Power Factor Correction

Power Factor Correction and Voltage Optimisation have been around since the turn of the
20th century and although in many cases their individual benefits and attributes make them a
viable form of energy reduction in the right environment, in truth it is only recently that they
have been considered as a powerful energy saving technology which when combined offer
complimentary correction to improve energy efficiency and reduce consumption across a
whole site.

There is now momentum towards a global low carbon economy with creation of the Paris
Agreement, the impact around climate change, increase in energy costs, introduction of
penalties for inefficient users and a need to reduce demand as electricity tariffs move
towards time of day demand based billing.

Power Factor Correction improves the overall efficiency of an electrical supply by the
controlled introduction of capacitors onto an electrical systems while Voltage Optimisation
reduces energy consumption in voltage dependent loads by reducing and in some cases
controlling voltage levels to within European Harmonised voltage levels to return an energy
saving.

What Does ‘Power Factor’ Mean?

Power Factor is basically a degree of electrical
efficiency and in an AC circuit, the ratio between
the useful power kW (true power needed to
perform a task) and apparent power kVA (a
combination of true power and reactive power -
power drawn in addition to useful power but does
not contribute to the task).

Reactive power exists in an AC circuit when the

current and voltage are not in phase, some
electrical equipment like motors and machines
used in industrial and commercial buildings
require a degree of ‘reactive power’ in addition to
real power in order to work effectively.
Reactive power generates the magnetic fields which are essential for inductive electrical
equipment to operate, this leads to excessive energy consumption as the reactive load is
recorded by the energy provider as an element on a half hourly meter.

Power Factor is displayed as a figure between 0.01pf to 1.00pf with a poor power factor
generally understood to be less than 0.95pf and a perfect power factor as 1.00pf known as
unity, in layman terms you could describe power factor as a % degree of electrical efficiency
and a good power factor in excess of 95% is normally deemed as electrically efficient.

Power factor can also be termed as lagging or leading, a lagging power factor signifies that
the load is inductive and in need of correction through the introduction of capacitors while a
leading power factor signifies that there is too much capacitance in circuit. A general
methodology exists between the network operators to
apply penalties in the form of a Reactive Power Charge to
users who’s power factor falls below 0.95pf either lag or
lead.

A Reactive Power Charge is sometimes termed as a

Wattless Charge or Power Factor Surcharge and is
normally applied in the Consumption or Distribution
charges section of an electricity bill.

Poor power factor can create a number of negative effects in both billing and infrastructure,
a European survey in 2007 discovered that poor Power Quality is seriously affecting business
results in the industrial and service sectors which amount to an annual total loss of €150
billion across Europe.
 Savings & Benefits of Power Factor Correction
In order to aid decision makers to form an opinion on whether power factor correction
would be beneficial to their organization, the economic advantages of installing power factor
correction are detailed below:

Removal of Reactive Power Charges

Targeting unity power factor and ensuring 0.95pf or better will in most cases remove the
reactive power penalties on electricity bills completely.

Reduction in Authorised Supply Capacity

Authorised Supply Capacity charges (Availability Charges) are normally charged in kVa at a
typical rate of £1/kVA/month, the charge relates to the Maximum Demand or maximum
power drawn from the network on a user's site and is generally in place to pay for the supply
network infrastructure required to deliver the declared (or drawn) degree of energy at any
time night or day.

Power factor in an AC power circuit is directly related to kVa and associated circuit currents,
an improvement in power factor would normally allow the user to target the correct / lower
capacity level to avoid exaggerated charges on monthly energy bills.

Excess Authorised Supply Capacity

Charges drawn over and above the declared
or agreed Supply Capacity,

Reduced kw/h consumption

Reduced kw/h losses in power cables,
switchgear and supply transformers with
benefits delivered to the whole electrical
system

Reduced Emissions
Higher, inefficient energy consumption inevitably results in an increase in CO 2 emissions and
associated penalties.
Reduced Investment in Infrastructure & Costly Network Upgrades
A site operating on a power factor close to unity would require less investment in associated
power plant (Transformers, Switchgear & Cables) as the reduction in kVA will allow for the
investment in associated plant to be minimized. Investments into costly network upgrades
due to an overloaded electrical supply can be avoided by improving power factor and at a
fraction of the cost of an upgrade

Improvement in Power Quality

The reliability and consistency of and electricity supply is critical to many energy users, a
European survey discovered that poor Power Quality is seriously affecting business results in
the industrial and service sectors which amount to an annual total loss of €150 billion across
Europe
 Types of Power Factor Correction
There are a number of different types of power factor correction although functionality
wise, they can be separated into two main categories:

● Fixed & Semi-Automatic Power Factor Correction

● Automatic Power Factor Correction

Fixed Power Factor Correction

Fixed or DOL capacitors were once a relatively low cost alternative to automatic correction
although recent changes in methodology to apply penalties for “leading” power factor have
made fixed capacitor less attractive due to potential over compensation.

Semi-Automatic Power Factor Correction

A compromise between Fixed & Automatic where a capacitor is energized via the motor
control circuitry. Semi-Automatic motor controlled capacitors do not however compensate
for whole site power factor and will only correct the individual motor to approximately
0.95pf

Automatic Power Factor Correction

Automatic power factor correction is achieved through the controlled introduction of
capacitor stages onto an inductive electrical system. Control is normally provided through
the integration of an electronic device in the form of a Power Factor Control relay which
monitors the actual uncorrected power factor and selects the appropriate capacitor stages
to correct the inductive load to a pre programmed “target” power factor normally set to
1.00pf or unity.

As most industrial loads fluctuate, automatic control ensures the desired target power factor
is maintained to avoid over compensation and target maximum savings.
 Design of Power Factor Correction
Selection of the correct design of power factor correction is vital to long term trouble free
operation. The main considerations in selection are based around the level of functionality
required and installation environment.

Considerations include voltage levels, ambient temperature, degree of harmonic distortion

present on the sites electrical system and the impact of imminent changes to infrastructure.

Functionality will depend mainly on load fluctuation and frequency of response required to
correct the loads accordingly.

Standard Power Factor Correction

Standard power factor correction is designed as a relatively low cost automatic solution for
the correction of a fluctuating inductive load when no significant non-linear loads are
present. Typical construction consists of a main incoming device, individual stage protection
(Stage Fuses), inrush limiting capacitor switching contactors, capacitors typically rated at
400-440v and a power factor control relay to automatically switch the capacitor in and out of
circuit as required.

De-Rated Power Factor Correction

De-rated power factor correction is of a similar construction to standard and designed
mainly as a low cost alternative to Detuned power factor correction where distortion levels
are not problematic or the environment is harsh in respect of higher voltage levels or high
ambient temperatures. Capacitors with a higher dielectric strength are employed, typically
525v – 690v although care should also be taken to ensure their output is also de-rated
accordingly and the correct amount of correction applied in accordance with system voltage
levels.

ie a 25kvar 525v capacitor operating on a system voltage of 415v will offer only 15.6kvar of
correction
Detuned Power Factor Correction
Detuned power factor correction sometimes known as “future proof” is typically used on
electrical systems containing a significant level of harmonic generating non-linear loads or
where loads are expected to contain in excess of 25% of non-liner loads. Construction is
similar to both the standard and de-rated designs although the capacitors are of a higher
dielectric strength and typically around 525v while the main difference is in the inclusion of
harmonic blocking detuning reactors or inductors connected in series with each capacitor
stage to protect the capacitors from harmful harmonic frequencies and to avoid harmonic
amplification or resonance.

Thyristor Switched Power Factor Correction

Thyristor switched power factor correction, sometimes known as “Real Time”, utilizes
thyristors to switch capacitor stages instead of contactors and is best utilised on rapidly
fluctuating high speed loads that require rapid correction that cannot be offered with
contactor based systems. Contactor based systems require the capacitor to discharge for
around 60 seconds before re-energisation, this is known as the discharge time and
programmable through the power factor controller. Failure to observe the discharge time
can result is serious damage to the power factor correction system and associated
switchgear. Thyristors typically switch capacitors at the ‘zero crossing’ of a sinusoidal
waveform, enabling the capacitors to be switched into and out of circuit multiple times over
short periods of time (typically 2-4 cycles) without observing discharge protocol.

Designed as Standard, De-rated or De-tuned, cost implications of Thyristor switched usually

encourages the user to invest in the more robust De-tuned systems to future proof their
investment.

Active Power Factor Correction

Probably the most functional although also most costly, active power factor correction
utilises IGBT’s to correct leading and lagging power factor with a very fast response to load
changes of around 2 cycles and can also be used to provide harmonic mitigation and load
balancing.
 Power Factor Correction System Installation
Installation is carried out in parallel with the main supply via a suitably rated form of
protective device although individual “local” power factor correction capacitors can also be
installed on individual motor loads.

When installing on individual motor loads it is important to ensure over compensation

cannot occur and that any associated controls will allow for the capacitor to discharge
between energization periods.

For more information visit www.energyace.co.uk