quality & technology harmonic problems in capacitor banks

QUALITY & TECHNOLOGY

HARMONIC PROBLEMS IN CAPACITOR BANKS

HARMONIC PROBLEMS IN CAPACITOR BANKS2/13

INTRODUCTION

CAPACITOR BANKSPROVIDE 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.


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

Icap = V / Zcap

IMPEDANCE Zcap

Z1

Z3

Z5

FUNDAMENTAL 3rd HARM. 5th HARM.

Zcap = 1 / (2·f·C)

FREQUENCY f


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

RESONANCEL

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.


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

RESONANCEL

C

Note: Resonance is a serious risk which shall not be under-estimated, especially in systems with low impedance.

DESTRUCTIVERESONANCE


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.

FREQUENCYf

IMPEDANCE|Z|

Resonancefrequency

Z = 2·f·L + [1 / (2·f·C)]

Capacitiveimpedance

InductiveimpedanceZ1

Z3

Z5

FUNDAMENTAL 3rd HARM. 5th HARM.

L

C

RTFX FILTERING INDUCTOR

Total current

I = V / Z L + C


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.


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


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

L

C

OVERVOLTAGE189Hz 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


RTFX: ADVANTAGES

ADVANTAGES

COPPER WINDINGS

PROBLEM FREE TERMINALS

CLASS F INSULATION

LOW TEMPERATURE RISE (<90ºC)

COMPETITIVE PRICES

NEW BUSBAR COPPER TERMINALS!!


RTFX: STANDARD CHARACTERISTICS

STANDARD CHARACTERISTICSLine voltage 400V, 50Hz

Capacitor voltage 440V, 50Hz

Resonance frequency 189Hz

Isolations Class F

Windings Copper, class HC-200ºC

Terminals Busbar copper

Test voltage 3kV (1 min, 50Hz)

Harmonic currents I3=8%, I5=31%, I7=13%

Thermal overload factor 5%

Over current 6%

Tolerance 3%

Protection degree IP-00

Ambient temperature 40ºC

Temperature rise <90ºC

Standards IEC/EN/UNE-EN 60289, CE

Includes Bimetal temperature sensor, 120ºC, nc

Other characteristics on request (please visit www.polylux.com)


FILTERING OF HARMONICS

FOR FILTERING HARMONICS OF THE ELECTRICAL NETWORK, WE OFFER:

COMPENSATOR HARMONIC FILTERSCOMPENSATOR 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

mailto:[email protected]?subject=Please%20send%20us%20your%20catalogue%20about%20harmonic%20filtering


POLYLUX

POLYLUX

C/ Boters 3B, Parc Tecnològic del Vallès08290 Cerdanyola del VallèsBarcelona – SpainTel. +34 93.594.65.41Fax +34 [email protected]

quality & technology harmonic problems in capacitor banks

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