Solectria Smart Inverters, Effective Grounding, and how to work with the Utility

Built for the real world Solectria Renewables / Company Confidential © 2014
www.solectria.com
Being Good Citizens of
the Grid
Claude Colp
Applications Engineer
Claude.colp@solectria.com
@ClaudeColp

Introduction
1. Company Overview
2. Relays 27, 59, 81, ect.
3. Effective Grounding
4. Power curtailment
5. Power Factor
6. Reactive power support
7. Solectria’ s work at ESIF
8. Reactive power support
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Solectria Renewables
Lawrence, MA

www.solectria.com
Company Overview

25 Year Development History
• Inverter power stage technology developed over 25 years of automotive and
military applications
• Proven reliability in harsh conditions
www.solectria.com
Efficient
Powerful
Reliable
Rugged
Commercial, Utility-Scale, and
Residential PV Inverters
Compact
Low Cost
EV Drives

Solectria History
Solectria divests
vehicle products to
Azure Dynamics
Original 10kW
UL Listed
Solectria
Corporation
Founded
Introduced the SGI 500XTM & SGI 750XTM
External Transformer
1989 2005 2006 2007 2008 2009 2010 2011 2012
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60/82/95KW
UL Listed
SolrenView Web
Monitoring Introduced
Capacity Expansion
to 200MW
PVI 60/77/90KW
UL Listed
PVI 13-15KW
UL Listed
PVI 3000-5300
Introduced
MSS
Introduced
Capacity Expansion to
800MW
Disconnecting String Combiners
Introduced
PVI 3800-7600TL,
PVI 14-28TL, 3-phase
transformerless inverters
SGI 500XT transformerless
600V DC inverter introduced
2013
2014
1Ph
transformerless
inverters
Introduced SGI 500 Premium Efficiency model
with 97.5% CEC efficiency – highest in the industry
Capacity
Expansion
to 350MW
Introduced PVI 50/60/75/85/100KW
& Premium Efficiency Models
• 1989 – Solectria Corporation founded
• 2005 – Solectria Corp. EV division sold to Azure
Dynamics
• 2005 – Solectria Renewables founded
• 2014 – Solectria became wholly owned
subsidiary of Yaskawa Electric
Solectria
Renewables
Founded
SGI Series
UL Listed
New SolrenView GUI
Introduced
Yaskawa Electric Acquires Solectria
Renewables as wholly owned subsidiary
ARCCOM (AFDI String Combiner)
Introduction

Yaskawa and Solectria
Yaskawa Electric Corp:
• $3.6 billion Japanese firm focused on motor drives, automation controls and other electrical components
• Company founded in 1915
• 5th largest Japanese inverter supplier, but no U.S. presence
• Global leader in quality
• Manufacturing locations in strategic PV markets
• Track record for technological advancement and leadership
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Yaskawa and Solectria
So what does this mean for our customers?
 Immediately enhanced bankability
 Warranty backing by bigger company
 Solectria is 100% wholly owned subsidiary
 Same team in place as before (sales, marketing, customer
services, executives)
 Same manufacturing locations and product offerings
 Potential for new market entry in the future
 Access to world class quality systems
www.solectria.com

2014 Company Highlights
• Introduction of three-phase string inverters
• Introduction of ARCCOM arc fault detection and rapid
shutdown combiner boxes for 600VDC and 1000VDC central
inverters
• Introduction of SGI 500XTM and SGI 750XTM
• Acquisition of Solectria Renewables by Yaskawa Electric
Corp.
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Protective Relaying

(Digital) Protective Relays
“Microprocessor based devices that that control PV plant
in response to voltage and current measurement”
USED WITH:
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… Interconnection Breaker
… Instrument Transformers
Potential Transformers (PTs) … for measuring Voltage
Current Transformers (CTs) … for measuring Current
…Sometimes
Uninterruptible Power Supply (UPS)… for Powering Relay
when grid goes down (not required in all systems)
“I thought inverters had voltage/frequency trip setpoints??!!
 They do. Required when utility desires Additional or
Redundant protection
Made by companies like SEL, ABB, Cooper, GE, …

ANSI Device Numbers
“Standard numbers used by utilities/relay companies to
indicate protective function”
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From PVI 50-100 Installation Manual

Example One Line
…Showing Protective Relay w/
ANSI Device Numbers
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Utility Control
What is SCADA?
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“Supervisory Control and Data Acquisition”
= Control and Monitoring
What would utility want to control?
 On/Off (Remote shut down)
 Ramp rate
 Real Power/Reactive Power/PF
How is this implemented?
 Control of Interconnection Breaker
 24V Remote Shutdown
 Shunt Trip
 Modbus RTU, Modbus TCP, DNP3
Utility usually interfaces with inverters
through RTU’s, Protective Relays, Plant Controller

Example One Line
…Showing the pieces
INVERTERS INVERTERS INVERTERS
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I

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Effective Grounding
of PV inverters

Non-Grounded Synchronous DG
Distribution
CB
COLOPSEEND
Va = Vb = Vc = 100%
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Feeder
Load
Vb = Vc = 173%
SLG
Fault
Sync. Gen.
Consider an islanded operation where the grid is disconnected and a single line to
ground fault is applied to the island.
Generator neutral shift generates the over-voltages on unfaulted phases.
Single phase loads can be damaged from the overvoltage.

Solidly Grounding Synchronous DG
Distribution
CB
Va = Vb = Vc = 100%
Grounding the generator neutral prevents over-voltages on unfaulted phases.
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Feeder
Load
COLOPSEEND
SLG
Fault
Sync. Gen.
Vb = Vc = 100%
Effective Grounding allows 125% over-voltage and impedance grounding
(for protection relay coordination)
푋0
푋1
< 3,
푅0
푋1
< 1
Ref: IEEE Std. 142, IEEE Std. C62.92 series

Does same happen with PV inverters?
Distribution
CB
Va = Vb = Vc = 100%
Even without the inverter neutral grounding (3-wire connection), over-voltage
will not be generated if the load is predominantly wye-connected.
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Feeder
Load
COLOPSEEND
SLG
Fault
PV Inverter
Vb = Vc = 100%
In contrast to the synchronous generator, a PV Inverter is a current source and
no overvoltage will be generated due to the neutral shifting.
“… When the inverter-based DG is isolated from the utility voltage source, there is no
derived neutral shift.”
- Dr. Michael Ropp, 39th Annual Western Protective Relay Conference, Oct. 2012.

PV inverter with pure delta loads
Distribution
CB
COLOPSEEND
Va = Vb = Vc = 100% PV Inverter
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Feeder
Load
Vb = Vc = 173%
SLG
Fault
Solectria’s simulation results showed a negligible voltage rise in unfaulted phases with
50% delta load and 50% wye grounded loads. With 80% delta-connected load, phase
voltages went up to 120%, which is still less than the maximum over-voltage with the
effective grounding. (125%)
In practical cases, most of the loads will be wye grounded in 3-phase 4-wire system.

Effective Grounding
 Several utilities require effective grounding by meeting X0/X1 ratio
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1.5 < X0/X1 < 2.5
NGRID, HECO, XCEL, PEPCO, BGE, Indianapolis…
Some utilities use separate guidelines for inverter based distribution
generation(DG) which makes more sense as the inverter characteristics is
quite different from the rotating machine type generators
XDG0 = 0.6*Zbase +/- 10%
GMP, Hydro One…

Suggested Design Practice
Case 1. PV plant effective grounding with one or multiple inverters (universal solution)
Grounding
Bank
51G
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 Minimal hardware and installation cost
 Need to coordinate with the main circuit breaker
 Can be used with any medium voltage transformer configuration

Effective Grounding
PVI 3ɸ-String Inverters
 Require grounding transformer for
effective grounding,
 Zig-Zag or Yg-Δ
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Grounding bank (transformer)
 A grounding bank is a small special transformer configured in Zig-Zag or Delta-Wye.
 A grounding bank is external to PV inverters and provides effective grounding, so
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that it does not impact the inverters transformer life.
 A single grounding bank can provide effective grounding for a large PV plant, which
minimizes the installation cost.
 For a SGI 500kW inverter installed at 480V distribution feeder, grounding bank cost
can be several $K.
PV Inverter
Grounding
bank
51G

Suggested Design Practice
Case 2. PV plant effective grounding with grounding inductor and a dedicated wye-delta MV Transformer
Grounding
inductor
51G
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 Can be used with a wye-delta medium voltage transformer only
 Can be effectively grounded with a grounding bank also
 Minimal hardware and installation cost

Effective Grounding Summary
 Most 3-phase 4-wire systems support single phase loads, which puts the
effective grounding requirement for PV inverters in question.
 Many utilities request effective grounding with a controlled impedance for
relay protection coordination.
 Solectria provides impedance tables for all commercial and utility scale PV
inverters to help customers design an effectively grounded PV system.
 Effective grounding using Zig-Zag transformer is a universal solution for
ungrounded DG.
 Many Solectria inverters have an internal wye-delta isolation transformer with
a neutral connection which can be used to provide effective grounding. When
used, neutral over-current protection is strongly recommended.
www.solectria.com

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Power Curtailment

Power Curtailment
80kW  50kW  80kW
90
80
70
60
50
40
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30
50 60 70 80 90 100
Power in KW
percentage
Pcmd
Pout

Advantages of Power Curtailment
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• 100kW interconnection Limit
PLC
700k
W
750k
W
~50k
W
Monday through Friday

Advantages of Power Curtailment
• 100kW interconnection Limit
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PLC
170k
W
70kW
~100kW
Saturday and Sunday
23% limit

Case Study – Xcel Energy
System Size 30 MW
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Product: 504, PVI 82KW – SCADA controlled, VAR supports
Modules Amonix
Installer Amonix, Cogentrix
Location Alamosa, CO

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Reactive Power

Inverter Capacity for VARs
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• Inverter and AC interconnection have to be sized to carry
both real and reactive current
Example: 500kVA @ 0.95 PF
475 kW
156 kVAr

Inverter Capacity for VARs
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475 kW
475 kW
156 kVAr

Inverter Capacity Allocation for VARs
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475 kW
156 kVAr
475 kW

Inverter Capacity Allocation for VARs
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
0 0.2 0.4 0.6 0.8 1
Q Reactive p.u.
P Active p.u.
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 Power factor control = +/- 0.8 (+/- 0.95 prefered)
 Maximum reactive power control = 60%
 May require power curtailment for reactive power control
 May conflict with the islanding detection

VAR support
(remote utility option)
1000
800
600
400
200
0
-720 -630 -540 -450 -360 -270 -180 -90 0 90 180 270 360 450 540 630 720
-200
-400
-600
-800
-1000
voltage current power (rms) real power (rms)
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• PPA owned (“in front of the fence”)
o UL1741 enforces a PF > 0.95

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Reactive Power Control
The waveform shows instantaneous transient response of the inverter
output current (red) from full inductive to full capacitive.

DNP3 Compliant Smart Grid Inverters
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High Penetration Scenario Example:
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• 1.7 MW site in Cedarville NJ
• 4.7 miles from substation 12kV feeder, 6MW mid-day load
• Concerns of local overvoltage
• Utility has closed circuit for more PV
0.5 MW
1.7 MW

Overvoltage Concerns
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3.0% of points
exceed +5% limit

The effect of reactive power on
distribution lines
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VAR Generation
PCC voltage is being
pushed up.
VAR Absorption
PCC voltage is being
pulled down.

Example: PF control
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• Feeder could be reopened for PV after PF adjustment to 0.97
• “Flicker” Mitigation (cloud induced voltage transients)
< 0.1% of points
exceed 5% limit

Benefit to Utility
Example: Volt-VAR control
• Reduced wear out of electromechanical voltage regulators
• Flatter voltage profile overall
Possible additional
Voltage Regulator
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Baseline – No PV
Inverter Volt-Var Control
20% PV Penetration
action

Increasing Hosting Capacity with Smart
Inverters
Without Volt/var Control Volt/var Control
ANSI voltage limit
Increasing penetration (kW)
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Matthew Rylander
5000 cases shown
Each point = highest primary voltage
ANSI voltage limit
160% increase in
hosting capacity
60% increase in
hosting capacity
Maximum Feeder Voltage (pu)
Maximum Feeder Voltages (pu)
Increasing penetration (kW)
No observable violations regardless of size/location
Possible violations based upon size/location
Observable violations occur regardless of
size/location
PV Hosting Capacity (kW)
Without Volt/var With Volt/var
Primary Voltage
Deviation
1st violation 938 >2500
50% scenarios with violation 1323 >2500
All scenarios with violation 1673 >2500
Primary
Over Voltage
1st violation 540 880
50% scenarios with violation 871 1464
All scenarios with violation 1173 2418
Slide courtesy of Matthew Rylander, EPRI

Solectria’s Work in this Field
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o Smart Grid Ready Inverter Development
 Implement and test grid support functions on existing
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commercial and utility scale inverters.
 Add DNP3 communication capability on to the existing inverters
 Hardware reliability enhancement and efficiency increase
 Cost Reduction
o Plant Master Controller Development
 Support smart grid inverters with the latest DNP3 protocol
 Plant level supervisory controller with customizable system
integration capability
 Secondary protection and preventive maintenance

Product Testing
• The Energy System
Integration Facility
(ESIF) at NREL was
chosen to test the SGI
500 features due to its
advanced capabilities
• The EPRI facility in
Knoxville, TN was
chosen to test the PVI
100KW for their
expertise in inverter
testing.
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NREL Test Setup Size
PV simulator 1MW
Grid Simulator 1.2MW
Output Power 400kW
Reactive Power + 300kvar

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Volt-var testing at ESIF
Test # EUT Terminal Voltage EUT Reactive Power Output Ramp
Time
(s)
Time
Window
(s)
Reversio
n
Time (s)
PASS
/FAIL
Volt % kvar % Max
available var
Test 2 432 90 300 100 5 60 Never
time
out
p
475.2 99 0 100
484.8 101 0 100
518.4 108 -309 100

Balanced LVRT/HVRT at ESIF
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10% Balanced sag for 120 cycles,
passive LVRT
Balanced voltage swell of 118%;
active ride through trip test
condition

Unbalanced LVRT (IEEE P1668)
at ESIF
• 89% of Faults are unbalanced faults
Balanced Sag Single phase sag
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ZVRT for 120 cycles

Frequency/Watt at ESIF
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Watts, Hz and Volts
• Utilities like their “Volts” and “Hz” to stay within boundaries.
• When generation is High (+Watts) system wide frequency rises
(+Hz)
 Functions that control “Watts” depending on “Hz”, such as
Frequency-Watt, are essential for being a good citizen on the grid.
• An increase in generation (+Watts) results in a local increase in
Voltage (+Volts)
 Functions that control “Watts” depending on ”Volts”, such as Volt-
Watt, can be useful to regulate local voltage when the vars are
exhausted.
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Questions?

Thank You!
One size doesn’t fit all,
But one company does
www.solectria.com

Solectria Smart Inverters, Effective Grounding, and how to work with the Utility

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