Earth Leakage Current; Selection Of Brake Resistor - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

3.6.1. Earth Leakage Current

3.7.1. Selection of Brake Resistor

To handle higher demands by generatoric braking a brake resistor is necessary. Using a brake
resistor ensures that the energy is absorbed in the brake resistor and not in the frequency con-
verter.
If the amount of kinetic energy transferred to the resistor in each braking period is not known,
the average power can be calculated on the basis of the cycle time and braking time also called
intermitted duty cycle. The resistor intermittent duty cycle is an indication of the duty cycle at
which the resistor is active. The below figure shows a typical braking cycle.
The intermittent duty cycle for the resistor is calculated as follows:
Duty cycle = t
T = cycle time in seconds
t is the braking time in seconds (of the cycle time)
b
By altitudes above 2 km, please contact Danfoss Drives regarding PELV.
Warning:
Touching the electrical parts may be fatal - even after the equipment has been dis-
connected from mains.
Also make sure that other voltage inputs have been disconnected, such as load
sharing (linkage of DC intermediate circuit), as well as the motor connection for
kinetic back-up.
Using VLT AutomationDrive FC 300: wait at least the amount of time indicated in
Safety Precautions
the -section.
Shorter time is allowed only if indicated on the nameplate for the specific unit.
Leakage Current
The earth leakage current from the FC 300 exceeds 3.5 mA. To ensure that the earth
cable has a good mechanical connection to the earth connection (terminal 95), the
cable cross section must be at least 10 mm
arately.
Residual Current Device
This product can cause a d.c. current in the protective conductor. Where a residual
current device (RCD) is used for extra protection, only an RCD of Type B (time de-
layed) shall be used on the supply side of this product. See also RCD Application
Note MN.90.GX.02.
Protective earthing of the frequency converter and the use of RCD's must always
follow national and local regulations.
NB!
Motor suppliers often use S5 when stating the permissible load which is an expres-
sion of intermittent duty cycle.
/T
b
MG.33.B9.02 - VLT ® is a registered Danfoss trademark
3. Introduction to FC 300
2 or 2 rated earth wires terminated sep-
3
43