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QUALITY & TECHNOLOGY HARMONIC PROBLEMS IN CAPACITOR BANKS

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2/13 INTRODUCTION CAPACITOR BANKS PROVIDE POWER FACTOR CORRECTION WHEN USED IN ELECTRICAL INSTALLATIONS WHERE HARMONICS ARE PRESENT, THE APPLICATION OF A CONVENTIONAL CAPACITOR BANK IS LIKELY TO SUFFER AND CAUSE SEVERAL PROBLEMS: 1) FAILURE AND SHORT TIME LIFETIME OF POWER CAPACITORS 2) ELEVATED VOLTAGE HARMONICS 3) DANGER OF RESONANCE BETWEEN CAPACITOR BANK AND MAIN TRANSFORMER Note: Nowadays, more and more non-linear loads (i.e. loads that draw current with a waveform that is not the same as that of the supply voltage) such us soft starters, UPS or frequency converters are used, causing elevated levels of harmonics.

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HARMONIC PROBLEMS IN CAPACITOR BANKS 3/13 FAILURE OF CAPACITORS THE CURRENT THROUGH THE CAPACITOR DEPENDS ON ITS IMPEDANCE, AND THIS PARAMETER IS MUCH LOWER FOR HIGHER FREQUENCIES (HARMONICS). THIS FACT MAY CAUSE THE OVERLOAD OF THE CAPACITOR, RESULTING IN ITS LIFE SHORTENING AND/OR DAMAGE CURRENT THROUGH THE CAPACITOR I cap = V / Z cap IMPEDANCE Z cap Z1Z1 Z3Z3 Z5Z5 FUNDAMENTAL 3rd HARM.5th HARM. Z cap = 1 / (2 ·f·C) FREQUENCY f

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HARMONIC PROBLEMS IN CAPACITOR BANKS 4/13 ELEVATED VOLTAGE HARMONICS THE CAPACITANCE ‘C’ OF THE CAPACITOR BANK AND THE SUPPLY INDUCTANCE ‘L’ (UPSTREAM NETWORK + LINE + TRANSFORMER) FORM AND L-C CIRCUIT WITH CERTAIN RESONANCE FREQUENCY. IF THIS PARAMETER IS CLOSE TO ONE OF THE PRESENT HARMONICS, THIS HARMONIC WILL BE AMPLIFIED, ESPECIALLY IN THE VOLTAGE. DISTRIBUTION TRANSFORMER CAPACITOR BANK HARMONICS CLOSE TO THE RESONANCE FREQUENCY RESONANCE L C Tip: To know the effect of the capacitor bank on the harmonics, compare measurements of harmonics with and without connecting the capacitor bank. Example: 30% of harmonics in the current, will normally cause around 3% of harmonics in voltage. However, a capacitor bank may increase the voltage harmonics to 8% or more.

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HARMONIC PROBLEMS IN CAPACITOR BANKS 5/13 COMPLETE RESONANCE IN CASE THE RESONANCE FREQUENCY OF THE L-C CIRCUIT FORMED BY THE CAPACITOR BANK AND THE SUPPLY INDUCTANCE COINCIDE WITH A PRESENT HARMONIC OF THE INSTALLATION, A COMPLETE RESONANCE OCCURS. THIS MAY HAVE DESTRUCTIVE RESULTS FOR THE CAPACITOR BANK, MAIN TRANSFORMER AND MAIN SWITHBOARD. DISTRIBUTION TRANSFORMER CAPACITOR BANK HARMONICS OF THE SAME FREQUENCY RESONANCE L C Note: Resonance is a serious risk which shall not be under- estimated, especially in systems with low impedance. DESTRUCTIVE RESONANCE

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HARMONIC PROBLEMS IN CAPACITOR BANKS 6/13 SOLUTION: FILTERING INDUCTOR RTFX THE FILTERING INDUCTOR PROVIDES A HIGH IMPEDANCE FOR HIGH FREQUENCIES (HARMONICS). THE TOTAL IMPEDANCE OF THE CAPACITOR + INDUCTOR STEP IS INDUCTIVE ABOVE THE SO-CALLED RESONANCE FREQUENCY. FREQUENCY f IMPEDANCE |Z| Resonance frequency Z = 2 ·f·L + [1 / (2 ·f·C)] Capacitive impedance Inductive impedance Z1Z1 Z3Z3 Z5Z5 FUNDAMENTAL 3rd HARM.5th HARM. L C RTFX FILTERING INDUCTOR Total current I = V / Z L + C

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HARMONIC PROBLEMS IN CAPACITOR BANKS 7/13 SOLUTION: FILTERING INDUCTOR RTFX BENEFITS FROM USING RTFX FILTERING INDUCTORS: -_HIGH IMPEDANCE FOR HARMONIC FREQUENCIES: Avoids high harmonic currents through the capacitor. -_ INDUCTIVE IMPEDANCE ABOVE RESONANCE FREQUENCY: Avoids amplification of harmonics and risk or resonance.

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HARMONIC PROBLEMS IN CAPACITOR BANKS 8/13 TECHNICAL CONSIDERATIONS THE RESONANCE FREQUENCY IS NORMALLY CHOSEN AT 189Hz (p=7%). HOWEVER, IN CASE SIGNIFICANT 3rd HARMONIC IS PRESENT, IT IS RECOMMENDED TO CHOOSE 135Hz (p=14%). THE RESONANCE FREQUENCY DEPENDS ON THE CAPACITOR ‘C’ AND THE INDUCTOR ‘L’. IT IS VERY IMPORTANT THAT BOTH COMPONENTS ARE WELL TUNED TO EACH OTHER. A WRONG FREQUENCY OF RESONANCE MAY RESULT IN HARMONIC ABSORTION CAUSING DAMAGE TO THE SYSTEM. BOTH CAPACITANCE AND INDUCTANCE VALUES MUST THEREFORE BE CORRECT AND STABLE TO GUARANTEE CORRECT TUNING. L C RTFX FILTERING INDUCTOR Total current I = V / Z L + C

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HARMONIC PROBLEMS IN CAPACITOR BANKS 9/13 TECHNICAL CONSIDERATIONS FILTERING INDUCTORS CAUSE A HIGHER VOLTAGE ON THE CAPACITOR TERMINALS. THE CAPACITORS SHOULD THEREFORE BE SUITABLE FOR THIS HIGHER VOLTAGES. Example, for a 400V and 50Hz network: Inductors tuned to 189Hz (p=7%) Use of capacitors for 440V, 460V, 480V, 500V or 525V Inductors tuned to 135Hz (p=14%) Use of capacitors for 480V, 500V or 525V The effective kVAr rating of the capacitor + inductor is calculated as follows: 189Hz: Q EFF = (V LINE /V CAP ) 2 x 1,075 x Q CAP 135Hz: Q EFF = (V LINE /V CAP ) 2 x 1,14 x Q CAP L C OVERVOLTAGE 189Hz 7,5% 135Hz 14% Note: Filtering inductors are recommended for electrical installations where the level of voltage harmonics THD(%) is 2,5..3% or more

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HARMONIC PROBLEMS IN CAPACITOR BANKS 10/13 RTFX: ADVANTAGES ADVANTAGES COPPER WINDINGS PROBLEM FREE TERMINALS CLASS F INSULATION LOW TEMPERATURE RISE (<90ºC) COMPETITIVE PRICES NEW BUSBAR COPPER TERMINALS!!

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HARMONIC PROBLEMS IN CAPACITOR BANKS 11/13 RTFX: STANDARD CHARACTERISTICS STANDARD CHARACTERISTICS Line voltage400V, 50Hz Capacitor voltage440V, 50Hz Resonance frequency189Hz IsolationsClass F WindingsCopper, class HC-200ºC TerminalsBusbar copper Test voltage3kV (1 min, 50Hz) Harmonic currentsI3=8%, I5=31%, I7=13% Thermal overload factor5% Over current6% Tolerance3% Protection degreeIP-00 Ambient temperature40ºC Temperature rise<90ºC StandardsIEC/EN/UNE-EN 60289, CE IncludesBimetal temperature sensor, 120ºC, nc Other characteristics on request (please visit www.polylux.com)

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HARMONIC PROBLEMS IN CAPACITOR BANKS 12/13 FILTERING OF HARMONICS FOR FILTERING HARMONICS OF THE ELECTRICAL NETWORK, WE OFFER: COMPENSATOR HARMONIC FILTERS -A NEW CONCEPT IN HARMONIC FILTERING – ● Filtering of 3rd, 5th, 7th, 9th, 15th, and 19th harmonic ● Several advantages respect to other filters in the markets: - Very good filtering level for competitive price - No electronics or capacitors; maintenance free and very reliable - No generation of high frequency distortions - No exhaustive study of the installation is necessary - Optionally with galvanic isolation Ask for our catalogue

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HARMONIC PROBLEMS IN CAPACITOR BANKS 13/13 POLYLUX C/ Boters 3B, Parc Tecnològic del Vallès 08290 Cerdanyola del Vallès Barcelona – Spain Tel. +34 93.594.65.41 Fax +34 93.580.96.03 export@polylux.com www.polylux.com

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