11 Mains
11.1 Mains Configurations
There are several types of AC mains systems for supplying
power to frequency converters. Each affects the EMC
characteristics of the system. The 5-wire TN-S systems are
regarded as best regarding EMC, while the isolated IT
system is the least preferred.
System
type
Description
TN mains
systems
There are 2 types of TN mains distribution systems:
TN-S and TN-C.
TN-S
A 5-wire system with separate neutral (N) and
protective earth (PE) conductors. It provides the
best EMC properties and avoids transmitting
interference.
TN-C
A 4-wire system with a common neutral and
protective earth (PE) conductor throughout the
system. The combined neutral and PE conductor
results in poor EMC characteristics.
TT mains
systems
A 4-wire system with a grounded neutral conductor
and individual grounding of the drive system. It has
good EMC characteristics when grounded properly.
IT grid
system
An isolated 4-wire system with the neutral
conductor either not grounded or grounded via an
impedance.
Table 11.1 AC Mains Systems and EMC Characteristics
11.2 Mains Terminal Connections
When connecting the mains, observe the following:
•
Size the wiring based on the input current of the
frequency converter. For maximum wire sizes, see
chapter 6.5 Power-dependent Specifications
.
•
Comply with local and national electrical codes
for cable sizes.
NOTICE
MULTIPLE MAINS CABLES
If connecting more than 1 set of mains terminals, use the
same number, size, and length of cables for each set of
terminals. For example, do not use 1 cable on one mains
terminal and 2 cables on another mains terminal.
2-drive module systems
and
show the mains
terminal connections for 6-pulse and 12-pulse 2-drive
systems, respectively.
•
If a common terminal design is used with a 6-
pulse, 2-drive system, there is 1 set of mains
terminals.
•
Common terminal design cannot be used with
12-pulse connection of mains in a 2-drive module
systems. The mains cables are connected directly
to the drive input terminals.
•
There are individual brake terminals available in
each drive module. Connect an equal number of
recommended cables to the individual brake
terminals.
4-drive module systems
shows the mains terminal connections for
4-drive systems. If a common terminal design is used, there
is 1 set of mains terminals in each cabinet.
11.3 12-pulse Disconnector Configuration
This section describes how to use a disconnector for a 12-
pulse drive system. When using disconnectors or
contactors, make sure to install an interlock. See
. When installed, both contactors or discon-
nectors must close to avoid 1 set of rectifiers not working.
Use NC auxiliary contacts with contactors or mains discon-
nectors. Connect the interlock in series with the Klixon
switch of the brake. If only 1 contactor/disconnector has
closed, the LCP shows the error
Brake IGBT Fault
and does
not allow the drive system to power the motor.
shows a BRF connection with 12-pulse
disconnector and interlock.
Mains
Design Guide
MG37N102
Danfoss A/S © 6/2016 All rights reserved.
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