Composite Insulators with Optical Fibers for HV Applications

Insulators

Fiber optics are used for signal transmission between high voltage and ground potential. In these applications they must be protected against the environment and equipped with the necessary creepage distance to avoid risk of ageing or flashover. Protection can be achieved by integration into an insulator, which depends widely on the equipment and the purpose of the fiber optics. Often, this insulator is of composite type, consisting of a fiberglass reinforced plastic (FRP) load-bearing core, connecting end fittings and a polymeric housing material, typically silicone rubber. The core can be solid, as for suspension and tension insulators on overhead lines or for station posts but can also be hollow, such as when the insulator is used as a housing for equipment that includes bushings, cable end terminations and instrument transformers.

Fig. 1: OCT with hollow core station post and integrated optical fibers.

Four important application areas for these types of insulators now include:

1. Signal columns installed on HVDC platforms that transfer digital signals from high voltage potential to ground without carrying significant mechanical loads;

2. Optical instrument transformers (OPTs) which incorporate post insulators equipped with fiber optics to transmit sensor measurements and also supply power for active sensors;

3. Circuit breaker supports in special applications equipped with fiber optics that must carry high bending forces;

4. Gas-filled station posts of 6-12 m length equipped with fiber optics.

Insulators equipped with fiber optics combine two totally different engineering disciplines in the areas of high voltage and information technology. This is reflected in the field of standardization, where a gap exists in the mutually influencing requirements and characteristics of the fiber optics and the HV insulators.

Up until recently, composite insulators with integrated optical fibers have typically been developed on an individual basis. While still regarded as niche products, experience in certain applications already covers decades. Now, with growing demand, fiber optics has been identified as a key component in these applications and IEC has reacted by setting up a project team (PT 63264) to create a technical specification that outlines minimum qualification requirements. Testing would have to reflect that these requirements are being fulfilled. For example, the combination of HV insulator and fiber optics influences existing test procedures for insulators, possibly requiring entirely new tests to assess performance of the fiber optics in the insulator.

Attend the 2022 INMR WORLD CONGRESS in Berlin where Technical Specialist, Volker Bergmann from Reinhausen Power Composites in Germany will provide examples of design solutions for different applications involving fiber optics and composite hollow core insulators. He will also review the results from testing such products.