Evaluation of Effectiveness and Safety of CO 2 Cleaning of Energized Contaminated Pad-Mounted Gear

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Kelly Edwards
6 years ago
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1 1 Evaluation of Effectiveness and Safety of CO 2 Cleaning of Energized Contaminated Pad-Mounted Gear Peter Tyschenko Manager, Distribution Standards Commonwealth Edison Company Shay Bahramirad and Terry Bellei

2 Problem - Surface Contamination Surface contamination (Dust /Dirt & Moisture) is the greatest deteriorating factor for insulation. Cable terminations Interrupters Insulators (stationary & rotating) Surge arresters Barriers 2

3 3 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..

Theory of operation: Generate dry compressed air & mix with CO 2.

4 4 CO 2 Cleaning - Theory of operation Dry ice cleaning uses compressed air to accelerate frozen carbon dioxide (CO 2 ) dry ice" pellets. Theory of operation: Generate dry compressed air & mix with CO 2. Transport the mixture to the hot stick/nozzle. Direct the CO 2 at the object to be cleaned. CO 2 sublimates & lifts off contamination. Illustration: Cold Jet LLC

5 5 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 CO 2 cleaning.. The test switchgear was originally installed in An effectively grounded 3 test source was used to energize the gear at 14.4 kv while performing the CO 2 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.

6 - and -GRD, spray wand to ground, and cabinet to ground leakage currents were monitored during the CO 2 cleaning process. 6

7 7 Cleaning Energized Switchgear With CO 2 Before After

8 8 Cleaning Energized Switchgear With CO 2 8

9 9 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. Be Aware of the Dirt Shadow

10 10 Other Observations The inadvertent CO 2 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 CO 2 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. CO 2 cleaning can effectively clean exposed insulating surfaces. CO 2 cleaning of energized equipment can be safely performed

11 APPENDIX 11

12 Lifting/Flaking Paint Due To Rusting 12

13 Lifting/Flaking Paint Due To Rusting 13

14 14 Safety Flash Zone Pad-Mounted Switchgear (PMG) 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 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. 14 Observation Zone

15 15 Test Setup Switchgear 480V Source Resistors For Limiting Fault Current Delta-Delta 3-1 Transformers (Set Up Test Volatge) Wye-Delta 3-1 Transformers (Grounding Bank) Resistors For Measuring Leakage Current

Inspection Recommendations

Inspection Recommendations S&C Vista SD Underground Distribution Switchgear Pad-Mounted and Vault-Mounted Styles Outdoor Distribution (17.5 kv and 29 kv) With Visi-Gap Load Interrupter Switches and Visi-Gap Fault Inetrrupters Inspection