IEEE Power & Energy Magazine - July/August 2017 - 91

discrete change in angle. It typically
took more time to set up and check out
a case than it did to solve it.
Transient network analyzers (Tnas)
were used to simulate transient phenomena beginning around 1950. Here,
too, a portion of the system was represented by bench-top system models
made up of pi-equivalent line sections,
model transformers, series capacitors, loads, and lightning arresters, all
selected from several shelves of model
elements. That required skill in scaling
principles to assure that fixed model
parameters accurately represented the
system under study. The circuit breaker
initiating a transient on the three-phase
system under study was comprised of a
series of 12-in (29-cm) diameter discs
mounted on a common rotating shaft.
The periphery of each disc was in
part conducting and in part insulating.
Thus, by adjusting the physical system of brushes, three poles of a circuit
breaker could be made to close at the
same time or be offset in time from one
another. preclosing resisters could be
simulated by the use of six such discs.
The resulting transient, being repeated
with each rotation of the switch, would
appear stationary on the oscilloscope
monitoring voltages and currents.
actual switches and transformers
with generators, static var compensators (SVCs), and HVdc links were
developed and added to the Tna. Real
control and protection systems could
also be wired to the Tna for testing.
Some extended transmission networks,
such as Hydro Quebec's 735-kV network, were modeled on very large
Tnas. Other very large analog Tnas
were built in Japan, India, and China,
and some remain in service today. an
analog simulator with HVdc capability is shown in Figure 3. It contains
four complete 12-pulse converters,
overhead line models, and five synchronous machines. Transmission
towers were replicated in miniature,
and impulses were applied along
streamers from HV sources. Voltage
across the miniature insulators were
compared for various tower and shield
wire configurations.
july/august 2017

For these analog simulators, Rayleigh's principle of similitude in dynamics was very important. The correct
representation of system damping was a
continual challenge, with artificial resistance and sometimes negative resistance needed to mimic the expected real
system behavior.

analog network analyzers remained
in wide use to the end of the 20th century. They became more and more
sophisticated, blending digital technology (such as a microprocessor hardware model of a lightning arrester) into
their component parts as hybrid digital/analog simulators. They gradually

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2017