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Surge Arrester silicone-housed PEXLIM

A flexible silicone-housed arrester family for line discharge class 2 to 5 and system voltage up to 550 kV

PEXLIM is a family of silicone-housed arresters of Hitachi ABB Power Grids that offer unique advantages by design to offer secure protection against overvoltages. With the silicone directly molded onto the internal components, the design is safe, secure and effective. They permit flexibility in installation and offer great value for money.

PEXLIM arresters are type tested according to IEC 60099-4 and ANSI/IEEE C62.11. Also, complying with customer-specific standards. Applicable to UHV (Ultra High Voltage) applications.
 

Applications

  • Protection of substation equipment 
  • Polluted areas 
  • Compact and angular installation
  • Seismic areas
  • Transformers and reactors
  • Capacitor banks
  • HVDC protection
  • Cables

Why Hitachi ABB Power Grids?

  • Minimum maintenance cost
  • Customizable mechanical and electrical design
  • Easy to install

Brief performance data

    R-Y  Q-Y P-Z  P-Y 
System voltage  kV  24 - 170 52 - 420 52 - 420  300 - 550 
Rated voltage kV 18 - 144  42 - 396  42 - 396 228 - 444 
Nominal discharge current kApeak 10  10  20  20
Arrester classification IEC 60099-4, Ed.3.0  Station; SL  Station; SM   Station; SH Station; SH 
Arrester classification IEEE Std. C62.11-2012 Station  Station  Station  Station 
Line discharge class Class 2 3 4 4
Mechanical strength (SSL)  Nm 1600 4000 6000 9000

Get to know more

The "open-cage" design adopted by us have one of the highest mechanical strengths of the molded polymer arresters in the market. In the design Hitachi ABB Power Grids has chosen silicone polymer which is highly hydrophobic and resistant to UV radiation. 

Each arrester is built up of one or more units. Each unit is a polymeric housing containing a single column of ZnO disks, all individually extensively routine-tested during manufacture, dispersed with the necessary spacers as determined by the electrical design for the arrester. 

Long arresters often require (and are supplied with) external grading rings to maintain a uniform and acceptable voltage stress along their length.

Silicone rubber is highly hydrophobic and resistant to UV radiation and has been shown to be the best insulation (compared to both porcelain and other polymers) based on worldwide independent laboratory and field tests. Hitachi ABB Power Grids uses special fillers to enhance these properties as well as giving it high pollution resistance, tracking resistance and fire-extinguishing features. 

For satisfactory performance, it is important that the arrester units are hermetically sealed. The HTV molding process under vacuum ensures this by efficient bonding between silicone and all internal parts along the entire length. Hence gaskets or sealing rings are not required.

When the arrester is stressed in excess of its design capability the arrester is short-circuited and an internal arc is established. Thanks to the open cage design, the arc burns through the soft silicone material, thereby permitting the resultant gases to escape quickly and directly. At the same time, the aramide fibers keeps all internal parts together and prevent the expulsion of the internal components. Hence, special pressure-relief vents are not required for the PEXLIM design.

The color of the silicon is grey. Seaworthy packing of the arresters is standard.

Safety belt-winding for maximum security

In order to protect other power equipment from dangerous overvoltages, the arresters themselves are employed in the most exposed locations. Hence, under extreme adverse conditions they may be overstressed. 

Surge arrester housings have traditionally been made of porcelain. However, today there is a strong trend, and often even a preference, towards the use of silicone insulators for arresters at all system voltages. There are a number of reasons why silicone is seen as an attractive alternative to porcelain, including potentially better short-circuit capability with increased safety for other equipment and personnel if correctly designed. 
It is false, however, to believe that safer short-circuit performance is automatically achieved simply by replacing the porcelain housing with one made of polymer. In the past, there has been the incorrect belief that all polymer-housed arresters, irrespective of design, were capable of carrying enormous short-circuit currents. This is not the case, and the design must be scrutinized carefully for each specific type. Please read the enclosed article (links section, right hand side) where you will see how Hitachi ABB Power Grids' patented safety belt winding results in an excellent short-circuit performance.

The most important component for the surge arresters is the ZnO blocks, the varistors. Stacked in the center of the surge arrester, the varistor is the heart of the surge arrester. The varistor consist of a mix of zink oxide and other metallic powders that are blended and pressed into cylindrical blocks. 

Hitachi ABB Power Grids manufactures ZnO varistors with full control of the process from the raw material to the finished electrically characterized varistors. A high degree of automation and a large number of quality tests at all stages, from raw material to ZnO blocks, approved for arrester manufacture, ensure that they fulfil their stated data.

Type tests has been performed for every size of ZnO varistor. Each varistor is verified by rigorous testing – over and above both IEC & ANSI standard requirements:

Tests on ZnO blocks

Energy withstand test on all blocks - The blocks pass three energy test cycles with cooling in-between. In each cycle, the injected energy is far in excess of the single impulse energy capability. Blocks with insufficient energy capability are automatically rejected.

Classification of all blocks

The blocks are classified at 1 mA (d.c.) and 10 kA (8/20 μs) and the residual voltages are printed on each block together with a batch identification. Finally all blocks are visually inspected. 

Accelerated life tests on samples

Power losses after 1 000 hours calculated from a test with shorter duration (approximately 300 hours) at an elevated temperature of 115 °C at 1.05 times Uc shall not exceed the losses at start of the test. Batches in which unapproved blocks appear are rejected.

Impulse current tests on samples

Blocks are subjected to high current impulses (4/10 μs) and long duration current impulses (2 500 μs) of amplitudes verifying catalogue data.

Read more about the testing of ZnO blocks here (link to pdf-file)

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