varing voltages

[ninosparkz]

2000a/ 480v MDP fed from utility transformer ... when a meter is put across phases it reads from 486v a to c , 497v b to c , 490v a to b phase. this is causing a 50 ton unit on the roof to trip at the motor overload protecter at night.
Down stream ( about 600 ft away) a 480v recerptacle meters at 486v across. any info or insight would help greatly.

monroe nj , industrial area

 

[chris kennedy]

...........

 

[chris kennedy]

2000a/ 480v MDP fed from utility transformer ... when a meter is put across phases it reads from 486v a to c , 497v b to c , 490v a to b phase.

These look like acceptable voltages to me.

this is causing a 50 ton unit on the roof to trip at the motor overload protecter at night.

And how have you determined this?

 

[ninosparkz]

the motor overload operates between 426vto 506v ... im geussing that overnight there is less demand and a spike in voltage

 

[ptonsparky]

That is only an imbalance of 1.2% give or take. Not much. What is the current on these phases? Balanced? What is the voltage at the Unit? Current? A recording device at either the Unit or the MDP would certainly help. Both if you have the equipment.

 

[brian john]

1. What are the phase loads?
2. Have you looked into any possible connection issues? IR Scan
3. What are the phase currents at the motor?
4. What is causing the motor to trip (UV relay, OCP?, Shunt Trip from another device)
5. All conductors sized properly.
6. How or were are the taps set on the transformer (if there are taps).

 

[ptonsparky]

the motor overload operates between 426vto 506v ... im geussing that overnight there is less demand and a spike in voltage

Rethink this.

 

[robbietan]

2000a/ 480v MDP fed from utility transformer ... when a meter is put across phases it reads from 486v a to c , 497v b to c , 490v a to b phase. this is causing a 50 ton unit on the roof to trip at the motor overload protecter at night.
Down stream ( about 600 ft away) a 480v recerptacle meters at 486v across. any info or insight would help greatly.

monroe nj , industrial area

the 426-506V could be the operating voltage of the motor. anything exceeding this should cause the protection to trip.

the voltages are fine, however, unless you monitor the voltage at night, your data will be incomplete

 

[don_resqcapt19]

the 426-506V could be the operating voltage of the motor. anything exceeding this should cause the protection to trip. ...

That would be a rare type of protection. Most equipment of this type has protection that only looks at the current. Some will have protection that looks at phase loss or reversal, but very few will have something that looks at the voltage.

 

[charlietuna]

Install your data logger at the motor and monitor the motor input voltage during a trip sequence and that will tell you the problem .

 

[mxslick]

By 50 ton I take it you're talking about an A/C chiller?

Did you consult with the HVAC folks?

Since it only seems to trip at night, is it possible that the chiller is freezing/icing up and overloading the compressor?

It could also be the POCO doing some sort of switching operation at night that is either over/undervolting or causing a phase loss that trips the overloads.

As suggested, either a data logger or set someone to stay up all night and monitor the situation.

 

[robbietan]

That would be a rare type of protection. Most equipment of this type has protection that only looks at the current. Some will have protection that looks at phase loss or reversal, but very few will have something that looks at the voltage.

I have come across some fancy chillers that have over/under voltage protection, phase loss protection as well as current unbalance protection. the operators have a devil of the time starting one and they wont shut down one unless there is a major problem.