Choosing an energy monitoring device that has the ability to measure power factor is important in gaining an accurate overall picture of energy usage and planning efficiency measures.
What is Power Factor?
Power factor is a measurement of how efficiently electrical
power is consumed. In high consumption premises, the operation of
plant and equipment such as motors, compressors, welding sets and
even fluorescent lighting can introduce varying levels of
electrical inefficiencies in the form of additional currents called
'inductive reactive currents' into a site's electrical supply.
The power dissipated in a load is the product of the voltage and
current. If a load is purely resistive, the voltage and current are
in phase and all the power can do useful work. If a load has a
reactive component (i.e. has capacitance or inductance) the voltage
and current are not in phase. The reactive load causes current to
flow but it can do no useful work.
The relationship between resistive (real) power and reactive
power can be described by the power factor or phase angle. A purely
resistive load has a power factor of one and a phase angle of zero
(i.e. there are no electrical inefficiencies). A purely reactive
load has a power factor of zero and a phase angle of 90.
The relationship between apparent power, real power and reactive
power can be represented in the power triangleshown here. Most
loads have a component of each: ideally in terms of consumption,
electrical efficiency would be around 1.00 PF (100% electrically
efficient), however in a typical commercial or industrial site this
inductive loading can cause it to be reduced to around 0.80 (i.e.
80% electrically efficient).
The Effect on Electricity Costs
Low power factors are not desirable. If a load has a low power
factor, more current must be supplied by the utility company than
is actually needed. This means heavier equipment, inefficient use
of energy and adding to the cost of electricity. Organisations with
a poor power factor are likely to be charged a premium for power by
the utility company.
Therefore organisations with a low PF may well be wasting both
energy and money: when it falls below a set figure, electricity
companies will have to supply extra (kVA) to make up for the loss
caused by poor power factor. They will often apply an additional
charge to the KW being consumed, or the whole supply may be charged
In addition to saving energy and reducing costs, as the power
factor of a system is improved, the release of electrical capacity
means that the total current flow will be reduced. This permits
additional loads to be added and served by an existing system.
Choosing the Correct Energy Data Logger
In making an assessment of overall energy efficiency, it is
important to use an energy data logger that records not only single
and three phase power usage, but also power factor. The ability to
measure PF in a facility will indicate how effectively electrical
power is being used. This will enable corrective measures to be
introduced which can target the inductive reactive currents,
counteract the inductive element of the load and increase
electrical efficiency to nearer the ideal target of 1.00 power
factor. Power factors can be corrected/improved by the installation
of newer equipment including dedicated integrated circuits, or
installing specialist equipment.
Some low end instruments only measure current and then assume
that the voltage is fixed. They also assume that the power factor
is 1.00, as they are not connecting to the voltage and comparing
its timing with the current flow. Therefore this can present a very
inaccurate picture of actual electricity usage. To present an
accurate measurement of power usage, it is important to choose an
energy logger that measures both voltage and current usage and
correlates the timing between the two to measure the power
The Tinytag Energy
data logger is a useful tool for identifying and evaluating
energy saving measures. Cost-effective, non-invasive and easy to
use, it monitors single and three phase power usage, and power
factor, and can be used for spot checks or left to record for
longer periods to help build up energy profiles throughout an