Will an inverter take out the spikes

[malcoa]

Hi guys,
We have a machine at around 30KW, the nature of the machine causes the current to bounce from circa 15A to 150A+ as goods go through it, its control is DOL.
The question is:
If i was to install an oversized inverter (which would have bigger capacitors in), would it absorb the current spike and take it out of the mains?
I have installed and set up many inverters but not for this purpose and i would just like to have your thoughts

 

[Knobhead]

What's it driving? If it's something like a crusher then not realy. Have you spoken to any of the inverter manufacturers?

 

[Darkwood]

Good call on the crusher/shredder Tony was just thinking that myself if that be the case it maybe undersized motor, i would guess full load on your motor maybe around 60amps if a standard induction motor and it should be geared onto a high inertia drum so to cope with product without straining but seems a bit concerning its ramping current up over twice FLC as part of its job.

Obviously a shot in the dark so more info please what exactly is the motors job as Tony has already asked.

 

[malcoa]

Yes its a shredder, i have asked inverter manufacturers and they say they dont know and they have never considered it, its just a thought i was toying around with.
The real issue is the business is having quite a few more machines in and its going to be taking us closer the the authorised supply, so it isnt the machine that is suffering at all, i was just thinking that an inverter may isolate the mains from the spikes and just pull a smoother load.

 

[Darkwood]

Ive worked on shredders before and except for the initial start up which may have a long start duty their should be enough inertia in the drum to do the job without straining the motor, the current will rise but shouldn't really be peaking over FLC while shredding product.... what tends to happen is the shredders are used beyond their limits to speed things up, we had a shredder doing 5mm plastic strips and it tended to sometime get to much product in for the motor to handle so i fitted a current monitor relay that stop the conveyer feed until the current dropped again giving the motor time to catch up with the quantity of material.

What are you shredding?

 

[Darkwood]

Also get a engineer to look over the machine, check the blades etc, damaged blades/teeth can have a great effect on the machines ability to do the job intended, the knock on effect of damaged or worn teeth/blades would give similar result as you are experiencing but noted that it has many causes.
Dont quote me on this but an inverter would most likely trip if spiking of that magnitude during running IMHO... i think you need to establish why its spiking rather than trying to get around it.

 

[Knobhead]

Is there a flywheel fitted? If there is that should be taking the worse of the shock loading out. With crushers, shedders and what have you it’s in the nature of the beast to impose surging loads.
The bottom line is what problems is it causing, if any?

 

[mechelec]

It sounds like you do need to sort out the loading especially if you are planning on fitting more machines. If your equipment causes voltage fluctuation on the DNO network and someone else complains, the DNO will force you to stop using it all. The only way round it is to have either/or a larger supply, bigger transformer or reinforcement of the existing network.

 

[malcoa]

Its shredding thin aluminium, the machine is driven via vee belts and yes if the blades or anvils are worn which they quickly become, the belts start to slip as expected. If i slow the feed conveyor right down its behavior is indifferent, when i ask about the history of the machine, it has apparently been the same from new, now i know the question is is it fit for purpose?
Non of the circuit breakers or overload trips during operation and neither are they too large for the job
Part of my thinking of using an oversized inverter was to avoid the overcurrent trip and perhaps the bigger capacitors within the inverter would buffer the spikes (my mind says its viable) keeping the mains isolated from the effects, but yes darkwood the burden of whats going on may still be too much for the inverter to deal with, ( in a way its just my mind wondering if inverters can be used for things other than what they were designed for)

I have just applied to be HV metered but thats a 6 month turnaround, i think the risk is marginal between now and then providing the upgrade is on time.
The situation made me focus on what makes the business vulnerable and this was on my list, maybe leverage for a capex application for a new and bigger machine.

 

[Darkwood]

Its a strange one, hard to call from a forum so many variables can give the same symptoms, i take it that its a heavy steel drum thats been turned by the belts to gain high inertia i can assume you have checked the motor is connected correctly for the voltage stated on the plate.
Although ive connected shredders and adapted controls im no expert on the construction of them my involvement was for shredding plastics and that came with its own issues that you probably wont have with metal but im supprised reducing the feed dosn't give benefits unless its the amount your dropping in thats causing problems, try reducing the amount of product on the conveyer by 50% (so the same product amount is spread over twice the length of conveyor than it is now).
I assume we are singing the same song here and the shredder is running constantly and not starting up when feed is ready ....might sound a dumb question but what ive seen in my yrs i thought it best to ask.

As goes the inverter suggestion my fear is they are that efficient in protecting the motor they may see 150amp surge as a fault in run mode and trip but your suggestion is one i couldn't answer as you already say you utilising it for a purpose its not truely designed for although the starting current would be reduced greatly.