Star delta motor overload

Mop101 · Dec 14, 2021

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

SparkySy · Dec 14, 2021

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)

Mop101 · Dec 14, 2021

SparkySy said:
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.

snowhead · Dec 14, 2021

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?

SparkySy · Dec 14, 2021

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)

brianmoooore · Dec 14, 2021

Dividing by 1.732 is the same as multiplying by 0.58. Dunce cap not required.

Mop101 · Dec 14, 2021

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 · Dec 14, 2021

Was the original starter ancient? Could it be that the original overload relay was just designed to take longer to trip?

SparkySy · Dec 14, 2021

@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?

Mop101 · Dec 14, 2021

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!

brianmoooore said:
Was the original starter ancient? Could it be that the original overload relay was just designed to take longer to trip

SparkySy · Dec 14, 2021

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.

brianmoooore · Dec 14, 2021

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.

Mop101 · Dec 14, 2021

SparkySy said:
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.

brianmoooore said:
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.

snowhead · Dec 14, 2021

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

[ElectriciansForums.net] Star delta motor overload

Mop101 · Dec 14, 2021

snowhead said:
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

View attachment 92986

Yeah looks like it. Not sure on the size though but bigger I think.
Yandles & Sons Timber & Sawmill - Yandles - https://www.yandles.co.uk/about-yandles/43-the-history-of-yandles Like the one there but its not that one.

Star delta motor overload

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