Grounded and Neutral on Delta Wye Transformer and Distribution. 1

[mtchufi]

Hi all,
I want to invite you all to discuss little case below.
I have joint for some different company. The problem is, they use some different system on their electrical installation. As normally we use in here is the Delta Wye Transformer 20KV/380V 50 HZ. The Secunder side is Wye Connection.
1. In some Factory, the Neutral point is grounded, and only one connection in the Transformer Area , in any other point is sparated between Neutral and grounded.
2. In other Factory, the Neutral is not connected with the ground. means the neutral and the grounding system is totally sparated.
Which is the right Connection, No1 or No2 according to International standard, or any other opinion, please welcome. Let me know any helpfull refference about this.
Thanks

mtchufi

 

[DanDel]

If there is a neutral connection at the transformer, and it is brought into the system and used for neutral wiring connections, and you are in the USA, per the NEC it has to be grounded, preferably at the transformer.
Since you state 380V, 50Hz, I know that you are probably not in the USA.
Tell us more about the loads on these systems.

 

[busbar]

Siding with DanDel, if there are phase-to-neutral-connected secondary loads, typical regional practice would be a solidly grounded neutral.

Getting an answer on the ungrounded case may not be easy, but there may be some reason, like, for instance, ground detection are in place to allow for orderly shutdown {and alarming} at first ground fault.

Arbitrarily grounding an ungrounded system may be troublesome—you may want to carefully study the system before making changes. It could be a real can of worms to do otherwise.

 

[jbartos]

Suggestion to mtchufi (Electrical) Nov 1, 2003 marked ///\\The problem is, they use some different system on their electrical installation. As normally we use in here is the Delta Wye Transformer 20KV/380V 50 HZ. The Secunder side is Wye Connection.
1. In some Factory, the Neutral point is grounded, and only one connection in the Transformer Area , in any other point is sparated between Neutral and grounded.
///The is often called the solidly grounded neutral system grounding. It is mandatory for 380V/220V three phase system to be safe.\\\
2. In other Factory, the Neutral is not connected with the ground. means the neutral and the grounding system is totally sparated.
///This is often called an ungrounded system without any system grounding. This is permitted to be used for dedicated loads only.\\Which is the right Connection, No1 or No2 according to International standard, or any other opinion, please welcome.
///It depends. See my reply above. Often, these grounding aspects are covered in safety codes and local Utility safety and good practices related literature.\\ Let me know any helpfull refference about this.
///IEEE Std 142-1991 IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems, (Green Book)

http://www.ieee.org

Similar standards are on

http://www.iec.ch

\\

 

[mtchufi]

Thanks to all repliers,
You are right that I do not work in USA area. I work in a second country in south east asia region, that the regulation of electrical installation is very soft.
Now, lets back to the case issued above, here is a sample case what happen in my factory last few month when I worked with the Factory that used “Ungrounded System” like jBartos said.
There was any short circuited in our load connection. The insulation of lead cable was
Broken and one phase was shorted to the ground. The Thermal protector was not tripped, because there was not any close loop current through the short cable.
When check on the single phase socket plug using the test pen, both of them are alive, its strange! When the three phase connection checked with a multi tester, its read that:
1. Phase to phase = 380 V (RS-ST-RT)
2. Phase to Neutral = 220 Vac
3. Ground to Phase R and S = 380V
4. Ground to Phase T is almost zero.
5. Ground to Neutral is 220 V.
By this way, I think that the connection with ungrounded system is not safe. In my opinion, Neutral should be zero or almost zero. So, This system is not reliable ( just in my opinion). May be my opinion is not right ?
I invite all of you to discuss about this with your own opinion and reasonable. Your answer would be very helpful for the technician of the second country like me.
Thanks and regards

Mtchufi

 

[DanDel]

The reasoning behind an ungrounded system is that one phase can go to ground and the system will still be up and running. Usually, there is some kind of indicator lights or alarm which will warn of the first grounbd fault, so that it can be traced out before another line faults.
You're right that it is not the safest approach.

 

[alehman]

In the U.S. ungrounded systems were very common about 50 years ago. There are very few now because of problems with transient overvoltages when faults occur, although such systems are permitted per our code (NEC) when there are no line-to-neutral connected loads. Much more common now is high-resistance ground, wherein a resistor is connected between the secondary neutral and ground. The resistor is sized so the ground fault current roughly equals the capacitive charging current of the system. This overcomes the overvoltage problems and provides a simple means for detecting ground faults. High-resistance gounded systems at 480V are fairly common for U.S. industrial plants. Both ungrounded and resistance grounded systems must be maintained by qualified personnel.

 

[jbartos]

Suggestion: The ungrounded system is used when the high-resistance grounding is circumvented by different protection schemes, e.g. overvoltage protection by TVSS and ground fault indicators. Usually, more expensive processes prefer to have some suitable time interval reserved for their proper power supply transfer or shutdown.

 

[mtchufi]

all of your unswer is Helpful to me.
What happen here is , a lot of our installtation (i think this what usually done in our Country) does not have the earth leakage or ground falut detector (relay).
Thats way in this case I still prefer to use the Neutral groundel as well, so when some ground fault occurs, the circuit breaker is tripped.
may be this is not applicable regarding the international standard, but the actual condition here is like that, mostly installation here does not have ground fault relay.
Its clear enough for me and i want to close discussion this matter, see you in another case/problem.
Thanks you

regards,
mtchufi