Nidec Control Techniques Unidrive M Modular Installation Manual page 46

Safety information
Calculation of temperature rise in enclosure inputs
Table 5-3 Example data
Output sharing choke loss under single unit (L2)
Total loss of single drive
Number of drives in enclosure
Width of enclosure
Depth of enclosure
Open area of roof vent (outlet)
Open area of inlet vent
External ambient
Altitude derate factor (Cf x Df)
For this example it is assumed the drive is in an altitude below 1000 m
and the enclosure it is mounted in has input and output ventilation.
Calculate open area % of venting and recirculation factor
Open area of roof + open area of inlet x 100
-------------------------------------------------------------------------------------------------------------------------- -
Open area of venting % =
= (0.27 + 0.15) x 100 / (2 x 0.8 x 0.5)
= 52.5%
From Figure 5-29 the re-circulation factor = 0.76.
Figure 5-29 Recirculation factor
1.2
1
0.8
0.6
0.4
0.2
0
0 20 40
This is an approximation of the amount of air that is re-circulated within
the enclosure due to inlet and outlet venting restrictions. The factor has a
safety factor built in to it to ensure a safe result. The factor has been
calculated using CFD software, testing the amount of heat flow back into
the drive when different vent restrictions are given. The factor can also
be applied to an Unidrive M size 9/10 E and separated Unidrive M size 9/
10 D.
Calculate loss which affects the drive inlet air temperature
Loss affecting drive temperature (Pr) = Lower choke Loss (Pc) +
(Total loss of single drive (Dp) x Recirculation factor (Rf))
= 250 + (4290 x 0.76)
= 3510 W
NOTE
This is the loss from 1 drive unit only as simulations have shown that
with drives mounted inline and in a symmetric system the losses are
shared equally.
46
Introduction Product information
4290 W
0.27 m
0.15 m
2 x cubicle width x cubicle depth
60 80 100
Open area (%)
System configuration
Calculate temperature rise
Table 5-4 Air flow rates
Modules
250 W
Inverter
2 Rectifier
0.8 m
Calculating temperature rise in enclosure
0.5 m
dT = 3kPr/V
3
Where:
3
V = Airflow in m
dT = Temperature rise
30 °C
Pr = Loss affecting drive temp
1
k = 1 / Altitude de-rate
Therefore ambient temperature rise (dT):
= (3 x 1 x 3510.4) / 305
= 34.5 °C
So,
Ambient temperature inside enclosure = External ambient +
temperature rise = 64.5 °C
This shows that with the maximum allowable ambient drive temperature
of 40 °C, the enclosure will overheat.
Processing results
Option 1: If the absolute temperature inside the enclosure is still less
than 50 °C, select a drive with the correct rating at 50 °C.
Option 2: Add more venting, if possible, to reduce the recirculation and
recalculate.
Option 3: Add an enclosure fan.
Option 4: Redesign the enclosure so that the drives can be through
panel mounted. This means that most of the heat can escape outside
the main enclosure, and the input air into the heat sinks will remain at the
external ambient and not be affected by recirculation. Refer to section
5.5.2 Through-panel mounting on page 37.
NOTE
Heat loss through the front of the drive still needs to be considered.
Adding enclosure fan
Calculate required flow rate
• Fan needs to remove the effect of re-circulation and the added
120
choke loss.
• Loss effecting drive temp (Pr) = 3510.4 W
• The above Loss of 3510.4 W is for one drive only, so with an
enclosure of 2 units the total loss to remove = 7020.8 W
Calculate the temperature rise allowed in the enclosure:
Temperature rise (dT) = (Allowable drive ambient - 5 {safety
= (40 - 5) - 30
= 5°C
Then using:
V = 3kPr/ (dT)
Flow rate required to remove loss = (3x1x7020.8) / 5
= 4212.5 m
Calculate back pressure on fan
Open area of venting %
Mechanical
Electrical Installation
Installation
Flow rate (m3/hr)
3
/hr (Unidrive flow rate = 305)
factor}) - External ambient
3
/hr
Open area of roof + open area of inlet x 100
= -------------------------------------------------------------------------------------------------------------------------- -
2 x cubicle width x cubicle depth
Unidrive M Modular Installation Guide
402
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Issue Number: 2