Grids That Communicate - Wacker Chemie AG

Grids That Communicate

At the applications laboratory in Burghausen, the quality of POWERSIL® Gel C 670 is checked before each batch is dispatched. The gel can be poured readily and penetrates into even the smallest of cavities. This helps avoid air bubbles and increases the dielectric strength. Furthermore, in its cured state, the gel adheres very well and can be stretched freely.

Protecting Sensitive Measurement Heads

Like everything else in high-voltage technology, the equipment used in the metrological monitoring of the grid depends on reliable electrical insulation. All of the equipment’s live parts – usually the entire measurement head – must be insulated from the ground and grounded equipment and are often positioned on a hollow-core insulator. “Where measuring instruments are operated outdoors, which is the case in many high-voltage substations, operators are increasingly relying on silicone composite hollow-core insulators,” says Dr. Armin Merten, head of development at Reinhausen Power Composites GmbH (RPC). This Bavarian company, headquartered in Regensburg, is one of the world’s leading manufacturers of silicone composite hollow-core insulators.

New-generation measurement heads deliver an optical signal; many measurement heads also require light in order to create information. Fiber-optic cables transport the light. They connect the measurement head to the connection point of the communication system. Up to now, the fiber-optic cables have been guided via a so-called insulator string – rod insulators joined together in a chain-like manner. The insulator string is an additional component alongside the post insulator that carries the measurement head. “The sensitive fiber-optic cables cannot simply be suspended freely, but must be mechanically supported to protect them against damage or breaking,” explains Merten. “At the same time, the support must not create an electrically conductive path to the ground or the grounded junction box. That’s why the fiber-optic cables are guided with the aid of an insulator string.”

Hollow core insulators

A hollow-core insulator is rather like an empty, electrically insulating pipe, around the outside of which are arranged annular, umbrella-like sheds. Hollow-core insulators particularly find use as exterior insulation for various kinds of electrotechnical equipment such as bushings, instrument transformers, circuit breakers and over-voltage protection devices. Hollow-core insulators have traditionally been made from a dark-brown or gray hard porcelain. Composite hollow-core insulators, on the other hand, consist of a glass-fiber-reinforced plastic (GRP) pipe, fitted with flanges at both ends, that carries sheds made of an elastic polymer. The material of choice for the sheds is a silicone elastomer. The GRP pipe provides the composite hollow-core insulator with the requisite mechanical strength and impermeability. The silicone sheds reliably confer electrical insulation. The flanges are used for assembling the insulator on location. Composite hollow-core insulators for high-voltage technology can assume large dimensions. As a rule of thumb, the length is around 1 meter per 100,000 volts.

However, this kind of insulator string represents additional costs for electricity grid operators, which they want to avoid, if possible. “A few years ago, a customer asked us whether it would be possible to guide the fiber-optic cables through the interior of the post insulator and so do without the insulator string,” remembers Merten. This question inspired RPC to develop a composite hollow-core insulator in which the fiber-optic cables are already integrated and guided safely. This kind of composite hollow-core insulator can act as a post insulator for a measurement head or sensor that no longer requires the additional insulator string.

Integrated Fiber-Optic Cables

This type of composite hollow-core insulator contains several ready-to-connect, plastic-coated fiber-optic cables. Slightly curved, they are guided through the glass-fiber-reinforced plastic (GRP) pipe – which is closed with metal lids and makes up the basic structure of the hollow-core insulator – and protrude from the insulator on both sides. The cavity of the GRP pipe is completely filled with a compressible silicone gel, so that the fiber-optic cables are embedded in the gel.

“The cavity must be filled with a highly insulating medium – air is insufficient in high-voltage applications, as its dielectric strength is too low,” explains Merten. The dielectric strength defines the maximum voltage at which no arc develops that could pass through the entire insulation medium.