How to determine fuse size for DC line for based on AC load?

[izuanabd]

Hi guys..
I'm newbie here..

Just need your help me in this to clarify this matter.

let say i have an AC motor (3phase) that supplied by DC line through an inverter.. And i want to put fuse in this dc line..

How to determine the value of fuse size?

Can I just divide the motor power by DC voltage?

i.e
DC input = 600V
AC motor (3phase)
P=80kW
V=530V
f.l.c= 100A

Thank you

 

[broadgage]

At the very least one would have allow for the both the starting current of the motor, and the (probably small) losses in the inverter.

Sounds rather unusual, is this a DC grid supply ? or a very large battery ? or perhaps an electric railway ?

In the absence of any manufactuerers instructions, I would size the fuse according to the maximum rated input of the inverter, and then select a suitable wire size, according to the NEC or other codes if not in the USA.
Ensure that the fuse is listed for 600 V DC.
Overload protection of the motor may be required, but this is often built into the inverter.

Some specialist applications, for example on board vehicles, or the internal wiring of an appliance/machine are not covered by the NEC or other nations codes. However such codes are still a useful guide as to correct sizing of fuses and cables etc, and should be followed so far as reasonable even if not mandatory.

 

[petersonra]

I would be inclined to divide the power the motor uses by the efficiency of the invertor and multiply the result by 1.25 to get the kw requirements for the DC side and size the fuse accordingly. Presumbaly with a dual element fuse.

 

[winnie]

As I recall, Hitachi VFDs have specific instructions for supplying power via the DC bus, bypassing the input rectifiers. These instructions probably discuss protection of the DC conductors.

-Jon