Control With Brake Function - Danfoss VLT AQUA Drive FC 202 Design Manual

Introduction
Leakage current
2 2
Illustration 2.22 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.
36
Design Guide
Leakage current
THVD=0%
THVD=5%
Illustration 2.23 Main Contributions to Leakage Current
Leakage current [mA]
Illustration 2.24 Influence of the Cut-off Frequency of the RCD
What is Responded to/Measured

2.14 Control with Brake Function

2.14.1 Selection of Brake Resistor
In certain applications, for instance centrifuges, it is
desirable to bring the motor to a stop more rapidly than
can be achieved through controlling via ramp down or by
free-wheeling. In such applications, dynamic braking with a
braking resistor can be utilised. Using a braking resistor
ensures that the energy is absorbed in the resistor and not
in the frequency converter.
If the amount of kinetic energy transferred to the resistor
in each braking period is not known, the average power
can be calculated based on the cycle time and braking
time also called intermittent duty cycle. The resistor
intermittent duty cycle is an indication of the duty cycle at
Danfoss A/S © Rev. 06/2014 All rights reserved.
RCD with low f
cut-
RCD with high f
50 Hz 150 Hz
Mains 3rd harmonics
cut-
f Frequency
sw
Cable
100 Hz
2 kHz
100 kHz
MG20Z202