130BA056.10
1
3
2
5
4
6
b
a
M
1 Power supply (SMPS) including signal isolation of V DC,
indicating the intermediate current voltage
2 Gate drive for the IGBTs
3 Current transducers
4 Opto-coupler, brake module
5 Internal inrush, RFI, and temperature measurement circuits
6 Custom relays
a Galvanic isolation for the 24 V back-up option
b Galvanic isolation for the RS485 standard bus interface
Illustration 3.1 Galvanic Isolation
Installation at high altitude
WARNING
OVERVOLTAGE
Installations exceeding high altitude
limits may not comply with PELV requirements. The
isolation between components and critical parts could be
insufficient. There is a risk for overvoltage. To reduce the
risk for overvoltage, use external protective devices or
galvanic isolation.
For installations at high altitude, contact Danfoss regarding
PELV compliance.
•
380–500 V (enclosures A, B, and C): Above 2000
m (6500 ft)
•
380–500 V (enclosures D, E, and F): Above 3000 m
(9800 ft)
•
525–690 V: Above 2000 m (6500 ft)
3.2 EMC, Harmonics, and Ground Leakage
Protection
3.2.1 General Aspects of EMC Emissions
Frequency converters (and other electrical devices)
generate electronic or magnetic fields that may interfere
with their environment. The electromagnetic compatibility
(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.
•
High-frequency interference.
Electrical devices generate interference and are affected by
interference from other generated sources.
Electrical interference usually occurs 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, 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
.
The use of a screened motor cable increases the leakage
current (see
) because screened cables have
higher capacitance to ground than unscreened 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
1
)
is carried back to the unit through the screen (I
3
), there is
only a small electro-magnetic field (I
4
) from the screened
motor cable, see
The screen reduces the radiated interference, but increases
the low-frequency interference on the mains. Connect the
motor cable screen to the frequency converter enclosure
as well as on the motor enclosure. The connection is best
done by using integrated screen clamps to avoid twisted
screen ends (pigtails). Pigtails increase the screen
impedance at higher frequencies, which reduces the screen
effect and increases the leakage current (I
4
).
If a screened cable is used for relay, control cable, signal
interface, and brake, mount the screen on the enclosure at
both ends. In some situations, however, it is necessary to
break the screen to avoid current loops.
If placing the screen on a mounting plate for the
frequency converter, use a mounting plate of metal to
convey the screen currents back to the unit. Moreover,
ensure good electrical contact from the mounting plate
through the mounting screws to the frequency converter
enclosure.
When using unscreened 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
System Integration
VLT
®
Refrigeration Drive FC 103
40
Danfoss A/S © 08/2015 All rights reserved.
MG16G202
3
3
