CAUSES OF LOW POWER FACTOR

Low power factor is caused mainly by induction motors, but also by inductive loads (such as transformers and magnetic lighting ballasts). Unlike resistive loads that create work entirely by consuming watts or kilowatts, inductive loads require some current to create a magnetic field, and the magnetic field facilitates the desired work. The total or apparent power required by an inductive device is a composite of the following:

_ Real power (measured in kilowatts, kW)

_ Reactive power associated with components that alternately store energy and release it back to the line during each AC cycle (measured in kilovars, kVAR) Reactive power required by inductive loads increases the amount of apparent power (measured in kilovolt amps, kVA) in your distribution system. The increase in reactive and apparent power is reflected by the increase of the angle between the two, causing the power factor to decrease.

WHY WE NEED TO IMPROVE POWER FACTOR?

Some of the benefits of improving your power factor are:

_ Your utility bill will be smaller. Low power factor requires an increase in the electric utility’s transmission and distribution capacity in order to handle the reactive power component caused by inductive loads. Utilities usually charge large customers with power factors less than about 0.95 an additional fee. You can avoid this additional fee by increasing your power factor.

_ Your internal electrical system’s capacity will increase. Uncorrected power factor will cause increased losses in your electrical distribution system and limit capacity for expansion.

_ Voltage drop at the point of use will be reduced (i.e. improved). Voltages below equipment rating will cause reduced efficiency, increased current, and reduced starting torque in motors. Under-voltage reduces the load motors can carry without overheating or stalling. Undervoltage also reduces output from lighting and resistance heating equipment.

POWER FACTOR

Power factor is a quantity which has important implications when sizing a UPS system and power distribution equipment. Power is a measure of the delivery rate of energy and in DC (direct current) electrical circuits is expressed as the mathematical product of Volts and Amps (Power = Volts x Amps). However, in AC (alternating current) power system, a complication is introduced; namely that some AC current (Amps) may flow into and back out of the load without delivering energy. This current, called reactive or harmonic current, gives rise to an “apparent” power (Volt x Amps) which is larger than the actual power consumed. This difference between the apparent power and the actual power gives rise to the power factor. The power factor is equal to the ratio of the actual power to the apparent power. The apparent power is expressed as the Volt-Amp or VA rating. Therefore, the actual power in any AC system is the VA rating multiplied by the power factor.

For many types of electrical equipment the difference between apparent power (VA) and actual power (Watts) is very slight and can be ignored, but for some computers the difference is very large and important. Many desktop personal computers present a nonlinear load to the AC supply. This is because they have a

power supply design known as a "capacitor input switch mode power supply". In a study done by PC Magazine, it was found that typical personal computer systems exhibit a power factor of .65 which means that the apparent power (VA) was 50% larger than the actual power (Watts)! Information Technology equipment including servers, routers, hubs, and storage systems almost universally use a different power supply design known as "Power Factor Corrected". These devices present a very linear load to the AC supply and do not generate harmonic currents. In fact they are one of the cleanest loads on the power grid and generate less harmonic current than many other devices such as fluorescent

lighting or variable speed motors. Ten years ago, these devices were nonlinear loads like Personal Computers, but today all of these loads are subject to international regulation IEC 1000-3-2 which require them to be made with the "Power Factor Corrected" design.

RELATION BETWEEN ACTIVE AND REACTIVE POWER

Active and Reactive Power

•         Active power (kW): real power used

•         Reactive power (kVAR): virtual power that determines load/demand

•         Utility pays for total power (kVA)

•         Active power, measured in kilowatt (kW), is the real power (shaft power, true power) used by a load to perform a certain task. However, there are certain loads like motors, which require another form of power called reactive power (kVAR) to establish the magnetic field. Although reactive power is virtual, it actually determines the load (demand) on an electrical system. The utility has to pay for total power (or demand)

•         The vector sum of the active power and reactive power is the total (or apparent) power, measured in kVA (kilo Volts-Amperes). This is the power sent by the power company to customers.

•         Here the different powers are represented of a power triangle where the vector sum of the active power and reactive power make up the total power used. This is the power sent by the power utility companies for the user to perform a given amount of work. Total power, also known as apparent power is measured in kilo Volts-Amperes.

•         You can see from the figure that the active power, and the reactive power required are 90 degrees apart vectorically in a pure inductive circuit. In other words reactive power kVAr lagging the active kW. The apparent power, kVA, is the vector sum of active and reactive power. Mathematically it may be represented with the following formula

kVA = Ö (KW)2 + (KVAR)2

ALL TYPE OF ELECTRICAL SYMBOLS

ABBREVIATIONS FOR MAINTENENCE

AC                   alternating current

AEIC               Association of Edison Illuminating Companies

ANSI              American National Standards Institute

AVR                automatic voltage regulator

BIL                  basic impulse insulation level

CBM               condition-based maintenance

CCVT              Coupling capacitor/voltage transformers

CFR                 Code of Federal Regulations

CIPP               Critical Infrastructure Protection Plans

CO2                carbon dioxide

DC                   direct current

DGA               dissolved gas analysis

EHV                extra high voltage

EPSS               Emergency Power Standby Systems

EPRI               Electric Power Research Institute

FIST                Facilities Instructions, Standards, and Techniques

GPRA             Government Performance and Results Act

GSU                generator step-up

HECP              Hazardous Energy Control Program

hp                   horsepower

HVDC             high-voltage direct current

Hipot             high potential tests

IEEE™             Institute of Electrical and Electronics Engineers

IR                    infrared

JHA                 job hazard analysis

kV                   kilovolt

kVA                kilovoltampere

NERC             North American Electric Reliability Council

NESC              National Electrical Safety Code

NFPA             National Fire Protection Association

OMB              Office of Management and Budget

O&M             operations and maintenance

OSHA             Occupational Safety and Health Administration

PEB                 Power Equipment Bulletin

PO&M           Power Operation and Maintenance

PM                 preventive maintenance

PSS                 power system stabilizer

RCM               reliability-centered maintenance

RSHS              Reclamation Safety and Health Standards

SCADA           Supervisory Control and Data Acquisition

SFRA              sweep frequency response analysis

Vac                 volts alternating current

Vdc                 volts direct current

WAPA            Western Area Power Administration

WECC             Western Electricity Coordinating Council

TYPES OF ELECTRICAL CIRCUITS

 

§  A circuit that only has one path for current to flow through is called a series circuit. If the path is broken, no current flows through the circuit.

§  A type of circuit that has more than one path for current is called a parallel circuit. If the path is broken, the current continues to flow through the circuit.