Danfoss VLT AQUA Drive FC 202 Design Manual page 64

System Integration
Load
3 3
Speed
Figure 3.18 Brake Resistor Duty Cycle
Calculate the intermittent duty cycle for the resistor as
follows:
Duty cycle=t
b
T =cycle time in seconds
t is the braking time in seconds (of the cycle time)
b
Danfoss offers brake resistors with duty cycles of 5%, 10%,
and 40%. When a 10% duty cycle is applied, the brake
resistors absorb braking energy for 10% of the cycle time.
The remaining 90% of the cycle time is used to dissipate
excess heat.
Ensure the brake resistor is dimensioned for the required
braking time.
Brake resistance calculation
To prevent the adjustable frequency drive from cutting out
for protection when the motor brakes, select resistor values
on the basis of the peak braking energy and the
intermediate circuit voltage. Calculate resistance of the
brake resistor as follows:
2
Udc
R = Ω
br
P
peak
The brake resistor performance depends on the DC link
voltage (U ).
dc
U is the voltage at which the brake is activated. The FC-
dc
series brake function is settled depending on the line
power supply.
62
ta tc tb to ta tc
T
/T
Danfoss A/S © 09/2014 All rights reserved.
®
VLT AQUA Drive FC 202
line power supply input
[V AC]
FC 202 3x200-240
FC 202 3x380-480
FC 202 3x525-600
tb to ta
FC 202 3x525-600
FC 202 3x525-690
Time
Table 3.18 DC link Voltage (U
1) Enclosure sizes A, B, C
2) Enclosure sizes D, E, F
Use the brake resistance R
frequency drive is able to brake at the highest braking
torque (M
R Ω =
rec
η
motor
η is typically at 0.98.
VLT
When a higher brake resistor resistance is selected, 160%/
150%/110% braking torque cannot be obtained, and there
is a risk that the adjustable frequency drive cuts out of DC
Link overvoltage for protection.
For braking at lower torque, for example 80% torque, it is
possible to install a brake resistor with lower power rating.
Calculate size using the formula for calculating R
Adjustable frequency drive D and F enclosure sizes contain
more than one brake chopper. Use a brake resistor for
each chopper for those enclosure sizes.
The VLT
most up-to-date selection data, and describes the
calculation steps in more detail, including:
•
•
•
•
Brake
active
[V DC]
390
778
1) 943
2) 1099
1099
)
dc
, to ensure that the adjustable
rec
) of 160%. The formula can be written as:
br(%)
2
U x 100
dc
P x M x η x η
motor br ( ) VLT motor
%
is typically at 0.90
®
Brake Resistor MCE 101 Design Guide contains the
Calculation of braking energy
Calculation of brake resistor peak power
Calculation of brake resistor average power
Braking of inertia
High Over
voltage voltage
warning alarm
[V DC] [V DC]
405 410
810 820
965 975
1109 1130
1109 1130
.
rec
MG20N622