HARMONIC PROBLEMS IN CAPACITOR BANKS

1. HARMONIC PROBLEMS IN CAPACITOR BANKS

2. 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. HARMONIC PROBLEMS IN CAPACITOR BANKS

3. CURRENT THROUGH THE CAPACITOR Icap = V / Zcap IMPEDANCE Zcap Z1 Zcap = 1 / (2·f·C) Z3 Z5 FREQUENCY f 3rd HARM. 5th HARM. FUNDAMENTAL 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 HARMONIC PROBLEMS IN CAPACITOR BANKS

4. L RESONANCE DISTRIBUTION TRANSFORMER HARMONICS CLOSE TO THE RESONANCE FREQUENCY C CAPACITOR BANK 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. 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. Tip: To know the effect of the capacitor bank on the harmonics, compare measurements of harmonics with and without connecting the capacitor bank. HARMONIC PROBLEMS IN CAPACITOR BANKS

5. L RESONANCE DISTRIBUTION TRANSFORMER HARMONICS OF THE SAME FREQUENCY C CAPACITOR BANK 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. Note: Resonance is a serious risk which shall not be under-estimated, especially in systems with low impedance. DESTRUCTIVE RESONANCE HARMONIC PROBLEMS IN CAPACITOR BANKS

6. RTFX FILTERING INDUCTOR IMPEDANCE |Z| L Z = 2·f·L + [1 / (2·f·C)] Total current I = V / Z L + C C Capacitive impedance Inductive impedance Z1 Z5 Z3 Resonance frequency FREQUENCY f 3rd HARM. 5th HARM. FUNDAMENTAL 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. HARMONIC PROBLEMS IN CAPACITOR BANKS

7. 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. HARMONIC PROBLEMS IN CAPACITOR BANKS

8. RTFX FILTERING INDUCTOR L Total current I = V / Z L + C C 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. HARMONIC PROBLEMS IN CAPACITOR BANKS

9. L OVERVOLTAGE 189Hz  7,5% 135Hz  14% C 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: QEFF = (VLINE/VCAP)2 x 1,075 x QCAP 135Hz: QEFF = (VLINE/VCAP)2 x 1,14 x QCAP Note: Filtering inductors are recommended for electrical installations where the level of voltage harmonics THD(%) is 2,5..3% or more HARMONIC PROBLEMS IN CAPACITOR BANKS

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

11. RTFX: STANDARD CHARACTERISTICS STANDARD CHARACTERISTICS Other characteristics on request (please visit www.polylux.com) HARMONIC PROBLEMS IN CAPACITOR BANKS

12. 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 HARMONIC PROBLEMS IN CAPACITOR BANKS

13. POLYLUX 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 HARMONIC PROBLEMS IN CAPACITOR BANKS