Motor starter contactors getting welded

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kapil_mohan21`

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Hello,

I am using a 3 phase 10HP Star delta motor starter in an 3 HP induction motor in a spinning mill machine.
The machines has two motors i.e one for forward rotation ( upper motor ) while second for reverse rotation( bottom one) ( both have independent supply)

The contactors of motor starter in reverse rotation motor ( bottom ) are getting welded (star & delta both). I have changed the contact tips many times but still contacts are getting welded.

For further troubleshooting I also interchanged the forward motor starter with reverse one , but the problem still exists for motor starter used for reverse rotation of motor.
Please suggest a method for resolving.


Thanks & Regards
Kapil_mohan21

motors photo in surat.jpg
 
What justifies the need for wye-delta starting on only a 3 HP motor?

Regardless sounds like complete contact replacement kit or replacement contactors need installed, and verify proper sequencing of wye-delta transition as well as verifying interlocking so forward and reverse can not happen simultaneously before burning out another set of contacts.

If there is frequent stopping and starting, maybe even a VFD instead

Looking at the picture, those motors seem a little large for 3 HP?
 
Does the machine come to a stop before energizing the reverse motor, or does that motor need to decelerate the load and then accelerate the opposite direction?

How much inertia does the load have if that is the case?
 
kapil_mohan21` said:
Hello,

I am using a 3 phase 10HP Star delta motor starter in an 3 HP induction motor in a spinning mill machine.
The machines has two motors i.e one for forward rotation ( upper motor ) while second for reverse rotation( bottom one) ( both have independent supply)

The contactors of motor starter in reverse rotation motor ( bottom ) are getting welded (star & delta both). I have changed the contact tips many times but still contacts are getting welded.

For further troubleshooting I also interchanged the forward motor starter with reverse one , but the problem still exists for motor starter used for reverse rotation of motor.
Please suggest a method for resolving.


Thanks & Regards
Kapil_mohan21

View attachment 17533
Click to expand...
Tried replacing the reverse motor?
 
Did you check the coil voltage at the starter coil? And under voltage condition can keep the contactor from fully engaging fast enough to limit arcing.
 
infinity said:
Did you check the coil voltage at the starter coil? And under voltage condition can keep the contactor from fully engaging fast enough to limit arcing.
Click to expand...
Or cause "chattering". Also look for poor contacts in any controls that would cause low or intermittent voltages.
 
What you are experiencing is not at all uncommon for Star-Delta, its inherent in the nature of how it works.

Junk the Star-Delta and put in a Reduced Voltage Solid State soft starter, problem solved. You can re-use the contactors for reversing. Yes the RVSS will be slightly more expensive, but you have already experienced the folly of choosing the cheapest method of reduced torque starter you can buy; it's only cheap for the original equipment mfr, not for those that must live with it long term.
 
Jraef said:
What you are experiencing is not at all uncommon for Star-Delta, its inherent in the nature of how it works.

Junk the Star-Delta and put in a Reduced Voltage Solid State soft starter, problem solved. You can re-use the contactors for reversing. Yes the RVSS will be slightly more expensive, but you have already experienced the folly of choosing the cheapest method of reduced torque starter you can buy; it's only cheap for the original equipment mfr, not for those that must live with it long term.
Click to expand...
The forward and reverse motor starters have been swapped and the fault persists with the reverse motor. This inclines me to the view that the problem may be the reverse motor.
 
Besoeker said:
The forward and reverse motor starters have been swapped and the fault persists with the reverse motor. This inclines me to the view that the problem may be the reverse motor.
Click to expand...
Sure, I don't disagree. Most likely that motor has more residual magnetism and residual magnetism can be a big problem with Star-Delta starting. Not with RVSS starting however, totally irrelevant.
 
Jraef said:
Sure, I don't disagree. Most likely that motor has more residual magnetism and residual magnetism can be a big problem with Star-Delta starting. Not with RVSS starting however, totally irrelevant.
Click to expand...
But if the reverse motor is knackered the RVSS won't fix that.
 
Besoeker said:
But if the reverse motor is knackered the RVSS won't fix that.
Click to expand...
True, in fact it will likely find any nascent flaws. In my experience when you use a solid state starter, the fact that it artificially limits the current for a longer time allows numerous motor defects to loom larger. When started electro-mechanically, it usually passes through those same early stage anomalies too fast to notice, until they become catastrophic.
 
STAR DELTA MOTOR STARTER BURNING

STAR DELTA MOTOR STARTER BURNING

infinity said:
Did you check the coil voltage at the starter coil? And under voltage condition can keep the contactor from fully engaging fast enough to limit arcing.
Click to expand...


Yes Sir
The coil voltage is suitable & I also checked for the supply voltage , there are no chances of under voltage to happen
 
ptonsparky said:
Is there a timing sequence that needs to be corrected in the control for the reverse motor?

Are the load characteristics different from forward to reverse?

I don't remember if I've ever had to troubleshoot that type of setup so I am curious.
Click to expand...



No, there is no time sequence

No difference in load characteristics , just upper one moving in forward rotation & simultaneously bottom one in reverse rotation.
 
STAR DELTA MOTOR STARTER BURNING

STAR DELTA MOTOR STARTER BURNING

Dear all

The motor starter at user's end now was replaced with another local make of star delta starter & the starter is working just fine, there is no problem of burning in reverse rotation of motor.

Please help me in understanding what may be the problem , as it confirms that motor doesn't seems to have problem. Old motor starter is of a good make.

Does forward & reverse rotation have different current consumption i.e. inrush or anything.

mean while I also checked that the contact gap between old & new one , new one has more contact gap. Can contact gap play a role for these condition.

Thanks
Kapil_Mohan 21
 
STAR DELTA MOTOR STARTER BURNING

STAR DELTA MOTOR STARTER BURNING

kwired said:
What justifies the need for wye-delta starting on only a 3 HP motor?

Regardless sounds like complete contact replacement kit or replacement contactors need installed, and verify proper sequencing of wye-delta transition as well as verifying interlocking so forward and reverse can not happen simultaneously before burning out another set of contacts.

If there is frequent stopping and starting, maybe even a VFD instead

Looking at the picture, those motors seem a little large for 3 HP?
Click to expand...



Sir,

The above picture shown is of 5 HP motor, it was just for ref purpose. The 3 hp motor are also similarity aligned lie this on spinning mill machine
 
kapil_mohan21` said:
No, there is no time sequence

No difference in load characteristics , just upper one moving in forward rotation & simultaneously bottom one in reverse rotation.
Click to expand...
If it is wye-delta starting method there has to be some sort of sequencing method for the starting process.

You can't power the machine for both directions simultaneously either. One motor may just be an "idler" so to speak while the other is driving the machine though.
 
kwired said:
If it is wye-delta starting method there has to be some sort of sequencing method for the starting process.

You can't power the machine for both directions simultaneously either. One motor may just be an "idler" so to speak while the other is driving the machine though.
Click to expand...

:thumbsup:

Quite possibly there is a difference in whether or not the spindle is already moving when power is applied to the motor.
If the two motors are in fact interchangeable, then the true test is to swap the motors and see whether the high current follows the motor or the location on the machine.
Just swapping the starters does not distinguish between the two possibilities.
 
kapil_mohan21` said:
Dear all

The motor starter at user's end now was replaced with another local make of star delta starter & the starter is working just fine, there is no problem of burning in reverse rotation of motor.

Please help me in understanding what may be the problem , as it confirms that motor doesn't seems to have problem. Old motor starter is of a good make.

Does forward & reverse rotation have different current consumption i.e. inrush or anything.

mean while I also checked that the contact gap between old & new one , new one has more contact gap. Can contact gap play a role for these condition.

Thanks
Kapil_Mohan 21
Click to expand...

The usual problem I had on wye-delta starters was when the delta contactor closes fast while the wye contacts have just broken/the contact arcs still not extinguished. The solutions I did were:
  1. choosing different-sized contactors. With a larger delta contactor (compared with the wye contactor), there will be a longer travel for the delta contactor shorting contacts to make from the instant of initiation, leaving the arcs at the wye contactor to die down first, or
  2. insert a small delay for the delta contactor closing.

You must allow the wye contacts to break clear before your delta contacts make.
 
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