Doubts in ETAP
2
1. What are the checks required for Load flow study and what is the min/max required value? i.e. what is U/V & O/V limits? Allowable %age voltage drop limit? Critical and marginal alert?if critical wht to do? For load flow study, you need to check the MW and MVAR of each feeder. The undervoltage limit, u can put as 97%-98% and overvoltage u can put as 103-104%. U need the change the tappings of the transformer manually if it is Off load tap changer. If the transformer is having OLTC, u need to just put the range and step of the tap. 2. Criteria for lump load? Which can be considered as lump load? Diff between lump load and static load? If you have data for all motors, you can place them in the SLD with the ratings of the motor. Or else you can sum up each MCC panel and make it lump load with 80% motor load and 20% lighting load. 1. During calculating PSM, CT ratio to be taken or primary current only? As PSM = Fault Current/ (PS x CT Ratio), if ratio is /1 then its not problem but it is /5 then PSM will change. See relay setting calculator. 2. Back up relay to set at what fault current? 3. To find PSM, fault current will be the current passing through relay or bus fault current? 4. What is the actual value of instantaneous setting and time delay? And where it is required? 5. Trafo HV relay. Back up of that relay will be relay above it. So back up relay shall be set according to which fault current? 6. Why through fault stability is required..? 7. Adding library of relay 8. Which co-ordination curves need to print? 9. Relay to set for min fault current or max fault current and why? 10. For relay TCC kA, relay will consider which fault current? TCC Clipping or TCC min current? 11. We have to consider initial sym short ckt current or steady state current? 12. What is pick-up 1.05-1.3 times setting?
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Transcript of Doubts in ETAP
1. What are the checks required for Load flow study and what is the min/max required value? i.e. what is U/V & O/V limits? Allowable %age voltage drop limit? Critical and marginal alert?if critical wht to do?For load flow study, you need to check the MW and MVAR of each feeder. The undervoltage limit, u can put as 97%-98% and overvoltage u can put as 103-104%. U need the change the tappings of the transformer manually if it is Off load tap changer. If the transformer is having OLTC, u need to just put the range and step of the tap.
2. Criteria for lump load? Which can be considered as lump load? Diff between lump load and static load?If you have data for all motors, you can place them in the SLD with the ratings of the motor. Or else you can sum up each MCC panel and make it lump load with 80% motor load and 20% lighting load.
1. During calculating PSM, CT ratio to be taken or primary current only?As PSM = Fault Current/ (PS x CT Ratio), if ratio is /1 then its not problem but it is /5 then PSM will change. See relay setting calculator.
2. Back up relay to set at what fault current?3. To find PSM, fault current will be the current passing through relay or bus fault current?4. What is the actual value of instantaneous setting and time delay? And where it is required?5. Trafo HV relay. Back up of that relay will be relay above it. So back up relay shall be set according to
which fault current?6. Why through fault stability is required..?7. Adding library of relay8. Which co-ordination curves need to print?9. Relay to set for min fault current or max fault current and why?10. For relay TCC kA, relay will consider which fault current? TCC Clipping or TCC min current?11. We have to consider initial sym short ckt current or steady state current?12. What is pick-up 1.05-1.3 times setting?13. Relay to be set as back up for relay below it or for bus fault current?14. Why relays are set on 3-ph fault and LG fault why not LL fault or LLLG fault?15. Why LG fault on trafo secondary appears as a LL fault on transformer primary?16. Use of X/R ratio for grid, trafo etc.
