Why the 480 & not the 240.

[ptonsparky]

Dairy called & said one of his 480v pumps would run but the other would click on off on off every second or two & now wouldn't run at all. Nice SQD overload relay contacts were stuck open. Okay, jumper the overload do a quick hand operation and you can hear the overlaods click click click. Amp check showed horrible imbalance of current. Voltage check showed 315, 250 and 315 to ground. Checked other motor and imbalance was there as well but it did not have the fancy overloads to detect the imbalance.

Problem was POCOs with some line regulators and related substation troubles the night before. There are two services to this dairy fed from the same primary. One is 3 ph 240 hi leg. The other is 480/277 with a 240/120 single phase derived from it. The only problem was with the 480v motors. The single phase fans derived from the 480v step down were just fine. The 240v 3phase service voltage was good and all the motors on it were working.

Can some one shed some light as to why only the 480 had problems & not anything else.

 

[mcclary's electrical]

Different POCO transformer, and maybe even different substation

 

[mivey]

Different POCO transformer, and maybe even different substation

Nope. Different transformers but same primary.

I'm thinking better voltage regulation and that one bank was delta and the other wye or even 3 pigs vs 2 pigs. Don't feel like drawing it out right now.

 

[cadpoint]

MO the Poco let the smoke out of those motors.
I think its time to meggar the motor!

From Tom Henry: "Higher tempertures caused by increased current or higher ambient temperatures produces
a deteriorating effect on the motor insulation and lubrication."

Did you re-check every aspects of the math for these motors?
What's the SF of the motors, did you check the motor againest the correct overload protection properties?
Is it the right size (for the heaters)?
Article 430.32(a)(1) Minimum size, Article 430.32(C) Maximum size

Where exactly are you taking the amperage measurements? You might need to check the street Line side right in front of the gear?

 

[mivey]

MO the Poco let the smoke out of those motors.
I think its time to meggar the motor!

From Tom Henry: "Higher tempertures caused by increased current or higher ambient temperatures produces
a deteriorating effect on the motor insulation and lubrication."

Did you re-check every aspects of the math for these motors?
What's the SF of the motors, did you check the motor againest the correct overload protection properties?
Is it the right size (for the heaters)?
Article 430.32(a)(1) Minimum size, Article 430.32(C) Maximum size

Where exactly are you taking the amperage measurements? You might need to check the street Line side right in front of the gear?

Ignoring the motors for a moment and just considering the voltage: The 480 volt service had a bad unbalance but the 240 service did not.

It does not matter what goes on with the motor until the 14.8% unbalance is corrected.

 

[Besoeker]

Dairy called & said one of his 480v pumps would run but the other would click on off on off every second or two & now wouldn't run at all. Nice SQD overload relay contacts were stuck open. Okay, jumper the overload do a quick hand operation and you can hear the overlaods click click click. Amp check showed horrible imbalance of current. Voltage check showed 315, 250 and 315 to ground.

Did you measure the line to line voltages?

 

[mcclary's electrical]

Nope. Different transformers but same primary.

I'm thinking better voltage regulation and that one bank was delta and the other wye or even 3 pigs vs 2 pigs. Don't feel like drawing it out right now.

How is it YOU are the one saying this? You're not the OP. I've seen different substations feeding the same plants in several different locations. How can you just say NOPE, without seeing it. I did work for a sawmill last month that has two different substations feeding it. In hospitals, they HAVE to have two substations. So tell me, where did this NOPE come from?

 

[mivey]

Did you measure the line to line voltages?

Good point. And I forgot, the unbalance formula may not be applicable for line-neutral voltages.

 

[hillbilly1]

Possible high line buck/boost transformer has been shunted on one phase somewhere down the utility line? Should affect the other service too though, if it is on the same primary. Our poco uses seperate buck/boosts for each phase to correct voltage drop on long lines, being a farm it is probally not close to a sub station.

 

[mivey]

How is it YOU are the one saying this? You're not the OP. I've seen different substations feeding the same plants in several different locations. How can you just say NOPE, without seeing it. I did work for a sawmill last month that has two different substations feeding it. In hospitals, they HAVE to have two substations. So tell me, where did this NOPE come from?

From the OP:

There are two services to this dairy fed from the same primary.

 

[mcclary's electrical]

From the OP:

Whewww,,,,I missed that. My apologies.

 

[mivey]

Whewww,,,,I missed that. My apologies.

No apology necessary, it's early yet. Time for another cup of coffee. :grin:

(or some Minute Maid Boost). :grin:

 

[wirenut1980]

As others have stated, voltage unbalance is calculated using phase to phase values. What voltage did you measure at the 240 V motors?

Some possibilities:

Depending on where the 2 services are in relation to each other, there might be voltage regulators in between them that would affect one service and not the other.

The high leg delta bank usually has a larger transformer to supply the single phase loads which might have offset some of the unbalance for the 240 V motor load.

The 480 V might have been loaded at a higher percentage of nameplate than the 240 V motors. A lightly loaded motor can tolerate more voltage unbalance than a motor that is running closer to full load.

Also, single phase motors do not care about voltage unbalance.

 

[K2X]

but the other would click on off on off every second or two

My Myers piston pump does that when the head pressure gets out of wack.

 

[ptonsparky]

The control system had faulted and nothing started until the owner went out to check. Overload that failed open, after a reset or so by owner, was a SQD MotorLogic. It dedected the imbalance and shut things down even though it was set at 90 amps instead of the 47 it should have been. I did not meg the motor. Probably should have.

I did not check L-L voltage.

Regulator is down the road a mile or so. Transformer banks are one span apart.

I checked voltage @ 240v Hi leg service disconnect and all was within reason.

 

[ptonsparky]

I now have a nice overload.
Took it apart to see why it would not reset. Design problem. I weigh 190 give or take and could not get it to reset. Add a little lube to the plastic parts & it works good now. Something else to sit on the shelf & never be used again.