage exists on two phases than in a neutral-grounded system.•Most electrical distribution equipment manufactured in North America is not rated for use on this system.•Fault switching (opening) is much more severe for the clearing device, and ratings may be greatly reduced.
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HVAC service tech here. Came across a Corner Ground Delta configuration today. Thought it was regular 3 phase and the customer simply had a faulty breaker. Oops
Corner grounded delta's can be tricky. I'm glad I'm on the Lineman side of the bank. So much troubleshooting on the electrician's side. :)
Thank you very much for explaining this so well. I have been a refrigeration service tech for 38 years and have never had it explained this well. Two questions. 1. what is the proper color to identify the grounded phase. 2. I was on a job yesterday where an electrician used a 2 pole disconnect and claimed the grounded phase did not need to be disconnected or switched or opened by a breaker. I did not like it but he has been in the field many years himself. I felt the need to follow the professionals advice. What say ye of this ?
Hello Mr. Thompson, sorry for the late reply but I was able to find a little bit of information to your questions. Hope this helps.
QUESTION 1: Important requirements for the grounded conductor of grounded electrical systems or services are found in Article 200, which deals with identification of grounded conductors and their terminals. The grounded conductor is required to be an identified conductor of the system or service. Sizes 6 AWG and smaller generally are required to be identified by white or natural gray insulation for its entire length. Sizes larger than 6 AWG are permitted to be identified by white or natural gray insulation; by three white or natural gray stripes along the entire length of the conductor’s insulation, on other than green insulation; or at their points of termination by distinctive white markings that encircle the conductor, such as colored tape or painting. This identification is required for both grounded conductors and corner-grounded delta systems.
QUESTION 2: This section contains a list of standards that are applicable to corner-grounded delta systems. These standards address three basic points:
1. Any two-pole circuit breaker intended for use on corner-grounded delta systems shall be tested and rated for such use.
2. No overcurrent device is permitted to be used to disconnect the grounded conductor, unless this device simultaneously disconnects all conductors of the circuit, including the ground.
3. If the system is a corner-grounded delta system and fuses will be used for motor overload protection, a fuse must be installed in the grounded conductor, but only at the motor controller.
@@jasonleary6717 Thanks that helps narrow it down somewhat. Lyndell