Voltage increases

[Hien.nguyenquoc]

Dear all,

It is nice to join and meet all of members in this forum. I am Hien from Vietnam.

I've got a problem with my low voltage system is that: Normally, it is 220VAC, but in one day. It goes up to 400VAC and destroys all of our equipments (fax machine, photocopy machine, PCs, air conditioners, fans, lamps...). This sumptom occurred only in the office area (another location such as workshop, machine room was normal).

Pls. help me to find out what was happened.

Thank you all of you.

Regards

Hien

 

[Guest123]

Hi.

Do you have a 3 phase supply to your office??

Also how are you aware that the voltage jumped from 220 to 400?? go you have a monitoring device??

 

[Hien.nguyenquoc]

Hi.

Do you have a 3 phase supply to your office??

Also how are you aware that the voltage jumped from 220 to 400?? go you have a monitoring device??

Hi Lenny,

Yep. I've got 3 phase, 400VAC, 5 wires (R,S,T, N, G).

I don't have any monitoring devices. Operators mesured by voltage meter at the outlet of each branch's MCBs. And the voltage was like that. This symptom lasted for 1 days and disappeared.

Regards,

Quoc Hien

 

[ian.settle1]

Dear all,

It is nice to join and meet all of members in this forum. I am Hien from Vietnam.

I've got a problem with my low voltage system is that: Normally, it is 220VAC, but in one day. It goes up to 400VAC and destroys all of our equipments (fax machine, photocopy machine, PCs, air conditioners, fans, lamps...). This sumptom occurred only in the office area (another location such as workshop, machine room was normal).

Pls. help me to find out what was happened.

Thank you all of you.

Regards

Hien

Sounds like you lost your neutral thus you will get 400v across your 220v equipment.

Check all your neutral connections from your supply to the distrbution boards.

May also be a problem with the suppliers equipment.


Had a similar thing few years back when equipment in a aircraft factory blow up, one peice of alone equipment was worth £150,000.

 

[Darkwood]

Can you confirm what they tested between when getting the 400v reading im assuming they are not electricians and may be confused with the readings they got?

Can you confirm what they tested between when getting the 400v reading im assuming they are not electricians and may be confused with the readings they got?

Also you say it only effected your offices and nowhere else in the premises this would suggest an internal wiring fault, was anyone doing any electrical work at all or messing about with the wiring because if all your office equipment blew up it does sound like a over-voltage problem but if its rectified itself its sounding a bit like someone is involved in this or as ian settle mentioned its possible the neutral supply to your office dist board is burning out somewhere.

 

[Hien.nguyenquoc]

Can you confirm what they tested between when getting the 400v reading im assuming they are not electricians and may be confused with the readings they got?


Also you say it only effected your offices and nowhere else in the premises this would suggest an internal wiring fault, was anyone doing any electrical work at all or messing about with the wiring because if all your office equipment blew up it does sound like a over-voltage problem but if its rectified itself its sounding a bit like someone is involved in this or as ian settle mentioned its possible the neutral supply to your office dist board is burning out somewhere.

Hi Darkwood,

Thank you!

The Office panel has 01 03-pole DS supplying 03-phase power to the busbars ( R,S,T busbar). And and neutral bar is separated from the DS (same like knife-switch). The operators measured voltage at the outlet of the branch MCBs which its hot line connected to the (R,S,T busbars) and its neutral line connected to neutral bar. All MCBs they measured showed 400VAC. All of DS, MCBs, and MCCBs were from Merlin Gerin (but made in China - I guess). The DS supplying power to the Office panel was located at the Main Distribution Board several meters away. It is also 03-pole type.

Internal wiring is OK.

Now, I thought that it was because of Neutral lost. I also heard from the operators (lamps got more dim whenever they switched on the other lamps). I would have to check all of them again.

Regards,

Hien

 

[xraytek]

Now, I thought that it was because of Neutral lost. I also heard from the operators (lamps got more dim whenever they switched on the other lamps). I would have to check all of them again.

If you lose the neutral connection that feeds a distribution board then you may find a drop in voltage on some circuits, and an increase on others on that board.
It all depends on how much equipment is connected at the time, and if all 3 phases are equally balanced then a loss of neutral will make no difference.

 

[Darkwood]

If you lose the neutral connection that feeds a distribution board then you may find a drop in voltage on some circuits, and an increase on others on that board.
It all depends on how much equipment is connected at the time, and if all 3 phases are equally balanced then a loss of neutral will make no difference.

It is highly unlikely this dist' board is balanced having numerous single phase outgoing supplies and if the neutral was disconnected you would in effect create a star point for the three phases the subsequent volt rise would blow all volt sensitive equipment as has happened in this case.
The danger here seems to be a possible intermittent fault and if their is a neutral issue is could give rise to a dangerous situation as it may choose an earth path through some unsuspecting person. Also if their is a neutral earth fault on any circuit it could cause a fire as the full neutral current tries completing the circuit on a undersized earth.

Hien it would be great if you could let us know of your findings, but may i advise you that because their is a possible chance of a loose main neutral connection it may create a highly dangerous situation and i would recommend isolating the effected dist' board and getting it checked out a.s.a.p., because its a possible neutral fault it would be better to be safe than sorry.

 

[Hien.nguyenquoc]

It is highly unlikely this dist' board is balanced having numerous single phase outgoing supplies and if the neutral was disconnected you would in effect create a star point for the three phases the subsequent volt rise would blow all volt sensitive equipment as has happened in this case.
The danger here seems to be a possible intermittent fault and if their is a neutral issue is could give rise to a dangerous situation as it may choose an earth path through some unsuspecting person. Also if their is a neutral earth fault on any circuit it could cause a fire as the full neutral current tries completing the circuit on a undersized earth.

Hien it would be great if you could let us know of your findings, but may i advise you that because their is a possible chance of a loose main neutral connection it may create a highly dangerous situation and i would recommend isolating the effected dist' board and getting it checked out a.s.a.p., because its a possible neutral fault it would be better to be safe than sorry.

Yeah! I thought that this DB’s current was balanced. They measured the current in 03 phases: 8A, 9A, 9A during the fault. And one more, the earth wire connected to the earth busbar were so loosen that the indication on Ohm scale was OL. I already retighten this wire when I came back to the factory. Today, (this morning,9:30AM in Vietnam, GMT+7). I requested them to check the connection of neutral wire running from the Main DP to this faulted DP.

I would like to described the situation during fault: The office was using fax machine, photocopy machine, air conditioner, PC... Regarding to air conditioners, the fuse protected the electronic board was blown up (even some of them were in standby mode, means power was available at the air conditioner’s input). Some parts of the board was destroyed. For ones that working, the outdoor unit’s contactor coil was blown up also. Fortunately, the small motors were still fine. For 03-phase air conditioner, they remained intact. Actually, this office is rather small. It was not in 100% opening in operation due to business difficulties. But thing is, if the fault happens in the big premise… the physical damage will be huge.


Will let you know what I will find there soon.

Regards,

Hien