Compatibility between Excitation Limiter models and Exciter models

PowerWorld Simulator has compatibility checks in place to prevent inappropriate UEL/OEL/SCL-exciter combinations. For example, excitation limiter OEL4C is not compatible with exciter ESST1A, because ESST1A only accepts a takeover gate OEL input signal but OEL4C can only provide a summation point OEL output signal.

The remainder of this topic lists the output and input related fields associated with limiter and exciter models. This helps in keeping track of whether models are compatible, which then allows for auto-correction and modification of limits to prevent initial limit violations. Ultimately, this ensures proper initialization of UELs, OELs and SCLs.

Exciter Models

Excitation Limiter Input Signal Type(s)

Depending on the specific type and instance of an exciter model, it might accept an UEL/OEL/SCL input signal at different locations. Exciter models have three fields that specify the input signal types that could be accepted from an UEL, an OEL and a SCL:
UEL Input Type(s) (UELInputTypes)
OEL Input Type(s) (OELInputTypes)
SCL Input Types(s) (SCLInputTypes)

Possible values for these fields are:

  1. [No Input] – The exciter type does not have an input for a limiter model.
    Many of the older exciter models do not have a SCL input, and a handful of the older exciter models do not have a UEL/OEL input.
    Renewable exciter models that actually represent power electronic controls are not compatible, and hence do not have a UEL/OEL/SCL input.

  2. [Summation Point] – The exciter type only has a summation point input for a limiter model.
    Many of the older exciter models only have a summation point UEL/OEL input.

  3. [Takeover Gate] – The exciter type only has a takeover gate input for a limiter model.
    Some IEEE Revision B exciter models only have a takeover gate UEL/OEL input.

  4. [Summation Point, Takeover Gate] – The exciter type can be configured to accept an UEL/OEL/SCL signal at its summation point input, or its takeover gate input, or not use the signal.
    All IEEE revision C and some revision A/B exciter models have configurable UEL/OEL/SCL input.

Excitation Limiter Input Signal Used

There are three additional fields at exciter models that specify the actual input signal used for an UEL, an OEL and a SCL:
UEL Input Used (UELInputUsed)
OEL Input Used (OELInputUsed)
SCL Input Used (SCLInputUsed)
If an exciter can be configured to accept either a summation point signal or a takeover gate signal from a limiter model, then these fields will reflect the current configuration of a specific exciter instance. Otherwise, these fields will show the same value as the single choice from the corresponding UEL/OEL/SCL Input Type(s) fields.

Possible values for these fields are:

  1. Summation Point – The exciter will use a summation point input signal.

  2. Takeover Gate – The exciter will use a takeover gate input signal.

  3. No Input – The exciter type does not have any input location for a UEL/OEL/SCL input signal.

  4. Not Used – The specific exciter instance is configured to ignore a UEL/OEL/SCL input signal.

Excitation Limiter Models

Output Signal Type(s)

Depending on the specific type and instance of an excitation limiter model, it might produce a summation point signal or a takeover gate signal. Excitation limiter models have one field that specifies the output signal type that could be produced by an UEL, or an OEL, or an SCL:
Output Type(s) (OutputTypes)

Possible values for this field are:

  1. [Summation Point] – The excitation limiter type only has a summation point output for an exciter model.

  2. [Takeover Gate] – The excitation limiter type only has a takeover gate output for an exciter model.

  3. [Summation Point, Takeover Gate] – The excitation limiter type can be configured to produce a summation point output signal, or a takeover gate output signal.

Output Signal Used

There is one additional field at excitation limiter models that specifies the actual output signal by the exciter:
Output Used (OutputUsed)
This field will take into consideration the expected input at the active exciter, and check its compatibility with the choices in the Output Type(s) field. If an excitation limiter can be configured to produce either a summation point or a takeover gate signal, then this field will check if the current configuration of a specific limiter instance is compatible with the exciter.

Possible values for this field are:

  1. Summation Point – The summation point output signal will be used by the exciter.

  2. Takeover Gate – The takeover gate output signal will be used by the exciter.

  3. No Input – The output signal will not be used, because the exciter type does not have any input location.

  4. Not Used – The output signal will not be used, because the specific exciter instance is configured to ignore an input signal.

  5. Not Suitable – The output signal is for a summation point, but the exciter has a takeover gate, or vice versa.
    Either the type of limiter or the type of exciter will need to be changed.

  6. Not Configured – The output signal is for a summation point, but the exciter is configured to accept an input at a takeover gate, or vice versa.
    Either the exciter configuration can be changed to match the limiter that is present, or the type of limiter can be changed to match the exciter configuration.

  7. No Exciter – The output signal will not be, because the exciter model instance is absent.

Cases i and ii would indicate that the limiter model is compatible with its exciter model.
Cases iii ‑ vii would be shown in red in case information displays.
Cases iii, iv and vii would be shown as a validation warning.
Cases v and vi would be shown as a validation error, and auto-correction will make the limiter model not active.