IEEE Power & Energy Magazine - November/December 2020 - 78

PV Plant Arc-Flash Incident Energy

DERs can increase arc-flash incident energy in two
major
ways. First, the step-up transformer windings, such MV
When field crews work on energized distribution feeders,
there is concern about accidental faults and arc flash (see wye-grounded and delta connection to the DER, provide a
Figure 4). The danger is measured by flash incident energy zero-sequence source. This setup can reduce ground current
in kilocalories per square centimeter. Arc flash correlates from the substation and delay fault clearing in the
with line voltage, fault-current magnitude, and fault-clearing upstream protective device. Second, after loss of the grid
time. DERs can contribute to arc flash. Industry practice is source and prior to plant tripping, DERs can back-feed into
to calculate arc-flash incident energy on a case-by-case basis the fault. This portion of arc-flash incident energy is correso that field personnel are provided adequate flame-resistant lated to the plant's run-on time before tripping.
PV plant mitigations for arc fault include neutral
safety clothing.
grounding resistors and recloser
relay settings installed at the POI.
Many utilities also enable highspeed fault clearing in feeder relays
when crews are working on a
line. Instantaneous clearing will
largely reduce the fault-clearing
time and the grid's contribution to
arc-flash exposure.
Large PV plants integrated into
the distribution system will often
require protection -coordination
studies to determine both the
feeder and plant relay settings.
Design reviews and a commissioning process are also necessary to ensure that the solar power
plant configurations meet protecfigure 4. A field crew working on energized lines at a Dominion Energy training
tion requirements.
facility. (Source: Dominion Energy.)

Area Exposed to Open Phase
Connected Single-Phase
Load Downstream of F01
F01
C Phase
Opened

Water Treatment
Facility

PV POI Protection
(No Customer
Loads)

Substation

Two of Five 1-MVA PV
Sites Energized at
Time of Events

figure 5. An example of an open-phase event upstream from a PV plant.
F01: phase C line fuse opened; R: site recloser.
78

ieee power & energy magazine

Single-Phasing
Happens
Given three-phase feeders, what
role will DERs play? Incidents of
open phase (or single phasing on
three-phase distribution circuits)
can happen. This brings several
concerns for PV plants. Depending
on the transformer configuration
and DER output to load, voltage
on the open phase might be regenerated. During the open-phase
incident, this leads to poor regulation or elevated voltages and can
potentially expose the public to a
live downed conductor.
These events are not rare in
a distribution system with independent phase protection, such
as single-phase reclosers. They
can happen in a single-phase fault
clearing if a single switch or fuse
is open or when a conductor is
broken. Figure 5 shows the case of
a blown fuse.
november/december 2020

IEEE Power & Energy Magazine - November/December 2020

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2020