If I understand you correctly, the conveyor is paralleling a high tension line. Could be a serious probelm depending on the earthing conditions. We have done a few of these. They are not pleasant to work around.. You need to ground the entire length with frequent earthing rods and test the soil for conductivity. Even cows in the pasture under these lines can get whacked.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Dear Brian,

What is the vertical & horizontal distance between the conveyor and the overhead cables.

What about the statutory requirements (minimum distance) of working area from the base of the pylons (towers) supporting the cables.

Regards,

Ishwar G Mulani

Author of Book : Engineering Science and Application Design for Belt Conveyors. ■

Dear Mr. Brian Moore,

Referring to my earlier message, I add the following information.

You are investigating to put belt conveyor along the route of overhead 66 kV transmission line.

The overhead conductors will have circular flux lines, concentric to the conductor and in plane perpendicular to the conductor.

In view of AC Current, the circular flux lines will appear to be emitted outwards and retreating back in to conductor (to & fro). Belt conveyor and thereby steel cords being parallel to the conductor; the steel cords have ideal orientation to be cut by to & fro motion of magnetic flux. Thus alternating voltage / current will be induced in steel cords (of belt). Similarly, conveyor length wise steel members (such as stringers) will also have maximum effect. Presently, we are analysing phenomenon. Its magnitude is a separate matter.

The belt and thereby steel cords motion is perpendicular to flux plane. Therefore, belt motion will not move across the flux lines, and also do not contribute for induced voltage / current. Thus induced voltage / current in steel cords will be same whether the belt is moving or standstill. Thus, belt motion will not contribute in electrical induction.

The magnitude of aforesaid voltage / current will depend upon conveyor distance from overhead cables. Electrical engineers can work out induced voltage and circulating current in steel cords as per resistance of steel cords and 3 phase situation.

In belt conveyor installation, 0.44 kV (440 V) power cables are often located within 2.5 m distance from conveyor center line, without adverse consideration to conveyor. If we assume 66 kV lines distance as 25 m from conveyor center line, then its equivalent effect at 2.5 m from conveyor would be as below :

66 x (square of 2.5 / 25) = 0.66 kV. Above is same as average installation. It seems electrical induction need not create an unusual situation. Shiftable conveyors also have HT cables close to conveyors, with much unfavourable effect.

The common sense says that the electrical authority will not install overhead lines which can disturb human activity at ground level. That is such overhead lines possibly should not affect working of vehicle ignition system, radio, quartz watches or may be even laptop computer. One can just go on the adjoining road and check how much is the effect even by using galvanometer. Transmission line authority may have readily available data for flux density at ground level.

It seems practical / psychological consideration would be more dominant here. The conveyor people will be uncomfortable all the times, in vicinity of such overhead lines, particularly during stormy / rainy condition. This will indirectly affect conveyor inspection / maintenance etc. I agree with Mr. Nordell that it is better to avoid close proximity to such overhead lines. The conveyor will need more earthings. However, earthing would not be possible for steel cords within belt.

What about statutory rules to have certain minimum distance for equipment / working area from overhead line installation? Also, operation of erection crane will be under restriction, as any accident can disturb public utility system, plunging some cities in darkness, apart from accident casualties.

My information indicates various probabilities. You may discuss with electrical experts and Transmission authority for magnitude of implications, and safe distance from overhead transmission lines etc. The issue looks to be fear of death leaping from overhead, but it very much matters.

Regards,

Ishwar G Mulani

Author of Book : Engineering Science and Application Design for Belt Conveyors. ■

Mr. Moore & Mulani,

Not to belabor the point, the structure is the first problem.

Conductive rubber can be used.

A number of conveyors have been successfully installed under electric grids.

Mr. Mulani says distance matters, and this is true.

I believe I know the installation and think this is a consulting matter beyond this point.

Lawrence Nordell

Conveyor Dyanmics, Inc. ■

Brian

On the subject of building conveyors under high tension lines, please see the paper written by David Bull

of Barccay Mowlem Company Ltd. and presented at Bulkes 2000 in Melbourne.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

DARN

Its: Barclay Mowlem Construction Limited (BMCL)

Sydney, Bisbane and Perth Australia.

LKN ■