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=

Single-line-to-ground is where fear creeps in.
=   =E2=80=A2 In =CE=94=E2=80=93Y, zero sequence loops inside the delta.=
  =E2=80=A2 Your HV side does not =E2=80=9Csee=E2=80=9D that = earth fault since zero sequence will not cross the delta.
  =E2=80=A2 It appears as a line-to-line fault across two pha= ses.
  =E2=80=A2 Your HV earth-fault relay stay silent while the L= V burns due to SLG fault.

 
 
 

That is a scary gap.
  =E2=80=A2 You want clarity, not surprises during utility review.=
  =E2=80=A2 You want settings that stand when someone asks =E2=80= =9Cwhy.=E2=80=9D
  =E2=80=A2 You want to stop over-protecting one side and leaving = the other exposed.

 
 
 

= Do this in your next study.
  =E2=80=A2 Model grounding honestly.
  =E2=80=A2 Solid, resistance, reactance, NGR.
  =E2=80=A2 Feed the right zero-sequence impedances.

 
 
 

= Create one fault at a time.
  =E2=80=A2 Single bus.
  =E2=80=A2 Then read both sides.
  =E2=80=A2 If you fault every LV bus together, you will hide the = reflection.
  =E2=80=A2 Track what you are plotting.
=   =E2=80=A2 For SLG fault in LV Side, I0 at HV is zero= in =CE=94=E2=80=93Y transformer.
  =E2=80=A2 Switch to phase= currents and you will catch the two-phase reflection.
  =E2=80= =A2 Watch the healthy-phase voltage.
  =E2=80=A2 With C-= factor at 1.1, it lifts toward line value.

 
 
 

=E2= =80=A2 Do not panic.
=E2=80=A2 It is expected behaviour.
= =E2=80=A2 Use load flow to set OLTC range and PF correction.
=E2= =80=A2 Use short circuit to set short-time duties for cables, CTs, bus= bars, and breakers.
=E2=80=A2 Map these to relays.
=E2=80=A2&n= bsp;Then write it in your report in plain language

=
What's the first thing that makes yo= u nervous when using ETAP?

Join our free ETAP masterclass this Sunday and take your power system s= tudies to the next level=E2=80=94register n= ow

 
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