The busbar system is the heart of any Low Voltage Panel, and it provides the electrical connections between the incoming Air Circuit Breaker and the outgoing units.
It is thus essential that the busbar system is a reliable tested system meeting the requirements of temperature rise, short circuit and other conditions as described in the International Standards.
 

  • Logstrup Busbar System

    The Logstrup Busbar System consists of modular components, which allows unlimited variations and ratings. Three, four and five wire systems can be designed with ease, and ratings up to 8500A are standard, and tested for both temperature rise and short circuit level.

    The Busbar System is based on a two bar per phase system, both horizontal and vertical, eliminating time consuming drilling and bending of copper bars. The Busbar joints are by means of bolts and nuts of 8.8 quality in connection with special spring washers type DIN 6796. When tightened with the recommended torque this ensures an highly efficient and reliable connection throughout the complete lifetime of the assembly, even during variations in operational and thermal conditions. 

    The connections between the horizontal and vertical bars are made by a special busbar connector system and it secures a good and stable connection. The spacer BXC 11649, has been tested to 2000A.

    When joining two panel sections special fishplate connections are used. They are easy to mount and secure a good and reliable connection, see the second image above.
    The fishplate connections range from 800A up to 8500A.

    The busbar holder components are manufactured from a high grade polymer which provides a high insulation for the copper bar, good mechanical and thermal strength to meet the stress during a short circuit and ability to withstand variations in temperature during service conditions.

     

  • Pressure

    It has been proved that contact pressure resistance is dependent more on the total applied pressure than on the area of contact. If the total applied pressure remains constant and the contact area is varied, as is the case of a switch blade moving between spring loaded contacts, the total contact resistance is practically constant.

    The greater the applied pressure the lower will be the joint resistance and therefore for high efficiency joints high pressure is usually necessary. This has the advantage that the high pressure helps to prevent deterioration of the joint.

    Joint resistance falls rapidly with increasing pressure, but above a pressure of 15 N/mm2  there is little further improvement. Certain precautions must be observed to ensure that the contact pressure is not unduly high, since it is important that the proof stress of the conductor material or its bolts and clamps is not exceeded.   

                                      
    As a bar heats up under load the contact pressure in a joint with steel bolts tends to increase because of the difference in expansion coefficients between copper and steel. It is therefore essential that the initial contact pressure is kept to such a level so that it is not excessive when at operating temperature. If the elastic limit of the bar is exceeded the joint will have a reduced contact pressure when it returns to its cold state due to the joint material having deformed or stretched.

    To avoid this A/S Løgstrup - Steel prescribes the use of disc spring washers, (according to DIN Standard 6796), whose spring rating is chosen to maintain a substantial contact pressure under cold and hot working conditions.

    The torque settings recommended by A/S Løgstrup - Steel, are applicable to high-tensile steel bolts and nuts with unlubricated threads for normal surface finish.

     

  • Configuration

    The system consists of modular components which allow unlimited variations. 3, 4, & 5 wire systems can be created with ease, while the space between phases can be increased to ease connection to large breakers and facilitate connections of multiple cables.

    The busbar support insulators are manufactured from a high grade polymer, which can withstand all the mechanical and thermal stresses involved. All polymers used in the system are CFC and halogen free.
     

    Systems up to 8000A can be assembled as standard. A 2 bar, 2x2 bar or 3x2 bar per phase arrangement is used. This allows connections and extensions to be made without drilling or bending of the copper.
     

    The high short circuit level of the busbar system and the mechanical robustness of the enclosures, guarantees a reliable, safe and long lasting system suitable for even the most demanding environments.

     

  • Resistance

    The contact interface between two faces of a busbar joint consists of a large number of separate point contacts, the area of which increases as more contact pressure is applied and the peaks are crushed.

    There are two main factors which therefore affect the actual interface resistance of the contact surfaces.

    1. The condition of the surfaces.
    2. The total applied pressure.

     

  • Condition of Copper Surface

    The condition of the contact surface of a joint has an important bearing on its efficiency.

    The surface of the copper should be flat and clean but needs not to be polished. Machining is not usually required. Perfectly flat joint faces are not necessary since very good results can be obtained merely by ensuring that the joint is tight and clean. This is particularly true where extruded copper is used.

    Copper like all other common metals, readily develops a very thin surface oxide film even at ordinary temperatures and when exposed to air. Therefore it is important to clean the surface to ensure that the oxide layer is thin enough to be broken as the contact surface peaks deform when the contact pressure is applied.

    Tinning of the contact surfaces is normally unnecessary, although advantages can be gained in certain circumstances.

    If the joint faces are very rough tinning may result in some improvement in efficiency.

     

  • Busbar Ratings

    The rating is based on the DIN Standard 43671 and the conditiond as described in the Rating Table attached below.

    Rating table for Copper Busbars according to DIN 43671
    Copper Specification according to standard EN ISO 10720 / ASTM B272

    Rating at 40°C ambient temperature (average temperature over 24 hours : 35°C)
    and maximum busbar temperature 120°C.

    The ratings are tested values and the tests are performed in a Form 4 type panel with a degree of protection IP 3X - 4X.

    Ratings X/Y & Z Plane
    Rating at 40°C ambient temperature (average temperature over 24 hours : 35°C)
    and maximum busbar temperature 120°C.

    The ratings are tested values and the tests are performed in a Form 4 type panel
    with a degree of protection IP 3X - 4X.

    Busbars top or bottom with bars lying on long section of the bar.
    Named X/Y plane in all Logstrup documents.

    Busbar top or bottom with bars standing on short section of the bar.
    Named Z plane in all Logstrup documents.

    The Logstrup modular busbar system is rated as listed in the Rating Table provided as a PDF file.