Emerson Unidrive M700 Installation Manual page 60

For high-inertia loads or under continuous braking, the continuous power dissipated in the braking
resistor may be as high as the power rating of the drive. The total energy dissipated in the braking
resistor is dependent on the amount of energy to be extracted from the load.
The instantaneous power rating refers to the short-term maximum power dissipated during the on
intervals of the pulse width modulated braking control cycle. The braking resistor must be able to
withstand this dissipation for short intervals (milliseconds). Higher resistance values require
proportionately lower instantaneous power ratings.
In most applications, braking occurs only occasionally. This allows the continuous power rating of the
braking resistor to be much lower than the power rating of the drive. It is therefore essential that the
instantaneous power rating and energy rating of the braking resistor are sufficient for the most
extreme braking duty that is likely to be encountered.
Optimization of the braking resistor requires careful consideration of the braking duty.
Select a value of resistance for the braking resistor that is not less than the specified minimum
resistance. Larger resistance values may give a cost saving, as well as a safety benefit in the event
of a fault in the braking system. Braking capability will then be reduced, which could cause the drive
to trip during braking if the value chosen is too large.
The following external brake resistors are available from the supplier of the drive for sizes 3 and 4.
Table 4-8 External brake resistors (40° C ambient) for drive sizes 3 and 4
Ohmic
Part Part
value
number desc
Pr10.061
DBR,
1220- 100 W,
20 Ω
2201 20R, 130
x 68, TS
DBR,
1220- 100 W,
40 Ω
2401 40R, 130
x 68, TS
DBR,
1220- 100 W,
80 Ω
2801 80R, 130
x 68, TS
The brake resistors can be used in a series or parallel to get the required resistance and power
depending on the size of the drive as per Table 4-7. The brake resistor is equipped with a thermal
switch. The thermal switch should be integrated in the control circuit by the user.
60
Cont Max inst Pulse
power power power
rating rating 1/120 s
Pr10.030 ton = 1 ms (ED 0.8 %)
100 W 2.0 MW 2300 W
100 W 1.6 MW 1900 W
100 W 1.25 MW 1500 W
Unidrive M/HS Frame 3 and 4 Power Installation Guide
Pulse Pulse
power power
5/120 s 10/120 s 40/120 s
(ED 4.2 %) (ED 8.3 %) (ED 33 %)
1000 W 650 W
900 W 610 W
775 W 570 W
Pulse
Time
power
constant
Pr10.031
250 W 20
240 W 16
230 W 12.5
Issue Number: 3