B. Disconnection of A3R line from Rosser and G1A line from
Grand Rapids station
In this arrangement, A3R-A4D and G1A lines are remained
energized by G2A line, which is still connected to Grand
Rapids station. In addition, connection of Vermillion and
Ashern station is interrupted by a breaker in Ashern station. In
effect of opening circuit breakers, A3R and G1A are
connected in series and changed to an open-end line whose
voltage is increased. Simulation is performed in two statusesand lasts for 10 s. At first, saturation characteristic of
transformers in Silver station is deactivated. Voltage in openend line also in Silver station is increased up to 310 kVpick prim
(pick value in primary side) whereas, no Ferroresonance
occurs in the system, hence; voltage and current waveforms
are remained in sinusoidal form.
In this paper, set of grading capacitor circuit breakers
(capacitors across open poles of breakers) in Dorsey station
are open. In addition, damping reactor in Ashern station is out
of service. It must be noted that the magnitude of voltage in
normal status in Silver station is 200 kVpick prim. All mentioned
voltage and current magnitudes in this paper are phase to
neutral values.
Another simulation is performed when saturation
characteristic of transformers in Silver station is activated with
specified values of magnetizing parameters. Ferroresonance
occurs in effect of saturation of transformer core in the time of
0.1 s from the beginning of simulation. Voltage and current
waveforms are misshaped and their magnitudes are increased
up to 464 kVpick primand 1.08 kApick primrespectively in Silver
station. Reciprocally, the magnitude of voltage in open end of
A3R line is increased up to 580 kVpick prim. The value and
waveform of parameters in Silver station are shown in Fig. 2.
As it was mentioned in advance, Grand Rapids is able to be
in service as both a generator and equivalent circuit. In order
to prevent instability in effect of sudden energizing at the
beginning of simulation, the station is changed to hydro
generator with constant speed along with Exciter and PSS in
the time of 1 s from the beginning of simulation. After 0.5 s,
when the condition is stable, generator is changed to full-
blown machine where governor and multi-mass torsional shaft
model are released. In generator mode, voltage and current
follow the same oscillations as previous state with lower
magnitudes of about 420 kVpick primand 0.955 kApick primin
Silver station.