Which Voltage Should I Choose?

[rdub]

I have a 3-phase, 440VAC, 50 Hz line supply (from a portable generator), with a load that can operate either on 380, 400, or 415, 50 Hz. I am hoping to find a "off the shelf" transformer here in the US that will step down the voltage to one of these levels. Is one of the above a better choice over the others?

 

[weh3]

What you want is a buck/boost transformer in a bucking (reducing) configuration. See Acme for example.

Wm

 

[ccjersey]

Before buying a transformer, If this load you mention is the only load on the generator, why not check and see if the voltage can be set down to the highest of the choices you have. Most generators have some adjustment.

Jim

 

[weh3]

Usually, you figure less current for a higher voltage. I would go with the highest one without knowing anything else about it.

Wm

 

[rdub]

All,

The main piece of equipment will be powered by 440V. This piece of equipment will only operate at one of the stated voltages and requires roughly a 90amp service. When looking at the 60hz specifications, do I only need to worry about input voltage de-rating since I am operating at 50 hz?

 

[ccjersey]

Take a look at this thread on the motors & control board of this site for a good discussion of the 50z/60hz switch. I think the voltages you mention are apropriate for 50hz. I would check the generator voltge at the 50hz speed before I bought anything. Some/most? generators will reduce the voltage proportionally to the speed/hz. If it was set for 460V at 60 hz, you may be allright when you slow it down.

http://www.eng-tips.com/viewthread.cfm?qid=117639&page=2

Jim

 

[BEPC13]

Before looking at a transformer I would also look at the load. Is it a motor? If so the rated nameplate voltage may take into account the voltage drop accross the feeder cables. For instance here our motors are typically rated for 460V nameplate and are connected to a 480 V system. I would make sure the name plate voltage does not take this into account, before I would go out and put a transformer in the circuit just to knock the voltage down 25 V.

 

[farhadkhaefi]

i think you dont need transformer , you can control voltage of generator with dc field.
second way i think you can use voltage divider with series resistance.
fafa

 

[weh3]

Rdub,

You are probably dealing with a piece of European equipment, but you will have to tell us what it is before we can recommend anything else about whether it is OK on the lower voltage or higher frequency. Generally, for iron-core equipment, 380V/50Hz looks the same as 480V/60Hz. Electronic equipment such as VFD's may not care what the input is, or you may just have to move a switch or something to tell it what the incoming power is. Check with the manufacturer.

Farhadkhaefi:
A voltage divider using resistance only wastes the energy in the top resistor. The same idea, only using inductance instead of resistance is accomplished with a buck/boost transformer, or an autotransformer.

Will-I-Am