3. System Design
MV3DB Series DB Units
ALSPA MV3000e Dynamic Braking Units
(07/06)
Page 3-4
Long term average power =
energy
total cycle time
=
3
2
1
2
2
4
.
182
)
(
t
N
N
J
−
where
t
3
= total stop-start cycle time in seconds.
Example:
Suppose we have an inertia of 0.9 kgm
2
, a top speed of 3000 r/min and we require to brake to
zero speed in 2 seconds repeated every 100 seconds.
Assume DB switching voltage is 732 V.
R =
)
(
2
.
91
1
2
2
1
2
N
N
JN
t
V
DB
−
=
)
0
3000
(
3000
9
.
0
2
732
2
.
91
2
−
×
×
×
×
= 12.07
Ω
Peak power
=
J N
N
N
t
(
)
.
2
1
2
1
91 2
−
=
2
2
.
91
3000
)
0
3000
(
9
.
0
×
×
−
×
= 44408 Watts or 44.4 kW
Long term average power =
3
2
1
2
2
4
.
182
)
(
t
N
N
J
−
=
100
4
.
182
)
0
3000
(
9
.
0
2
×
−
×
= 444 Watts
Current in resistor
=
R
V
DB
=
07
.
12
732
= 60.6 A
Hence MV3DB092S5 in frame size 4 will achieve this duty.
3.6
Equivalence of Duty Cycles
Ratings in Table 2-1 are given for a braking time of 18 seconds.
3.6.1
For braking times longer than 18 seconds:
•
The graph shown in Figure 3-3 can be used to find the derating factor for the peak power.
•
The long term average power must not exceed 10% of the “Nominal Power during 18
seconds ON time” given in Table 2-1.
