CO2 Cleaning and Its Effectiveness
in Cleaning Energized
Medium-Voltage Equipment
Abstract
This paper provides an overview of how CO2 cleaning works on energized electrical equipment. It also presents
the procedures S&C Electric Company used to test the effectiveness of CO2 cleaning in reducing leakage currents
due to contamination.
Carbon Dioxide (CO2) Cleaning
CO2 cleaning is a proven, practical method for removing contaminants from the insulating surfaces of energized
electrical equipment rated at up to 34.5 kV. Contaminants such as dust, salt spray, dirt, and ash can significantly
reduce the dielectric strength of insulating materials. These contaminants can cause increased levels of leakage
current to pass over dielectric materials, leading to electrical breakdown due to surface tracking. Such conditions
can result in flashovers, which often damage
electrical equipment and cause unplanned service
outages, as well as safety concerns. CO2 cleaning
has been shown to reduce leakage current by more
than 96%.
The CO2 cleaning process uses solid CO2 (dry ice
shavings or pellets), projected through an insulated
wand at a specific nozzle pressure. These highdensity dry ice particles (approximately the size
of salt granules) are rapidly accelerated using
compressed air through a dry air blast line, which
requires a compressor that can deliver 150 pounds
per square inch (PSI) of pressure at a flow rate of
350 cubic feet per minute. When the CO2 particles
strike a contaminated equipment surface, the
impact removes the surface contaminants without
damaging insulating or underlying materials.
CO2 cleaning system.
How CO2 Cleaning Works
On impact with the equipment surface being
cleaned, the CO2 undergoes sublimation, transitioning
from the solid phase to the gaseous phase, without
passing through an intermediate liquid phase. The
cleaning process works in three different ways:
Scan this QR code for a video
showing how CO2 Cleaning Works.
Thermal-shock effect: The sudden temperature difference between the CO2 particles (–109.5 °F) and the insulating
surface weakens the bond that holds the contaminant intact, causing it to break apart.
Thermal-kinetic effect: During sublimation, the CO2 gas expands, lifting the remaining contaminants from the
insulating surface.
Kinetic energy: The accelerated CO2 blows contaminants off of insulating surfaces.
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CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
CO2 cleaning is non-toxic and does not produce secondary waste; only the lifted contaminants fall from equipment
surfaces. CO2 is also non-conductive, which allows cleaning of many types of energized electrical equipment
(rated at up to 34.5 kV), including overhead and underground distribution switching equipment; metal-enclosed
switchgear for indoor and outdoor distribution; distribution transformers; substation power transformers, circuit
breakers, and buses; and other equipment prone to contamination. Unlike other cleaning methods, such as water
blasting and cleaning with solvents, CO2 cleaning does not require equipment de-energization and grounding; it
allows electrical equipment to be cleaned without a planned outage.
S&C’s CO2 Cleaning Services
As part of an overall asset management program, CO2 Cleaning Services are intended for routine maintenance of
electrical equipment.
CO2 Cleaning Services are particularly beneficial for equipment exposed to harsh conditions in coastal and desert
regions, high-humidity areas, and other contamination-prone environments. With routine CO2 cleaning, costly
equipment flashovers can be significantly reduced in any environment, and equipment life can be extended. In
addition, the supply of CO2 is recycled from other industry processes, making it an environmentally friendly option.
CO2 cleaning is the only method that allows cleaning of energized equipment without generating secondary waste,
saving the time, costs, and labor associated with planned outages. With reduced set-up and take-down times, CO2
cleaning enables the cleaning of more equipment in one day than other methods.
Working with utilities, S&C estimated the substantial cost savings CO2 Cleaning Services can provide over current
methods. Because CO2 cleaning does not require an outage, it eliminates the need for technicians to de-energize
and re-energize equipment and prevents utility revenue losses due to outages, which can cost on average $1,000 per
hour for each piece of equipment taken out of service. When all costs are considered, S&C’s CO2 Cleaning Services
can provide utilities with a typical cost savings of more than 60% over their current cleaning method. If there is no
current cleaning method used to maintain equipment, this can cause tracking to develop and could eventually lead
to a flash-over in the equipment causing an unexpected outage.
Before performing CO2 cleaning, S&C conducts a
complete equipment safety inspection, establishes
a clearly defined safety perimeter and signage,
and provides immediate support if equipment is
determined unsafe to clean or requires repair. S&C
provides detailed equipment condition inspection
reports, which frequently meet routine maintenance
mandates in some states. S&C’s team of extensively
trained Power Systems Solutions field technicians
wear appropriate personal protective equipment
(PPE) and adhere to S&C’s safety procedures while
cleaning energized electrical equipment.
2
S&C uses proven safety protocols for CO2 cleaning.
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
How S&C Tested CO2 Cleaning on Electrical Equipment
S&C has investigated the use of CO2 cleaning on energized electrical equipment at its onsite Advanced
Technology Center and at utility sites across the U.S. in order to provide a reliable, efficient, and economical
service.
S&C’s testing includes two comprehensive sets of CO2 cleaning tests conducted at S&C on heavily contaminated
pad-mounted gear.
TEST SET 1: Testing the Safety and Efficacy of CO2 Cleaning on Energized Gear
In 2010, S&C evaluated whether CO2 cleaning could be performed safely and effectively on the two
compartments of an energized S&C PMH‑9 Pad-Mounted Gear unit, which was heavily contaminated. A core test
objective was to determine whether any appreciable leakage current would occur during the CO2 cleaning process
that could be sufficient in magnitude to cause a flashover in the equipment. Taken out of service for use as a test
sample, the pad-mounted unit selected for the test was originally installed by a utility in 1986 at an airport, where
contaminant levels were high.
Multiple rounds of tests were conducted to determine
whether CO2 cleaning of the energized gear could be
performed without producing a fault, assess whether
CO2 cleaning is an effective means of cleaning
contaminated switchgear, establish precisely how
the CO2 cleaning process should be conducted, and
determine the effects of inadvertent CO2 cleaning of
non-insulating gear components (switch contacts, arc
compressors, silencers, etc.).
S&C used an effectively grounded three-phase test
source to energize the gear at 14.4 kV during CO2
cleaning. Phase-to-phase, phase-to-ground, spray wand
to ground, and cabinet to ground leakage currents
were monitored and recorded for the entire time the
gear was energized in order to determine the presence
of any leakage current during the CO2 cleaning process.
S&C’s test setup for CO2 cleaning of energized PMH‑9
Pad-Mounted Gear.
3
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
Test Set 1 Results
CO2 Cleaning of Contaminated Insulators in Compartment 2
Before CO2 cleaning, all of the insulators inside compartment 2 of the PMH‑9 Pad-Mounted Gear unit were heavily
contaminated.
Compartment 2 Mini-Rupter® Switch: Heavy contamination on
insulators.
CO2 cleaning of A-phase Mini-Rupter Switch rotating
strut inside energized gear.
4
Rotating strut and lower insulator on
B-phase before CO2 cleaning.
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
While conducting CO2 cleaning on the insulators inside the energized gear, S&C measured the leakage current
levels.
S&C’s analysis of the leakage current measurements during CO2 cleaning indicated a significant number of shortduration discharges (SDDs), which varied in magnitude, with a typical duration of 0.5 milliseconds (ms). Because
the SDD durations were so brief, S&C determined the running root mean square (RMS) value of the leakage current
on a half-cycle by half-cycle basis in order to measure the effective leakage current over that half cycle.
Chart 1 and Chart 2 plot the relative frequency of the SDD equivalent RMS discharge level based on the leakage
current magnitude.
Chart 1. Data curve during CO2 cleaning of Mini-Rupter Switch.
Chart 2. Bottom of data curve magnified.
Charts 1 and 2 show that the percentage of time the leakage current exceeds the abscissa decreases dramatically
with increasing leakage current. The leakage current never exceeded 34 milliamperes (mA).
5
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
CO2 Cleaning of Contaminated Insulators in Compartment 1
Before CO2 cleaning, all of the insulators in compartment 1 of the PMH‑9 Pad-Mounted Gear unit were heavily
contaminated. While conducting CO2 cleaning on the insulators inside the energized gear, S&C measured the
leakage current levels.
As with the cleaning test on compartment 2, S&C’s analysis of the leakage current measurements during CO2
cleaning indicated a significant number of SDDs, which varied in magnitude, with a typical duration of 0.5 ms.
Chart 3 and Chart 4 plot the relative frequency of the SDD equivalent RMS discharge level based on the leakage
current magnitude.
Chart 3. Data curve during CO2 cleaning of Mini-Rupter Switch.
Chart 4. Bottom of data curve magnified.
Charts 3 and 4 show that the percentage of time the leakage current exceeds the abscissa decreases dramatically
with increasing leakage current. The leakage current was significantly less than that measured during
compartment 2 cleaning, never exceeding 8 mA.
6
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
Inspection of Compartments 1 and 2 After CO2 Cleaning
Compartments 1 and 2 were thoroughly inspected after the gear was de-energized. During and after each test,
S&C made the following key observations:
• CO2 cleaning tests were performed without a flashover on energized gear.
• CO2 cleaning was very effective in removing contamination from the front of the insulator surfaces (with no
flying debris).
• No apparent damage was sustained by any gear components due to CO2 cleaning.
• Discharge duration and SDDs decreased dramatically with increasing leakage current.
• The CO2 cleaning nozzle was not effective in cleaning the back of the rotating strut or the backs of the
support insulators; the nozzle design required additional development.
Additional Non-Energized Tests
Additional tests were conducted on the gear when
it was de-energized. Two tests determined the effect
of inadvertent cleaning of non-insulating components
(switch contacts, arc compressors, silencers, etc.).
One test involved coating the switch contacts with
grease and then cleaning the contacts with CO2.
As anticipated, the grease was unaffected by CO2
cleaning of the contacts.
Another test involved CO2 cleaning of the arc
compressor (front and side) in compartment 2 to
determine if the device would sustain any damage
from cleaning. Disassembly and inspection of the arc
compressor revealed no internal or external damage
as a result of CO2 cleaning.
Test 1 Summary
Mini-Rupter Switch in compartment 2 after CO2 cleaning.
S&C’s tests, which evaluated the feasibility of CO2 cleaning on energized equipment and the effectiveness of
CO2 cleaning on the insulators and rotating struts inside pad-mounted gear, demonstrated that CO2 cleaning is an
extremely effective method for cleaning exposed insulating surfaces. After performing the energized tests, analysis
of leakage current measurements indicated that the occurrence of SDDs decreased significantly as the leakage
current increased (SDDs were non existent above 34 mA).
S&C’s analysis of the leakage current demonstrated that CO2 cleaning of energized pad-mounted gear can be
performed effectively, provided that personnel are properly trained and equipped with the appropriate PPE
(full flash suit, safety glasses, rubber gloves, insulating mat, proper shoes, etc.). Inadvertent CO2 cleaning of
non-insulating gear components (switch contacts, arc compressors, silencers, etc.) revealed that no damage was
sustained by these components and that grease was not removed from switch contacts as a result of CO2 cleaning.
A number of different nozzle designs were tested to determine their effectiveness in cleaning the backsides of
the insulating surfaces. The results strongly indicated that a nozzle design, which would effectively clean entire
insulator surfaces (including the backsides), could be developed.
7
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
TEST SET 2: Testing the Effectiveness of CO2 Cleaning in Reducing Leakage Currents in
Contaminated Gear
In 2012, S&C evaluated the effectiveness of the
CO2 cleaning process for reducing leakage current
measurements on contaminated S&C PMH‑10
Pad-Mounted Gear and S&C PMH‑9 Pad-Mounted Gear
units. To simulate typical contamination and evaluate
the effectiveness of CO2 cleaning, all insulators and
rotating struts (S&C Mini-Rupter Switches) inside both
pad-mounted gear units were artificially and heavily
contaminated using hair spray as the bonding agent
and diatomaceous earth as the contamination medium.
First, each insulator and each rotating strut was
coated with hair spray. Diatomaceous earth was then
blown onto the insulators, heavily coating both the
front and back sides of all insulating surfaces with the
contaminant.
Mini-Rupter Switch rotating strut with high levels of
contaminants applied.
To simulate field conditions, both heavily
contaminated PMH‑10 and PMH‑9 Pad-Mounted Gear
units were later subjected to a “dry” test and a “dew”
test, where dew was allowed to form on the insulators.
During these tests, the insulators were energized at a
three-phase test voltage of approximately 15 kV, and
the leakage current on each phase and the leakage
current of the pad-mounted gear enclosure-to-ground
were measured. The insulators inside both padmounted gear units were then cleaned with CO2,
and the tests were repeated.
Dew on the insulators was created by placing each
pad-mounted gear unit into S&C’s environmental
test chamber (during separate tests) and cooling it
overnight to –12°C. After each unit’s temperature
reached equilibrium, the chamber temperature was
quickly elevated to 18-20°C while raining on the
unit for 15 minutes to create an extremely humid
environment, which resulted in heavy dew formation
on all insulator surfaces.
Typical dew formation on heavily contaminated insulator
during dew tests.
An effectively grounded three-phase test source was used to energize the gear at 15 kV. The test source was
connected to each phase of one of the Mini-Rupter Switches, and each fuse or switch was closed, allowing all
insulators inside the unit to be energized.
8
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
Test Set 2 Results
Leakage Currents on PMH‑10 and PMH‑9 Pad-Mounted Gear Before CO2 Cleaning
The contaminated PMH‑10 Pad-Mounted Gear unit and the contaminated PMH‑9 Pad-Mounted Gear unit were
energized at approximately 15 kV; the leakage currents were then measured when each unit was cold (dry test)
and after dew had formed on the insulators (dew test).
For both the PMH‑10 and PMH‑9 Pad-Mounted Gear units, the dry and dew tests were repeated to verify
consistency of results. A five-minute interval was allowed between dew tests to enable new dew to form on the
insulator surfaces. For the PMH‑9 unit, initial leakage currents for the last test were, in some phases, more than
double those observed during previous tests. The higher initial leakage current likely resulted from increased dew
on the insulator causing additional wetting and flow of contaminants on insulator surfaces. The final dew test
leakage currents were closer to each other, particularly for energized tests of 56 seconds or longer.
Leakage Currents on PMH‑10 and PMH‑9 Pad-Mounted Gear After CO2 Cleaning
After testing and removing the contaminated PMH‑10 Pad-Mounted Gear unit and the contaminated PMH‑9
Pad-Mounted Gear unit from the environmental chamber (during separate tests), each unit was cleaned using
S&C’s CO2 cleaning process.
A black rag was then used to wipe the back side of each insulator to determine how effective CO2 cleaning was for
“hard-to-reach” areas of the insulators. Very little residue was found on any of the insulating surfaces in the PMH‑10
Pad-Mounted Gear unit, as shown by the negligible amount of residue left on the black rags. Virtually no residue
was found on any of the insulating surfaces in the PMH‑9 Pad-Mounted Gear unit.
CO2 cleaning of back side of rotating strut (with special
curved nozzle) in PMH‑10 unit.
Black rag test shows minute amount of contamination
left on back sides of insulators.
9
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
The PMH‑10 Pad-Mounted Gear unit and PMH‑9 Pad-Mounted
Gear unit were then moved back into the environmental
chamber (at separate times) so that post-cleaning dew
tests could be performed. As previously described, each
unit was cooled overnight to –12°C and then subjected to
high-humidity conditions so that a heavy dew could form
on the insulating surfaces. Each unit was energized at a
three-phase test voltage of 15 kV; the leakage currents were
then measured when each unit was cold (dry) and after dew
formed on the insulators (dew).
For both the PMH-10 and PMH-9 Pad-Mounted Gear units,
the dew tests were repeated to verify consistency of results.
Again, a five-minute interval was allowed between dew tests
to enable new dew to form on the insulator surfaces. These
results show that the leakage current under dew conditions
is essentially equivalent to that under dry conditions.
The black rag test results and the significant reduction
in leakage current demonstrated that CO2 cleaning was
extremely effective in removing contamination from all
insulating surfaces in the PMH-10 and PMH-9 Pad-Mounted
Gear units.
Heavy dew formation on fuse support insulator
inside PMH-9 unit.
Tables 1 and 2 show the leakage currents measured during tests on the energized PMH-10 Pad-Mounted Gear unit
before and after CO2 cleaning:
Table 1. Leakage currents on PMH-10 gear before
CO2 cleaning.
Leakage
Measurement
10
Leakage Current (mA)
Initial
Final
A-Phase
3.01
3.00
B-Phase
2.85
2.87
C-Phase
2.75
2.75
A-Phase
44.0
7.82
B-Phase
49.1
5.61
C-Phase
38.6
5.62
Table 2. Leakage currents on PMH-10 gear after
CO2 cleaning.
Type
Test
Duration
Seconds
Leakage
Measurement
Dry
120
Dew
176
Leakage Current (mA)
Initial
Final
A-Phase
2.98
3.04
B-Phase
2.79
2.74
C-Phase
2.17
1.76
A-Phase
3.21
3.23
B-Phase
3.07
3.07
C-Phase
2.89
2.89
Type
Test
Duration
Seconds
Dry
58.2
Dew
58.0
CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
Tables 3 and 4 show the leakage currents measured during tests on the energized PMH-9 Pad-Mounted Gear unit
before and after CO2 cleaning:
Table 3. Leakage currents on PMH-9 gear before
CO2 cleaning.
Leakage
Measurement
Leakage Current (mA)
Initial
Final
A-Phase
2.94
2.89
B-Phase
2.76
2.74
Table 4. Leakage currents on PMH-9 gear after
CO2 cleaning.
Type
Test
Duration
Seconds
Leakage
Measurement
Dry
8.04
Leakage Current (mA)
Initial
Final
A-Phase
2.84
2.88
B-Phase
2.71
2.74
C-Phase
2.70
2.73
C-Phase
2.68
2.72
A-Phase
68.7
29.5
A-Phase
3.15
3.13
B-Phase
94.6
20.8
B-Phase
3.03
3.02
C-Phase
62.3
11.8
C-Phase
3.24
2.94
Dew
56.6
Type
Test
Duration
Seconds
Dry
55.7
Dew
58.1
Test 2 Summary
S&C’s tests, which evaluated the effectiveness of CO2 cleaning on the insulators and rotating struts inside
pad-mounted gear, revealed several key results. The black rag wiping tests identified only a minute amount
of contamination remaining on the back sides of
Maximum Leakage Current Measured on
insulating surfaces after the PMH-10 and PMH-9
Pad-Mounted
Gear Units Energized at 15 kV
Pad-Mounted Gear units were cleaned. These tests
also confirmed that a specially curved nozzle was
extremely effective in cleaning the back sides of the
100
insulating surfaces.
90
Leakage Current—Milliamperes
The dew tests confirmed that CO2 cleaning is an
extremely effective method of cleaning the exposed
portions of the insulating surfaces. Chart 5 shows the
significant reduction in leakage current achieved by
performing CO2 cleaning on the pad-mounted gear
units.
80
70
60
50
40
30
20
10
0
■ PMH-9
Leakage Current
■ PMH-10
Leakage Current
Before C02 Cleaning
After C02 Cleaning
94.6
3.13
49.1
3.23
Chart 5. CO2 cleaning can reduce leakage current by more
than 96%.
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CO2 Cleaning and Its Effectiveness in Cleaning Energized Medium-Voltage Equipment
Conclusion
Over several years of comprehensive testing, S&C has proven that the CO2 cleaning process can be conducted
effectively on energized electrical equipment (rated at up to 34.5 kV) by trained, properly equipped personnel,
without damaging insulating surfaces or underlying materials. S&C’s extensive tests on contaminated gear
definitively show that CO2 cleaning can reduce leakage current by more than 96%. After CO2 cleaning is completed,
the equipment will continue to perform safely at its rated capacity and is better protected from flashovers, thereby
helping to prevent damage and unplanned service outages while extending equipment life.
For more information or a quote for S&C’s CO2 Cleaning Services please visit
our website at sandc.com/co2paper or e-mail us at CO2cleaning@sandc.com
Testing services and this test report are provided subject to S&C’s Standard Terms and Conditions for Services,
Price Sheet 181. No interpretations of this test report should be made beyond the description of the tests
performed on the specific equipment tested and the results of the tests as presented. This test report may not
be reproduced or published in any form, except as a complete copy in its entirety, without the express written
permission of S&C Electric Company, 6601 North Ridge Boulevard, Chicago, Illinois 60626, U.S.A.
Phone: (773) 338 -1000, Power Systems Solutions Fax: (773) 338 - 4254.
Printed in U.S.A.
©2013 S&C Electric Company
The information contained in this document is proprietary, and is not to be used, reproduced, copied, or
distributed without the express written consent of S&C Electric Company.
August 26, 2013 ©
sandc.com • twitter.com@SandC_US • twitter.com@SandC_UK
180-T104