Delta Motor Connected to Star

Good Morning,

What is their before (Brief history)? Why you need to connect in Star?

B'coz, If that invertor is programmed, That motor data will be differ with inverter feed data. If it is card drive then, card need to change...!

Thanks

Thanks for the reply. The background is our electrical contractor mistakenly connect star instead of delta. After several days of running the motor burned. Our contractor admitted they made the wrong connection but claimed that star connection wont cause the motor to burn.

My understanding is in star connection the motor to run with low voltage, in this case 220V. Will it causes the motor to burn?

It will mean that your motor will lose capacity. The starting torque will vary by the square of the voltage reduction. The effective voltage when connected in Star when it is supposed to be Delta would be 58% (1/ the sq. rt. of 3). So starting torque will be reduced to 33% of normal (.58²). This often results in the motor failing to accelerate the load and it stalls.

Even if it happens to accelerate, running torque will then be reduced by the direct voltage drop, so running torque will be 58% of normal. The synchronous speed will remain the same because you have not changed the frequency. But because of the loss of torque, the slip will increase severely and the current will increase as the motor strains to attempt to return to its normal slip speed. The result is an overloaded motor.

Why did it burn up though? Most likely because your inverter was also incorrectly programmed and did not detect the increased current as it should have.

One doesn't solve a problem by having an argument.

How would the contractor know what the motor was turning and whether it was correctly selected for star operation (rhetorical question - NNTR)?

If the "approved for construction" drawings formally issued to the contractor say delta and the contractor wired star, then get the contractor to replace the motor and connect it correctly at the contractor's expense, witholding payment on the final invoice until it is correct, though how did the device get commissioned in that condition (rhetorical question - NNTR)?

Unless, of course, the wrong cable appears in the "approved for construction" Cable Schedule document formally issued to the contractor, the contractor did the only thing possible with too few cable cores and it was 'commissioned' in that condition and the contractor's final invoice was paid, in which case the contractor walks away from it and the individual that commissioned it gets hauled in to answer a few questions about the impending project cost over-run through needing to replace the motor and the consequent delay to Operations through failure of the device that the motor is turning to perform correctly and the lack of provision of a standby device by design for something that is process-critical.

So, it depends on what the paperwork says, really, which cannot be seen from here.

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I would say if the "approved for construction" drawings say something different from the motor nameplate, the nameplate should rule. But inform the drawing office of course.

Not sure what you mean by "too few cable cores" - 3 line cores in the supply cable are needed for star or delta connection .

Simply the motor plate says 380V Delta, and since the source is 380, the contractor should connect to delta. Motor supplier said its the wrong connection and the contractor said its the overload circuit wasnt working.

As you said in #2, the contractor connected it in star, ignoring the nameplate, so it's his fault. Maybe the overloads should have protected the motor, but the contractor is still at fault.

The motor will not burn out if the overload protection device in the circuit is set to trip at the star full-load-current for the motor.

If the circuit trips and the setting is correct, then the motor is overloaded, and an engineering re-assessment of the mechanical and electrical arrangements would become due.

Is it 380V star or 380V delta? The nameplate will tell you. If there are 6 terminals it should say either 380V star, 220V delta or 380V delta, 660V star. Connect it for 380V. If there are 3 terminals and it says 380V there's no choice. Then on 380 V supply it's OK.

BTW, connection of motors in "wrong" way has been discussed on this forum at some length, if you search the history.

Firstly thank you for your reply. The motor is 380V Delta, so Star should be 220V. The motor rated curent is 44A so does the inverter overload set at. In other word. the motor is set to trip at delta full load, which is 44A but was run at star full load due to wrong connection. Will this cause the motor to burn?

See #4↑.

meaning if u connect to star, the motor will burn at lower ampere?

See #4↑.

That's the wrong way round. 380V Delta is 660V Star. See #5↑.

Let's go back to fundamental.

Say the thermal relay set at 44Amps for delta running motor.

In motor the Phase current would be 44/sqrt3 Amps. This is safe value for motor to operate.

Now Motor is connected in Star and same thermal relay (44 Amps setting) and allowed to draw 44 Amps from source without tripping.

The winding of each phase is designed to carry safely 44/sqrt3 Amp. As a result thermal relay will not protect motor up to 44 amps phase current for motor winding of which can carry 44/sqrt3

As I and PWSlack have said, repeatedly in his case, if the motor OL protection in the drive is set correctly, it should have protected the motor from burning out regardless of how it was connected. If it was set for 44A and the motor pulls 60A it doesn't know if it is pulling 60A at 380V, 220v, or even 10V; amps are amps are amps and it should have tripped before the motor was damaged.

So again, either something is wrong with the settings of you VFD motor protection scheme, or it "burned up" for some other reason. you do not provide enough information for us to help you more than that, but here are some possibilities even IF the protection is set correctly.

1. The drive has current limit or stall prevention enabled. Normally, this functions to limit the speed as a way to keep the motor from overloading or stalling, regardless of the commanded speed. So if you commanded it to run at 50Hz, but it gets to 44A at 10Hz because of the lack of torque from the motor being misconnected, then it will remain at 10 Hz indefinitely. The current is still below the OL setting, so the VFD is happy, but now the motor is spinning very slow, yet at FLA. There is not enough cooling air (or water) flow at that speed so even though the OL is not tripping, the motor over heats anyway.

2. It has nothing to do with the load on the motor or the voltage, the "burn out" was a failure of the insulation at the first turn of the windings. This would indicate damage from what are called "standing waves", pulses of very high voltage created by a capacitive coupling effect in the motor leads and the high speed switching of the VFD transistors. You can learn more about this by searching that term, but it is very real and there are engineering considerations that must be followed in applying VFDs to avoid them. Without knowing more about your application, it's jet a guess though.

Shadowz,

I am glad you have responded a couple times to the answers, but you have ignored the essential questions asked by JRaef and others. I suspect you are not an electrician and are simply trying to get help in this situation where you feel something was wrong but the electrician is denying anything more than a simple oops.

Get an outside consultant to look at it--and get a written report of his/her findings. This would include a review of the inverter's programmed settings and a professional evaluation of the likely cause of failure. This may cost you some up front, but if the outside consultant agrees with your feelings, then the contractor will have to cover your costs.

Otherwise, pay for the error you didn't create. Hopefully you and the contractor will both have learned well from this (and not learned how to "get away with it" or "ignore it".)

--JMM

Dear Mr. shadowz

The answer for your question is YES for which there are 3 reasons, for burning out

as explained by other CR4 Members, and I need not repeat.

DHAYANANDHAN.S