Danfoss 3ph motor inverter causing hot cables.

netblindpaul · Apr 1, 2011

jtw/Bennetselec,
The fundemental operating principal of these devices means that they can cause interference to the mains supply.
The load they present to the mains is non linear, think switched mode power supply and you will be on similar lines.
jtw,
We had a manufacturing facility and support int he States and we often had to send guys over from the UK or Germany to sort these sorts of problems and it was rare they were caused by our kit. (NOT DANFOSS I hasten to add, but a competitor)
There are EU wide standards that have to be met along with the EMC & LVD in the EU, which the EU kit does for CE mark.
Not saying that US kit is not of a similar standard, however, it was always weakness in the supply infrastructure IIRC that caused the US problems.

Bennets,
I did not realise that we were up at 75kW, nor that we were talking about supply cable harmonics alone.
The way I understood it to date was overheating of supply side cb's though no confirmation yet.
Overheating of the motor side cabling?

Anyone, is this the case, or is all the "damage" one side, if so which side?

Crusty,

I trust they are GXD/CXT or is it AXT type, I only use GXT type but there is another as well.
Please don't use stuffing glands or skintops.
16mm 4c may be more than is needed, what are the motor details?
What are you pumping?
Why inverters, do you have closed loop control back to the inverters for flow or pressure?
Or, are they just glorified soft starts?
Have you/can you monitor start up performance?
Do they have a duty cycle or are they S1 & used continuously?

Crustycracker · Apr 11, 2011

Hi chaps, sorry I was called away to another site for almost a week. Back here for 1 day only. Still not done the new install as I am desperately short of time and I don't trust anybody else to do the work. I had a check thru' some more boxes, counted the GXD glands and found one 32mm (which is correct) and 19 40mm which I could put my arm thru'. So have had to re-order them.
The pumps are for chilled water and in my opinion they are just glorified soft starts as the pumps cannot run at reduced speed due to the size of the system. Basically the client was baffled with science and ripped off. I can't imagine how much these drives must have cost each.

silva.foxx · Apr 11, 2011

Thanks for keeping us posted and not disappearing.

So... just out of curiosity... do these pumps all run at the same time, or do they kick-in in a duty:standby arrangement?

Is there any control to prevent them starting simultaneously?

What common control do they share?

Knobhead · Apr 11, 2011

Heaven preserve us from production walhas specifying engineering parts. Took the sales spiel hook, line and sinker.
I can’t understand why such small pumps even need a soft start, just go DOL.

Engineer54 · Apr 12, 2011

Soft starts would have been a hell of a lot cheaper, and DOL would have been about as cheap as you could get!!!! And both would have served well for the purpose that these pumps are being used for!!!

It's not only the production walla's that don't understand these types of drive controls, There are plenty of so-called Engineers that don't fully understand when, and more importantly, ...''when Not'' to specify inverter controls....

netblindpaul · Apr 12, 2011

Engineer54,
Why do you think I started with the 20 questions interrogation!

Crustycracker · Jun 17, 2011

Hi all, sorry about the dissapearing act for a while, working away. Plus I lost my password to the site and couldnt reply to anybody.

Pumps rewired now with SY cable, 16mm 4c. What total b***ards the glands where to make off. Especcially in the inverter box. You cant even wear gloves while you do it. All done according to Danfoss install instructions. Only downer is that I had to install an MCB in the DB but it is a 63A (max permitted with this inverter). But it is barely warm whereas the old 25A one got so hot it crumbled away.
The cables are not in the slightest bit warm. I'll keep my eye on it just in case things warm up but i'm confident it should be ok.
Somebody commented on why were inverters used. The answer is, I dont have a clue. My guess is that the site was over engineered. I also think that whoever requested them probably thought that a soft start was the same item. In this situation the pumps must either run 100% or nowt. If they run at a lower value then we get low pressure alarms. Basically its a crap setup and we have to make the best of what we have, there is no money to rip it all out and start again.