ABB ACQ810 - Fuses (IEC); Calculation Example

Technical data 107
Fuses (IEC)
gG and aR fuses for protection against short-circuit in the input power cable or drive are
listed below. Either fuse type may be used if it operates rapidly enough. Choose between
gG and aR fuses according to the table under Quick guide for selecting between gG and
aR fuses on page 110, or verify the operating time by checking that the short-circuit
current of the installation is at least the value given in the fuse table. The short-circuit
current can be calculated as follows:
where
I
k2-ph
= short-circuit current in symmetrical two-phase short-circuit (A)
U = network line-to-line voltage (V)
R
c
= cable resistance (ohm)
Z
k
= z
k
· U
N
2
/S
N
= transformer impedance (ohm)
z
k
= transformer impedance (%)
U
N
= transformer rated voltage (V)
S
N
= nominal apparent power of the transformer (kVA)
X
c
= cable reactance (ohm).
 Calculation example
Drive:
• ACQ810-04-414A-4
• supply voltage U = 410 V
Transformer:
• rated power S
N
= 3000 kVA
• rated voltage U
N
= 430 V
• transformer impedance z
k
= 7.2%.
Supply cable:
• length = 170 m
• resistance/length = 0.112 ohm/km
• reactance/length = 0.0273 ohm/km.
I
k2-ph
=
2 ·
R
c
2
+ (Z
k
+ X
c
)
2
U
·
(430 V)
2
3000 kVA
= 4.438 mohm
Z
k
= z
k
·
U
N
2
S
N
= 0.072
m
·
0.112
ohm
km
= 19.04 mohm
R
c
= 170