Navy Public Work Center (PWC) personnel are required to periodically clean large electrical switchgear known as Load Interrupter (LI) switches. The presence of foreign matter on high voltage power distribution equipment can cause dielectric breakdown and arcing between otherwise non-conductive surfaces. The result is expensive equipment damage and power outages.

Carbon dioxide (CO₂) pellet media blasting is a technique that can be used to clean energized power distribution equipment. Contaminants are removed from the LI switch by the impact of the CO₂ pellet. The pellet compresses and mushrooms out, creating a high velocity snow flow that flushes the surface. The dry ice shears and lifts the contaminant off the surface with no or very minimal damage and leaves no residual waste. This shearing or lifting force is caused by the sublimation (direct transition from solid phase to gaseous phase) of the dry-ice pellets resulting in a sudden 400 fold increase in volume of the gas directed along the plane of the substrate. The contaminant is swept up, or in the case of outdoor switches, blown out of the enclosure. The released CO₂ gas is a naturally occurring atmospheric compound and presents no significant environmental concern.

Operationally, CO₂ pellets have a dielectric constant of 3.1 kV/mm at ambient pressure (about equal to dry air), enabling users to clean energized equipment with no safety hazard. The theory of operation is to generate a large volume of compressed VERY DRY air, transport it to the hot stick/nozzle assembly, mix it with CO₂ pellets in the hot stick, and then direct the mixed stream in a safe manner to the object to be cleaned. The air must be extremely dry because of the tendency for a high voltage arc, often called flashover or tracking or arc blast, to develop along contaminated or wet surfaces.

The required equipment installed on the Navy truck consists of the following components:

• CO₂ blaster/mixer, Alpheus MiniBlast model PLT-5HV.
• Air compressor, Sulair, Model 300H, 80-150 psi at 300 cfm.
• After cooler/air dryer & filter, Domnick Hunter, PNUEDRI; with dew point indicator, Model 8097; and ZEKS Air Dryer Corp, Model 301ACHA540; and heat exchanger, shell and tube type, API-Ketema, Inc., size 5-Y-18, 200 psig, 300^oF.
• Diesel electrical generator, Acme Motori, Model ADX 740, 10KW, 120/240 Volt Duplex.
• Non conductive hot stick air gun with safety ring, assorted blast hoses, Model A. B. Chance hot sticks and nozzles. All either Alpheus designs or manufactured to A.B. Chance specifications.

Use of non-ODS solvents or mechanical cleaning methods for degreasing and cleaning activities will help facilities meet the requirements under 40 CFR 82, Subpart D and Executive Order 12843 requiring federal agencies to maximize the use of safe alternatives to class I and class II ozone depleting substances, to the maximum extent practicable. In addition, the elimination of ODSs at the facility decreases the possibility that the facility will meet any of the reporting thresholds for those chemicals under 40 CFR 355, 370 and EO 12856. Chemicals used as substitutions should be reviewed for SARA reporting issues.

Using mechanical cleaning methods may also reduce the amount of hazardous waste generated and therefore, helps facilities meet the requirements of waste reduction under RCRA, 40 CFR 262, Appendix. The reduction of hazardous waste may also help facilities reduce their generator status and lessen the amount of regulations (i.e., recordkeeping, reporting, inspections, transportation, accumulation time, emergency prevention and preparedness, emergency response) they are required to comply with under RCRA, 40 CFR 262. Additionally, using mechanical cleaning methods in place of solvents may decrease the need for a facility to obtain an air permit under 40 CFR 70 and 40 CFR 71 and meet NESHAPs requirements for halogenated solvent cleaning under 40 CFR 63.

The compliance benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g. the amount of workload involved.

The CO₂ pellets have a surface temperature of 110^o F and require gloves for material and equipment handling. In the cleaning process the dry-ice particles are propelled at high velocities from a nozzle to impact and clean a surface. Air pressure in the range of 80-100 pounds per square inch is used to create airflow rates up to 300 cubic feet per minute and dry-ice pellet flow rates of 2-3 pounds per minute.

The operator must wear all required personal protective equipment and be trained in the use of the CO₂ cleaning components as well as be suitably qualified for "high voltage" work as is the standard PWC practice. The personal protective equipment will generally consist of eye protection including face shield, hearing protection, safety shoes, hard hat, gloves, and "Nomex" type non-conductive clothing.

Consult your local Industrial Health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing any of these technologies.

The current LI maintenance practice is to de-energize the equipment with a scheduled power outage, then manually wipe surfaces with rags using synthetic oil, grease, or a chlorinated solvent. PWCs would like to clean the switches without using solvents and de-energizing the circuits. Doing so eliminates the need to schedule power outages and costly overtime pay for work performed at night or on weekends when most scheduled power outages are permitted to occur.

This system has several benefits over cleaning methods currently in use. The technology was demonstrated at Naval Station San Diego. A series of seven tests were conducted on L.I. switches located throughout the Naval Station, including some at active piers. All switches were energized at 13.8 kV standard line voltage. The test results showed that the CO₂ cleaning process can be safely used to clean energized LI switches. The CO₂ process is efficient and does not cause any damage to the component parts. Furthermore, the process is environmentally friendly, improves system reliability, and lowers maintenance costs by reducing station power outages.

The benefits of the CO₂ process are realized by having a LI switch maintenance cleaning program that eliminates or minimizes the need for scheduled power outages. The benefits of using the CO2 cleaning technology are summarized as:

• Cost effective.
• Electrically safe and effective process.
• Improved power system reliability.
• Improved customer service by reducing power outages.
• Improved quality of life for Navy personnel.
• Eliminates the usage of hazardous material.

During wet or highly humid days, the cleaning of high voltage electrical equipment should not be attempted for either this technique or the current technique. The reason is the tendency for a high voltage arc, often called flashover or tracking or arc blast, to develop along contaminated or wet surfaces.

Using a conservative estimate of savings of 1.5 man-hours per switch cleaned, and one power outage avoided per year, the yearly savings would be about $40K/yr. A simple pay back of the $125K capital cost of the equipment is about 3 years. The cost for this treatment system must be determined on a site-by-site basis. The capital cost does not include the Navy truck, about $30K if one is not available.

Approval is controlled locally and should be implemented only after engineering approval has been granted. Major claimant approval is not required.