Wye Delta Breaker Tripping Problem 1

[indjer]

Scenario is as follows:

I have a 460VAC, 60Hz,3 phase, 1750RPM, 500Amp induction motor designed to
operate on a 480VAC Wye start/ Delta run starter system.

When a different motor was tested on this machine, it starts properly and
there is little load on the dual output shafts(About 25% of the full load
amps).
Each shaft has a hydraulic pump attached that spins easily.

The Main breaker trips off when the problematic motor transfers from Start
to Run.
Why?

The motor has 12 leads.
They are numbered as follows: 1,1 2,2 3,3 4,4 5,5 and 6,6.

The motor leads continuity test as follows:
1,1 to 4,4.
2,2 to 5,5.
3,3 to 6,6.

The motor is connected to the starters as follows:
L1 to 1,1 L2 to 2,2 L3 to 3,3 on the Main breaker (no Main contactor)
L1 to 6,6 L2 to 4,4 L3 to 5,5 on the Delta run contactor
6,6 4,4 5,5 on the Wye start contactor also.

The phasing from the Main breaker to the motor leads connections has been
verified as correct for the Wye/Delta configuration.

The Main breaker is a 700Amp shunt trip breaker. It can be shunt tripped from the Overload relay or motor thermal sensors, as well as tripping from overcurrent. The adjustable trips are set at Maximum.

The starting sequence is:
The Wye start contactor is closed first.
The motor ramps up to speed in the correct rotation.
After 5 seconds the Wye start contactor opens and the Delta run contactor
immediately closes.
Wham! The breaker trips.

Why?

 

[Zogzog]

What type of breaker, what trip unit and functions? Have you tested the breaker?

 

[electricpete]

Maybe it can be gleaned from info you posted, but I assume this is open transition?
what is the instantaneous setting of the breaker?
setting should be selected just as high as if it was dol start imo

=====================================
(2B)+(2B)' ?

 

[jraef]

This is a very well known problem with Open Transition Wye-Delta starting. it has to do with the phase shift that takes place when switching from Wye to Delta and how that interacts with any residual magnetism in the motor at that moment, and the point in the sine wave at that moment, etc. etc. etc. there are numerous papers written about this available on the Internet if you want to get into the nitty gritty. the archives of this forum have links to some of them that I and others have posted in the past, but it's been a few years now since anyone has brought this up again.

You essentially have 3 viable options:
[ol]
[li] You can try "rolling" your conductors. That means just swap A to B, B to C, and C to A. this changes the Phase Shift relationship and sometimes takes advantage of slight existing differences in the motor winding resistance to reduce the magnitude of the transition spike. There is about a 30% change of that taking care of it, worth a try.[/li]
[li] You can change to a Closed Transition Wye Delta Starter, very expensive to retrofit, and it requires transition resistors that are left in the circuit to absorb that transition spike (readers digest version)[/li]
[li] Junk that Wye Delta starter and replace it with a Solid State starter. it will be less expensive than a Closed Transition W-D starter and has no transition issues.[/li]
[/ol]

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[Skogsgurra]

Rolling the conductors may not help. The motor is windings are usually very identical. But if you change phase sequence (rotation) from graid to starter and also from starter to motor (to maintain motor rotation direction), it may help.

The reason is that the phase shift described by Jeff then changes from negative (or positive, you never know) to positive and if the shift you get with the actual connection is bad for the start, it is probable that the other shift helps.

I think it is worth a try. But, with 500 A, the cables may be a bit stiff and hard to change.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

Read grid, not graid. There's also a redundant "is".

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

Eng-Tips Search Link

Article by Robert Wooddall that I often refer to, but the earlier links in the above are broken:
"Why Wye Delta Starting Cause Breakers to Trip"

The company that published that article, Master Controls, make Fire Pump controllers and breaker trips from transition spikes is, to put it mildly, HIGHLY undesirable on Fire Pump controllers. I used to be a Service Rep for them years ago. They taught me the conductor shift trick, it did work. They came up with a device called a "Leading Phase Monitor" that monitors the phase angles of the current and voltage and gave an LED indicator when it was OK, so we would shift the conductors to attain this. After they did that, they stopped telling everyone that there was a "free" fix to try first, because they wanted to sell their starters with that device built-in.

Instruction Sheet

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[dpc]

Jeff,

Thanks for link and the education.

Dave