Highest Prospective Short Circuit Current Isc which a Generator can feed in case of Short Circuit fault is as given Bellow:
| Generator Parameters | 2500 KVA | 2000 KVA | 1500 KVA | 1000 KVA | 900 KVA | 750 KVA | 625 KVA | 600 KVA | 500 KVA | 400 KVA | 380 KVA | 320 KVA | 250 KVA |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Line Voltage Volts | 415 | 415 | 415 | 415 | 415 | 415 | 415 | 415 | 415 | 415 | 415 | 415 | 415 |
| Sub Transient X”d | 18 | 17 | 17 | 16 | 16 | 15 | 14 | 12 | 11 | 10 | 10 | 10 | 10 |
| Genset Full Load Current FLA Amps | 3478 | 2782 | 2087 | 1391 | 1252 | 1043 | 870 | 835 | 696 | 556 | 529 | 445 | 348 |
| Genset Isc KA | 19.3 | 16.4 | 12.3 | 8.7 | 7.8 | 7.0 | 6.2 | 7.0 | 6.3 | 5.6 | 5.3 | 4.5 | 3.5 |
| Short Circuit Ratio | 0.43 | 0.43 | 0.43 | 0.43 | 0.42 | 0.49 | 0.42 | 0.43 | 0.48 | 0.43 | 0.42 | 0.55 | 0.55 |
| Short Circuit withstand current for 5 to 10 Sec | 10434 | 8347 | 6261 | 4174 | 3756 | 3130 | 2609 | 2504 | 2087 | 1669 | 1586 | 1336 | 1043 |
| Genset Main Circuit Breaker In Amps | 4000 | 3200 | 2500 | 2000 | 1600 | 1250 | 1000 | 1000 | 800 | 630 | 630 | 630 | 400 |
| CB In Panel Rating At 45*C Ambient Room Temperate | 3500 | 2900 | 2300 | 1800 | 1500 | 1100 | 900 | 900 | 700 | 550 | 550 | 550 | 365 |
Prospective Short Circuit Current of Multiple Generators connected at Synchronising panel is Cumulative Short Circuit KA of all individual Generators.
Generator Prospective Short Circuit current compared to Similar KVA rating of Transformer, is typically 5 times weaker.
Short Circuit is a fault which allows the current to flow through its unintended path with very low impedance, which results into excessive current flow through the path.
It is the Reactance of Sub Transient period, which is immediately after short circuit on the generator, this period lasts for typically 10 mSec to 20 mSec. Typical Sub Transient Impedance is 10% to 20%.
It is the Reactance of Transient period which is immediately after Sub Transient period of the generator, this Reactance period lasts till the short circuit fault settles, this settled value is typically less then rated current of Generator. Normally Transient Impedance is 15% to 25% and it lasts from 100 mSec to 500 mSec.
Short Circuit ratio of Generator is the ratio of field current required to produce rated voltage on No Load to field current required to produce rated voltage on Short Circuit condition.
With Higher SCR, Xd will be low, Result will be Good Voltage Regulation and Increase in Alternator stablity.
With Lower SCR, Xd will be High, Result will be low value of Short Circuit Current.
It is the ability or Resilience of Generator to return to Steady State condition after observing disturbance.
Total Short Circuit current on the HBB of Synchronizing Panel is Cumulative sum of all individual Generator Short Circuit Currents.
| Short Circuit Impedance | Typical reactance (%) | Short Circuit Current Isc multiple of In | Typical time |
|---|---|---|---|
| Subtransient Phase X”d | 10% to 20% | Isc = 6xIn to 12xIn | 10 mSec to 20 mSec |
| Transient Phase X’d | 15% to 25% | Isc = 1.5xIn to 2xIn | 100 mSec to 500 mSec |
| Steady state Phase Xd | 200% to 300% | Isc = 0.5xIn | > 500 mil Sec |