Dynamic Braking; Selection Of Brake Resistor - GE AF-650 GP Design And Installation Manual

Application Set-Up Examples

6.6.2 Dynamic Braking

Dynamic Brake established by:
•
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 (parameter B-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 overheats the motor (parameter B-10 Brake
Function = [2]).
•
DC brake: An over-modulated DC current added
to the AC current works as an eddy current brake
(parameter B-02 and B-03 ≠ off).
6 6

6.6.2.1 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 converter. For more information, see the Brake
Resistor Design Guide, DET-700
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
which the resistor is active. Illustration 6.22 shows a typical
braking cycle.
NOTICE
Motor suppliers often use S5 when stating the
permissible load which is an expression of intermittent
duty cycle.
The intermittent duty cycle for the resistor is calculated as
follows:
Duty cycle = t
b
T = cycle time in s
t is the braking time in s (of the cycle time)
b
70
/T
Illustration 6.22 Typical Braking Cycle
NOTICE
Make sure that the resistor is designed to handle the
required braking time.
The maximum permissible load on the brake resistor is
stated as a peak power at a given intermittent duty cycle
and can be calculated as:
The brake resistance is calculated as shown:
R Ω =
br
where
P = P
peak motor
As can be seen, the brake resistance depends on the DC-
link voltage (U
Size
3 x 200–240 V
3 x 380–500 V
3 x 525–600 V
3 x 525–690 V
Table 6.22 Main Areas for Brake Function
1) Power size dependent
NOTICE
Check that the brake resistor can cope with a voltage of
410 V, 850 V, 975 V, or 1130 V.
The recommended brake resistance guarantees that the
frequency converter is able to brake at the highest braking
torque (M
br(%)
R Ω =
rec P
motor
η is typically at 0.90
motor
η is typically at 0.98.
DRIVE
For 200 V, 500 V, and 600 V frequency converters, R
160% braking torque is written as:
200 V : R
rec
DET-767c All rights reserved.
2
U
dc
P
peak
x M [%] x η x η [W]
br motor DRIVE
).
dc
Brake active Warning
before cut
out
390 V (UDC) 405 V
1) 810 V/795 V 840 V/828 V
943 V 965 V
1084 V 1109 V
) of 160%. The formula can be written as:
2
U x 100
dc
x M xη x η
( % )
br DRIVE motor
107780
= Ω
P
motor
Cut out (trip)
410 V
850 V/855 V
975 V
1130 V
at
rec
MG35M402