GE AF-650 GP Series, Design And Installation Manual

Page: 78 / 166

Figure 6.22
NOTE!
Make sure the resistor is designed to handle the required
braking time.
The max. 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
br
Ω =
U
dc
2
P
peak
where
P
peak
= P
motor
x M
br
[%] x η
motor
x η
DRIVE
[W]
As can be seen, the brake resistance depends on the
intermediate circuit voltage (U
dc
).
The AF-650 GP brake function is settled in four areas of
line power.
Size Brake active Warning before cut-out Cut-out (trip)
3 x 200–240 V 390 V (UDC) 405 V 410 V
3 x 380–480 V* 810 V/795 V 840 V/828 V 850 V/855 V
3 x 525–600 V 943 V 965 V 975 V
3 x 525–690 V 1084 V 1109 V 1130 V
Table 6.22
* Power size dependent
NOTE!
Check that the brake resistor can cope with a voltage of
410 V, 850 V, 975 V or 1,130 V.
The recommended brake resistance guarantees that the
adjustable frequency drive is able to brake at the highest
braking torque (M
br(%)
) of 160%. The formula can be
written as:
Rrec Ω =
Udc
2 x 100
Pmotor x Mbr (%) x
η
DRIVE x
η
motor
η
motor
is typically at 0.90
η
DRIVE
is typically at 0.98
For 200 V, 480 V and 600 V adjustable frequency drives,
R
rec
at 160% braking torque is written as:
200
V : Rrec =
107780
Pmotor
Ω
480
V : Rrec =
375300
Pmotor
Ω 1)
480
V : Rrec =
428914
Pmotor
Ω 2)
600
V : Rrec =
630137
Pmotor
Ω
690
V : Rrec =
832664
Pmotor
Ω
1) For adjustable frequency drives ≤ 10 hp [7.5 kW] shaft
output
2) For adjustable frequency drives 11–75 kW shaft output
NOTE!
If a brake resistor with a higher ohmic value is selected,
the 160% braking torque may not be achieved because
there is a risk that the adjustable frequency drive cuts out
for safety reasons.
NOTE!
If a short circuit in the brake transistor occurs, power
dissipation in the brake resistor is only prevented by using
a line switch or contactor to disconnect the line power for
the adjustable frequency drive. (The contactor can be
controlled by the adjustable frequency drive).
NOTE!
Do not touch the brake resistor, as it can get very hot
during/after braking. The brake resistor must be placed in
a secure environment to avoid fire risk.
CAUTION
Unit size 4x to 6x adjustable frequency drives contain more
than one brake chopper. Consequently, use one brake
resistor per brake chopper for those frame sizes.
Application Setup Examples AF-650 GP
TM
Design and Installation Guide
DET-767A 6-23
6 6