SGP410 Restricted Earth Fault Protection of Transformer

Lectures on Switchgear & Protection By Dr. Tirupathiraju Kanumuri, Assistant Professor, NIT Delhi
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[@madhavrabinbipin2116]

the explanation of why we require REF is excellent

[@surendrakverma555]

Excellent lecture Sir. Thanks

[@venkatesanvijaya5104]

Sir,
Thank you for your clear explanation.
If I we will use only CT4 for REF protection it is sufficient for detecting Inzone faults.

[@hussainmayouf5835]

Sure not, because any fault at downstream (extenal fault) will happen, the current will flow through CT4 which will make the trip and this trip is not intended.

[@abdullahadawi3055]

Thank you Dr for the valuable lucture

[@himanshu2232]

थैंक यू सर,it is very useful me.

[@mohammadpathan4668]

Well explained !

[@srikrishnathurlapati8671]

Please explain about Low impedance and high impedance Ref protection by including stabilizing resistor

[@surugayatri2062]

Sir in the 1st case delta side
What if a earth fault occurs on line between generator and transformer primary ??
Then also this relay will operate because of zero sequence current..
Is this correct interpretation??

[@pulkitjain1426]

Sir for delta side on transformer .....does relay operates for the fault outside protected zone as there is no CT on neutral ( no CT4).......

[@kris9811]

Hi what is the difference between Low Impedance and High Impedance REF? Is there any issue if a CT with higher magnetising current (190mA) is chosen for Low Impedance REF instead of CT with low magnetising current (40mA)?

[@rajeshtk1246]

Can you describe the process to find the value of the Stabilizing Resistor for the REF protection scheme, please?

[@surekhagaikwad5195]

Sir wen its delta we normally say zero seq comp flows in d closed delta. Now wen in d 1st case with delta prim and earth fault on delta wdg why don't we say that zero seq comp ....closed delta. Only if we trace d ckt we find that it flows thru the line and çt connected in dat line causes current flow in the relay.
Also wat if instead of delta prim we had star prim and all other conds same as explained. How wud it affect.

[@jitendramanisoni9518]

Why Dyn11 is used for DT

[@akhilsm6840]

Sir, if we have lot of single phase loads at secondary side and assume the loads are unbalanced, will this trip the Ref relay . Because since loads are unbalanced zero sequence current will be flowing through each CT but not through the neutral CT

[@hussainmayouf5835]

Hi Sir, if we have unbalanced condition means there is zero sequence component (Remember IN = Ia+Ib+Ic which will be not equal to zero in case of unbalance case) and this will be available both side at line CT and neutral CT. So, no trip will happen
I hope it is clear.

[@007drana]

Sir ,
My power trafo is operating on HV REF as there is no internal faults but also my 20 MVA tripping .
We have checked IR values of HV side of trafo but we got good values about Giga ohms. What might be reasons of tripping.

[@adnansworld744]

Reason of unwanted tripping might be 1) CT polarity may be connected wrognly in any one phase or Neutral CT . 2 ) Loose connection in CT secondray wiring . 3) CT Excitation current much difference for other CTs .

[@amsaid9169]

Why the connection is different in both side?!

[@nagamantriudaykumar4200]

How zero sequence current zero at start side c. T