Review of the Impacts of Distributed
Generation on Distribution Protection
Robert F. Arritt
Senior Member, IEEE
Roger C. Dugan
Fellow, IEEE
2015 IEEE Rural Electric Power Conference
Asheville, NC
April 20th-22nd, 2015
Background
• This report focuses on the results of an industry survey
EPRI has conducted on distribution protection practices to
accommodate DG*.
• The ultimate goal of this survey was to review existing
protection practices and determine what lessons have been
learned.
• From this research, gaps/needs have been identified that
will result in further EPRI research.
*EPRI Survey on Distribution Protection: Emphasis on Distributed Generation Integration
Practices. EPRI, Palo Alto, CA: 2013. 3002001277.
2
Overvoltage Concerns
• 75% of participants selected overvoltages and islanding as
biggest concern
DTT
Single-Line
To Ground
Fault
69/34.5
Substation
DG
34.5/.66
+
69kV/_0
Sub_Gnd
V_Source
+
+
+
DG_Gnd
Va
DG
1.73 pu
Vc
1.73 pu
Vb
Events resulted in sustained
overvoltages on the primary side of
the substation transformer
3
660V
5 MW
Interconnection Transformer
• Inverter based system
• Non-inverter based system
Grounded-wye / Grounded-wye
Grounded-wye / Grounded-wye
No preference
Grounded-wye / Delta (primary
side grounded)
Grounded-wye / Delta (primary
side grounded)
Delta / Grounded-wye (primary
side delta)
Delta / Grounded-wye (primary
side delta)
No preference
Grounded-wye / Delta (With a
reactively grounded primary side
wye)
Grounded-wye / Delta (Including
reactively-grounded primary side
neutral)
Delta / Grounded-wye (With a
reactively grounded wye on the
DG side)
No interconnection transformer
required
No interconnection transformer
required
0%
0%
10% 20% 30% 40% 50%
4
10% 20% 30% 40% 50%
Ground Fault Overvoltage Testing
Delta / Wye
• 2014 EPRI Report:
– Product ID: 3002003233
“Protecting the Modern
Distribution Grid: Preliminary
Inverter Characterization for
Overvoltages”
Wye / Wye
5
Protection Supervision Concerns
• Multiple events of inverters not turning on or cycling off due
to overvoltages associated with high penetration.
Voltage
After DG
ANSI Range A
Upper Limit
ANSI Range A
Lower Limit
Substation
Before DG
Distance
End of Feeder
• Reported problems of DG operators changing initial
protection settings resulting in high voltages at PCC
– Resulted in complaints from other customers of electronic
equipment problems/failures
6
Impacts of System Overvotages
• If you ever experienced any
sustained primary overvoltages
associated with DG
interconnections, what was
impacted, if anything?
• Surge arrester failure would be
one expected consequence,
particularly on US systems that
exploited reduced insulation
levels to apply lower-cost, lowervoltage arresters.
No Damage
• Relay operation for overvoltages
is also a common complaint,
particularly for solar PV systems.
Surge Arrester Failures
Resulted in relaying
activation due to
overvoltages or…
Load Failures
Transformer Failure
0% 10% 20% 30% 40% 50% 60%
7
Anti-Islanding
• Have communications
technologies been added to your
system to communicate between
the feeder relaying and
interconnected DG?
• How is anti-islanding being
addressed?
Under/Over Voltage
Fiber Optic
Under/Over Frequency
Radio
Depend on inverter Controls
Telephone
Transfer Trip
None added
Reverse Power Protection as
backup
Spread Spectrum
Communications
Minimum to Maximum
Generation Limits placed on
DG penetration
Power Line Carrier
Rate of Change of Frequency
(ROCOF)
Two-Way Pagers
0% 20% 40% 60% 80% 100%
Not applicable
Note: No utilities that were interviewed actually use Rate of Change of
Frequency (ROCOF) for islanding detection although 20% of
respondents recognized it as an option for protection.
0%
8
10%
20%
30%
40%
50%
60%
Additional Gaps Identified
• Open-Phase protection
– Some stated that it is the responsibility of the customer.
– Some determined that it meets the requirements of IEEE
Std 1547 the DG is able to protect against this event.
– Two utilities identified open-phase concerns in
commissioning tests.
9
Conclusions
• The survey results found that DG interconnection protection
practices vary significantly from utility to utility.
• Despite different practices, the basic objectives:
– operate reliably and safely,
– operate without degrading electric service to nearby
customers,
– and operate without compromising utility system
integrity.
• By far, the protection issue of most concerns are islanding
and overvoltages, in particular, overvoltages occurring
following an islanding event.
10
2015 EPRI Work
• Continue testing with
additional islanding
scenarios, e.g. fault current
contribution, islanding,
open conductor, etc.
• Testing of additional
inverter models to
establish a representative
sample
• Continue to build on the
inverter models with
improved test data.
• Provide model verification
with this additional test
data.
Incorporate new modeling
techniques to allow for additional inputs
that impact inverter response.
2014 Tech update
Lab Testing
Incorporate test results into the
model to predict system response.
2015 Technical Update
11
Together…Shaping the Future of Electricity