Evaluation of Effectiveness and Safety of CO2 Cleaning of Energized Contaminated

Pad-Mounted Gear

Peter Tyschenko Manager, Distribution Standards Commonwealth Edison Company

Shay Bahramirad and Terry Bellei

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Problem - Surface Contamination • Surface contamination (Dust /Dirt & Moisture) is the

greatest deteriorating factor for insulation. – Cable terminations – Interrupters – Insulators (stationary & rotating) – Surge arresters – Barriers

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Switchgear Failure - Typical Sequence

• Buildup of airborne contamination on the barriers or other components of the switchgear. – Vulnerable to contamination (proximity to roadways).

• Contamination supports leakage currents. – Standing water in the foundation can result in repetitive

condensation cycles that can extend the duration & severity of tracking.

• Tracking can result in excessive leakage currents, which can lead to flashover.

• The flash develops a cloud of conductive gas which subsequently supports - and -GRD flashovers.

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CO2 Cleaning - Theory of operation

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• Dry ice cleaning uses compressed air to accelerate frozen carbon dioxide (CO2) “dry ice" pellets.

• Theory of operation: Generate dry compressed air & mix with CO2. Transport the mixture to the hot stick/nozzle. Direct the CO2 at the object to be cleaned. CO2 sublimates & lifts off contamination.

Illustration: Cold Jet LLC

Testing To Evaluate Effectiveness And Safety • An energized test program was conducted on a heavily

contaminated S&C PMH-9 (2 line, 2 fuse) switchgear to

determine whether any leakage current could cause a

flashover during CO2 cleaning.. – The test switchgear was originally installed in 1986.

• An effectively grounded 3 test source was used to energize

the gear at 14.4 kV while performing the CO2 cleaning. – The test source consisted of backfed 480V transformers. – 1 resistors were connected to limit the high-side fault current.

• Leakage current measurements indicated : – Short duration discharges (SDD) lasting ~0.5ms in duration.. – leakage current never exceeded 34mA.

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- and -GRD, spray wand to ground, and cabinet to ground leakage currents were monitored during the CO2 cleaning process.

Cleaning Energized Switchgear With CO2

Before After

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Cleaning Energized Switchgear With CO2

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Be Aware of the “Dirt Shadow” Disconnect cleaned in the “CLOSED” position and rotated into the “OPEN” position to display results. Alternate nozzle designs and cleaning techniques proven in subsequent testing have eliminated this problem.

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Other Observations • The inadvertent CO2 cleaning of non-insulating components within

the gear (switch contacts, arc compressors, silencers, etc.) revealed that there was no damage to any of these components. – Grease was not removed from the contacts as a result of this cleaning.

• While dust and dirt and other airborne contaminants can be successfully removed by the CO2 cleaning process, not all switchgear units are good candidates for cleaning. – Lifting/flaking paint due to rusting is deemed to pose a potential hazard. – Conductive ferrous residue can become dislodged under the pressure of the

compressed air, resulting in a flashover.

• CO2 cleaning can effectively clean exposed insulating surfaces. • CO2 cleaning of energized equipment can be safely performed

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APPENDIX

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Lifting/Flaking Paint Due To Rusting

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Lifting/Flaking Paint Due To Rusting

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Safety – Flash Zone

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Safety Zone 1

Body 2ft from PMG

Qualified Operator only.

HRC Level 4 Suit (40+ Cal)

Safety Zone 2

Body 4ft from PMG

HRC Level 2 Clothing

(8+ Cal)

2ft

4ft

8ft

Observation Zone

Pad-Mounted Switchgear

(PMG)

Work Conditions •Do not perform work

during inclement weather. –Potential to introduce

conductive water

•Do not perform clean equipment with rust, deterioration.

•Disable reclosing on source circuit(s) during cleaning.

• Equipment must be readily accessible –Truck access from an

improved roadway.

Test Setup

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480V Source Delta-Delta

3-1 Transformers (Set Up Test Volatge)

Wye-Delta 3-1 Transformers (Grounding Bank)

Resistors For Limiting

Fault Current

Resistors For Measuring

Leakage Current

Switchgear