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

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.

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.

Sunny/Overcast Comparison (kW) Solar Site 1 Solar Site 1 Peak: 708.283 kW Peak: 706.617 kW Peak: 88.5682 kW Peak: 83.5855 kW

24 Hours Sunny Day (kvar) pf = .996 Peak: 63.1176 kvar Solar Site 1 Solar Site 1 Solar Site 1 Peak: 63.1176 kvar Peak: 61.4996 kvar

4 Month Profile (P) The profile peak is 75.9% of the Solar Site 1 Solar Site 1 Peak: 537.762 kW The profile peak is 75.9% of the Illustrated sunny day peak.

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% 2.52 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

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

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 0.04678 99th CP 0.2200 Solar Site 1 Solar Site 1 Max 2.190 Avg 0.04836 99th CP 0.1900 Solar Site 1 Solar Site 1 Max 2.700 Avg 0.04127 99th CP 0.1400

Total Harmonic Distortion (THD) Solar Site 1

Total Demand Distortion (TDD) Solar Site 1

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 2.200 Avg 1.308 99th CP 1.900 Max 5.600 Avg 2.078 99th CP 4.800 90th CP 3.55 Solar Site 1 Solar Site 1 Max 2.100 Avg 1.066 99th CP 1.800 Max 7.200 Avg 2.111 99th CP 5.500 90th CP 3.25 Solar Site 1 Solar Site 1 Max 2.400 Avg 1.256 99th CP 2.100 Max 6.900 Avg 2.194 99th CP 5.600 90th CP 3.46

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.

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

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

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

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.

Solar Site 1 Solar Site 1

Sunny/Overcast Comparison (kW) Solar Site 2 Peak: 2516.4 kW Peak: 2515.9 kW Peak: 502.5 kW Peak: 440.3 kW

24 Hours Sunny Day (kvar) pf = 0.93 at this site Peak: 1034.4 kvar Solar Site 2 Solar Site 2 Peak: 1034.4 kvar Peak: 1034.3 kvar pf = 0.93 at this site

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: 1790.5 kW

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

Voltage 105% 7.56kV Max 7.62kV Avg 7.42kV 99th CP 7.57kV Max 7.673kV Solar Site 2 Solar Site 2 105% 7.56kV 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%

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

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

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

Sunny/Overcast Comparison (kW) Solar Site 3 Peak: 16639.79 kW Peak: 16630.43 kW Peak: 5356.94 kW Peak: 4298.60 kW

24 Hours Sunny Day (kvar) pf = .998 Peak: 951.538 kvar Solar Site 3 Solar Site 3 Peak: 951.538 kvar Peak: 949.823 kvar

4 Month Profile (P) The profile peak is 70.3% of the Solar Site 3 Solar Site 3 Peak: 11709.03 kW The profile peak is 70.3% of the Illustrated sunny day peak.

Voltage 105% 27.88kV Max 27.75kV Avg 27.02kV 99th CP 27.39kV Solar Site 3 Solar Site 3 105% 27.88kV 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

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

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 taken @ metering point

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

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

(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.

V sag response – 3 phase vs 1 phase

Sunny/Overcast Comparison (kW) Solar Site 4 Solar Site 4 Peak: 879.791 kW Peak: 879.658 kW Peak: 286.014 kW Peak: 213.901 kW

24 Hours Sunny Day (kvar) pf = .997 Peak: 67.8672 kvar Solar Site 4 Solar Site 4 Peak: 67.8672 kvar Peak: 67.8265 kvar

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: 609.542 kW

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

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

Tree fell on 115kv line.

Sunny/Overcast Comparison (kW) Solar Site 5 Peak: 29708.42 kW Peak: 29657.62 kW Peak: 3449.527 kW Peak: 2306.53 kW

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

4 Month Profile (P) The profile peak is 70.9% of the Illustrated sunny day peak. Peak: 21083.24 kW

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

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

EMI and PV Systems Issue: cases AM band (540-1600 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

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

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.