Star Delta Contactors Got Burnt When Starting the Motor but The Main Contactor Did Not 9

[imannul98]

Hello

I have a 45 kw induction motor with starting method using star delta method. The star and delta contactors of the motor have been for several occasions got burnt. However, I haven't figured out why the contactors got burnt. The FLA is 93 A, and the contactors have a rating current of 105 A, breaking current of 930 A, and making current of 1050 A. I figured that it was probably caused by the star and delta contactors being closed at the same time during the transition. Hence, I added 1.6 seconds after the star contactor opened for the delta contactor to close. However, it got burnt again.

And then I realized that because the current that flows through the star and delta contactor also flows through the main contactor, thus, if the star and delta contactors got welded, then there should be three contactors that got burnt, not just 2. Does anyone know what seems to be the problem that causes the star and delta contactors to get burnt but the main contactor doe not? Thank You

P. S.
The timer for the star contactor in the close position is 4 seconds.

 

[che12345]

Dear Mr. Marke
1. M. "...When star-delta (wye-delta) starters were in common usage, there was ..... Those of us with grey hair have lived through this and generally have ..... their usage and design...."
C. I am a septuagenarian. I am in full agreement with your learned opinion.
2. M. "... Today, the number of new star/delta starters that I see is very small, less than one per year...."
C. My observation for the past fifty years and up to to-date, differs greatly from yours. Among various "reduce-voltage" starters , Star-delta starting is acceptable world-wide, used on land and in marine installations. It is very effective, very low in cost and in foot-print etc. Soft-starter seems to be an alternative, but has its limitation.
3. M. ..." In terms of the "phase shift" argument, .... as a means of reducing the "auto reclose" or "open transition" switching transient. ....at full synchronous speed, the rotor .... the [motor connected in star] and running at full synchronous speed, the [rotor] will be in direct synch with the supply...".
C. Disagreed. Under no-load or loaded, the motor will never reach the " synchronous speed "
4. M. " ... At the point when .... the winding is connected to. ....i.e. assuming that the phase sequence is L1 - L2 - L3, and we consider the winding connected to L2. We have the choice by the wiring to the delta contactor, to connect the end of the winding to either L1 or L3....will result in a much lower transient current... "
C. Agreed. The theory is accepted.
5. M. "... The switching transient is very short and will not over heat the contacts..."
C. Agreed.
6. M. " ... Auto reclose and open transition switching results in a very high "inrush" current to the motors. This exceeds the LRC by quite some margin, but is only present for a couple of cycles. Associated with this inrush current, there is a severe torque transient that is responsible for much mechanical damage, broken chains, broken couplings broken gearboxes etc."
C. For the past fifty years, all the star-delta starters [were] wired "out-of-phase transition" There were unfavorable (mechanical damages) " reports" , but I am yet to see any (broken shaft) due to high out-of-phase switching transient.
7. M. "...Inrush current is not the same as starting current which can last for seconds."
C. Agreed. High Inrush or transient current last for 1/2 -1 cycle only.
8. C. This would be my repeated request No. 4. , for a wiring connection for cw and ccw rotation.
Che Kuan Yau (Singapore)

 

[waross]

The safest way to reverse is to interchange any two incoming phases to the contactor.
No diagram needed for this.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr. waross
1. W. " ....The safest way to reverse is to interchange any two incoming phases to the contactor.
No diagram needed for this."
C. I disagreed. Let us wait for another ten (10) days for [other expert's opinion].
2. This would be my repeated request No. 5. , for a wiring connection for cw and ccw rotation..
Che Kuan Yau (Singapore)

 

[LionelHutz]

Google it or draw it out. It's not hard, and it wasn't asked by the OP so kind of off topic. But anyways, use 4 contactors by putting main reversing contactors ahead of the star and delta contactors.

I'm trying to understand why someone who is insistent with their advice regarding these starters keeps asking basic functional questions about these starters.

 

[edison123]

che

Stop hijacking this thread with irrelevant harangue. RF'ed.

Muthu

http://www.edison.co.in

 

[waross]

Mr. Che.
I am not sure what you are asking?
Are you asking how to connect so that the transition phase shift is correct?
Honestly, I have not seen a star-delta starter for quite a few years now.
I have several good text books on motor connections.
Knowing the importance of the preferred transition phase shift, and in the event that I am faced with a star-delta starter, I will refer to my texts and refresh my memory before proceeding to make connections.
I will probably try to verify my connections before leaving the site.
How will I verify my connections?
At this time I can't say.
The verification method will depend quite a lot on what test equipment is available.
"It depends"


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr. edison123 (Electrical)24 Feb 21 00:42
E. "... Stop hijacking this thread with irrelevant harangue..."
C. No intention of "hijack" or " harangue" . Just wish to clear the air as the sub-subject of "in-phase transfer transient" had been raised. Just answering to the point, no more.
Che Kuan Yau (Singapore)

 

[che12345]

Dear Mr. waross (Electrical)24 Feb 21 04:42
M. "... I am not sure what you are asking?..."
C. This would be my repeated request No. 5. , for a wiring connection for cw and ccw rotation..
Che Kuan Yau (Singapore)

 

[davidbeach]

Swap two phases, as stated long ago.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

C. This would be my repeated request No. 5. , for a wiring connection for cw and ccw rotation..

REQUEST DENIED.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr. davidbeach (Electrical)25 Feb 21 03:55
D. ".Swap two phases, as stated long ago. "
C. 1. Look into the major European and US contactor manufacturers' recent publications, you will see for yourself that "... Swap two phases as stated long ago... " may? NOT be the best/correct?.
I am a young septuagenarian and have being practicing for the past fifty years. I had noticed the "recent development" which takes the "in-phase transition" into consideration; in the recent say five years.
2. This would be my repeated request No. 5. , for a wiring connection for cw and ccw rotation.
Che Kuan Yau (Singapore)

 

[che12345]

Dear Mr. waross (Electrical)25 Feb 21 05:58
1. W. Quote: " REQUEST DENIED."
C. " denied " noted with regret. The request is valid for another five (5) more days, (with extension if necessary)! We respect your very prompt learned advice regularly.
2. This remain my repeated request No. 5. , for a wiring connection for cw and ccw rotation.
Che Kuan Yau (Singapore)

 

[itsmoked]

Mr. Che; I'm sure you understand reversing a three phase motor by swapping leads so I'm also sure you're not asking for a diagram of just that.

Could you please clarify what diagram you seek?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[che12345]

Dear Mr. itsmoked (Electrical)26 Feb 21 12:19
I. " ... I'm sure you understand reversing a three phase motor by swapping leads so I'm also sure you're not asking for a diagram of just that. Could you please clarify what diagram you seek? "
C. Please read my mail dated 25th Feb. answering to Mr. davidbeach's learned advice.
Repeat: Look into the major European and US contactor manufacturers' recent publications, you will see for yourself that "... Swap two phases as stated long ago... " may? NOT be the best/correct?.... I am a young septuagenarian and have being practicing for the past fifty years. I had noticed ...".
Inform me if you still failed to see/dispute with the "recent development", I may have to show you, to make sure that you " fully understand". I wish to refrain from "hijack" or " harangue" this forum.
Che Kuan Yau (Singapore)

 

[waross]

Mr. Che.
imannul98 posted the following issue:

Star Delta Contactors Got Burnt When Starting the Motor but The Main Contactor Did Not

While we sympathize with your problem, it is not within the scope of this thread.
If you wish information in regards to reversing a Star-Delta motor, please do not Hi-Jack this thread.
Start a new thread with your question.
Off topic posting is contrary to the site rules.
Thank you.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr waross
W. "... While we sympathize with your problem, it is not within the scope of this thread.
If you wish information in regards to reversing a Star-Delta motor, please do not H....".
C. You had on 25th Feb. declared " REQUEST DENIED." loud and clear.
I have to "denied" any further discussion on this subject. Case closed, FULL STOP.
Che Kuan Yau (Singapore)

 

[waross]

imannul98 :
Another possibility.
In a problem installation with marginally sized contactors, it may be preferable for the star contactor to close ahead of the main contactor.
If the main contactor closes first, the star contactor will be closing on starting current.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!