All loads set to zero. All shunts set to zero. I get current in other phases when i short circuit one phase only meaning single line to ground phase. By theory current should only flow in faulted phase as all the loads are open circuited, all shunts are ignored in all sequences etc
In a network there will be currents flowing in the healthy phases at LG-faults, even if all loads and shunts are ignored.
At LG-fault the sequence currents are equal at the fault location, but the impedance and layout of the positive, negative and zero sequence systems are different.
So, normally there are currents in the healthy phases of the lines/transformers feeding the faulted bus.
EDIT: An example with a simple non-loaded system with only reactances as shown below:
The Thevenin positive sequence reactance at bus 3 is 0.45 pu and the zero sequence reactance is 0.08 pu. The zero sequence reactance for the branches is 0.6 pu each, and the zero sequence reactance of each grounded transformer is 0.1 pu.
LG-fault at bus 3 gives the following results with ASCC:
AT BUS 3 [C 400.00] AREA 1 *** FAULTED BUS IS: 3 [C 400.00] *** 0 LEVELS AWAY ***
PRE FAULT (kV L-G) VA:/230.94/30.00
POST FAULT (kV L-G) V+:/124.90/30.00 V-:/106.04/-150.00 V0:/18.85/-150.00 VA:/0.00/0.00 VB:/201.99/-68.05 VC:/201.99/128.05
THEVENIN IMPEDANCE, X/R (PU) Z+:0.000000+j0.450000, 9999.999 Z-:0.000000+j0.450000, 9999.999 Z0:0.000000+j0.080000, 9999.999
X------------------------------------LINE TO GROUND (LG) FAULT-----------------------------------X
X----------- FROM ------------X AREA CKT I/Z /I+/ AN(I+) /I-/ AN(I-) /I0/ AN(I0) /3I0/ AN(I0) RE(Z0) IM(Z0) APP X/R
2 [B 400.00] 1 1 AMP/PU 73.6 -60.00 73.6 -60.00 14.7 -60.00 44.2 -60.00 0.000000-0.200000 9999.999
2 [B 400.00] 1 2 AMP/PU 73.6 -60.00 73.6 -60.00 14.7 -60.00 44.2 -60.00 0.000000-0.200000 9999.999
4 [D 135.00] 1 1 AMP/PU 0.0 0.00 0.0 0.00 117.8 -60.00 353.5 -60.00 0.000000 0.000000 0.00000
INITIAL SYM. S.C. CURRENT(I''k)(RMS) AMP 147.3 -60.00 147.3 -60.00 147.3 -60.00 441.8 -60.00
--------------------------------------------------------------------------------------------------
X----------- FROM ------------X AREA CKT I/Z /IA/ AN(IA) /IB/ AN(IB) /IC/ AN(IC) RE(ZA) IM(ZA) APP X/R
2 [B 400.00] 1 1 AMP/PU 162.0 -60.00 58.9 120.00 58.9 120.00 -0.00000 0.236364 9999.999
2 [B 400.00] 1 2 AMP/PU 162.0 -60.00 58.9 120.00 58.9 120.00 -0.00000 0.236364 9999.999
4 [D 135.00] 1 1 AMP/PU 117.8 -60.00 117.8 -60.00 117.8 -60.00 -0.01540 0.108889 7.07254
INITIAL SYM. S.C. CURRENT(I''k)(RMS) AMP 441.8 -60.00 0.0 0.00 0.0 0.00
---------------------------------------------------------------------------------------------------------------------------------------------------
There is only fault current in phase A at bus 3 (441 ...
Why do i get current in B and C phase if only A phase is grounded. By theory current in B and C phase should be zero if all loads and shunts are ignored.
i think you may have missed some important things in your example. Transformer connection codes and phase shift! According to theory there should be current in only A and C phase coming from Bus 4. PSSE PAG Vol 1 has a nice section dedicated to wrong SC calculations if phase shift is ignored.
11.2.5.2 Effect of Neglecting Transformer Phase Shift <-----section of PSSE PAG Vol 1
still not convinced! In unloaded system no current should flow in other phases. Only Delta-star transformer can make the fault current on one phase of star side to flow in two phases on delta side. thats the theory
A nooby question. Why are currents flowing from bus 4 which is essentially a floating bus?
X----------- FROM ------------X AREA CKT I/Z /IA/ AN(IA) /IB/ AN(IB) /IC/ AN(IC) RE(ZA) IM(ZA) APP X/R 4 [D 135.00] 1 1 AMP/PU 117.8 -60.00 117.8 -60.00 117.8 -60.00 -0.01540 0.108889 7.07254
117 ampere current in all ABC phases with phase angle of -60 flowing from bus 4
It´s the zero sequence current flowing into the grounded Y-winding. Please read about symmetrical components and zero sequence for grounded WhyDelta transformers. The current is flowing in the 400 kV winding. There is no current in the 135 kV winding, i.e. no current flowing from bus 4!!!
I know results shows I0=117.8A but why does results under IA, IB, IC showing 117.8 A from bus 4? Maybe i am reading it wrong. Maybe from bus column means current coming from the direction of bus 4 towards bus 3 not necessarily from bus 4 itself. It makes sense then. Currents coming from Y side.
Asked: 2023-01-04 23:32:53 -0600
Seen: 631 times
Last updated: Jan 13 '23
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