Page 1
Utilisation of Electrical Energy
Dept. of EEE VEMU IT
Page 2
Utilisation of Electrical Energy
Dept. of EEE VEMU IT
Utilisation of Electrical Energy
electromagnetic field in a device and creates reactive power. An inductive load draws current that
lags the voltage, in that the current follows the voltage wave form. The amount of lag is the
electrical displacement (or phase) angle between the voltage and current. n the absence of
harmonics, apparent power (also known as demand power) is comprised of (vectorial sum) both
real and reactive power and is measured in units of volt-amps (VA) or kilovolt-amps (kVA).
Power factor (PF) is the ratio of the real power to apparent power and represents how
much real power electrical equipment uses. It is a measure of how effectively electrical
power is being used. Power factor is also equal to the cosine of the phase angle
between the voltage and current Electrical loads demand more power than they
consume. Induction motors convert at most 80% to 90% of the delivered power into
useful work or electrical losses. The remaining power is used
to establish an electromagnetic field in the motor. The field is alternately expanding and
collapsing (once each cycle), so the power drawn into the field in one instant is returned to
the electric supply system in the next instant. Therefore, the average power drawn by the
field is zero, and reactive power does not register on a kilowatt-hour meter. The
magnetizing current creates reactive power. Although it does no useful work, it circulates
between the generator and the load and places a heavier drain on the power source as
well as the transmission and distribution system. As a means of compensation for the
burden of supplying extra current, many utilities establish a power factor penalty in their
rate schedule. A minimum power factor, usually 0.85 to 0.95, is established. When a
customer’s power factor drops below the minimum value, the utility collects a low power
factor revenue premium on the customer’s bill. Another way some utilities collect a low
power factor premium is to charge for kVA (apparent power) rather than kW (real power).
With a diverse range of billing rate structures imposed by electrical utilities especially for
large users, it is imperative to fully understand the billing method employed
Improving power factor:
Adding capacitors is generally the most economical way to improve a facility’s power
factor. While the current through an inductive load lags the voltage, current to a
capacitor leads the voltage. Thus, capacitors serve as a leading reactive current
generator to counter the lagging reactive current in a system.
The expression “release of capacity” means that as power factor of the system is improved, the
Page 3
Utilisation of Electrical Energy
Dept. of EEE VEMU IT
Utilisation of Electrical Energy
electromagnetic field in a device and creates reactive power. An inductive load draws current that
lags the voltage, in that the current follows the voltage wave form. The amount of lag is the
electrical displacement (or phase) angle between the voltage and current. n the absence of
harmonics, apparent power (also known as demand power) is comprised of (vectorial sum) both
real and reactive power and is measured in units of volt-amps (VA) or kilovolt-amps (kVA).
Power factor (PF) is the ratio of the real power to apparent power and represents how
much real power electrical equipment uses. It is a measure of how effectively electrical
power is being used. Power factor is also equal to the cosine of the phase angle
between the voltage and current Electrical loads demand more power than they
consume. Induction motors convert at most 80% to 90% of the delivered power into
useful work or electrical losses. The remaining power is used
to establish an electromagnetic field in the motor. The field is alternately expanding and
collapsing (once each cycle), so the power drawn into the field in one instant is returned to
the electric supply system in the next instant. Therefore, the average power drawn by the
field is zero, and reactive power does not register on a kilowatt-hour meter. The
magnetizing current creates reactive power. Although it does no useful work, it circulates
between the generator and the load and places a heavier drain on the power source as
well as the transmission and distribution system. As a means of compensation for the
burden of supplying extra current, many utilities establish a power factor penalty in their
rate schedule. A minimum power factor, usually 0.85 to 0.95, is established. When a
customer’s power factor drops below the minimum value, the utility collects a low power
factor revenue premium on the customer’s bill. Another way some utilities collect a low
power factor premium is to charge for kVA (apparent power) rather than kW (real power).
With a diverse range of billing rate structures imposed by electrical utilities especially for
large users, it is imperative to fully understand the billing method employed
Improving power factor:
Adding capacitors is generally the most economical way to improve a facility’s power
factor. While the current through an inductive load lags the voltage, current to a
capacitor leads the voltage. Thus, capacitors serve as a leading reactive current
generator to counter the lagging reactive current in a system.
The expression “release of capacity” means that as power factor of the system is improved, the
Utilisation of Electrical Energy
total current flow will be reduced. This permits additional loads to be added and served by the
existing system. In the event that equipment, such as transformers, cables, and generators,
may be thermally overloaded, improving power factor may be the most economical way to
reduce current and eliminate the overload condition. Primarily, the cost-effectiveness of power
factor correction depends on a utility’s power factor penalties. It is crucial to understand the
utility’s rate structure to determine the return on investment to improve power factor.
Maintaining a high power factor in a facility will yield direct savings. In addition to
reducing power factor penalties imposed by some utilities, there may be other
economic factors that, when
considered in whole, may lead to the addition of power factor correction capacitors that
provide a
justifiable return on investment. Other savings, such as decreased distribution losses,
improved voltage reduction, and increased facility current carrying capacity, are less
obvious. Though real,
often these reductions yield little in cost savings and are relatively small in comparison
to the savings to be gained from reducing power factor penalties.
Harmonic current considerations:
This article intentionally assumes that a facility does not have significant harmonic
currents present. However, some caution must be taken when applying capacitors in a
circuit where harmonics are present (true power factor). Although capacitors
themselves do not generate harmonics, problems arise when capacitors for power
factor correction improvement are applied
Page 4
Utilisation of Electrical Energy
Dept. of EEE VEMU IT
Utilisation of Electrical Energy
electromagnetic field in a device and creates reactive power. An inductive load draws current that
lags the voltage, in that the current follows the voltage wave form. The amount of lag is the
electrical displacement (or phase) angle between the voltage and current. n the absence of
harmonics, apparent power (also known as demand power) is comprised of (vectorial sum) both
real and reactive power and is measured in units of volt-amps (VA) or kilovolt-amps (kVA).
Power factor (PF) is the ratio of the real power to apparent power and represents how
much real power electrical equipment uses. It is a measure of how effectively electrical
power is being used. Power factor is also equal to the cosine of the phase angle
between the voltage and current Electrical loads demand more power than they
consume. Induction motors convert at most 80% to 90% of the delivered power into
useful work or electrical losses. The remaining power is used
to establish an electromagnetic field in the motor. The field is alternately expanding and
collapsing (once each cycle), so the power drawn into the field in one instant is returned to
the electric supply system in the next instant. Therefore, the average power drawn by the
field is zero, and reactive power does not register on a kilowatt-hour meter. The
magnetizing current creates reactive power. Although it does no useful work, it circulates
between the generator and the load and places a heavier drain on the power source as
well as the transmission and distribution system. As a means of compensation for the
burden of supplying extra current, many utilities establish a power factor penalty in their
rate schedule. A minimum power factor, usually 0.85 to 0.95, is established. When a
customer’s power factor drops below the minimum value, the utility collects a low power
factor revenue premium on the customer’s bill. Another way some utilities collect a low
power factor premium is to charge for kVA (apparent power) rather than kW (real power).
With a diverse range of billing rate structures imposed by electrical utilities especially for
large users, it is imperative to fully understand the billing method employed
Improving power factor:
Adding capacitors is generally the most economical way to improve a facility’s power
factor. While the current through an inductive load lags the voltage, current to a
capacitor leads the voltage. Thus, capacitors serve as a leading reactive current
generator to counter the lagging reactive current in a system.
The expression “release of capacity” means that as power factor of the system is improved, the
Utilisation of Electrical Energy
total current flow will be reduced. This permits additional loads to be added and served by the
existing system. In the event that equipment, such as transformers, cables, and generators,
may be thermally overloaded, improving power factor may be the most economical way to
reduce current and eliminate the overload condition. Primarily, the cost-effectiveness of power
factor correction depends on a utility’s power factor penalties. It is crucial to understand the
utility’s rate structure to determine the return on investment to improve power factor.
Maintaining a high power factor in a facility will yield direct savings. In addition to
reducing power factor penalties imposed by some utilities, there may be other
economic factors that, when
considered in whole, may lead to the addition of power factor correction capacitors that
provide a
justifiable return on investment. Other savings, such as decreased distribution losses,
improved voltage reduction, and increased facility current carrying capacity, are less
obvious. Though real,
often these reductions yield little in cost savings and are relatively small in comparison
to the savings to be gained from reducing power factor penalties.
Harmonic current considerations:
This article intentionally assumes that a facility does not have significant harmonic
currents present. However, some caution must be taken when applying capacitors in a
circuit where harmonics are present (true power factor). Although capacitors
themselves do not generate harmonics, problems arise when capacitors for power
factor correction improvement are applied
Utilisation of Electrical Energy
to circuits with nonlinear loads that interject harmonic currents. Those capacitors may lower
the resonant frequency of that circuit enough to create a resonant condition. Resonance is a
special condition in which the inductive reactance is equal to the capacitive reactance. As
resonance is approached, the magnitude of harmonic current in the system and capacitor
becomes much larger than the harmonic current generated by the nonlinear load. The current
may be high enough to blow capacitor fuses, create other “nuisance” problems, or develop into
a catastrophic event. A solution to this problem is to detune the circuit by changing the point
where the capacitors are connected to the circuit, changing the amount of applied capacitance,
or installing passive filter reactors to a capacitor bank, which obviously increases its cost. Use
of an active harmonic filter may be another solution.
Capacitor bank considerations and associated costs:
The selection of the type of capacitor banks and their location has an impact on the cost of
capacitor banks. More difficult than determining the total capacitance required is deciding
where the capacitance should be located. There are several factors to consider, including:
Should one large capacitor bank be used, or is it better to add small capacitors at
individual loads? Should fixed or automatically switched capacitors be employed? In
general, since capacitors act as a kVAR generator, the most efficient place to install them
is directly at an inductive load for which the power factor is being improved.
Fixed capacitor location schemes include:
This will generally improve losses, although it is not an optimal solution .Distributing
the capacitors using the motor sizes and the NEMA tables as a guide. This solution
does not reflect the need for more released capacity, if this is a goal. Capacitors sized
for small loads are often proportionally much more expensive than larger fixed
capacitors, primarily because of installation costs.
Capacitor switching options include:
Switching a few of the capacitors with larger motors is an option. The capacitors may be
physically installed either directly connected to the motor or through a contactor on the motor
control center that is tied in with the motor control. If the motors are large enough to use
capacitors of the same size as were being considered for the fixed capacitor scheme, little
additional cost is incurred for installing them on the motors. Where the economy is lost is when
Page 5
Utilisation of Electrical Energy
Dept. of EEE VEMU IT
Utilisation of Electrical Energy
electromagnetic field in a device and creates reactive power. An inductive load draws current that
lags the voltage, in that the current follows the voltage wave form. The amount of lag is the
electrical displacement (or phase) angle between the voltage and current. n the absence of
harmonics, apparent power (also known as demand power) is comprised of (vectorial sum) both
real and reactive power and is measured in units of volt-amps (VA) or kilovolt-amps (kVA).
Power factor (PF) is the ratio of the real power to apparent power and represents how
much real power electrical equipment uses. It is a measure of how effectively electrical
power is being used. Power factor is also equal to the cosine of the phase angle
between the voltage and current Electrical loads demand more power than they
consume. Induction motors convert at most 80% to 90% of the delivered power into
useful work or electrical losses. The remaining power is used
to establish an electromagnetic field in the motor. The field is alternately expanding and
collapsing (once each cycle), so the power drawn into the field in one instant is returned to
the electric supply system in the next instant. Therefore, the average power drawn by the
field is zero, and reactive power does not register on a kilowatt-hour meter. The
magnetizing current creates reactive power. Although it does no useful work, it circulates
between the generator and the load and places a heavier drain on the power source as
well as the transmission and distribution system. As a means of compensation for the
burden of supplying extra current, many utilities establish a power factor penalty in their
rate schedule. A minimum power factor, usually 0.85 to 0.95, is established. When a
customer’s power factor drops below the minimum value, the utility collects a low power
factor revenue premium on the customer’s bill. Another way some utilities collect a low
power factor premium is to charge for kVA (apparent power) rather than kW (real power).
With a diverse range of billing rate structures imposed by electrical utilities especially for
large users, it is imperative to fully understand the billing method employed
Improving power factor:
Adding capacitors is generally the most economical way to improve a facility’s power
factor. While the current through an inductive load lags the voltage, current to a
capacitor leads the voltage. Thus, capacitors serve as a leading reactive current
generator to counter the lagging reactive current in a system.
The expression “release of capacity” means that as power factor of the system is improved, the
Utilisation of Electrical Energy
total current flow will be reduced. This permits additional loads to be added and served by the
existing system. In the event that equipment, such as transformers, cables, and generators,
may be thermally overloaded, improving power factor may be the most economical way to
reduce current and eliminate the overload condition. Primarily, the cost-effectiveness of power
factor correction depends on a utility’s power factor penalties. It is crucial to understand the
utility’s rate structure to determine the return on investment to improve power factor.
Maintaining a high power factor in a facility will yield direct savings. In addition to
reducing power factor penalties imposed by some utilities, there may be other
economic factors that, when
considered in whole, may lead to the addition of power factor correction capacitors that
provide a
justifiable return on investment. Other savings, such as decreased distribution losses,
improved voltage reduction, and increased facility current carrying capacity, are less
obvious. Though real,
often these reductions yield little in cost savings and are relatively small in comparison
to the savings to be gained from reducing power factor penalties.
Harmonic current considerations:
This article intentionally assumes that a facility does not have significant harmonic
currents present. However, some caution must be taken when applying capacitors in a
circuit where harmonics are present (true power factor). Although capacitors
themselves do not generate harmonics, problems arise when capacitors for power
factor correction improvement are applied
Utilisation of Electrical Energy
to circuits with nonlinear loads that interject harmonic currents. Those capacitors may lower
the resonant frequency of that circuit enough to create a resonant condition. Resonance is a
special condition in which the inductive reactance is equal to the capacitive reactance. As
resonance is approached, the magnitude of harmonic current in the system and capacitor
becomes much larger than the harmonic current generated by the nonlinear load. The current
may be high enough to blow capacitor fuses, create other “nuisance” problems, or develop into
a catastrophic event. A solution to this problem is to detune the circuit by changing the point
where the capacitors are connected to the circuit, changing the amount of applied capacitance,
or installing passive filter reactors to a capacitor bank, which obviously increases its cost. Use
of an active harmonic filter may be another solution.
Capacitor bank considerations and associated costs:
The selection of the type of capacitor banks and their location has an impact on the cost of
capacitor banks. More difficult than determining the total capacitance required is deciding
where the capacitance should be located. There are several factors to consider, including:
Should one large capacitor bank be used, or is it better to add small capacitors at
individual loads? Should fixed or automatically switched capacitors be employed? In
general, since capacitors act as a kVAR generator, the most efficient place to install them
is directly at an inductive load for which the power factor is being improved.
Fixed capacitor location schemes include:
This will generally improve losses, although it is not an optimal solution .Distributing
the capacitors using the motor sizes and the NEMA tables as a guide. This solution
does not reflect the need for more released capacity, if this is a goal. Capacitors sized
for small loads are often proportionally much more expensive than larger fixed
capacitors, primarily because of installation costs.
Capacitor switching options include:
Switching a few of the capacitors with larger motors is an option. The capacitors may be
physically installed either directly connected to the motor or through a contactor on the motor
control center that is tied in with the motor control. If the motors are large enough to use
capacitors of the same size as were being considered for the fixed capacitor scheme, little
additional cost is incurred for installing them on the motors. Where the economy is lost is when
Utilisation of Electrical Energy
the capacitors are placed on several small motors. There is relatively little difference in
installation costs for large and small 480-V units.
The second switching option is to consider an automatic power factor controller
installed in the Capacitor bank. This will switch large capacitor banks in small steps (25
through 50 is common)
to follow the load. Automatic power factor capacitor banks should be installed at the
motor control center rather than on the main bus, if optimal distribution loss is a goal.
The economics of purchasing, installing
Improving Load Factor Your company could increase efficiency by improving load factor.
Increasing your load factor will reduce the average unit cost (demand and energy) of the
kWh. Depending on your situation, improving your load factor could mean substantial
savings. The load factor corresponds to the ratio between your actual energy consumption
(kWh) and the maximum power recorded (demand) for that period of time.
WHAT IS LOAD FACTOR? Consumption (kWh) during the period x 100 /Demand
(kW) x hours in that period
By analyzing your load profile and your needs, you may be able to improve your load
factor by doing the following:.
Demand Reduction Reduce demand by distributing your loads over different times or
by installing load management systems.
Increase Production Keeping the demand stable and increasing your consumption is often a
cost-effective way to increase production while maximizing the use of your power. In both
cases, the load factor will improve and therefore reduce your average unit cost per kWh.
The peak demand
The peak demand of an installation or a system is simply the highest demand that has occurred
over a specified time period (Gönen 2008). Peak demand is typically characterized as annual, daily
or seasonal and has the unit of power. Peak demand, peak load or on-peak are terms used in
energy demand management describing a period in which electrical power is expected to be
provided for a sustained period at a significantly higher than average supply level. Peak demand
fluctuations may occur on daily, monthly, seasonal and yearly cycles. For an electric utility
company, the actual point of peak demand is a single half-hour or hourly period which
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