What is Power factor
Power factor is the ratio of active power which is consumed by the load to apparent power supplied by the generating source. The power factor is a unitless no. which is the cosine angle between actual power consumed to apparent power supplied.
The power factor is an indicator of the amount of power that is used to create actual by the load. power factor closer to 1(one) mean power supplied by the source is mostly consumed by the load. And losses as reactive power is minimum. In this article will see the motor power factor table and Capacitor Rating Chart for Motor.
Power Factor Unit
A power factor is a unitless number. its range is between 0 to 1. As it is the ratio of two powers i.e Active Power (KW) and Apparent Power (KVA), there is no unit.
Power factor of motor formula
PF = P / S
where
PF = power factor = Cos α
P = √3V I cos α =active (true or real) power (Watts)
S = √3V I= Apparent power (VA, volts amps)
hence, Power factor of motor formula is
Cos α =√3 VI Cos α / √3 VI
From the following diagram, you can easily understand why the power factor is cosine between apparent power and a real power.
What is Reactive Power
Reactive Power can best be described as the quantity of “unused” power that is developed by reactive components in an AC circuit or system.
What is Active Power
The power which is actually consumed or utilized in an AC Circuit is called True power Active power or Real power. It is measured in kilowatt (kW) or MW.
What is Apparent Power
The product of the root mean square (RMS) value of voltage and current is known as Apparent Power. This power is measured in kVA or MVA.
symbolically from the following diagram of the glass of beer, we can easily understand what is active power and what is reactive power.
Benefits of Power Factor Corrections
- Lower electricity bills – avoiding low power factor penalty from the electricity company
- An increased rating of electrical equipment – additional loads can be added without overloading the system
- Improved system operating characteristics by reducing line loss – due to less current
- improved system operating characteristics by gaining voltage – excessive voltage drops are avoided
Motor Power Factor Table
The power factor of the motor varies according to the rating of the motor, speed of the motor, and load applied on the load side of the motor. Power Factor Value of motor for different range of motor rating as follows. Motor Power Factor Table :
| Horsepower | Speed | Power factor | Power factor | Power factor |
| (HP) | (RPM) | If Load =1/2 of full load | If Load =3/4 of full load | If the motor is on Full load |
| 0 – 5 | 1800 | 0.72 | 0.82 | 0.84 |
| 5 – 20 | 1800 | 0.74 | 0.84 | 0.86 |
| 20 – 100 | 1800 | 0.79 | 0.86 | 0.89 |
| 100 – 300 | 1800 | 0.81 | 0.88 | 0.91 |
Capacitor Rating Chart for Motor
Recommended sizes of capacitor rating for motor in KVAR units needed for correction of induction motors to approximately 95% power factor. hence following is the Capacitor Rating Chart for Motor :
| Induction Motor Rating | Motor Speed = 3600 RPM | Motor Speed = 1800 RPM | Motor Speed= 1200 RPM |
| Capacitor Rating | Capacitor Rating | Capacitor Rating | |
| (HP) | (KVAR) | (KVAR) | (KVAR) |
| 3 | 1.5 | 1.5 | 2.5 |
| 5 | 2 | 2.5 | 3 |
| 7.5 | 2.5 | 3 | 4 |
| 10 | 4 | 4 | 5 |
| 15 | 5 | 5 | 6 |
| 20 | 6 | 6 | 7.5 |
| 25 | 7.5 | 7.5 | 8 |
| 30 | 8 | 8 | 10 |
| 40 | 12 | 13 | 16 |
| 50 | 15 | 18 | 20 |
| 60 | 18 | 21 | 22.5 |
| 75 | 20 | 23 | 25 |
| 100 | 22.5 | 30 | 30 |
| 125 | 25 | 36 | 35 |
| 150 | 30 | 42 | 40 |
| 200 | 35 | 50 | 50 |
| 250 | 40 | 60 | 62.5 |
| 300 | 45 | 68 | 75 |
| 350 | 50 | 75 | 90 |
| 400 | 75 | 80 | 100 |
| 450 | 80 | 90 | 120 |
| 500 | 100 | 120 | 150 |
conclusion:
Many a time we required to know the power factor at different load at motor output side. hence, in this article, we have discussed Motor Power Factor Table which give power factor (pf) for different rating size motor and at different load at motor. what rating of capacitor will be proper hence we also provide Capacitor Rating Chart for Motor.
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