Revision history [back]

All your three criteria are related to machine angle. For simplicity I prefer the first.

Instability of the system is about how the remaining system performs post-fault conditions, subject to all tripping activated by the protection system. Does it reach a stable condition (in V, F) at the end of the simulation? Good and sufficient modeling is needed for this kind of assessment.

For a test event, system instabilty can be monitored by:

• angle of generators, relative to reference machine like a nuclear plant or base unit. [generic model available in PSSe] Realistic criteria for the protection relays is needed (why trip a unit when its relative angle is 100 deg and not at 120 deg.?) Tripping of a unit might not render a system unstable.

• buses voltage level leading to voltage collapse or high-voltage cascading. Add UVLS relays [generic v-monitoring model available in PSSe, also UV/OV relays] Add load dynamic model reflecting V & F dependance. Air-conditioner loads?

• undamped oscillation, is damping > 3%?. Use Prony analysis after filtering visually all plots.

• system frequency (or Pelectric - Pload), add UFLS relay and UF/OF relays.
• thermal overload cascading by tripping overloaded lines using distance relays availale in PSSe.

CCT studies help to set the initial protection of generators for angle separation but not needed to asses the stability of a system. Dynamic stability studies take time, need running multiple scenarios under many fault tests. I recommend driving PSSe in parallel processing for that.

All your three criteria are related to machine angle. For simplicity I prefer the first.

Instability of the system is about how the remaining system performs post-fault conditions, subject to all tripping activated by the protection system. Does it reach a stable condition (in V, F) at the end of the simulation? Good and sufficient modeling is needed for this kind of assessment.

For a test event, system instabilty can be monitored by:

• angle of generators, relative to reference machine like a nuclear plant or base unit. [generic model available in PSSe] Realistic criteria for the protection relays is needed (why trip a unit when its relative angle is 100 deg and not at 120 deg.?) Tripping of a unit might not render a system unstable.

• buses voltage level leading to voltage collapse or high-voltage cascading. Add UVLS relays [generic v-monitoring model available in PSSe, also UV/OV relays] Add load dynamic model reflecting V & F dependance. Air-conditioner loads?

• undamped oscillation, is damping > 3%?. Use Prony analysis after filtering visually all plots.

• system frequency (or Pelectric - Pload), add UFLS relay and UF/OF relays.
• thermal overload cascading by tripping overloaded lines using distance relays availale available in PSSe.

CCT studies help to set the initial protection of generators for angle separation but not needed to asses assess the stability of a system. Dynamic stability studies take time, need running multiple scenarios under many fault tests. I recommend driving PSSe in parallel processing for that.