3 Phase Stuff..!

[DurhamSparky]

going for a job interview tuesday and well i have got to do a trade test

stuff i should know but have not used it for a while!! as i never really needed it..!

had a good heads up so far but 2x Niggly stuff which i not really had much to do with..!

Star / Delta Motors...! am i correct in saying delta is when the phases are connected i.e

L1 - U1 - W2
L2 - V1 - U2
L3 - W1 - V2



and the following Test carried out for insulation are IR MEG Ohms L1 - E / L2 - E / L3 - E and or Continuity set to Ohms and between same points....

and just racking my brains a IR test can only be carried out on the phases if you have each side of the phase available..!


shoot me down in flames if you need...! alternatively correct me!


the other niggly one is relays and time delayed relays but i will just blag that one lol..!

 

[Guest123]

It's like map reading......along the corridors = STAR, up the stairs = DELTA.

 

[Knobhead]

Motor tests:

Star:
Do CR first There’s no point doing the IR if a phase is broken. U1>V1 V1>W1 W1> U1. You can skip one of the tests if 2 are in balance.
Earth IR just test one lead, they’re all connected together.

Delta:
CR U1>U2 V1>V2 W1>W2
IR U1>V1 V1>W1 W1>V1
Earth IR just link U1,V1,W1 and test as a job lot unless you find one is down then you have to do separate tests.

Relays:
NO/NC all operate together
Timers:
Delay on. NO/NC all operate together after delay
The wobbly is delay off, this needs a permanent independent supply to the relay for it to work. All contacts operate at the same time NO/NC at power on, but after a delay at power off.
They can be bought as a sandwich block that fits between 8 or 11 pin relays and the base or as a self contained unit.

 

[pmac10]

Durham, check out my post on skill test, should give you a few good pointers, also silvafoxx if he is lurking, can provide some good info.

 

[silva.foxx]

As it happens I'm in the process of drawing one up now... just for fun!

I'll post it when done - nothing too complicated but covered what I see as neccessary stuff for a 'factory spark' ie. motor starters, inverters/softstarters, PLCs, sensors, etc...

Many people can't get there head around PNP & NPN sensors, how they differentiate, how they are wired, etc...


I'm back in work tomorrow a.m. but I'll try and get something together before Tuesday... but any questions - ASK THEM ALL BEFORE THE TEST - no better place than here to sure up your knowledge. Good luck!

 

[silva.foxx]

Pictures always speak volumes, and great for understanding!

Star Delta always causes some confusion. I know some sparks who have refused to work on these connections as they don't understand them. Simple really... though they do make you 'twitch like a rabbits nose' when you fire them up after you wire it!

Star connection

Delta connection. I know sparks who can't get the two connections right.

Delay-on - times out before switching over.
Delay-off - switches over immediately but times out before switching back.


Any other questions? Plenty of knowledgable guys in this section.

 

[pmac10]

control for star contactor through N/C aux contacts on delta contactor and vice versa, what can possibly go wrong?? hee hee!!

 

[Guest123]

Another useful little PDF on Star/Delta.

 

[Des 56]

Sorry for hijacking,just a quick question to whoever
Did a repair on a star delta driven joinery machine on friday,I havn't done much with motors for years
No contactors
It was a rotary switch,manually changing from star to delta run
I wired the switch and new motor and it worked

My question to you current maintenance guys
Are these rotary switches still in normal use,or was this machine just very old

 

[pmac10]

never encountered those des, especially with no contactors, we use many machines that have two speed control that run in a star configuration then switch to delta for high speed, if i was to wire one up tomorrow i would use a variable speed drive with potentiometer control, like you said. probably just old.

 

[Des 56]

Thanks for the reply pmac10
Every one I have encountered always had at least change over contactors
Even the extra old ones had a handle to manually swing the contactors from star to delta

Given that the currentlevel needs monitoring for overload it was surprising it was directly fed
It was an old german machine,so maybe they know things we dont

 

[pmac10]

ahh, zee germans! cant complain Des, they make good gear, knipex, elora, siemens, over efficiently sickening!!

 

[silva.foxx]

Industrial Control - Bulletin 194L Control and Load Switches

Halfway down, Des.

How about moving to a soft starter?

 

[pmac10]

youll ace it Durham Sparky

 

[DurhamSparky]

cheers all...! just refreshing up as i type!