General Aspects Of Emc; Overview Of Emc Emissions - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

Product Overview
CAUTION
INSTALLATION ENVIRONMENTS
Do not install the frequency converter in environments
with airborne liquids, particles, or gases that may affect
or damage the electronic components. Failure to take
3 3
necessary protective measures increases the risk of
stoppages, potentially causing equipment damage and
personnel injury.
Liquids can be carried through the air and condense in the
frequency converter and may cause corrosion of
components and metal parts. Steam, oil, and salt water
may cause corrosion of components and metal parts. In
such environments, use equipment with enclosure rating
IP54. As an extra protection, coated printed circuit boards
can be ordered as an option (standard on some power
sizes).
Airborne particles such as dust may cause mechanical,
electrical, or thermal failure in the frequency converter. A
typical indicator of excessive levels of airborne particles is
dust particles around the frequency converter fan. In dusty
environments, use equipment with enclosure rating IP54 or
a cabinet for IP20/TYPE 1 equipment.
In environments with high temperatures and humidity,
corrosive gases such as sulphur, nitrogen, and chlorine
compounds cause chemical processes on the frequency
converter components.
Such chemical reactions rapidly affect and damage the
electronic components. In such environments, mount the
equipment in a cabinet with fresh air ventilation, keeping
aggressive gases away from the frequency converter.
An extra protection in such areas is a coating of the
printed circuit boards, which can be ordered as an option.
Before installing the frequency converter, check the
ambient air for liquids, particles, and gases. This is done by
observing existing installations in this environment. Typical
indicators of harmful airborne liquids are water or oil on
metal parts, or corrosion of metal parts.
Excessive dust particle levels are often found on instal-
lation cabinets and existing electrical installations. One
indicator of aggressive airborne gases is blackening of
copper rails and cable ends on existing installations.

3.4 General Aspects of EMC

3.4.1 Overview of EMC Emissions

Frequency converters (and other electrical devices)
generate electronic or magnetic fields that may interfere
with their environment. The electromagnetic compatibility
36
®
VLT HVAC Basic Drive FC 101
(EMC) of these effects depends on the power and the
harmonic characteristics of the devices.
Uncontrolled interaction between electrical devices in a
system can degrade compatibility and impair reliable
operation. Interference may take the form of mains
harmonics distortion, electrostatic discharges, rapid voltage
fluctuations, or high-frequency interference. Electrical
devices generate interference along with being affected by
interference from other generated sources.
Electrical interference usually arises at frequencies in the
range 150 kHz to 30 MHz. Airborne interference from the
frequency converter system in the range 30 MHz to 1 GHz
is generated from the inverter, the motor cable, and the
motor.
Capacitive currents in the motor cable coupled with a high
dU/dt from the motor voltage generate leakage currents,
as shown in Illustration 3.52.
The use of a shielded motor cable increases the leakage
current (see Illustration 3.52) because shielded cables have
higher capacitance to ground than unshielded cables. If
the leakage current is not filtered, it causes greater
interference on the mains in the radio frequency range
below approximately 5 MHz. Since the leakage current (I
is carried back to the unit through the shield (I
only a small electro-magnetic field (I
motor cable according to Illustration 3.52.
The shield reduces the radiated interference, but increases
the low-frequency interference on the mains. Connect the
motor cable shield to the frequency converter enclosure as
well as on the motor enclosure. This is best done by using
integrated shield clamps to avoid twisted shield ends
(pigtails). Pigtails increase the shield impedance at higher
frequencies, which reduces the shield effect and increases
the leakage current (I
If a shielded cable is used for relay, control cable, signal
interface, and brake, mount the shield on the enclosure at
both ends. In some situations, however, it is necessary to
break the shield to avoid current loops.
If the shield is to be placed on a mounting plate for the
frequency converter, the mounting plate must be made of
metal, to convey the shield currents back to the unit.
Moreover, ensure good electrical contact from the
mounting plate through the mounting screws to the
frequency converter chassis.
When using unshielded cables, some emission
requirements are not complied with, although most
immunity requirements are observed.
To reduce the interference level from the entire system
(unit+installation), make motor and brake cables as short
as possible. Avoid placing cables with a sensitive signal
Danfoss A/S © 04/2016 All rights reserved.
), there is
3
) from the shielded
4
).
4
MG18C702
)
1