Control With Brake Function - Danfoss VLT AQUA Design Manual

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VLT AQUA Drive Design Guide
Leakage Current
The earth leakage current from the frequency converter 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
separately.
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 delayed) shall be used on the supply side of this product. See also RCD Application Note MN.90.Gx.yy.
Protective earthing of the frequency converter and the use of RCD's must always follow national and local regulations.

2.13. Control with brake function

2.13.1. 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 may be utilized. 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 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
b
T = cycle time in seconds
t is the braking time in seconds (as part of the total cycle time)
b
Danfoss offers brake resistors with duty cycle of 5%, 10% and 40% suitable for use with the FC202 AQUA drive series. If a 10% duty cycle resistor is
applied, this is able of absorbing braking power upto 10% of the cycle time with the remaining 90% being used to dissipate heat from the resistor.
For further selection advice, please contact Danfoss.
NB!
If a short circuit in the brake transistor occurs, power dissipation in the brake resistor is only prevented by using a mains switch or
contactor to disconnect the mains for the frequency converter. (The contactor can be controlled by the frequency converter).
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MG.20.N3.02 - VLT is a registered Danfoss trademark
2. Introduction to VLT AQUA Drive
2
or 2 rated earth wires terminated
2
35