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DannyD
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Join Date: Oct 2009
Location: kuruman NC. SOUTH AFRICA
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Good Answers: 1

Coupled Neutral Bar

04/11/2012 9:22 AM

Hi Guys

I have two transformers 22KV/400V star connected on the secondary side supplying Substation A. In Substation A we have two main circuit breaker supplied by the two transformers with a bus-coupler in-between(meaning three, 3ph Master pack circuit-breaker) for incase we have problem on one incomer we can use the bus-coupler to supply other side. From subsation A I have two feeders/supplies which supplies Substation B, and substation B has the same set up like substation A (meaning Substation B have two incomers from Substation A. three, 3ph master pack circuit breaker which one is a bus-coupler).

The neutral bars of both transformers are linked/connected together at Substation A and Substation B MCC.

The two Circuit breaker that supplies sustation B at sustation A are eguipt with earth leakage relay (1000mA New Elec).

THE LOADS THAT ARE SUPPLIED BY BOTH SUBSTATIONS MCC'S ARE 400 V AND 230 V

PROBLEM: The two Circuit breaker that supplies Substation B keeps on tripping on earth fault due to the coupled neutral bar.

Solution: We decided to un-couple/remove the link that link the two neutral bar at Substation A to solve the tripping problem. And if we have a problem with one Transfomer or Incommer one must first couple/connect the two neutral and close the bus coupler.

Question: If one transfomer/Incommer has a problem, What will happed if the bus-coupler is closed to suppler other side without connecting/coupling the neutral bus-bar.

REMEMBER I HAVE 230 VOLTS LOADS ON MY CIRCUITS.

Please Help.

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DannyD
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Location: kuruman NC. SOUTH AFRICA
Posts: 51
Good Answers: 1
#1

Re: Coupled neutral bar

04/11/2012 9:26 AM

In addition of the above, we are using 3 phase 4 wire system (400 Volts)

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cuba_pete
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Join Date: Dec 2010
Posts: 1895
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#2

Re: Coupled Neutral Bar

04/11/2012 2:59 PM

My answer to the actual question you posed would be this: You wouldn't have a proper neutral nor neutral/ground bond for your system. This would be bad.

The neutrals for the primaries and secondaries at each substation are bonded directly? Why? Why not use a normal bonding and earthing scheme? You haven't mentioned earthing for any of this system, so I have to ask.

The transformers in question are what type? What are the full specs? Are they all the same type?
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DannyD
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Location: kuruman NC. SOUTH AFRICA
Posts: 51
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#3
In reply to #2

Re: Coupled Neutral Bar

04/12/2012 6:04 AM

The two transformer are delta (primary) and star (seconadry) connected, so we dont have primary neutrals. And the star points/Neutral is Earth and we are you the NER and NEM (Adit relay) to monitor our neutral currents.

my big consent is: what will happen to my load when the neutral link is not connect and the bus coupler is closed and why?

TRANSFORMER INFORMATION: 5.36 OHM (Impedence);22KV/400V;800 KVA; 1155 A; Dyn11

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TonyS
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#4

Re: Coupled Neutral Bar

04/12/2012 6:41 AM

Replace the neutral link a substation "A" and remove the link at "B". You're getting circulating currents in the neutral link at substation "B" being detected by the earth leakage units at substation "A"

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DannyD
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Location: kuruman NC. SOUTH AFRICA
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#5
In reply to #4

Re: Coupled Neutral Bar

04/12/2012 10:57 AM

on both substations (A&B) MCC'S I have single phase loads (230 V), which are connected from one phase to neutral (on all phases), and remember the neutral is acommon of 3phases.

Remember my line voltages are +-400V and my phase voltages are +-230V, so if i remove/disconnect the links meaning there is no return current path to the star point of my transformer. but I am not sure what will happen to the 230V loads that are connected?

From my understanding which i am not sure of is that my 230V loads will be now connected across line voltages (400V) because the main neutral is disconnected by the the links. And this will damage/burn my 230V equipments. PLEASE CORRECT IF I AM WRONG, AND SOME MORE EXPLANATION

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cuba_pete
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#6
In reply to #4

Re: Coupled Neutral Bar

04/12/2012 2:38 PM

Delta Star clears this up a little. I am not sure why they would use the configuration which I think I am understanding. It's a little hard with the wording.

IEEE Green mentions this as a bad idea anyway...essentially for just these reasons.

GA
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iftikhar129
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#7

Re: Coupled Neutral Bar

04/13/2012 1:48 PM

there is no danger......actually nothing will work which is connected to the uncoupled neutral busbar....Open circuit..
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toink
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Join Date: May 2012
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#8

Re: Coupled Neutral Bar

05/15/2012 3:07 AM

danny , the problem you have now is not good pls check the name plate of both TR if same but if not youneed to replace one of then with same spec , to be able to correct the tripping in sycronized connection, and you need to check also the facing connect of you cable wire

have a good day !!!!

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DannyD
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Location: kuruman NC. SOUTH AFRICA
Posts: 51
Good Answers: 1
#9
In reply to #8

Re: Coupled Neutral Bar

05/16/2012 6:22 AM

MY two Transformers are exctly the same.

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