Motor externally by spraying water?

Dear Friends

This answer may a little bit different with our friends idea before, but its recognized and its our field experiences during repair / outage of electrical machine at site works or in our workshop, even the manufacturer used these method also.

The best method to clean-up is using dry ice, but this equipments is very expensive…….

CLEANING METHOD

Ref : IEEE Std . 56

Following cleaning method for Rotating Electric Machinery taken from IEEE std 56.

The method of cleaning can be adapted to the type of contamination and the buildup of contamination, the listed in the following paper are in increasing order of severity and possible damaged to the winding.

1. Vacuum cleaning

Dry contaminants such as carbon dust and fly ash can be removed with a vacuum cleaner. Contaminants can be dislodged for vacuum pickup by:

- Rubbing with dry cloth

- Brushing with a bristle brush

- Scrapping with soft wood or fiber scrapper (wire brushes or metal scrapper should not be used because of possible damage to the insulation and the dangerous possibility of introducing magnetic or other metallic particles into the winding or core assembly)

- Nozzle shapes should be varied as required to enable directing the vacuum cleaning into hidden, difficult to clean area

2. Air Lance cleaning

Care must be exercised , additional cleaning can be done employing shaped nozzle to direct high velocity clean dry air to dislodge trapped contaminants. Its is recommended that air pressure be limited to avoid damaging the insulation

3. Solvent cleaning

Care must be exercised in the choice and application of cleaning solvents from the standpoint of worker safety and risk of damage to the insulation

Solvent type:

- Petroleum solvent can be used for removing oily and greasy contaminants from asphaltic or synthetic resin type of insulation. These solvent should be used sparingly, quite often a lint free cloth, dampened in solvent, is adequate for rubbing off the contamination. Saturation of asphaltic type insulations should be avoided to prevent softening of the insulation materials.

- When a stronger or faster drying solvent is required a chlorinated safety solvent can be used on asphaltic and synthetic resin type of insulation, solvent dampened cloths are often sufficient for wiping off contamination.

- Mixture of petroleum solvents and chlorinated solvents can be used with better cleaning capability than the petroleum solvents alone

- Carbon tetrachloride and benzene are highly toxic solvents and are not to be used for cleaning. Gasoline , naphtha and similar liquids are not to be used for cleaning because of fire and explosion hazards.

Risk of damage

Liquid solvents are effective in removing oily contaminants but there are risk involved, particularly from spray applications of solvents, the solvents may carry contaminants into crack, crevices or inaccessible area and cause the insulation resistance to decrease to unsafe levels

Chlorinated solvents must not be used on stainless steel components because of the possibility of stress corrosion caused by the chlorides, and must also not to be used on aluminum or copper components because of chloride attack.

Solvent cleaning of cylindrical rotors should be avoided, cleaning of cylindrical rotors should be limited to vacuuming, blowing with dry compressed air, wiping with dry or solvent dampened cloth, or combination of these three methods.

Neither petroleum solvents nor chlorinated solvents be used on silicone insulation winding because of degrading effect on this type of insulation.

Example of stainless steel components:

- Non magnetic retaining rings and wedges on turbine generator rotors

- Stator cooling air or water systems on turbine generator

Heavy contaminants carbon dust mixed oily on stator generator 44 MVA, 11.5 kV

Solvent cleaning combined with very soft plastic brush and cloth to remove the heavy contaminants on the winding

4. Abrasive cleaning

Another method for removing contaminants utilizes an air blast of ground corn cobs or ground nut shells. This method is often successful for removing oily contaminants. The air abrasive blast must not be held too long on any one area or the insulation will be damaged by abrasion. Care must be exercised to avoid blowing the abrasive material in to inaccessible areas where it cannot be completely removed and may block ventilating passages or cause mechanical imbalance during operation.

Abrasives cleaning to removed heavy cement dust contaminants on the DC rotor 900 KW

5. Steam cleaning

The steam jenny method of cleaning utilizes a high-velocity jet of steam and water containing a mild non conductive detergent. The detergent spray is followed by multiple steam and water spray is without detergent to provide adequate rinsing. The machine must then be dried or backed to remove all moisture from the windings and to be obtain an acceptable insulation resistance value. If an overvoltage test is applied after steam cleaning, there is a risk of insulation failure if all moisture has not been removed or the insulation is defective.

Water jet cleaning to remove heavy oily contaminants on 3500 HP rotor dc motor

Used drying insulation systems, initial dry out temperature should not exceed 75 – 85⁰C ( reached at a maximum rate of 5⁰C/h), in exceptional cases where insulation resistance does not respond to this limit after 24 hrs, the maximum temperature may be carefully increased to 100 – 105⁰C, at temperature of 100⁰C or higher the possibility of insulation rupture 9as water change to steam) should be prime consideration in the time temperature schedule selected. Ventilating is required to remove the water vapor during the heating cycle.

The steam cleaning method is effective to remove on heavily contaminated winding and windings subjected to flooding or salt contamination.

The steam cleaning method usually can be used on silicone-insulated winding.

Drying method on the stator winding (motor or generator) by using direct current injection if baking oven is not available especial for site works

Drying on the 185 MW generator rotor by using DC MG-Set to supply current up to 500 Amps to the winding ( this method can be used on the rotor / stator winding)

6. Cleaning by water immersion or water hose

The machine involved in this guide are generally too large for immersion, but heavily contaminated or flooded machine can be washed with a hose. Baking and drying precaution noted under steam cleaning would also apply for water immersion.

Silicone insulated windings can be generally cleaned using the water hose method .

Boiled Water immersion cleaning on the traction rotor to remove heavy contaminant after flooding

Reinsulation coating after all of winding (rotor / stator) finish cleaning and dry-out

SPECIAL EQUIPMENT

Cleaning using Dry Ice method