Transformer Rating

Me thinks you have made a large mistake... 1500 kVA or 2500 kVA. You mean 1.5 kVA or 2.5 kVA right?

I meant 1.5kva and 2.5kva you're right thanks. I have 16 powerflex 40 drives. When we activate the estop it kills the 480 to the drives. On power up sometimes we lose the internal supply in the drive and have to replace it. We want to reconfigure the circuit by adding a contactor between the drive output and the motor.we keep the power on the drive constantly and active the contactor during an estop. I need to upgrade my transformer to handle the inrush current from the additional contactors. 16 total. 10amps of inrush current. We are currently we using a 480\120 1.5kva. What do I go to to handle the added current? 2.5kva?

Kva is way overkill; 1000va might even suffice. The inrush load will be brief. However, I would check with the transformer and coil manufacturers that the momentary voltage dip is still enough to pull in the coils.

Would it be possible to energize some and then the remainder of the coils in two steps?

I am a little confused. Based on your previous question you appear to be trying to start 16 motors simultaneously using what appear to be DOL motor starters. Why DOL and why simultaneously? How large are the motors and what are the motors driving?

What exactly are you trying to do and why are you not using either soft starters, 480V control coils without the transformer, etc. Are you qualified to perform this work as the content of your posts is worrying?

Can you please provide more information on your application.

We have allen bradley powerflex 40.whenever the estop is hit it kills the 480 to the drive. On power up the drive loses the internal power supply. We wanted to keep the power on the drive continuously and add a contactor on the output to isolate the motor from the drive during an estop. I have 16 drives to isolate. I need to upgrade the control transformer to feed the additional contactors

If it were me I would run the E-stop to the drive's E-stop to allow the drive ramp down function if necessary (load dependent) along with keeping the electronics live for rapid restart and then use padlockable isolators next to the motors for electrical isolation (visual indication of electrical isolation and ability to lockout for maintenance are important safety features recommended or required in many countries).

However it depends on your countries local codes.

Also be aware that opening contactors on the live output side of the drive can result in drive damage and parallel contactors won't help if a single motor needs to be taken off line for maintenance.

You still haven't said why you want to restart all these motors at once. I fear for the main supply fuses. Bu%%er the control transformer!

We have 16 powerflex 40 drives. Whenever the estop circuit is activated it kills the 480 to the drives. On power up sometimes we lose the drives internal power supply and have to replace the drive. We wanted to add a contactor between the drive and the motor so when we activate the estoppel the 480 stays on the drives and the contactor isolates the drive and motor. We are currently using a 480\120 1.5kva control transformer. The additional contactors pickup current is 10 amps total. Would going to a 480\120 2.5kva provide enough current for the additional contactors?

Would going to a 480\120 2.5kva provide enough current for the additional contactors?

Sure, but I don't recommend this contactor system as a way of isolating the motors, especially if the drive is going to still be running under load when the contactor on the drive output opens.

The drive manual should indicate that this is not recommended by the manufacturer as it could cause damage to the drive, and it certainly isn't recommended if you plan on leaving all the drives running at full output then throw all the contactors closed to restart the motors for obvious safety and maintenance reasons (ie using the contactors as motor controllers rather than no-load isolators).

Thanks you guys were very helpful. Norris534

13 of the drives are 2hp, 3 are 1hp and l'd planned on connecting the enable through the aux contactors to shut down the drives. Currently and additional MCR contactor removes the 480 from all drives when the estop is activated. Total inrush^2 + total sealed^2 square root is coil impedance, correct? Recommended 525 but we have to upgrade the plc also. Company would rather replace the unit than do that. It's a pallet wrap machine. Should I use a transformer just to feed the contactors alone? That's what I had in mind. PLC is a 500.

MAde a mistake, total power not impedance. Planned on Using AB C12 Contactors

FOr JRAEF post How do I determine my primary and secondary current values for fusing? Need some help

Use the code book.

1500va - Slow blow fuses, wire sized at least 125% of fuse rating, fuse rating to protect transformer and wire large enough to handle the fuses - looks approximately 10 amp time delay fuse and 16 AWG(min) TEW/AWM wire on the secondary. Primary current is reduced be the voltage ratio - about 1/4 with 480 volt primary - choose next largest standard fuse - say 3 amps - slow blow -if it blows on inrush use the next larger fuse.

Cheap transformers have high inrush - check with supplier - you may end up with a 15 amp primary fuse and 14 AWG wire. Many of the small transformers can be ordered as a kit with the primary and secondary fuses mounted on their terminal boards (IE: Hammond)