IEEE Electrification Magazine - March 2014 - 80

Case C: Protection in
Weak-Infeed Loop Fault

The IIT microgrid
uses the localized
differential
protection scheme
as the centralized
control suffers from
time delays.

in this case, we assume that the
microgrid operates in grid-connected
mode and a single-phase-to-ground
fault occurs at t = 1 s on loop 1 immediately after loop-feeder A (see figure 9).
the total fault current and fault currents through loop-feeders A and b are
shown as i_fault, i_feederA, and i_feederB
in figure 16, the loop Pott protection
scheme failed because of low-fault current sensed by loop Pd A1. this small
fault current is shown by i_feederB from
1 s to about 1.6 s as marked in figure 16. As a backup protection for loop 1, the nondirectional oc relay at loopfeeder A trips at 1.6 s after 0.6 s delay. this time delay
includes the relay and breaker operating time and timeoc delay of relay A. the entire fault current flows through
loop-feeder b in 1.6-2.2 s, which triggers the nondirectional relay at loop-feeder b after 0.6 s delay at 2.2 s. the total
fault current is lower in 1.6-2.2 s compared to 1-1.6 s,
because of the higher loop impedance in the latter period.

Conclusion
it is shown that the hierarchical protection strategy based on
the communication-assisted directional oc relays and the
localized differential scheme would provide efficient protection schemes for the iit microgrid in both grid-connected
and island modes. the communication-assisted relays adopt
adaptive settings for their operation to respond to the higher
fault currents in grid-connected mode and lower fault
currents in island mode. the synchronous generator in the
microgrid provides sufficient fault current for the implementation of the oc-based protection strategy. the simulation
results for grid-connected and island modes demonstrated
the effectiveness of the proposed protection scheme.

Acknowledgments
this project was partially supported by the u.s. department of energy under grant de-fc26-08nt02875.

For Further Reading
M. shahidehpour, M. e. Khodayar, and M. barati, "campus
microgrid: High reliability for active distribution systems,"
in Proc. IEEE Power Energy Society General Meeting, July
2012, pp. 1-2.

I E E E E l e c t r i f i c ati o n M agaz ine / MARCH 2014

M. shahidehpour and M. e. Khodayar, "cutting campus energy costs
with hierarchical control: the economical and reliable operation of a
microgrid," IEEE Electrification
Mag., vol. 1, no. 1, pp. 40-56, sept.
2013.
M. e. Khodayar, M. barati, and M.
shahidehpour, "integration of high
reliability distribution system in
microgrid operation," IEEE Trans.
Smart Grid, vol. 3, no. 4, pp. 1977-2006,
dec. 2012.
Perfect power prototype at illinois institute of technology. [online]. Available: http://
www.iitmicrogrid.net
A. flueck and Z. Li, "destination: Perfection," IEEE
Power Energy Mag., vol. 6, no. 6, pp. 36-47, nov. 2008.
t. Horan, J. K. niemira, and J. f. clair. (2010). detailed
functional specification and analytical studies results for
high reliability distribution system (Hrds) of illinois institute of technology, s&c electric company, Project no. 3568
and 3953. [online]. Available: http://www.sandc.com
g. tsai. (2011). Perfect power system-design of the
scAdA system for the high reliability distribution system
at illinois institute of technology, s&c electric company.
[online]. Available: http://www.ieeechicago.org/Linkclick.
aspx?fileticket=nda3t6rgHig%3d&tabid=1559
seL-351 optimize protection, automation, and breaker
control. [online]. Available: https://www.selinc.com/workarea/
downloadasset.aspx?id=5527

IEEE Standard for Interconnecting Distributed Resources with
Electric Power Systems, ieee standard 1547-2003, pp. 7, 2003.

Biographies
Liang Che (lche@hawk.iit.edu) is with the electrical and
computer engineering department, illinois institute of
technology, chicago.
Mohammad E. Khodayar (mkhodayar@smu.edu) is
with department of electrical engineering, southern
Methodist university, dallas, texas.
Mohammad Shahidehpour (ms@iit.edu) is with the
electrical and computer engineering department, illinois
institute of technology, chicago.

http://http:// http://www.iitmicrogrid.net http://www.sandc.com http://www.ieeechicago.org/Linkclick https://www.selinc.com/workarea/

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