Danfoss 3ph motor inverter causing hot cables.

[Crustycracker]

PHEW!!!. My coffee just went down the wrong hole after reading that.

Well, I guess its time to decide. I'm going to order some 16mm 4c SY cable, some 16mm CPC and 45A MCBs. I don't quite know how I will get the instalation to look half decent but I'll come up with something. When its in, hopefully later this week, I'll come back to this thread and update you all.
It has been one hell of a thread I can tell you all, very consuming and interesting. Like SF, I don't have a clue about harmonics. Its like rocket science, did it at college and glazed over then. I have never installed inverters, during my time on the tools they were quite rare, but I have maintained site that already had them, they worked, you left them alone. That's my experience with them, grim I know. Anyhow thankyou all for your donations here its been an experience.
I'm off to make my order. I'll let you know how much it cost as well. I'm glad it's not my time and money.

 

[netblindpaul]

silva,
The way an inverter messes with the normal a.c. sinewave can cause all sorts of issues.
The switching frequency could be up to 16kHz, ours were 2.3, 4, 8 & 16 in the PWM drives, the standard inverters had combined controls & I can't remember the exact frequencies off the top of my head.

I'll have to re-read the OP in a couple of days.
Though i'm not sure that throwing some new sy at it will necessarily work?
What glands are you going to use, please don't say skintop, trs or plastic stuffing!

As far as I can see I would need soem more info on the drives and motors really to comment.
If I was doing the application from scratch then I would not have done it the way it is coming across.
BTW I used to work for a competitor of Danfoss doing service & applications.

 

[silva.foxx]

As we're 4/5 pages on from OP, here's a summary;

3 off installs of:

Danfoss VLT 6022 3ph inverter supplying a 15kw pump motor (Armstrong Starline 80-200-15 (15kw). Currently an 8m 6mm2 singles feed via 32A mcb (previously 25A) in 3" steel trunking to inverter. Singles out to motor via Kopex.

Problem: overheating mcb and first 3" of feed singles becoming brittle.

Cables pulling 23A (read by clamp meter). Inverter displaying 27A (motor draw).

Inverter plate details http://www.electriciansforums.net/a...ng-hot-cables-danfoss-inverter-info-plate.jpg

MerlinG dist. board with no provision to retro-fit using BS88 fuses externally.

Undersized supply and harmonics appear to be the main 'topics of debate'.

OP uprating inverter feed cable and mcb this week. Update to follow.


.

 

[netblindpaul]

Thanks silva,

Quick comment over dinner.
How are the singles run exactly, are they all through the same apperture in the ferrous enclosures?
Are there any photos kicking around?
Has the OP clamped the motor.
I'll have to dig out the inverter manual unless anyone has a link?

Be back later.

 

[silva.foxx]

Manual -

 

[netblindpaul]

Crusty,
The MCB's are on the supply side of the inverter yes?
Are there any devices between the inverter & the motor?
Do you have the motor rating plate data?
What is the R2 between the inverter earth plate and the motor?
The 23A clamp reading is on the ip to the inverter or the op from?
The 27A is from the inverter display yes?

 

[jtw11373]

Where I'm from the harmonics issue is handled by the power company at the substation, has something to do with frequency(hertz) I believe jtw

 

[Crustycracker]

All, sorry, been away for a couple of days. My stuff has arrived to install cabling according to the Danfoss install manual.

Using 4c x 16mm SY flex (with screen) and an extra 16mm CPC. Using 45A MCBs from Merlin DB and isolator before the inverters as there will be no local isolation. Using fused isolator, like an MEM switch fuse, 63A rated with 40A BS88 fuses in it. Quite expensive all that lot.

Trouble is cant do it until late next week now as i been called off to another site for a few days. Pain in the rear side.

 

[BennettsElec]

hi,
In my opinion Harmonics are not causing this problem.
Many large drives 75kw and upwards would cause Harmonic problems with heat etc at your supply transformer, not on your supply cables. Make sure you use some kind of screened cable and earth BOTH ends, also make the screen off as close to the inverter terminals as possible thus not introducing an ammplifying effect. (sorry just good practice)
Approximately 28amp FLC on a 15kw (either 2p or 4p) motor. Depending on manufacturer.
The nature of the inverter is to give more current out than that of being taken in, and if the drive is giving 27amps out then i would suggest that the motor is nearing on FLC.
it looks like, as usually happens, they have done an upgrade on their pumps but not taken into account the supply cables. these motors should never have been supplied/ protected by 25amp breakers.
Rich

 

[Crustycracker]

Got all the stuff delivered today. Not installed SY this big before. You want to see size of the special SY glands. 32mm hole, never realised that, going to give me a headache getting them drilled into the DB. Job planned out now, just need some time to do the install. Will start next Thursday when I'm back on site. Bit annoyed really, would like to have steamed into in Monday but never mind.
Won't be updating until then guys. Will get the first one done and fill you in. Thanks for all your contributions.

 

[netblindpaul]

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]

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]

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]

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]

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....