Adapted from CIM data models. The class represents IEEE Std 421.5-2005 type ST5B model. The Type ST5B excitation system is a variation of the Type ST1A model, with alternative overexcitation and underexcitation inputs and additional limits. Reference: IEEE Standard 421.5-2005 Section 7.5. Note: the block diagram in the IEEE 421.5 standard has input signal Vc and does not indicate the summation point with Vref. The implementation of the ExcIEEEST5B shall consider summation point with Vref.