IEEE Power & Energy Magazine - September/October 2015 - 96

in my view

A.G. Phadke

PMU memories
looking back over 40 years

I am often asked how the
phasor measurement unit (PmU) idea
originated and how the technology has
evolved over the years. this story is intimately connected with my work and
that of my colleagues over the last 40
years. I am going to recount the events
of these 40 years as faithfully as I can,
but inevitably there may be some omissions-in particular, the names of my
graduate students and colleagues-for
which I apologize in advance. omissions
are not intentional; they are just artifacts
of memory loss due to advancing age.

American Electric Power
this story begins with my joining the
american electric Power (aeP) service
Corporation in new York City at the
invitation of Glenn stagg, whom I had
come to know through our joint summer school teaching at the University of
wisconsin. I joined aeP in 1969, and
soon thereafter I was asked to look into
the technology of computer relaying
that was gaining considerable attention
in the Ieee Power engineering society
(Pes) Power system Relaying Committee. at aeP, I worked in the Computer
applications department, which was
led by Glenn stagg and later by tony
Gabrielle, two of the most enlightened
managers I had the good fortune to work
for. I was also pleased to have the backing in this enterprise of a famous relay
engineer, stan horowitz, who led the
aeP Relaying department. the team
Digital Object Identifier 10.1109/MPE.2015.2431218
Date of publication: 18 August 2015

ieee power & energy magazine

working on computer relaying included
another distinguished relay engineer,
mohammed Ibrahim. also joining our
group were ted hlibka, Jerry Jauch,
and mike Price. we had a number of
co-op students from various universities
on short-term assignments, and among
them was mark adamiak from Cornell,
who later joined aeP and is now with
General electric Company.

SCDR Development
to accommodate transmission line
protection algorithms in the microcomputers of those days, we developed a
new efficient relaying principle called
symmetrical component distance relay (sCdR). the 1977 paper describing this idea, "fundamental Basis for
distance Relaying using symmetrical
Components" by Phadke, Ibrahim, and
hlibka, won the outstanding relaying
paper award from the Pes Power system Relaying Committee.
about this time we were joined by
Jim thorp, a professor at Cornell University who became affiliated with our
group while on sabbatical. among other
things, he developed an analysis of relay
speed and its relationship to the transient components in voltage and current signals during faults. the resulting
1979 paper, "Limits to Impedance Relaying" by thorp, Phadke, horowitz,
and Beehler, is considered by many to
be of fundamental importance in relaying literature. Jim continued with our
group at aeP in many capacities and
was an important member of the team
that developed PmU technology and its

applications to power system problems.
[much later, Jim joined Virginia tech as
the head of the department of electrical
and Computer engineering, where he
continues to work as a research professor. he remains very active in research
in the field of PmUs and wide-area
montioring systems (wams).]
I was awarded a patent for the invention of sCdR. a principal component
of sCdR development was the accurate measurement of positive, negative,
and zero sequence components of voltages and currents in subcycle time. our
first attempt to measure sequence components for sCdR application was to
use analog circuits that would produce
the necessary phase shifts in signals of
phase quantities and then use the combinations of these signals to produce symmetrical components. It soon became
clear that this is entirely unnecessary;
one could get the required phase shifts
by using the discrete fourier transform
of the sampled data. all symmetrical
components could then be obtained very
efficiently and without the need for any
special analog signal processing.

First Phasor
Measurement Paper
about this time, it was becoming clear
that there were many interesting uses
for the phasor measurements. one early
concept was to use the phase angle of
the positive sequence voltage measurement to determine local frequency and
rate of change of frequency. this was
(continued on p. 93)
september/october 2015

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