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Hi
I got called out to a faulty star delta starter on an old Stenner band saw Monday (was getting stuck in star and blow fuses) - So I ordered a new one to suit the 22kw 400v motor having calculated the overload to be 22.04A going by the plated current saying 38A. 38*0.58
Fitted it all today but having troubles with the overload tripping out on starting in star (it needs a good 30seconds to reach speed) which isn't surprising seeing its drawing 60-70A over that time.
Have I sized something wrong? The old overload was on 43A which wouldn't protect the motor once its running in delta.
The only other thing I can see that's different is this one the overload is on the delta contactor where the star contactor connects to where as it was on the main before.

Hopefully I'm missing something very obvious.
Tim
 
TL;DR
Star delta motor tripping overload on start up.
Which fuses were the ones blowing, Were they the main fuses or control circuit?
Have you tested the motor windings for insulation resistance and continuity and what were the values you got?
Have you clamped it to find out how much it is using in start up?
30seconds sounds a long time before it swaps into delta! What is the motor actually doing?
Is it Mechanically free and bearings in good condition?
The overload in the delta contactor would usually be set by taking the full load current and dividing it by 1.732 (as far as I remember, may not be the correct number)
 
Which fuses were the ones blowing, Were they the main fuses or control circuit?
Have you tested the motor windings for insulation resistance and continuity and what were the values you got?
Have you clamped it to find out how much it is using in start up?
30seconds sounds a long time before it swaps into delta! What is the motor actually doing?
Is it Mechanically free and bearings in good condition?
The overload in the delta contactor would usually be set by taking the full load current and dividing it by 1.732 (as far as I remember, may not be the correct number)
Cheer for your reply.
The main fuses were blowing - I checked the windings like you said once I'd worked out what was going on, got cleat on insulation and each set of windings were about 60 ohms form what I remember but all near the same.
The saw has two quite big cast fly wheels the band saw blade goes round maybe 3 or 4 ft in diameter so does take some moving. It turns freely as they do that to check the blade each morning.
I've had the clamp meter on it while trying to start and its drawing 70A then gradually creeps down as its getting quicker but I've not seen it below 60A - guessing it needs the extra torque in delta to properly get going.
I checked with Schneider when I was ordering about the overload calculation - full load current x 0.58. Europa who's contactor I used also said the same.
 
The Motor should get up to full speed quicker than 30 secs, as it's driving a saw blade it should have hardly any load on it untill wood is put through it.

Edit, forget that if it's got flywheels

Have you tried reducing the Star time to see if it will pick up in Delta sooner without slowing?
 
Still the flywheels shouldn't cause that much load if I take it these are the ones the blade runs on?!
Strange that it is taking the main fuses out, how many fuses is it blowing?
I know this may be teaching you to suck eggs so will apologise in advance Are you sure you got the motor windings in the correct sequence when you replaced the starter?
(*0.58 is duly noted and I have put my dunce cap on)
 
Think there was a bit of confusion - was blowing fuses as the timer was faulty not switching the contactors fully. Not blown any since. Its the overload that trips now.

I've tried various times but have been assured that it always took 30seconds before to change over, also they said the slow time it takes to get to full speed is the way it always been too.
Checked the cables from the contactors back to the motor and all seems fine (was my thought as well first).

I did take the overload out to see how it starts (shhh) I can't see its near 80/90% of full speed by 30 seconds when I've read the timer should be set to? Steadily creeps down then the 30 seconds kicked in, got gowning on delta and was drawing 18amps.
 
@brianmoooore dunce cap still on and now sitting in the corner for not realising!
@Mop101 sorry my misunderstanding there!
That is an odd one, do you know what the original overload was set at?
 
The original one was set on 43amps which is probably why it worked. It never tripped - whenever they had a problem it blew the main fuses instead. Not a lot of point in having it!
Was the original starter ancient? Could it be that the original overload relay was just designed to take longer to trip
 
Mmm this is sounding like it may be a motor fault, if the main fuses were going before and now the overload is going instead, the only thing that is constant in this is the motor and supply as you have changed the panel?!
Could be that the overload is faulty, If you removed it and it's run properly without it then it's possible I suppose.
 
It sounds like to me that this set up has likely never worked properly. The original installer found that the overload tripped during start up, and simply wound it up so that it didn't. The motor simply isn't up to the job of spinning up the flywheels in the time that it should.
 
Mmm this is sounding like it may be a motor fault, if the main fuses were going before and now the overload is going instead, the only thing that is constant in this is the motor and supply as you have changed the panel?!
Could be that the overload is faulty, If you removed it and it's run properly without it then it's possible I suppose.
Difference now is the motors got an overload on it that's the correct size 43A down to 22A.

It sounds like to me that this set up has likely never worked properly. The original installer found that the overload tripped during start up, and simply wound it up so that it didn't. The motor simply isn't up to the job of spinning up the flywheels in the time that it should.
I agree its probably never been right. I can't imagine Stenner would have fitted the wrong size motor? It's probably been there 40 years - wouldn't be an easy job to change the size of it.
Maybe a drive is the way to go.
 
Is it something like this, with another wheel under for the blade to go around.
This one is 36", apparently there were 48 and 54 ones as well

Star delta motor overload Stenner saw.PNG - EletriciansForums.net
 
The regs (iec) allow for up to 125% setting on the overload, with some this is not included in the overload itself, some it is , and some like schneider have 115% internally, meaning that you need to actually set up the overload protection up to 125%, 100% or 110% for the above 3 cases respectively.

However, none of the standard thermal overloads could handle more than 30/60 seconds of start up/lr current as far as I am aware.

To protect this properly I think you would need to go really old school with oil dashpots (you chose the viscosity of the oil to match tripping time), or modern with electronic overload.

I can't remember the exact schneider ones, but it's something like lt47 or 57 - this allows you to set the overload time for star, then delta for startup after which it reverts to a standard thermal overload.
(3 settings Current, time1, and time2)

Don't know if Europa do similar
 
That's interesting ok. I like the idea of one you can set different overloads on.
Just put in a 36amp overload and runs up fine but doesn't fit very well - the stop button doesn't line up now 🤦
I'm not sure how long the contactors will put up with that current either. All questions for Europa I think.

The regs (iec) allow for up to 125% setting on the overload, with some this is not included in the overload itself, some it is , and some like schneider have 115% internally, meaning that you need to actually set up the overload protection up to 125%, 100% or 110% for the above 3 cases respectively.

However, none of the standard thermal overloads could handle more than 30/60 seconds of start up/lr current as far as I am aware.

To protect this properly I think you would need to go really old school with oil dashpots (you chose the viscosity of the oil to match tripping time), or modern with electronic overload.

I can't remember the exact schneider ones, but it's something like lt47 or 57 - this allows you to set the overload time for star, then delta for startup after which it reverts to a standard thermal overload.
(3 settings Current, time1, and time2)

Don't know if Europa do similar
Vvb
 
There are so many things here that could be at play-
Where was the overload in the original unit, the overload can be sited in various positions and on high inertia loads they were often bypassed in star.
Is the motor definitely wired correctly, when buying star delta starters they can come in 2 formats, already phased crossed in the factory wiring or expecting you to phase cross the windings when you connect, a full understanding of star delta control and connection is a must here.
I find it strange the original fault gave you popping fuses this would not be consistent with star locking, its ampage draw is reduced, this could indicate a fault, have you insulation tested the motor, the winding resistances you measured earlier should all be more or less balanced but remove all cabling to ensure no feedback from possible cable faults.
Can you show the motor name plate, looking at that machine it shouldn't take long to get to speed, I am curious why 30 seconds it seems excessive.
Take the blade off and slowly turn the motor shaft, use your hands to feel for any coarseness, scraping of bearings, it should run perfectly free and smooth, no vibrations.

Just a few to get you started on.
 
The only other thing I can see that's different is this one the overload is on the delta contactor where the star contactor connects to where as it was on the main before.

This is important. If the overload was originally connected in the supply lines it needed to be set to the 38A FLC, not the 0.58x FLC (22A) which is the maximum permissible winding current. In delta it would have offered full protection, because tripping at 38A line corresponds to 22A winding current. But in star the protection was not adequate, because then the winding current and line current are equal and the 22A windings were running on a 38A O/L setting. This would mean that it did not trip so readily at startup and did not offer protection against serious overcurrent when the starter got stuck in star and the machine came under load, hence the fuses blew (what rating were they?)

If the new O/L relay is in the motor winding circuit, it needs to be set at 0.58x FLC and will protect equally well in both star and delta because it senses the winding current directly and always trips at the 22A maximum. Hence the new starter is more troublesome with this long, heavy start.

Steadily creeps down then the 30 seconds kicked in, got gowning on delta and was drawing 18amps.

18 amps line current even allowing for the magnetising current of a larger motor suggests it's taking 7-10hp of mechanical load at that time, just to rotate, without sawing anything. Mainly turning to heat; some of it is windage but much of it is oil in bearings and gears (assuming that motor also drives the feed?)

I don't do woodworking machinery but that seems a hefty load for a saw running light, imagine a dozen bearings each dissipating 500W, it would be glowing after half an hour. If the machine was cold for this test, perhaps the lubrication is too viscous. They can roll the blade around slowly for inspection but the bearings drag badly at speed until it warms up.

How closely equal are the line currents? I think if there is much of a discrepancy or the motor runs hot there is still a possibility of some shorted turns that are not evident on the coil resistance test. (You mentioned 60 ohms but can't be right otherwise it could never take more than 6.7A.) Is it possible to drop the coupling or belts and see how the motor behaves by itself?


The saw has two quite big cast fly wheels the band saw blade goes round maybe 3 or 4 ft in diameter

If by flywheels we are talking about the band wheels, although they are large and heavy the relatively low rotational speed means they don't store a huge amount of energy (which is proportional to the square of the speed.) I work on organ blowers that have shrouded impellers up to about 2'6" in diameter spinning at 1450 RPM which store enough energy to run on for a minute or two after hitting the stop. Plus the delivery has no backpressure at runup due to the reservoirs, so the whole thing is in overload until up to speed, and the longest I ever have to set the star time to is about 8-10 seconds. And yes, normal overloads sometimes complain on the larger units. Some have oil dashpots, some original 1930s starters don't have any O/L relay at all (!)

I doubt there is a coil phasing error even with the high current running light. The largest motor I have seen wired wrongly was a 5hp, which started in star and then had a crossed coil in delta, and that got so hot so quickly it set the smoke alarms off about 1 minute after startup and tripped a D32 MCB (1930s starter had no overload relay) suggesting the current was around 8-10x FLC.
 
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