Warning 110 | [Various software] | SIMPLEFAULT negative impedance
Relevant software:
Emitted message:
SIMPLEFAULT: When calculating the fault impedance for this fault, the calculation has negative impedance. This is likely due to a low SCR, or a very shallow fault close to the Thevenin equivalent source voltage. The applied fault may not appear at all - or may appear as a bolted fault. We recommend you replace this SIMPLEFAULT command with a VDISTURBANCE command - and consider using the VCHANGEPU= argument.
Description:
This warning indicates that when calculating the fault impedance for a SIMPLEFAULT command, the calculation resulted in a negative impedance value.
This is likely caused by using a SIMPLEFAULT command with a very low short circuit ratio (SCR) and a very shallow fault high residual voltage, such as FZ=95%.
Possible impact:
- The dynamic result may fail to converge, not appear at all or default to a bolted fault - in all cases, leading to incorrect simulation results compared to other software packages.
Potential fixes:
This occurs due to SIMPLEFAULT using a simple voltage divider calculation when determining fault impedances.
If the short circuit ratio is very low and the generator is very large, this simple calculation can generate fault impedances which are negative (specifically only if Vtarget is greater than Vinf - which only typically occurs under very low SCR).
To fix, consider replacing the SIMPLEFAULT command with the more advanced VDISTURBANCE command with the optional OP=COMPENSATED argument.
This optional argument uses an alternative calculation methodology and automatically switches between a fault and capacitor to achieve the target voltage as per the command.
Details: