Harmonics and PFC The love story By Pol Nisenblat

2 THE FUTURE OF POWER QUALITY DEFINITIONS PROBLEMS “DETUNED” SOLUTIONS TUNED SOLUTIONS HOW TO CHOOSE OPEN DISCUSSION

3 ELECTRICAL POWER SOURCE  It is worldwide common practice to assume that utilities generate a near perfect sine wave voltage  Typical electrical energy source is introduced by “voltage” source

4 DISTRIBUTION TRANSFORMER  Typical Internal Impedance is only 2-7% of the fully loaded Secondary

5 IDEAL ENERGY SOURCE  Simplified power control by periodical switching (chopping)  Nonlinear load operation generates current waveform distortion

6 HARMONICS - DEFINITIONS  Harmonics are integral multiples of some fundamental frequency that, when added together, result in a distorted waveform f(x) = sin(x) f(x) = sin(5x) 5 + f(x) = sin(x) + sin(5x) 5 =

7 HARMONICS - DEFINITIONS  Harmonic order are MULTIPLES of the fundamental frequency.  Typical Harmonics are the 3 rd, 5 th, and 7 th  Where H3 = 150 Hz, H5 = 250 Hz, H7 = 300 Hz (at 50Hz world)  In fact, any waveform may be constructed from a sine wave and some number of its harmonics like:

8 HARMONICS – MOST IMPORTANT DEFINITIONS  Harmonics are originated at the load side!  Harmonics are created in the current!  Harmonic sources are - current sources

9 HARMONIC SOURCE  High internal impedance  The harmonic current is being PUSHED towards lowest external impedance path

10 HARMONIC CURRENT FLOW  Typical harmonic current flow is towards distribution transformer  1 Ohm0.01 Ohm 

11 HARMONICS – PROBLEMS?  I 2 r losses + “skin” effect  Voltage distortions  Iron-core losses  Cables/transformers overheat  Upstream pollutions  But, the real problems are yet to come

12 HARMONIC CURRENT WITH PFC  Where the H5 current should go now?

13 PARALLEL RESONANCE Parallel resonance = Infinity impedance

14 PARALLEL RESONANCE  High impedance at the resonance frequency  The resonance frequency changes with changed number of capacitor groups (N)

15 PARALLEL RESONANCE

16 PARALLEL RESONANCE  Harmonic current turns back to the loads  Harmonic VOLTAGE raises dramatically  Harmonic current circulates (ping pong) between capacitors and distribution transformer V

17 PARALLEL RESONANCE – WHAT TO DO?  Xl1 reactor in series to the capacitor moving parallel resonance frequency downstream  The new resonance frequency at: Xc=Xl+Xl1 Locate parallel resonance frequency below lowest dominant harmonic

18 PARALLEL RESONANCE FREQUENCY –”RULE OF THUMB”  Where h r is the harmonic number of the parallel resonance  Unfortunately, not accurate enough h r = kVA sc kVAC

19 HOW TO CALCULATE PARALLEL RESONANCE FREQUENCY?  For those who love formulas:

20 HOW TO CALCULATE PARALLEL RESONANCE FREQUENCY?  Unfortunately, Xl (Xtr) value which is actually the total distribution network inductance at the frequency of interest - is unknown But, we do know that the parallel resonance frequency would always be located downstream to the serial resonance frequency between Xl1- Xc

21 “DETUNED” SOLUTION

22 WHAT FREQUENCIES ARE SAFE?  Even” harmonics are normally not present  “Triple” harmonics are canceled on DELTA connected loads with balanced 3 rd harmonic  On balanced loads and 3 phase DELTA capacitors cases, tuning in H3.5-H4.2 ranges are most popular

23 DETUNED SOLUTION - DEFINITIONS  Tuned frequency is defined by serial resonance point  Serial connected reactors are defined by % rather then Henries  Reactor’s % defined as impedance at the fundamental frequency with respect to the capacitor’s impedance at the same frequency Reactor50Hz60HzHarmonic 7%189Hz227HzH3.78 6%204Hz245HzH %134Hz160HzH %210Hz252HzH4.2

24 7% “DETUNED” SOLUTION

25 TUNED SOLUTIONS - FILTERS  Passive filters are “tuned” to just below the harmonic frequency  Care should be taken – not to overload! Low impedance path at 5 th harmonic

26 TOO HIGH HARMONIC LEVELS?  Disconnect ALL PFC capacitors and check again  Significant difference? – Use detuned solution  No difference? – Use tuned solution  2 nd and 4 th harmonics too high? - Check voltage converters  Weak network? 14% detuned solutions are preferred  Balanced 3 rd harmonic in current? – Use % solutions  Unbalanced compensation? – Use 14% solutions only  Voltage harmonics without current sources?  Don’t use filters! Speak to utility.

Questions? Contact: Asaf Laifer  