Main purpose of Wye-Delta starter or other starter? 1

[elecmechcadet]

1.)Is it true that the motor especially induction motor has always had a 5-6 times at starting?
2.)Does the motor has a capability to return to its FLA durin g starting without any strting protection like wye-delta start?

 

[rbulsara]

1). Yes, only when starting at full voltage or Direct On Line.
2). Yes. Motor draws what it needs to draw. Wye-delta starter is not the reason for it. Y-D starter helps to minimize the starting current during the starting period, in wye connection. This also produces much less torque during the starting. Torque varies in proportion to square of the voltage applied to the motor.

Google search on the topic or read some good books on the subject.

Rafiq Bulsara

http://www.srengineersct.com

 

[itsmoked]

2.)Does the motor has a capability to return to its FLA during g starting without any starting protection like wye-delta start?

Yes! And much much more.

Delta-wye starters are notorious for protection tripping and fuse blowing because they can cause huge current spikes.

During the transition the motor is disconnected from the network but still has a magnetic field - hence is a generator. This 'generator' goes into a random non-synchronized electrical position with regard to the power source. During the delta-reconnection the 'generator' can end up 180 electrical-degrees out of sync. This then causes an even greater,(much greater), current spike than a direct connection start. Hence, the blown fuses and tripped protection. It's also unpredictably random.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Oh so the answer your title question:

Main purpose of Wye-Delta starter?

Starters are supposed to help start a motor with a reduced current surge.

Delta-Wye starters are specifically to trade a fixed repeatable starting current surge for a reduced fixed repeatable starting surge with random, occasional, very large, damaging current spikes.

As jraef stated elsewhere it's not a reduced voltage starter it's a political starter.

Use a modern soft starter if at all possible.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

You have learned well grasshopper...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[itsmoked]

Hai Sensi!!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[elecmechcadet]

Thanks to all!

Cheers to everyone!

 

[Noway2]

In my previous job, involving high horse power motor starters, Y-D starters were the most common configuration sold. Their response to the issue of random, large spikes was the offering of a wye-delta 'closed transition' starter, as compared to the normal one which was called the 'open transition'. It has been too long for me to remember the exact details, but if I recall correctly, the closed transition used an extra contactor to temporarilly apply a shunt resistor across the windings and prevent such spikes. There was always some debate amongst the more knowledeable reps and the company sales department was to wether or not it had any real effect.

 

[jraef]

Yes, closed transition Y-Delta works to take care of the spikes. It is also more expensive compared to a solid state soft starter and has way more moving parts to wear out. The only theoretical advantage Y-Delta has over SS is cost. Closed transition defeats that, so there is no justification for it any longer.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376