Abstracts Book - IMRC 2018

• SC2-O026
COMPOSITE MATERIALS FOR ELECTRIC STRESS GRADING ON
HIGH VOLTAGE EQUIPMENT FED BY PWM VOLTAGES
Fermin P Espino Cortes 1 , Carlos Gomez Yanez 2 , Myriam Paredes Olguin 3
1 Instituto Politecnico Nacional, IPN - SEPI-ESIME-Zacatenco, Electrical Engineering Department,
Mexico. 2 Instituto Politécnico Nacional - IPN - ESIQIE, Departamento de Metalurgia y
Materiales, Mexico. 3 Universidad Politécnica del Valle de México, División de Ingeniería en
Nanotecnología, Mexico.
In many high voltage components, the rate of the long-term degradation of their
insulation depends largely on the reliability of electric stress grading (SG) systems.
Avoiding high electric fields in insulation systems is critical in order to increase the
service life of high voltage devices, so various techniques have been adopted to
reduce or eliminate field enhancements. In general, the solutions can be divided
into shape optimization and use of coatings with stress grading materials. Modern
power systems include a considerable amount of power electronic converters
related to the introduction of renewable energy sources, High Voltage Direct
Current systems, adjustable speed drives, etc. These components introduce
repetitive pulses generated by the commutation of semiconductor switches,
resulting in overvoltages with very steep fronts and high dielectric stresses.
Although stress grading materials have performed well under normal power
frequency, their first exposure to pulse width modulated (PWM) voltage source
converters (VSC) led to early failures of these coatings. It was found that SG
materials were not capable of controlling the high stress on the surface of coil ends
of medium voltage motors and on cable terminations. Hot spots or partial
discharges in the SG coatings were observed when they worked under PWM-VSC.
Partial discharges and hot spots resulted in failure of the coating, and with time, the
complete failure of the insulation system. These problems were found only in
conductive SG coatings as they are greatly affected by high dV/dt associated with
PWM-VSC. In this presentation, it is discussed how high permittivity composites
prepared with doped and functionalized barium titanate powder can be used to
control the electric stress on the cable terminals. First, it is described how the
properties of the filler were improved and then it is shown how the prepared
polymer/ceramic composite can modify the voltage profile along a cable
termination. In the case of stress grading systems in form-wound coils, it is shown
how the use of materials with different conductive properties can be used to control
the electric stress and heat.
Keywords: Stress grading, high voltage, converter
Presenting authors email: fpespino@gmail.com