Investigations of modified nonlinear electrical materials for end corona protection in large rotating machines

Characterization of the voltage and electric field stresses in multi-cell solid-state transformers

“…A semiconducting tape features a low, but non-zero conductivity. Here, a linear tape is used (conductivity does not depend on the electric field) but similar effects could also be achieved with nonlinear tape [26]. The electrical parameters (permittivity and conductivity) are also assumed not to be frequency dependent.…”

“…With all these results, it is possible to make a recommendation for the choice of the conductivity of the tape, given that it is possible to control the electrical properties of the tape with the production process [26], [28]. The conductivity has to be chosen together with the thickness of the tape since increasing the conductivity has the same effect as increasing the thickness.…”

Nonlinear Electrical Conduction in Polymer Composites for Field Grading in High-Voltage Applications: A Review

“…The air near the end-turn insulation breaks down, leading to surface corona discharges. Not only corona discharges but also internal discharges can directly accelerate the deterioration of polymers due to highly localized electrical stress concentrations and ultimately, lead to the failure of the insulation material [ 28 , 29 ].…”

“…Evaluating system performance by simulating the electric field and potential distributions in the overhang region showed that a highly conductive stress-grading tape reduces the maximum electric field at this region [ 40 ]. Usually, the main insulation is provided with outer corona protection applied by multilayer semiconducting paints or wrapping tapes [ 28 ]. Carbon-based semiconductive tapes and SiC-based nonlinear grading tapes have been widely used to control the field where the stator bar exits from the slot in form-wound large rotating machines [ 41 ].…”

“…For example, in HV motor windings, it is possible to find nonlinear resistance tapes as stress grading materials [ 21 ]. Materials with nonlinear dielectric behaviors are applied to rotating electrical machines for the control of the electrical field strength in the insulation system of stator end windings [ 28 ]. Nonlinear conductive materials enable the grading of electric-field distributions in polymeric outdoor insulators, particularly near the high-voltage and ground terminals [ 125 ].…”