Harmonic Filter Design

HARMONICS FILTERING

Harmonic filter design

Summary 1- Generalities 2- Application domain 3- Necessary technical informations 4- Filter selection 5- Harena 2 simulation software 6- Reminder of rules recommended by Rectiphase 7- Recommended levels of performances 8- Sizing criteria 9- Example 10- 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.

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ϕ

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.

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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 nonlinear 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.

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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 5 5-7 5-7-11

5th 1 0,7 0,6

7th

11th

0,3 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: Sn: Gh:

short-circuit at the point of coupling nominal power of the supply transformer power of the harmonic generators

- if Sn > 2MVA and

Gh>Scc/30

- if Sn < 2 MVA and Gh > 0.6 x Sn Example: Sn = 1MVA Gh = 700kVA Gh > 0.6 x Sn

=> installation of harmonic filter is recommended

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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 3 5&7 11 & 13 >13

Ih/ Isc (%) 4 5 3 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 3 5 7 11 13 17 19 23 25

Uh % 5 6 5 3,5 3 2 1,5 1,5 1,2

Total Harmonic Distortion: < 8%

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As a precaution, the rule adopted by Rectiphase is to ensure lower distortion levels: Order h 3 5 7 11 13 17 19 23 25

Uh % 3 4 3 2,5 2 1,5 1 1 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 standard capacitor oversized capacitor detuned bank: tuning factor: 2,7 tuning factor: 3,8 tuning factor: 4,3

Imax/I1 1,3 1,45 1,1 1,2 1,3

• 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.

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9- Example Transformer: nominal power: short-circuit voltage:

Sn = 1MVA Ucc = 6%

Subscribed power: Subscribed current:

Psc = 1MVA Isc = 1440A

Total power of harmonic generators: Gh = 700 kVA Harmonic currents (Igh): typical spectrum (see table) Initial harmonic distortion: Order 5 7 11 13 17 19 23 25 THD (%)

Igh (%) 30 16 9 6 4 2,5 1,5 1 36

Ih (%) 21 11 6 4 3 2 1 1 25

Vh (%) 7 5 4,5 3,5 3 2 1,5 1 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 5 7 11 13 17 19 23 25 THD (%)

Ih (%) 3,7 4,2 2,6 1,8 1,2 0,7 0,4 0,3 6

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Vh (%) 1,4 2,4 2,2 1,5 1,4 1 0,7 0,5 4,3

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Individual harmonic voltages in LV 8 6 Vh (%)

4 2 0

Vh 3

Vh 5

Vh 7

Vh 11 Vh 13 Vh 17 Vh 19 Vh 23 Vh 25

1st column = without filter 2nd column = with filter

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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 ( Results: rms current:

I rms =

Fundamental current:

S 3U

I1 =

300.10 3

=

3.400

= 433A

I rms 1 + THD

Order 1 5 7 11 13 17 19 23 25

2

=

433 1 + (0,28) 2

% 100 25 6 8 4 5 3 3 2

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= 416 A

A 416 104 25 33 17 21 12 12 8

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