motor operation voltage 440-480 5

[systemsaver]

Dear engineers,
If one reads in a 3 phase motor plate the voltage, 440-480 and 65.5 as amperes, does it mean that the motor should not work above or under that voltage range or one can assume that it still works 10% +- that range ? why is the same current for 440 or 480 when what happens is that the current should go up when the voltage lowers and goes down when the voltage is up to maintain the power required?
Looking forward to your help on this matter. Thank you.

 

[waross]

Do you have a picture of that nameplate?
Standard motor rated voltages in North America are multiples of 115 Volts.115V, 230V, 460V and 575V (in Canada).
Heat is the enemy of the motor and 65.5 Amps is the maximum Amps that the motor may draw without overheating in a 30 deg C ambient, regardless of the applied voltage.
Standard supply voltages in North America are multiples of 120 Volts. The discrepancy (5V/120V x 100 = 4.17%) is to allow for a 4.17% voltage drop in feeders and branch circuits.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[systemsaver]

Thank you Waross for your prompt answer. Enclosed is the plate of the motor.

 

[jraef]

Chinese motor, likely not built to normal standards and/or they clearly don’t know what to put on the nameplate. That nameplate would not conform to North American standards (assuming you are in NA because you are looking at that voltage).

They probably just put “440-480V” to avoid phone calls from users who don’t understand that North American voltages are going to vary slightly from place to place depending on age. I get calls all the time saying “your motor says 460V, I have 480V, is that going to work?” It’s kind of a PITA to be honest, so this may have been their attempt to avoid that.

NEMA standards would have been for the motor to be designed as 460V +-10%, so that it can operate fine at 440V or 480V, at +-5% as the utilities are supposed to deliver. There will be additional heating at 480V, but within the acceptable tolerance, and there will be decreased torque at 440V, but also within acceptable tolerance.

Being that this motor does not appear to be made to NEMA standards, there is no way to tell what it is capable of handling and what effects there will be. You would have to contact that mfr (if they still exist) or just take your chances.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[systemsaver]

thank you Jraef for your comments. this motor drives a refrigeration compressor and the voltage input from the electrical company is not stable. See the Screenshot enclosed. We have to calibrate the tap from the power transformer to lower in 2,5 % the incoming voltage because otherwise, the motor will stop more due to the phase voltage supervisor that is set to 480 volts as maximum voltage operation value unless you recommend that could handle voltage above 480 and less than 440v.do you think we could set it 5% above 480 and 5% under 440 to let the compressor run or with that values the life of the motor will be shorted?

 

[itsmoked]

systemsaver; What I would do is clamp an ammeter onto the various phases then run it. If the amperage stays below 65.5A it doesn't matter what the voltage is. Watch it as it gets up around 480. If it's still low you can run up the trip setting.

There is a hitch however. A refrigeration compressor's load is a function of temperature. As the temp goes up the load goes up. You can't run the above test on a not hot day and get the required results without some savvy cheating. Things like blocking air flow such that the local ambient goes up.

An alternative is to instead put in a current monitor and set it to 65.5A.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[systemsaver]

itsmoked , thank you for the recommendation to work with the overcurrent protective device and set it to 65.5 instead of the phase voltage protective device. Just for the record enclosed is the behavior of the current of 3 motors in the same time range. The machine has 3 compressors, each draws 65.5 maximal operation amperes

 

[waross]

A warning about higher voltages.
As the voltage increases, the flux density in the motor core increases. There is a condition called "magnetic saturation". When higher voltage drives the core into saturation, the current increases alarmingly with only a little increase in voltage. Time to burnout may be measured in minutes. Possibly minutes in single digits.
Your voltage monitor must be set to disconnect before the motors go into saturation.
Is this a hermetic or semi hermetic compressor? Such units are cooled by the suction gas entering the case. With higher ambient temperatures, the returning gas on some machines will be hotter and provide less cooling.
It this is an ice machine, the temperature of the returning gas is more related to the temperature of the water, than by the ambient temperature. The higher ambient will cause higher head pressures and temperatures and add load to the motor.
If the current is running too high you may make a small reduction by increasing the super-heat. If you need more current reduction, try the next smaller size expansion valve.
Reducing the superheat may not be effective on a type of ice machine that uses a vessel flooded with refrigerant rather than linear coils.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

I'm a little unclear with that second picture. Are you saying with ALL THREE compressors running the current is only hitting 110A? If so then you should not have any problems.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[systemsaver]

Thank you waross and itsmoked for your answers. Now to your questions :
1.- It is a Bitzer , german brand, a semi-hermetic reciprocating motor compressor .
2.- It is an ice machine.
3.- Yeah only 110 amperes total for the 3 units of the ice machine but as I wrote before it stops because of an increase in voltage although the amperage value is fine.
I think that the best idea is to increase the phase voltage to let's say 500 volts and in case the amperage value increases because of magnetizing current the overcurrent monitor will stop the motor when its value goes beyond 65.5 per motor and that way prevents burnout.
Do you agree with this final setup to keep the machine producing ice without stopping?

 

[waross]

Suggestion:
1. Increase the voltage setting by Volts and see if it holds. If it trips on overvoltage, increase another 5 Volts. If it trips on over current, immediately reduce the voltage setting to the previous setting and live with it.
2. 110A/3=37A, If the motors are drawing only 37 Amps despite the 65.5 Amp rating, it may be wise to lower the current trip ratings to around 40A or 45A. There are two reaons for this:
a) Just a few Volts into saturation may push the current over 100 Amps.
b) Motor current overload devices normally work on an inverse time curve. The overloads typically trip on a temperature or on a similar electronically modelled curve. If the motor is running at 37A, a 40 Amp setting will trip faster than a 65.5 Amp setting.
If you are going into saturation, you want to trip as fast as possible.

While you are playing with the settings, how do you know if an over-current trip is due to saturation or due to too low a trip setting?
Look at your current recordings.
If the current is holding above your trip setting (40A or 45A) but below 65.5 Amps, increase the trip setting 5 Amps.
Changes in ambient temperature or changes in feed-water temperature may drive the current up, without being dangerous.
The curve will be flat or a gentle incline.
If the current abruptly spikes above 65.5 Amps, at the same time that the voltage is peaking, you are saturating. Immediately reduce your voltage trip setting. That is the best that you will get.

The nameplate appears to read "Mate in China". If I read that correctly, that says it all.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

I agree with Bills suggestions. If you're using standard overload protections which will be slow set it below 65A so it trips faster on a saturation event. If it's an electronic fast OC unit you could leave it much closer to 65A. If your OV setting is now at 480V and nuance tripping then yes turn it up a bit. If the voltage goes up frequently it may be a daily event cycle. You could be there to see how the current actually responds to the 'over voltage' events for piece of mind.

Let me say they are lucky to have someone of your ability to support them.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[systemsaver]

waross and itsmoked ,
you have been very helpful with your final advice. Very kind especially on weekend days!
We will do it that way. Hopefully, customer will increase the daily ice production.
Thanks again for your helpfulness .
Best regards

 

[edison123]

With such wildly varying voltages, a correctly spec'ed servo voltage stabilizer at the input end would protect the motors as well as other loads. One time cost, lifetime of peace.

Muthu

http://www.edison.co.in

 

[itsmoked]

edison; In Ecuador, perhaps a lifetime of searching for a servo stabilizer?

It will be very good to get this sorted out as tripped-off compressors take a real beating for not being properly pumped down before stopping them.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[systemsaver]

Good point itsmoked .
Edison, if we talk of 17 ice machines, do you have any idea how much the servo voltage stabilizer will cost and where to get it?

 

[edison123]

You can spend now, or you can spend later by way of burnt motors, lost production etc, your choice. Servo stabilizers are available up to even 2000 KVA and you can split your motors to suit the sizes of servos you want.

I use a 200 KVA stabilizer for my shop running smoothly for over 25 years with much less motor, lighting and computer failures.

Muthu

http://www.edison.co.in

 

[systemsaver]

OK Edison123 . We will consider that as plan B. Thank you.

 

[Gr8blu]

Systemsaver: There are other effects (other than increased core loss, that is) associated with raising the line or phase voltage of a machine. For this size machine, the individual conductors of the winding are - generally speaking - going to be enamel over copper, wound as multiple small wires in hand to produce a larger turn cross-section. The difficulty is that you have no idea how good that enamel coating is - nor if the machine was wound properly (with appropriate barriers between phases) in the first place. The machine nameplate does not show maximum allowable ambient temperature (nor altitude); use caution!

Raising the line voltage also increase the apparent voltage across adjacent turns and/or coils (particularly where one phase is adjacent to another). The increase to something above the upper nameplate limit (to say 500 V) may be enough to bridge the insulating value of the enamel and will almost certainly do so between adjacent phases where TWICE that value occurs. This assumes the strand insulation was in good shape to begin with!

The machine rating is - almost certainly - a "standard" rating. It will only draw sufficient current for the process: if the compressor remains lightly loaded, then it won't draw nameplate amperage (obviously, since the combination of three compressors only draws 110 A). It would be a good idea to check each compressor independently if possible - just to be sure the load is being shared proportionally to each motor/compressor rating. Wouldn't want to have that 65 A motor drawing 100 of those 110 A! If the load is correctly balanced between the compressors, then thermal issues should be the least of your worries - at least until the compressors start loading up sometime down the road.

Converting energy to motion for more than half a century

 

[systemsaver]

Gr8blu,
thank you for your technical comments. For your information, it is a part winding start operation with 2 contactors and 2 thermic over current protection and the delay time unit. We will follow your advice and confirm that each motor draws about the same current value before we increase the voltage cut-off value in the voltage phase supervisor ICM.