Short circuit calculation for railway substation
Short circuit calculation for railway substation
(OP)
With a current project I have some problem with customer engineers about SC current level on MV side of railway substation.
It is existing substation, where I have to calculate relay protections settings and to set-up relays.
Scheme is following:
Busbar 110 kV, 3-phase SC current 16.3 kA (3420 MVA)
Power Transformer, 110/27.5 kV, 12.5 MVA, Uk=7.61%, connected between phases B and C on 110 kV side.
MV Switchgear is 27.5 kV, one terminal of the transformer is connected to contact wire, second one - to the rail.
I made a model using ETAP and NEPLAN - in both cases SC current on 27.5 kV busbar is 5.8 kA (or 6.4 kA if factor 1.1 is applied according to IEC 909). But the client insists that SC current here, calculated from long time ago is 3.6 kA (my result, divided by 1.73).
I would like to present him calculation by hand, because he is an old man and doesn't rely on computers
I am OK with calculations in 3-phase network, but this case is a bit non-standard for me. And of course I am affraid if I miss something in modeling.
It is existing substation, where I have to calculate relay protections settings and to set-up relays.
Scheme is following:
Busbar 110 kV, 3-phase SC current 16.3 kA (3420 MVA)
Power Transformer, 110/27.5 kV, 12.5 MVA, Uk=7.61%, connected between phases B and C on 110 kV side.
MV Switchgear is 27.5 kV, one terminal of the transformer is connected to contact wire, second one - to the rail.
I made a model using ETAP and NEPLAN - in both cases SC current on 27.5 kV busbar is 5.8 kA (or 6.4 kA if factor 1.1 is applied according to IEC 909). But the client insists that SC current here, calculated from long time ago is 3.6 kA (my result, divided by 1.73).
I would like to present him calculation by hand, because he is an old man and doesn't rely on computers
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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant






RE: Short circuit calculation for railway substation
It seems that the sqrt(3) discrepancy may be a result of a misunderstanding regarding topology. Or was the old calculation assuming the wrong phase configuration?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Short circuit calculation for railway substation
Attached is SLD - actually some mix of 3-line and 2-line diagram. Important for me is SC level on 27.5 kV busbars - I would like to check my calculation for busbar's SC, next points along the grid are not a problem.
------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
RE: Short circuit calculation for railway substation
I think that someone someetime wrongly transformed the system from three-phase to single phase and arrived at 3.6 kA and that that number was accepted and is now 'difficult' to change.
Interesting diagram, by the way. Russian?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Short circuit calculation for railway substation
This is typical system in Bulgara, but I work for a first time for railways. Our usual field are utilities - www.triel.bg
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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
RE: Short circuit calculation for railway substation
RE: Short circuit calculation for railway substation
RE: Short circuit calculation for railway substation
MV bus is labeled 52 kV, but this have to be isolation level. I don't know why the switchgear is for 52 kV - I entered the project on the very last stage, just for relay protections settings.
Bus works on 27.5 kV and your calculation matches my results and Gunnar's.
------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant