Download Diapositiva 1

QUALITY & TECHNOLOGY
HARMONIC PROBLEMS IN
CAPACITOR BANKS
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
2/13
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
IMPEDANCE
Zcap
CURRENT THROUGH
THE CAPACITOR
Icap = V / Zcap
Z1
Zcap = 1 / (2·f·C)
Z3
Z5
FUNDAMENTAL
3rd HARM.
5th HARM.
FREQUENCY
f
HARMONIC PROBLEMS IN CAPACITOR BANKS
3/13
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.
L
RESONANCE
DISTRIBUTION
TRANSFORMER
C
CAPACITOR BANK
Example: 30% of harmonics in
the current, will normally cause
around 3% of harmonics in
voltage. However, a capacitor
HARMONICS CLOSE TO
bank may increase the voltage
THE RESONANCE
harmonics to 8% or more.
FREQUENCY
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
4/13
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.
L
RESONANCE
DISTRIBUTION
TRANSFORMER
C
HARMONICS OF THE
SAME FREQUENCY
Note: Resonance is a serious
risk which shall not be underestimated, especially in systems
with low impedance.
CAPACITOR BANK
DESTRUCTIVE
RESONANCE
HARMONIC PROBLEMS IN CAPACITOR BANKS
5/13
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.
IMPEDANCE
|Z|
Z = 2·f·L + [1 / (2·f·C)]
Capacitive
impedance
Z1
Z5
Inductive
impedance
L
RTFX FILTERING
INDUCTOR
Total current
C
I = V / ZL+C
Z3
Resonance
frequency
FUNDAMENTAL
3rd HARM. 5th HARM.
FREQUENCY
f
HARMONIC PROBLEMS IN CAPACITOR BANKS
6/13
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.
HARMONIC PROBLEMS IN CAPACITOR BANKS
7/13
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
RTFX FILTERING
INDUCTOR
Total current
C
I = V / ZL+C
HARMONIC PROBLEMS IN CAPACITOR BANKS
8/13
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: 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
L
OVERVOLTAGE
189Hz  7,5%
135Hz  14%
C
HARMONIC PROBLEMS IN CAPACITOR BANKS
9/13
RTFX: ADVANTAGES
COPPER WINDINGS
PROBLEM FREE TERMINALS
ADVANTAGES
CLASS F INSULATION
LOW TEMPERATURE RISE (<90ºC)
COMPETITIVE PRICES
NEW BUSBAR COPPER TERMINALS!!
HARMONIC PROBLEMS IN CAPACITOR BANKS
10/13
RTFX: STANDARD CHARACTERISTICS
STANDARD CHARACTERISTICS
Line 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)
HARMONIC PROBLEMS IN CAPACITOR BANKS
11/13
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
HARMONIC PROBLEMS IN CAPACITOR BANKS
12/13
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
[email protected]
www.polylux.com
HARMONIC PROBLEMS IN CAPACITOR BANKS
13/13