1. Power Quality at Solar Distributed Generation Facilities
September 8, 2015
Marty Page, P.E.
All sensors are on EST DST.
All sensors after 11/2/14 are running an hour ahead.
Events from STOMP/Morning Report are given in CST
Events from Dashboard/DisIntel are given in EST

2. Description
Georgia Power began monitoring the power quality at five solar sites in September of 2014.
Power monitoring was accomplished at the solar revenue meter at each site.
The sites include:
700kW site served at 4.16kv (customer substation)
2.4MW site served at 12.47kv
16MW site served at 46kv
30MW site served at 115kv
800kw site served at 12.47kv
The summary data includes information related to the kw and kvar output of the site, steady state voltage characteristics, instantaneous voltage change characteristics (in the form of flicker values), and harmonic characteristics.

3. The power monitoring of the five sites
Five sites have specialized meters (PSL PQube) at the solar revenue metering point. Data is transmitted daily via wireless communications.
The PQube trends data (minimum, maximum, and average) at one minute intervals.
The meter captures total 3 phase power measurements as well as individual phase measurements.
System events, such as adjacent circuit operations, trigger waveform captures allowing us to analyze the solar inverter performance during such events.

4. Sunny/Overcast Comparison (kW)
Solar Site 1
Solar Site 1
Peak: kW
Peak: kW
Peak: kW
Peak: kW

5. 24 Hours Sunny Day (kvar) pf = .996 Peak: 63.1176 kvar
Solar Site 1
Solar Site 1
Solar Site 1
Peak: kvar
Peak: kvar

6. 4 Month Profile (P) The profile peak is 75.9% of the
Solar Site 1
Solar Site 1
Peak: kW
The profile peak is
75.9% of the
Illustrated sunny day peak.

7. Voltage 105% 2.52 kV Max 2.61kV Avg 2.51kV 99th CP 2.59kV Max 2.641kV
Solar Site 1
Solar Site 1
105% kV
Max 2.61kV
Avg 2.51kV
99th CP 2.59kV
Solar Site 1
Solar Site 1
Max 2.641kV
Avg 2.526kV
99th CP 2.618kV
Solar Site 1
Solar Site 1
Max 2.642kV
Avg 2.538kV
99th CP 2.625kV

8. Voltage peaks are not coincident with solar power peaks
Voltage peaks are not coincident with solar power peaks. (This is an unregulated transmission served customer site. Typical max is <110%)
Solar Site 1

9. Flicker Max 2.860 Avg 0.04678 99th CP 0.2200 Max 2.190 Avg 0.04836
Solar Site 1
Solar Site 1
Solar Site 1
Max 2.860
Avg
99th CP
Solar Site 1
Solar Site 1
Max 2.190
Avg
99th CP
Solar Site 1
Solar Site 1
Max 2.700
Avg
99th CP

10. Total Harmonic Distortion (THD)
Solar Site 1

11. Total Demand Distortion (TDD)
Solar Site 1

12. THD & TDD Max 2.200 Avg 1.308 99th CP 1.900 Max 5.600 Avg 2.078
Solar Site 1
Solar Site 1
Max
Avg
99th CP
Max
Avg
99th CP
90th CP 3.55
Solar Site 1
Solar Site 1
Max
Avg
99th CP
Max
Avg
99th CP
90th CP 3.25
Solar Site 1
Solar Site 1
Max
Avg
99th CP
Max
Avg
99th CP
90th CP 3.46

13. Serendipity
The occurrence and development of events by chance in a beneficial way.
The next few slides will help illustrate why we bother to check for such things as harmonic limits compliance.

14. Solar site harmonic investigation Sept 3rd, 3:30.39pm.
Site output of approximately 975 amps
Current distortion <1.25% Voltage distortion <1.75%

15. Solar site harmonic investigation Sept 3rd, 3:30.52pm.
Site output of approximately 990 amps
Current distortion >12.5% Voltage distortion >5%

16. Solar site harmonic investigation Sept 3rd, 3:34 pm.
Site output of approximately 975 amps
Current distortion <0.6% Voltage distortion <1.75%

17. GPC is presently working with the site owner and inverter manufacturer in order to resolve the harmonics issue at the site. The short term solution was to shut down part of the production capability of the site so as to limit the total current distortion being injected into the system during the periods of high current distortion.

18. Solar Site 1
Solar Site 1

19. Sunny/Overcast Comparison (kW) Solar Site 2
Peak: kW
Peak: kW
Peak: kW
Peak: kW

20. 24 Hours Sunny Day (kvar) pf = 0.93 at this site Peak: 1034.4 kvar
Solar Site 2
Solar Site 2
Peak: kvar
Peak: kvar
pf = 0.93 at this site

21. 4 Month Profile (P) The profile peak is 71.1% of the
Solar Site 2
Solar Site 2
The profile peak is
71.1% of the
Illustrated sunny day peak.
Peak: kW

22. 4 Month Profile (Q) pf = 0.93 Peak: 727.8 kvar Solar Site 2

23. Voltage 105% 7.56kV Max 7.62kV Avg 7.42kV 99th CP 7.57kV Max 7.673kV
Solar Site 2
Solar Site 2
105% kV
Max 7.62kV
Avg 7.42kV
99th CP 7.57kV
+2.7%
Solar Site 2
Solar Site 2
+3.2%
Max 7.673kV
Avg 7.436kV
99th CP 7.582kV
Solar Site 2
Solar Site 2
Max 7.652kV
Avg 7.444kV
99th CP 7.587kV
+2.8%

24. Camp Solar Solar Site 2 Phase A Phase B Phase C 0.230 0.220 0.210
Flicker (99%) (<0.4)
0.230
0.220
0.210
THD (Max)
3.700
4.100
3.500
THD (95%)
2.800
3.200
2.500
THD (90%) (<5.0)
2.585
2.870
2.300
TDD (Max) 2
1.900
TDD (95%)
1.500
1.400
TDD (90%) (<5.0)
1.331
1.300

26. Feeder R0802 Recloser operations. Tree fell on line.
Solar Site 2
Feeder R0802 Recloser operations. Tree fell on line.
Solar Site 2

27. A 2 second circuit outage lead to A 5 minute solar inverter outage.
Solar Site 2
A 2 second circuit outage lead to
A 5 minute solar inverter outage.
(GPC requirement in order to meet
IEEE 1547.)
Solar Site 2
Solar Site 2

28. Sunny/Overcast Comparison (kW) Solar Site 3
Peak: kW
Peak: kW
Peak: kW
Peak: kW

29. 24 Hours Sunny Day (kvar) pf = .998 Peak: 951.538 kvar
Solar Site 3
Solar Site 3
Peak: kvar
Peak: kvar

30. 4 Month Profile (P) The profile peak is 70.3% of the
Solar Site 3
Solar Site 3
Peak: kW
The profile peak is
70.3% of the
Illustrated sunny day peak.

31. Voltage 105% 27.88kV Max 27.75kV Avg 27.02kV 99th CP 27.39kV
Solar Site 3
Solar Site 3
105% kV
Max 27.75kV
Avg 27.02kV
99th CP 27.39kV
Solar Site 3
Solar Site 3
Max 27.13kV
Avg 26.84kV
99th CP 27.03kV
Solar Site 3
Solar Site 3
Max 27.20kV
Avg 26.70kV
99th CP 26.94kV

32. Solar Site 3 Phase A Phase B Phase C 0.2600 0.2200 0.1300 THD (Max)
Flicker (99%) (< 0.35)
0.2600
0.2200
0.1300
THD (Max)
2.000
1.900
2.400
THD (95%)
1.600
1.500
THD (90%) (<5.0)
1.360
1.375
1.827
TDD (Max)
1.700
TDD (95%)
1.300
TDD (90%) (<5.0)
1.261
1.2648
1.265

33. 16MW Solar Disconnect Test
Main purpose of this testing was to 1) measure TOV produced by inverters during load rejection (loss of utility) and 2) observe when generator starts producing once utility source returns to normal For each test: Inverters were programmed to comply with IEEE 1547 and anti-islanding detection was ON.
Breaker 202 was operated
for each test
All measurements are
metering point

34. 16MW Solar Disconnect Test
Breaker
opened
Generator starts
Producing again
Breaker
closed
Transformer Inrush Current

35. 16MW Solar Disconnect Test
Note TOV produced by inverters
160% TOV
Breaker
opened

36. (same as previous slide but zoomed in for more info)
16MW Solar Disconnect Test
(same as previous slide but zoomed in for more info)
160% TOV
How much TOV is acceptable per GPC ?
For capacitor bank switching, a 2.0 pu TOV is possible and allowed.
For solar DG tests, voltage transients ranging from 1.51 pu to 2.0 pu must not exceed 3 cycle duration.

37. V sag response – 3 phase vs 1 phase

38. Sunny/Overcast Comparison (kW)
Solar Site 4
Solar Site 4
Peak: kW
Peak: kW
Peak: kW
Peak: kW

39. 24 Hours Sunny Day (kvar) pf = .997 Peak: 67.8672 kvar
Solar Site 4
Solar Site 4
Peak: kvar
Peak: kvar

40. 4 Month Profile (P) The profile peak is 69.3% of the
Solar Site 4
Solar Site 4
The profile peak is
69.3% of the
Illustrated sunny day peak.
Peak: kW

41. Voltage 105% 7.56kV Max 7.55kV Avg 7.42kV 99th CP 7.52kV Max 7.519kV
Solar Site 4
Solar Site 4
105% 7.56kV
Max 7.55kV
Avg 7.42kV
99th CP 7.52kV
Solar Site 4
Solar Site 4
Max 7.519kV
Avg 7.431kV
99th CP 7.503kV
Solar Site 4
Solar Site 4
Max 7.550kV
Avg 7.431kV
99th CP 7.525kV

42. Solar Site 4 Phase A Phase B Phase C 0.2300 0.2100 0.2000 THD (Max)
Flicker (99%) (<0.4)
0.2300
0.2100
0.2000
THD (Max)
2.200
2.700
2.500
THD (95%)
1.400
1.600
THD (90%) (<5.0)
1.310
1.525
1.331
TDD (Max)
3.800
4.200
4.100
TDD (95%)
3.200
3.500
3.400
TDD (90%) (<5.0)
3.085
3.365
3.155

43. Tree fell on 115kv line.

44. Sunny/Overcast Comparison (kW) Solar Site 5
Peak: kW
Peak: kW
Peak: kW
Peak: kW

45. 24 Hours Sunny Day (kvar) pf = 0.96 Peak: 8698.063 kvar

46. 4 Month Profile (P) The profile peak is 70.9% of the
Illustrated sunny day peak.
Peak: kW

47. Voltage 105% 69.72kV Max 69.19kV Avg 67.27kV 99th CP 68.57kV

48. Solar Site 5 Phase A Phase B Phase C 0.1800 0.1600 0.110 THD (Max)
Flicker (99%) (< 0.35)
0.1800
0.1600
0.110
THD (Max)
1.900
2.000
THD (95%)
1.300
1.400
1.500
THD (90%) (< 2.5)
1.265
1.298
1.313
TDD (Max)
3.200
2.400
3.000
TDD (95%)
2.100
1.800
TDD (90%) (< 2.5)
1.720
1.462
1.625

50. EMI and PV Systems
Issue: cases AM band ( kHz) RF interference detected while inverters are producing power (PV farms in Georgia)
Status: Collected radiated emission data in the field, investigation in progress
PV inverters have switching frequencies in the kHz-10’s kHz range.
Harmonics can extend beyond 100 kHz
Present emission and immunity standards are not protecting adequately the 9 kHz-150 kHz range
Revision of EMI standards in progress at the IEC level

51. EMI and PV Systems
Investigation in progress at a few Georgia Power PV farms to study causes and possible countermeasures related to inverter EMI
AM spectrum and demodulated audio noise spectrum tuned to 750 kHz at one such PV farm. Noise at switching frequency and harmonics is detected during daytime operation but is not present at night.
AM Band Spectrum
Audio Spectrum
Day
AM Band Spectrum
Audio Spectrum
Night

52. Conclusions
The solar output of each of the sites is significantly lower than the peak capability when averaging in the impact of poor solar output days. (Avg 71.5% of maximum)
The Solar Site 2 is a good example of how voltage concerns can be mitigated by requiring the site to receive vars at a set power factor.
The sites flicker characteristics confirm that the cloud transients at those locations do not produce significant instantaneous voltage changes and flicker.
The sites harmonic characteristics confirm that IEEE 519 limits are maintained at those sites.
The waveform capture events show that the inverters at those sites do not produce substantial fault current contributions and that they often shut down and restart due to system events.
Some central inverter sites have am radio noise that is detectable near the site and near the distribution line serving the site. More investigation is underway.