An active harmonic filter is a type of analogue electronic filter. Uses OP AMP. Needs external power. Injects phase opposite harmonic. Have energy losses. AHF design needs passive components like capacitor and resistor. The inherited capacitor helps in increasing load power factor.

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Active Harmonic Filter - a Case study of its Advantages & Disadvantages.
An active harmonic filter is a type of analogue electronic filter. Uses OP AMP.
Needs external power. Injects phase opposite harmonic. Have energy losses. AHF
design needs passive components like capacitor and resistor. The inherited
capacitor helps in increasing load power factor.
It malfunctions while handling high-intensity power and harmonic pollution wherein
the total voltage harmonic distortion (THDv) is above 10%. Many OEM
recommends not to use it when THDv is more than 10% as it malfunctions. In this
Case Study, we have independently verified this feature.
AHF's another disadvantage it requires real-power in kW for injecting phase
opposite harmonic current at downstream at the connected non-linear load that
causes 3% to 7% real energy losses in kWh term. Though OEM catalogue mention
only about 3% energy loss, that's measured under an ideal condition as like car-
mileage claim. Energy-intensive industries employ hundreds of VFD drives within
one transformer say 2000 KVA and operate in between 70 to 90% load factor. In
addition, the active harmonic filter requires higher impedance typically over 3% in
series with VFD drive which injects further kW losses. Thus the 3% energy loss
data may be valid for low-intensity load. But for higher load-factor and THDv, it may
go up to 7%.
* PowerQualitySolutionsandTotalPowerManagement* EnergyManagement* Trouble-shootingfailures *TuneHarmonicFilter* DesignAudit * EnergyAudit

2. It has a known problem connecting with backup diesel generator (DG) if plant loads
are higher and need variable reactive power compensation. The active harmonic
filter can't deliver that as it inherits only the fixed type design capacitors and needs
additional equipment. A STATCOM to work in conjunction with it or the SATCOM to
be inbuilt within it or it requires an external capacitor APFC bank which many OEM
refers to as the Hybrid Harmonic Filter.
By design Active Harmonic Filter doesn't remove harmonics from downstream
power line but cancels it by injecting anti-harmonics. Its application is to limit
upstream harmonics within IEEE-519 norm. Whereas passive filter being a
harmonic absorption type sucks up harmonics by short-circuiting it both from
downstream loads and upstream power systems within its range. By doing so, it
cleans up the circulating-harmonics from downstream loads which otherwise get
absorbed in the downstream equipment and In turn, increase voltage harmonic
distortions within the electrical power system of the supply transformer. In a chain
reaction, it magnifies current harmonics extent of which depends upon the fault
level of the load bus PCC. Thus, by design passive filter relieves downstream non-
linear load by removing circulating-harmonics and eliminates equipment failure,
break-down and nuisance tripping issues. In-addition protection relay functioning
improves. We have uploaded another case study about it for an automobile industry
with a 1.0 MW Solar Power Plant. Read it at Solar Power Inverter with Harmonic
Filter.
ActiveHarmonicFilter-advantages
The active harmonic filter does not require to be custom built since it is mostly
impedance independence except the design capacitors and resistors. It does not
need any load specific frequency tuning. Active harmonic filter manufacturers claim
that it can filter wideband harmonic frequencies. On the other hand, the passive
filter needs extensive engineering efforts and are custom built with load specific
design. Passive filters need tuning for load specific harmonic frequencies. However,
it is also true that actual load never generates beyond a few harmonic frequency
bands. For example, computer, server and switch mode power supply (SMPS)
loads produce 3rd and 9th harmonics to the extent of 80% and 15%
respectively. Six pulse drive loads produce 5th (60%), 7th (20%) and balance in
11th and 13th harmonic currents. 12-Pulse inverter loads generate 11th (50%), 13th
(30%) and balance in other frequency harmonic currents.

3. ActiveHarmonicFilter-disadvantages
Active Harmonic Filter has a known issue in handing high-intensity loads wherein
THDv is above 10% at which many OEM recommends not to use it. It also creates
energy losses which vary from 3% for low-intensity loads and goes up to 7% for
high-intensity loads and voltage distortions. Whereas passive filter being harmonic
absorption type saves 3 to 5% real energy in kWh for moderately polluted harmonic
loads. When it comes to massively polluted harmonic load like rolling mill drive with
fourth quadrant regeneration operation, induction furnace etc., it delivers an even
higher percentage of energy saving. The same higher percentage energy saving is
possible when the transformer or DG operates at a higher load factor typically in
between 80 to 90%.
Fig.1. Plant harmonics without active or
Passive Filter
ActiveHarmonicFilter-problem
with high intensityvariableload
While the active harmonic filter
can regulate variable harmonic
currents from the downstream non-linear load, it can't control reactive power on its
own unless it works in conjunction with STATCOM. It inherits the fixed design
capacitors which restrict it from scaling up for higher loads that including applying it
at the transformer or DG PCC for the full utility load which may include hundreds of
VFD drives and other non-linear loads. Instead, active harmonic filter manufacturers
install it in numbers across several and smaller non-linear loads within the same
transformer. Back up diesel generator (DG) requires a closer power factor (PF)
management. It's a known issue for applying it at the generator terminal.

4. Passive filter though needs custom engineering effort is custom built for any
variable load. It's applied conveniently at transformer's main income or DG terminal
for the entire supply load which may comprise hundreds of variable speed drive
(VSD), DC drive, converter, inverter, computer server and other non-linear loads. It
is custom built to regulate any variable reactive power demand from the
downstream load. Be it the most challenging fourth quadrant regeneration drive
which operates at a power factor of about 0.06 lag, and generates in between 80%
to 120% current harmonic with a corresponding voltage harmonic generation. We
have applied passive filters across thousand of diesel generators (DG) and also at
Turbo generators (TG) since our inception in 1995. With the elimination of both
voltage and current harmonics, it debottlenecks
Fig.2. Plant harmonics with Passive Harmonic Filter
DG/TG's capacity limitation
which allows extra load on the
DG to the extent of 30%,
solves its hunting, AVR voltage
fluctuation problem and saves
good energy and fuel.
ActiveHarmonicFilter-failure
issue withpowersurgeand
voltagefluctuation
Unlike the passive filter, an
active harmonic filter is not an energy storage device. One of the advantages of the
passive filter it's an energy storage device which acts as an electrical flywheel and
eliminates equipment tripping due to momentary voltage fluctuation which
originates either from factory's internal power system or external from the utility's
grid supply. The consequences of poor power quality vis-a-vis voltage sag tripping
are high. Industries worldwide lose billions of dollars every year on account of
equipment nuisance tripping due to voltage fluctuation.

5. Whereas active harmonic filter being dependent on an external power source is
susceptible to failure on voltage fluctuations. Several active filter manufacturers
void their warranty if failure happens on account of a voltage fluctuation which can
be a subjective clause. Besides, it needs air-conditioned room for its installation.
Passive filter, on the other hand, is rough and tough and is installed within the
ordinary electrical panel room. Several of our clients are in the path of monsoon
wind and have had a history of equipment tripping with its sensitive process drives
and server networks. Since our inception in 1995, we have been supplying
hundreds of passive filters for eliminating
nuisance tripping with VFD drive, DC drive,
computer, server network and electrical
equipment due to grid power surge and
voltage fluctuation.
Fig.3 700A frame Passive Harmonic Filter
ActiveHarmonicFilter-stabilityissue
The passive filter provides guaranteed
stability and its sustainable through the test
of time. It can be scaled up practically for
any voltage, current and reactive power
compensation need. We have supplied it for
all industrial voltage rating up to 36kV and
current rating up to 5,000 amps in a single filter. Whereas, the active harmonic filter
is susceptible to maloperation if installed in a harmonic-rich power system. While
cancelling harmonics across large frequency ranges, it ends up in generating
another range harmonic frequency. As shown in the top harmonic bar-chart, it
faulted and generated a 2nd harmonics. It's failure rates are high. The disposal for
failed electronic components is always environmentally challenging. Whereas,
passive filter even though requires a custom design, is for a lifetime.
ActiveHarmonicFilter and arc flashand shortcircuitcompatibility
Active filters don't comply with arc flash and short circuit compatibility norms. It has
high failure rates and has a shorter lifespan. Its operation and maintenance are a
challenge that needs highly experienced personnel. Whereas, passive filters
comply with arc flash and short circuit norms and can handle the entire transformer
or DG loads. Its designed for full load variation with automatic operation including
changeover from utility power to back up DG and vice versa. It's fit and forget type
and does not require any special maintenance except regular maintenance as like
with any electrical equipment.
Active Harmonic Filter- a case study

6. In this case study, a set of active harmonic filters applied in conjunction with
STATCOM at the main PCC of a transformer with back up DG for the entire
transformer load in the automobile industry. Followings are brief project
specification.
Industry: Automobile
Transformer size: 2500 KVA, 11kV/ 433V
Transformer Load: Thyristor Heating Furnace, 2nos 600kW and 1no 1200kW
Transformer Load Factor: Average 70%.
Back up DG: Fully backed up by DG in case of power failure
Active Harmonic Filter Specification: 3nos each 450A
AHF Brand: from a leading MNC company.
STATCOM: 4nos +/- 300 kVAr
Brand: from a leading MNC company.
ActiveHarmonicFiltervs Passive-harmonicsbeforeand afterfilters
Plant Harmonic level without any Harmonic Filter: Shown in Fig.1
Plant Harmonic level with a 700A Passive Filter: Shown in Fig.2
700A Frame Passive Harmonic Filter: Shown in Fig.3
Plant Harmonic with Active Harmonic Filter: Shown in the top caption picture.
The problem with active harmonic filter is that while mitigating wideband harmonic
frequencies, it randomly generated some other frequency harmonic causing
unbalance in the power supply of the furnace. Its manufacturer could not resolve
the problem which created voltage unbalance and occasional earth fault trip
resulting in productivity losses.
The active filter itself failed repeatedly. Eventually, we installed a passive filter. It
resolved the unbalance and tripping problems. The mitigated harmonic spectrum
with passive filter shown in Fig.2 which is self-explanatory. It mitigated the plant's
overall harmonic level at the supplying transformer PCC better than IEEE 519
standard.