Motor wiring, bit of a bang!

[dobbslc]

This is a work thing not my own doing but I'm intrigued to know what the three phase motor experts here think. A large pump control panel went bang and we are getting the blame for a "power surge", when I got sent the photos I spotted that contactor K2 looks linked out on the load side, the photos are quite bad though.
I was later sent the schematic where it also appears to suggest that once contactor K2 is switched it will result in a large Billy banger!
I've not seen this in the flesh but surly it isn't right.
All thoughts and thread drift welcome

 

[daleyd]

At first glance it’s a star delta starter? It s”should” be ok, but the other contactors need to energise/de energise in sequence, if they don’t then it could well go bang.

At a guess this is what’s happened, rather than an inherent design issue.

 

[Guineafowl]

Is the K123 thing a star/delta start?
K1 and 2 for star
K1 and 3 for delta

If K2 or 3 are sticking you’ll short the phases.

^^ posts crossed.

 

[Blobber]

Id have said star/delta, the 2 contactors to the right should have some sort of mechanical interlock so only one or the other can make a circuit

 

[Dave-sparks]

As above K2 is the star contactor so does short the 3 together to create a star point for starting, this would normally be electrically and mechanically interlocked with K3 to prevent them both closing at the same time.
There may be electrical interlocking there but there's definately not mechanical.

K2 looks like it has got rather too hot at some point, could be a loose connection, overload of the contactor or it has closed at the same time as K3.

Blaming a 'power surge' always seems to be the default for anyone who doesn't understand electricity.

 

[daleyd]

I don’t know that design of starter but it looks like the outputs for the contactors k1/2/3 come out of top, 21,22,23.

K2 and K3 look to be interlocked electrically, so even if there is a demand from the controller to energise K2, it can’t until K3 is de energised, and vice versa (using aux contacts K2-1 and K3-1)

 

[dobbslc]

Blaming a 'power surge' always seems to be the default for anyone who doesn't understand electricity.

We got this a lot! ^

I'm no motor expert but maybe the sequencing went wrong and kept both K2 & K3 closed at the same time?

 

[Dave-sparks]

We got this a lot! ^

I'm no motor expert but maybe the sequencing went wrong and kept both K2 & K3 closed at the same time?

It shouldn't be possible due to the electrical interlocking @daleyd mentioned, assuming that has been correctly connected!

 

[Pete.]

Looks like they have under-sized K2 and it's burned itself shut. I only see the two coil wires going to it so it doesn't appear to be looped into the interlock for K3, so even if the pull-in coil was dropped out if the contacts are welded shut there's nothing to stop K3 closing at the same time.

 

[Dave-sparks]

Looks like they have under-sized K2 and it's burned itself shut. I only see the two coil wires going to it so it doesn't appear to be looped into the interlock for K3, so even if the pull-in coil was dropped out if the contacts are welded shut there's nothing to stop K3 closing at the same time.

It's hard to know whether it's undersized or not without more information, the star contactor can be smaller than the main and delta contactor.

There's 3 grey control wires going into K2 from above and probably some coming in from below

 

[Barking Mat]

Looks like the magic smoke has come out the bottom middle of K2.

I don't understand that wiring, lost on me.

Why join three phases together ?

 

[daleyd]

Looks like the magic smoke has come out the bottom middle of K2.

I don't understand that wiring, lost on me.

Why join three phases together ?

You shouldn’t be joining 3 phases - it should short out only the contacts on the motor end so connecting to either a star or delta configuration. The whole idea is that it’s interlocked (or should be) so there should be no possibility of it shorting the phases out.

 

[Dave-sparks]

Looks like the magic smoke has come out the bottom middle of K2.

I don't understand that wiring, lost on me.

Why join three phases together ?

It's a star-delta starter, the motor is connected in star for reduced current starting then switches over to delta for normal running.

The contactor K2 creates the star connection by joining 3 ends of the motor windings together. Normally with a straightforward star connected motor this connection would be made with a shorting link in the motor terminal box (or internally in the motor)

Once a set time has elapsed for the motor to start and get up to speed K2 opens and K3 closes connecting the motor in delta.

In the first picture you can see 3 brown wires coming out of the bottom of each of K1 and K3, these will be connected to the 6 ends of the motor windings.

 

[Brad93]

This is why it pays to use a mechanically interlocked starter like schneider and abb sell.

 

[ajlelectronics]

Why join three phases together ?

Motor braking? But K2 and K3 must be interlocked somehow and so prevented from energising simultaneously.

 

[Barking Mat]

It's a star-delta starter, the motor is connected in star for reduced current starting then switches over to delta for normal running.

The contactor K2 creates the star connection by joining 3 ends of the motor windings together. Normally with a straightforward star connected motor this connection would be made with a shorting link in the motor terminal box (or internally in the motor)

Once a set time has elapsed for the motor to start and get up to speed K2 opens and K3 closes connecting the motor in delta.

In the first picture you can see 3 brown wires coming out of the bottom of each of K1 and K3, these will be connected to the 6 ends of the motor windings.

Thanks, still don't understand, but don't worry about it.

 

[dobbslc]

Pretty pictures.

 

[dobbslc]

The ones on the right are what you'll see when you open up a three phase motor terminal box.
The copper links can be moved to different positions.

 

[evobilly666]

Potentially a loose connection on K2 caused it to over heat and weld itself closed, allowing both to be closed simultaneously.

 

[Bornfree]

Star delta contractors are normally electrically and mechanically interlocked.