Danfoss Handling aggressive environments Application guide

Drives and Controls

VLT®is a trademark of Danfoss A/S

Frequency Converter

Danfoss VLT®DrivesDanfoss VLT

Handling aggressive environments

Frequency Converters

■ It pays to protect against harsh
environments

Electronic equipment is sensible to the environment,
i.e. moisture, dust and temperature can influence
the reliability of electronics. Reduced reliability
causes downtime in the application with reduced
earnings as a result. Therefore it is important to
choose the right solution for the actual application.

This instruction informs about the possibilities to pro­tect a frequency converter and other electronic de­vices against influence from an environment where
aggressive gasses and moisture are present.

Basically it is important to protect the electronics
from a harsh environment. The best way to do that,
is to avoid the harsh environment by placing the
electronics outside the harsh environment. Danfoss
offers different solutions:

· Our different drives can control a motor with long
motor cables. This means that the customer can
place the drive far away from the critical environ­ment.

Handling aggressive environments

·

Our small drives are designed for placement di­ rectly in a typical industrial control cabinet. The
control cabinet can be fitted with air-conditioning
units ensuring that the critical environment does
not get in contact with the drives and other
electronics.

· Some drives are fitted with a cold plate. With this

solution you can place the drive inside a closed
cabinet and via the cold plate the heat is trans­mitted to the outside. With this solution the drive
is kept away from the critical environment.

· The FCM is fitted with a tight enclosure. The en-

closure protects the electronics from the outside
environment.

· For selected drive series we give the customer

the possibility to buy a frequency converter with
coated electronics as an option. These drives
have a higher reliability in environments where
aggressive gasses and moisture are present.

This instruction will help you choose the right protec­tion.

■ How critical is the environment?

You cannot directly see how critical the environment
is. It depends mainly on 4 factors, the concentration
of pollutants present, dirt, the relative humidity and
temperature.

To find out how critical the environment is, look for
some signs indicating the amount of aggressive gas­ses, moisture and time of wetness in the environ­ment. This will be described in the following. In many
applications typical conditions are known and for
some of these we have added a table showing typi­cal constituents.

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Signs to look for

In existing plants it is possible to see if an aggressive
environment is present. Take a look at a copper
lead having been placed in the installation for a least
some months. If a critical environment is present,
the copper will turn dark.
I.e. unscrew a copperlead in a connector. The part
where the screw presses is nice, but the area
where screw or insulation does not protect is a
good indicator for the environment. If it is black (cor­roded), the environment can be critical. If the cop­per is uncorroded, the environment is expected to
be uncritical.

Examples of critical applications

The below table shows typical gasses in some se­lected applications which can be critical. It can give
you some hints of applications that can be critical.
The information in the table is not necessarily cover­ing all actual constituents in the application.

Application Constituent Symbol
Sewage plants Ammonia NH

3

Hydrogen sulphide H2S
Active organic nitrogen N

2

Paper mills and Hydrogen sulphide H2S
wood pulping Carbon monoxide CO
Chlorine's Cl, Cl
Active organic nitrogen N

Hydrocarbons Cn, H
Water Hydrocarbons Cn, H

2

2

n

n

treatment

Handling aggressive environments

The different constituents attack metals. I.e. sulphur
dioxide attack all metals except noble metals, nitro­gen dioxide, ammonia and ammonia salts attack
copper and brass and hydrogen sulphide attack sil­ver and copper.

Determining the severity level

Generally the environments can be classified in groups
as defined in IEC721-3-3. The classification is di­vided into 4 groups, 3C1 to 3C4. ANSI/ISA S71.04­1985 also divides the environment into 4 groups, G1

- Gx.
Compared with the classification in ANSI/ISA
S71.04-1985, G2 is comparable to 3C2 and G3
comparable to 3C3.
From a Nordic research project the following model
for classification of the environment has been devel­oped.

Use the figure below to make a brief estimate of the
actual application.

Combustion of Hydrogen sulphide H
fossil fuels/ Sulphur dioxide SO
automative Nitrogen oxides NO

S

2

,SO

2
x

emmisions Carbon monoxied CO
Sulphuric acid Hydrogen Chloride HCL

manufacture Hydrocarbons C

n

, H

n

Fertilizer Hydrogen flouride HF
manufacture Ammonia NH

3

Steel manu- Hydrogen flouride HF
facture and Hydrogen sulphide H
ore smelting Sulphur dioxide SO

S

2

,SO

2

Aluminium Hydrogen flouride HF
manufacture Chlorine's Cl, Cl

2

Foundries Mercaptans SB, R-SH
Carbon C

Cleaning of Ammonia NH
products Chlorine's Cl, Cl

3

2

3

3

Reference No. 2

τ1 to τ6 is the time of wetness and P1 to P5 is the
pollution degree. P1 is a low pollution degree, P5 is
a high degree.
Examples of environments have been put in the fi­gure to give an overview.

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Handling aggressive environments

For an exact classification it is necessary to test the
environment. A way to do that is by making a
standardised test.
A standard copper coupon is exposed in the actual
environment for 28 days. The corrosion activity is
measured as the amount of corroded copper.
Based on the measured value the environment is
classified in one of four classes. The coupon test is
made by the Swedish Corrosion Institute:

Swedish Corrosion Institute.
Roslagsvägen 101, hus 25
S-104 05 Stockholm
Int. phone: [phone]
Int. fax: [phone]
Homepage: http://www.corr-institute.se

■ How to protect units against corrosion

Basically the best way to avoid problems is to keep
the aggressive environment away from the electrical
installations. This is possible in many applications,
but in some applications not possible. In such cases
other precautions must be taken to reduce the risk
for problems.

Precautions during planning and installation

To avoid problems in an application we recommend
to follow the general guidelines below in the order
stated. If it is not possible to choose the first recom­mendation, then go for the second and so on.
Beside the point below, You also have to choose
the appropriate enclosure type (IP class) to be used
in the environment, taking dust, water and objects,
such as screwdrivers and fingers, into account.

Alternatively we recommend you to contact an
engineering agency to help you determining the
environments.

1. 1.

1. Plan the installation in such a way that the drives

1. 1.
and other electronics are placed apart from the
harsh environment. Doing that extra costs can
be totally avoided. As the Danfoss frequency
converters are capable of driving motors with
long motor cables, it is possible to place the
drives apart from the machinery.
Examples of such solutions are control rooms in a
factory where the drives are installed or complete
cabinets from OEM’s are placed. These rooms
are sometimes also equipped with climatic
control such as air conditioning.

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2.2.

2. If it is not possible to place the drives and other

2.2.
electronics apart from the harsh environment,
then a closed cabinet combined with a heat
exchanger can be used. The harsh environment
is kept away from the electronics and the solu­ tion is comparable with the first solution, except
for commissioning where you have to open the
cabinet.
Another possibility is to keep the harsh environ­ ment away from the electronics by supplying the
control cabinet with fresh clean air.
As the speed of the corrosion process is low at
low relative humidity and low temperature, an air­ conditioning unit can also minimize the corrosion.
In this case it is important that the relative humi­ dity and the temperature is kept on a low level.

Handling aggressive environments

4. 4.

4. If it is not possible to keep the harsh environment

4. 4.
away from the electronics, a solution can be to
select a coated drive. Coating gives a better pro­ tection of the drives than an uncoated solution,
but even if you choose a coated drive, precau­ tions must be taken into account. The harsh en­ vironment can attack copper in the installation or
other electronics connected to the drives, such
as PLC’s or other control devices which are not
protected. In this case it is important to keep the
relative humidity as low as possible in the environ­ ment, as a high relative humidity forces corrosion.
In such a case an air-conditioning unit can help
controlling the relative humidity.

3.3.

3. Alternatively choose an integrated frequency con-

3.3.
verter and motor, FCM300, which has a tight
enclosure for the electronics.

General aspectsGeneral aspects

General aspects

General aspectsGeneral aspects
No matter which solution you choose, it is important
that the solution is maintained and the installation is
made according to the requirements. Filters for air­conditioning units and fans must be cleaned accord­ing to the specifications and the control cabinets
and control rooms must be kept closed to keep the
harsh environment outside.

MN.90.I1.02 - VL T is a registered Danfoss trademark4

Select the appropriate VLT frequency converter

®

The VLT

frequency converter is available in different
enclosures. Additionally some of the VLT frequency
converters are available with coated printed circuit
boards for increased protection. See technical litera­ture for your different possibilities to choose between
the different drives and options.

■ Technical information

When referring to aggressive gases and electronics
basically 2 standards are relevant, IEC721-3-3 and
ANSI/ISA-S71.04.
The corrosion process is described briefly in the fol­lowing.

Handling aggressive environments

What causes corrosion

Corrosion of electronics is determined by several
factors. 4 main factors determine if corrosion
occurs: concentration of aggressive gases, dirt,
moisture and temperature.

· Presence (concentration) of aggressive gases
Different metals are present in electronics such
as copper, tin, lead, silver and aluminum. These
metals react with different aggressive gases
such as sulfur compounds, chlorides, nitrogen
oxides and ammonia.

· Moisture

At a relative humidity below 50% the corrosion
process is very slow. At increasing relative
humidity the corrosion process increases.

· Temperature

If the temperature is below 0 ° C corrosion is
negligible.

· Dirt
Dust can be conductive as well as it can contain

moisture.

A Nordic research project has developed a model
for corrosion classification. This model is described in
short form below. The model has been developed
with the American ANSI/ISA S71-04 standard as
reference.

The influence from the relative humidity is
determined by how long the electronics is exposed
to a critical humidity and temperature, called “Time
Of Wetness”.
The term time of wetness has been defined as:
Hours per year where the temperature is above 0°C
and the relative humidity is above 80%.

Time of wetness is divided into 6 categories, τ 1 to
τ 6.
The critical zones are primarily the last 3 locations,
as the time of wetness is minimum 10% per year.

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Handling aggressive environments

Time of wetness

Time of wetness

Category

Category

CategoryCategory

1 <10 <0.1 Indoor air with climatic control.
2 10-250 0.1-3 Indoor air in normal rooms for living or working condition.
3 250-1000 3-10 Indoor air storage rooms.

4 1000-2500 10-30

5 2500-5500 30-60

6 >5500 >60 Outdoor air in tropical zone. Indoor air in greenhouse.

Reference no. 2

The term pollution degreee has been defined based
on different pollutants. P1 is a very low polluted
environment and P5 is a high polluted environment.
See table below.

Time of wetnessTime of wetness

Hours/year

Hours /ye ar % of year

Hours/yearHours/year

% of year

% of year% of year

Example of o ccurrence.

Example of o ccurrence.

Example of o ccurrence.Example of o ccurrence.

Indoor air in some production rooms. Ourdoor air in cold zone,
dry zo ne, par t s of t emperated zone.

Outdoor air in parts of temperated zone, parts of warm zone.
Indoo r ai r i n a nimal h o uses.

Category

Category

CategoryCategory

P1
(very low)

P2
(low)

P3
(medium)

P4
(high)

P5
(very high)

1) Limits if silver is used. 2) Limits for other materials than silver

SO

2

<10 <25 <3 <1 <10 <1 <2

10-30 25-250

30-100 150-500

100-300 500-1000

>300 >1000

NO

2

H2SCI2NH3+NH

1

3-10

)

2

3-20

)

1)

10-50

2)

20-100

50-1001)

2)

100-200

>1001)
>2002)

Reference no. 2

3333

µµµµg/m

Pollutants

Pollutants

Pollutants Pollutants

g/m

g/mg/m

+

1-2 10-250 1-5 2-20

2-5 250-1000 5-10 20-75

5-10

>10 >10000 >50 >150

1000­10000

-

CI

10-50 75-150

Soot

Remarks

Remarks

RemarksRemarks

Rooms
purified

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Handling aggressive environments

In ANSI/ISA S71-04-85 4 severity levels are defined.
The different severity levels are described as follows:

- Severity level G1- Mild
An environment sufficiently well-controlled such
that corrosion is not a factor in determining
equipment reliability.

- Severity level G2 - Moderate
An environment in which the effects of corrosion
are measurable and may be a factor in
determining equipment reliability.

- Severity level G3 - Harsh
An environment in which there is a high
probability that corrosive attack will occur. These
harsh levels should prompt further evaluation
resulting in environmental controls or specially
designed and packaged equipment.

- Severity level GX - Severe
An environment in which only specially designed
and packaged equipment would be expected to
survive. Specifications for equipment in this class
are a matter of negotiation between user and
supplier.

In the figure some examples of application catego­ries have been identified based on the project.
These categories must only be used as guiding ex­amples. In case of doubt, you have to investigate
how the actual application is classified.

References

1. IEC 721-3-3 - Classification of environmental
conditions part 3: Classification of groups of envi­ronmental parameters and their severities. Sta­tionary use at weatherprotected locations.

2. Corrosion of Electronics - A Handbook based on
Experiences from a Nordic Research Project.
ISBN 91-87400-02-2 by the Swedish Corrosion
Institute, 1991.

3. ANSI/ISA S71.04-1985 - Environmental Condi­tions for Process Measurement and Control Sys­tems: Airborne Contaminants.

Time of wetness and polution degree have been
combined with the ANSI/ISA S17-04 standard in the
figure below.

Reference no. 2

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Handling aggressive environments

®

Drives

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175R0375 MN90I102

Danfoss can accept no responsibility for possible errors in catalogues, brochures and other printed material.
Danfoss reserves the right to alter its products without notice. This applies to products already on order provided that such altera­tions can be made without subsequential changes being necessary in specifications already agreed.

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