Danfoss 3ph motor inverter causing hot cables.

[Crustycracker]

SF - I have a phot of the spec. plate on the side of the inverter unit. I am trying to get it attached but not sure if it will work. Never done it before so here goes....

 

[silva.foxx]

IN: 3x380-460V 50/60Hz 32A 27A

3ph 415v 50Hz input with a max. current of 32A

You must admit a 32A mcb is a little near the mark for this supply. All the heat is centred around this mcb, ie. device and cable, perhaps due to 'current restriction through the tight passage of the mcb!'

I'd still go for the mcb and feed cable upgrade...

What do you have upstream of the mcb?

 

[Crustycracker]

SF - The 32A MCB is part of a Merlin G dist bd. Down stream of that is obviously the main switch which is fed in something like 120mm singles from an adjacent Asco change-over switch which is fed from a BS88 type fuse carrier in the main mechanical services panel from 2 seperate feeds (A & B).
Thing is tho' if the cable is only carrying about 23A, tong tested, why the heat???? It must be something to do with the harmonics. Altho Danfoss recommend the use of SWA or SY cable and cartridge fuses they don't make it clear what would happen if you don't.
I am getting costs for the SY on Monday. I have to get this problem tied up next week, have all the managers doing a site walkabout the week after so I need to get all the trunk lids and covers back.
I may use them link blocks (MGTB1001) and put an extra cartridge fuse for each pump also.
I wish I had an open check book for this because I still prefer using the existing metal trunking for this and the Kopex as it looks more in keeping with the pump bay. Its going to be a real pain in the rear side having to run in a seperate route for 3 new surface mounted cables. Plus I am quite limited on wall space for mounting this extra stuff.

 

[benji]

I think you would have to change cable from inverter to pump from singles to swa or sy to give it some form of screening

 

[johnboy6083]

for interest, i found this link for info about harmonics, an ways of minimzing effects.

HARMONICS

 

[Crustycracker]

Thanks, I have saved as a favourite for the time being. Will have a look in the morning.

Done my sentence at work for the day. Back with renewed vigour (just about) in the morning. I'll probably print it all out depending how long it is.

 

[silva.foxx]

SF - The 32A MCB is part of a Merlin G dist bd. Down stream of that is obviously the main switch which is fed in something like 120mm singles from an adjacent Asco change-over switch which is fed from a BS88 type fuse carrier in the main mechanical services panel from 2 seperate feeds (A & B).
Thing is tho' if the cable is only carrying about 23A, tong tested, why the heat????

So there's plenty of room for increasing supplies to these inverters...
Manual states inverter want a steady input current of 27A with instantaneous currents up to 32A (as in the rating on the nameplate you provided) and is to be protected by 40A motor rated fuses... not an undersized mcb.

Manual -

It must be something to do with the harmonics. Altho Danfoss recommend the use of SWA or SY cable and cartridge fuses they don't make it clear what would happen if you don't.

It's easy to blame 'harmonics - the bit we don't understand' but the install sounds as if it's undersized on the supply side. You have to get that bit right first, probably lowest cost, before getting into adding filters and magic boxes.

The fuses will give better protection.

All installs should be done to manuf. recommendations - they're the ones who've researched their products and put the pointers in place to make it work as intended.

 

[boballum]

Cable calcs are based upon a conductor operating temp of 70c (as Im sure you know!!) the simple solution is to increase the conductor CSA to reduce the heat, your harmonics will flow down the CPC and this must be sized appropriatley to comply with the regs on fault current

Pay attention to all manufacturers instructions (its a reg now!!) even if they seem over the top then you have something to fall back on if it goes ---- up!

 

[Knobhead]

Will anyone listen!
Contact Danfose about inline reactors to reduce harmonics.

 

[Crustycracker]

I'm off home in 10mins but I thought I'd just see how this thread was running.

I have had another look at the area around the dist bd. There is absolutely no way that 3 new cartridge fuse isolators will fit externally around the db. I am tempted by SF to order a 45A MCB (Type C), some tri-rated 10mm singles (RS 628-5493...rated @75A) and the same in 16mm earth (CPC size as required in the manual) and install just one new circuit and suck it and see. The length of run is about 7.5mts from the MCB to the inverter in 75mm steel trunking.
It's annoying because I wish I had known this 4 years ago when the contractors installed it. I could have made them rip it out at their expense. Chances are they were totally unaware of the potential problem themselves. Due to the way all the trunkings and conduits are now running along the walls it is impossible to fit SY cable and glands without making the job look like a pigs ear. I certainly wouldn't want to put my name to it. I dont think 3 x 10mm SY cables could all run inside the trunking either.
Just out of interest, is the CPC a 'live' or functional earth? For example, if I was to disconnect it while the inverter was running then would there become a voltage potential on the flying CPC until it was grounded down to the metalwork again. If this is not the case then would it be possible to link the inverter CPC's and carry a single one back the db instead of having individual 3 CPC's going into the db? This is just a loud thought.

Will catch up tomorrow, thanks all.

 

[Crustycracker]

Tony, Danfoss were quite helpful when I originally asked them about this problem but after all that they pointed me to the installation manual on the website which I had never seen before (nor sure if you are aware...we inherited this set up when we moved into the site).
They mentioned harmonics but said that if the cables were screened (SWA or SY) then it should stop or reduce harmonics. I only wish that with my knowledge now I could have put this lot in yself from scratch. Wonderful thing hindsite.

 

[silva.foxx]

@Tony... with the greatest of respect we are listening to what you've stated, but we have to look at the basics first. I, plus a few others, believe the supply to the inverters is undersized, and the install clearly does not match the requirements of the Danfoss design guide, written by Danfoss to provide trouble free operation of a Danfoss product.

To me, the heat is concentrated at and around the mcb. The mcb is conducting currents it can't handle thermally. The mcb appears to be the bottle-neck in the supply.

Please explain to me (or us) the phenomena of harmonics so we can understand. How do you assimilate the symptoms of harmonics to what the OP has stated in this thread?

I'm quite thick so please supplement the following document with layman's terms, please? Technical notes - Reducing harmonics caused by variable speed drives - Fact File

More info Expertise in HVAC Drives

Danfoss "facts worth knowing" http://daneenergy.co.uk/Documents/Facts Worth Knowing.pdf


As the OP has mentioned... try uprating one circuit first... if no joy... get professionals in to do Harmonics analysis.

Crustycracker... thanks for the continuation of this thread. Good info.

 

[netblindpaul]

IF the installer was not fully aware of the possibilities of Harmonics or other phenomena from VSD's then they should never have installed the equipment as they were not competent to do so.
They would be legally required to have full understanding of the manufacturers instructions to comply with 7671 which may or may not apply depending on the exact situation, there is also, 60204-1, PUWER98 & EAWR89 & the management regs to consider.
We never allowed isolators or any control devices between our drives and motors to comply with our instructions when I worked for a VSD/Servo drive manufacturer end of story, any subsequent controls rendered the drive & motor warranty invalid, thus would render the compliance with any statutory etc. legislation invalid also.
Harmonics can be a complex field Silva, there are many things that can affect their generation and any affect they have.
This is not something that can be taught via an internet forum IMHO sorry.

 

[silva.foxx]

Harmonics can be a complex field Silva, there are many things that can affect their generation and any affect they have.
This is not something that can be taught via an internet forum IMHO sorry.

Great

Not interested in learning about harmonics... just interested to understand how others here can suggest without evidence that harmonics is at work in the install described by the OP.

As said... I'm as thick as a gurkha's... so the science of harmonics is way above me... so I'd never diagnose a problem with such... but I'd like to think I could diagnose a failure, with use of the design guide of a product.

Perhaps netblindpaul, with your drive background, you could offer some valid argument to the heating problems identifed in the 1st post.

Pretty good read without being too techie: http://hi-techelectricalsystems.com/effects_of_harmonic_currents.htm

.

 

[raithrovers1]

The output of the inverter will not be a true sine wave and therefore measuring the output with a current clamp can give false readings. It is always better to use the inverter display for current readings as it is electronically measured. I suspect the drive is supplying at least 27A.
Here is an extract from an article:

"Harmonics, non-linear spikes, and reflections are common power distortions. In rush currents is an additional problem that the motor and cable are subjected to. Harmonics are multiples of a fundamental frequency. As an example if the fundamental frequency is 60 Hertz, the 5​

th harmonic is 300 Hertz (5x60). Power distortions are caused by harmonic frequencies. Some harmonic frequencies are “in-phase” with the fundamental frequency and rotate in the same direction as the field, except more quickly due to the higher harmonic frequency. This condition causes the power, both voltage and current of each harmonic to add to the voltage and current of the fundamental frequency. Keep in mind that the power in the fundamental frequency is all that is needed or wanted. The additional power from the harmonic frequencies cause overheating, high voltage
stress and also confuse electronic functions that depend on the fundamental frequency for clock or timing functions. The added harmonic power also affects the motor and power supply cables."
I know its a bit brain numbing but it is why they suggest using the correct sheilded cable to reduce harmonics.​