Introduction to Harmonics and Power Quality

Transcription

1 NWEMS Introduction to Harmonics and Power Quality August 20 24, 2018 Seattle, WA Track B Anaisha Jaykumar (SEL) Class Content» Definition of power quality (PQ)» Impact of PQ problems» Sources of poor PQ» Troubleshooting» Case studies 2 1

2 PQ Refers to Voltage and Current Characteristics Poor PQ refers to changes in electric power supply that can cause equipment to fail, misoperate, or degrade Noisy transformers Overheating Blown fuses 3 Amplitude and Frequency Characteristics of a Waveform 1. Amplitude 2. Frequency = 1 Hz T 4 2

3 Wave Shape Characteristics of a Waveform 3. Waveform distortion 5 Duration of Poor PQ Is An Important Characteristic Transient (<1 cycle) Short term (0.5 cycle up to 1 minute) Long term (>1 minute) 6 3

4 Several Factors Affect PQ Nonlinear loads Large load changes Faults 7 Nonlinear Loads Distort Waveforms Incandescent Bulb With Dimmer Current 0.15 A peak 0.07 A rms Voltage 169 V peak 120 V rms 8 4

5 LED Lights Provide Energy Efficiency But Distort Waveforms Current (A) LED light 0.11 A peak 0.04 A rms Incandescent bulb with dimmer 0.60 A peak 0.44 A rms Time 9 What Is the Cost of Poor PQ? Equipment Failure, Misoperation, and Degradation Manufacturing facilities have costs ranging from $10,000 to millions of dollars associated with a single interruption to the process. Mark McGranaghan and Bill Roettger Economic Evaluation of Power Quality 10 5

6 EPRI 2001 Study of Typical PQ Phenomena Line noise Outages Spikes, transients 10% 5% 5% Harmonics Frequency variations 5% 5% 46% Voltage sags Overvoltage 7% Undervoltage 7% 10% 11 Voltage swells Voltage Sag, Swell, and Interruption (VSSI) 12 6

7 VSSI Are Described by Depth and Duration Voltage (V) V sag peak 60 V rms 100 ~3 cycles Sag event waveform Analyze Sag Event Using Waveform or RMS Plots 100% 50% 50 ms 1,000 ms V A rms V B rms V C rms 0% Time stamps 14 7

8 Overvoltage and Undervoltage Are Long Term Phenomena PQ Phenomena Amplitude Range Duration Sag 10 90% 0.5 cycles up to 1 minute Undervoltage 80 90% >1 minute Swell 110% 0.5 cycles up to 1 minute Overvoltage % >1 minute 15 Lightning Strikes Cause Voltage Sags Lightning strikes power pole Insulators flash over and fault current flows Flashover Instantaneous voltage drop occurs Protective relays operate Circuit breakers open 16 8

9 Power System Faults Can Cause Voltage Sags Voltage Profile of a Three Phase Fault 17 Effect of voltage disturbance is more at the fault point of fault and less away from it Motor Operation Can Cause Voltage Sags Motor Mechanical load 18 9

10 University Uses Voltage Sag Data to Continue Operations and Buy Planning Time 700 hp pump 19 Optimized Motor Shutdown Reduces Sag and Eliminates Problems Startup Shutdown Before After Startup Shutdown Current Voltage 20 10

11 Voltage Events Damage Motors and Sensitive Processing Equipment $1,300 $1,300 $65, VSSI Data Reveal Stuck Load Tap Changer 41 minutes Time stamps 22 11

12 Voltage Unbalance Damages Motors» Causes temperature rise» Reduces life expectancy Photo courtesy of Electrical Apparatus Service Association 23 Unbalance Occurs When V A + V B + V C 0 V V B V C V A 120 Magnitude (pu) Unbalanced Balanced Three Phase Waveforms A Phase B Phase C Phase Unbalance Cycles 24 12

13 Typical Voltage Unbalance Levels in U.S. Three Phase Power Delivered to Industrial Plants <1% Operates normally 1 3% Causes overheating and premature aging >3% Can cause significant damage 66% 32% 2% 25 Facilities Operator Uses Data to Balance Loads 26 13

14 Unbalanced Magnitude Phasor Magnitude (V) Time (t) A Phase B Phase C Phase V 0 27 Common Causes of Unbalance» Faulty distribution equipment» Random phase loading (arc furnaces)» Unbalanced distribution feeders 28 14

15 Harmonics Occur as Multiples of 60 Hz 29Voltage (pu) Fundamental: 60 Hz Third harmonic: 60 x 3 = 180 Hz Harmonics Occur as Multiples of 60 Hz 30Voltage (pu) Fundamental: 60 Hz Fifth harmonic: 60 x 5 = 300 Hz 15

16 Low Harmonics Are More Common in Power System Third order Fifth order 31 Fiftieth order Harmonics Cause Humming in Transformers 32 16

17 Harmonics Described as Percent of Fundamental Frequency Harmonic Order Frequency (Hz) RMS Value Fundamental (1) rd th th Sum of squares of harmonics THD 6.9% Amplitude of fundamental Total Harmonic Distortion (THD) Is High Under Low Load Conditions Although Impact Can Be Low LED light Current THD: 45% 0.04 A rms Incandescent bulb with dimmer Current THD: 20% 0.44 A rms 34 17

18 Harmonic Trending Pinpoints Cause of Lighting Ballast Failures Image 2016 Google 35 Electronic Ballasts Cause Fifth Harmonic Disturbance Current harmonics (%) :30 a.m. 5:30 a.m. 5:30 a.m. Day 1 Day 2 Day

19 Adjustable Speed Drives Cause Harmonics Current (amperes) 6 pole adjustable speed drive creates fifth and seventh harmonics 37 Identify Sources of Harmonics» Nonlinear loads» HVdc interties» Saturated transformers» Arcing devices» Renewable energy generation» Electronic ballast fluorescent lights 38 19

20 Turning on Water Results in Voltage Variation That Affects Lights Variable-frequency drive (VFD) for constant water pressure 39 VFD Not Running 512 Samples Per Cycle 40 20

21 VFD Running 512 Samples Per Cycle 41 Reduce Harmonic Disturbances» Isolate voltage sources for sensitive devices from harmonic generating devices» Use K rated transformer or derate transformer» Install filters between drive and power system 42 21

22 Flicker Affects Human Eye Brain Response Amplitude modulation of voltage when signal carries another signal Voltage (V) 43 Nonlinear Loads Cause Unwanted Zero Crossings That Affect Digital Clocks 44 22

23 PQ Problems May Affect Metering Accuracy ANSI C , Accuracy Class 0.1 Adds New Tests Test 39: 90 degree phase fired waveform Test 40: quadriform waveform Test 41: peaked waveform Current Voltage Test 42: pulse waveform Test 43: multiple zero crossing Test 44: multiple zero crossing Current 45 Voltage Phase angle Phase angle Phase angle Summary» PQ issues are changes in electric power supply that can cause equipment to fail, misoperate, or degrade» Common PQ phenomena are VSSI, harmonics, voltage unbalance, and transients» PQ characteristics can be described by amplitude, duration, frequency, and wave shape 46 23

24 Troubleshooting Summary» Look for patterns in disturbances by noting time of day, duration, and how often events occur» Correlate PQ events with load changes, switching capacitor banks, and so on» Remember that PQ events are typically worse near the source of the problem» Note that a high neutral current can indicate third harmonics 47 NWEMS Questions? 24