12-08-2014, 03:04 PM
Power Factor Correction for Power Systems
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Abstract
Wasted energy capacity, also known as poor power factor, is often overlooked. It can
result in poor reliability, safety problems and higher energy costs. The lower your power
factor, the less economically your system operates.
The actual amount of power being used, or dissipated, in a circuit is called true power.
Reactive loads such as inductors and capacitors make up what is called reactive power. The
linear combination of true power and reactive power is called apparent power.
Power system loads consist of resistive, inductive, and capacitive loads. Examples of
resistive loads are incandescent lighting and electric heaters. Examples of inductive loads are
induction motors, transformers, and reactors. Examples of capacitive loads are capacitors,
variable or fixed capacitor banks, motor starting capacitors, generators, and synchronous
motors.
Power factor correction (PFC) is usually achieved by adding capacitive load to offset
the inductive load present in the power system. The power factor of the power system is
constantly changing due to variations in the size and number of the motors being used at
one time. This makes it difficult to balance the inductive and capacitive loads continuously.
There are many benefits to having power factor correction. As a customer the cost
doesn’t get passed on for having a low power factor. As a utility company, equipment has a
much longer life span and maintenance costs remain low
Types of ypes of ypes of Power
The actual amount of power being used, or dissipated, in a circuit is called true power.
It is measured in watts and is symbolized mathematically by the capital letter P. True power is
a function of the circuit’s dissipative elements, such as resistances ®. [1]
Reactive loads such as inductors and capacitors dissipate zero power, but the fact that
they drop voltage and draw current gives the perception that they do dissipate power. This
“dissipated power” is called the reactive power and is measured in Volt-Amps-Reactive (VAR).
Reactive power is represented by the capital letter Q, and is a function of a circuit's reactance
–Methods of Power Factor Correction Methods of Power Factor
Correction Methods of Power Factor Correction
In the real world, utilities normally only require a power factor of 0.9. Although a unity
power factor provides the most efficient power system, a unity power factor leaves the power
system susceptible to harmonic problems. Harmonic problems cause excessive heating in
motors, nuisance tripping, and premature failure of solid state components.
Power factor correction (PFC) is usually achieved by adding capacitive load to offset
the inductive load present in the power system. The power factor of the power system is
constantly changing due to variations in the size and number of the motors being used at
one time. This makes it difficult to balance the inductive and capacitive loads continuously.
In addition, harmonic problems can be introduced if the capacitors are not sized with
the specific power system characteristics in mind. The utility company may also restrict or deny
the introduction of KVARs into their power system. These are all considerations that need to
be addressed prior to making any decisions about the size or type of power factor correction.
Conclusions and Conclusions and Conclusions and Future Plans Future
Plans Future Plans
Since this is the project’s first semester, there is a lot more in store. Our future plans
include learning Siemens Power System Simulator for Engineering (PSS/E) and helping the fall
EE461 students learn and use PSS/E. In order to learn PSS/E we will be utilizing the labs - 12 -
created by the WAPA System Study Senior Design Group. In addition to the learning PSS/E
our plans include a system impact study of the proposed Colorado State University Windfarm.
Projects are given $50 per person per semester. Since this first semester was mostly
spent doing research, we came in extremely under budget. The only real expenses were
group members’ time.