An ungrounded Delta system contains a neutral point?
- Thread starter mta145
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there are a few methods for grounding a a delta system they all take place at the transformer.
You can take the mid-point of any one phase and ground it for a 120/240 volt system on like a house.
You can corner ground where you ground where 2 phases meet.
You can also use a zigzag grounding transformer.
But true ungrounded systems don't have a neutral, they use ground detectors to identify faults. If there is a fault either a light will go on or go off depending on how the system is designed. If a second fault occurs before the first fault occurs it can cause phase to phase faults
You can take the mid-point of any one phase and ground it for a 120/240 volt system on like a house.
You can corner ground where you ground where 2 phases meet.
You can also use a zigzag grounding transformer.
But true ungrounded systems don't have a neutral, they use ground detectors to identify faults. If there is a fault either a light will go on or go off depending on how the system is designed. If a second fault occurs before the first fault occurs it can cause phase to phase faults
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LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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- Electrical Contractor
Welcome to the zoo! :smile:
An ungrounded Delta is considered to be 'floating', but there is enough capacitance bewteen each line and earth (including conduits and enclsures, nearby grounded surfaces, etc., as well as the planet itself) that a high-impedance voltmeter would indicate that each conductor has approximately the same voltage to ground.
This "phantom neutral" is probably what the book is referring to. A load cannot be connected between one line and ground (the system's EGC is still present and connected) and be expected to receive any useable power. Only line-to-line (1ph or 3ph) loads will be powered.
Um, don't agree.
A star (Y) winding has a neutral point. It is still a neutral point whether or not it is grounded.
Grounding and neutral are two different matters.
Conventional three phase systems, delta or wye configured, have a circular voltage relationship. After all, the generated emf is a result of rotating windings in a magnetic field. Given the preceding, plot the three voltage vectors of a either wye or delta or both. The neutral will always be at the center of a circle which intersects the three voltage points. Just the nature of the beast.
To verify, start with an energized delta secondary, grounded or not does not matter. Connect three appropriately-sized resistors (e.g. heating elements) of equal value in a wye configuration (or you could use a 3? wye-configured motor). Measure the voltage line to wye intersection. It will be, subject to practical tolerances, the line-to-line voltage divided by the square root of three.
a star winding is a delta ?
we were talking abut delta systems not wyes
Well, of course not.
I was simply addressing the point made by nunu161 that ungrounded systems don't have a neutral.
I was disagreeing with that point.
It is perfectly possible for an ungrounded system to have a neutral.
I have seen a few posts in this forum where "ground" and "neutral" tend to be used interchangeably. I just happen to think that it is important to have clarity in the distinction between the two.
If it is truly delta, grounded or otherwise, there is no neutral.
A wye system has to be grounded/neutral i'm not stupid i knew what i was talking about when speaking of a delta system.
winnie
Senior Member
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- Springfield, MA, USA
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- Electric motor research
I contend that on a delta system you can define a neutral _voltage_. There is no system terminal at this voltage.
In a balanced wye system, the common terminal is at the neutral voltage, and we call it the neutral terminal.
-Jon
In a balanced wye system, the common terminal is at the neutral voltage, and we call it the neutral terminal.
-Jon
Different point. See post #8.
Grounding one corner of the delta does not make it a neutral.
The neutral doesn't have have to be grounded to make it a neutral. Grounded or otherwise, it would still be a neutral.
I did not mean to infer that you are stupid. If it came across that way, I unreservedly apologise.
My comments referred to the subject matter and not directed at the poster. Personal insults are proscribed in this forum. Rightly so, in my opinion.
glene77is
Senior Member
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- Memphis, TN
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Well, the code requires grounding of a neutral. His point was that Mother Nature does not. Please be less sensitive.
It's Mother Nature that gives ungrounded systems the capaciticely-coupled "neutral" that triggered the OP's question.
am i understanding this correct?
am i understanding this correct?
Even though a delta transformer is ungrounded there still is a neutral point that exists in the middle of one of the phases even though it is not attatched to so the statement that a ungrounded delta system contains a neutral point is true? it just may not be used?
am i understanding this correct?
Even though a delta transformer is ungrounded there still is a neutral point that exists in the middle of one of the phases even though it is not attatched to so the statement that a ungrounded delta system contains a neutral point is true? it just may not be used?
brian john
Senior Member
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- Leesburg, VA
I have been on a site with a 3 phase wye supply transformer, system was ungrounded all loads were 3 phase 3 wire No nuutral and for sure nor a grounded conductor. I guess I am stupid?
Kartracer087
Member
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- Milwaukee WI
My question would then be why would people still deal with Delta systems when you can get a lot more versatility out of a 4-wire uni-grounded or multi grounded wye system? You can get two 1? voltages from the system and it is a good system for quickly clearing line to ground faults.
brian john
Senior Member
- Location
- Leesburg, VA
And if I wanted to operate this transformer as a 3 phase delta with a grounded conductor how would I get to the grounded conductor connection point? Assuming you did not specify a 4 wire delta when you ordered the transformer.
brian john
Senior Member
- Location
- Leesburg, VA
You cannot utilize the 4 wire/neutral NO SINGLE PHASE LOADS to neutral.
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