Drives and Controls
Frequency Converters
Frequency Converter
Danfoss VLT® Drives
Handling aggressive environments
VLT® is a trademark of Danfoss A/S
Handling aggressive environments
■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.
·Our small drives are designed for placement directly 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 enclosure 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.
MN.90.I1.02 - VLT is a registered Danfoss trademark |
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Handling aggressive environments
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 |
NH3 |
|
Hydrogen sulphide |
H2S |
|
Active organic nitrogen |
N2 |
Paper mills and |
Hydrogen sulphide |
H2S |
wood pulping |
Carbon monoxide |
CO |
|
Chlorine's |
Cl, Cl2 |
|
Active organic nitrogen |
N2 |
|
Hydrocarbons |
Cn, Hn |
Water |
Hydrocarbons |
Cn, Hn |
treatment |
|
|
|
|
|
Combustion of |
Hydrogen sulphide |
H2S |
fossil fuels/ |
Sulphur dioxide |
SO2,SO3 |
automative |
Nitrogen oxides |
NOx |
emmisions |
Carbon monoxied |
CO |
|
|
|
Sulphuric acid |
Hydrogen Chloride |
HCL |
manufacture |
Hydrocarbons |
Cn, Hn |
Fertilizer |
Hydrogen flouride |
HF |
manufacture |
Ammonia |
NH3 |
Steel manu- |
Hydrogen flouride |
HF |
facture and |
Hydrogen sulphide |
H2S |
ore smelting |
Sulphur dioxide |
SO2,SO3 |
|
|
|
Aluminium |
Hydrogen flouride |
HF |
manufacture |
Chlorine's |
Cl, Cl2 |
|
|
|
Foundries |
Mercaptans |
SB, R-SH |
|
Carbon |
C |
|
|
|
Cleaning of |
Ammonia |
NH3 |
products |
Chlorine's |
Cl, Cl2 |
|
|
|
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.
Reference No. 2
τ1 to τ 6 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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MN.90.I1.02 - VLT is a registered Danfoss trademark |
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