Installation Guide
Danfoss Drive PM.doc Page 2 of 3
b. Because the loading of the air filters can vary dramatically from one installation to another, it
is important to initially check the air filters frequently to establish the required inspection
interval.
4. Check the tightness of connections.
a. Loose power connections can cause extra heating and/or arcing. The heating reduces
efficiency and can actually melt down connectors. The arcing can cause intermittent currents
and electrical noise. These can disrupt the operation of the drive.
b. Loose or corroded ground connections can cause electrical noise problems. All of the VLT
drives have some degree of electrical noise filtering. Some of this electrical noise is sunk to
earth ground. Without a reliable ground connection the noise filters cannot operate as
designed. In addition, a poor ground connection can become a safety issue.
c. Loose control wires can cause intermittent operation of equipment. Loose or missing
shielding for signal wires can cause erratic operation of the drive. In a extreme case this can
even cause the drive to trip off.
d. The preventive maintenance procedure would involve first turning off power to the drive and
waiting until the DC bus capacitors have discharged to a safe level. Then all of the
accessible connections should be inspection for corrosion and checked for tightness. It
should not be necessary to disassemble the drive to perform this operation.
e. This should be performed once the drive is installed and at least annually afterward. If the
drive is subjected to vibration or wide temperature variations, it should be checked more
frequently.
5. Check cooling fans.
a. Cooling fans are used to remove heat from the drive. Proper operation of the cooling fans
helps ensure long drive life by keeping the drive’s components cool. The cooling system
should be inspected at least annually, more frequently when the drive is exposed to extreme
conditions.
b. Inspect the heat sinks, air inlets, and air outlets to ensure that there is an open path for air
flow.
c. The cooling fans in many VLT drives will turn themselves off when the drive’s temperature is
low enough to not require forced ventilation. To check for proper fan operation if the fans are
not running, remove power from the drive. When power is reapplied the fans should start
and run for a few seconds.
d. Listen for unusual noises from the fans when they are running.
e. The VLT drives use a heat sink temperature sensor to help indicate if there is a problem with
the cooling system. If the drive issues a HEAT SINK OVERTEMP. warning or alarm, check
the cooling system carefully.
6. Check bus capacitors for voltage balance and/or physical damage.
a. The large DC bus capacitors in the drives are subject to deterioration over an extended
period of time. It generally takes a significant number of years before any problems occur,
although high ambient temperatures and other factors can accelerate this process.
b. Problems with the DC bus capacitors generally first show up as a large “AC ripple voltage”
being superimposed on the DC bus. The VLT 6000 continually monitors for excessive DC
bus ripple, so it will generally provide an early warning of bus capacitor problems. If the drive
gives a MAINS PHASE LOSS warning or alarm and a check of the input AC power line
shows it to be balanced under loaded conditions, the DC bus capacitors should be checked
carefully.
c. On drives with an input power line voltage of 380 V AC or larger, the DC bus capacitors are
connected as two banks that are in series with each other. With power applied to the drive,
the voltage across the positive half should be within 10% of the voltage across the negative
half.