Tips & News - Spring 2018

Table 2. Insulating technologies for condenser type bushings

CONDENSER TYPE

INTERNAL INSULATION

EXTERNAL INSULATION

Oil Impregnated Paper

Oil & Paper

25kV - 500kV

Resin-Impregnated Paper

Epoxy & Paper

Porcelain or Composite (Silicone)

Solid Cast Epoxy

Epoxy

Epoxy or Silicone

Apart from usual selection criteria, overloading conditions, environment, seismic requirements, angle of installation, etc. play a determining role in selecting the bushing

Not all bushings are equal The most common types of bushing used on power transformers are capacitance graded bushings such as the PCORE Electric and Electro Composites PRC®, POC® and SDC™ technologies. Bulk type or solid type bushings can also be used in instances. A bulk type or solid type bushing is the most basic type of bushing manufactured and is defined by the IEEEE C57.19.00 as: “A non-capacitance graded bushing in which the major insulation is provided by a ceramic or analogous material placed around the energized conductor”. This type of bushing is usually limited to 34.5 kV. Due to no capacitance grading, partial discharge can be an issue with these designs. To withstand higher voltages, the bushing must be physically larger which then causes a challenge in meeting the maximum diameters specified in the IEEE standard. When considerations are being made for high voltage bushings, a capacitance graded bushing is the current industry’s preferred bushing design. Capacitance graded bushings are defined by the IEEE as “A bushing in which metallic or nonmetallic conducting layers are

arranged within the insulating material for the purpose of controlling the distribution of the electric field of the bushing, both axially and radially”. There are now many different types of insulating materials used to make capacitance graded bushings available on the market. How may we serve you? PCORE Electric and Electro Composites are one of the leaders when it comes to not only providing a diverse, high quality, evolving bushing offering but also has the ability to offer the technical support to its customers to help select the correct product for the application. It is this ability that PCORE Electric and Electro Composites’ customers have come to expect. Please visit Hubbell’s new website: www. hubbell.com/hubbellpowersystems/en for more information on bushing products and the wide range of other distribution, transmission and substation products offered by Hubbell Power Systems. Contact: PCORE Electric - Electro Composites

Figure 3. 25 kV SDC™ GSU bushing

Product Support Team bushings@hubbell.com

®

PCORE Electric Company, Inc. 135 Gilbert Street, LeRoy, New York 14482 USA T 585-768-1200 / F 585-768-1212 ISO 9001:2008 Certified

Electro Composites (2008) ULC 325 Scott Street, St-Jerome, QC J7Z 1H3 Canada T 450-431-2777 / F 450-431-2717 ISO 9001:2008 Certified

Figure 4. 25 kV PRC® oil-free bushing

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