برق. قدرت. کنترل. الکترونیک. مخابرات. تاسیسات.

دایره المعارف تاسیسات برق (اطلاعات عمومی برق)

آرایش کابل ها
Selection of materials and their shape depends on the following criteria:
  • Severity of the EM environment along cableways (proximity of sources of conducted or radiated EM disturbances)
  • Authorised level of conducted and radiated emissions
  • Type of cables (shielded?, twisted?, optical fibre?)
  • EMI withstand capacity of the equipment connected to the wiring system
  • Other environmental constraints (chemical, mechanical, climatic, fire, etc.)
  • Future extensions planned for the wiring system

Non-metal cableways are suitable in the following cases:

  • A continuous, low-level EM environment
  • A wiring system with a low emission level
  • Situations where metal cableways should be avoided (chemical environment)
  • Systems using optical fibres

For metal cableways, it is the shape (flat, U-shape, tube, etc.) rather than the cross-sectional area that determines the characteristic impedance. Closed shapes are better than open shapes because they reduce common-mode coupling. Cableways often have slots for cable straps. The smaller the better. The types of slots causing the fewest problems are those cut parallel and at some distance from the cables. Slots cut perpendicular to the cables are not recommended (see Fig. R9).


Fig R09.jpg

Fig. R9: CEM performance of various types of metal cableways


In certain cases, a poor cableway in EMI terms may be suitable if the EM environment is low, if shielded cables or optical fibres are employed, or separate cableways are used for the different types of cables (power, data processing, etc.).
It is a good idea to reserve space inside the cableway for a given quantity of additional cables. The height of the cables must be lower than the partitions of the cableway as shown below. Covers also improve the EMC performance of cableways.
In U-shaped cableways, the magnetic field decreases in the two corners. That explains why deep cableways are preferable (see Fig. R10).


Fig R10.jpg

Fig. R10: Installation of different types of cables


Different types of cables (power and low-level cables) should not be installed in the same bundle or in the same cableway. Cableways should never be filled to more than half capacity.
It is recommended to electromagnetically separate groups from one another, either using shielding or by installing the cables in different cableways. The quality of the shielding determines the distance between groups. If there is no shielding, sufficient distances must be maintained (see Fig. R11).
The distance between power and control cables must be at least 5 times the radius of the larger power cable.


Fig R11.jpg

Fig. R11: Recommendation to install groups of cables in metal cableways


Metal building components can be used for EMC purposes. Steel beams (L, H, U or T shaped) often form an uninterrupted earthed structure with large transversal sections and surfaces with numerous intermediate earthing connections. Cables should if possible be run along such beams. Inside corners are better than the outside surfaces (see Fig. R12).


Fig R12.jpg

Fig. R12: Recommendation to install cables in steel beams


Both ends of metal cableways must always be connected to local earth network. For very long cableways, additional connections to the earthing system are recommended between connected devices. Where possible, the distance between these earthing connections should be irregular (for symmetrical wiring systems) to avoid resonance at identical frequencies. All connections to the earthing system should be short.
Metal and non-metal cableways are available. Metal solutions offer better EMC characteristics. A cableway (cable trays, conduits, cable brackets, etc.) must offer a continuous, conducting metal structure from beginning to end.
An aluminium cableway has a lower DC resistance than a steel cableway of the same size, but the transfer impedance (Zt) of steel drops at a lower frequency, particularly when the steel has a high relative permeability µr. Care must be taken when different types of metal are used because direct electrical connection is not authorised in certain cases to avoid corrosion. That could be a disadvantage in terms of EMC.
When devices connected to the wiring system using unshielded cables are not affected by low-frequency disturbances, the EMC of non-metal cableways can be improved by adding a parallel earthing conductor (PEC) inside the cableway. Both ends must be connected to the local earthing system. Connections should be made to a metal part with low impedance (e.g. a large metal panel of the device case).
The PEC should be designed to handle high fault and common-mode currents.

Implementation

When a metal cableway is made up of a number of short sections, care is required to ensure continuity by correctly bonding the different parts. The parts should preferably be welded along all edges. Riveted, bolted or screwed connections are authorised as long as the contact surfaces conduct current (no paint or insulating coatings) and are protected against corrosion. Tightening torques must be observed to ensure correct pressure for the electrical contact between two parts.
When a particular shape of cableway is selected, it should be used for the entire length. All interconnections must have a low impedance. A single wire connection between two parts of the cableway produces a high local impedance that cancels its EMC performance.
Starting at a few MHz, a ten-centimetre connection between two parts of the cableway reduces the attenuation factor by more than a factor of ten (see Fig. R13).


Fig R13.jpg

Fig. R13: Metal cableways assembly


Each time modifications or extensions are made, it is very important to make sure they are carried out according to EMC rules (e.g. never replace a metal cableway by a plastic version!).
Covers for metal cableways must meet the same requirements as those applying to the cableways themselves. A cover should have a large number of contacts along the entire length. If that is not possible, it must be connected to the cableway at least at the two ends using short connections (e.g. braided or meshed connections).
When cableways must be interrupted to pass through a wall (e.g. firewalls), low-impedance connections must be used between the two parts (see Fig. R14).


Fig R14.jpg

Fig. R14: Recommendation for metal cableways assembly to pass through a wall


Single-layer ceiling mounting

6417027_mg31.jpg

Observe the minimum spacing "a" to the fire protection ceiling. Values can be taken from the survey.

Two-layer ceiling mounting

6417027_mg35.jpg

Two-layered, one over another, with small side mounting space.

Double-sided mounting under the ceiling

6417027_mg38.jpg

To reduce the space required in a downwards direction at maximum load.

Two-layered on a bracket

6417027_mg34.jpg

Additional variants for room use and to reduce the spacing downwards.

Ceiling mounting with cross-section

6417027_mg37.jpg

Simple variant with 1 m maximum support spacing. Also suitable for supporting existing systems in existing buildings.

Single-layer wall mounting

6417027_mg32.jpg

Wall mounting is possible in variants.

Mounting preparations

6417027_mg6.jpg

Screw the U suspended support into the pre-mounted fire protection clamp. For support lengths > 1 m to 2 m, the distance "a" is increased by 10 mm.

Pre-mounting of brackets

6417027_mg7.jpg

Mount the connection bracket on the tip of the bracket using the included bolts.

Bracket mounting

6417027_mg33.jpg

Fasten the brackets through the two hips of the U suspended support with a hexagonal bolt and spacer.

Connector mounting

6417027_mg22.jpg

Interconnect cable trays using two straight connectors and a joint plate.

Tray mounting

6417027_mg9.jpg

Fasten the cable trays on the bracket with truss-head bolts.

Threaded rod locking

6417027_mg13.jpg

Mounting of the threaded rod through the connection bracket on the tip of the bracket.

Threaded rod in fire protection clamp

6417027_mg10.jpg

Attach the threaded rod to the fire protection clamp. Then tighten the nuts.

Threaded rod in internal thread anchor

6417027_mg12.jpg

Alternatively, screw the threaded rod in the internal thread anchor. Then tighten the nuts.

Finished mounting

6417027_mg14.jpg

Fire protection-safe fastening of the electrical installation including proof of the deformation behaviour during a fire. This avoids destruction of the classified ceiling


http://catalog2.obo-bettermann.com/catalogue/catalogue.do?act=showIO&catId=&lang=en&forward=showInstallationExamples&favOid=bss_458847


http://www.electrical-installation.org/enwiki/EMC_implementation_-_Cable_running

صفحات جانبی

نظرسنجی

    لطفاً نظرات خود را درمورد وبلاگ با اینجانب در میان بگذارید.(iman.sariri@yahoo.com)نتایج تاکنون15000مفید و 125غیرمفید. با سپاس


  • آخرین پستها

آمار وبلاگ

  • کل بازدید :
  • تعداد نویسندگان :
  • تعداد کل پست ها :
  • آخرین بازدید :
  • آخرین بروز رسانی :