Initialization of Excitation Limiters

The activation logic is first evaluated based on the initial network conditions.

Some models do not have an explicitly defined activation logic, but calculate an error signal that feeds into an Integral or Proportional‑Integral or Proportional‑Integral‑Derivative block.

For an error that is used to determine the UEL/SCL_UEL signal, the error is normally negative when the signal is not limiting.
i.e., if error > 0 then activation logic = True, else activation logic = False.

For an error that is used to determine the OEL/SCL_OEL signal, the error is normally positive when the signal is not limiting.
i.e., if error < 0 then activation logic = True, else activation logic = False.

• If activation logic = False, then the UEL/OEL/SCL_UEL/SCL_OEL signal is considered idle.
  i.e., Activation Status = 0, or UEL Activation Status = 0, or OEL Activation Status = 0

  States are initialized such that the signal UEL/SCL_UEL = V_UEL-MIN and/or the signal OEL/SCL_OEL = V_UEL-MAX.

• If activation logic = True, then the UEL/OEL/SCL_UEL/SCL_OEL signal is considered saturated.
  i.e., Activation Status = 2, or UEL Activation Status = 2, or OEL Activation Status = 2

  States are initialized such that the signal UEL/SCL_UEL = V_UEL-MAX and/or the signal OEL/SCL_OEL = V_UEL-MIN.

• States are typically not initialized such that (V_UEL-MIN < UEL/SCL_UEL < V_UEL-MAX) and/or (V_UEL-MIN < OEL/SCL_OEL < V_UEL-MAX).
  i.e., Activation Status ≠ 1, or UEL Activation Status ≠ 1, or OEL Activation Status ≠ 1

If the "Modify Limits and Run" option is chosen in Transient Stability options, then certain limits might be modfied during the initialization stage. This would occur before the initial UEL/OEL/SCL states values are assigned, hence the above-mentioned method of initialization remains the same.