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Yaskawa Electric America Harmonic Currents, Voltages and Your Building Power System 7/08/2002 PP.AFD.07 Harmonic Quality 1 of 49 Discussion Points 7/08/2002 Power Factor Harmonics The Building Power System Current Distribution Limits Power System Solutions PP.AFD.07 Harmonic Quality 2 of 49 Power Factor Power Factor is the ratio of the actual power (kW) being used to the apparent power being drawn from the line (kVA) Measurement of the effectiveness of power usage • 7/08/2002 The higher the PF, the more efficient the system PP.AFD.07 Harmonic Quality 3 of 49 Power Factor To determine Power Factor, divide kW by apparent power (kVA) Low Power Factor increases cost of supplying power •Overloads generators, transformers, distribution lines, etc. •Utilities penalize large users for low power factor 7/08/2002 kVA PP.AFD.07 Harmonic Quality kVAR kW Power Factor = kW / kVA kVAR is reactive power Maintains the electromagnetic field 4 of 49 Power Factor • AC Drives power factor follows concept except current not a pure sinewave, they contain harmonics • Current closer to a square wave than sine wave • Most VFD manufacturers use displacement power factor • Displacement PF = The cosine of the angle between the fundamental kVA and kW 7/08/2002 PP.AFD.07 Harmonic Quality 5 of 49 Power Factor • The effect of harmonics reduces true power factor kVA ( Harmonic) Harmonic kVAR • Power factor measurement by utilities only measure fundamental current, therefore only measure displacement PF. kVA kVAR kW 7/08/2002 PP.AFD.07 Harmonic Quality 6 of 49 Power Factor .95 .95 PF PF % SPEED % SPEED 100% FIG 1 100% FIG 2 • Fig 1. Six step VFD Power Factor Linear with speed • Fig 2. PWM VFD PF constant with speed • Harmonics reduce PF for both but can be improved using DC Link Reactors, AC Line Reactors, etc 7/08/2002 PP.AFD.07 Harmonic Quality 7 of 49 Power Factor Summary 7/08/2002 The higher the PF, the more efficient the system Harmonics may result in reduction in power factor All non-linear loads add to harmonics Utilities may penalize for low power factor Utilities measure displacement PF. Bottom Line: Not being penalized? No Problem! PP.AFD.07 Harmonic Quality 8 of 49 Harmonics: What Are They? Fundamental - the Base Frequency • Harmonic - Multiples of the Fundamental • 7/08/2002 For Power Lines 60 Hz is Fundamental Fifth Harmonic is (5 x 60) or 300 Hz Only Associated With Periodic Waveforms PP.AFD.07 Harmonic Quality 9 of 49 Harmonics: What Are They? IEEE 519 defines harmonics as: 7/08/2002 • A sinusoidal component of a periodic waveform or quantity having a frequency that is a multiple of the fundamental frequency • They are steady state state distortion of the AC line, unlike transients, surges and other things that typically only last a few cycles. They cause stress in the distribution system and can cause heating of motors and transformers • Reduces the operational life of these devices PP.AFD.07 Harmonic Quality 10 of 49 Harmonics: What are they? Harmonics can also affect the power supplies of other VFDs Can cause spurious fuse blowing and circuit breaker trips 7/08/2002 PP.AFD.07 Harmonic Quality 11 of 49 Harmonic Waveforms Fundamental Third and Fifth Harmonic Seventh 7/08/2002 Harmonic - 60 hz - 180 and 300 hz (420 hz) and Resultant PP.AFD.07 Harmonic Quality of Fundamental, 3, 5, 7 12 of 49 Calculating Harmonic Distortion Harmonic and Fundamental Currents • • 7/08/2002 Not Added Directly “Square Root of Sum of Squares” Total Harmonic Distortion (THD) = ( I32 + I52 + I72 + I92 + I112 + . . . )) / Ifund Total Current = Ifund2 + Iharm2 ) PP.AFD.07 Harmonic Quality 13 of 49 Harmonic Current and THD • • • • • • System Voltage - 100 v Load 1 - A Personal Computer Power Supply Load 2 - 125 hp HVAC Air Handler Motor Iharm = Ifund * THD (in %) * .01 Ifund = Watts / Volts Itot = Ifund2 + Iharm2 ) Computer Power - Watts Harmonic Distortion (%) 60 hz Current - amps Harmonic Current - amps Total Current 7/08/2002 PP.AFD.07 Harmonic Quality 100 100 1 1 1.41 HVAC Motor 100,000 1 1000 10 1000.05 14 of 49 Building Power System Building Loads • • 7/08/2002 Repetitive and Synchronous Random and Asynchronous Distribution System • Service Entrance/Distribution Transformers • The Bus/ Riser System • The Power/Lighting Distribution Panels • Circuit Breakers PP.AFD.07 Harmonic Quality 15 of 49 Building Load Types 7/08/2002 Repetitive and Synchronous • Resistive • Reactive • Nonlinear Random and Asynchronous • Transients • Noise PP.AFD.07 Harmonic Quality 16 of 49 Resistive Loads 7/08/2002 Examples of Resistive Loads • Incandescent Lighting • Electric Heater Elements Resistive Load Current • I load = V load / R load • I Waveform Proportional to V Waveform PP.AFD.07 Harmonic Quality 17 of 49 Resistive Waveshapes Voltage and Current are In Phase and Proportional pltivres.cgm 7/08/2002 PP.AFD.07 Harmonic Quality 18 of 49 Reactive Load 7/08/2002 Examples of Reactive Loads • Electric Motors • Contactors, Relays, Solenoids • Transformers, Line Reactors Reactive Load Current • I load = V load / (R2 load + L2 load) • Current Phase Shifted with respect to Voltage • I Waveform Proportional to V Waveform PP.AFD.07 Harmonic Quality 19 of 49 Reactive Waveshapes Current Lags Voltage But Waveforms Are Proportional pltivind.cgm 7/08/2002 PP.AFD.07 Harmonic Quality 20 of 49 Non-Linear Loads Examples of Non-Linear Loads • • Computers, Faxes, Printers, Phone Systems Variable Frequency Drives (VFDs) Non-Linear Load Current (Single Phase) • I load = (sin 1f) + (sin 3f) *n3 + (sin 5f) *n5 + (sin 7f) *n7 + (sin 9f) *n9 + (sin 11f) *n11 + ... • I load Characteristics – – 7/08/2002 Zero for 120 Degrees of Half Cycle High Crest Factor Surge for 30 Degrees PP.AFD.07 Harmonic Quality 21 of 49 Non-Linear Waveshapes Voltage is sinusoidal; Current is high harmonic waveform. pltivnll.cdr 7/08/2002 PP.AFD.07 Harmonic Quality 22 of 49 Non-Linears Rich in Harmonics Non-Linear Loads Are Rich In Harmonic Fundamental Third, Fifth, and Seventh (60hz) (180 hz, 300 hz, 420 hz) Resultant 7/08/2002 Current Current Waveform PP.AFD.07 Harmonic Quality Currents Harmonic Currents nllharm.cdr 23 of 49 3 Phase Rectifier Current % o f Three Phase Harmonic Spectrum 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 31 29 27 25 23 21 19 17 15 13 11 9 7 0 5 F u n d a m e n t a l Harmonic Number 7/08/2002 PP.AFD.07 Harmonic Quality 24 of 49 Transient Load Characteristics 7/08/2002 Examples of Transient Loads (at turn-on/turn-off) • Elevator Motors • A/C Compressor Motors • Short Circuit / Breaker Clear Transient Load Current • Itransient Is Unpredictable and Asynchronous • Itransient Approximates a Step Response PP.AFD.07 Harmonic Quality 25 of 49 Transient Waveshapes Transient Voltage Currents is Zero Cause at High Large Current, Voltage Spikes Disturbances at Current Decay f aulti.cgm 7/08/2002 PP.AFD.07 Harmonic Quality 26 of 49 Noise Characteristics 7/08/2002 Example of Noise • VFD Power Converter Switch Spikes • Relay Openings and Closures Noise Currents • Inoise Large and of Short Duration (uSec) • Inoise May be Common or Differential Mode PP.AFD.07 Harmonic Quality 27 of 49 IEEE 519-1992 Table 10-3 Isc/ IL Harmonic Current (Odd) % THD <11 11<h<17 17<h<35 35<h <20 4.0 2.0 1.5 0.6 0.3 5.0 20-50 7.0 3.5 2.5 1.0 0.5 8.0 51-100 10.0 4.5 4.0 1.5 0.7 12.0 101-1000 12.0 5.5 5.0 2.0 1.0 15.0 >1000 15.0 7.0 6.0 2.5 1.4 20.0 IEEE 519 - 1992 Table 10-3 Recommended Practice Max Harmonic Current Distortion of the Fundamental 7/08/2002 PP.AFD.07 Harmonic Quality 28 of 49 Current Distortion Limits PCC (Point of Common Coupling) • • Most important and most controversial item in IEEE Defined as: – (ISC) Max Short Circuit Current at PCC – 7/08/2002 The electrical connecting point between the utility distribution system and the users electrical distribution system Determined by the size, impedance, and voltage of the service feeding the PCC. PP.AFD.07 Harmonic Quality 29 of 49 IEEE 519 (IL) Max demand load current at PCC – – (ISC/IL)The ratio of available current at the PCC to the max demand load current at the same point. – 7/08/2002 Facilities should measure this over a period of time and average it. If not possible - calculate the anticipated peak operation of the facility Measures the stiffness of the electrical system relative to the load. The larger the power source in relationship to the load, the stiffer the system. PP.AFD.07 Harmonic Quality 30 of 49 IEEE 519 TDD - Total Demand Distortion – PCC 1 as measuring point – – – TDD allowed to be 12% 5th and 7th 15% No filtering needed PCC 2 as measuring point – – – 7/08/2002 The measure of the total harmonic current distortion at the PCC for the total connected load. TDD allowed to be 5% 5th and 7th 4% Filtering needed PP.AFD.07 Harmonic Quality 31 of 49 IEEE 519 13,800V 69KV PCC1 PRIMARY OF SERVICE TRANSFORMER 20,000 KVA TR-1 8.5% PCC2 480V PCC1 - if THE COMPANY OWNS THE XFORMER, UTILITY WILL MEASURE HERE PCC2- IF UTILITY MEASURES 480V PCC 2 IS INTERFACE 200kVA 200kVA 200kVA VFD 7/08/2002 PP.AFD.07 Harmonic Quality 32 of 49 IEEE 519 Voltage Distortion Limits per IEEE 519 Defines the quality of power on the electrical distribution system. – – 7/08/2002 Individual Voltage Distortion 3% Total Voltage Distortion 5% allowed PP.AFD.07 Harmonic Quality 33 of 49 Harmonic Solutions No Filtering • Isolation Transformers • • 7/08/2002 Loads less than 25%- must be very stiff Very costly Not required by PWM drives except as harmonic filters PP.AFD.07 Harmonic Quality 34 of 49 Harmonic Solutions 7/08/2002 AC Line Reactors - 25% Load • Greatly improves voltage distortion • Current distortion improvement similar to DC Link Reactor • More cost effective than Isolation Transformer • Usually effective means of meeting IEEE requirements • Improves power factor • Protects VFDs from transients PP.AFD.07 Harmonic Quality 35 of 49 Harmonic Solutions DC Link Reactor up to 40% Load • • • • • DC Link w/ AC Line Reactor • • 7/08/2002 More cost effective than AC Line Reactor Reduces Voltage Distortion effectively Reduces Current Distortion somewhat less effectively Improves PF but not as well as AC Reactor Smaller than AC Reactors Somewhat better than either system alone Similar results as DC Link Reactor PP.AFD.07 Harmonic Quality 36 of 49 Harmonic Solutions Harmonic Trap Filter - 60% Loaded • • • 7/08/2002 5th Harmonic Trap Filter in series with AC 5% Line Reactor Effective at reducing Voltage and Current distortion Very expensive PP.AFD.07 Harmonic Quality 37 of 49 Harmonic Solutions 7/08/2002 12 Pulse (Dual Diode) Transformer 80% or more • Most effective method of Harmonic Distortion reduction • Not as expensive as Trap Filters • Similar in size to Isolation Transformers • Last resort PP.AFD.07 Harmonic Quality 38 of 49 Harmonics Conclusions 7/08/2002 All non-linear power structures cause harmonics Harmonics reduce power factor Filtering requirements depend on where you are measuring harmonics Knowing all harmonic distortion and using appropriate filtering on a system wide approach, insures a more reliable, cost effective solution. PP.AFD.07 Harmonic Quality 39 of 49 Typical Harmonic Contents Harmonic Content of Typical Commercial Building Electrical Equipment Equipment Harmonic Content - % 1 Phase 3 Phase Magnetic Ballasts Electronic Ballasts Personal Computers Fax, Phone, Printer Motors VFDs VFDs w/Line Reactors 7/08/2002 19-40 <20 80-140 80-140 ------- PP.AFD.07 Harmonic Quality >7 <5 +/-40 +/-40 3 25-80 <25 40 of 49 Distribution System Service Entrance Transformers Power Distribution Transformers Lighting Distribution Transformers “Isolation” Transformers The Building Riser System Power/Lighting Panels, Circuit Breakers 7/08/2002 PP.AFD.07 Harmonic Quality 41 of 49 All Transformers Are Inductive Rxfmr Lxfmr Zxfmr 7/08/2002 PP.AFD.07 Harmonic Quality 42 of 49 Transformer Impedance vs. Hz Transformer Impedance Rises Proportionally With Frequency 1.35 ohm 0.27 ohm 60 hz 7/08/2002 300 hz PP.AFD.07 Harmonic Quality 43 of 49 Vdistort Increases With Frequency Zxfmr = 2P * freq * Lxfmr Vdrop = Iharm * Zxfmr 7 6 5 4 3 2 1 0 Series1 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 Series2 1 Blue - Harmonic Current Red - Distortion Voltage Harmonic Spectrum and Voltage Drop (Distortion) Harmonic Number 7/08/2002 PP.AFD.07 Harmonic Quality 44 of 49 Current Is Problem, Not THD Assume all 5th Harmonic Current Use 1.35 ohm Transformer Z Vdrop = Iharm * Zxfmr Computer Pow e r - W a tts Ha rmonic Distortion (%) 60 hz Curre nt - a mps Ha rmonic Curre nt - a mps Tota l Curre nt Volta ge Distortion (%) 7/08/2002 PP.AFD.07 Harmonic Quality 100 100 1 1 1.41 1.35 HVAC Motor 100,000 1 1000 10 1000.05 13.5 45 of 49 Result: Voltage Distortion Harmonic Voltage Current Cause - Blue and High System Voltage Distortion Current Impedance - Red pltv dist.cgm 7/08/2002 PP.AFD.07 Harmonic Quality 46 of 49 Summary: Harmonic Current Total Harmonic Distortion - THD • • Causes Nothing It Is a Factor, a Percentage Harmonic Current Can be a Problem • • A Function of Total Current And Total Harmonic Distortion (THD) Iharmonic Modern Loads on the Power Bus • • 7/08/2002 Current Can Cause Voltage Produce High Harmonic Current Cause Spikes, Transients, Noise PP.AFD.07 Harmonic Quality 47 of 49 Summary: Distribution The Power System - Inductive in Nature Impedance Increases With Frequency The Bus Distributes to Other Loads: 7/08/2002 • Distorted System Voltage • Voltage Dropouts • Voltage Spikes, Surges, Transients • System Resonances PP.AFD.07 Harmonic Quality 48 of 49 Conclusions for the Industry Retrofits Reduce Total Building Current Harmonics - No Problem w/Lighting Circuit • • • Harmonics - Problem with Power Panels • • • 7/08/2002 Loads are Typically Balanced Ballasts Have Low Harmonic Current Electronic Ballasts Reduce Harmonic Current Loads may be Unbalanced Loads Produce High Harmonic Current Loads are Susceptable to Distorted Voltage PP.AFD.07 Harmonic Quality 49 of 49