Machine fault, I HATE, 1ph motors!

[Sidewinder]

OK,

I'll be honest, I've not got this running yet.

Another guy has had a go, and fixed part of the fault.

Single motor machine, DOL, 1ph.

3 contactor starter.

Start, run & capacitor contactors.

Start & run, electrically interlocked.

Starter operates fine without motor connected.

i.e. goes through the required contactor status.

I have yet to check the o.p. voltages of the starter.

I have a drawing of the starter, very poor, as is the wiring, no colour coding, or numbering.

The motor has 3 sets of windings.

Z1/Z2, R = 2.4 ohms

U1/U2, R = 1.0 ohms

U5/U6, R = 1.4 ohms

No rating plate on motor, or any motor rating info on drg.

All insulation resistances between windings & to earth >500M ohms on motor & cable to motor.

Supply cable tests OK on IR & continuity also.

No RCD's involved to simplify things.

Motor will not run up to speed, and upon change over from start to run, trips mcb, B20, which it was running on fine.

Manual changeover on release of start button.

Motor wired to drawing, as long as winding tails in motor are correct.

Starter & motor wired to drawing.

No mechanical issues.

Caps are 100 uF each and test OK alone & in parallel which is how they are wired in starter, both for capacitance, and as far as I can tell ESR.

I don't have an AT31/33, anyone?...

I need ideas for a quick fix.

I'm the 2nd person to check this out, 1st guy was very familiar with machines too!

It has already had 3 new contactors & aux's.

Had not found any wiring issues with the previous repairs.

Suggestions...

 

[Jono Pashley]

Not going to help you but i get sick of the amount of things with nothing identified no paperwork etc and now it doesnt work and your getting grief for not fixing it in 5 mins...

 

[OnOff]

Have you checked the centrifugal switch?

 

[steptoe]

I think Andy may be your man,

cos Im most definately not,

sorry.

you know way more about this stuff than me, and if you are stuffed, then I am floundering.

 

[batty]

Me too Steps.

 

[Sidewinder]

Have you checked the centrifugal switch?

No switch, it's done in the starter.

 

[M107]

Sorry Sidey I'm with Steps & Batty..............

But keep us informed as we love to learnO)

 

[Zeespark]

A total shot in the dark here (still learning the basics of this kind of thing) but could it be to do with your B20 MCB needing to be a C or D at all? I am ready to be shot down

AndyGuinness

 

[Sidewinder]

Could be, but that does not explain why it worked for 2 years on this mcb before failure!

 

[Zeespark]

I apologise Sidey, this has got Me stumped and I will be thinking about it, is the new MCB in good working order?

AndyGuinness

 

[batty]

Maybe DNO have reduced the voltage hence more current is now flowing.

 

[Sidewinder]

Same mcb, but, it could have "weakened" trouble is no way of realistically testing an mcb.

 

[Evans Electric]

OOoooo I hate SP motors too , I'm keeping out of this , can't help . Those things are weird . 3PH nice and simple.

Is there any extra load on the machine , whatever it is ?? Seeing as the starters work without the motor?

 

[steptoe]

adding to Dekes thoughts,

is there any extra loading on the shaft? bearings on the way out etc,,,,,,

probably just grasping, but may be worth thinking about,

 

[apprentice87]

Hi Paul,

Perhaps the thing is not wired up right.... someone else has been messing with it after all...

Do not know if this will be any use.... Only thing i could find for a motor with three windings...

It is interesting that you resistance readings add up EXACTLY in the way described below...

"For a single phase compressor your highest resistance reading between any two connection points should be found from the start (S) terminal to the run ® terminal.

Once you determine where you get your highest

reading, this will identify the common © terminal as

the terminal you were not using when you found the

highest reading.

Write down or remember the highest reading value for the moment.

The next test will be from the common © terminal to each of the other two compressor terminals, S and R.

Whichever has the highest reading from the common © terminal will be the start (S) winding terminal and the lowest reading will be from the common © terminal to the run ® terminal.

If the compressor windings are good the resistance values will add up correctly. For example, if the highest reading found was 10.5 ohms (S to R). Then the next highest reading was 8.4 (C to S), then the lowest would have to be 2.1 (C to R) for the compressor windings to be good. (C to S) + (C to R) =

(S to R) would indicate the compressor windings are

good for a single phase compressor.

Normally your readings may not be exact to the decimal point (your meter could round up or down the values) but should be really close if the compressor windings are good.

Hope this helps....

john...

 

[steptoe]

you go John,

show these so called professionals how to do it.

good post BTW, Ive got sandra to note it all down for me and she will bring it round tomorrow as soon as her new dress arrives,

you did say it was size 11 stilletoes, didnt you, Deke?

 

[apprentice87]

Hi Steps....

I am still busy trying not to burn down the local steel stockholders with my newbie wiring!!!! They might be needing some new motors soon!!!

john..

 

[steptoe]

AH, I see, canoey has you on commission.......

 

[apprentice87]

Makes you wonder...Two o'clock in the morning and we are all on here worrying about electric motors, and i have just re-assembled a lathe chuck!! Not much exciting ever happens around here...

john..

 

[Sidewinder]

It's slightly different, in that I have 3 windings, both ends of which are brought out to the motor terminal box.

From there only 2 windings have 1 end linked, thus I have 5 winding ends at the starter.

I have to hope that the winding tails entering the terminal box are correctly identified, else I'm goosed!

I have checked these winding ends to the drawing & back to the starter through the motor cable and all seemed OK.

No caps in / on the motor, only the 2 in the starter, which test OK.

The main fault really is the under speeding.

The starter operates in a very similar manner to a star / delta.

When the run contactor kicks in with the motor underspeed, it could just be going out on over current, due to the inrush of it trying to achieve synchronous speed.