Application Note

3 Fluke Corporation Energy studies with the Fluke 1735 Power Logger
5. Download and review the
measurements. For 30 days
of recording, with a measure-
ment every 15 minutes, you
will have 2880 sets of mea-
surements. Use Power Log
to graph this data, find the
average current or power on
each phase, compare the three
phases and report the largest
number. Figure 4 shows three
phase-current recordings,
zoomed in to show detail.
Power Log has a built-in
report generator that includes
graphs of current and real
power. Your report can range
from a single current or power
number to a full-blown docu-
ment with graphs and tables.
But the ultimate goal is still
the same: Get an accurate
picture of the system load,
help design a safe upgraded
system and satisfy electrical
authorities.
Figure 3. An example of the recorder screen at the end of the
duration, verifying all data is being stored.
Figure 4. Power Log graphs showing detailed current records.
Figure 5. Power Log statistics view showing average current.
Why does power factor
matter?
Large utility customers (typi-
cally those with 100 kW+
loads) contract to buy their
power based on power factor
(the utility requires these big
customers to do this to ensure
they get paid an amount of
money that truly reflects the
cost of the infrastructure they
need to install to service the
customer). Usually the util-
ity requires the customer
maintains a power factor of
0.95 or more (this will vary
depending on the contract),
if the customers power factor
goes below the agreed level
an additional charge is made
to the customer. So power
factor has a direct effect on
the customers bill.
What is power factor?
Power factor is the ratio of
working power or energy
(kilowatts or kW) to appar-
ent or total power (kilovolt-
amperes or kVA) delivered by
the utility. It measures how
effectively total delivered
power is being used. A high
power factor signals effective
utilization of electrical power,
while a low power factor
indicates poor utilization of
electrical power. However,
this is not to be confused
with energy efficiency or con-
servation which applies only
to energy or kW. Improving
the efficiency of electrical
equipment reduces energy
consumption but does not
improve the power factor.
What causes a low
power factor?
The main contributors to low
power factor are motors oper-
ated at less than full load.
This often occurs in cycle
processes such as saws, con-
veyors, compressors, grinders,
etc.—where a motor must be
sized for the heaviest loads.
HVAC fans often have a low
power factor due to running
at reduced load.