IEEE Power & Energy Magazine - July/August 2017 - 58

This article addresses the solution for protecting TNY grid,
microgrid, and submicrogrid networks, keeping in mind all the new
developments that are happening and are about to happen.
phase angle difference is within the limits defined by IEEE
1547a, and the frequency range is from 59.3 to 60.5 Hz.

Steady-State Frequency Range,
Voltage Range, and Power Quality
The islanded microgrid in steady-state operation should have
the frequency in the range 59.3 Hz < f < 60.5 Hz, while the voltage should be in the range of 0.95 pu < V < 1.05 pu at the PCC,
and power quality at the PCC in compliance with customerspecific requirements on the GridSTAR side of the meter.

Protection
A microgrid must provide adequate protection in both gridconnected and islanded states; however, the challenges differ
in these two states. The development of microgrid protection requirements is guided by the following three general
principles, in order of priority:
1) Prevent injury to personnel and ensure public safety.
2) Prevent or minimize equipment damage.
3) Minimize loss of load within the constraints of 1 and 2.
4) Avoid unnecessary interruptions.
Microgrid Protection Research,
Design, and Development

The protection solution is designed to utilize intelligent
switches and digital relays that are equipped with the appropriate communication facilities. The solution includes advanced
features, such as reliable and fast response, and can adapt to
various operational modes. The DOE-MGCS project requires
the detection and isolation of faults, vulnerabilities, and threats.
This article addresses the solution for protecting TNY grid,
microgrid, and submicrogrid networks, keeping in mind all the
new developments that are happening and are about to happen.
The solution will meet the DOE project objectives, goals, and
performance objectives. The protection procedure validates
the solution for microgrids that can protect distribution system
components, which are very expensive assets. Conventional
protection solutions designed for passive radial distribution circuits commonly rely on time-delayed overcurrent protection,
which is insufficient for the increasingly complex and active
networks. These networks may have a radial and looped topology integrated with diverse distributed generation resources.
The design of such systems for emerging distribution systems
needs a totally new protection paradigm, architecture, and philosophy that make use of new protective algorithms; the new
paradigm leverages an advanced communication infrastructure for fast fault interruption and service restoration as well.
58

ieee power & energy magazine

It also enables the protection system to adaptively respond to
changing operation conditions (such as variations of distributed
generator outputs) and varying network topologies. Thus, the
technical approach adopted for developing the advanced and
adaptive protection system includes the selection of computerbased protective devices. These will facilitate flexible coordination, which will be more likely to be global at the substation
level, unlike the local coordination philosophy that has been
adopted for classical distribution systems.
For protecting distribution networks in the presence of
distributed generation, most techniques use adaptive methods such as changing setting groups based on operating condition and network configuration. However, these methods
are designed for implementation in an individual protective relay, and they do not fully consider the coordination
with distributed generation protection and the coordination
between grid and microgrid protection. Most can only be
applied to a specific distribution network. Some existing
microgrid protection methods require communication, while
others do not. Both methods cannot protect a microgrid in
all situations.
✔ Bus protection: Bus differential protection is provided for detecting a fault within substation 664; the
bus differential scheme provides the needed protection by opening the respective breakers on all lines
that supply power to the bus. If there is a fault on the
main bus at substation 664, then the circuit breakers
at TNY substations must trip. If one of these breakers
fails, then it is necessary for PECO to trip the other
end of the line.
✔ Feeder protection: If a fault occurs on feeder 1392
out of substation 664 (which supplies the GridSTAR
microgrid), the existing overcurrent relays associated
with the feeder detect the fault and trip feeder 1392
shown in Figure 4. If the breaker fails to trip, then
the next higher-level breaker at the supply side of the
substation 664 should trip. If for any reason circuit
breaker 1392 does not trip, then the circuit breakers
on all the incoming supply lines from PECO trip after
a predetermined coordination time interval of approximately 0.3 s.
✔ Protection algorithms: Here only one scenario of fault
protection is covered for the grid-connected mode. The
team will examine all possible fault location scenarios
and follow the same philosophy and develop procedures and algorithms for the relay settings and coordination to cover the entire spectrum of fault locations
july/august 2017

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