Joethemechanic
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On AC do they have a power factor? They have iron in them, I don't imaging that they run at unity. Does anyone know?
Universal AC/DC Motors and PF
- Thread starter Joethemechanic
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gar
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- Ann Arbor, Michigan
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120127-1135 EST
Yes. Everything has a power factor. This includes when operating on DC. PF ranges from 0 to 1.0 . On DC everything has a PF = 1.0 .
The definition of power factor is Power/VA, and I believe it makes sense to require V and A to be RMS values.
Specifically my Black & Decker 1043-09 reads about 0.94 at 60 Hz with no load, and at nominal speed.
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Yes. Everything has a power factor. This includes when operating on DC. PF ranges from 0 to 1.0 . On DC everything has a PF = 1.0 .
The definition of power factor is Power/VA, and I believe it makes sense to require V and A to be RMS values.
Specifically my Black & Decker 1043-09 reads about 0.94 at 60 Hz with no load, and at nominal speed.
.
Joethemechanic
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- Electro-Mechanical Technician. Industrial machinery
gar
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- Ann Arbor, Michigan
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- EE
120127-2400 EST
An experiment drilling into wood caused the PF to drop to about 0.93. This was not a real high load.
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An experiment drilling into wood caused the PF to drop to about 0.93. This was not a real high load.
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Joethemechanic
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But this topic is not about any other motors on AC otherwise you ought to include synchronous condensers.
Joethemechanic
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And PF of squirrel cage induction motors improves as the mechanical load approaches 100% of the motor's capacity.
gar
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T.M.:
One type of standard single phase induction motor has a very bad power factor at no load, like 0.25. As load is increased the PF improves reaching a maximum towards full load.
A capacitor run single phase induction motor has a much higher no load PF, like 0.8, and may approach 1.0 around full load.
One curve I have for a three phase induction motor has a PF of 0.25 at no load, and increasing to a maximum of about 0.9 somewhat above full load, and then slightly drops.
,
T.M.:
One type of standard single phase induction motor has a very bad power factor at no load, like 0.25. As load is increased the PF improves reaching a maximum towards full load.
A capacitor run single phase induction motor has a much higher no load PF, like 0.8, and may approach 1.0 around full load.
One curve I have for a three phase induction motor has a PF of 0.25 at no load, and increasing to a maximum of about 0.9 somewhat above full load, and then slightly drops.
,
Not unusual for asynchronous induction motors.
We recently did a retrofit for a 1300kW synchronous induction motor. The second on the project is underway now.
Excitation is adjusted to get about 0.98 lagging pf but leading pf can also be set.
On the same upgrade project there were a couple of smaller (330kW) drives that had also been synchronous induction motors with unit transformers. During the course of the project the client decided to replace them with asynchronous cage induction motors. This was a bit of a headache for us. The original sync motors ran at unity power factor but the replacement cage motors had a fairly low power factor. The drive unit transformers were of insufficient kVA rating to meet the new requirements. In the event, the client found a spare 2MVA transformer on site and that was plumbed in to replace the two old unit transformers. A seemingly simple solution at system level. But a load of changes for my encumbered project engineer. Different type of starter, uprated power cabling, revised protection settings, different indication and controls and instrumentation on the operator's desk ....stuff
Joethemechanic
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I've never seen a squirrel cage motor with a PF that improves when you mechanically unload it. How is that even possible?
Did anyone claim that it was possible?
Joethemechanic
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- Hazleton Pa
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- Electro-Mechanical Technician. Industrial machinery
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T.M.Haja Sahib
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Voltage also has an influence on power factor, when the motor is operated on A.C.
No problem. Most of us do that from time to time.
Some of us even admit it!!
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