Brake Functions; Mechanical Holding Brake; Dynamic Braking - Danfoss VLT AutomationDrive FC 300 Design Manual

Product Introduction
3 3
Illustration 3.29 Influence of Line Distortion on Leakage
Current
NOTICE
When a filter is used, turn off 14-50 RFI Filter when
charging the filter to avoid a high leakage current
making the RCD switch.
If the leakage current exceeds 3.5 mA, EN/IEC61800-5-1
(Power Drive System Product Standard) requires that earth
grounding must be reinforced in one of the following
ways:
•
Earth ground wire (terminal 95) of at least 10
2
mm
•
2 separate earth ground wires both complying
with the dimensioning rules
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:
•
Use RCDs of type B only, 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
See also Protection Against Electrical Hazards.
Illustration 3.30 Main Contributions to Leakage Current
46
VLT
Leakage current [mA]
THVD=0%
THVD=5%
RCD with low f
L [mA]
cut-o
leakage
RCD with high f
cut-o
50 Hz 150 Hz f
f [Hz]
sw
Mains 3rd harmonics Cable
f
s
®
AutomationDrive FC 300 Design Guide 90-1200 kW
Illustration 3.31 Influence of the Cut-off Frequency of the RCD
What is Responded to/Measured

3.8 Brake Functions

The braking function - either static or dynamic - is used for
braking the load on the motor shaft.

3.8.1 Mechanical Holding Brake

A mechanical holding brake is an external piece of
equipment mounted directly on the motor shaft that
performs static braking. Static braking is when a brake is
used to clamp down on the motor after the load has been
stopped. A holding brake is either controlled by a PLC or
directly by a digital output from the frequency converter.
NOTICE
A frequency converter cannot provide a safe control of a
mechanical brake. A redundancy circuitry for the brake
control must be included in the installation.

3.8.2 Dynamic Braking

Dynamic braking is accomplished internally within the
frequency converter and is used to slow down the motor
to an eventual stop. Dynamic braking is applied using of
the following methods:
•
Resistor brake: A brake IGBT keeps the
overvoltage under a certain threshold by
directing the brake energy from the motor to the
connected brake resistor (2-10 Brake Function=[1])
•
AC brake: The brake energy is distributed in the
motor by changing the loss conditions in the
motor. The AC brake function cannot be used in
applications with high cycling frequency since
this will overheat the motor (2-10 Brake
Function=[2])
•
DC brake: An over-modulated DC current added
to the AC current works as an eddy current brake
(2-02 DC Braking Time≠0 s)
MG34S202 - Rev. 2013-08-19
Leakage current [mA]
100 Hz
2 kHz
100 kHz