Technical data 163
Derating
The load capacity (I
N
, I
Ld
, I
Hd
; note that I
max
is not derated) decreases in certain
situations. In such situations, where full motor power is required, oversize the drive so
that the derated value provides sufficient capacity.
Note: The DriveSize dimensioning PC tool available from ABB
(http://new.abb.com/drives/software-tools/drivesize
) is also suitable for derating.
Note: If several situations are present at a time, the effects of derating are
cumulative.
Example 1: How to calculate the derated current
The IP21 drive type is ACS580-01-062A-4, which has motor current 62 A. Calculate the derated
motor current (
I
N
) at 4kHz switching frequency, at 1500 m altitude and at 50 °C ambient
temperature as follows:
Switching frequency derating (page 167):
No derating needed for 4 kHz.
Altitude derating (page 166):
The derating factor for 1500 m is 1 - 1/10 000 m · (1500 - 1000) m = 0.95.
The motor becomes I
N
= 0,95 · 62 A = 58.9 A.
Ambient temperature derating, IP21 (UL Type 1) (page 164):
The derating factor for 50 °C ambient temperature = 0.90.
The derated motor current becomes then I
N
= 0,90 · 58.9 A = 53.01 A.
Example 2: How to calculate the required drive
If your application requires continuous 12.0 A of motor current (I
N
) at 8 kHz switching frequency,
the supply voltage is 400 V and the drive is situated at 1500 m altitude and at 35 °C ambient
temperature, calculate the appropriate IP21 drive size requirement as follows:
Switching frequency derating (page 167):
The minimum size required is I
N
= 12.0 A / 0.65 = 18.46 A,
where 0.65 is the derating for 8 kHz switching frequency (frames R2…R3).
Altitude derating (page 166):
The derating factor for 1500 m is 1 - 1/10 000 m · (1500 - 1000) m = 0.95.
The minimum size required becomes then I
N
= 18.46 A / 0.95 = 19.43 A.
Ambient temperature derating, IP21 (UL Type 1) (page 164):
No derating needed for 35 °C ambient temperature.
Referring to I
N
in the ratings tables (starting from page 160), drive type ACS580-01-026A-4
exceeds the I
N
requirement of 19.43 A.
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