Glossary entry (derived from question below)
English term or phrase:
cos (phi) 0,69
English answer:
Power Factor
Added to glossary by
Ramesh Madhavan
Jun 23, 2004 08:53
19 yrs ago
3 viewers *
English term
cos (phi) 0,69
English
Other
Engineering: Industrial
Part of specifications list for a drive motor.
Other items on the list:
electrical data:
output:
cos (phi):
motorspeed:
etc.
Hope you can help.
Other items on the list:
electrical data:
output:
cos (phi):
motorspeed:
etc.
Hope you can help.
Responses
| 5 +3 | Power Factor |
Ramesh Madhavan
|
| 4 | See comment |
Saleh Chowdhury, Ph.D.
|
Responses
+3
2 hrs
Ramesh Madhavan
Native in English
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Native in: English 
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Works in: English, Tamil to English, Hindi to English, and 4 more.
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Power Factor
Voltage and Current are vectors; they have magnitude AND direction. If they work together in THE SAME DIRECTION, you will get maximum work done. However, this happens only in theory. For all practical reasons, they do not have the same direction. They work in different directions. Because of this, there is wastage. The angle between Voltage & Current is called PHI (Greek letter shown as a zero with a slash). The Cosine of this angle is Cos (Phi). Cos0=1 and Cos90=0. So, when the angle is less Cos (Phi) will be more and the machine is more efficient in converting Electrical energy to Mechanical energy. By using such a motor, you power bill will come down!
Peer comment(s):
| agree |
Vicky Papaprodromou
0 min
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Thank you Papaprodromou
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| agree |
Tony M
: Yes, exactly! Often abbreviated in English to just p.f. or the Greek letter 'phi', either of which would be the equivalent abbreviation in your given context
19 hrs
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Thanks Dusty
|
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| agree |
Alfa Trans (X)
8 days
|
4 KudoZ points awarded for this answer.
Comment: "Thank you very much. Good explanation."
6 mins
Saleh Chowdhury, Ph.D.
Bangladesh
Bangladesh
Bangladesh
NAATI Accredited 21 yrs in Medical Trans
Native in: Bengali 
Works in: English to Bengali, Bengali to English, Bengali, and 1 more.
See comment
cos phi of the motor is the power factor of the motor. This does not however affect the power factor on the input of the drive.
By definition, power factor is the ratio between KW and KVA. If the voltage and current are sinusoidal, the power factor is equal the the cosine of the angle between them (Cos phi). If the voltage and/or current and not sinusoidal, then the cos phi does not indicate the true power factor. This is particularly true of inverter drives where the input current is a series of pulses ocuring at the crest of the voltage waveform. This current is the current required to charge the DC bus capacitors. The conduction angle of these pulses will vary from very narrow with some drives to as wide as 120 degrees maximum, depending on the design of the inverter input stage and the impedence of the supply. In this case, as the current is in phase with the voltage, the cos phi is often correctly stated as better than 0.95, but the true power factor is usually less than 0.75 As this power factor is low due to harmonic currents, it can not be corrected by capacitors, and needs expensive filtering systems to make an improvement.
By definition, power factor is the ratio between KW and KVA. If the voltage and current are sinusoidal, the power factor is equal the the cosine of the angle between them (Cos phi). If the voltage and/or current and not sinusoidal, then the cos phi does not indicate the true power factor. This is particularly true of inverter drives where the input current is a series of pulses ocuring at the crest of the voltage waveform. This current is the current required to charge the DC bus capacitors. The conduction angle of these pulses will vary from very narrow with some drives to as wide as 120 degrees maximum, depending on the design of the inverter input stage and the impedence of the supply. In this case, as the current is in phase with the voltage, the cos phi is often correctly stated as better than 0.95, but the true power factor is usually less than 0.75 As this power factor is low due to harmonic currents, it can not be corrected by capacitors, and needs expensive filtering systems to make an improvement.
Discussion