Meet HydroFlex PhD Candidates:

Reza Sargazi (NTNU)

Reza Sargazi is a PhD candidate at the Norwegian University of Science and Technology (NTNU) at the Department of Electric Power Engineering (IEL). Reza has been working on monitoring and diagnostic of rotating machines with focus on Hydraulic Generators.

His main interests are high voltage insulation, partial discharge detection and finite element method (FEM) for simulation of rotating machines.

In the HydroFlex project, Reza Sargazi conducts research in Task 4.4 under WP4.

PhD Project: The Effect of Static Converters on Electric Field Grading Insulation Layer in Rotating Machines

In order to obtain the highest efficiency of hydropower plants, an implementation of static converters for variable speed in motor mode is necessary. Recently, with the introduction of transformerless converters and their usage in hydro-power generator systems, the voltage and electric field distribution of the insulation systems has drastically changed. In terms of form-wound stator windings, there are five major insulation systems, including turn insulation, mainwall insulation, phase to phase insulation, semiconductive coating (slot discharge protection) and stress grading (silicon carbide) layer. Clearly, the key elements in connection of convertors to rotating machines are: 

  • Impulse rise time

  • Fundamental frequency of converter and its repetition rate

  • Peak to peak voltage imposed on machine terminal with respect to pulse overshoot voltage and the length of connected cables.

The aim of this PhD project is the investigation of silicon carbide microvaristors performance under fast repetitive impulses due to static converters. Silicon carbide microvaristors are the most common type of stress grading materials which are being used in the design of coils and bars. The major challenges are as follows:

  • Determination of microvaristors response in wide range of electric field, frequency and temperature

  • Behavior of stator winding and its internal voltage distribution during such fast repetitive impulses.