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Power Factor Correction & Harmonic filter

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Power Factor Correction & Power Factor Correction & Harmonic filterHarmonic filter

Definition:Definition:

Power Factor, Harmonics, Transients, Power Factor, Harmonics, Transients,

Voltage and frequency variations and other Voltage and frequency variations and other

disturbances in electric power supply disturbances in electric power supply

networksnetworks

Power Quality

Adjustable Speed Drives

Notching on the input can interfere with other loads on the same branch circuit

Flat topping of Drive input voltage, heavily distorted current

Examples for poor power quality

Past Past -- load:load: most loads were linearmost loads were linear

InductionInduction--motors, heating, bulbsmotors, heating, bulbs

voltage was followed by current voltage was followed by current -- only a few problemsonly a few problems

Changing load structure

Features Customer benefits

Simple and rugged design

No commutator

High degree of protection

High reliability

Long lifetime

Favourably-priced

Unrestricted operation for partial- and overload conditions

Low maintenance (only the bearings)

Can be universally used

Todays Todays -- loads:loads: most loads act non linearmost loads act non linear

Computer, motorComputer, motor--control, drives, etc.control, drives, etc.

Current is pulse shapedCurrent is pulse shaped

Current is no longer following the sinusoidal wave shapeCurrent is no longer following the sinusoidal wave shape

Result: HarmonicsResult: Harmonics

-- Increasing number of sources causing disturbancesIncreasing number of sources causing disturbances

-- Equipment become more and more sensitive Equipment become more and more sensitive

-- DeDe--regulated energy marketregulated energy market

Changing load structure

Problems caused by 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!

Origin of harmonics

Voltage-source DC link converter

Current-sourceDC link converter

Cycloconverter

Design

Features

Driveconverter

Voltage is impressed in the DC link

SIMOVERT MASTERDRIVESSIMOVERT MVSIMOVERT ML

Current is impressed in the DC link

SIMOVERT ASIMOVERT ISIMOVERT S

Cycloconverter, no DC link

SIMOVERT D

~=

=~

M3~

~=

M3~

~=

~=

~=

=~

M3~

Modern drives a main source for harmonics

0%

20%

40%

60%

80%

100%

Order number

6-pulse

12-pulse

6-pulse 100,00% 29,00% 9,00% 6,00% 3,50% 2,50% 2,00% 1,20% 1,10%

12-pulse 100,00% 2,90% 0,90% 6,00% 3,50% 0,25% 0,20% 1,20% 1,10%

1 5 7 11 13 17 19 23 25

HARMONICS fed back by 6/12 pulse rectifier

Voltage characteristic at the drive converter output (PWM)

Voltage characteristic at the drive converter output (PWM)

Current characteristic at the drive converter output

Current characteristic at the drive converter output

Example of a non-linear load: Switched mode power supply

AC Current Voltage

Current

LOAD

Example for single phase Non-Linear load

Harmonic currents or voltages are integer (whole number) multiples of thefundamental frequency.

Harmonicorder

F 3rd 5th 7th

Frequency 50 150 250 350

Understanding harmonics

Overheating of transformers (K-Factor), and rotating equipment

Increased hysteresis losses

Neutral overloading / unacceptable neutral-to-ground voltages

Distorted voltage and current waveforms

Failed capacitor banks

Breakers and fuses tripping

Unreliable operation of electronic equipment, and generators

Erroneous register of electric meters

Wasted energy / higher electric bills - KWD & KWH

Wasted capacity - Inefficient distribution of power

Increased maintenance cost of equipment and machinery

Problems caused by HARMONICS

HARMONICS

Time

Am

plitu

de

Fundame

h3

h5

h7

SUM

Additional investment due to faster equipment deratingShorter life time of equipmentHigher energy consumptionHigher downtime of production equipmentHigher maintenance and repair costReduced product qualityReduced production outputInvestment for stronger equipments/components

alternatively

One time investment for harmonic filter

COST caused by HARMONICS

Tripping of circuit breakers and fuses Due to resonance effects, the current levels may rise to multifold levels which results into tripping ofcircuit breakers and melting fuses. This situation results into serious problems in industries which relyon the quality of power for the continuous operation of their sensitive processes (e.g. semiconductor)

Overloading / decrease of life time of transformersTransformers are designed to deliver power at network frequency (50/60Hz). The iron losses arecomposed 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 amplitudesof the harmonic voltages result into higher currents which are detrimental tothe capacitors: I = U * 2 * 3.14 * f * C.

Losses in distribution equipmentHarmonics in addition to the fundamental current cause additional losses inthe 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 theneutral conductor. In systems with substantial amount of the non linear single phase loads, the neutral currents may riseto a dangerously high level. There is a possibility of excessive heating of the neutral conductor sincethere are no circuit breakers in the neutral conductors like in the phase conductors.

Malfunctioning of the electronic controls and computersElectronic controls and computers rely on power quality for their reliable operation. Harmonics resultinto distorted waveforms, neutral currents and over voltages which affect the performance of thethese gadgets.

Measurement errors in the metering systemsThe Accuracy of metering systems is affected by the presence of harmonics. Watt-hour metersaccurately register the direction of power flow at harmonic frequencies, but they have magnitudeerrors 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!

Effect of harmonics

3rd harmonic in the neutral conductor

3rd harmonic in the neutral conductor

Synthesis of a wave form

Limit for harmonics

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

Summary

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

EPCOS Harmonics solution

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 anfrequency close to existing harmonic frequencies. In such a caseharmonic 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!

Resonance

Parallel resonance

Meter: 0001 K-f ac tor: 1.041 V olts : 277 Frequenc y :60.01 Hz

H# % H# % T.H.D.: 2.8% max : 2 .9% min: 0.5% 1 100.0 0 2 0.0 69 3 0.4 116 4 0.1 68 5 2.1 272 6 0.0 69 7 1.6 41 8 0.0 70 9 0.2 133 10 0.0 6811 0.4 11 12 0.0 6813 0.7 36 14 0.1 6815 0.1 68 16 0.0 6817 0.2 37 18 0.0 15819 0.1 69 20 0.0 15821 0.1 327 22 0.0 6923 0.0 69 24 0.0 6925 0.1 301 26 0.0 827 0.0 158 28 0.0 24829 0.1 319 30 0.0 30931 0.2 20 32 0.0 68

Meter: 0001 K-f ac tor : 1.829 V olts : 290 Frequenc y :59.97 Hz

H# % H# % T.H.D.: 18.8% max : 21.6% min: 1.9% 1 100.0 0 2 0.1 26 3 0.5 352 4 0.3 31 5 18.8 203 6 0.0 259 7 1.2 126 8 0.0 259 9 0.0 80 10 0.0 20011 0.1 312 12 0.0 25913 0.0 80 14 0.0 8015 0.1 116 16 0.0 20017 0.0 320 18 0.0 16919 0.0 319 20 0.0 25921 0.1 192 22 0.0 25923 0.0 169 24 0.0 34925 0.1 259 26 0.0 25927 0.1 259 28 0.0 34929 0.0 259 30 0.0 25931 0.1 31 32 0.0 79

Harmonics MAGNIFICATION

No PFC capacitors With PFC capacitors

Meter: 0001 K-f ac tor: 1.533 A mps : 1716 Frequenc y :60.01 Hz

H# % H# % T.H.D.: 13.6% max : 18.1% min: 2.1% 1 100.0 0 2 0.5 100 3 0.4 29 4 0.1 119 5 12.3 53 6 0.4 66 7 5.5 356 8 0.1 91 9 0.7 299 10 0.2 2911 1.3 7 12 0.1 2913 0.1 210 14 0.0 2915 0.3 29 16 0.0 11917 0.3 285 18 0.0 2919 0.0 210 20 0.1 9021 0.1 90 22 0.0 2923 0.0 210 24 0.0 11925 0.1 29 26 0.1 2927 0.0 29 28 0.1 11929 0.1 29 30 0.1 11931 0.0 29 32 0.0 209

Meter: 0001 K-f ac tor: 32.38 A mps : 2033 Frequenc y : 59.97 Hz

H# % H# % T.H.D.: 89.5% max : 152.3% min: 3.6% 1 100.0 0 2 2.3 9 3 1.0 169 4 2.9 79 5 150.0 263 6 3.8 259 7 8.7 141 8 1.2 300 9 1.5 280 10 1.5 25911 1.6 259 12 0.8 31013 1.7 279 14 0.5 25915 1.2 79 16 1.1 29417 0.5 260 18 0.3 819 1.0 331 20 0.5 25921 1.5 259 22 0.5 31223 1.2 339 24 0.1 25925 0.5 180 26 0.6 34927 0.9 182 28 0.3 30729 0.7 349 30 0.2 1931 0.6 292 32 0.0 259

V o

l t a

g e

Cu

rre

nt

Real case of parallel resonance in KL/Malaysia

point of view

In

harm onicload

X Lmotor

X Ttransformer

X N, networkimpedance

X Ccapacitor

Parallel resonance

Harmonics present on LV side of the transformer

Transformer together with PFC capacitors on LV-side

acts as a parallel resonant circuit

At resonant frequency the inductive reactance is

equal the capacitive reactance

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

1) I is constant and imprinted

DC

AC

I Ic IL

UZ

What happens in case of parallel resonance?

1) + 2) voltage U (ohmic law)

3) With U Ic = IL

2) Impedance Z

Parallel resonance

U = 20 KVSk = 500 MVA

P = 500 KW, 6-pulseI50 Hz = 720AI250 Hz = 144AI350 Hz = 103AI550 Hz = 65AI650 Hz = 55AI850 Hz = 42AI950 Hz = 38A

DCAC

P = 100 KW

M

I350 Hz = A720

7

S = 1000 kVA

uk = 6%Transformer

U = 400 V

Qc = 400kvar

Parallel resonance: example

Attention:close to the 7thharmonic!

DCAC M

SKLV = STr

uk 100

SKLV = 1000 kVA

6100 = 16.67MVA

frp = 50Hz SKLV

Qc

= 322 Hzfrp = 50 Hz 16.67 MVA

0.4 Mvar

Parallel resonance: exampleKC

TR uQ

Sf

=

10050

System bus bar: impedance vs. frequency

Resulting harmonic voltage for 350 Hz :322 Hz is close to the 7th harmonic

00,20,40,60,8

11,21,41,6

50 150 250 350 450 550

o

322Hz

Frequency Hz

350 Hz

0.5

DCAC M

I350 Hz = 103 Amp

U350 = 0.5 * 103A = 51.5V

Parallel resonance: example

12.7% 400V51.5V

Resonance?

11 kV level

132 kV level

Parallel resonance

I

I

Series resonance

I

Capacitorbank

Transformer1000 kVA, uk = 5 %

DC drive600 kWcos = 0.65

...

415 V level

Transformer630 kVA, uk = 5 %

Capacitorbank

300 kWcos = 0.65

...

415 V level

3

if fr = f Xc 0 Ic

Se rie s re so na nce

0

24

68

10

1214

16

50 100 150 200 250 300 350 400Frequency

Impe

danc

e

Induc tance

Reactance

Im pedance

fr

Series resonance

S

L

C

Series resonant circuit

S=signal source

KCNR eQ

Sv

=

1

100

The point of series resonance is given by the following formula:

Series resonant circuit formed by combination of inductive and capacitive reactance. The impedance behavior of this circuit is as illustrated in the diagram. It is seen that at resonant frequency the impedance reduces to a minimal value. Thus the circuit offers very low impedance at the input 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.

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

Remedial measures

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 proof capacitors

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 circuitThe 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 circuitThe 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 its full kvar load as a PFC capacitor.

Harmonic filter circuits

De-tuned harmonic 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

Customer benefits of detuned filters

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:

p = (f / fres) 100 (in %)

fres =fn

p / %100

De-tuned harmonic filter

EXAMPLES FOR DETUNING-FACTORS (f=50Hz)

5 % 224 Hz5.5 % 213 Hz

5.67 % 210 Hz6 % 204 Hz7 % 189 Hz8 % 177 Hz

12.5 % 141 Hz14 % 134 Hz

Supply Voltage Un + Overvoltage:

fn: 50 Hz

Calculation of a 7%-detuned filter:

400 V

p: 7 % fres: 189 Hz

Un = 400 V

1.534

430 V

0.767

Nc / kvar: 25

Uc: 430 V Design: Ucr: 440 V

Qcr / kvar: 28.13 56.27

50

Ln / mH:

154.26 308.52C / F:

462.78 925.56Cy / F:

De-tuned harmonic filter

MDC

AC

Previous Example, now for 7%-detuned filter

Resulting harmonic voltage e.g. :

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

Kvar: 400

189H

oo

00,020,040,060,08

0,10,120,14

50 150 250 350 450 550

De-tuned harmonic filter

Im p e d a n c e b e h a v io u r o f a s e r ie s in d u c t a n c e c ir c u it

- 3

- 2

- 1

0

1

2

3

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0

F r e q u e n c y

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

r e s o n a n t f r e q . f r

c a p a c it iv e b e h a v io u r

in d u c t iv eb e h a v io u r

De-tuned harmonic filter

De-tuned harmonic filter

ImpedanceImpedance

o

00,020,040,060,08

0,10,120,14

50 150 250 350 450 550

189Hz5th 7th 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

Summary: detuned filter

Tuned harmonic filter

Power factor correction & Filtering harmonics (cleaning the grid)

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.:

MDCAC

5 th 7 th 11 thkvar: 200 400 100

System bus bar: impedance vs. frequency

Frequency Hz

5th (250Hz): 0.01 Ohm 144 A = 1.4V 0.4%

7th (350Hz): 0.01 Ohm 103 A = 1.0V 0.2%

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

50 150 250 350 450 550

oo o

Tuned harmonic filter

Switching sequence of tuned filter: LIFO

Switching in:

Switching out:

3rd 5th 7th 11th

11th7th5th3rd

Tuned harmonic 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

7th 11th

0

0,050,1

0,15

0,2

0,250,3

0,35

0,4

50 150 250 350 450 550

oo o

5th

Summary: tuned filter

ImpedanceImpedance

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%

Harmonic filters

EPCOS PFC

1 - Reduces KW Demand2 - Reduces KWH Consumption3 - Eliminates Power Factor Penalty4 - Reduces Monthly Electricity Bill5 - Reduces Maintenance & Downtime

1 - Reduces KW Demand2 - Reduces KWH Consumption3 - Eliminates Power Factor Penalty4 - Reduces Monthly Electricity Bill5 - Reduces Maintenance & Downtime

1 - Improves Voltage2 - Balances Three Phases3 - Filters Surges, Transients4 - Filters Harmonics5 - Improves Power Factor

1 - Improves Voltage2 - Balances Three Phases3 - Filters Surges, Transients4 - Filters Harmonics5 - Improves Power Factor

Savings

Power Quality

+

Up to 34% Savings

Less than 2 Year Payback SatisfiedCustomer

Enhanc

ed Pow

er Quali

ty

Reduce

d Down

time &

Mainte

nance

Return on Investment

All components for harmonic filters