Brake Functions - Danfoss VLT AutomationDrive FC 300 Design Manual

Introduction
WARNING
Touching the electrical parts could be fatal - even after the
equipment has been disconnected from mains.
Also make sure that other voltage inputs have been
disconnected, such as load sharing (linkage of DC
3 3
intermediate circuit), as well as the motor connection for
kinetic back-up.
Before touching any electrical parts, wait at least the
amount of time indicated in Table 2.1.
Shorter time is allowed only if indicated on the nameplate
for the specific unit.
Follow national and local codes regarding protective
earthing of equipment with a leakage current > 3,5 mA.
Frequency converter technology implies high frequency
switching at high power. This will generate a leakage
current in the earth connection. A fault current in the
frequency converter at the output power terminals might
contain a DC component which can charge the filter
capacitors and cause a transient earth current.
The earth leakage current is made up of several contri-
butions and depends on various system configurations
including RFI filtering, screened motor cables, and
frequency converter power.
Illustration 3.28 Cable Length and Power Size Influence on
Leakage Current. Pa > Pb
Illustration 3.29 Line Distortion Influences Leakage Current
NOTE
When a filter is used, turn off 14-50 RFI Filter when
charging the filter, to avoid that a high leakage current
makes the RCD switch.
44
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Leakage current [mA]
a
b
Cable length [m]
Leakage current [mA]
THVD=0%
THVD=5%
MG33BE02 - VLT
®
VLT AutomationDrive FC 300 Design Guide, 0.25-75 kW
EN/IEC61800-5-1 (Power Drive System Product Standard)
requires special care if the leakage current exceeds 3.5mA.
Earth grounding must be reinforced in one of the
following ways:
•
•
See EN/IEC61800-5-1 and EN50178 for further information.
Using RCDs
Where residual current devices (RCDs), also known as earth
leakage circuit breakers (ELCBs), are used, comply with the
following:
Illustration 3.30 Main Contributions to Leakage Current
Illustration 3.31 The Influence of the Cut-off Frequency of the
RCD on What Is Responded to/measured
See also RCD Application Note, MN90G

3.8 Brake Functions

Braking function is applied for braking the load on the
motor shaft, either as dynamic braking or static braking.
®
is a registered Danfoss trademark
Earth ground wire (terminal 95) of at least 10
mm 2
Two separate earth ground wires both complying
with the dimensioning rules
Use RCDs of type B only which are capable of
detecting AC and DC currents
Use RCDs with an inrush delay to prevent faults
due to transient earth currents
Dimension RCDs according to the system configu-
ration and environmental considerations
RCD with low f
L [mA]
leakage
RCD with high f
50 Hz 150 Hz f
sw
Mains 3rd harmonics
Cable
f
s
Leakage current [mA]
100 Hz
2 kHz
100 kHz
cut-off
cut-off
f [Hz]