3ph delta star switch, delta tripping fuse

[T0RN4D0]

Double V belt. The motor tab says 2940 rmp, if im reading it correctly, you know how they are on old motors. How much drag is a mottor like that supposed to have on its own? I'm suspecting the bearings on the table (the shaft coupling the belts and the blade) need to be changed. The whole thing stops pretty quick once shut off, and it has decent drag if you turn it by hand.

I'm thinking high drag could be causing it to pull more power when starting, but the 10kw motor is an overkill for the blade its using right now (30ish cm blade) so it still works normally.

 

[Darkwood]

If there is no obvious braking you could try drop the belts off and spin the motor pulley by hand then also try the blade un-belted i suspect the star-delta timer was correct but blade bearings have probably corroded slightly most likely the blade bearing and also suspect its probably been in storage in a cold damp area for a while letting this bearing degrade if it was already aged or damaged.

 

[Deleted member 72666]

Unless I've got this totally wrong but It sounds to me from what you have said that it's a manual star delta starter(via this 8 pole switch you speak of) and the time is operator controlled, is this correct? If so do you have any means of under voltage protection? What else other than the switch and mcb's are in the control panel and Is this setup a 'home build'?
Like DW points out 10kw is an odd size motor and seems somewhat an overkill for that size of blade. Also there sounds to be too much drag on the motor bearings/shaft which is causing excessive current to be drawn.

 

[T0RN4D0]

Yes, there is no timer as its manually controlled. There isn't any motor protection, the whole setup is a home made unit. I think it might not be a bad idea to add one, but its not up to me. It won't run without operator presence so if there's something wrong it will be shut down manually.

Heres the tag, i see you have trouble believing me its a 10kw motor. I think a 7.5 would be ideal for this, but they probably used what they could get for the right price. The small blade was on it because it was just used (recently) for trimming slabs of wood. Now its probably gonna get a 60cm blade and you need some decent power to go through long cuts without too much hassle.



I'll suggest checking out and replacing the bearings.

 

[Knobhead]

Only just spotted this thread.

Manual Y∆ used to be common, we had them on 3.3KV Ward Leonard sets. It would be common for the operator to operate the change over before the run up had finished, tripping the quarry 3.3KV header main OCB on O/C.
Some did it deliberately so they had a longer tea break.
At change over if the poles are out of synchrony the peak current can be 10X FLC as opposed to 6X for DOL.

This is for a 300HP 550V MG set. (It was my pet).

DW, your comment on direction of a machine like this is very pertinent. The blade mandrel being designed to tighten with acceleration and load. I had quite an argument over a grind stone. The fitter had installed the stone before I’d direction checked the new motor. Production management were screaming about the time to take the stone off again. It went the wrong way, but I’d stuck to my guns. Had I not, a 3Cwt 2’6” diameter stone would have launched it’s self out of the machine.
We’ve talked about production management before. This time I was invited to watch the management arse kicking party, I was usually the guest of honor!

The bottom line for anyone.
Machines like saws, grind stones, etc. Check the direction before attaching the load.

The same goes for:
Centrifugal pumps.
Fans.
Compressors.
Some gearboxes have anti run back.
The list is endless.

Check the direction first. It will be your arse in the fire when you’ve just f**ked up £XXXX of kit.

 

[D Skelton]

You'd have thought the bump tests non loaded would be second nature to an electrician?! I had this drilled into me over and over again when I was an apprentice! "Bump in star, check rotation!", "bump in delta, check rotation again!".

 

[Darkwood]

The OP is a student in Energetics? ... not an Electrician which is a bit worrying as although he seems to have a grasp on rigging this saw he lacks knowledge of safe procedure commissioning and faulting which is essential knowledge for his own safety and of others and also having connected it up he holds responsibility that it is safe to use ....judging by the manual star/delta we can only assume the saw itself is also many decades out of regulation but as im not from Slovenia i can't comment on their standards.

 

[D Skelton]

My response was mainly aimed at Tony DW. The fact that he feels the need to remind people to check motor rotation before attaching the load tells me that he has lost much faith in the current standard of electrician! lol.

The thought that there are probably many people out there who would simply forget this most basic yet most important of tasks worries me!

 

[shanky887614]

My response was mainly aimed at Tony DW. The fact that he feels the need to remind people to check motor rotation before attaching the load tells me that he has lost much faith in the current standard of electrician! lol.

The thought that there are probably many people out there who would simply forget this most basic yet most important of tasks worries me!

They just don't train people properly anymore.

Ive learnt more off one guy in the last 2 months than from the rest of the firm in a year.

 

[Guest111]

They just don't train people properly anymore.

Ive learnt more off one guy in the last 2 months than from the rest of the firm in a year.

Another tip,when installing a machine which you are unfamiliar with,make sure phase sequence is correct at the machines incoming terminals then get someone who knows how to operate it to start it up,that way there's no chance of being blamed for any damage caused by operator error.Yes we know how to connect machines up but operating them can be expensive if we don't know how to do it correctly.

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