resistor problem

this is not a plc problem, but as many smart questions and answers i see on this site, i hope someone can help me.i have a machine which the manufacturer says has to run on 460v. we have 500v comming in. i know i can buy transformers to do this but that is going to be expensive. can i use a resistor to bring the voltage down? if so how do i figure what i need? the control transformer is 460 to 110 and 24(foriegn built). this is where my voltage is high. the manufacturer says the voltage must be this, no exceptions. any help would be appreciated!
rodney

Just get a new transformer

500 V Pri - 110V and 24V secondary

From a theoretical point of view to work out the resistor you will need to provide the transformer details

KVa, inrush current (if stated) etc

But i would just get a new transformer

Theortically a resisteor would work, but DO NOT DO IT THAT WAY. You didn't state amperage, but assuming only 20 Amps and a 20 Volt drop, you are talking about dissipating over 300 watts on each resistor. (W = V x I x 1.73)That is a lot of heat and a waste of energy.

Most good quality control transformers and all power transformers have multiple tap points for exactly this purpose. Find the correct tap and you are in business. Even if you need to buy a new transformer, that is the way to go!

And tell your supplier that NEMA standards are ± 10% tolerance on voltage for motors and most other devices, so he should upgrade his equipment!

roddbodd said:

i have a machine which the manufacturer says has to run on 460v. we have 500v comming in.

Click to expand...

Why 500vac incomming ? Contact your POCO (Power Company) about this.

The nominal Supply voltage in the USA is 480vac. Motors are Utilization equipment that have a voltage rating of 460vac. Many are confused by this. If the Mfg is demanding a 460vac supply, I would question this.

Your 500 vac is a tad more less than 5% from 480vac. Surely you have other machines that have 3 phase motors ?

The control transformer (480/120) should have some primary taps that be used for higher than normal voltage, if not and you need to, get an Acme Xfmr: http://www.electricalpowertransformer.com/acme-dry-distribution.html

That has happened to me before also. I spoke with the power company in that instance and they told me that after we put the power line under more load, it would come down and it did. It started out at 500V, but after we started putting load on the new transformer it dropped down to 480v.

Is this a new power drop or is it an existing one? If it's new, then how much load are you going to put on it? If it's existing power, I agree with everyone else and recommend to get a different control transformer.

Just my thoughts.

this is a small business in a VERY large building. the power company set the transformers for the old owners who had lots of equipment which would cause the voltage to drop to about 480 when the plant was running. we have been trying to get the power company to change their taps. they say it might be six weeks. the controls are all that needs to be corrected. the manufacturer says the motors will be ok. the controls are running at 135v and 28v. the total control load is about 5 amps. i might just have to go the transformer route. i was just trying to save a little cash!! thanks for all of your input!