bejoyengineer
Member
I am a bit confused on the relation between the primary and secondary currents of a transformer. As I am into instrumentation, I would like to get an understanding on basics of electrical engineering. Kindly do take some time and answer these question ?Please
Now say we got a transformer and it's MVA rating is 50 MVA, Delta ?star and steps down from 115 KV to 13.8 KV.Now the primary side has a CT ratio of 2000/5 Amps and secondary has got a CT ratio as 3600/5 amps and these are connected to the differential relay . There is NO ?" ICT" connected and the CT's are star connected. Now my first question would be
1 What would be the value of current in the primary side and what would be the value at the secondary side. I assume that ? if we have a full load of 50 MVA being used ?then the currents values at primary would be 600 and at secondary-3600.Am I right??
2 so if the above is right as per my thought- then say the load is 25 MVA, so that would mean that the primary current would now be 1000 A and secondary would be 1800 A. so depending on the load the primary and secondary currents also changes while the voltage remains the same. Hope I am right??
3. On what basis or using which formula do we decide that the primary current should be 2000 and sec should be 3600? Is it the formula:::: Power=root 3 x voltage x current or is it only ::::: Power= voltage x current. When I used both these formulas to find current in the primary side, I was not able to get the current as 2000 A(I used P=50 MVA ,V=115000)but 3600 Amps was the answer when I used the formula::::: Power= voltage x current for the secondary side (I used P=50 MVA ,V=13.8KV).
4. Is 3600 Amps and 2000 Amps know as the Line current (ILine) of the primary and secondary ?
Now say we got a transformer and it's MVA rating is 50 MVA, Delta ?star and steps down from 115 KV to 13.8 KV.Now the primary side has a CT ratio of 2000/5 Amps and secondary has got a CT ratio as 3600/5 amps and these are connected to the differential relay . There is NO ?" ICT" connected and the CT's are star connected. Now my first question would be
1 What would be the value of current in the primary side and what would be the value at the secondary side. I assume that ? if we have a full load of 50 MVA being used ?then the currents values at primary would be 600 and at secondary-3600.Am I right??
2 so if the above is right as per my thought- then say the load is 25 MVA, so that would mean that the primary current would now be 1000 A and secondary would be 1800 A. so depending on the load the primary and secondary currents also changes while the voltage remains the same. Hope I am right??
3. On what basis or using which formula do we decide that the primary current should be 2000 and sec should be 3600? Is it the formula:::: Power=root 3 x voltage x current or is it only ::::: Power= voltage x current. When I used both these formulas to find current in the primary side, I was not able to get the current as 2000 A(I used P=50 MVA ,V=115000)but 3600 Amps was the answer when I used the formula::::: Power= voltage x current for the secondary side (I used P=50 MVA ,V=13.8KV).
4. Is 3600 Amps and 2000 Amps know as the Line current (ILine) of the primary and secondary ?