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Windspeed Ltd (Vector Instruments), 115 Marsh Road, RHYL, N. Wales, LL18 2AB, United Kingdom.
Windspeed Limited (trading as Vector Instruments)
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 Sunday, April 30 2017  Home   Products   Special/Options   Surge Protection Search site:  

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(Rhyl, N.Wales, UK)
Wind Speed:  7.3 mph
Wind Direction:  188 °
Air Temp.:  10.4 °C
Rel. Humidity:  69.4 %
Rain (last Hr):  0.0 mm
(updated at: 01:18 UK time)

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    *** Celebrating more than 40 years manufacturing & servicing High Quality Vector Instruments Anemometers and Windvanes at Windspeed Ltd ***
    Surge Protection for Anemometers and Windvanes
     
    Our A100M, A100K and A100S anemometers include "anti-surge" protection as standard and the A100L2, A100LK, A100LM, A100 and A100H anemometers, and W200P windvanes (excluding W200P/L), can have it fitted as an option (/PC3 suffix).

    The A100R anemometer has no sensitive internal electronics so this option is not available for it.

    This "anti-surge" protection is intended to protect the electronics in the instrument against any surge voltages/currents induced in the instrument cable by a nearby lightning strike (e.g. a strike where the main energy is routed away down a lightning conductor). The /PC3 option is not designed to protect any equipment connected to the instrument (such as a datalogger: additional protection may need to be fitted at the equipment/datalogger end of the cable, or inside the datalogger).

    Note that it is virtually impossible to protect an anemometer or windvane against a direct lightning strike - there is simply too much energy in the strike.

    LIGHTNING PROTECTION GUIDELINES FOR ANEMOMETERS AND WINDVANES:

    Please note that: We do not supply lightning protection equipment (other than anti-surge accessories for some instruments/equipments as mentioned above) however some notes/guidelines are provided below for your information...

    GENERAL
    In order to obtain the best conditions for measurement of windspeed and direction, it is necessary to site anemometers and windvanes in positions suitably exposed to the elements usually on a mast or pole of some kind which may be free standing, guyed, fitted to the roof or side of a building etc.
    These sites by their nature are also susceptible to lightning damage. As 50% of lightning strikes involve currents of more than 28000 amps it is obvious that a strike (or flashover from an adjacent structure) directly onto an anemometer or windvane will cause physical damage to the instrument as well as destroying any electronics within.
    Cups can be blown off rotors, pieces melted out of fins, moving parts welded together etc. Instruments damaged in this way are usually irreparable with few parts being recoverable necessitating a replacement instrument.
    Damage can be reduced by using a lightning rod, heavy duty copper tape and earth rods to divert the main portion of any strike away from the instruments.
    Surges will still be induced in the instrument cabling, however electrical anti-surge protection measures can be fitted to restrict surges to prevent damage to the electronics within the instrument and any control, display, signal-conditioning at the other end of the cabling. It should be noted that due to the amount of energy involved in lightning strikes, it is impossible to devise an economic system which will guarantee total immunity, protection measures can only attempt to restrict the damage by trying to divert most of the energy in the strike to earth by-passing sensitive instruments and electronics.

    PROTECTION
    Protection is discussed in detail in British Standard BS6651:1990 "Protection of structures against lightning" (and subsequent revisions), which also gives advice on estimating the risk of strikes to various structures in various parts of the world. As discussed above, the key elements to lightning protection are:
    • 1) divert the strike to a good low-resistance earth
      - BS6651 advises that the earth must be close to the structure and have a resistance of less than 10 Ohms. Earths of 1 Ohm or better are recommended by many suppliers of surge-protection equipment.
      If instruments are being sited on (or near to) a building with existing lightning protection measures, it may be possible to bond to the existing earth.
      Note that the "mains earth" is not (normally) sufficient for lightning protection, although a bond may be required between it and a 'lightning protection' earth - refer to BS6651 for advice.
      If a suitable earth is not available, one can be achieved using several galvanised steel rods (16mm dia by at least 1.5metres long) driven vertically into the ground, the number depending upon the local conditions. BS6651 also suggests the use of a closed-loop at least 20m dia & 0.6m below the surface, or radial conductors totalling at least 20m buried 0.6m below the surface, the reinforcing in concrete foundations may be used in some circumstances. A disconnection box is usually fitted for periodic checking of the earth resistance.
    • 2) use a lightning rod to attract any strikes away from the instruments
      - BS6651 specifies a pointed vertical rod of galvanised steel having a diameter of >8mm. The area protected by such a rod is in the form of a cone with it's tip at the tip of the rod and it's base on the ground, the angle between the sloping side of the protective cone and the vertical being typically around 45? provided that the height of the rod is less than 20m above the ground (standard height for wind measurement is 10m, structures above 20m are also prone to strikes from the side as well as above, complicating the protection needed). The anemometer and windvane must be sited within this protective cone, the logical place for the rod, when a pair of instruments are used, is centrally between them.
      Unfortunately, the presence of a vertical rod causes turbulence in the airflow which can cause additional errors in the readings obtained from an anemometer or windvane. It is therefore necessary to come to a compromise to maximise protection and minimise errors. Increasing the spacing between the instruments and the central vertical lighting rod will reduce turbulence effects (longer than standard cross-arms for pairs of instruments and long side-arms for single instruments are available), however it will be necessary to increase the height if the rod to keep the instruments within the protected area.
      Note that the rod will often have to be thicker than the suggested 8mm minimum simply for strength and to prevent it swaying about excessively, 16mm is typical. It is also possible to use one or more lightning rods on adjacent masts provided that the mast with the instruments is short enough and near enough to fall within the protected area provided by them.
    • 3) low resistance cabling between the rod and earth
      - Connection is often made using flat copper tape typically 25mm x 3mm cross-section (75mm?) due to the simplicity with which this tape can be clamped to lightning rod and earth rod with a large contact surface area for low resistance, although it could be possible to use a more conventional cable of similar cross section it may be more difficult to get low enough resistances at the joints.
      Note that any down conductor must not have any sharp bends, kinks or loops in it. When a conductive mast is used, provided that all the joints within the mast structure make good electrical contact and are protected from corrosion, it is possible to bond/screw/bolt the lightning rod directly to the top part of the mast and use the mast itself as the down-conductor (providing it has sufficiently low resistance) with tape/cable between the mast base and the earth rods.
      Note that if any joints in the down-cable or mast become corroded (and thus high resistance), there will be heating and possibly welding/arcing there, also the high resistance caused by a bad joint will encourage flash-over onto adjacent items (eg the instruments) or buildings.
      Note that maximum separation should be maintained between sensor/extension-cables and the earth down-conductor, eg route the sensor cables down the opposite side of the mast from the down-conductor. It may also be necessary to bond adjacent conductive items (eg metal drainpipes, window-frames etc) to the down-conductor, refer to BS6651.
    • 4) surge protection measures on the instruments and other equipment
      - It is important to realise that surge-protection measures MUST be used in conjunction with the other measures discussed in this document to provide adequate protection from a direct strike, however if instruments are sited where they fall within an area covered by existing protection measures or on a site with low likelihood of a strike, anti-surge protection alone may give sufficient protection from nearby strikes.
      Most Vector Instruments sensors either incorporate surge-protection or can have it fitted within the instrument body at the time of ordering. Anti-surge mast-head junction boxes can also be fitted in place of the standard units to protect from surges induced in the sensor-cables or extension-cables. Similarly, anti-surge is available as a built-in option or add-on box for most display/signal-conditioning equipments. Please call our sales desk for more information.
    It is also possible to use commercially available signal line protection modules (ask our sales desk for a list of names and addresses) however units with low end-end resistance (<15 Ohm) with clamping voltage in the range 16-20v should be selected (normal working voltage range of most Vector Instruments systems is between 0 and 15V dc, however some units may use voltages up to 30V dc). The resistance introduced into the cables by these modules can introduce extra errors in some instruments depending upon how they are connected, especially potentiometer windvanes and resistance temperature sensors, also some types of protection modules may cause the 0V and earth to become connected which may cause problems. In the case of signal-conditioners and displays which provide output signals, it may also be advisable to connect galvanic isolators and/or surge protection in the output circuits to protect from surges picked up on the output cable run or to remove problems due to earth loops. It is also possible to fit surge-arrestor units to the supply of mains powered units to prevent surges coming from/going to the mains supply.
    Disclaimer: Windspeed Ltd. have provided this information in good faith and whilst every effort has been made to eliminate errors, Vector Instruments and any employees thereof cannot be held responsible for any loss, damages, consequential loss or injury which can be attributed to the use of any information or claims made in this document. Lightning protection is a specialist subject and Vector Instruments do not claim to be experts. It is strongly recommended that a consultant or engineer with experience and qualifications relating to lightning protection, IEE Wiring Regulations and the equipment/installation standards pertaining thereto be consulted by any customers considering purchasing instruments or systems for use on sites where lightning protection is a consideration.
    Windspeed Ltd (Vector Instruments)
    Windspeed Limited (trading as Vector Instruments),
    115 Marsh Road, RHYL, North Wales, LL18 2AB, United Kingdom
    Tel: +44 (0) 1745 350700   Fax: +44 (0) 1745 344206
    Email: sales@windspeed.co.uk
     
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