That's not what his diagram shows - the one at the top of the article.
Two speed one winding motor troubleshooting advice
- Thread starter phineascage
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magnetizing i ~ fla x sqrt(1 - pf^2)
= 290 x (1 - 0.85^2) = 152
losses will add a bit, call it 160, ~4% losses
low voltage increases pf, -10% v inc 10-15 points
hi voltage decreases pf +10% v dec 10-15 points
the shop to field delta (8 + 14)/460 = 5% or 1/4 the above range
assuming 20% delta ~ 25 points, 5% ~ 6 points
say shop 0.15 then field 0.09
a huge change in pf likely accounting for the 150 to 190 delta
the i magnitude would increase a bit in both cases from the 460 rated
= 290 x (1 - 0.85^2) = 152
losses will add a bit, call it 160, ~4% losses
low voltage increases pf, -10% v inc 10-15 points
hi voltage decreases pf +10% v dec 10-15 points
the shop to field delta (8 + 14)/460 = 5% or 1/4 the above range
assuming 20% delta ~ 25 points, 5% ~ 6 points
say shop 0.15 then field 0.09
a huge change in pf likely accounting for the 150 to 190 delta
the i magnitude would increase a bit in both cases from the 460 rated
Or a defective motor.
mivey
Senior Member
That would be a big nope. You evidently are not too familiar with motor nameplate vs system nominal voltages in the US. I'm not sure how it rolls in other countries but you would be way off base here.
Please explain but first go through the paper in post#37.
Look at the very first diagram in it.
Already looked at it. But the author stated linearity up to rated voltage only ( point B in the diagram ). However, he extended the linearity beyond that point in the diagram to include induction motors with iron core of larger iron content such as U design induction motor.
mivey
Senior Member
Motors here are designed to give satisfactory performance at well above 480 volts so are not going to be saturated at less than that. I doubt anything in the paper is going to change that fact.
Suppose the induction motor operates in the linear V versus I portion. The no load speed remains same in work shop and field. The current for a voltage of 452V is 152A. So for a voltage of 476V, the current would be 476*152/452=160A. But the actual current is 197A and that may be due to saturation which may be confirmed if OP applied another somewhat greater voltage and corresponding motor current value recorded by OP in the field/workshop. If that voltage and current values are also nonlinear, it proves motor core is saturated and not winding fault. I assume winding fault, if it exists, follows Ohm law during OP testing.
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mivey
Senior Member
Suppose the motor is designed per required standards to give satisfactory performance at 460 +/- 10%. Do you expect a non-damaged motor to be saturated at 476 volts?Suppose the induction motor operates in the linear V versus I portion. The no load speed remains same in work shop and field. The current for a voltage of 452V is 152A. So for a voltage of 476V, the current would be 476*152/452=160A. But the actual current is 197A and that may be due to saturation which may be confirmed if OP applied another somewhat greater voltage and corresponding motor current value recorded by OP in the field/workshop. If that voltage and current values are also nonlinear, it proves motor core is saturated and not winding fault. I assume winding fault, if it exists, follows Ohm law during OP testing.
kwired
Electron manager
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:thumbsup:
I see 460 volt rated motors that see input of 490 to 500 volts all the time. They are designed to be able to take that.
:thumbsup:
I see 460 volt rated motors that see input of 490 to 500 volts all the time. They are designed to be able to take that.
Suppose the induction motor operates in the linear V versus I portion. The no load speed remains same in work shop and field. The current for a voltage of 452V is 152A. So for a voltage of 476V, the current would be 476*152/452=160A. But the actual current is 197A and that may be due to saturation which may be confirmed if OP applied another somewhat greater voltage and corresponding motor current value recorded by OP in the field/workshop. If that voltage and current values are also nonlinear, it proves motor core is saturated and not winding fault. I assume winding fault, if it exists, follows Ohm law during OP testing.
imo there is no issue with the motor
no one can explain the 150 vs 190 shop to field NLA difference
I looked and could not find the motor data sheet
need the part numbers, they are on the data plate but can't be read
kwired
Electron manager
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- NE Nebraska
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So your diagnosis is there is no problem and OP should just continue to use this motor as is?
Neither seems plausible for a healthy motor.
sure it does
the NLA for a 100 HP, 900/1800, 1w2s 8P motor is 50% of FLA
same mfg, Marathon
need model number of the op's motor
imo the issue is not the motor
I would swap motors with another tower and see what results
as it is now runs <rated in low, and +15% in high
Yes, the obvious thing to try and I think the OP knows that.
190/290 is 66%.
kwired
Electron manager
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- NE Nebraska
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- EC
Easy to say from your keyboard
Maybe easy to do with a 2 or even 25 HP motor when compared to a 250 Hp motor.
With that big of a motor, I might be more likely to pull it and have them run it on some kind of dynamometer and if it passes that, time to look into the driven load. But has been mentioned time and time again that the problem exists even without the load coupled to the motor, so unless there is significant voltage change measured as well as high current there about has to be an issue in the motor, but maybe one possibly tries an alternate feed (even if temporarily installed) to this motor if there is any suspicion in the supply circuit.
Yes, it has been tried on two different supplies. The plant where it is installed and in the motor shop.Easy to say from your keyboard
Maybe easy to do with a 2 or even 25 HP motor when compared to a 250 Hp motor.
With that big of a motor, I might be more likely to pull it and have them run it on some kind of dynamometer and if it passes that, time to look into the driven load. But has been mentioned time and time again that the problem exists even without the load coupled to the motor, so unless there is significant voltage change measured as well as high current there about has to be an issue in the motor, but maybe one possibly tries an alternate feed (even if temporarily installed) to this motor if there is any suspicion in the supply circuit.
One possibility is that the stator has shorted turns (resulting from contact by the rotor) and this makes the damaged motor more susceptible to saturation.
That would explain the different no-load currents.
Whatever, this motor does not behave the same way others on the plant do. Difficult to interpret that as anything other than a motor issue.
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