An ungrounded Delta system contains a neutral point?

[Besoeker]

Correct.
Neutral is Neutral. Must be seen as different from a 'ground'.

My point exactly.
Expressed better.
For that, I thank you.

 

[Cold Fusion]

Well, the code requires grounding of a neutral.

Larry -
Not necessarily. Not even if restricted to low voltage (<1000)

Whoops - maybe you consider "impedance grounded" to be "grounded" if so, then I wouldn't disagree.

carl

 

[LarryFine]

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?

There is no 'real' neutral in an ungrounded Delta. However, because of capacitance between the three lines and the surrounding world, the lines tend to hover around the same voltage to earth that a sensitive voltmeter (i.e., one with a high input impedance) would actually read that voltage.

However, if one tried to connect a low-impedance tester or a real load between any line and the earth (i.e., a grounded conductor), the voltage would collapse to almost zero, because the capacitance is of such a high impedance that the voltage drop across it would be almost the entire voltage.

 

[LarryFine]

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?

Because one may have only three-phase loads, so no neutral is needed, or one may have machinery whose operation cannot withstand an unplanned shutdown without damage or danger.

In such cases, an ungrounded supply can be used. Because there's no bonding, the first accidental of a ground fault will not cause a shutdown, so the fault can be found before a second fault.

 

[LarryFine]

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.

That's easy: bond one of the three lines. It gets's colored white and isolated from ground after the main, and can be switched or breaker'ed, but not fused.

 

[LarryFine]

Larry - Not necessarily.

I was referring to the absolute declaration here:

A wye system has to be grounded/neutral

In the sense of the OP, there is no mandated bonding.

 

[glene77is]

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.

Try a "Delta feeding a Zig_Zag Wye"
which produces a Neutral
referenced to the Delta which drives this system.

Anybody care to discuss this kind of neutral?

Is it tolerant of Off-Balanced loads?
That is, does the Line-to-Neutral voltage vary much
as the balance of the three lines varies?

Comments?

 

[brian john]

Because one may have only three-phase loads, so no neutral is needed, or one may have machinery whose operation cannot withstand an unplanned shutdown without damage or danger.

In such cases, an ungrounded supply can be used. Because there's no bonding, the first accidental of a ground fault will not cause a shutdown, so the fault can be found before a second fault.

But that is not what the poster said he said he could pick up a neutral off any delta transformer (if I understood him correctly).

 

[LarryFine]

But that is not what the poster said he said he could pick up a neutral off any delta transformer (if I understood him correctly).

If you mean the OP, I thought he was asking how come a non-grounded Delta measures like a Y with a voltmeter.

 

[brian john]

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 attached to so the statement that a ungrounded delta system contains a neutral point is true? it just may not be used?

This statement BUT after reading it a 3rd time I see he mentions a neutral that exist. I still say this DOES NOT exist unless the purchaser specifies it.

 

[mull982]

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?

Having even an ungrounded wye system can lead to potentially dangerous overvoltages in the event that there is a re-striking or arcing ground fault on one of the three phases.

 

[brian john]

Having even an ungrounded wye system can lead to potentially dangerous overvoltages in the event that there is a re-striking or arcing ground fault on one of the three phases.

I neither design or install the systems I was there strictly to test cerain aspects of the distribution system

My question would be why would a ungrounded wye pose more issues that an ungrounded delta. If the neutral remains ungrounded and is not utilized?

 

[winnie]

_Any_ ungrounded system (delta, wye, zig-zag...) is subject to transient overvoltage caused by restriking faults. I'm sure that there are subtle differences between ungrounded wye versus delta systems (eg. response to harmonics) but my understanding is that they are similar on the whole.

If you have an ungrounded system with a wye secondary, you have the easy option of installing a grounding resistor and making what is known as a 'high resistance grounded' system. This has the continuity of service benefit of an ungrounded system, combined with the voltage limiting of a grounded system.

-Jon