GROUNDED PHASE

[smur]

I read on a 3 phase system in Taiwan the following voltages:
3 phase system
one phase to ground 6volts
2nd phase to ground 208v
3rd phase to ground 208v
This is delta system
Isit possible that 1 phase is grounded through a fault ?
Or it is intentionally grounded ?
because of this our tools is blowing controllers.
thanks

 

[itsmoked]

[green]"Is it possible that 1 phase is grounded through a fault ?"[/green]

YES!



[blue]"Or it is intentionally grounded ?"[/blue]

Can be!

The question is should it be intentionally grounded at your facility? If not, then you need someone to track the problem down. If it is supposed to be grounded then you may need a transformer in front of your drives to make them happy. There is an active thread on this very subject at the moment. Look for it.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[itsmoked]

Here's the thread:

thread237-164884

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[smur]

Hi Keith
This is not the same case I am having. I read only 6 volts to ground on one phase and 208 between the other phases. So either it is intentionally grounded or there is a ground fault. if one ground fault appears in a delta or ungrounded system, then you have too wait for another fault to appear to trip the breaker. Or use indicators to catch the GF.
murli

 

[rbulsara]

Did you ask the people faimiliar with the faciltiy as to what type of system they have?

It could be either as keith indicated, In either case it should not blow any conrollers. What do you mean by blow? What happens? What are the rating of the tools/controllers?

I suspect, this is a corner grounded delta system. 6V may be due to the current in that phase. As you move aways from source(point of grounding) you will measure some voltage equal to IR over the grounded conductor..

 

[olebob]

hello smur,what reading do you get a-b-c etc.?

 

[waross]

When you are reading the 6 volts, connect a 100 watt light bulb in paerallel with your meter. If the 6 volt reading is leakage it should drop considerably. If the 6 volt reading is an indication of an IR drop, there won't be much change in the reading.
respectfully

 

[smur]

A TO B = 6V
B-C = 208
C-A=208

In US they have a stinger leg. But do they have corner delta grounded ? Some elctronic equipment will not like ph to ground of 0 volts. So it blows up the controllers, I guess. So it is possible that the transfomer corner is grounded?

 

[smur]

Sorry. That should read
A-B = 208
B-C = 208
C-A= 208
A TO GND=6
B TO GND=208
C TO GND=208

 

[waross]

smur;
Can you recheck your post as to which is the;
"A" to ground voltage.
"B" to ground voltage.
"C" to ground voltage.
And which is the;
"A" to "B" voltage.
"B" to "C" voltage.
"C" to "A" voltage.
If your last post was correct, you have more problems than a grounded phase.
respectfully

 

[olebob]

smur, if the voltage between a-b is 208,and b-c is 208,and c-a is 208,then it may indeed being a delta grounded system,is there a neutral? ,the system i work on is a 480 volt delta ground there is no neutral,the grounded phase is not a ground!!to get 120-240 for lighting,tools etc,we use a transformer.if you tools are 120volt ,they well smoke.the grounded phase is a safety deal, therefore you always have one ground fault,one more will trip it.in the u.s the grounded phase should be marked all the way through the system.be aware also,the grounded phase may not be fused,it maybe slugged,alway consider it hot!!DONOT USE THE GROUNDED PHASE AS A NUETRAL.

 

[davidbeach]

waross, the voltages in smur's 23:13 post all work as a corner grounded delta if things are rounded off a bit. I'd be surprised if all the 208 readings are actually 208, never seen a 3-phase system with exactly the same voltage between each pair of phases. So, if anything close to 208 is recorded as 208, and the one voltage close to zero is recorded with the actual reading, that's what you would get.

 

[smur]

Hi
Is this normal to have a corner grounded system ? The 6 volts may be the voltage drop due to IR. But that would mean that further you go, the ground will be displaced.
murli

 

[resqcapt19]

208 is not a standard voltage for a delta system in the US. A delta would normally be 240 phase to phase.
Don

 

[rbulsara]

Smur:

If the system is corner grounded delta, there is nothing wrong with what you are measuring. The grounded phase is as a grounded conductor (not ground or grounding conductor), meaning it carries current in normal condition. You still need to run a separate equipmnet grounding conductor. Both the grounded conductor and the grounding condutor are connected together only at one point that is at the source, the transformer or the first disconnet.

You bond all your equiment enclosure and non-current carrying metal parts to that equipment grounding conductor and not to the grounded phase.

This is no different than a neutral, where neutral is a grounded condutor and you still run green grounding conductor with each circuit.

Refer to NEC 250 more clearer definitions.

The cause of your equipmnet burn out is something different. You have not still described what kind of equipment is failing, how and what is their rating and configuration. It appears that you already have made an assumption and now trying to justify your assumption rather than investigating the actual problem and systematically analyzing it.

 

[waross]

Hi davidbeach;
You are right, but I was responding to the 23:10 post.
smur;
The six volts seems a little high for an IR drop. It is possible but unusual.
If you connect a 100 watt light bulb in parallel with your meter and still read 6 volts, it is most likely IR drop.
If the voltage drops considerably with the light bulb connected you are seeing leakage.
respectfully