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Why do it get current in other phases when i short circuit one phase (Single line to ground fault). IEC 60909 calculations

asked 2023-01-04 23:32:53 -0600

CynicalSuka gravatar image

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

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answered 2023-01-10 12:05:04 -0600

perolofl gravatar image

updated 2023-01-13 07:53:30 -0600

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:

image description

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 ... (more)

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Comments

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.

CynicalSuka gravatar imageCynicalSuka ( 2023-01-12 10:39:26 -0600 )edit

See my updated answer!

perolofl gravatar imageperolofl ( 2023-01-13 04:31:48 -0600 )edit

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.

CynicalSuka gravatar imageCynicalSuka ( 2023-01-13 10:57:46 -0600 )edit

11.2.5.2 Effect of Neglecting Transformer Phase Shift <-----section of PSSE PAG Vol 1

CynicalSuka gravatar imageCynicalSuka ( 2023-01-13 10:59:02 -0600 )edit

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

CynicalSuka gravatar imageCynicalSuka ( 2023-01-13 11:33:34 -0600 )edit

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Asked: 2023-01-04 23:32:53 -0600

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Last updated: Jan 13