Problem with Power Cabinet blowing fuses

[collin1443]

Hi there,

I have a ----y problem as follows:

I have a ABB disconnect switch Fused at 60A, supplying 3 phase 575V(North America) to a Power Cabinet.

The Power Cabinet has several motors and a 6000VA transformer, that steps down the voltage to 230VAC/120VAC single phase.

The Cabinet also powers another Cabinet, a 15A Control Cabinet at 120VAC

Twice now, the fuses on the Power Cabinet have blown on the primary side of the transformer, and 2 VFD's
when the ABB disconnect is either being closed or opened.(We turn the disconnect off at night, and turn it on in the morning. It has only happened 2x but we have closed the disconnect probably 30-40X already.

The Transformer is fused as 6000/575V = 12A Time Delay

The 2 Motor VFD's are both 2A, and are Fused at 3.5A

What could be causing the Fuses to blow? is the transformer surging the 3 phase line?

The whole 3phase line seems to be surging, since the transformer, and the 2 motor VFD's are
the only device drawing current in the Cabinet.

Any suggestions to debug this issue?
Collin

 

[Deleted member 9648]

There is always a huge surge when a transformer magnetises on being energised....usually 6x plus the normal full load current. You could try a type D mcb on the primary side.

 

[Darkwood]

As mentioned above transformers have a high inrush current and you may need to consult fuse manufacturers for correct type needed, but also consider the switchfuse itself if its old and the make and breaks is sluggish this will spike your suppy or if their is delay between the different phases making and breaking when you switch it on or off, the difference may only be a fraction of a second in some cases to cause problems.