EPCOS
Power Factor Correction & Harmonic filter
Power Quality
Definition: Power Factor, Harmonics, Transients, Voltage and frequency variations and other disturbances in electric power supply networks
Examples for poor power quality Adjustable Speed Drives
Flat topping of Drive input voltage, heavily distorted current
Notching on the input can interfere with other loads on the same branch circuit
Changing load structure Past - load: most loads were “linear” Induction-motors, heating, bulbs voltage was followed by current - only a few problems Features • Simple and rugged design
Customer benefits – High reliability – Long lifetime – Favourably-priced
• No commutator
– Unrestricted operation for partial- and overload conditions – Low maintenance (only the bearings)
• High degree of protection
– Can be universally used
Changing load structure
Today’s - loads: most loads act “non linear” Computer, motor-control, drives, etc. Current is pulse shaped Current is no longer following the sinusoidal wave shape Result: Harmonics
- Increasing number of sources causing disturbances - Equipment become more and more sensitive - De-regulated energy market
Problems caused by harmonics
Origin of harmonics Non linear loads Loads which have non linear voltage-current characteristics are called non linear loads. When connected to a sinusoidal voltage, these loads produce non sinusoidal currents. Modern power electronic systems result into non sinusoidal currents when connected to the sinusoidal networks.
The non linear devices can be classified under the following three major categories: 1. Power Electronics: e.g. rectifiers, variable speed drives, UPS systems, inverters, ... 2. Ferromagnetic devices: e.g. transformers (non linear magnetizing characteristics) 3. Arcing devices: Arcing devices, e.g. arc furnace equipment, generate harmonics due to the non linear characteristics of the arc itself.
Harmonic disturbances are created by non-linear loads!
Modern drives a main source for harmonics
Voltage-source DC link converter
Current-source DC link converter
Cycloconverter
Design ~
~ =
= ~
=
=
= ~
M 3~
~
~ =
=
~ M 3~
Features
Voltage is impressed in the DC link
Current is impressed in the DC link
Drive converter
SIMOVERT MASTERDRIVES SIMOVERT MV SIMOVERT ML
SIMOVERT A SIMOVERT I SIMOVERT S
M 3~
Cycloconverter, no DC link
SIMOVERT D
HARMONICS fed back by 6/12 pulse rectifier Voltage Voltagecharacteristic characteristic at the drive at the driveconverter converter output (PWM) output (PWM)
100%
80%
6-pulse 12-pulse
60%
40%
20%
Current Currentcharacteristic characteristic at atthe thedrive driveconverter converter output output
0% 6-pulse
1
5
7
11
13
17
19
23
25
100,00%
29,00%
9,00%
6,00%
3,50%
2,50%
2,00%
1,20%
1,10%
2,90%
0,90%
6,00%
3,50%
0,25%
0,20%
1,20%
1,10%
12-pulse 100,00%
Order number
Example for single phase Non-Linear load
Example of a non-linear load: Switched mode power supply
AC Current
Voltage Current
LOAD
Understanding harmonics
Harmonic currents or voltages are integer (whole number) multiples of the fundamental frequency.
Harmonic order Frequency
F
3rd
5th
7th
50
150 250 350
Problems caused by HARMONICS
Overheating of transformers (K-Factor), and rotating equipment Increased hysteresis losses Neutral overloading / unacceptable neutral-to-ground voltages Distorted voltage and current waveforms
HARMONICS
Fundame
Failed capacitor banks
h3
Breakers and fuses tripping
h7 Amplitude
Unreliable operation of electronic equipment,
h5
SUM
and generators Erroneous register of electric meters Time
Wasted energy / higher electric bills - KWD & KWH Wasted capacity - Inefficient distribution of power Increased maintenance cost of equipment and machinery
COST caused by HARMONICS Additional investment due to faster equipment derating Shorter life time of equipment Higher energy consumption Higher downtime of production equipment Higher maintenance and repair cost Reduced product quality Reduced production output Investment for stronger equipments/components alternatively
One time investment for harmonic filter
Effect of harmonics Tripping of circuit breakers and fuses Due to resonance effects, the current levels may rise to multifold levels which results into tripping of circuit breakers and melting fuses. This situation results into serious problems in industries which rely on the quality of power for the continuous operation of their sensitive processes (e.g. semiconductor) Overloading / decrease of life time of transformers Transformers are designed to deliver power at network frequency (50/60Hz). The iron losses are composed of the eddy current loss (which increase with the square of the frequency) and hysteresis losses (which increase linearly with the frequency). With increasing frequencies the losses also increase, causing an additional heating of the transformer. Overloading of the capacitors Capacitive reactance decreases with the frequencies. Even smaller amplitudes of the harmonic voltages result into higher currents which are detrimental to the capacitors: I = U * 2 * 3.14 * f * C. Losses in distribution equipment Harmonics in addition to the fundamental current cause additional losses in the cables, fuses and also the bus bars.
Effect of harmonics Excessive currents in the neutral conductor Under balanced load conditions without harmonics, the phase currents cancel each other in neutral, and resultant neutral current is zero. However, in a 4 wire system with single phase non linear loads, odd numbered multiples of the third harmonics (3rd, 9th, 15th) do not cancel, rather add together in the neutral conductor. In systems with substantial amount of the non linear single phase loads, the neutral currents may rise to a dangerously high level. There is a possibility of excessive heating of the neutral conductor since there are no circuit breakers in the neutral conductors like in the phase conductors. Malfunctioning of the electronic controls and computers Electronic controls and computers rely on power quality for their reliable operation. Harmonics result into distorted waveforms, neutral currents and over voltages which affect the performance of the these gadgets. Measurement errors in the metering systems The Accuracy of metering systems is affected by the presence of harmonics. Watt-hour meters accurately register the direction of power flow at harmonic frequencies, but they have magnitude errors which increase with frequency. The accuracy of demand meters and VAr meters is even less in the presence of harmonics. Wrong multi meter readings. Use true RMS meter!
3rd harmonic in the neutral conductor
3rd harmonic in the neutral conductor
Synthesis of a wave form
Limit for harmonics
Summary Consumer structure has changed from linear to non linear loads
Harmonics in the net are increasing Increasing unknown energy losses Unknown overloads Problems in the net become more complex Beside convent. PFC, filters become more and more important De-tuned filters for most applications Active filters for a niche market
EPCOS Harmonics solution
Unlike other solutions that:
Waste energy Connect in series Generate higher harmonics (through injection) Have limited fixed sizes and are not expandable Are bulky and expensive
The Solution – EPCOS AG offers: Specific harmonic filtering of any magnitude Enhanced power quality Elimination of associated wasted energy Modular and expandable circuitry, to include additional load
Resonance 1. Harmonics can overload PFC capacitors due to over voltage and over current created by the harmonic source and reduced reactance of PFC capacitors at higher frequencies. 2. But more critical are applications in which the application configuration (PFC capacitor and transformer) form a resonance circuit with an frequency close to existing harmonic frequencies. In such a case harmonic currents stimulate the resonance circuit and create resonance amplification with harmful over voltages and over currents.
Resonance is one of the main reasons for failed PFC capacitors or short life cycle of PFC capacitors!
Parallel resonance
Harmonics MAGNIFICATION
H#
%
φ
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
100.0 0.4 2.1 1.6 0.2 0.4 0.7 0.1 0.2 0.1 0.1 0.0 0.1 0.0 0.1 0.2
0 1 16 2 72 41 1 33 11 36 68 37 69 3 27 69 301 158 319 20
K-f ac tor: 1.0 41 H# 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
Meter: 0001 H#
%
φ
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
100.0 0.4 12.3 5.5 0.7 1.3 0.1 0.3 0.3 0.0 0.1 0.0 0.1 0.0 0.1 0.0
0 29 53 3 56 2 99 7 2 10 29 2 85 2 10 90 2 10 29 29 29 29
% 0.0 0.1 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
φ 69 68 69 70 68 68 68 68 158 158 69 69 8 248 309 68
V olts : 27 7 T.H.D.:
K-f ac tor: 1.5 33 H# 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
% 0.5 0.1 0.4 0.1 0.2 0.1 0.0 0.0 0.0 0.1 0.0 0.0 0.1 0.1 0.1 0.0
φ 1 00 119 66 91 29 29 29 119 29 90 29 119 29 119 119 209
2.8 %
Fr equenc y :60.01 Hz max :
A mps : 17 16 T.H.D.:
13.6%
2 .9%
min:
0.5%
Frequenc y :60.01 Hz max :
1 8.1%
min:
2.1%
Meter: 000 1 H#
%
φ
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
100 .0 0.5 18.8 1.2 0.0 0.1 0.0 0.1 0.0 0.0 0.1 0.0 0.1 0.1 0.0 0.1
0 352 203 126 80 312 80 116 320 319 192 169 259 259 259 31
K-f a c tor : 1.829 H# 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
Meter: 000 1 H#
%
φ
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
100 .0 1.0 150.0 8.7 1.5 1.6 1.7 1.2 0.5 1.0 1.5 1.2 0.5 0.9 0.7 0.6
0 169 263 141 280 259 279 79 260 331 259 339 180 182 349 292
% 0.1 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
φ 26 31 25 9 25 9 20 0 25 9 80 20 0 16 9 25 9 25 9 34 9 25 9 34 9 25 9 79
K-f ac tor: 32.3 8 H# 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
% 2.3 2.9 3.8 1.2 1.5 0.8 0.5 1.1 0.3 0.5 0.5 0.1 0.6 0.3 0.2 0.0
φ 9 79 25 9 30 0 25 9 31 0 25 9 29 4 8 25 9 31 2 25 9 34 9 30 7 19 25 9
V olts : 2 90 T.H.D.:
18.8%
A mps : 2033 T.H.D.:
89.5%
Frequen c y :5 9.97 Hz max :
21.6%
min:
1.9%
Voltage
Meter: 0001
With PFC capacitors
Freq uenc y : 5 9.97 Hz max : 152.3%
min:
3.6%
Current
No PFC capacitors
Real case of parallel resonance in KL/Malaysia
Parallel resonance Harmonics present on LV side of the transformer Transformer together with PFC capacitors on LV-side acts as a parallel resonant circuit X N , network im pedance
At resonant frequency the inductive reactance is equal the capacitive reactance
point of view
XT transform er
In
The resultant impedance of the circuit increases to very high value at resonant frequency Excitation of a parallel resonant circuit results into a high voltage across the impedances and very high circulating currents inside the loop Transformers and capacitors are additionally loaded which may cause overloading of them
harm onic load
XL m otor
XC cap acitor
Parallel resonance What happens in case of parallel resonance? 1) Iν is constant and imprinted 2) Impedance Z → ∞
Iν AC DC
Z
U
Ic
1) + 2) ⇒ voltage U → ∞ (ohmic law) 3) With U → ∞ ⇒ Ic = IL → ∞
IL
Parallel resonance: example U = 20 KV Sk = 500 MVA
S = 1000 kVA Transformer uk = 6%
U = 400 V
AC
Qc = 400kvar
M
DC P = 500 KW, 6-pulse I50 Hz = 720A I250 Hz = 144A I350 Hz = 103A I550 Hz = 65A I650 Hz = 55A I850 Hz = 42A I950 Hz = 38A
P = 100 KW I350 Hz =
720 7
A
f R = 50 ⋅
Parallel resonance: example STr SKLV =
ST ⋅100 QC ⋅ u K
· 100
uk
1000 kVA AC DC
M
SKLV =
·100 = 16.67MVA 6
SKLV frp = 50Hz · Qc 16.67 MVA
= 322 Hz
frp = 50 Hz · 0.4 Mvar
Attention: close to the 7th harmonic!
Parallel resonance: example →
51.5V
≈ 12.7%
400V
AC DC
System bus bar: impedance vs. frequency
M
I350 Hz = 103 Amp
0.5
322Hz
1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0
o 50
150
250
350
450
550
Frequency Hz
322 Hz is close to the 7th harmonic 350 Hz Resulting harmonic voltage for 350 Hz : U350 = 0.5 Ω * 103A = 51.5V
Resonance? if fr = fν
132 kV level
Xc 0 Ic ∞
Iν
11 kV level
Iν
Transformer 1000 kVA, uk = 5 %
415 V level
Transformer 630 kVA, uk = 5 % Series resonance
Parallel resonance
415 V level
Iν
DC drive 600 kW cos ϕ = 0.65
... Capacitor bank
3˜
300 kW cos ϕ = 0.65
... Capacitor bank
Series resonance Series resonant circuit formed by combination of inductive
Series resonant circuit
and capacitive reactance. The impedance behavior of this circuit is as illustrated in the diagram. It is seen that at
L
resonant frequency the impedance reduces to a minimal
S
value. Thus the circuit offers very low impedance at the input C
signal at this frequency which results into multiple fold increase in the current. The voltage drop on the individual component increases moving closer to resonant frequency.
S=signal source
Induc tanc e
Se rie s re so na nce 16
R eac tanc e
14
Im pedanc e
Impedance
12
fr
10
The point of series resonance is given by the following formula:
8
100 vR = S N ⋅ QC1 ⋅ eK
6 4 2 0 50
100
150
200 250 Freque ncy
300
350
400
Remedial measures Limiting total output of harmonic sources Limiting the number of simultaneously operating harmonic sources Balanced connection of single phase loads to the three phases Pull in extra neutral wires Isolated ground separated from the safety ground Tuned filter circuits De-tuned HARMONIC filters Using equipment with higher pulse number Active harmonic filter
Harmonic proof capacitors Various supplier of capacitors offer so called “Harmonic proof capacitors”. “Harmonic proof capacitors” are special designed capacitors, e.g. mixed dielectric, ALL PP or MPP with thicker dielectric As explained before the main problem for capacitor failures is resonance amplification due to series or parallel resonance Both cases can not be solved with “harmonic proof capacitors” From physical point of view only one passive solution is known:
Harmonic filter circuits (de-tuned or tuned)
Harmonic filter circuits Filter circuits, which are in series connected reactors and capacitors, form a series resonance circuit. Design and dimensioning of the components has to be done in such a way, that one of the following points will be fulfilled: De-tuned filter circuit The main purpose of de-tuned filter is to avoid resonance condition of the capacitor with the transformer inductance. Depending of the de-tuning frequency more or less harmonic currents will be sucked from the grid. Very common is a de-tuning to a frequency of 189 Hz (7 %) with a reduction of harmonics of app. 30-50 %. Tuned filter circuit The tuning has to be done for each harmonic frequency, means each harmonic frequency requires its own filter circuit. The harmonic current will be reduced by approximately 90 %.
For the fundamental frequency both types are reactive and are working with nearly it‘s full kvar load as a PFC capacitor.
De-tuned harmonic filters
Customer benefits of detuned filters Improvement of Power Factor Reduction of harmonics Reduction of ohmic losses, real kW energy savings Elimination of reactive energy consumption Elimination of power utilities penalties on low power factor Power Quality improvement Climatic protection, reduction of greenhouse gas emissions Reduction of new investment for distribution equipment (transformers, LV switchgear, ) Reduction of equipment maintenance cost and down time of production equipment Improvement of production process stability
De-tuned harmonic filter
De-tuned harmonic filter WHAT IS THE DEGREE OF DETUNING? The most common degree of detuning is p = 7 %. At fn=50Hz as the fundamental network frequency, this degree of detuning corresponds to a resonance frequency fres of 189 Hz, which can be calculated as follows:
fres =
fn p/% 100
p = (f / fres)² · 100 (in %)
EXAMPLES FOR DETUNING-FACTORS (f=50Hz) 5% 5.5 % 5.67 % 6% 7% 8% 12.5 % 14 %
224 Hz 213 Hz 210 Hz 204 Hz 189 Hz 177 Hz 141 Hz 134 Hz
De-tuned harmonic filter Calculation of a 7%-detuned filter: Supply Voltage Un + Overvoltage: fn:
50 Hz
p:
7%
400 V
Nc / kvar: Uc:
430 V
25
50
440 V
Design: Ucr: Qcr / kvar:
Un =
189 Hz
fres:
28.13
56.27
1.534
0.767
Cy / µF:
462.78
925.56
C ∆ / µF:
154.26
308.52
400 V Ln / mH:
430 V
De-tuned harmonic filter Previous Example, now for 7%-detuned filter Resulting harmonic voltage e.g. : AC DC
M
Kvar: 400
5th (250Hz): 0.025 Ohm · 144A = 3.6V 0.9% 7th (350Hz): 0.045 Ohm · 103A = 4.6V 1.1%
System busbar: impedance vs. frequency 0,14 0,12 0,1 0,08
o
0,06
o
0,04 0,02 0 50
150
250
350
450
550
De-tuned harmonic filter I m p e d a n c e b e h a v i o u r o f a s e r ie s i n d u c t a n c e c i r c u i t 3 c a p a c it iv e b e h a v io u r
in d u c t iv e b e h a v io u r
2
1
In d u c t iv e r e a c t a n c e C a p a c it iv e r e a c t a n c e R e s u lt a n t im p e d a n c e
0 0
100
200
300
400
-1 re s o n a n t fre q . f r
-2
-3 F re q u e n c y
500
600
700
800
De-tuned harmonic filter
Summary: detuned filter
Impedance 0,14 0,12 0,1
o
0,08 0,06 0,04 0,02 0 50
150
189Hz
250
350
5th
7th
450
550
11th
Summary: detuned filter • Resonance frequency not close to any harmonic • Filter frequency ffilter < fharmonic • A certain reduction of harmonic distortion • Export of some harmonics content to the HV-system • Capacitors are blocked against resonance, therefore de-tuned filters are also known as anti-resonance- filter
Tuned harmonic filter Power factor correction & Filtering harmonics (cleaning the grid)
Tuned harmonic filter
Tuned harmonic filter A typical tuned filter bank at 50Hz fundamental frequency consists of :
• 1 filter for the 5th harmonic ( 250Hz), tuned to 245 Hz • 1 filter for the 7th harmonic ( 350Hz), tuned to 345 Hz • 1 filter for the 11th harmonic (550Hz), tuned to 545 Hz
Tuned harmonic filter Previous Example, now for a TUNED FILTER Resulting harmonic voltage e.g.: 5th (250Hz): 0.01 Ohm ·144 A = 1.4V 0.4%
AC DC
M
5 th kvar: 200
7 th 400
11 th 100
7th (350Hz): 0.01 Ohm ·103 A = 1.0V 0.2%
System bus bar: impedance vs. frequency 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 50
150
o
o
250
350
Frequency Hz
o 450
550
Tuned harmonic filter Switching sequence of tuned filter: LIFO Switching in: 3rd
5th
7th
11th
5th
7th
11th
Switching out: 3rd
Summary: tuned filter • Resonance frequencies of the series filter circuits are very close to existing harmonics • Excellent reduction of harmonics on the bus bars • Capacitors are charged with high harmonic currents „cleaning“ of the network • No export of additional harmonic load to the HV-system „torture“ for the capacitors, if they are not rated for this high effective current • Risk of sucking-off harmonic currents from HV side!!
Summary: tuned filter
Impedance
0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 50
150
o
o
250
350
5th
7th
o 450
550
11th
Harmonic filters FINAL COMPARISON: Remaining harmonic voltage level, for instance for the 7th harmonic: • Capacitor bank without reactors:
12.7%
• 7% - detuned filter:
1.1%
• tuned filter:
0.2%
Return on Investment s g n i Sav
EPCOS PFC
11--Reduces ReducesKW KWDemand Demand 22--Reduces ReducesKWH KWHConsumption Consumption 33--Eliminates EliminatesPower PowerFactor FactorPenalty Penalty 44--Reduces ReducesMonthly MonthlyElectricity ElectricityBill Bill 55--Reduces ReducesMaintenance Maintenance& &Downtime Downtime Up Le to ss 34 tha % Sa n2 vin Ye gs ar Pa yba ck
+
Satisfied Customer
Pow er
Qua
lity
11--Improves ImprovesVoltage Voltage 22--Balances BalancesThree ThreePhases Phases 33--Filters FiltersSurges, Surges,Transients Transients 44--Filters FiltersHarmonics Harmonics 55--Improves ImprovesPower PowerFactor Factor lity nce a Qu tena r in we a o M dP e& e c tim an n h E n Do w d ce u d Re
All components for harmonic filters
