IEEE Power & Energy Magazine - March/April 2015 - 44

Wednesday, 12 March/Morning

1.1

Wednesday, 12 March/Morning

1,500

1.09
1,000

1.07
P Line (KW)

VAN at POI (p.u.)

1.08
1.06
1.05
1.04
1.03
1.02

500
0
-500

1.01
1

6

7

8
9
10
Time of the Day (h)
(a)

11

12

-1,000

6

7

8
9
10
Time of the Day (h)
(b)

11

12

figure 1. Extensive overvoltage due to reverse power flow at noon: (a) voltage profile and (b) power flow.

Utility Experiences and Concerns
The main areas of concerns from utility engineers when
dealing with a high penetration of PV systems are
✔✔ unintentional islanding prevention for feeders with
a large number of distributed PV systems, as well
as the unknown effects of the presence of rotational
machine-based DERs (e.g., synchronous generators)
on the active antiislanding schemes of PV inverters
✔✔ drastic changes in feeder voltage profiles, leading to voltage increases beyond permissible operating thresholds
(e.g., above 1.05 p.u.), as well as increases in the operation of line voltage regulators and switched capacitors
✔✔ issues with the effective grounding of the system and
the danger of exposing feeder equipment and customers to extensive temporary overvoltages after the
disconnection of feeder breakers, while the islanded
system is fed by ungrounded generation sources
✔✔ increases in the available fault current of the feeders that affect the interruption capacity of the feeder
switching equipment (circuit breakers and reclosers)
and the protection coordination of fault interruption
devices (circuit breakers, reclosers, fuses, and so on)
✔✔ nuisance tripping of a large number of distributed PV
inverters on a feeder, or on multiple feeders of a substation, due to voltage transients initiated on the transmission system subsequent to faults and line switching
✔✔ adverse impacts on distribution automation (DA)
schemes, such as automated capacitor switching for
reactive power management, automated load shedding, and feeder restoration, in cases where large
amounts of DERs were not initially planned for in the
design of DA systems.
In addition, more technical challenges are being introduced
by certain other power quality-related issues, such as increases
in the harmonic contents of feeders, high-frequency resonances,
44

ieee power & energy magazine

sudden voltage excursions due to intermittency and change of
power flow direction, and dynamic interactions among power
electronic devices on the same feeder. High PV penetration also
adds to the operational requirements for interconnecting to distribution systems. Utilities are expecting granted remote controls and autonomous monitoring for system operators so as to
ensure the controllability and visibility of PV systems above a
certain size (for example, larger than 500 kW).

Changes in Feeder Profiles and
Overvoltage Conditions
There have been reports of an increase in the frequency of nuisance tripping of PV plants due to overvoltage conditions on a
circuit and overuse of line regulator tap operations to adjust voltage as a result of the reverse power flows caused by PV systems.
Figure 1 shows an example of an extensive voltage increase during a time of high PV production and the misoperation of line
voltage regulators under the influence of reverse power flow.
Because distribution systems are becoming more dynamic,
one way to identify power quality issues and take corrective action is to deploy appropriate measurement sensors
and metering equipment close to large concentrations of PV
systems. Monitoring devices and disturbance recorders with
high sampling rates and precision provide invaluable data with
which to characterize and analyze the dynamics of a distribution system in the emerging high-PV-penetration environment.

Multiple PV Inverter
Antiislanding Protection
The key area of concern with the antiislanding protection methods used in PV inverters is when there are multiple distributed
generation (DG) technologies on the same feeder, such as a mix
of inverter-based and rotating machine-based generators. Simulation analysis (see Figure 2) and some field evaluation have shown
that system dynamic behaviors will be highly influenced by the
march/april 2015



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2015

IEEE Power & Energy Magazine - March/April 2015 - Cover1
IEEE Power & Energy Magazine - March/April 2015 - Cover2
IEEE Power & Energy Magazine - March/April 2015 - 1
IEEE Power & Energy Magazine - March/April 2015 - 2
IEEE Power & Energy Magazine - March/April 2015 - 3
IEEE Power & Energy Magazine - March/April 2015 - 4
IEEE Power & Energy Magazine - March/April 2015 - 5
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IEEE Power & Energy Magazine - March/April 2015 - 9
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IEEE Power & Energy Magazine - March/April 2015 - 56
IEEE Power & Energy Magazine - March/April 2015 - 57
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IEEE Power & Energy Magazine - March/April 2015 - 81
IEEE Power & Energy Magazine - March/April 2015 - 82
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IEEE Power & Energy Magazine - March/April 2015 - 84
IEEE Power & Energy Magazine - March/April 2015 - 85
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IEEE Power & Energy Magazine - March/April 2015 - 88
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IEEE Power & Energy Magazine - March/April 2015 - 91
IEEE Power & Energy Magazine - March/April 2015 - 92
IEEE Power & Energy Magazine - March/April 2015 - 93
IEEE Power & Energy Magazine - March/April 2015 - 94
IEEE Power & Energy Magazine - March/April 2015 - 95
IEEE Power & Energy Magazine - March/April 2015 - 96
IEEE Power & Energy Magazine - March/April 2015 - Cover3
IEEE Power & Energy Magazine - March/April 2015 - Cover4
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