Star-Delta Starter

[muneeb altaf]

why we use star delt connection for motr

star telta connection my be use to redused inrush current of motor inrush current of motor in star 3 to 4 time of its normal current and ind 6 to 8 time due to this we use star delta startor in havy motors.?

 

[rsdoran]

???? You hunted down a 3 year old thread to post the obvious?

 

[504bloke]

FYI There is an easy non-destructive way to tell the 1's from the 2's, but it requires the use of a low voltage AC supply (DC won't do!).

If you label the wires as A&A, B&B, C&C, then connect one of the B's to one of the C's
Connect the low voltage supply to the wires A&A

Then check for an induced voltage across the wires B & C that are not joined together. If a voltage is present the you have connected a B1 to a C2 - if not then you have connected a B1 to a C1. A voltage of 10VAC supplied to A&A will give about 4VAC across the B&C wires.

Then use this method again with the A&C wires joined and voltage applied to wires B1 & B2

Hope this all makes sense

Goody,
I am glad that you mentioned about having the motor leads hanging out with no numbers and no way to tell which is which. That happens a lot - it seems that electricians like to just snip off the leads when pulling motor, instead of disconnecting them. Many times the wire numbers will get cut off also, or worn off from hard use.

I had a customer that requested a PLC device to determine which motor lead is which number. At first I thought this would be an IMPOSSIBLE job, but one day the proverbial light bulb went off, and I found a way, using only a Automation Direct DL-205 with ONE analog voltage input and some on/off inputs and outputs. The customer retired and sold his share of the business before I got it finished, but it seems to find all 9 exact leads of a 9 lead, 3-phase motor, every time. There are about 64,000 combinations! You may see this motor tester at http://www.forsytheandlong.com/.. Anyone interested in details?

We have an AllTest winding tester from martindale and this is able to tell us the 1's and 2's

 

[504bloke]

Be careful if you have 3 contactors, if you have 9 terminals in your motor you have a "Dhalander" wound star delta starter with high/low speed. I have some here and they do not work like a normal star-delta starter, sorry I connot tell you more than that. Anyone know more about this system?

9 wire dahlander connections see pic 6

 

[Calistodwt]

Using Star/Delta starting will usually require that steps are taken to ensure that the drive is started off-load or at reduced load otherwise there may not be enough starting torque developed to accelerate up to normal speed. Starting torque for Star / Delta starting is about 1/3 * Direct-On-Line starting torque.

 

[nonuke]

We have a rule in Europe: If the motor is =< 5.5 KW we use a DOL starter. If the motor is > 5.5 KW we use the old Star-Delta starter or the new Soft-Starter. the reasons were already explained since 2004

 

[PeterW]

???? You hunted down a 3 year old thread to post the obvious?

This could be taken as a challenge, we should alls earch for the oldest thread we can add a post too. The oldest wins.

Perhaps a bonus point as well if it contains Terry Woods.

 

[rsdoran]

This could be taken as a challenge, we should alls earch for the oldest thread we can add a post too. The oldest wins.

Perhaps a bonus point as well if it contains Terry Woods.

Better yet would be all the Nelson's.

 

[bornwild]

Star Delta, the first time you come across it can be confusing. I have had many calls from experienced electricians that do not know how to connect a star/delta motor up.
For that matter I do not think there is a standard method. It all depends how the wires are connected at the contactors.
Some connect at the contactor end A1 B1 C1 A2 B2 C2 and some connect A1 B1 C1 B2 C2 A2.

This is where the confusion sets in. because sometimes if you follow the connections at the contactor side in the motor, it doesn’t always work correctly.
Several things can happen.
On start up the motor starts in star but at changeover to delta the motor slows down and stops. If you use a volt meter at the motor, there are the full 3 phases present but it is not turning.
This is because the 3 windings at the motor have the same phase at each end of the winding.
This is cured by shuffling the 2’s wires down one terminal and the last wire back to the beginning.

The next thing that can happen is that the motor goes in to star and delta ok but is going the wrong way.
This is usually cured by changing two of the line phases around. But, this is not always possible and sometimes you have to change the direction at the motor terminals.
To do this you have to change 4 wires around. For instance A1 and B1 and then A2 and B2.
Not many people know how to change the direction of a star/delta motor at the motor terminals; it is a handy trick to have in your repertoire.

And the final thing that can happen is; star ok then heck of a buzzing noise in delta and usually it trips out.
This is because 2 windings have full voltage and the other one has the same phase at each end.
This is nasty and needs the 6 wires to be belled out correctly.

Then there is the worst scenario; the 6 winding wires are hanging out of the motor with no markings. (I have had this)
You cannot tell which are 1’s and which are 2’s.
You can find the three windings but you cannot tell which side they should go on..
It is down to trial and error and if you get it wrong, 2 windings are trying to go one way and the third is trying to go the other. The motor makes some great noises and if you are not quick, you let the smoke out.

Thanks Goody. Alright is this the right way to change directions at the motor terminals.

@bold
Also i am not sure about the lines you explained

 

[jvdcande]

Wow! Didn't realise star-delta was such a big problem. 9 and a half years to get the grasp!

Talk about bringing the dead (thread) back to life.

 

[bornwild]

I am sorry for resurrecting the thread. I am just a kid

 

[Lancie1]

Bornwild, That is okay. I always like to see the old posts by Ron Doran, a long-time contributor now deceased.

 

[iant]

Bornwild, That is okay. I always like to see the old posts by Ron Doran, a long-time contributor now deceased.

Is Terry still arround?

 

[Lancie1]

The last post from Terry Woods was March 31, 2009.

http://www.plctalk.net/qanda/showthread.php?t=46234