Supplying a VFD with power. 1

[itsmoked]

I'm going in circles here.

This is what the maker describes but how does this distill into hardware?

The drive draws 48A. Wire size 125% x 48A = 60A
That's a 30,60,100 disconnect.

But then they state a 75A breaker. I'd expect the breaker would be in the main panel. But, It's going to need wire for 75A x 125% after it?

Then they state a 100A fuse which is one of those ultra-high-speed fuses to protect the drive from rapid disassembly issues.

How I'm taking it that this is: a 75A breaker feeding 75 x 125A (75°C) wire to the control panel.

At the control enclosure a 100A sized Disconnect loaded with 100A Ultra Fast Fuses.

Seems wrong that a 48A load is demanding 100A hardware and 75A++ wiring.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[RedSnake]

Usually you can drive it 150% for short amounts of time.

48A * 1,5 = 72 A

From a sellers site.

150% rated current for 1 minute (120% Frames 5 & 6), 200% instantaneous

https://www.factorymation.com/TD400-4025-3PH

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[waross]

75 Amp breaker: Max 80% continuous load = 60 Amp.
100 Amp fuse: Minimum conductor rating = 100 Amps @ 75 degrees.
Is that a choice between fuses or a breaker or are the fuses internal?
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RedSnake]

It seams it is a choice between fuses or breakers.
From the manual.

Section 2.3 is the picture that Itsmoked have in his first post.

https://download.factorymation.com/FMX/TD400/TD400_Series_User_Manual.pdf

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Marke]

The issue is the difference between a sinusoidal current and a distorted current.
The input current to the drive is not a clean sinewave, it will be rich in harmonics.
Typically, a three phase input drive with no reactor (AC or DC) will have a current distortion of close to 100% (THDi) and if it has either a DC Bus choke or AC line reactor, the THDi will be closer to 40%. The distorted waveform will cause a significant increase in the power dissipation in all series elements in the supply, including fuses and breakers.
If the THDi is in the order of 40%, then the true power dissipation in the supply components will increase by up to 35% depending on the shape of the current waveform. As the fuses and breakers are subject to the thermal current, they must be upsized to accomodate the harmonic heating effects.

Best regards,


Mark Empson
Advanced Motor Control Ltd

 

[itsmoked]

That makes sense. I always toss in a line reactor as I don't like polluting the rest of the power in a facility or inheriting new problems. Thanks Mark.

Keith Cress
kcress -

http://www.flaminsystems.com