32
Digitax HD M75X Series Installation and Technical Guide
Issue Number: 5
Where:
V
Air-flow in m
3
per hour (1 m
3
/hr = 0.59 ft
3
/min)
T
ext
Maximum expected temperature in °C
outside
the enclosure
T
int
Maximum permissible temperature in °C
inside
the enclosure
P
Power in Watts dissipated by
all
heat sources in the enclosure
k
Ratio of
Where:
P
0
is the air pressure at sea level
P
I
is the air pressure at the installation
Typically use a factor of 1.2 to 1.3, to allow also for pressure-drops in dirty air-filters.
Example
To calculate the size of an enclosure for the following:
•
Three drives operating
•
External EMC filter for each drive
•
Braking resistors are to be mounted outside the enclosure
•
Maximum ambient temperature inside the enclosure: 40 °C
•
Maximum ambient temperature outside the enclosure: 30 °C
For example, dissipation of each drive: 101 W and dissipation of each external EMC filter: 6.9 W (max).
Total dissipation: 3 x (101 + 6.9) = 323.7 W
Insert the following values:
T
int
40 °C
T
ext
30 °C
k
1.3
P
323.7 W
Then:
=
126.2 m
3
/hr (74.5 ft
3
/min)
(1 m
3
/ hr = 0.59 ft
3
/min)
3.11 Enclosure design and drive ambient temperature
Drive derating is required for operation in high ambient temperatures
Totally enclosing the drive in either a sealed cabinet (no airflow) or in a well ventilated cabinet makes a significant difference on drive cooling.
The chosen method affects the ambient temperature value (T
rate
) which should be used for any necessary derating to ensure sufficient cooling for the
whole of the drive.
The ambient temperature for the four different combinations is defined below:
1. Totally enclosed with no air flow (< 2 m/s) over the drive T
rate
= T
int
+ 5 °C
2. Totally enclosed with air flow (> 2 m/s) over the drive T
rate
= T
int
Where:
T
ext
= Temperature outside the cabinet
T
int
= Temperature inside the cabinet
T
rate
= Temperature used to select current rating from tables in Chapter 6
3.12 Drive cooling fan operation
The drive is ventilated by an internally mounted fan(s).
The drive cooling fan on all sizes is variable speed. The drive controls the speed at which the fan runs based on the drive's thermal model system.
The maximum speed at which the fan operates can be limited in Pr
06.045
. This could incur an output current derating. Refer to section 3.18
on page 43 for information on fan removal.
3.13 Braking resistor
3.13.1 Compact braking resistor
Po
Pl
-------
V
3 1.3
323.7
40 30
–
---------------------------------------
=
When using the compact brake resistor the drive must be mounted vertically.
WARNING
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