Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 423)

Component Definition and Maintenance 6-79
7000 “C” Frame 7000L-UM300I-EN-P – June 2013
Coolant
The cooling fluid is a mixture of de-ionized water and ethylene
glycol. De-ionized water has been purified of most ionized solids
and has very low conductivity. The ethylene glycol is an iron- and
chloride-free type and also has low conductivity.
Water is an active solvent and gathers contaminants from everything
it contacts. In nature, ionized solids such as Sodium (Na
+
), Calcium
(Ca +2 ) and chloride (Cl
-
) are stripped from rocks and soil by water.
Also found in water are organic molecules from decaying debris,
bacteria and microbes that normally grow in water, and dissolved
ionized gases such as chlorine (Cl
2
) and carbon dioxide (CO
2
).
Conductivity is primarily the result of ionized solids and gases in
water. The other materials in water contribute very little to electric
current flow. When a voltage is impressed on water, current flows by
using the ionic molecules as stepping stones for the current. Most
bacteria and organic materials offer few stepping stones for current,
so if the ionized solids and gases are removed, the water becomes
relatively non-conductive.
Dissolved ionized solids and gases can be removed by using ion
exchange resins. Such resins attract ions in the water replacing them
with H
+
and OH
-
ions, which ultimately join to form water. Ion
exchange resins are synthetic polymers with several ion exchange
sites attached to the surface. The ion exchange resins gradually lose
their effectiveness and need to be replaced or recharged.
NOTE: Do not recycle the de-ionizing cartridge because it has been
contaminated by ethylene glycol and would contaminate the
recycling facility.
It is imperative that iron- and chloride-free ethylene glycol is used.
This is pure ethylene glycol without corrosion inhibitors and other
additives, which increase the conductivity of the coolant. In addition,
de-ionized water may be added to the system for top up. Distilled
water can only be used when no de-ionized water is available, and
when it is necessary to run the drive on line. Using distilled water
will significantly reduce the life of the ion exchange resin, and also
reduce the life of mesh filters.