This paper deals with the most recent improvements in the process technology and equipment for manufacturing HCIs. During the last few years the market for HCIs has grown considerably. It is therefore more essential to have optimized manufacturing systems.

The improvements have been driven predominantly by the manufactures of HCIs. However, equipment manufacturers have also made a great deal of effort to increase productivity. As a result of these improvements, a combined manufacturing system has been introduced.

This system is based on Advanced Vulcanization Technology (AVT), which was introduced last year, and reduces the cycle time by more than 30%.

 

1.1. Roots

The first steps to manufacture HCIs were taken some decades back. The first were manufactured with low viscosity silicone (RTV-2) by Brown Boveri AG in Switzerland.

Even today, HCIs are manufactured by the successor company – now one of the leading companies in the field of HCI – on the clamping machines originally supplied by Vogel. Building on these first steps, silicone technology was developed further. A milestone in the productivity of the manufacturing process was laid with the invention of the 1:1 LSR low viscosity system.

1.2. Technologies

In the early days of HCI manufacturing technology, many different types of methods were developed. The different types were invented because engineers had many different ideas on designing the electrical insulating apparatus. At that stage it was more important to be able to manufacture all types of insulators derived from the porcelain types already used than to focus on productivity.

1.3. Future

In the future we will see a concentration of manufacturing methods; because of the costs generated during the manufacturing process, no more than two methods will survive for high volume manufacturing. It is therefore important for machine and material suppliers to have the best products ready for the manufacture of HCIs. Nevertheless, I would like to stress the importance of manufacturing HCIs according to the relevant standards, and focusing on the importance of the overall process and the quality of all the parts used for an HCI rather than just concentrating on the silicone to be used and its cost and specification. All apparatus manufacturers should be focusing on designing and delivering a product that encourages utilities to make increased use of HCIs.

This paper deals with the most popular method of low pressure mould filling of LSR silicones for the manufacture of high voltage hollow core insulators (HCIs). This is the preferred method for new projects under consideration worldwide. This method uses dosing and mixing equipment to process the silicone for injection into the mould, which is mounted into the clamping machine.

While all the other methods are also well accepted for manufacturing HCIs, with increasing demand for composite insulators the main focus is on productivity. Equipment manufacturers are more and more willing to adapt to the diameters offered by the different suppliers. Many of the diameters of mold systems were fixed more than 10 or 15 years ago.

The major components in the LSR production process are the clamping machine, the mold system and the dosing equipment. The layout and the complexity of these components vary from client to client.

3.1. Dosing & Metering Equipment

The dosing and metering equipment is responsible for the proper processing of the silicone. For different purposes, different sizes and set-ups are available. The picture below shows an installation with two barrels per component. This set-up allows a continuous production process. The changeover from one barrel to the other is done automatically. This saves process time and materials; all barrels can be used until they are empty.

3.2. Clamping Machines

These days clamping machines are tailor-made to the needs of the different HCI manufacturers. Nevertheless, clustering seems possible. There are two main classes of HCI to be manufactured, and governs the size of the clamping machine: - 170 kV HCIs are manufactured in one shot

- 230 kV HCIs are manufactured in one shot

All other voltage classes are manufactured in a two-shot process. The dimensions and necessary pressures are adapted to these requirements. Nowadays clamping machines have integrated systems to fix the mould system into the clamping machine, as well as a crane system to handle the prepared tube and the flange and readymolded HCI. In addition to these handling systems, for optimal process timing flange heating systems are also used to ensure perfect curing of the silicone close to the aluminum flanges.

3.3. Mould Systems

Many variations on the design of the moulds have also been developed in the last few years in response to the specific requirements of the different apparatus manufacturers. The block design method was developed to facilitate the set-up of a mould for individual moulding. With this setup up to four large and small sheds are in one block, which saves a lot of preparation time. These days it is even possible to produce undercut designs. The individual blocks are available in the 4:2:1 set-up; all necessary lengths are possible to arrange. Another part of the mould system is the demolding device for the HCI. This special device makes it easy to handle the insulator after the curing process. The picture above shows a molud system for manufacturing a 230 kV HCI. For easy operation, automatic, hydraulically driven silicone injection nozzles are used.

3.4. Heating Systems

Nowadays two different heating systems are primarily used. One is the water heating system. This allows the shortest process times, but is very costly. For this reason, up to a certain size electrical heating systems are used.

In recent years, all major manufactures have been more and more focused on the cycle times of the whole manufacturing process. Price pressure from apparatus manufacturers and competition from the porcelain side has started a competition between the HCI manufacturers to reduce cycle times for LSR processing in the clamping machine. As a member of the Hedrich group of companies, Vogel has the great advantage of having access to the patent which was originally developed for epoxy processing, called Ultra Fast Curing (UFC). This patent has been modified to the needs of LSR processing. At the beginning of the trials the method was only used to manufacture large volume cable joints using 50 liters of silicone or more. The results have been more than promising. In the subsequent trials, this method was also tested during the manufacturing process for 170 kV HCIs. Here the volume to be filled with silicone is in the range of 10 to 12 liters, depending on the shed design. All the results have shown a reduction in cycle time of more than 30%. Contrary to initial beliefs, this method also works perfectly for manufacturing direct molded surge arresters, even with dosing and mixing equipment from other suppliers. The test results have shown a reduction of up to 40% in the total cycle time. Under these conditions, the payback time for the additional equipment is less than one year.

4.1. Advanced Vulcanization

Technology (AVT) This method was derived from the UFC method. The silicone is heated up in a heat exchanger after both LSR components have passed through the static mixer of the dosing and metering equipment. The silicone used is a specially adapted type of Powersil from Wacker. The silicone is heated to approx. 70°C, as shown in the following diagram: The AVT equipment itself comes with all the necessary control equipment. The box has to be placed closed to the mould to be filled with preheated silicone. In recent months, intensive customer tests have been carried out, with outstanding results. The system yields the best results in terms of productivity if existing systems are running at their limits. Even though AVT is an autonomous working device, it can be integrated in the overall control system of the LSR process. The following diagram shows the working principle: With a given mould temperature, a high injected silicone temperature gives the best results in terms of reducing the cycle time for the moulding process. The invention of AVT has resulted directly in a complete integrated manufacturing system comprising all existing and new inventions.

4.2. Integrated Manufacturing

System (IMS) The new IMS is designed to manufacture a large number of 170 kV HCIs at the lowest possible LSR molding process costs. The equipment is designed to manufacture thousands of insulators a year, depending on the mould system and the silicone used. In the last few years, the major customers of Vogel equipment have used Powersil 630 XLR in their process for manufacturing HCIs. Using the expertise of two leading suppliers of manufacturing equipment and silicone, the invention of the IMS was the logical step into the future. The IMS is mounted on one base frame comprising all the elements forming a production system:

- dosing & metering

- clamping

- mould system (electrical)

- handling system

- controls

- AVT, when needed

To reduce investment costs it is essential to ensure that starting from the initial design, and on the basis of the task the equipment is designed to perform, all the functional groups together give the best performance characteristics. The IMS is designed to be completely tested during manufacturing. The majority of HCIs are manufactured in the voltage class 170 kV and below. It is therefore more than logical to start with a system serving this production range, in other words HCI tubes with an OD below 300 mm.

4.3. IMS for 170kV HCI Manufacturing

Below a 3D CAD drawing of a 170 kV is shown, also using an AVT system for maximum productivity. Complete testing will be done in the factory, followed by transport in a 20- foot container for easy installation and commissioning. The system shown above is a standardized system combining all the advantages of the LSR manufacturing system for HCIs with low investment costs.

In the future we will see a growing market for HCI manufacturing systems. More and more manufacturers want to backward or fully integrate their production facilities. On this basis, integrated, easy to handle systems have good prospects of success.

For many years the development of manufacturing equipment was focused on tailor-made equipment adapted to the specific needs of clients. With increased demand for composite insulators and the necessity of optimized process systems, as described above IMSs will have a future in the industry.

 

From: insternet