C.P. Arnold

Operational capability of generator-HVDC convertor units

The authors demonstrated the limitations of the formulation based on the concepts of commutating voltage and commutating reactance when applied to unit connected generators-HVDC convertors. In general each individual application requires extensive dynamic analysis to determine the harmonic ratings and the external characteristics of the unit connection scheme in periodical steady state. Such information is derived for a typical test case with the aid of a state variable solution. The results show, as expected, a reduction in harmonic current levels caused by the increased commutation overlaps. However, the generator harmonic voltages in the presence of rotor saliency are considerably higher. while the unit connection can be designed to provide any specified nominal power, the absence of filters limits the operation capability at larger current levels and thus reduces the ability of the HVDC link to provide temporary power increases. >

Simulation of HVDC system disturbances with reference to the magnetizing history of the convertor transformers

Following HVDC (high-voltage direct-current) system disturbances, the converter transformers may be subjected to overexcitation, DC magnetization, and in-rush effects, all of which must be accurately represented in dynamic simulation studies. A description is given of practical ways of modeling the magnetic history of the converter transformer. The authors use them to assess the relative importance of saturation and hysteresis when simulating converter recoveries from large disturbances. >