extended voltage range motors. 1

[GOTWW]

In going through specifications, I have consistantly encountered the statement: "Extended voltage range motors shall not be permitted". What are these type of motors, and why are they apparently so bad to use.

 

[aolalde]

Some manufacturers offer motors to work on systems ranging from 208 volts to 240 volts 60 Hz or even 50/60 HZ.

My personal opinion is that the optimum performance of a motor fits only one voltage and frequency. A motor could work in a broad range of voltage and frequency but with detrimental characteristics like; Efficiency, Power Factor, Torque and temperature rise.

 

[Barry1961]

I have run into several problems with people running 208/240V motors on 208V. Most of the time it was trying to start under load. A 240V motor can be run on 208V but just barely. If you have line loss or slightly unbalanced voltage on your lines or starting under a load it fails. I like to have the voltage within 5% of design myself.

Barry1961

 

[jbartos]

Suggestion: Dual voltage rated motor will be suitable for the terminal voltage range 200V-230V. The manufacturer is supposed to design the motor for this range. A motor can be designed for wider terminal voltage range than NEMA MG-1 states, namely ±10%. Essentially, windings and magnetic circuits are oversized.

 

[aolalde]

jbartos.

Could you please explain the relationship of "Extended voltage range motors" with "dual voltage motors" in your post?

 

[busbar]

The (200)208- versus (230)240-volt compromise is described in a “treaty” of sorts between a committee of electric utility and appliance-/equipment-manufacturer representatives, currently in ANSI{NEMA} Std C84.1-1995 Electric Power Systems and Equipment—Voltage Ratings (60 Hertz)

The matter is further complicated in that constant-resistance-load power varies with the square of terminal voltage, and electromagnetic devices are closer to constant-kVA, where, roughly, current decreases with increased terminal voltage.

[Coincidentally, the ‘gap’ shows up at 4.16-4.8, 12.0-13.8 (or 14.4) and 115-138kV levels. The voltage ratio is very close to (2-[√]3)/2, where inherently a factor of 2 relates to equal series/parallel components and [√]3 relates to ø-ø/ø-n quantities.]

IEEE Std 141-1993 [Red Book] Chapter 3 discusses ‘accepted norms’ in fair detail, but still leaves the end user with less-than-ideal circumstances for most efficient operation over a ~13% voltage span.

 

[jbartos]

Comment: Nema motors nameplates show motor terminal rated voltage that are lower than the ANSI/NEMA C84.1 system voltages.
e.g.
ANSI Motor Nameplate
208V 200V
240V 230V
480V 460V
4.16kV 4.0kV
etc.
The reason for this is that the motor manufacturers and associated standards e.g. NEMA expect the motor terminal voltage be lower than the ANSI system voltage due to the voltage drop in the motor feeder, which is not a bad idea.

 

[jbartos]

Comment on aolalde (Electrical) Mar 6, 2004 marked ///\\jbartos.
Could you please explain the relationship of "Extended voltage range motors" with "dual voltage motors" in your post?
///These expressions are often used interchangeably, probably because they are not defined in IEEE Std 100 Dictionary. However, dual voltage motor expression is often related to a different motor design, e.g. 230V/460V(240V/480V) motor nameplate rated.
Visit

http://www.sannet.gov/mwwd/business/cwpspecs/pdf/16040.pdf

for:
1. Motors below 1/2-hp shall be rated 115 volts, single-phase, 60-Hz. Dual voltage motors rated 115/230-volts, 115/208-volts, or 120-240 volts are acceptable.
2. Motors 1/2-hp and larger shall be rated 460 volts, or 4160 volts, 3-phase, 60-Hz. Dual voltage motors rated 230/460 volts or 208/230/460 volts are acceptable.

http://www.usmotors.com/SP101/footnotes.pdf

etc. for more info\\\