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WHAT IS POWER FACTOR? AND HOW TO IMPROVE POWER FACTOR



What is Power Factor?
Most loads in modern electrical distribution systems are inductive. Examples include motors, transformers, gaseous tube lighting ballasts, and induction furnaces. Inductive loads need a magnetic field to operate. 
Inductive loads require two kinds of current:
• Working power (kW) to perform the actual work of creating heat,light, motion, machine output, and so on.
• Reactive power (kVAR) to sustain the magnetic field

Working power consumes watts and can be read on a wattmeter. It is measured in kilowatts (kW). Reactive power doesn’t perform useful “work,” but circulates between the generator and the load.
It places a heavier drain on the power source, as well as on the power source’s distribution system. Reactive power is measured in kilo volt-amperes-reactive (kVAR).
                          
Working power and reactive power together make up apparent power. Apparent power is measured in kilo volt-amperes (kVA).

Fundamentals of Power Factor:
Power factor is the ratio of working power to apparent power. It measures how effectively electrical power is being used. A high power factor signals efficient utilization of electrical power, while a low power factor indicates poor utilization of electrical power.

To determine power factor (PF), divide working power (kW) by apparent power (kVA). In a linear or sinusoidal system, the result is also referred to as the cosine θ.
                                              PF =KW/KAV = cosineθ

For example, if you had a Wind mill that was operating at 100 kW and the apparent power consumed was 125 kVA, you would divide 100 by 125 and come up with a power factor of 0.80.
                                         PF =kw/kva =100/125=0.8 cosineθ

What can i Do To Improve Power Factor?
You can improve power factor by adding power factor correction capacitors to your plant distribution system. When apparent power (kVA) is greater than working power (kW), the utility must supply the excess reactive current plus the working current. Power capacitors act as reactive current generators.
By providing the reactive current, they reduce the total amount of current your system must draw from the utility.

95% power factor provides maximum benefit

Theoretically, capacitors could provide 100% of needed reactive power. In practical usage, however, power factor correction to approximately 95% provides maximum benefit.

Advantages of Installing Power Capacitor:
Power capacitors provide many benefits:
• Reduced electric utility bills
• Increased system capacity
• Improved voltage
• Reduced losses

Where Should I Install Capacitors in my Plant Distribution System?
At the load
Because capacitors act as kVAR generators, the most efficient place to install them is directly at the motor, where kVAR is consumed.
Three options exist for installing capacitors at the motor.

Location A—motor side of overload relay
• New motor installations in which overloads can be sized in accordance with reduced current draw
• Existing motors when no overload change is required

Location B—line side of starter
• Existing motors when overload rating surpasses code.

Location C—line side of starter
• Motors that are jogged, plugged, reversed
• Multi-speed motors
• Starters with open transition and starters that disconnect/reconnect capacitor during cycle
• Motors that start frequently
• Motor loads with high inertia, where disconnecting the motor with the capacitor can turn the motor into a self-excited generator

               

At the service feeder
When correcting entire plant loads, capacitor banks can be installed at the service entrance, if load conditions and transformer size permit. If the amount of correction is too large, some capacitors can be installed at individual motors or branch circuits. When capacitors are connected to the bus, feeder, motor control center, or switchboard, a disconnect and over current protection must be provided.

Capacitor Bank Maintenance:
Capacitors have no moving parts to wear out and require very little maintenance. Check fuses on a regular basis. If high voltages, harmonics, switching surges, or vibration exists, fuses should be checked more frequently. If the case is cold, check for blown fuses, open switches, or other power losses. Also check for bulging cases and puffed-up covers, which signal operation of the capacitor interrupter.
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