Page 44 - Energize September 2022

TECHNICAL

Improving accuracy of power and

power quality measurements

By Dave Coombes, Fluke

ccurate measurement of electrical power is becoming Problems with this approach
more important, as electrical power becomes a more This approach relies on the fact that errors and uncertainties in
Aessential and valuable commodity. It is also becoming the source are effectively cancelled out by using the same source
more crucial to measure more attributes of electrical power, as for measurements made with the UUT, and with the reference.
deregulation and distributed generation systems result in huge In the case of power measurement, the source is generally the
increases in the number of transactions taking place where mains power line, or is derived from the mains power line with
electricity is bought and sold.
Buyers obviously are keen to ensure they are getting what
they paid for, and distributors are keen to ensure that power
supplied does not adversely affect the integrity of their network.
The US National Institute of Standards and Technology (NIST)
has stated that “additional low-uncertainty measurements are
needed to ensure the accurate sale of power”, and “more precise
measurements of standard billing parameters will be needed (e.g.,
energy, demand) to support contract management”. 1
At the same time, many driving forces are in place to make this
measurement more difficult and error-prone. Power is becoming
dirtier and more distorted, and measurements beyond straight
power and energy (such as flicker) become commonplace. The
impacts of this are obviously many. Two perhaps are of concern to Figure 1(a): Series connection arrangement
us in the metrology community.
Firstly, how do we maintain integrity, and improve
uncertainties on measurements being made that have previously
been well understood i.e., power and energy, but where
measurement conditions are now quite substantially different
from those in the past?
Secondly, how do we ensure adequate uncertainty
measurements are made on some of the newer measurements
being called for today, such as flicker?

Existing methods
Figure 1(b): Parallel connection arrangement
Reference measurement devices
The use of reference measurement devices is a well understood
technique in today’s metrology. The same measurement is made
with the unit under test (UUT) and with a reference instrument
whose uncertainties are well defined. A comparison made
between the two measurements yield the errors in the UUT.
Depending on the nature of the instruments and measurements
involved, the two measurements may be made at the same
time using some kind of series and/or parallel connection,
or sequentially by switching or substitution (Figure 1). In the
measurement of power, this technique is employed widely,
particularly with power meters and revenue meters (kWh meters). Figure 1(c): Instrument substitution arrangement

energize | September 2022 | 42