Fitzpatrick USC 2015 Presentation
Utility AC Interconnection Inspections of Customer Owned PV Plants Shawn Fitzpatrick, P.E. NC Advanced Energy Corporation April 29, 2015
Inspection Background • Half-day PV system AC interconnection inspections • Size range: 250 kW – 2 MW • Located throughout NC • Inspections conducted Sept – Dec 2014
Inspection Scope • Confirm the inverters and transformers installed agree with the interconnection documentation on file with the utility • Confirm the installed inverters are UL1741 listed • Determine transformer vector groups are in compliance with inverter requirements • Determine inverter interconnection protection settings • High-level system performance evaluation
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Transformer Requirements - SMA Inverters • 6 of 15 sites inspected use SMA America Sunny Central inverters • SMA specifies the permissible transformer vector groups in a supplemental transformer requirements document • SMA documentation cautions the inverter does not always detect a primary (medium voltage) open phase condition if a solidly grounded wye transformer primary is used
Transformer Requirements - SMA Inverters • 4 of 6 sites with SMA inverters have a solidly grounded wye transformer primary – Desensitizes the inverter’s ability to detect a medium voltage open phase condition
• 2 of 6 sites use SMA inverters but have delta transformer primaries – No problem with open phase condition anticipated
Transformer Requirements - Other Inverters • The other 9 sites had the following inverter manufacturers: – Satcon – Schneider Electric
– PV Powered – Advanced Energy
• These 9 sites comply with the inverter manufacturer’s transformer vector group requirements
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Interconnection Documentation • The as-built site configuration for 9 of 15 sites did not comply with the interconnection documentation on file with the utility Parameter Differing from Interconnection Documentation Site No.
AC kW
Inverter Type
Transformer kVA
Site 3
X
Site 8
X
Site 9 Site 1 0
X X
X
X X
X
Site 1 3
X
X X
Site 1 4 Site 1 5
X
X
Site 1 1 Site 1 2
Transformer Vector Group
X X
X
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Interconnection Protection Settings • Utility requires inverter interconnection protection settings to be adjusted from factory default Utility Required Interconnection Protection Settings Parameter Under voltage #1 (27-1) Under voltage #2 (27-2) Over voltage #1 (59-1) Over voltage #2 (59-2) Under frequency (81U) Over frequency (81O)
Setpoint 0.90 per unit 0.90 per unit 1.10 per unit 1.10 per unit 57.0 Hz 60.5 Hz
Time Delay (sec) 0.16 0.16 0.16 0.16 0.16 0.16
Interconnection Protection Settings
Interconnection Protection Settings Under Frequency • Utility requirement: 57 Hz, 0.16 sec • At all sites: 59.3 Hz, 0.16 sec • Some sites also have a “fast” under frequency setting of 57 Hz, but the time delay is set at 0.16 seconds Result: All sites will trip offline at 59.3 Hz, before the utility desires
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
NEC Violations Missing Service Disconnect • 2 of 15 sites did not have a customer owned service disconnect located at the PV site, creating unsafe situations • 1 of these 2 did have a customer owned service disconnect, but it was located ½ mile away at a poorly marked pad-mount disconnect switch
PV inverters and transformers
Pad mount service disconnect
NEC Violations Missing AC Ground Detectors • 8 of 15 sites have ungrounded AC inverter feeders and do not have AC ground detectors installed • Required by NEC 250.21(B)
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Performance Evaluations • Site performance is given in terms of performance factor (PF): PF = measured kW ÷ expected kW
• At the time of inspection, weather conditions were acceptable for testing at 10 of 15 sites – Solar Irradiance > 200 W/m2
Performance Evaluations Site No. Site 1 Site 2 Site 3 Site 4 Site 7 Site 8 Site 9 Site 1 0 Site 1 3 Site 1 4
Total Weighted PF
AC Rated Performance Notes Capacity (MW) Factor (PF) 1 0.50 0.55 2 1 2 2 0.52 1 2 12.57 --
80.2% 94.0% 93.1% 79.8% 92.5% 98.7% 85.9% 85.5% 86.2% 91.8% -88.6%
8% of array was out of service
Substantial vegetation shading 4.4% of array was out of service
Performance Evaluations Solar/tree farm – 85.9% performance factor
Summary • 27% of sites have a transformer configuration that creates an open phase detection problem • As-built configuration at 60% of sites does not comply with interconnection documentation on file with the utility • No sites comply with the utility’s required interconnection protection settings • 53% of sites have significant NEC violations • 50% of sites have a performance factor
Inspection Background • Half-day PV system AC interconnection inspections • Size range: 250 kW – 2 MW • Located throughout NC • Inspections conducted Sept – Dec 2014
Inspection Scope • Confirm the inverters and transformers installed agree with the interconnection documentation on file with the utility • Confirm the installed inverters are UL1741 listed • Determine transformer vector groups are in compliance with inverter requirements • Determine inverter interconnection protection settings • High-level system performance evaluation
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Transformer Requirements - SMA Inverters • 6 of 15 sites inspected use SMA America Sunny Central inverters • SMA specifies the permissible transformer vector groups in a supplemental transformer requirements document • SMA documentation cautions the inverter does not always detect a primary (medium voltage) open phase condition if a solidly grounded wye transformer primary is used
Transformer Requirements - SMA Inverters • 4 of 6 sites with SMA inverters have a solidly grounded wye transformer primary – Desensitizes the inverter’s ability to detect a medium voltage open phase condition
• 2 of 6 sites use SMA inverters but have delta transformer primaries – No problem with open phase condition anticipated
Transformer Requirements - Other Inverters • The other 9 sites had the following inverter manufacturers: – Satcon – Schneider Electric
– PV Powered – Advanced Energy
• These 9 sites comply with the inverter manufacturer’s transformer vector group requirements
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Interconnection Documentation • The as-built site configuration for 9 of 15 sites did not comply with the interconnection documentation on file with the utility Parameter Differing from Interconnection Documentation Site No.
AC kW
Inverter Type
Transformer kVA
Site 3
X
Site 8
X
Site 9 Site 1 0
X X
X
X X
X
Site 1 3
X
X X
Site 1 4 Site 1 5
X
X
Site 1 1 Site 1 2
Transformer Vector Group
X X
X
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Interconnection Protection Settings • Utility requires inverter interconnection protection settings to be adjusted from factory default Utility Required Interconnection Protection Settings Parameter Under voltage #1 (27-1) Under voltage #2 (27-2) Over voltage #1 (59-1) Over voltage #2 (59-2) Under frequency (81U) Over frequency (81O)
Setpoint 0.90 per unit 0.90 per unit 1.10 per unit 1.10 per unit 57.0 Hz 60.5 Hz
Time Delay (sec) 0.16 0.16 0.16 0.16 0.16 0.16
Interconnection Protection Settings
Interconnection Protection Settings Under Frequency • Utility requirement: 57 Hz, 0.16 sec • At all sites: 59.3 Hz, 0.16 sec • Some sites also have a “fast” under frequency setting of 57 Hz, but the time delay is set at 0.16 seconds Result: All sites will trip offline at 59.3 Hz, before the utility desires
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
NEC Violations Missing Service Disconnect • 2 of 15 sites did not have a customer owned service disconnect located at the PV site, creating unsafe situations • 1 of these 2 did have a customer owned service disconnect, but it was located ½ mile away at a poorly marked pad-mount disconnect switch
PV inverters and transformers
Pad mount service disconnect
NEC Violations Missing AC Ground Detectors • 8 of 15 sites have ungrounded AC inverter feeders and do not have AC ground detectors installed • Required by NEC 250.21(B)
Key Findings • Transformer winding requirements • Interconnection documentation vs. actual installation • Interconnection protection settings • NEC violations • Performance evaluations
Performance Evaluations • Site performance is given in terms of performance factor (PF): PF = measured kW ÷ expected kW
• At the time of inspection, weather conditions were acceptable for testing at 10 of 15 sites – Solar Irradiance > 200 W/m2
Performance Evaluations Site No. Site 1 Site 2 Site 3 Site 4 Site 7 Site 8 Site 9 Site 1 0 Site 1 3 Site 1 4
Total Weighted PF
AC Rated Performance Notes Capacity (MW) Factor (PF) 1 0.50 0.55 2 1 2 2 0.52 1 2 12.57 --
80.2% 94.0% 93.1% 79.8% 92.5% 98.7% 85.9% 85.5% 86.2% 91.8% -88.6%
8% of array was out of service
Substantial vegetation shading 4.4% of array was out of service
Performance Evaluations Solar/tree farm – 85.9% performance factor
Summary • 27% of sites have a transformer configuration that creates an open phase detection problem • As-built configuration at 60% of sites does not comply with interconnection documentation on file with the utility • No sites comply with the utility’s required interconnection protection settings • 53% of sites have significant NEC violations • 50% of sites have a performance factor
