Transmission Products (T-1201)

Corona Protection of Quadri*Sil® Transmission Insulators A Better Design. A Better Insulator. Quadri*Sil insulators are designed to be RIV and corona free through 161 kV. The term “corona free” is a reference to visible corona. The use of an external corona shielding ring is required at voltages above 161 kV to ensure there is no visible corona. Research by the Electric Power Research Institute (EPRI) on the effects of wet and dry corona; have led to the recommendation of applying corona rings at lower transmission voltages. Depending upon the magnitude of the electric field on the surface of the polymer material, it is possible for water droplets to go into corona as their shape distorts and spreads on the surface of the polymer material. EPRI is recommending that corona rings be applied to an insulator if the electric field magnitude on the surface of the polymer material exceeds 420 V/mm over a 10 mm section. This implies if the electric field magnitude drops below 420 V/mm over a 10 mm section, there is not enough energy in the electric field to put the water droplet into corona. Based on this recommendation, it requires the installation of corona rings on the “conductor side” of the insulator at voltages as low as 138 kV. In some configurations, it may require the application of corona rings at voltages as low as 115 kV in order to ensure the magnitude of the electric field is below the 420 V/mm threshold as referenced above. If your goal is to comply with the EPRI recommendation, the best way to ensure you do this for a particular application is via analysis of the E-field. This can be done with 3D modeling software and provides the transmission engineer with the necessary data. It is important to note, all polymer insulator designs are different and the size of the integral corona ring on the end-fitting plays an important role in protecting the polymer material at lower transmission voltages. The Quadri*Sil insulator was designed with one of the largest integral corona rings (on the end fitting) used in the industry. The following table was developed as a general rule to comply with the EPRI recommendation. It should be noted that the E-field magnitudes can vary by configuration and structure design and should be verified by reviewing the E-field model of the complete assembly.

QUADRI*SIL® INSULATORS

Corona Ring Diameter

Ground End Inches (mm)

Line End Inches (mm)

Line Voltage

138 kV 161 kV 230 kV 345 kV 400 kV 500 kV

None None None None

8 (203) 8 (203) 8 (203) 12 (305) 12 (305) 15 (381)

8 (203) 8 (203)

If you need assistance with any applications regarding Quadri*Sil polymer transmission insulators, please contact your local Hubbell Power Systems representative.

Page 400 | July 2016