Application Note

Application Note
Introduction
The need to manage power is
never more critical than when
power prices skyrocket and
power quality becomes suspect.
Electrical technicians today are
more aware of power consump-
tion and are on the watch for
consumption that’s higher than
anticipated. Once that occurs,
technicians must become detec-
tives and try to trace the power
consumption back to its source.
Fluke single and three phase
power quality analyzers are
excellent tools for conducting the
portable energy audits necessary
to track down energy draining
devices.
This application note details
the procedures for using Fluke
power quality analyzers for
average watt measurements and
converting those to watt-hours.
Average wattage to
watt-hours conversion
Fluke power quality analyzers
can provide a reading of average
wattage over time, a value that
can be easily used to determine
watt-hours. To convert average
watts to watt-hours, simply mul
-
tiply the average watts reading
by the amount of time over which
the a
verage was measured
.
F
or example, the follow
ing
calculations are for continuous
loads (for c
ycling loads, see
load
cycle considerations
):
•
A one-watt averaged load
measured for one hour is equal
to one watt-hour; a 1000-watt
averaged load measured for
one hour is equal to one k
ilo
-
watt-hour
.
•
A 60-watt averaged load
measured for two hours is
equal to 120 watt-hours.
•
A 60-watt averaged load
measured for 15 minutes
(one-quarter hour) is equal to
15 watt-hours.
This technique for measuring
real power consumption (kWh)
can also be applied to apparent
power (kVA) and reactive power
(kVAR). Simply set the power
quality analyzer to calculate the
running average kVA or kVAR,
then multiply by the recording
time to get kVAh or kVARh used
by the load.
Load cycle
considerations
When making average watt
measurements, be sure to take
into consideration the load cycles
you’re working with.
Long cycle loads: If the load
creating the watt draw has a
long on/off cycle, like a refrigera-
tor, be sure to measure long
enough to include several on/off
cycles to get a good representa-
tion of the average watts. If pos-
sible, tr
y to stop the
measurement at an even numb
er
of on/off cycles to reduce meas-
urement errors
.
Short cycle loads: If loads
can cycle on and off or make
large changes faster than one
per minute, use an advanced
three phase analyzer to ensure
the wattage valves are captured
.
Making a
verage watt
measurements with the
Fluke 430 Series
On the three phase 430 power
quality analyzers, the energy
function automatically measures
and calculates W
atts/
V
A
/
V
ARs.
Simply c
onnect the clamps and
leads and select energy from the
menu
.
From the Fluke Digital Library @ www.fluke.com/library
Making watt-hour
measurements
with Fluke power
quality analyzers
Using the Fluke 43B Power Quality Analyzer for average
watt measurements.