Electrostatic Mist-Blowing

electrostatic mist blowing scheme

Electrostatic Mist-Blowing

E.D.F. – France Electricity Dep.

Energy Conveyance Service and Telecommunications,
Supply Centre of the Conveyance
Network – Travaux du Mans

128, Avenue Felix Geneslay,
72100 Le Mans – FRANCE
Tel. 43.84.72.33 E.D.F.
R.C. Paris B 552 081 317

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Person in charge:
Mr MAIRESSE

To the
BRICAUD ESTATE Techno agricultural
570, Rue du Maréchal Foch 44370
V A R A D E S – FRANCE
Attn.: Mr. BRICAUD

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Le Mans, July 6th, 1989

Re: Electrostatic Mist-Blowing

Dear Sirs,

We wish to thank you for making available the equipment for spraying orchards with the electrostatic mist-blowing system.
A range of tests were carried out on our request at the E.D.F. High Voltage laboratory in Renadières (Moret sur Loing) with a view to answering the following questions:

Can the electric field caused by a 400 kV line over the fruit trees affect the efficiency of the electrostatic mist-blower? Is there any danger involved if the conductor cables are directly wetted by the mist-blower?

We would like to mention that the questions derive from the operating principle of the electrostatic mist-blower: charging the chemical droplets with a negative electrical charge, so that when they reach the trees, having an opposite polarity (+) they are attracted by the two faces of the leaves.

Some hundred tests were carried out, reproducing the real field conditions:

electrical field on the ground below a 400 kV line perpendicularly to its lowest point = 5.4 kV/m (1)
at 1.5 m from the ground below a conductor placed 8.5 m from the ground (minimum height and maximum operating temperature of the 400 kV lines).

Horizontal and vertical slot rain gauge; to measure the volumes of chemicals caught during a 10 minutes’ treatment. The rain gauge was connected to the ground and placed at a height of 3 to 5 m over the mist-blower.

At comparable weather conditions (in particular wind speed and direction) the tests showed that:
the electrostatic system is efficient (the quantity of product caught is 30 to 40% higher than with non-electrostatic systems)
the electric field of a 400 kV line does not modify the efficiency of the mist-blower.

As concerns the safety in use of electrostatic mist blowers below 400 kV lines, more tests were carried out and the most unfavourable conditions were chosen (electric field 6.8 kV/m at 1.5 m from the ground, perpendicularly to the lowest point of the conductor instead of 5.4 kV /m below the lines; chemical product with the highest conductivity, maximum spraying rate by the blower, straight wetting of the conductor, mist blower connected to the ground).
The very low current levels through the blower were always below the values that might cause pathological effects as listed in the C.E.I. 479 publication.

(1) Max. value affecting a small surface below the line (500 sq.m. for a length of 500 m).
(2) C.E.I. = International Electro technical Committee

As a conclusion, the presence of a 400 kV line over the orchards does not affect the efficiency of the treatments with electrostatic mist blowers and poses no danger.

Thanking you again for your cooperation, we are

Yours sincerely,

The Le Mans Base Chief
J. P. MAIRESSE

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