IEEE Electrification Magazine - June 2016 - 63

to flow back into the fault, and the breaker starts conducting. One way to counter this problem is to have a
system where only breakers E and F
have paired control, while other
breakers have local control. However, there are other disadvantages of
local control. For example, every
time the fault is at the input end of
the breaker, the breaker is signaled
to turn on the SCRs. This does not
necessarily result in the breaker
conducting because the SCRs do not
allow a path for negative current to
flow through, even if they are gated.
However, there is a risk-if the fault
happens to have resonance and the
SCR remains gated, then unwanted
current can be injected back into
the system, which could cause some
other breakers to turn off. Table 2
shows results of a simple resistive fault, but it is possible for the fault to resonate current back into the system if SCRs of adjacent breakers are gated.
As discussed in the section "Paired Breaker Control,"
if the faults at junctions 5 and 9 are ignored, which is a
reasonable assumption, the paired breaker control
scheme provides the ideal response, which is similar to
central control without the complex communication
architecture. For a fault at location 3, all sources are disconnected from the system, so it does not matter that
paired control sends gate signals to the rest of the
breakers. Central control still holds an advantage in
terms of coordinating starting gate signals and using
the breakers as dc switches to reconfigure the system.

Even with paired control, some variation of centralized
control can exist for these operations, but the breakers
will no longer require continuous
current data to be sent or continuous gate signals to be received.
It would be useful to observe the
current through these dc breakers
for some of the cases from Table 2.
The paired control scheme is
employed in the simulation and, for
the first case, a fault is created at
location 4. Figure 5 shows the input
current flowing through breakers C,
G, and J, and the output current of
breaker C. The first two plots in Figure 5 show the input and output
currents for breaker C. Only the output current of the breaker C shows
the fault current, but the input current goes to zero instantly. Breaker
G's current is shown in the third plot. There is some
disturbance at the time of the fault, but the steadystate current through breaker G is the same before and
after the fault as it is feeding the load. The fourth plot
shows the output current through breaker J that roughly doubles because branch 11 has to provide current to
all the loads now that branch 4 has been isolated from
the system.
The next case is for a fault at location 6. Figure 6
shows the output current for breakers E, G, and K are
shown, as well as the input current for breaker G. The
first two plots in Figure 6 show the input and output currents through breaker G, respectively. The fault is at the
output of breaker G, so only the output current shows the

After 0.4 s, the
breaker turns back
on and the output
current is now
negative, demonstr-
ating that the
direction of current
through breaker
E has changed.

5

10
100 ms

0

is,G (A)

is,C (A)

10

400

io,G (A)

io,C (A)

0

2

io,E (A)

is,G (A)

0

Figure 5. The current response to fault at location 4.

6

io,K (A)

is,J (A)

0

0
-2

20
10

200
0

20
10

200 ms

0

600
300

5

4
2

Figure 6. The current response to fault at location 6.
IEEE Electrific ation Magazine / j une 2 0 1 6

63



Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2016

IEEE Electrification Magazine - June 2016 - Cover1
IEEE Electrification Magazine - June 2016 - Cover2
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