Harmonic Filter Design

HARMONICS FILTERING

Harmonic filter design

Summary

1- Generalities2- Application domain3- Necessary technical informations4- Filter selection5- Harena 2 simulation software6- Reminder of rules recommended by Rectiphase7- Recommended levels of performances8- Sizing criteria9- Example10- Further information

1- Generalities

As part of the Harena 2 project, a simplified process has been developped for the design of an harmonic filter.

This process can be considered for study cases meeting some conditions.

It is possible to propose rapidly a solution, with the only reading of the characteristics of the installation.

No on-site measurement is necessary.

The Harena 2 simulation software is used during this process in order to validate the design.

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2- Application domain

2-1 Customer’s motivation:

The simplified process can be undertaken if the customer’s request is motivated by:• a preventive action, before connection of harmonic generating equipments, likely to disturb the installation• the compliance of the installation with standards or recommandations

If the customer’s request is the consequence of a misoperation, prior on-site measurements are recommended.

2-2 Installation characteristics:

In order to be able to use the tools of the simplified process, the installation must meet some criteria:• standard values of supply voltages (208, 240, 400V, ...)• simple configuration• harmonic currents and kvar within given limits• typical non-linear loads

The studied installation can be represented the following way:

- a 3-phase balanced power source, supplying balanced loads, all being represented by a single phase equivalent circuit- a coupling point to the distribution network, defined by its short-circuit power- a MV/LV transformer- a linear load generating no harmonic currents- an harmonic current generator

On this basic circuit, the designer can study the effect of power factor correction and filtering devices:- capacitor bank- detuned bank- passive filters of order 5, 7 or 11- active compensator

These devices can be selected separately or by combination. So it is possible to analyse the effect of any type of filter: passive, active or hybrid.

See on the following figure: single phase equivalent circuit.

Harmonic document.doc 2/14

Pre-calculated passive filters

Pre-calculated passive filters have been developped by Rectiphase for 400V/50Hz networks.A data base including the characteristics of these filters has been integrated into the validation software.

Other pre-calculated filters have been developped by Schneider - Canada for standard supplies: 208V/60Hz, 240V/60Hz, 380V/50Hz, 480V/60Hz, 600V/60Hz. The datas concerning these filters are also integrated.

2-3 Expected level of performances

The simplified process does not guarantee a level of performances if on-site measurements have not been made. It gives the improvement obtained with the proposed equipment, based on the estimated characteristics of the installation.

2-4 Harmonic orders

The only orders of harmonics to be considered are: 3, 5, 7, 11, 13, 17, 19, 23, 25.


3- Necessary technical informations

Some technical characteristics of the installation are needed in order to make the harmonic analysis. For example, the generated harmonic currents must be known.

These datas can be obtained:• directly by on-site measurement performed by the customer• by estimations

3-1 Essential technical datas

Essential datas which must be given by the customer are the following:

- Supply frequency- Medium Voltage nominal value- Low Voltage nominal value- Apparent power of the MV/LV transformer- Short-circuit voltage of the MV/LV transformer- Active or apparent power of the linear load- Requested reactive power- Generated harmonic currents: on-site measurement or knowledge of the type and power of the non-linear loads

3-2 Estimation of non-measured datas

If no precise datas are available, the other characteristics of the installation can be estimated (use of typical values):

- Short circuit power of the supply network: equal to 100 times the apparent power of the transformer- Reference current: use the subscribed current in LV, or calculate the transformer nominal current- Pre-existing harmonic voltages: Vh5: 2%

Vh7: 1,5%Vh11: 1%

- Harmonic currents: by the type and power of the non-linear loads

(See in annex the waveshape and spectrum for typical loads)

4- Filter selection

Depending on the installation characteristics and the objective of performances, the designer selects a type of filter distinguished by:

• the order of the harmonic to be eliminated• the requested reactive power• the amplitude of the harmonic currents to be eliminated

4-1 Order of the harmonic to be eliminated

The selection of the number of harmonic orders to be filtered depends on the performances in view:

• the higher is the number of filtered harmonics, the better are the performances• active or hybrid configurations are able to reduce all the harmonic orders from 3 to 25

4-2 Requested reactive power


The reactive power of filters is generally limited to 20% of the transformer apparent power.

The additional reactive power if necessary must be supplied by detuned banks.

When a combination of passive filters is used, the distribution of the kvar is carried out on the following way:

Combination 5th 7th 11th5 1

5-7 0,7 0,35-7-11 0,6 0,2 0,2

4-3 Amplitude of the harmonic currents to be eliminated

- Passive filters: the selection of pre-calculated modules must be made first depending on the requested reactive power, then depending on the harmonic current to be eliminated on its tuning frequency

- Active compensator: depending on the current rating, partial or total elimination of the harmonic currents is possible

5- Harena 2 simulation software

The Harena 2 software is used to validate the design of a filter. An iterative process must be used to check that the right level of performances is reached and that the power rating of the components is correct.

The harmonic analysis is made on orders 3, 5, 7, 11, 13, 17, 19, 23, 25 exclusively.

The instructions for use of the software can be found in the document manual.doc

6- Reminder of rules recommended by Rectiphase

Considering the power factor correction when harmonic generators are present, Rectiphase is recommending the installation of harmonic filters in the following condtions:

Scc: short-circuit at the point of couplingSn: nominal power of the supply transformerGh: power of the harmonic generators

- if Sn > 2MVA and Gh>Scc/30

- if Sn < 2 MVA and Gh > 0.6 x Sn

Example:

Sn = 1MVAGh = 700kVA

Gh > 0.6 x Sn => installation of harmonic filter is recommended


7- Recommended levels of performances

Objective:

The objective of these recommandations is to provide simple rules in order to determine if harmonic mitigation is necessary.

Application field:

These rules apply to:

- the design of new installations or the connection of new harmonic generators (preventive action)

- the analysis of existing installations (curative action)

Current limits:

In case of a preventive action, the proposed rules consist in respecting current emission limits.

After connection of the harmonic generators, the installations must comply with the limits recommended by EDF (Emeraude contract).

These recommendations consider the harmonic currents as a function of the subscribed power. The applicable limits do not depend on the characteristics of the network at the point of connection.

The limits are established as a function of the subscribed power and the corresponding current ISC:

Order Ih/ Isc (%)3 4

5 & 7 511 & 13 3

>13 2

These limits must be compared to the simulation results obtained with no pre-existing harmonic voltages. Only the harmonic currents generated by the installation itself are considered.Voltage limits:

If a curative action is undertaken, the proposed rules consist in respecting voltage distortion limits.

The measured or calculated distortion must never exceed the levels given in IEC 61000-2-2.

Order h Uh %3 55 67 5

11 3,513 317 219 1,523 1,525 1,2

Total Harmonic Distortion: < 8%


As a precaution, the rule adopted by Rectiphase is to ensure lower distortion levels:

Order h Uh %3 35 47 311 2,513 217 1,519 123 125 1

Total Harmonic Distortion: < 5%

These limits must be compared to the simulation results obtained with pre-existing harmonic voltages. The global harmonic distortion is thus considered.

8- Sizing criteria

Objective:

The objective of these criteria is to provide simple rules in order to determine whether the components of power factor correction and filtering are not subject to unacceptable stress.

Limits:

For capacitor and detuned banks, the relevant parameter is: Imax / I1, ratio: max. permanent current / fundamental current

The maximum permissible values are:

Type of component Imax/I1standard capacitor 1,3oversized capacitor 1,45detuned bank:

tuning factor: 2,7tuning factor: 3,8tuning factor: 4,3

1,11,21,3

For pre-determined filters, the maximum values for the harmonic current and the total rms current are given explicitely by the Harena 2 software.

In case the maximum permissible values are exceeded, a particular study is necessary.


9- Example

Transformer:nominal power: Sn = 1MVAshort-circuit voltage: Ucc = 6%

Subscribed power: Psc = 1MVASubscribed current: Isc = 1440A

Total power of harmonic generators: Gh = 700 kVAHarmonic currents (Igh): typical spectrum (see table)

Initial harmonic distortion:

Order Igh (%) Ih (%) Vh (%)5 30 21 77 16 11 511 9 6 4,513 6 4 3,517 4 3 319 2,5 2 223 1,5 1 1,525 1 1 1

THD (%) 36 25 11

Considering a new installation, the harmonic currents are exceeding the limits recommended by EDF. The connection of all the harmonic generators is not possible, unless mitigation measures are undertaken.

Considering an existing installation, the measurement or the calculation of the voltage distortion show that the compatibility levels are exceeded, and that there is a significant risk of misoperation. Harmonic mitigation is necessary.

Possible solution:

Hybrid filter including a passive filter, référence A07 (163kvar, 368A) and a 90A active compensator.

Results:

Order Ih (%) Vh (%)5 3,7 1,47 4,2 2,411 2,6 2,213 1,8 1,517 1,2 1,419 0,7 123 0,4 0,725 0,3 0,5

THD (%) 6 4,3


Individual harmonic voltages in LV

Vh (%)

0

2

4

6

8

Vh 3 Vh 5 Vh 7 Vh 11 Vh 13 Vh 17 Vh 19 Vh 23 Vh 25

1st column = without filter2nd column = with filter


10- Further information

10-1 Selection guide for an harmonic filter

The following table gives the main characteristics and limitations of the different structures of harmonic filters:

Solution Main chracteristics Limitations

Passive filter - power factor correction- filtering of 1 or 2 harmonic orders- « network » filter- for high power installation (>250kVA)

- risk of overload by external pollution- no total emimination of the harmonic currents- risk of overcompensation at light load

Active compensator

- elimination of several harmonic orders- « network » or « machine » filter

- high price by Amp.- power factor correction possible but expensive

Hybrid filter(passive filter +

active compensator)

- power factor correction- elimination of several harmonic orders- for high power installation (>250kVA)- « network » filter- performances / cost compromise solution

- risk of overload of the passive part by external pollution- no total emimination of the harmonic currents - risk of overcompensation at light load

Hybrid filter(detuned bank +

active compensator)

- power factor correction- elimination of several harmonic orders- for medium power installation (<250kVA)- « network » filter

- no total emimination of the harmonic currents - risk of overcompensation at light load


10-2 Additonal tools

The Harena 2 software is a simple and fast tool for validation of an harmonic filter solution in basic configurations. Most of the applications may be covered.

Some functions have not been included in order to keep it user-friendly.

The following table gives a list of other useful functions in harmonic analysis, as well as the name of different softwares including these functions and used by the Schneider teams.

Function Software OriginUnbalanced systems Superharm ElectrotekVector analysis Harmonie

SelenaRectiphaseSER =S=

Tree complex circuits Harmonique 5.1HarmonicsHarmonie

Superharm

EDFCEAT

RectiphaseElectrotek

Meshed complex circuits SelenaHarmonique 5.1

SER =S=EDF

Impedance curve drawing Harmonique 5.1HarmonicsHarmonie

Superharm

EDFCEAT


Probabilistic analysis Harmonie RectiphaseTarification signals at 175/188Hz

Harmonique 5.1 EDF

Fundamental frequency analysis

SuperharmHarmonie

ElectrotekRectiphase

Time representation SuperharmHarmonics

ElectrotekCEAT

Calculation of all harmonic orders

Harmonique 5.1HarmonicsHarmonie

Superharm

EDFCEAT


Other models of filters Harmonique 5.1Harmonie

Superharm

EDFRectiphaseElectrotek

Parameter scanning Harmonie Rectiphase

Recommanded software

In addition to the Harena 2 software, the Harmonique 5.1 (EDF) software is recommanded.

Indeed, most of the applications not treated by Harena 2 can be treated by Harmonique 5.1.French and English versions exist and EDF is responsible for the evolutions and maintenance.

The Selena software (Schneider ELEctrical Network Analysis) now under development is designed to be the common and universal tool for network analysis inside Schneider.


Annex

Spectrum of typical loads

Rectangular current (theoretical)

Waveshape and spectrum of harmonic currents:


Thyristor rectifier (UPS, DC drive)Typical waveshape and harmonic current spectrum:

Diode rectifier (AC drive)Typical waveshape and harmonic current spectrum:


Harmonic content in % of the fundamental:

Order Rectangular wave

DC driveUPS

AC drive Average spectrum

5 20 25 40 307 14 6 15 1611 9 8 7 913 7,7 4 4 617 5,9 5 3 419 5,3 3 2 2,523 4,3 3 2 1,525 4 2 1 1

THD (%) 30 28 44 36

Calculation example

- Type of non-linear load: DC drive

- Supply voltage U: 400V

- Apparent power S: 300kVA

=> Results:

rms current: IS

UArms

3

30010

3 400433

3.

.

Fundamental current: II

THDArms

1 2 21

433

1 0 28416

( , )

Order % A1 100 4165 25 1047 6 2511 8 3313 4 1717 5 2119 3 1223 3 1225 2 8


Documents

Harmonic Filter Design